David L. Ellis and Bradley A. Lerch

Glenn Research Center, Cleveland, Ohio

Improvement of GRCop-84 

Through the Addition of Zirconium

NASA/TM—2012-216985

June 2012
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David L. Ellis and Bradley A. Lerch

Glenn Research Center, Cleveland, Ohio

Improvement of GRCop-84 

Through the Addition of Zirconium

NASA/TM—2012-216985

June 2012

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

The authors would like to acknowledge the many technicians who worked on the testing, 

including Ronald Phillips, William Brown, John Juhas, and Adrienne Veverka.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

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Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identification 

only. Their usage does not constitute an official endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-216985 1 

Improvement of GRCop-84 Through the Addition of Zirconium 

David L. Ellis and Bradley A. Lerch

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135 

Summary

GRCop-84 (Cu-8 at.% Cr-4 at.% Nb) has excellent strength, creep resistance, low cycle fatigue (LCF) 

life and stability at elevated temperatures. It suffers in comparison to many commercially available 

precipitation-strengthened alloys below 500 °C (932 °F). It was observed that the addition of Zr consistently improved the mechanical properties of Cu-based alloys especially below 500 °C. In an effort to 

improve the low-temperature properties of GRCop-84, 0.35 wt% Zr was added to the alloy. Limited 

tensile, creep, and LCF testing was conducted to determine if improvements occur. The results showed 

some dramatic increases in the tensile and creep properties at the conditions tested with the probability of 

additional improvements being possible through cold working. LCF testing at room temperature did not

show an improvement, but improvements might occur at elevated temperatures. 

1.0 Introduction

GRCop-84 (Cu-8 at.% Cr-4 at.% Nb) is a NASA-developed alloy designed for use in rocket engine 

combustion chamber liners and other high-temperature, high-heat-flux applications. The microstructure 

consists of Cr2Nb particles in a nearly pure Cu matrix. Available literature exists that contains the 

mechanical properties of several Cu-based alloys of approximately equal composition with and without 

the addition of small amounts of Zr (0.1 to 1 wt%) (Refs. 1 to 5). Examples include Cu/Cu-Zr and 

Cu-Cr/Cu-Cr-Zr. As is shown in Figure 1, the addition of small amounts of Zr, normally accompanied by 

cold work, increases the low cycle fatigue (LCF) life twofold to thirtyfold. Similar increases have been 

observed for other mechanical properties of interest, such as tensile strength and creep life. Prior work has 

indicated that the addition of Zr results in a CuxZr precipitate, with x being 4, 4.5, or 5 (Ref. 6). Even in 

the presence of large amounts of Cr, which could form a Cr2Zr phase, the CuxZr phase is favored (Refs. 7 

to 9). On the basis of these observations, the authors hypothesized that adding Zr to GRCop-84 would 

result in the formation of a third phase that could strengthen the alloy and improve its properties further. 

Only 0.17 wt% Zr can be dissolved into solid Cu at the eutectic temperature of 972 °C (1781 °F), 

with the solubility decreasing rapidly at lower temperatures (Ref. 6), but the available literature indicates 

that only small amounts of Zr are required to result in large changes in mechanical properties. Commercially available Cu-Zr contains only 0.15 wt% Zr, yet it is much stronger than pure Cu following heat 

treatment (Ref. 2). It was decided to attempt to add 0.35 wt% Zr to GRCop-84. The level was selected on 

the basis of the apparent need for at least 0.15 wt% Zr for effective strengthening, the Cu-Zr phase diagram, and an expectation that some Zr would be lost through vaporization during the melting process. 

A CuxZr phase is precipitated in two steps. First the Zr is placed into solid solution using a hightemperature-solutioning heat treatment step. Typically this is carried out between 900 and 950 °C (1652 

and 1742 °F). The temperature is limited to 972 °C (1782 °F) by the Cu-rich Cu-Zr eutectic (Ref. 6).

Higher temperatures carry the risk of incipient melting. A water quench is used to prevent precipitation of 

CuxZr precipitates during cooling to room temperature. An aging heat treatment at a moderate temperature range, such as 425 to 525 °C (800 to 975 °F), is used to precipitate fine CuxZr particles from the 

Cu-Zr supersaturated solid solution. The fine precipitates strengthen the alloys. They also retard recovery, 

recrystallization, and grain growth, so the benefits of cold work are retained at higher temperatures 

(Ref. 10).
NASA/TM—2012-216985 2 

Figure 1.—Beneficial effects of small Zr additions on low cycle fatigue (Refs. 1 to 5). 

This work was conducted under NASA Glenn Research Center’s Director’s Discretionary Fund 

program. Two goals were established in this work to improve the mechanical properties of GRCop-84. 

The first was a 15-percent increase in the yield strength between room temperature and 400 °C (752 °F).

The second was an increase of 50 percent in the LCF life of the alloy. If these were successful, additional 

properties, such as conductivity, would be measured and a preliminary database would be established.

No specific application was targeted by this work, but if the low- and middle-temperature mechanical 

properties could be improved, the alloy would become competitive with the Cu-Cr, Cu-Zr, Cu-Cr-Zr, and 

Cu-Be alloys. These alloys and others are used in a wide variety of applications, including terminals and 

connectors for electrical, electronic, and automotive applications; springs for relay contacts and switchgear; integrated circuit leadframes; busbars; rotor bars; armatures; commutators; spot welding electrodes; 

heavy electrical switchgear; molds for continuous and static casting; and tuyéres for steelmaking blast 

furnaces (Ref. 11). In addition, improved mechanical properties would be beneficial for rocket engine 

combustion chamber liners, the primary application for GRCop-84. 

It was decided to first determine the best solutioning temperature. The alloy was to be tested in the 

as-received condition, the aged condition, the cold-worked then aged condition, and the aged then coldworked condition. The last two conditions were selected on the basis of the processing typical of Cu-Zr 

alloys (Ref. 6). Because funding was terminated early, only the as-received and aged conditions were 

tested. The aging temperature and time would be determined from the tensile tests, but the first attempts 

would use the same conditions typically used to process Cu-0.15 wt% Zr (Refs. 11 and 12).
NASA/TM—2012-216985 3 

2.0 Experimental Procedure

Under Glenn’s Director’s Discretionary Fund task, the tensile, creep, and LCF properties were 

surveyed to determine if the addition of Zr improved GRCop-84 properties. The microstructure was also 

examined in the as-received and heat-treated conditions to determine what changes could be observed.

Because the program was terminated early, the complete test matrix, which included cold working the 

material to a full hard state, was not completed. Only material in the as-extruded and aged conditions was 

examined prior to completion of the current work. Microstructural characterization also was limited.

2.1 Alloy Design and Production 

The addition of Zr to Cu results in the formation of an intermetallic CuxZr phase. Various reports in 

the literature have indicated that the value of x can be 4 (Ref. 13), 4.5 (Ref. 14), or 5 (Ref. 15) for Cu-rich 

alloys. Some early work even indicated that x could be as low as 3 (Ref. 16). The accepted value of x in a 

binary Cu-Zr alloy is 4.5 (Ref. 6), but in the ternary Cu-Cr-Zr alloy, x was observed to be 5 (Ref. 9). The 

composition and structure of the precipitates will have an effect on the volume fraction and, hence, the 

total strengthening that can be achieved. The exact composition was not as important for this survey as 

was proving the ability to produce precipitates that result in significant improvements in the mechanical 

properties. 

So that the target composition of the alloy could be determined, it was assumed that 100 percent of 

the Zr would be used in the formation of CuxZr precipitates, and x was set to 5 on the basis of the Cu-CrZr experience. The amount of Cr and Nb were adjusted slightly downward from the GRCop-84 nominal 

composition to reflect the change in overall composition and to keep the volume fraction of Cr2Nb precipitates constant at 14 vol%. In practice the differences were negligible and fell well within normal variability observed in past GRCop-84 production runs. The target composition, given in Table I, retained the 

slight excess of Cr used to control hydrogen embrittlement in GRCop-84. For reference, the nominal 

composition of GRCop-84 also is given in Table I. The Cu-Cr-Nb-Zr alloy was designated GRCop-84Z 

to indicate that it was GRCop-84 modified by the addition of Zr. 

TABLE I.—GRCop-84 AND GRCop-84Z COMPOSITIONS

Composition, wt% (at.%)

Element

Cr Nb Fe Hf O Zr Cu 

GRCop-84Z target composition

6.65 (8.17) 5.81 (3.99) <0.0050 <0.0020 <0.0400 0.35 (0.25) Balance

GRCop-84 nominal composition

6.69 (8.20) 5.83 (4.00) <0.0050 (a) <0.0400 (a) Balance a

Not applicable.

Prior experiences with Cu-Cr-Nb (Ref. 17) and Cu-Cr-Zr (Ref. 9) indicated that conventional casting 

techniques produce very coarse precipitates not at all suited for strengthening an alloy. A finer 

microstructure is required. As with GRCop-84, commercial argon gas atomization was selected to refine 

the microstructure. Atomization was done at Crucible Research in Pittsburgh, Pennsylvania—the same

company responsible for producing GRCop-84 powder. The same production methods and procedures 

were used as for GRCop-84 to minimize differences that would result from processing changes. 

The same high-purity (minimum 99.99 wt%) elemental melt stock that was used for GRCop-84 was 

used for the production of GRCop-84Z except Zr was added. A 99.9 wt% Zr+Hf (maximum 2 wt% Hf) 

melt stock was used for the Zr addition. Approximately 23 kg (50 lb) of –140 mesh (<106-μm-diameter) 

powder was produced. The powder was produced, sieved, and stored under Ar to prevent oxidation. A 

small representative sample was sieved to produce a size distribution. The remaining powder was placed 
NASA/TM—2012-216985 4 

into a 15.2-cm- (6-in.-) diameter 1018 carbon steel can and evacuated. Once the argon was removed, the 

fill tube was crimped and welded shut. 

The powder was consolidated using direct hot extrusion at HC Starck in Coldwater, Michigan. The 

extrusion parameters and practices for GRCop-84 were again used to minimize processing effects. The 

extrusion billet was extruded into a rectangular bar with a 3.8- by 6.4-cm (1.5- by 2.5-in.) cross section. 

The total reduction in area was 7.5. On the basis of prior experience with GRCop-84, the authors expected

that this would result in complete consolidation of the powder. 

A Varian, Inc., Vista-PRO Inductively Coupled Plasma (ICP) Atomic Emission Spectrometer was 

used for chemical analysis of the major elements and Fe. The unit also was used to search for trace

contaminants. Oxygen was analyzed with a LECO Corporation TC–436 Nitrogen-Oxygen Analyzer. ATI 

Powder Metals1 analyzed the starting powder using ICP atomic emission spectroscopy and a LECO

nitrogen-oxygen analyzer. Both units were comparable to Glenn’s analytical instruments.

2.2 Heat Treatment Development

Because the extrusion billet was held at elevated temperature for extended periods of time, any Zr that 

was in solution would probably precipitate prior to extrusion. This meant that a two-step heat treatment 

would be required to solution and precipitate the Zr. 

All heat treatments were done at Glenn. Samples approximately 3.8 by 6.4 by 2.5 cm (1.5 by 2.5 by 

1 in.) were cut from the nose of the extruded bar. One specimen each was heat treated at 900, 925, and 

950 °C (1652, 1697, and 1742 °F) for 30 min and water quenched (WQ). Higher temperatures would have 

been desirable, but the Cu-Zr phase diagram indicated the possibility of partial melting if the temperature 

was raised further (Ref. 6). The hardnesses of the samples were measured before and after heat treatment 

to determine if the hardness decreased, indicating that Zr was going into solution. A portion of the heattreated material was also examined metallographically to determine if the CuxZr phase could be observed 

and seen to decrease relative to the as-received material.

The hardness was measured using a Newage Testing Instruments ME–1 hardness tester. The unit was 

calibrated prior to testing the samples using the procedure and standard calibration blocks supplied by 

New Age. Calibration blocks for Rockwell B scale hardnesses of 65, 75, and 85 HRB were used for the 

calibration since they were expected to cover the entire range of sample hardnesses. A minimum of five 

measurements were taken to determine the average hardness of the material in the as-extruded, solutionheat-treated, and aged conditions.

The results of the solutioning heat treatment, which are detailed in Section 3, led to the selection of 

950 °C as the solutioning temperature. Cu-Zr alloys are typically aged at 425 °C (800 °F) if they have

been cold worked prior to aging and at 525 °C (975 °F) if they have not been cold worked (Refs. 2, 11, 

and 12). These temperatures plus 475 °C (890 °F) were selected for the current material. Two aging times 

were selected for each temperature as well to determine if the alloy underwent slow or rapid precipitation 

kinetics or would be prone to overaging at reasonable aging times. For 425 and 475 °C, times of 30 and 

90 min were selected, and for 525 °C, times of 30 and 60 min were selected. All samples were air cooled 

(AC). As will be explained in Section 3, the maximum time for the 525 °C age was extended to 90 min 

because the precipitation and growth of the CuxZr precipitates was sluggish and because it was desired to 

have only two aging times. 

2.3 Phase Identification

X-ray diffraction (XRD) with a Bruker D8 ADVANCE XRD unit with a Cu x-ray tube and K-α

radiation was used to determine the major phases present in as-extruded GRCop-84Z. Multiple slow 

scans were conducted to determine which phases were present, and angles that corresponded to possible 

Cu-Zr phases received additional scans. Only the as-extruded bar was tested. 

 

1

ATI Powder Metals was formerly Crucible Research, Pittsburgh, PA.
NASA/TM—2012-216985 5 

Figure 2.—Tensile and creep specimen design. All dimensions are in inches unless marked otherwise; scale is 1:1.

2.4 Tensile Testing

Tensile testing was conducted at room temperature and 500 °C (932 °F) using a modified Instron 

TT series load frame that allowed computer control and data acquisition using MTS Systems Corporation 

TestWorks 4 software. The software-frame combination also allowed strain rate control testing. A strain 

rate of 0.005 (mm/mm)/min was selected to be consistent with past GRCop-84 testing. For the room 

temperature testing, a clip-on MTS Model 634.12 extensometer was used to measure the strain.

For testing at 500 °C, an MTS 632.59B−04 high-temperature water-cooled extensometer was used.

The sample was heated to temperature at a rate of at least 1000 °C/h (1800 °F/h), stabilized for 5 min, and 

tested. Ar was flowed through the furnace cavity at a rate between 1 and 2 liters/min (0.4 to 0.8 SCFM) to 

minimize oxidation, which would change the cross section of the samples. 

The design shown in Figure 2 was used for both room and elevated temperature tensile testing. The 

design is consistent with ASTM E8 (Ref. 18). The design also was used in past GRCop-84 testing. Five 

sets of samples were made from as-extruded material and from material aged at 425 and 525 °C for 

30 and 90 min.

2.5 Creep Testing

Vacuum creep testing was conducted to determine the steady-state creep rate and creep life. A 

temperature of 500 °C (932 °F) was selected to both provide a direct comparison to past GRCop-84 

testing and to provide a temperature low enough to highlight the anticipated benefits of the Zr addition. 

Three stresses were selected: 109.2, 125.5, and 144.5 MPa (15.8, 18.2, and 20.9 ksi). These stress levels 

were again consistent with past GRCop-84 creep testing and would provide direct comparisons to the 

baseline alloy. Duplicate tests were conducted for as-extruded samples and samples aged at 425 and 

525 °C for 30 and 90 min. The design shown in Figure 2 also was used for the creep specimens.

Vacuum creep testing was conducted in test frames from the Brew Corporation. The vacuum chamber 

was evacuated to a pressure below 1.3 mPa (1×10–5 torr), with most tests being conducted near 0.4 mPa 

(3×10–6 torr). The sample was heated to temperature at a rate of at least 1000 °C/h (1800 °F/h). The temperature of the sample was measured and controlled using a Type R (Pt/Pt-13 wt% Rh) thermocouple tied 

to the center of the sample.

During heating, a small load equivalent to 0.5 kg (1 lb) was applied to keep the load train aligned 

under a slight tension. Once at temperature, the sample temperature was stabilized, and the preload was 

removed. The weight pan was raised with a jack, the proper mass was placed on the pan, and the pan was 

lowered again with the jack. For consistency and quickness, an electric drill was used to raise and lower 

the weight pan at a constant rate. A 10:1 load arm was used, so a weight 1/10th of the desired sample load 

was used in the weight pan. A Honeywell Sensotec Type 31 precision miniature load cell in the load train 

allowed for monitoring and recording the actual applied load. 
NASA/TM—2012-216985 6 

A linear variable resistor (LVR) was attached to the load frame outside of the chamber to measure the 

creep strain. Because it was outside of the chamber, the sensor measured the total displacement of the 

load train, which included any slack in the system and any deformation that occurred outside of the 

reduced section. The slack appeared as a large initial change in position. It is likely that most of the 

displacement recorded in the first one or two data points following application of the load came from the 

removal of this slack. The deformation outside of the reduced section was miniscule (Ref. 19) and was 

ignored in the calculation of the creep strain. 

An Optical Gaging Products Focus Contour Projector optical comparator was used to determine the 

initial length of the reduced section. The creep strain was calculated by dividing the total displacement by 

the initial reduced section length. The steady-state creep rate was determined by calculating the slope of 

the creep curve (creep strain versus time) in the region where the curve was linear and exhibited a minimum in the slope of the curve. All samples exhibited a lengthy steady-state regime, so there was no 

difficultly in identifying the section of the curve to be used in calculating the steady-state creep rate.

Data were acquired with a custom data acquisition (DAQ) system and associated software. The DAQ 

system measured and recorded the sample temperature in three sample locations, as well as the vacuum, 

displacement, and load. Typically, data were recorded every second during the first 5 min and every 10 or 

15 min thereafter. The DAQ system also interrogated the instruments every 10 s and stored the data in a 

ring buffer. Upon detecting failure, as defined by a 90-percent decrease in the load channel reading, the 

data for the past hour that had been stored in the ring buffer were also recorded to the data file. This 

allowed excellent resolution of the creep life and extra detail in the creep curve immediately prior to 

failure.

Equation (1) was entertained to determine if the Zr addition and the aging heat treatments had any 

effect on the creep properties: 

10 0 1 10 2 1 10 3 2 10

4 3 10 5 4 10 6 5 10

log ( ) log ( ) log ( ) log ( )

log ( ) log ( ) log ( )

Y BB

BBB

=β +β σ +β σ +β σ

+β σ +β σ +β σ (1) 

Here Y is the response variable (creep rate in inverse seconds or creep life in hours), and σ is the applied 

stress in megapascals, β0 to β6 are the coefficients for the terms, and B1 to B5 are blocking variables representing the aging heat treatments shown in Table II. A blocking variable was set to 1 if the specimen had 

that heat treatment and to 0 if it did not. If all blocking variables were 0, then the sample was a GRCop-84 

specimen in the as-extruded condition. The as-extruded GRCop-84 was used as the baseline for the 

comparison. 

By using forward stepwise regression, it is possible to determine which terms are statistically 

significant and which are not. Terms with a blocking variable that enter the final regression model 

indicate that the condition corresponding to that blocking variable produced a statistically significant 

change in the response variable. The sign of the coefficient of the term βx indicates if the change is 

beneficial or detrimental. By including the baseline as-extruded GRCop-84Z data and comparing it with

the as-extruded GRCop-84 data, it is possible to determine if adding Zr alone produces a significant 

difference or if aging is required. 

TABLE II.—GRCop-84Z HEAT TREATMENTS CORRESPONDING 

TO EQUATION (1) BLOCKING VARIABLES

Blocking variable Heat treatment

B1 As received

B2 425 °C/30 min/air cooled (AC)

B3 425 °C/90 min/AC

B4 525 °C/30 min/AC

B5 525 °C/90 min/AC
NASA/TM—2012-216985 7 

2.6 Low Cycle Fatigue Testing

So that material would be conserved and tests would be consistent with past GRCop-84 LCF testing, 

specimen blanks approximately 1.2 cm in diameter by 6.4 cm long (0.46 in. in diameter by 2.5 in. long) 

were wire electrical discharge machined from the as-extruded and the heat-treated GRCop-84Z bars. 

Type 310 stainless steel extensions were inertia welded onto both ends by Interface Welding of Carson, 

California, to extend the length of the samples to approximately 15.2 cm (6 in.).

The samples were machined to the design shown in Figure 3. As with tensile and creep testing, 

samples were tested in the as-extruded condition and following aging at 425 and 525 °C for 30 and 

90 min. Aging was done prior to inertial welding to prevent any distortion or other problems with thermal 

expansion mismatch between the GRCop-84Z and the Type 310 stainless steel that might be encountered 

in a post-machining heat treatment.

LCF testing was done at Glenn using a hydraulic MTS load frame. The specimens were tested in 

strain control with the strain being measured by an MTS 632.53 extensometer. Total strain ranges ∆εtotal 

of 0.8, 1.0, and 1.2 were used in the testing, and the strain rate was 0.002 m/m/s in all tests. The testing 

used a fully reversed (R = –1) triangular waveform for the strain with no dwell. All testing was conducted 

at room temperature.

Heat treatment appeared to have some effect on the LCF lives of GRCop-84. Equation (2) was entertained to determine if there were statistically significant differences in the LCF lives of GRCop-84Z with 

various heat treatments and the baseline as-extruded GRCop-84: 

10 0 1 10 1 2 2 3 3 4 4 5 5 6

1 7 10 2 8 10

3 9 10 4 10 10 5 11 10

log ( ) log (life)

log (life) log (life)

log (life) log (life) log (life)

T BBBBB

B B

BB B

∆ε = β + β + β + β + β + β + β

+β + β

+β + β + β

 (2) 

Here log10(∆εT) is the common logarithm of the strain range, log10(life) is the common logarithm of the 

life, B1 to B5 are blocking variables representing the various heat treatments of the GRCop-84Z specimens, and β0 to β11 are the coefficients to be fit through the regression analysis. If the blocking variable 

was 1, the specimen received the heat treatment represented by the blocking variable as shown in Table 

II. If all the blocking variables were 0, the data point was for the baseline as-extruded GRCop-84. 

A forward stepwise regression analysis was conducted using SigmaStat Version 3.5. For this analysis, 

F statistic values (the value of the F distribution for X degrees of freedom associated with the numerator 

and Y degrees of freedom associated with the denominator) of 4 to enter and 3.9 to leave were selected.

These values correspond to an approximate 95-percent confidence that the variable should be included or 

excluded. The inclusion of terms with one of the blocking variables indicates that the corresponding aging 

heat treatments had a statistically significant effect upon the LCF properties.

Figure 3.—Low cycle fatigue specimen design. All dimensions are in centimeters; ℄ indicates the centerline.
NASA/TM—2012-216985 8 

Equation (3) was modified to examine if the stress range for GRCop-84Z was statistically different 

from as-extruded GRCop-84: 

10 0 1 10 1 2 2 3 3 4 4 5 5 6

1 7 10 2 8 10

3 9 10 4 10 10 5 11 10

log ( ) log ( )

log ( ) log ( )

log ( ) log ( ) log ( )

P

P P

PPP

BBBBB

B B

BB B

∆σ = β + β ∆ε + β + β + β + β + β

+ β ∆ε + β ∆ε

+ β ∆ε + β ∆ε + β ∆ε

 (3) 

where log10(∆σ) is the natural logarithm of the stress range, log10(∆εP) is the natural logarithm of the 

strain range, and B1 to B5 are the blocking variables given in Table II. A forward stepwise regression 

analysis was conducted using SigmaStat and the F values to determine if there was a statistically 

significant difference between the as-extruded GRCop-84 and the GRCop-84Z with the various heat 

treatments.

2.7 Optical Microscopy

In addition to mechanical testing, optical microscopy was used to examine the alloy in the 

as-extruded and heat-treated conditions. Samples were mounted in Bakelite (Union Carbide and Carbon 

Corporation) or epoxy and were mechanically polished through 0.05-μm colloidal silica using the same 

procedures used with GRCop-84. The material was etched using a solution of 25-ml NH4OH—50 ml 

(NH4)2S2O8 solution (2.5 g/100 ml solution)—25-ml H2O that was diluted by adding 5 parts distilled 

water to 1 part etchant. Dilution was required to prevent overetching the samples. A Reichert ME3

metallograph was used for all optical observations.

2.8 X-Ray Mapping 

The optical microscopy samples were also examined in a JEOL 840A Scanning Electron Microscope. 

X-ray mapping was used to assess the qualitative abundance of Cu, Cr, Nb, and Zr in the observed phases. 

3.0 Results

The following subsections give results for the microstructural evaluation and the mechanical properties. No results are presented for cold-worked GRCop-84Z because the task was terminated before 

samples could be produced and tested. 

3.1 Chemical Composition

Table III presents the chemical composition of the starting powder provided by ATI Powder Metals. 

The composition of the extruded bar, which was measured at Glenn, also is shown, and for reference, the 

target composition is presented. The results show that the composition of the GRCop-84Z produced is 

very close to the desired composition. 

TABLE III.—GRCop-84Z CHEMICAL COMPOSITION

Composition, wt% (at.%)

Element

Cr Nb Fe Hf O Zr Cu

Target

6.65 (8.17) 5.85 (4.02) <0.0050 <0.0020 <0.0400 0.35 (0.25) Balance

Crucible Research powder

6.75 (8.29) 5.86 (4.03) 0.004 0.005 0.0205 0.44 (0.31) Balance

Glenn extruded bar

6.61 (8.12) 5.86 (4.03) <0.005 <0.001 0.0103 0.43 (0.30) Balance
NASA/TM—2012-216985 9 

The amount of Zr is slightly higher than the target of 0.35 wt% but well within the range of 0.25 to 

0.5 wt% used to specify the alloy for production. In this case, a slight excess of Zr was deemed to be 

desirable since uniformly adding Zr to Cu alloys during production can be difficult. It is likely that 

practices can be developed to adjust the addition to the desired level with additional production heats. 

The remaining elements fall well within the historical ranges for GRCop-84. Oxygen was low and 

remained so after consolidation. Fe from the Cr melt stock was present at a very low level as well. Other 

trace impurities associated with the refractories used for the melting were not present at detectable levels. 

In addition to the normal impurities for GRCop-84, a small amount of Hf from the Zr melt stock was 

detected in the powder sample but not in the consolidated material. Lack of Hf in the extruded bar analysis is probably a detection limit issue rather than an actual lack of Hf because it is known that some Hf 

entered the alloy with the Zr and a small amount was detected in the powder sample. The difference was 

not considered to be significant.

3.2 Powder Sieve Analysis

The sieve analysis, presented in Table IV, shows that 57.2 percent of the powder was –325 mesh, or less 

than 44 μm in diameter. This is a greater proportion of –325 mesh powder than is typically observed for 

GRCop-84 atomized under similar conditions. However, the maximum size of the powder particles based 

on the sieve analysis was 125 μm, which is slightly greater than the desired 105-μm diameter specified. The 

fraction of the oversize powder was small (2.4 percent) and was not considered to be significant.

TABLE IV.—SIEVE ANALYSIS OF GRCop-84Z POWDER

Sieve size ----- –120 –140 –200 –230 –270 –325

+120 +140 +200 +230 +270 +325 -----

Nominal diameter range, μm >125 105 to 125 74 to 105 62.5 to 74 53 to 62.5 44 to 53 <44

Percent of particles in range 0 2.4 16.2 9.8 6.7 6.2 57.2

Anecdotal evidence from the loading of the extrusion can and handling of the powder, such as a lower 

packing factor for GRCop-84Z (0.63 versus 0.67), also indicates that the GRCop-84Z powder was finer 

than similarly atomized GRCop-84 powder. It appears that the addition of Zr had the unintended effect of 

increasing the fluidity of the molten metal and improving the atomization of the powder. 

3.3 Phases Present

Figure 4 shows the x-ray diffraction results from the as-extruded GRCop-84Z. The major phases present were Cu and Cr2Nb. This is consistent with the results obtained for GRCop-84, the base of GRCop-84Z. 

The relative intensities of the two phases were very large compared with the minor phases identified.

The four minor phases identified were Cr, CuZr2, Cu5Zr, and Nb0.6Cr0.4O2. Elemental Cr was present 

because there was a slight excess of Cr in the alloy to lower the activity of Nb in the Cr2Nb and prevent 

possible hydrogen embrittlement. The Nb0.6Cr0.4O2 was most likely a tenacious surface oxide that either 

was not completely removed from the sample or that formed during the course of the scans. It also may 

have been incorporated oxide from the powder that had 205 ppm O. 

CuZr2 was not expected because it is the most Zr-rich of the several Cu-Zr compounds. It may 

be indicative of Zr entering the melt and not being well dissolved and mixed prior to atomization. 

Subsequent solution heat treatments would probably dissolve the Zr into the Cu as a solid solution and 

reduce or eliminate this phase. Because of this, it is not considered to be a major strengthening phase for 

GRCop-84Z and will not be included in the discussion even though a small amount still may be present. 

Cu5Zr has been observed in the past in Cu-Cr-Zr alloys (Ref. 9). From the Cu-Zr phase diagram (Ref. 6), 

the expected phase was Cu9Zr2 for a low-Zr alloy. It appears that the presence of Cr modifies the activities 

of Cu and Zr such that the formation of Cu5Zr is favored over Cu9Zr2. 
NASA/TM—2012-216985 10

Figure 4.—X-ray diffraction scan results. (a) Overview of results. (b) Detail of results highlighting minor 

phase peaks. 

3.4 Heat Treatment Development

The hardness data from the solution heat treatments (SHTs) were analyzed using an Analysis of 

Variance (ANOVA) test to determine if statistically significant differences at a 95-percent confidence 

level existed in the hardnesses measured before and after the heat treatments. Table V shows the average 
NASA/TM—2012-216985 11

hardness for the as-received and solution-heat-treated conditions and the results of the ANOVA. For an

F value of 1.8, no statistically significant differences were observed between the conditions in the study, 

so optical microscopy and metallurgical principles were used to determine the solution heat treatment 

temperature.

TABLE V.—ANALYSIS OF VARIANCE (ANOVA) RESULTS 

FOR SOLUTION-HEAT-TREATED GRCop-84Z

Group namea Number of 

readings

Mean Rockwell B hardness,

HRB

Standard deviation of hardness, 

HRB

As-received 10 68.99 3.41

900 °C SHT 9 67.45 3.20

925 °C SHT 10 69.46 2.39

950 °C SHT 10 70.38 1.29 a

SHT, solution heat treatment.

Sources of 

variation

Degrees of freedom,

ν

Sum of squares

(SS)

Mean square

(MS)

F valueb Probability

Between groups 3 39.465 13.155 1.843 0.158

Residual 34 242.629 7.136 -------- --------

Total 37 282.094 -------- -------- -------- b

Value of the F distribution for X degrees of freedom associated with the numerator and Y degrees of 

freedom associated with the denominator.

Figure 5 shows typical optical micrographs from the as-extruded and solution-heat-treated samples.

The microstructures exhibit a Cu matrix and readily discernable bluish-silver Cr2Nb precipitates. In 

addition, there are smaller, dark-gray precipitates. X-ray maps of the as-extruded sample indicated that 

the small precipitates were rich in Zr. There was no indication of Zr in the other phases. This, along with 

the x-ray diffraction analysis, led to the identification of the smallest precipitates as Cu5Zr. Examination 

of the micrographs indicates that there is apparently some decrease in the area fraction of Cu5Zr 

precipitates as the solution heat treatment temperature increases. At 972 °C (1782 °F), the eutectic 

temperature, the solid solubility limit of Zr in solid Cu is 0.17 wt% (Ref. 6), so it is likely that there will 

always be some Cu5Zr precipitates in the GRCop-84Z that cannot be dissolved. The solid solubility 

decreases rapidly at lower temperatures, so it was expected that more Cu5Zr precipitates would be 

observed at lower solution heat treatment temperatures. This appears to be consistent with the observed

microstructures.

The phase diagram, the composition of the alloy, and the optical microscopy were considered in the 

decision to use a solutioning temperature of 950 °C to maximize the amount of Zr that could be placed in 

solution. This was also considered to be a reasonable upper temperature limit to prevent incipient melting 

due to small fluctuations and spatial variances in the furnace temperature.

With the solutioning heat treatment fixed at 950 °C/30 min/WQ, the aging heat treatment was 

examined. The hardness of the samples after solutioning and after aging were examined to determine if 

the hardness increased from the aging heat treatment. Because the variance of the hardness data was fairly 

high, a t-test between the data for the same sample in the solutioned condition and in the aged condition 

was used to determine if the measured differences were statistically significant. All data sets passed 

normality and equal variance testing. Table VI shows the results. In all cases the averages are statistically 

different, with the aged material being harder. In some cases the power of the test was lower than the 

desired value of 0.8, so there is a chance that there is a false positive in the results. Given that the trend is 

consistent and the expected result, this is not considered to be likely.
NASA/TM—2012-216985 12

TABLE VI.—RESULTS FOR GRCop-84Z AGING HEAT TREATMENTS

Heat treatmenta Condition Average Rockwell B 

hardness,

HRB

Standard deviation

of hardness,

HRB

Increase in

hardness,

HRB

425 °C/30 min/AC SHTb 69.4 3.2 6.4 Agedc 75.8 2.3

425 °C/90 min/AC SHTb 72.1 4.4 6.3 Agedc 78.4 2.3

475 °C/30 min/AC SHTb 73.1 1.3 3.4 Agedc 76.5 2.6

475 °C/90 min/AC SHTb 72.2 1.4 6.8 Agedc 79.0 2.58

525 °C/30 min/AC SHTb 73.4 2.3 5.0 Agedc 78.4 3.1

525 °C/60 min/AC SHTb 72.3 3.5 5.1 Agedc 77.4 3.3 a

AC, air cooled.

b

Solution heat treatment at 950 °C for 30 min, then water quenched. c

Aged using indicated heat treatment.

Figure 5.—Optical micrographs of solution-heat-treated GRCop-84Z samples. (a) As-extruded. 

(b) 900 °C/30 min/water quenched (WQ). (c) 925 °C/30 min/WQ. (d) 950 °C/30 min/WQ. 
NASA/TM—2012-216985 13

The hardness values show no clearly preferable aging temperature. They also show that the precipitation process is probably fast since the hardnesses at 30 min are nearly identical to those at 60 and 

90 min. The growth kinetics do not appear to be fast because the longer times did not result in a large 

decrease in hardness due to substantial overaging.

Because of these results, material aged at 425 and 525 °C was selected for testing. The aging time 

was set to both 30 and 90 min to see if there were any discernable differences in tensile strength that 

would indicate a preferred time. The resulting mechanical property test matrix, therefore, had five heat 

treatment conditions: as-extruded, SHT/425 °C/30 min/AC, SHT/425 °C/90 min/AC, SHT/525 °C/ 

30 min/AC, and SHT/525 °C/90 min/AC. 

3.5 Tensile Testing

Figure 6 presents the results of the tensile testing as well as baseline GRCop-84 data as a comparison 

(Ref. 20). Figure 7 shows the relative change in the tensile properties.

At room temperature, the Zr-modified GRCop-84 exhibited less necking and failure at higher 

loads than did the baseline GRCop-84. The result was less reduction in area but more uniform tensile 

elongation. Although lower than desired, the reductions in area still ranged from 25 to 33 percent, so 

GRCop-84Z retained good, if somewhat lower, ductility. The deformation appeared to remain uniform 

with no instability for a longer time, and the tensile elongations increased as a result. Most tests were in 

the 25- to 28-percent range.

Figure 6.—Room temperature GRCop-84Z tensile test results. 
NASA/TM—2012-216985 14

Figure 7.—Relative room temperature tensile properties of GRCop-84Z compared with baseline GRCop-84. 

The room temperature 0.2% offset yield strength shows an increase for GRCop-84Z over GRCop-84 

in all conditions. The 425 °C/30 min/AC condition has the least increase, which is consistent with the 

hardness data (Table VI) and is, in fact, lower than the as-extruded GRCop-84Z. This might indicate a 

failure to precipitate the Cu5Zr phase completely after the solution heat treatment or insufficient growth of 

the precipitates to a size that provides the best impediment to dislocation motion. The 425 °C/90 min/AC

heat treatment achieved the goal of a 15-percent increase in the room temperature yield strength. Both 

525 °C aging heat treatments produced an increase in yield strength of 20 percent, so they meet the yield 

strength goal as well.

The strongest room temperature strength benefit of adding Zr was seen in the ultimate tensile strength 

(UTS). For all conditions tested, the UTS increased by 20 to 29 percent in comparison to the baseline 

GRCop-84. There was no goal for increasing the UTS, but this is a benefit for the material in many 

potential applications, such as those discussed in the Introduction. 

At 500 °C, the CuxZr precipitates were anticipated to coarsen and produce less strengthening.

However, Figure 8 shows a strong, positive effect of the Zr addition on all tensile properties. Figure 9 

shows the change in properties relative to the baseline GRCop-84 properties. 

Ductility was increased greatly relative to GRCop-84. At 500 °C the elongation increased by over 

50 percent, and the reduction in area generally doubled. 

The 500 °C 0.2% offset yield strength showed an increase of 25 percent for the as-extruded material 

and an increase between 37 and 64 percent for the aged material relative to GRCop-84. These results 

indicate that in the short term the CuxZr precipitates do not coarsen to the point that overaging occurs.

This is consistent with the hardness measurements, which indicated slow growth kinetics.

The 500 °C UTS data indicate that the addition of Zr has a pronounced positive effect. In the 

as-extruded condition, the UTS increased by 24 percent in comparison to GRCop-84. Much more 

dramatically, the UTS increased between 43 and 68 percent for the aged GRCop-84Z specimens.
NASA/TM—2012-216985 15

Figure 8.—500 °C GRCop-84Z tensile test results. 

Figure 9.—Relative 500 °C tensile properties of GRCop-84Z compared with those of baseline GRCop-84. 
NASA/TM—2012-216985 16

Figure 10.—Typical GRCop-84Z stress-strain curve. (a) Curve at room temperature 

for sample Z−T4−525−90−2 with solution heat treatment of 950 °C/30 min/water

quenched and age of 525 °C/90 min/air cooled (AC). (b) Curves at 500 °C for sample 

Z−T2−425−30−2 with solution heat treatment of 950 °C/30 min/water quenched 

and age of 425 °C/30 min/AC. 

Figure 10 shows typical room temperature and 500 °C stress-strain curves. For comparison, typical 

GRCop-84 stress-strain curves are also presented in the plots. The room temperature stress-strain 

behavior of GRCop-84Z is typical for most ductile materials and is consistent with GRCop-84. The 

500 °C tensile curve is markedly different and atypical. The specimens undergo a near linear increase 

until the yield strength is exceeded, and a relatively small strain between yield and ultimate tensile loads 

occurs. The sample continues to elongate after the UTS is exceeded, and necking begins. The deformation 
NASA/TM—2012-216985 17

is considerable and accounts for most of the observed ductility. This is not consistent with typical 400 °C 

GRCop-84 stress-strain curves, though it is similar to the 600 °C stress-strain curves. The cause for this 

change in shape is not understood at the present time. 

3.6 Creep Testing

Figure 11 shows a typical GRCop-84Z creep curve. The GRCop-84Z creep curves were very similar 

in shape to the GRCop-84 creep curves. Both normally exhibited a primary creep regime lasting about 

10 percent of the total life followed by steady-state and tertiary creep regimes that were nearly equal in 

duration. Transitions between the regimes were gradual. As a result, the steady-state creep rate was taken 

from only the portion of the curve that had plainly achieved linearity.

Figure 12 shows the creep rate plotted against the creep life for GRCop-84Z samples in the 

as-extruded and aged conditions. The results for as-extruded GRCop-84 are also presented for comparison. The data were first examined as three data sets (as-extruded GRCop-84, as-extruded GRCop-84Z, 

and aged GRCop-84Z). The Monkman-Grant (Ref. 21) regression lines for the three data sets were 

coincident, so it was determined that the three data sets could be pooled. 

The regression line for the pooled data with a 95-percent confidence interval is presented in Figure 

12. The regression equation has a life exponent of −1.17±0.10 compared with −1.11±0.04 for GRCop-84 

(Ref. 22). Although there was no statistically significant difference in the two slopes, the small 

dissimilarity was investigated further to see if it was possible to explain the difference. Examination of 

the plot in Figure 12 shows one data point that lies on the lower 95-percent confidence limit line. This 

data point was not treated as an outlier and was included in all subsequent analyses because there was no 

clear experimental or other reason to exclude the test results. The data point does influence the slope, and 

its removal does increase the slope to −1.16, but it alone does not explain the small change in slope. 

Without additional testing, it is not possible to determine if there is an effect on the Monkman-Grant 

curve from the Zr. Regardless, the change in slope does not represent a major difference from an 

engineering standpoint. 

Figure 11.—Typical GRCop-84Z creep curve for GRCop-84Z specimen aged at 

425 °C/30 min/air cooled and tested at 500 °C/125.6 MPa. 
NASA/TM—2012-216985 18

Figure 12.—GRCop-84Z Monkman-Grant curve. Creep rate = 10–0.286(creep life–1.17); 

coefficient of determination, R2 = 0.9832.

The data presented in Figure 13 clearly demonstrate that the aged GRCop-84Z creep properties are 

much improved over the GRCop-84 creep properties. The as-extruded GRCop-84Z test results were more 

complex. The as-extruded GRCop-84Z specimens tested at 125 and 144 MPa were comparable in life to 

the baseline as-extruded GRCop-84 data. However, the as-extruded GRCop-84Z specimens tested at 

109 MPa demonstrated rates and lives more consistent with the aged GRCop-84Z. It appears that 

there was a change in the creep mechanism or dislocation movement between 109 and 125 MPa for 

GRCop-84Z at 500 °C. This observation needs to be further explored to better understand how the Zr 

affects and benefits the creep properties. 

The similarities for the aged GRCop-84Z results led to the decision to examine just the aged specimen data to see if the four data sets were statistically different. A forward stepwise regression analysis 

was conducted using a simplified version of Equation (1) with three blocking variables and just the four 

aged GRCop-84Z data sets. The results show that there were no statistically significant differences 

between the four aging treatments, so the aged GRCop-84Z data were pooled into a single data set. 

The possible change in creep behavior of the as-extruded GRCop-84Z and the pooling of the aged 

GRCop-84Z data meant that the model in Equation (1) needed to be modified. Blocking variables B2 to B5

were reduced to just B3, and B3 was set to 1 if the GRCop-84Z had been aged and was set to 0 otherwise.

The as-extruded GRCop-84Z data were subdivided into low (109-MPa) and high (125- and 144-MPa)

stress regimes, and the model was adjusted to add new blocking variables B1 (low-stress test) and B2

(high-stress test) to account for the two creep regimes.
NASA/TM—2012-216985 19

Figure 13.—Creep data for GRCop-84Z tested at 500 °C. (a) Creep rates. 

(b) Creep lives. 
NASA/TM—2012-216985 20

Table VII presents the results of the forward stepwise regression of the revised data sets. There are

statistically significant differences between the low-stress, as-extruded GRCop-84Z and GRCop-84 and 

between the aged GRCop-84Z and the baseline GRCop-84Z. There is no statistical difference between 

the high-stress as-received GRCop-84Z and GRCop-84. This appears to be consistent with the data in 

Figure 13. 

TABLE VII.—RESULTS OF FORWARD STEPWISE REGRESSION ANALYSIS OF CREEP DATA

(a) Creep rate.

[Coefficient of determination, R2 = 0.880; standard error of estimate, SY.X = 0.314.] 

Groupa Coefficient Standard error F valueb Probability

Constant −27.230 1.722 ----------- --------- 

log10(σ) 10.060 .831 146.388 <0.001

B1log10(σ) (low-stress as-extruded) −.401 .0843 22.641 <.001

B3log10(σ) (aged GRCop-84Z) −.777 .0512 230.573 <.001

(b) Creep life. 

[Coefficient of determination, R2 = 0.838; standard error of estimate, SY.X = 0.310.] 

Groupa Coefficient Standard error F valueb Probability

Constant 19.665 1.571 ----------- ---------

log10(σ) −8.678 .758 130.909 <0.001

B1log10(σ) (low-stress as-extruded) .416 .0769 29.305 <.001

B3log10(σ) (aged GRCop-84Z) .637 .0467 186.236 <.001

a

σ, stress; B1 and B3, blocking variables indicating as-received material and material with a

425 °C/90 min/air cooled treatment, respectively. b

Value of the F distribution for X degrees of freedom associated with the numerator and Y degrees of 

freedom associated with the denominator.

Table VII also presents the standard error of estimate SY.X and the coefficient of determination R2 for 

the rate and life models. Both indicate a reasonably good fit of the revised data sets by the models. The 

remaining error for the models is about 1/3 order of magnitude, which represents the combined experimental error for the test rig and the random variability of the materials. The error term was consistent with 

prior GRCop-84 testing (Ref. 19) using the same test machines and probably represents the minimum 

achievable. 

3.7 Room Temperature Low Cycle Fatigue Testing

Table VIII summarizes the LCF results, and Figure 14 presents the life as a function of total strain 

range. Prior as-extruded GRCop-84 room temperature LCF test data (Ref. 23) is presented as a baseline 

for comparison. The total strain range in this data set ranges from 0.004 to 0.06. The life scale was limited 

to better display the GRCop-84Z data, but all GRCop-84 data were used in the statistical analyses. The 

upper and lower 95-percent confidence limits for the as-extruded GRCop-84 data are also presented.
TABLE VIII.—LOW CYCLE FATIGUE TEST RESULTS SUMMARY

[Test temperature, 20 °C.]

Sample Total 

strain,a

∆εt, 

in./in.

Life, Nf,

cycles

First cycle,

N = 1

Cycle at half life,

Nf /2

RayleighTaylor

modulus,

Msi

Modulus,

Msi

Strain 

range, 

∆εP, 

in./in.

∆εP/2,

in./in.

Stress 

range, 

∆σ,

psi

∆σ/2,

psi 

σmin,

psi 

σmax,

psi 

Modulus,

Msi

∆εP,

in./in.

∆εP/2,

in./in.

∆σ,

psi 

∆σ/2,

psi 

σmin

psi 

As extruded

T1−13 0.0070 16 502 17.24 17.00 0.0030 0.0015 64 591 32 296 −30 629 33 962 17.38 0.0028 0.0014 72 503 36 252 −36 08

T1−11 .0080 5 588 18.55 18.76 .0039 .0019 75 165 37 583 −36 501 38 664 18.72 .0036 .0018 80 978 40 489 −40 50

T1−12 .0100 5 586 19.22 18.89 .0056 .0028 78 011 39 006 −38 929 39 082 17.77 .0047 .0024 83 755 41 878 −41 95

T1−10 .0120 3 275 15.91 16.24 .0068 .0034 78 689 39 345 −38 556 40 133 16.40 .0066 .0033 87 308 43 654 −43 63

Heat treatment, 425 °C/30 min

T2−11 0.0080 7 622 18.45 18.07 0.0039 0.0020 69 732 34 866 −33 055 36 677 18.49 0.0036 0.0018 80 224 40 112 −39 93

T2−12 .0100 2 595 19.48 19.09 .0057 .0029 76 706 38 353 −37 852 38 854 19.49 .0052 .0026 89 812 44 906 −44 99

T2−13 .0119 2 141 19.32 19.10 .0072 .0036 77 867 38 934 −38 042 39 825 17.75 .0067 .0034 91 065 45 533 −45 35

Heat treatment, 525 °C/30 min

T3−13 0.0080 7 714 18.78 19.33 0.0037 0.0019 77 175 38 588 −36 844 40 331 18.94 0.0034 0.0017 86 036 43 018 −42 99

T3−12 .0100 3 338 19.37 18.84 .0052 .0026 82 170 41 085 −40 135 42 035 18.24 .0048 .0024 93 667 46 834 −46 79

T3−11 .0120 2 635 18.54 17.98 .0068 .0034 84 691 42 346 −41 903 42 788 17.89 .0065 .0032 97 501 48 751 −48 68

Heat treatment, 525 °C/90 min

T4−10 0.0070 17 889 18.63 18.45 0.0026 0.0013 78 110 39 055 −38 037 40 073 18.41 0.0024 0.0012 84 580 42 290 −42 29

T4−12 .0080 9 352 18.54 18.61 .0034 .0017 79 092 39 546 −38 014 41 078 18.03 .0031 .0016 86 382 43 191 −43 56

T4−13 .0100 3 506 19.17 18.61 .0051 .0025 85 282 42 641 −41 584 43 698 18.13 .0047 .0023 95 259 47 630 −47 63

T4−11 .0120 1 853 19.47 19.38 .0068 .0034 91 168 45 584 −45 312 45 856 18.55 .0064 .0032 101 662 50 831 −50 8

Heat treatment, 425 °C/90 min

T5−12 0.0070 10 652 19.05 18.68 0.0027 0.0014 75 225 37 613 −35 189 40 036 18.52 0.0025 0.0012 83 096 41 548 −41 45

T5−10 .0080 5 538 18.83 18.61 .0033 .0017 81 744 40 872 −39 597 42 147 18.42 .0030 .0015 91 407 45 704 −45 69

T5−13 .0100 3 490 19.17 18.93 .0051 .0026 83 860 41 930 −40 919 42 941 18.19 .0048 .0024 93 931 46 966 −46 96

T5−11 .0120 1 496 19.95 19.40 .0067 .0034 90 555 45 278 −45 038 45 517 18.35 .0062 .0031 104 075 52 038 −51 94

a

Total of the absolute values of the positive and negative strains.

NASA/TM—2012-216985 21
NASA/TM—2012-216985 22

Figure 14.—Fatigue life as a function of total strain range. 

Table IX gives the results for the forward stepwise regression analysis of the data fitted to the model 

in Equation (2). The negative coefficients indicate that, for a given life, the aging heat treatment lowered 

the strain range that could be sustained, or conversely, at a given strain range, the GRCop-84Z life was 

lower after receiving a 425 °C age. The exclusion of terms corresponding to the as-received and 525 °C 

aged GRCop-84Z samples indicates that, at a 95-percent confidence level, there were no statistically 

significant differences between GRCop-84Z in these heat-treated conditions and the baseline as-extruded 

GRCop-84. 

Furthermore, no Bxlog10(life) (where x = 1 to 5) terms made it into the regression model. These terms 

would indicate a change in slope for the regression lines corresponding to each condition. Since these 

terms do not enter the equation, there is a constant offset between the curves when there is a statistically 

significant difference in properties but no difference in the slopes. This indicates that there is no change in 

mechanism over the range of conditions studied. 

Figure 15 shows the life as a function of plastic strain range at the half-life of the specimens. The 

two-sided 95-percent confidence limits for the as-extruded GRCop-84 data are also presented. The data 

show a similar result compared with the life as a function of the total strain (Figure 14). This was 

expected because, even at room temperature, both GRCop-84 and GRCop-84Z undergo little elastic 

deformation during LCF testing. 
NASA/TM—2012-216985 23

TABLE IX.—RESULTS OF FORWARD STEPWISE REGRESSION ANALYSIS 

FOR LIFE VERSUS TOTAL STRAIN RANGE, ∆εT 

(a) Goodness of fit.

Multiple correlation coefficient, R 0.983

Coefficient of determination, R2 .967

Adjusted R2 .964 

Standard error of estimate, SY.X .0534 

(b) Analysis of variance.

Group Degrees of

freedom

Sum of squares Mean square F valuea Probability

Regression 3 3.047 1.016 356.665 <0.001

Residual 37 0.105 0.00285 ---------- ---------

(c) Variables in model.

Variableb Coefficient Standard error F valuea Probability

Constant –0.727 0.0376 ----------- --------- 

log10(life) –.341 .0106 1036.543 <0.001

B2 –.0721 .0322 5.021 .031

B3 –.0806 .0283 8.119 .007

(d) Variables not in model.

Variableb F valuea Probability

B1 0.497 0.485

B4 2.710 .108

B5 1.930 .173

B1 log10(life) .464 .500

B2 log10(life) .253 .618

B3 log10(life) .449 .507

B4 log10(life) 2.705 .108

B5 log10(life) 1.468 .233

a

Value of the F distribution for X degrees of freedom 

associated with the numerator and Y degrees of freedom 

associated with the denominator.

b

B1 to B5 are blocking variables indicating the treatments 

the material received (see Table II).
NASA/TM—2012-216985 24

Figure 15.—Fatigue life as a function of plastic strain range. 

To determine if there were statistically significant differences between specimens with different heat 

treatments, the data were fit to Equation (2) with the plastic strain range being used instead of the total 

strain range. The results of the forward stepwise regression are given in Table X. The analysis indicated 

that the as-extruded GRCop-84Z has a slightly higher plastic strain range at a given life or a longer life at 

a given plastic strain. The plastic strain range difference increases as life increases rather than being a 

constant offset. 

Figure 16 shows the cyclic strength at half-life (∆σ) for GRCop-84 and GRCop-84Z as a function of 

plastic strain range at the half-life of the specimens (∆εP). The results indicate that GRCop-84Z had a 

consistently greater strength than GRCop-84 at room temperature. This is consistent with the increase in 

room temperature strength shown in Figure 6 and Figure 7. A forward stepwise regression analysis using 

Equation (3) was done to confirm that the strengths were statistically significantly greater. As shown in

Table XI, the statistical analysis revealed that, in all heat-treated conditions, the strength of GRCop-84Z 

was significantly different from the as-extruded GRCop-84 strength. Even the as-received GRCop-84Z 

specimens had a higher strength, albeit only slightly greater than that of GRCop-84. Furthermore, the 

differences were a constant offset, indicating that the GRCop-84Z curves had the same slope as the 

as-received GRCop-84 regression curve.

Following testing the fracture surfaces were examined optically. A typical optical fractography 

appears in Figure 17. The initiation sites tended to be at the surface or at near-surface imperfections. No 

changes in the initiation sites were observed between GRCop-84 and GRCop-84Z specimens.
NASA/TM—2012-216985 25

TABLE X.—RESULTS OF FORWARD STEPWISE REGRESSION ANALYSIS 

FOR LIFE VERSUS PLASTIC STRAIN RANGE, ∆εP

(a) Goodness of fit.

Multiple correlation coefficient, R 0.988

Coefficient of determination, R2 .976

Adjusted R2 .975 

Standard error of estimate, SY.X .0721 

(b) Analysis of variance.

Group Degrees of

freedom

Sum of 

squares

Mean 

square

F valuea Probability

Regression 2 8.044 4.022 773.268 <0.001

Residual 38 0.198 0.00520 ---------- --------

(c) Variables in model.

Variableb Coefficient Standard error F valuea Probability

Constant –0.304 0.0510 ------------ --------

log10(life) –0.566 0.0145 1533.251 <0.001

B1 log10(life) 0.0222 0.0101 4.886 0.033

(d) Variables not in model.

Variableb F valuea Probability

B1 0.127 0.723

B2 .0482 .827

B3 3.108 .086

B4 .377 .543

B5 .306 .584

B2 log10(life) .0736 .788

B3 log10(life) 2.874 .098

B4 log10(life) .386 .538

B5 log10(life) .495 .486 a

Value of the F distribution for X degrees of freedom 

associated with the numerator and Y degrees of freedom 

associated with the denominator.

b

B1 to B5 are blocking variables indicating treatments 

that the material received (see Table II).
NASA/TM—2012-216985 26

Figure 16.—Cyclic strength as a function of plastic strain range. 
NASA/TM—2012-216985 27

TABLE XI.—RESULTS OF FORWARD STEPWISE REGRESSION ANALYSIS 

FOR PLASTIC STRAIN RANGE, ∆εP, VERSUS STRESS RANGE, ∆σ

(a) Goodness of fit.

Multiple correlation coefficient, R 0.987

Coefficient of determination, R2 .974

Adjusted R2 .969 

Standard error of estimate, SY.X .0155 

(b) Analysis of variance.

Group Degrees of

freedom

Sum of squares Mean square F valuea Probability

Regression 6 0.302 0.0504 209.233 <0.001

Residual 34 0.00819 0.000241 ---------- --------

(c) Variables in model.

Variableb Coefficient Standard error F valuea Probability

Constant 3.157 0.0125 ------------ -------

log10(σ) .188 .00556 1149.830 <0.001

B1 .0380 .00849 20.032 <.001

B2 .0547 .00956 32.740 <.001

B3 .105 .00852 150.650 <.001

B4 .0851 .00957 79.096 <.001

B5 .0994 .00852 136.146 <.001

(d) Variables not in model.

Variableb F valuea Probability

B1 log10(σ) 0.0501 0.824

B2 log10(σ) .0682 .796

B3 log10(σ) .159 .693

B4 log10(σ) .0168 .898

B5 log10(σ) .0188 .892

a

Value of the F distribution for X degrees of freedom 

associated with the numerator and Y degrees of 

freedom associated with the denominator.

b

B1 to B5 are blocking variables indicating the 

treatment that the material received (see Table II).
NASA/TM—2012-216985 28

Figure 17.—Typical optical fractograph of GRCop-94Z low cycle fatigue specimen aged at 425 °C/30 min/air cooled. 

Total strain range, 1.2-percent; life, 2141 cycles. (a) Fracture surface. (b) Detail of fracture initiation site. 

4.0 Discussion

A comparison of GRCop-84 and GRCop-84Z revealed several beneficial changes resulting from the 

addition of Zr. Unfortunately, an increase in LCF life was not one of the observed benefits; though, as 

discussed later, there may be a benefit at elevated temperatures.

4.1 Tensile Properties

The tensile test data indicate that the addition of 0.4 wt% Zr to GRCop-84 had a beneficial effect 

relative to the baseline as-extruded GRCop-84 properties. Fairly strong effects in the as-extruded and 

aged conditions were observed. It had been expected that the benefits would be greatest at room temperature. Significant increases were seen for the aged GRCop-84Z samples with increases in yield 

strength of 20 percent being achieved for the specimens aged at 525 °C. However, the greatest benefits 

were seen in specimens tested at 500 °C. The yield strength at 500 °C increased at least 35 percent for 

the aged GRCop-84Z specimens. Three of the four aging conditions increased the yield strength over 

60 percent. 

Even the as-extruded GRCop-84Z showed an increase in yield strength, probably because it had a 

higher total volume fraction of Cr2Nb and Cu5Zr precipitates. Cu5Zr precipitates can act as impenetrable 

barriers to dislocation movement and provide additional strengthening. The Cu5Zr precipitates were 

expected to contribute approximately 2 vol% precipitates on the basis of the composition. That raises the 

total volume fraction of precipitates to 16 vol%. This represents an increase of 15 percent in the precipitate volume fraction. 

If the simplifying assumptions are made that the precipitates are spherical and widely spaced, the 

Ashby-Orowan equation (Ref. 24) can be expressed as

1

2

K ln f V r

r b

      σ ≅          

(4) 

Here σ is the yield strength of the material (in megapascals); K is a constant equal to 0.1836 Gb, where G

is the shear modulus in megapascals and b is the Burgers vector in the slip direction in nanometers; Vf is 

the volume fraction of precipitate; and r is the average radius of the precipitates in nanometers. Although 
NASA/TM—2012-216985 29

the simplifications may not apply to GRCop-84Z, it is possible to use this equation to estimate order-ofmagnitude changes. 

According to the Ashby-Orowan model, the increase in volume fraction of precipitates from 14 to 

16 vol% alone would increase the strength by 7 percent. Since the CuxZr precipitates are finer, the AshbyOrowan model also predicts a considerable increase in strength from the reduced precipitate size. No 

quantitative measurements were made of the CuxZr precipitate size, but if one uses an estimate of the 

CuxZr precipitate diameter being one-quarter to one-third of the diameter of the Cr2Nb precipitates and 

assumes the strengthening of each type of precipitate to be additive, the total strength increase would be 

on the order of 23 to 39 percent. This estimate for the increase in strength is consistent with the observed 

difference in the room temperature strengths of GRCop-84 and GRCop-84Z. This indicates that the Cu5Zr 

precipitates are acting as expected to provide additional strengthening.

The very large increase in 500 °C strength and ductility was unexpected. It had been assumed that the 

Cu5Zr precipitates would start to overage at this test temperature and not contribute such a substantial 

increase in strength. Instead, they had the greatest effect at this temperature. It appears from the creep data 

that the beneficial effects persist at this temperature over an extended period of time since creep tests 

lasting up to approximately 3000 h did not show any clear signs of overaging. It appears that the kinetics 

of precipitate growth are slow even at this temperature. Additional work will need to be done to determine 

the maximum temperature at which the Cu5Zr precipitates will still have a useful effect.

There is an apparent incongruity in the ductility of GRCop-84Z relative to GRCop-84. The ductility 

of GRCop-84Z as measured by the elongation of the gauge section increased at room temperature. 

Examination of the samples after testing showed that the reduced section was fairly constant in diameter.

Little or no necking or other dimensional instabilities were noted. Apparently the deformation remained 

uniform for longer than occurred in GRCop-84. This dimensional stability prevented the formation of a 

neck during tensile testing. Without a pronounced neck, as is typical of GRCop-84 and most other 

Cu alloys, there was less reduction in area at the fracture site. The failure stress was also higher because 

the sample still had a large area relative to a sample that undergoes considerable necking. In fact, the 

fracture strength was only a bit less than the UTS as shown in Figure 10(a). The change to a more 

uniform deformation throughout the entire gauge section increased the elongation, but the lack of a neck 

decreased the reduction in area. This gave ambiguous results as to whether or not the addition of Zr 

improves the ductility. For many applications, the uniform tensile elongation is the more important 

measure of ductility, and if this criteria is used, the Zr addition was beneficial. 

One interesting possible benefit from the lack of necking at room temperature is that GRCop-84Z 

may prove to be more formable. The uniform nature of the deformation should allow bending and other 

forming operations to occur without thinning and the potential failure of the part. No work has been 

performed in this area, but it is a potential area for future study.

The increase in ductility at 500 °C was caused by a combination of more uniform elongation in the 

reduced gauge length combined with more necking once a dimensional instability appeared. The increase 

in temperature presumably decreased the shear stress and may have allowed dislocation climb to occur 

around the Cu5Zr precipitates. The increase in temperature also could have activated one or more additional slip systems. These changes allowed more shear deformation to occur in the neck region. Because 

of the shear, the samples could deform more than at room temperature. This resulted in more necking and 

a larger reduction in area. The increased strength and more uniform deformation allow GRCop-84Z to 

deform more than GRCop-84, so the reduction in area at 500 °C increased. The large increases in both 

tensile elongation and reduction in area unambiguously demonstrate that addition of Zr increased the 

ductility at 500 °C. 

One goal of adding Zr to GRCop-84 was to increase the room temperature yield strength by at least 

15 percent. This goal was exceeded. Beyond the increase in room temperature yield strength, the Zr 

addition increased the room temperature UTS and the 500 °C yield strength and UTS while generally 

improving the ductility. The benefits are substantial, and the addition of Zr clearly improved the tensile 

properties. 
NASA/TM—2012-216985 30

4.2 Creep Properties

The creep data indicate that the addition of Zr has a very strong positive effect on creep properties in 

aged GRCop-84Z. As shown in Table VII, at 500 °C, samples aged at 425 and 525 °C had their creep rate 

decreased by a factor of 100.78, or 6 times, and their creep life increased by a factor of 100.64, or 4.4 times. 

The fine Cu5Zr precipitates created during aging act as strong barriers to dislocation movement. The 

increased yield strength also means that the creep specimens are tested at stresses below the 0.2% offset 

yield strength, so the amount of macroscopic plastic deformation upon loading is greatly decreased, 

though not completely eliminated. 

The increase in 500 °C ductility does not appear to be a major contributing factor to the improvement 

in creep life. The as-extruded GRCop-84Z specimens have better ductility than the GRCop-84 specimens, 

but only the low stress creep tests demonstrated better lives. If increased uniform elongation had been 

improving creep lives by providing a larger “pool” of ductility and extending the time in steady-state 

creep, it would be expected that all of the as-extruded GRCop-84Z specimens would exhibit at least some 

increase in life. This was not observed. 

The as-extruded GRCop-84Z showed two distinct regimes in its creep properties. At higher stresses, 

the material behaved similarly to GRCop-84. This was expected since the material lacked the finer CuxZr 

precipitates created by a solution and aging heat treatment. At the lowest stress tested, the as-extruded 

GRCop-84Z exhibited much better creep properties than GRCop-84. The as-received specimens’ rates 

and lives approached those of the aged GRCop-84Z specimens. As shown in Table VII, the creep rate 

decreased by a factor of 100.40, or 2.5 times, and the creep life increased by a factor of 100.42, or 2.6 times. 

It appears from this behavior that there is a minimum stress required to overcome the barriers presented 

by the coarser CuxZr precipitates in the as-extruded GRCop-84Z. Most likely, this is a stress associated 

with dislocation climb or another similar mechanism. Once the minimum stress was achieved and the 

dislocations could climb or otherwise circumvent the barriers, the as-extruded GRCop-84Z acted similar 

to the as-extruded GRCop-84. The finer precipitates in the aged GRCop-84Z specimens probably require 

a higher stress for dislocation climb to become active, or dislocation climb is not active in aged specimens 

for some unknown reason. 

4.3 Low Cycle Fatigue Properties

The addition of Zr to GRCop-84 did not have the beneficial effects on LCF lives anticipated from

Figure 1. Instead the LCF specimen lives for all GRCop-84Z heat treatments were generally within the 

95-percent confidence limit for GRCop-84. Those that were not within the 95-percent confidence limits 

were just below the lower confidence limit. The lives tended toward the lower limit when plotted against 

total strain, but lives based on plastic strain were similar to those for GRCop-84. The cyclic strength of 

GRCop-84Z did show a definite improvement over GRCop-84, which is consistent with GRCop-84Z’s 

higher strength. 

In general, ductility correlates well with the fatigue life of a material as was explained by Coffin and 

Manson (Ref. 25). Materials with large amounts of ductility can absorb and tolerate large amounts of 

damage prior to failure. The relative room temperature ductility of GRCop-84Z as measured by the tensile 

elongation is 3.4 to 29.8 percent greater than that of GRCop-84, but the ductility as measured by the 

reduction in area is reduced by 23.9 to 45.2 percent. The differing amounts of ductility make it unclear if 

the room temperature LCF lives of GRCop-84Z should increase or decrease. In both cases, the absolute 

ductility remained above 15 percent, so GRCop-84Z never became brittle and it still exhibited good 

LCF lives. 

Examination of the fracture ignition sites indicated that cracks generally initiated at the surface. The 

cracks propagated inwards until they linked up to form a single crack that propagated to eventual failure 

of the specimen. Some cracks initiated at small surface defects, small inclusions, and pores, as was 

observed in GRCop-84 LCF fractures. These small defects did not appear to have a strong effect on 

the LCF lives of GRCop-84 or GRCop-84Z. Rather they were just the sites of the highest local stress 
NASA/TM—2012-216985 31

concentration or of a microscopic preexisting crack. Given the similar fracture surface morphologies and 

behaviors of GRCop-84 and GRCop-84Z, the authors concluded that adding Zr to make GRCop-84Z 

probably did not change the fracture mechanism or sensitization from that of GRCop-84. 

Because of the early termination of the program, the unexpectedly lower lives of GRCop-84Z could 

not be examined in the level of detail desired. The authors speculate that the area of the GRCop-84Z in 

the plane perpendicular to the applied load near the crack tips that undergoes plastic deformation is 

smaller. This is based on the lower macroscopic reduction in area observed for GRCop-84Z during tensile 

testing. With less material undergoing plastic deformation, damage accumulates quicker and the cracks 

can propagate more readily. This effect is partially countered by the greater tensile ductility, which 

increases the amount of material in the direction of the applied load undergoing deformation. The 

presence of more obstacles in the form of fine CuxZr precipitates can also have a beneficial effect both in 

strengthening the GRCop-84Z and in preventing persistent slip bands. If one assumes that all three 

mechanisms are operative, the reduction in volume appears to be slightly more influential than the 

combined effects of greater tensile ductility and more precipitates. 

Figure 6 and Figure 7 show that the 0.2% offset tensile yield strength of GRCop-84Z is 2.3 to 

20.6 percent greater than for GRCop-84 and that the UTS is 19.9 to 26.8 percent greater. The higher 

tensile strength is consistent with the higher cyclic strength and indicates that the fine Cu5Zr precipitates 

do strengthen GRCop-84Z during fatigue. 

As noted in the results for the forward stepwise regression analyses (Table IX and Table X), the 

425 °C aging appeared to have a greater effect on the room temperature GRCop-84Z LCF life than the 

525 °C aging did. The effects also tended to be negative rather than positive: for example, the LCF 

life based on total strain (Table IX) was statistically lower than for GRCop-84 and the 525 °C aged 

GRCop-84Z. This may indicate that a 425 °C aging temperature could have a long-term detrimental 

effect. Examination of samples given longer aging times is recommended if a combustion chamber liner 

or other GRCop-84Z part is to be operated in this temperature range. 

Although the LCF testing was conducted only at room temperature, some speculation was given to 

the benefits of Zr on elevated temperature LCF lives and cyclic stresses. As shown in Figure 8, the 500 °C 

tensile strength of aged GRCop-84Z is much greater than that of GRCop-84. The 0.2% offset yield 

strength increases 35.6 to 63.5 percent, and the UTS increases 42.9 to 67.6 percent. It is anticipated that 

this large increase in elevated temperature strength will translate into GRCop-84Z having much greater 

500 °C cyclic stresses than GRCop-84. 

Unlike the room temperature tests, the 500 °C data show large increases in both the tensile elongation 

(56.7 to 84.6 percent) and reduction in area (89.7 to 128.0 percent). Assuming that the elevated temperature LCF lives follow the common trend of increased life with increased ductility, the authors believe 

that the 500 °C LCF lives will show benefits from the addition of Zr to GRCop-84. Unfortunately, this 

hypothesis could not be tested before the experimental work concluded. The authors hope that additional 

GRCop-84Z LCF testing at 500 °C can be done in the future.

The forward stepwise regression analyses allow the observed effects of heat treatment and adding Zr

to be quantified. For the lives, the statistically significant differences observed mostly show an offset in 

the response relative to the baseline. This indicates that GRCop-84 and GRCop-84Z probably have the 

same failure mechanism. It is also consistent with the fractography observations. In the one case where 

the slope changes, there is only a small difference in slope, which could well be influenced by only 

having three data points. It is likely that the difference would either disappear or the dependency would 

change to an offset with additional data for as-received GRCop-84Z.

The regression analysis of the strengths also shows offsets in the curves with the addition of Zr and 

the various heat treatments. The lack of a change in slope again indicates that the mechanisms operating 

probably remain the same. The addition of Zr and the formation of fine Cu5Zr precipitates is probably just 

additively strengthening GRCop-84Z as expected.
NASA/TM—2012-216985 32

4.4 Aging Temperature and Time

There are clear strength and creep benefits to a solution and aging heat treatment for GRCop-84Z.

The as-extruded GRCop-84Z, although it has CuxZr precipitates that are finer than most of the Cr2Nb 

precipitates, does not achieve the property increases of aged GRCop-84Z. The effects of aging are not as 

unambiguous for the tensile ductility and LCF lives. The authors believe that overall the addition of Zr 

and the use of a solution and age heat treatment will improve the properties of GRCop-84Z and make 

them generally superior to those of GRCop-84. 

The optimum aging temperature and time were not determined in this study because of the limited 

material and data available, but the data indicated that both 425 and 525 °C are good choices. Neither 

appears to overage the Cu5Zr precipitates even after 90 min. The creep data, which extend to 3000 h at 

500 °C, also support aging in this temperature range. The creep properties of the aged GRCop-84 specimens do not indicate that the CuxZr precipitates undergo overaging even after very extended times at 

500 °C. This indicates good stability for the CuxZr precipitates and slow growth kinetics. These are 

desirable traits for a precipitate.

Higher aging temperatures may yield comparable and perhaps better results, but it is more likely that 

overaging will occur instead. Lower temperatures will require longer times, which are not desirable in a 

commercial aging process. It appears that the currently used temperatures, if not optimum, are suitable.

Overall, it appears that aging at 425 °C for 90 min gives the best combination of mechanical properties. This temperature is probably a good choice for aging cold-worked GRCop-84Z as well. Applications 

that require the highest LCF lives and that can tolerate a small decrease in tensile and creep properties 

may need a 525 °C aging temperature since LCF lives were shown to be slightly decreased by aging at 

425 °C. More testing to optimize the aging time and temperature is required, but the preliminary survey 

shows great promise for aged Cu-Cr-Nb-Zr alloys in the temperature range of this study. 

4.5 Cold Rolling

Cold rolling is a major strengthening mechanism. Cu-Cr and Cu-Cr-Zr alloys typically use cold 

work followed by an aging step to increase their strengths (Refs. 11 and 12). Similar processing with 

GRCop-84Z had been planned, but time and funding did not permit this work to proceed to the point 

where quantitative results could be obtained. Some observations do allow speculation as to the benefits 

that may be obtained by cold working and aging GRCop-84Z. 

There are considerable differences between the yield strengths and UTS of the GRCop-84Z samples.

GRCop-84Z also has good ductility. Prior work with GRCop-84, which has similar properties, showed

that GRCop-84 can be cold rolled 90 percent or more. The authors believe that GRCop-84Z also could be 

cold rolled extensively. Such rolling should increase at least the room temperature yield strength of 

GRCop-84Z. This is consistent with the improvements seen in cold-worked Cu-Zr specimens (Ref. 26).

The addition of Zr to Cu-Cr alloys has been shown to retard annealing at 500 °C through the precipitation of CuxZr precipitates (Ref. 27). It is likely that the same will happen in GRCop-84Z. Prior work 

with hard-drawn Cu-0.15 Zr and Cu-1 Cr-0.1 Zr has shown, on the basis of the alloys’ retention of high 

strength, that the cold work is not lost at 500 °C (Refs. 5 and 28). This indicates that the CuxZr precipitates are not coarsening or dissolving much at this temperature. If this is also the case for GRCop-84Z, 

which seems likely from the current results, then the tensile properties up to 500 °C could be improved 

further by cold working. 

At the present time it is unknown how much improvement could be realized, but the yield strength of 

cold-worked GRCop-84Z is likely to approach that of cold-worked Cu-Zr and Cu-Cr-Zr alloys between 

room temperature and 500 °C. This will make GRCop-84Z more competitive with these and similar 

alloys.
NASA/TM—2012-216985 33

5.0 Future Work

The program terminated early with many questions remaining unanswered. The authors suggest that 

any follow-on work include the following: 

1. The thermal and electrical resistivity of GRCop-84Z must be measured to determine if the Zr 

addition has a negative effect and how large the effect is. The authors believe that the addition of 

more fine precipitates to act as electron scattering points will decrease the thermal conductivity 

slightly, but this may be countered to some extent by removing oxygen from the matrix. 

2. Cold-worked material must be tested. Cold working is a major strengthening mechanism for 

competitive alloys. The addition of Zr is expected to retard the recovery and recrystallization so 

that cold-worked material could be used up to at least 500 °C. The actual point where the benefits 

of cold work are lost needs to be determined to examine the potential benefits for rocket engine 

and other applications.

3. The LCF properties at 500 °C must be tested to determine if adding Zr improves LCF properties 

at elevated temperatures. It was anticipated that the addition of Zr would primarily benefit the 

alloy at low temperatures, but the unexpected improvements in 500 °C properties indicate that Zr 

has a larger positive effect at the upper range of the anticipated operating temperatures. 

4. The tensile properties of GRCop-84Z should be tested at more temperatures to determine the 

intermediate tensile properties and at what temperature the benefits of adding Zr cease. Testing 

at intermediate temperatures will also determine if the unusual changes in the ductility of 

GRCop-84Z relative to GRCop-84 occur above room temperature.

5. Although the current aging temperatures and times are suitable for most applications, they cannot 

be considered to be optimized. Tensile testing with additional aging temperatures to determine the 

optimum temperature for both solution-heat-treated and cold-worked GRCop-84Z may reveal that 

further benefits can be gained through better heat treatments.

6.0 Summary and Conclusions

It was observed that literature values of mechanical properties for Cu-based alloys increased when

small amounts of Zr were added, so a preliminary examination was undertaken to determine if the 

addition of Zr to GRCop-84 would produce beneficial effects. 

The addition of Zr clearly produced changes in the tensile properties of GRCop-84 at both room 

temperature and 500 °C. At room temperature, the 0.2% offset yield strength was increased between 

2.3 and 20.6 percent depending on the aging treatment. The 500 °C yield strength increased even more, 

with gains between 25.2 and 63.5 percent, again depending on the aging treatment. Similar increases in 

the ultimate tensile strength and tensile elongations occurred. The reduction in area actually decreased at 

room temperature because less necking occurred, but it increased 99.7 to 128.0 percent at 500 °C.

The 500 °C creep properties of aged GRCop-84Z showed considerable improvements over 

GRCop-84. Aged GRCop-84Z samples had a nearly 2-order-of-magnitude decrease in creep rate and over 

1-order-of-magnitude increase in creep life in comparison to GRCop-84. Even the unaged, as-extruded 

GRCop-84Z was superior to GRCop-84 by similar margins at the lowest applied stress tested and equal at 

higher applied stresses.

The room temperature low cycle fatigue (LCF) lives of GRCop-84Z were generally equal to those of 

GRCop-84. Only the GRCop-84Z samples aged at 425 °C showed a potential slight decrease in the LCF 

life relative to GRCop-84, and the difference was probably not of great engineering significance. The 

stress range for GRCop-84Z exceeded that of GRCop-84 by 50 to 115 MPa depending on the heat treatment. Since LCF lives are generally related to ductility, the authors speculate that the 500 °C LCF lives 

of GRCop-84Z would exceed those of GRCop-84 since GRCop-84Z has much greater tensile ductility 

(>50-percent increase in elongation and >95-percent increase in reduction in area). Likewise, the increase 

in 500 °C strength will probably translate into increased stress ranges at 500 °C.
NASA/TM—2012-216985 34

The addition of Zr to GRCop-84 showed clear benefits in most of the mechanical properties tested. 

Aging appeared to enhance these benefits. Additional benefits to the mechanical properties should be 

realized if the material is cold worked prior to testing. Cold working may be required to improve the room 

temperature mechanical properties to make them competitive with other high-strength, high-conductivity 

Cu-based alloys. Although most of the benefits of Zr were expected to occur at room temperature, in fact 

the greatest benefits occurred at 500 °C.

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and William F. Brown, Jr., eds., 40th ed., vol. 6, CINDAS, West Lafayette, IN, 2002. 

21. Monkman, F.C.; and Grant, N.J.: An Empirical Relationship Between Rupture Life and Minimum 

Creep Rate in Creep-Rupture Tests. Proc. ASTM, no. 56, 1956, pp. 593–620. 

22. Ellis, D.L.; Walley, J.L.; and Ferry, M.H.: The Effects of Processing Upon the Creep Properties of 

GRCop-84, to be published. 

23. Lerch, Bradley A.; Ellis, David L.; and Yun, HeeMan: Low Cycle Fatigue Behavior of GRCop-84. 

NASA/TM—2010-216737, 2010. Available from the Center for Aerospace Information. 

24. Ashby, M.F.: The Theory of the Critical Shear Stress and Work Hardening of Dispersion-Hardened 

Crystals. Oxide Dispersion Strengthening, Proceedings of Metallurgical Society Conferences, 

vol. 47, New York, NY, 1968, p. 143. 

25. Meyers, Marc André; and Chawla, Krishan Kumar: Mechanical Metallurgy: Principles and 

Applications. Prentice-Hall, Inc., Englewood Cliffs, NJ, 1984, Sec. 21.1.4, Fatigue Strength or 

Fatigue Life, pp. 695–699. 

26. Horn, D.D.; and Lewis, H.F.: Property Investigation of Copper Base Alloys at Ambient and Elevated 

Temperatures. AEDC–TR–65–72, 1965. 

27. Su, J.H., et al.: Recrystallization and Precipitation Behavior of Cu-Cr-Zr Alloy. J. Mater. Eng. 

Perform., vol. 16, no. 4, 2007, pp. 490–493. 

28. de Groh, H.C.; Ellis, D.L.; and Loewenthal, W.S.: Comparison of GRCop-84 to Other Cu Alloys 

With High Thermal Conductivities. J. Mater. Eng. Perform., vol. 17, no. 4, 2008, pp. 594–606. 
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1. REPORT DATE (DD-MM-YYYY)

01-06-2012 

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Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Improvement of GRCop-84 Through the Addition of Zirconium 

5a. CONTRACT NUMBER

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5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Ellis, David, L.; Lerch, Bradley, A. 

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WBS 463169.04.03.05.01 

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National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

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Subject Category: 26 

Available electronically at http://www.sti.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

GRCop-84 (Cu-8 at.% Cr-4 at.% Nb) has excellent strength, creep resistance, low cycle fatigue (LCF) life and stability at elevated 

temperatures. It suffers in comparison to many commercially available precipitation-strengthened alloys below 500 °C (932 °F). It was 

observed that the addition of Zr consistently improved the mechanical properties of Cu-based alloys especially below 500 °C. In an effort to 

improve the low temperature properties of GRCop-84, 0.35 wt.% Zr was added to the alloy. Limited tensile, creep, and LCF testing was 

conducted to determine if improvements occur. The results showed some dramatic increases in the tensile and creep properties at the 

conditions tested with the probability of additional improvements being possible through cold working. LCF testing at room temperature did 

not show an improvement, but improvements might occur at elevated temperatures.

15. SUBJECT TERMS

Copper alloys; Mechanical properties 

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