NASA USAAVSCOM

Contractor Report 175052 Technical Report 86-C-14

Axial and Torsional Fatigue

Behavior of Waspaloy

(NASA-CS.-175052) AXIA L AND TOESIONAL

 % N86-25U54

FATIGUE BEHAVIO E OP WASPALO Y Final Report

(Pennsylvania State Uiiiv.) 27 p

HC A02/HP A01 CSC1 11F Unclas

63/26 .

S. 'Zamrik, M. Mirdamadi, and F. Zahiri

The Pennsylvania State University

University Park, Pennsylvania

April 1986

Prepared for

Lewis Research Center

Under Grant NAG 3-264

NASA

National Aeronautics and

Space Administration
AXIAL AND TURSIONAL FATIGUE BEHAVIOR OF WASPALOY

S. Zamrlk, H. M1rdamad1, and F. Zahlrl

The Pennsylvania State University

Engineering Science and Mechanics Department

University Park, Pennsylvania 16802

INTRODUCTION

This 1s a brief progress report describing the failure modes observed 1n

completed cyclic and hold-time tests conducted on Waspaloy material at 1200 °F.

The Waspaloy material was made of two grain structures, Identified as fine

grain (16 ym) and coarse grain (124 \an). The material has y1 precipitates

of two sizes, one small (50 A) associated with coarse grain and one large

(1000 A) associated with fine grain.

TESTS CONDUCTED

Axial and torslonal cyclic tests were completed on the two types of

grained structure at room temperature and 1200 °F. Also hold-time tests with

90 sec hold 1n the tension side of the axial loading and 1n the counterclockwise side of the torslonal loading. The type of wave shape that was applied

Is shown on the Individual macrograph.

LOW-CYCLE FATIGUE TORSIONAL TESTS (COARSE GRAIN)

Figure 1 shows the failure mode of a coarse grained test specimen that

failed under torslonal shear strain range continuous cycling at 1200 °F.

The failure mode shows a transition from shear observed at room temperature

to tensile stage at 1200 °F. To verify this 45° crack mode, duplicate tests

were conducted at two levels of plastic shear strain ranges, one at

Ay = 0.52 percent to failure and the other at Ay = 92 percent to

failure. In both cases, the failure mode was tensile with cracks at 45° mode

as shown 1n figure 2.

Microscopic examination was conducted using replicas and scanning

electron microscopy techniques. Figure 3 shows the general cracking path at
45° with respect to specimen axis. The zigzagging crack path shown 1n

figure 3(b) was studied with an enlargement shown 1n figure 3(b). The

progress of the crack was hindered by grains that saw little plastic

deformation (slip bands activities) and were 1n elastic condition forcing the

crack to deviate. This 1s shown clearly 1n figure 3(c). Furthermore, at

1200 °F, carbides and precipitates were observed on slip bands and on grain

boundaries as shown 1n figure 3(e). Therefore, the tensile failure mode can

be attributed to the embrlttlement of these carbides, assisted by an oxidation

that enhanced the embrlttlement process. Embrittled regions are sensitive to

normal stresses. Figure 3(e) also shows additional large particles. The

chemical composition of these large particles was found, by x-ray energy

spectrum analysis (fig. 4), to be the same material as that of the matrix.

These large particles have also Initiated crack sites that contributed to

mode I cracking. With respect to the slip mode characteristic, It was found

1n all cases to be planar slip that resulted 1n y' particles shearing.

TORSIONAL HOLD-TIME TEST (COARSE GRAIN)

The test at 1200 °F under 90 sec hold time showed similar failure

characteristics (45°) to that observed under continuous cyclic with little

effect of creep as shown 1n figure 5. Replicas taken on the surface after

failure showed extensive grain boundary cracking, planar slip and some

twinning as shown 1n figure 6. Also observed, an extensive oxidation on slip

bands and grain boundaries. In general, the microscopic behavior of the

hold-time test was similar to that under continuous cyclic except for the

amount of oxidation. The crack growth was also at 45° with respect to

specimen axis.

AXIAL HOLD-TIME TEST (COARSE GRAIN)

The axial hold-time test at 1200 °F, showed the failure to be normal to

the loading axis as shown 1n figure 7. Scanning electron microscopy analysis

2
of the gauge surface, figures 8 and 9, showed mixed ode crack Initiation:

grain boundary cracking and slip band cracking. However, the propagation was

mostly transgranular.

Microscopic comparison between the axial and torslonal hold-time failure

characteristics, revealed extensive multiple slip system activity as well as

twinning to have taken place 1n the axial case. Also the axial case showed a

greater grain boundary cracking. The creep effect was observed to be minimum.

TORSION HOLD-TIME TEST (FINE GRAIN)

The torslonal hold-time test of the fine grained specimen resulted 1n a

shear mode failure (longitudinal crack along specimen axis) as shown 1n

figure 10. The microscopic examination of the gauge surface showed extensive

grain boundary oxidation and some grain boundary cracking that resulted 1n

Inter- and transgranular crack growth. Ill defined oxidized wavy slip bands

(fig. 11), were observed rather than the strict planar slip that was seen 1n

other described tests. Replicas taken on the surface are shown 1n figure 12.

Creep showed an effect when compared to data obtained on coarse grain test.

AXIAL HOLD TIME (FINE GRAIN)

The axial hold-time test of the fine grained specimen showed the failure

to be normal to the loading axis as shown 1n figure 13. The microscopic

examination of the gauge surface showed extensive grain boundary cracking,

wavy slip and considerable oxidation. These features are shown 1n figures 14

and 15. The comparison between the torslonal and the axial hold-time tests of

the fine grained specimen showed distinct features:

(1) The axial hold time produced excessive grain boundary cracking.

(2) The torslonal hold time showed excessive oxidation and less grain

boundary cracking.

(3) Creep effect was greater 1n the axial case.
CYCLIC STRESS-STRAIN RESPONSE

Hysteresis loops for both types of axial and torslonal hold time taken at

half lives are Included 1n figures 16 to 20. The variation 1n the shear

stress range for the case of continuous shear strain cycling at room and

1200 °F shows an Interesting behavior for each type of grained specimen on a

cycle basis. The fine grained material exhibited substantial stress

relaxation during the 90 sec hold time under both axial and torslonal loading,

as may be seen 1n figures 16 and 17. The 90 sec strain hold resulted 1n about

25 percent stress relaxation 1n both cases: for torslonal loading, the cyclic

stress amplitude was about 48 ks1, with 12 ks1 relaxation during the hold.

Similarly, under axial loading the cyclic amplitude was 104 ks1, with 22.4 ks1

relaxation after the 90 sec strain hold.

In comparison, the coarse grained material showed very little stress

relaxation after 90 sec strain hold, as may be seen 1n figures 18 and 19.

This 1s partly due to the softer (lower peak cyclic stresses) condition of the

coarse grain material. Also, 1f time dependent deformation occurs

predominantly at grain boundaries, the coarse grain material would afford a

reduced opportunity for time dependent deformation to occur.

The torslonal cyclic stress-strain behavior of both the fine grain and

coarse grain material 1s summarized 1n figure 20. The fine grain material

shows substantial hardening (about 10 percent Increase over Initial cyclic

stress range) up to 10 to 20 percent of life, followed by softening out to

failure. This behavior was exhibited at both room temperature and 1200 °F.

The coarse grain Waspaloy on the other hand, showed either a flat response at

room temperature, or monotonlc softening at 1200 °F.
CONCLUSIONS

(1) There appears to be reasonable correspondence between axial and

torslonal low-cycle fatigue (LCF) 1n fine grained Waspaloy tested at both 75

and 1200 °F.

(2) There 1s also reasonable correspondence between the damage mechanisms

observed 1n axial and torslonal LCF 1n coarse grained Waspaloy at 75 °F.

However, at 1200 °F a tensile dominated failure mechanism was activated 1n

torslonal loading whereas a plasticity dominated mechanism was activated 1n

axial loading. Also, there was a difference between the fine grained and

coarse grained Waspaloy damage mechanisms at 1200 °F.

(3) During cyclic hold-time experiments, fine grain Waspaloy demonstrated

substantial stress relaxation at 1200 °F, under both axial and torslonal

loading. Very little relaxation was observed in coarse grain Waspaloy. Also,

cyclic hardening was observed 1n fine grain Waspaloy at both room temperature

and 1200 °F; coarse grain Waspaloy exhibited either flat cyclic response or

monotonlc softening.

(4) These experiments demonstrate that LCF damage depends on the material

and heat treatment, the test temperature and the state-of-stress.
ORIGINAL PAGE-13

OF POOR QUALITY

(a)

(b)

Fig. 1 a) Macrophoto of Waspaloy course grain

torsional 1200°F. (Spec.

BF27,ATT=1 .58$,AYP = 0.655& § Nf/2,

Nf=4528) Note primary cracking at

45° to specimen axis on planes of

maximum tensile stress.

b) Applied wave form (10 cpm).
ORIGINAL PAGE IS

OF POOR QUALITY

(a)

(b)

Fig. 2 a) Macrophoto of Waspaloy course grain

torsional 1200°F. (Spec.

BF4,/VYT=1 .34?,AYp=0.52$ to failure,

Nf=5500) Note primary cracking at

**5° to specimen axis on planes

maximum tensile stress.

b) Applied wave form (10 cpm).
SPEC. AXIS

a

0 1 '3 k x 1 0k v 127*

(a)

SPEC. AXIS

(b)

Fig. 3 a) Primary crack at 45° to the specimen

axis (Spec. BF^) on planes of maximum

tensile stress.

b) Enlarged region of (a) showing slip band

formation and crack orientation and

propagation. It also shows undeformed

grain ahead of the crack front forcing

the crack to change direction.
ORIGINAL PAGE IS

OF POOR QUALITY

I

SPEC. AXIS

(c)

SPEC. AXIS

(d)

Fig. 3 c) Enlarged region of (b), showing further

details of the crack arrest and

orientation.

d) Micrograph showing the major crack was

due to large particles (inclusions) in

the grain.
SPEC. AXIS

50k x 1 0k M 131

(e)

Fig. 3) Micrograph showing the crack was initiated

on the maximum tensile stress and

propagated at 45° to the slip bands, Mode

I crack propagation. Note large particle

formation.

10
Fig. 4) X-Ray energy spectrum analysis revealed

the content of the particles (inclusions)

to be Ni, Cr, Mo, Co, Ti.
(a)

1.5 sec

(b)

Fig. 5 a) Macrophoto of Waspaloy course grain:

Torsion with hold time. (Spec.

BF25,AYT=1 .55/&,AYin=0.6435& @ Nf/2,

Nf=2691, T=1200°F, t-90 Sec.)

Note primary crack at 45° to the

specimen axis on plane of maximum

tensile stress.

b) Applied wave form.
ORIGINAL PAGE 13

OF POOR QUALITY

SPEC. AXIS

(a)

(b)

Fig. 6 a,b) Replicas of gage surface along the

major crack at 40X. Mixed mode cracking is shown, grain boundary cracking,

twining deformation, multiple slip

system are observed.

13
(a)

1.5 sec 90 sec

(b)

Fig. 7 a) Macrophoto of Waspaloy course grain:

Axial with hold time. (Spec.

BF8,AeT=0.7$,Aeln=0.295£ @ Nf/2,

Nf=987, T=1200°F, t=90 Sec.)

Note primary crack normal to the

loading axis.

b) Applied wave form.

14
ORIGINAL PAGE 53

OF POOR QUALITY

SPEC. AXIS

030k x 1 0 k v 403

(a)

(b)

Fig. 8 a) Micrograph showing primary crack normal

to the loading axis.

b) Mixed mode crack initiation and transgranular crack propagation. Note multiple

slip systems operating, also deformation

twining is observed.

15
SPEC. AXIS

f

0 . 78k x 18kv 404

(a)

( b)

Fig. 9 a,b) Slip bands intersecting oxidized

grain boundaries induced cracking,

also multiple slip systems and

deformation twining is observed.

16
ORIGINAL PAGE 13

OF POOR QUALITY

(a)

1. 5 sec — •90 sec-

(b)

Fig. 10 a) Macrophoto of Waspaloy fine grain:

Torsion with hold time. (Spec.BAlS,

AYT=1.9^,AYin=0.5585£ & Nf/2,Nf=1653,

T=1200°F,t=90 Sec.).

Note primary crack is along the specimen

axis

b) Applied wave form.

17
SPEC. AXIS

\ (a)

.•l**:*»*v *

II

(b)

Fig. 11 a) Primary crack along the specimen axis,

intergranular and transgranular cracking

is observed, extensive oxiedation on the

grain boundaries.

b) Note wavy and oxidized slip bands.

18
ORIGINAL PAGE 13

OF POOR QUALITY

SPEC. AXIS

(a)

I

(b)

19
(a)

1.5 sec- 90 sec

(b)

Fig. 13 a) Macrophoto of waspaloy fine grain:

Axial with hold time. (Spec.

BA30,AeT=1.01$,Aeln=0.32$ g Nf/2,

Nf=587, T=1200°F, t=90 Sec.)

Note primary cracking normal to the

loading axis.

b) Applied wave form.

20
ORIGINAL PACE !

OF POOR QUALITY

SPEC. AXIS

(a)

(b)

Fig. 14 a) Twin boundary cracking, oxidized slip

bands are observed

b) Cracking along the grain boundaries,

also note wavy slip bands
SPEC. AXIS

(b) \

Fig. 15 a,b) Replicas of the gage surface at

extensive grain boundary cracking

above and below the primary crack

are observed.

.

•

22
700 750

Fig. 16) Torsional hysteresis loops for small grain Waspaloy (Spec. BA13), tested at 1200 °F under 90 sec hold time.

(AyT= 1.94%, Ayin • 0.558% at Nf/2. Nf • 1653).

,a=28.02ksi

Fig. 17) Uniaxial hysteresis loops for small grain Waspaloy (Spec. BA30), tested at 1200 °F under 90 sec tension

hold time. (AET • 1.01%, Aein • 0.32% at Nf • 587).

23
|

TCCW

1000 1087 1178

Fig. 18) Torsional hysteresis loops for large Waspaloy (Spec. BF25), tested at 1200 °F under 90 sec hold time.

(Ayr - 1.55%, Ayjn - 0.643 at Nf 12, Nf • 2691).

351 400 449 450 451 500

Fig. 19) Uniaxial hysteresis loops for large grain Waspaloy (Spec. BF8), tested at 1200 °F under 90 sec tension hold

time. (AeT • 0.70%, Aein • 0.29% at Nf 12. Nf • 987).

24
10 100

Cycles, N

1000

SG,RT,AyT = 1.98%, Ayl

LG,RT,ArT= 1.53%, Ay

SG,HT,Ay

LG,HT,AyT

LG,HT,AyT

LG,HT,AyT

a 56%

0.52%

l.94%, Ayp-0.56%

1.93%, Ay^=0.92%

1.58%, Ayp-0.65%

1.34%, Ay p*- 0.52%

type of Strain Control Test.

10000

Fig. 20) Shear stress range variation with cycle for small grain (SG) and large grain (LG) Waspaloy, tested under

continuous cycling (10 cpml at room (RT) and 1200 °F (HTI temperatures.

25
1. Report No. NA$A CR_! 75(552

USAAVSCOM TR-86-C-14

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

Axial and Torslonal Fatigue Behavior of Waspaloy

5. Report Date

April 1986

6. Performing Organization Code

7. Author(s)

S. Zamrlk, M. M1rdamad1, and F. Zah1r1

8. Performing Organization Report No.

None

10. Work Unit No.

9. Performing Organization Name and Address

The Pennsylvania State University

Engineering Science and Mechanics Dept.

University Park, Pennsylvania 16802

11. Contract or Grant No.

NAG 3-264

12. Sponsoring Agency Name and Address

U.S. Army Aviation Research and Technology Activity -

AVSCOH, Propulsion Directorate, Lewis Research Center,

Cleveland, Ohio 44135 and NASA Lewis Research Center,

Cleveland, Ohio 44135

13. Type of Report and Period Covered

Contractor Report

14. Sponsoring Agency Code

505-63-11

15. Supplementary Notes

Final report. Project Manager, Robert C. Bill, Propulsion Directorate, U.S. Army

Aviation Research and Technology Activity - AVSCOM, Cleveland, Ohio 44135.

16. Abstract

The cyclic flow response and crack growth behavior of Waspaloy at room temperature and 650 °C under tensile loading and torslonal loading was studied, for two

conditions of Waspaloy: fine grain, large y1 size; coarse grain, small y'

size. The fine grain material showed 5 to 10 percent hardening after about 10

percent of life, with sequent softening to failure at both temperature levels.

The coarse grain material showed either stable response or monotonlc softening to

failure. Early crack Initiation was observed on planes of maximum shear, with

eventual branching to principal planes under torslonal loading; cracks were

always normal to load axis under tensile loading. Also, crack paths were Intergranular at 650 °C, mostly transgranular at room temperature.

17. Key Words (Suggested by Authcrfs))

Fatigue; Tension; Torsion; High

temperature; Superalloy; Waspaloy

18. Distribution Statement

Unclassified - unlimited

STAR Category 26

9. Security Classlf. (of this report)

Unclassified

20. Security Classlf. (of this page)

Unclassified

21. No. of pages

22

22. Price*

A02

'For sale by the National Technical Inlormation Service, Sprlnglield, Virginia 22101
National Aeronautics and

Space Administration

Lewis Research Center

Cleveland. Otiio 44135

Official Business

Penally for Private Use $300

SECOND CLASS MAIL

ADDRESS CORRECTION REQUESTED

Postage and Fees Paid

National Aeronautics and

Space Administration

NASA-451

NASA