NBSIR 74-576

Metallurgical Analysis of Wear

Particles and Wearing Surfaces

A. W. Ruff

Metallurgy Division

Institute for Materials Research

Mational Bureau of Standards

V.ashington, D. C. 20234

September 15, 1974

Quarterly Report

Contract 4-8049

Prepared for Naval Air Engineering Center

Philadelphia, Pa. 19112

NBSIR 74-576

METALLURGICAL ANALYSIS OF WEAR

PARTICLES AND WEARING SURFACES

A. W. Ruff

Metallurgy Division

Institute for Materials Researcti

National Bureau of Standards

Washington, D. C. 20234

September 15, 1974

Quarterly Report

Contract 4-8049

Prepared for Naval Air Engineering Center

Philadelphia, Pa. 19112

1 o»

•"•f.u o« *

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

I. OBJECTIVE

The objective of the project has been to characterize the wear particles

and surface degradation produced by wear in bearing and gear tests in

which the effect of several variables on failure of the wearing sur- faces has been examined. The information obtained has been correlated

with the results of allied studies conducted by others in an attempt to

develop an understanding of the processes producing wear and degradation

of metal surfaces in sliding, rubbing, rolling, and/or rotating contact

and the effects of- lubricants , lubricant additives, bearing materials,

etc. on these processes. The characterization of the wear particles and

wearing surfaces should aid in the establishment of the interrelationships

between wear particle shape, size, size distribution, chemical compositions,

metallurgical structure, and surface damage prior to failure.

II. APPROACH

The initial approach has been concerned primarily with the examination

of particles recovered by the Ferrographic technique from samples of

lubricating oils taken periodically during tests and service of bearings,

gears, sliding surfaces, etc., in which such experimental variables as lubricants, lubricant additives, bearing materials, loads, etc., have

been studied. Our examinations have been conducted principally using

both Scanning and Transmission Electron Microscopy techniques, observing

particle shapes, sizes, surface structures and other parameters as functions of distance along the Ferrogram and determining a semiquantitative elemental chemical analysis of selected and typical particles.

These electron microscope techniques have been used to characterize the

wear particles and associated surface degradation produced in the bearing

and gear tests conducted by others. They provide information on particles

and surface details too small for study by optical microscopy methods.

•After suitable techniques have been developed for examining and characterizing both the wear particles and the surfaces that produced them, these

methods will be used to examine and evaluate specimens removed or obtained

from programmed wear tests being conducted on associated projects.
III. RESULTS

Particle Microanalysis

Correct quantitative identification of particles and determination of

their composition in the size range below 100 ym requires careful

experimental measurements and the performance of periodic calibrations

in order to insure accuracy. The particles of interest here may have

been worn from various components of the system under study or may be

foreign impurities drawn into that system. X-ray emission from bulk

materials under electron beam excitation is an analytical process that

has been studied in detail in recent years. However, X-ray emission

from particulates has not been sufficiently well examined. At the

electron beam voltages of interest (about 10-30kV) considerable electron

penetration of thin particles occurs and significantly affects the

accuracy of X-ray analysis.

Calculations have been conducted using the Monte Carlo technique of

the X-ray emission from spheres and cylinders of nickel and iron having

diameters below 100 um. The technique calculates electron trajectories

through the solid and provides information on the generation of X-rays.

Figure 1 shows the calculated trajectories in copper for three different

electron energies. The increasing penetration with increasing energy

is indicated. The calculations provide the required corrections relative to X-ray emission from bulk materials. They would apply to

particle analysis as conducted in this program. Figure 2 shows the

calculated values for iron cylinders of various diameters up to 10 ym.

The intensity ratio relative to a bulk sample is given. The curve

also applies fairly closely to the case of spherical particles. A

particle 1 um in size is predicted to generate only about 50% of the

X-ray intensity of bulk material. Particles larger than 2 \m can be

analyzed without significant thickness correction required. Experimental

measurements have been made on nickel wire and on particles filed from

NBS-SRM 483, an Fe-3 Si alloy, certified for bulk chemical homogeniety.

A specimen of the particulates mounted on a De substrate is shown in

Figure 3. An individual particle is also shown having a tip section of

diameter smaller than 1 um. The experimental results given in Figure 2

-2-
are in satisfactory agreement with the calculated curve. The measured

intensities fall about 10% too low in the size range 2 to 10 ym.

This may be due to the rough surface topography of the particles and

to difficulties in dimensional measurements. Data are also available

for aluminum and for nickel particles.

Ferrograph Evaluation

Experiments have been conducted to explore the effect of oil sample

dilution on subsequent Ferrograph analysis. The aim here was to determine the quantitative capability for sizing particles through the

Ferrograph method. A Ferrogram was obtained of an oil sample from an RM8B engine. The particles were then removed as completely as possible

from the Ferrogram, introduced into fresh oil at a dilution of 5:1

relative to the original sample, and reevaluated. The ratio of initial

deposit volume and the percent area coverage ratios at 54 mm and 50 mm

are given in Table I. These results indicate that quantitative com- parisons can be made under these conditions to an accuracy of about

30%.

A second experiment designed to indicate the quantitative capability of

the Ferrograph using particles of controlled size and magnetic moment

has been conducted. Porous silica spheres of diameter about 5 \m

have been obtained and impregnated with nickel to serve as ferromagnetic

particles of known size, shape, and magnetic moment. Initial experiments

have involved dilutions of the 5 ym spheres in SAE 30 oil at two concen- trations having a ratio of 10:1. Ferrograms were produced from those

two samples. Figure 4 shows one of the Ferrograms as seen in the

optical microscope.

It is clear that the particle deposit density decreases with distance

down the Ferrogram as expected. The individual strings of particles

are seen to generally be well formed in this case where particle shape

is constant and particle size lies within fairly narrow limits. Figure 5

shows the 5 um spheres as observed in the SEM (not a Ferrogram specimen).

X-ray measurements of the nickel content of randomly selected spheres were conducted. The results are shown in Figure 5, giving the time

required to accumulate 5,000 counts under controlled conditions. That
data indicate some nonuniformi ty in Ni content of the spheres and appear

to be related to the optical appearance of some of the spheres. Table I gives the results of this dilution experiment. The initial deposit

volume ratio was 11 for the 10:1 dilution, a satisfactory agreement.

It is believed that two measures provided by the Ferrogram may be

reasonably quantitative indicators of the particle distributions in

size and in different oil samples. These are (1) initial deposit

volume and (2) optical density at the 50 to 54 inni locations.

Preliminary experiments were conducted with a mixture of ni ckel -coated

spheres of size 5 pm and 0.7 um. That specimen will permit an evaluation of size selection capability. Optical photographs of two regions

on one Ferrogram are shown in Figure 6. Those experiments will continue.

Examination of Bench and Field Test Specimens

Wear particle analyses of oil specimens have continued in conjunction

with evaluation of Ferrograms at Trans-Soni cs . F2925 was produced

from an oil sample from bearing #126 tested at SKF. That oil sample

had been stored for some period of months and changes appeared to have

taken place relative to earlier Ferrogram examinations. In addition

various particle types were analyzed in order to verify certain optical

microscope identification procedures. Figure 7 shows the initial deposit

region, including a large nonmagnetic particle. Figure 8 shows this same region at higher magnification. The agglomeration and contamination

of particles is seen in the right side of this area as compared to the

left side region where usual wear flakes are seen. Figure 9 depicts

two areas on this Ferrogram where the strings contain oxide particles,

clumps and one spheroid. An extraneous brass particle is shown in

Figure 10.

Another Ferrogram involving oil from a jet engine that experienced

bearing failure was examined. It was found to contain numerous spheroidal

particles of unusual appearance and transparency. An example of these

spheroids is shown in Figure 11. Analysis of several spheroids was conducted and the results are shown in Figure 12. In all cases these

rough, porous spheroids contain much less iron that the lamellar wear

particles. Their mode of formation and significance with regard to the

failure or wear processes is under study.

-4-
Figure Captions

Fig. 1. Monte Carlo calculation results for copper showing electron

trajectories and X-ray emission.

Fig. 2. Reduction in X-ray emission vs. particle size.

Fig. 3. Particles of SRM 483 (Fe - 3Si) produced by filing (a) on Be substrate, (b) submicron tip.

Fig. 4. Ferrogram of nickel-coated silica spheres, 5 pm diameter,

2000:1 dilution. F2897.

Fig. 5. Nickel-coated Si02 spheres and X-ray emission results.

Fig. 6. Ferrogram of nickel -coated silica spheres, mixture of 5 ym

and 0.5 ym diameter, 2000:1 dilution. F2902.

Fig. 7. F2925. Ball bearing test, SKF #126, 293 M revs, entrance

deposit. Large particle is transparent, blue, contains Al

,

Si , small Fe.

Fig. 8. F2925. Area of entrance deposit.

Fig. 9. F2925. Strings of wear particles, (a) ide particle (dark)

is iron oxide with sulfur present, (b) Spheroid is Fe, as

is end clump.

Fig. 10. F2925. Extraneous brass particle associated with iron

particle string.

Fig. 11. F2916. Jet engine oil, bearing failure. Rough speroidal

particles.

Fig. 12. F2916. X-ray analysis of (a) spheroid and (b) iron wear

particles. Full scale 5 x 10-^ cts.
EE in 1 1 0 r— • 1 1 0 1 1 cr

fO

SO) cr r--» 1

10 1 1 > • * • 1 1 o 0 LO 0 r~«. 0 1 1 (_) in

<T3 E

S- E cvj ro <c • • • • rj- 00 V£J in 0 CO

+-> tn E c fO

O) &- 0 O)

i~ n3 in 0

0) r- • tCL. +-> ^ c\j 1 s_

•r—

m 1— 1 1— 1 (U c

1—

CI

M E E E E +-> a a t :i a 1 $-

••— 1 1 0

U) in ^ 1 ro c\4 1 0 KO CM CVl 1

a 0

OJ S- Q vn •4-

l£> MD 0 1

a> 0 0 0 1"O

fO E r— r— r—

•r— Z3

X sz

4-> f—

XX

X in |

0 r ' fO

c: > UD 0 UD CVJ 1 10 1— VO r- 0 1^ O)

s-O)

-3.

CO 1 O) 0 </> * no u

a. cn E 0 r-^ •• 0 -t-> (O 1 0 -r- S- oo in -M 00 +J (TJ Q- ^ r— J_ *
1

r'

1

\t

0-b|jrn

Fig. 1 Monte Carlo calculation results for

copper showing electron trajectories and

X-ray emission.

Fig. 3 Particles of SRM 483 (Fe - 3Si) produced

by filing (a) on Be substrate, (bj submicron tip.
4
Fig. 5 Nickel-coated SiO^ spheres and X-ray ! emission results.

Ni/SiOg

Spheres

T = I80 ±40 sec

100 200 300

Time for 5x10 Counts (sec)
00 O0) o$-

0) CM sza. -

to s-0)

lO -M u O)

•r- E

r— ITJ to "O ? S

(U 3 M ^

to lf> O • 0 O

•— -o

01 c ^ ns o

•r- E CVJ

«+- in cvj o u. E o • fO c ^0)0

C7) J_ -1- O 3 +J

S- 4-> 3

i. Xr—

0) T- -1-

iJL. E -O
0. 1 /wn^

Fig. 7 F2925. Ball bearing test, SKF #126,

' 293 M revs, entrance deposit. Large

particle is transparent, blue, contains

Al , Si , smal 1 Fe.

IO>uw.

F2925. Strings of wear particles, (a)

ide particle (dark) is iron oxide with

sulfur present, (b) Spheroid is Fe, as

IS end clump.
Fig. 10 F2925. Extraneous brass particle asso ciated with iron particle 'string.
Fig. n F2916. Jet engine oil, bearing failure.

Rough spheroidal particles.
Fig. 12 F2916. X-ray analysis of (a) spheroid and

(b) iron wear particles. Full scale

5 X 10^ cts.

Si K Ta

Si K Ti

1 Fe

r Zn

Background 1.00 .33 .09 .06 .06

Spheroid (1) 1.00 .34 .11 .14 .04

Spheroid (7) 1.00 .18 .05 .12 .03

1 Iron particle 1.00 .24 .08 .82 .03 1

use OMM NBS DC
NtS-IMA (RCV. 7-731

U..S. DEPT. OF COMM. 1. PUBLIC ATION OP Ht- I'ORT NO. 2. Gor't Accession

BIBLIOGRAPHIC DATA No. SMfiT N8SIR 74-576

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Metallurgical Analysis of Wear Particles and Wearing Surfaces

5. Publication Date September 1974

6. Performing Organization Code

7. AUTHOR(S)

A. W. Ruff

8. Performing Organ. Report No. NBSIR 7ir-576

PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OP COMMERCE

WASHINGTON, D.C. 20234

10. Project /Taak/Wofk Unit No. 3120437

11. Contract /Grant No. 4-8049

12. Sponsoring Orgmnization Name and Complete Address (Street, City, Stale, ZIP)

Naval Air Engineering Center

Phllad^lnhla rill 1 ciuv ipiiioif Paro* 19112 i7iifc

13. Type of Report & Period

(JliiPf^rly Report

Ending 9/15/74

14. Sponsoring Agency Code

1$. SUPPLEMENTARY NOTES

14. ABSTRACT (A 300-word or leaa Imctuel aummary ol tnoat ai0iHicant m formation. If document includes a aigfiificant

bibliogrmptty or literature survey, mention it here.)

Results are presented from a program involved in characterizing the wear particles

and surface degradation produced by wear in bearing and gear tests In which the

effects of several variables on failure of the wearina surfaces has been examined

The infonnation obtained has been correlated with the results of allied studies

conducted by others in an attempt to develop an understanding of the processes

producing wear and degradation of metal surfaces in sliding, rubbing, rolling, and/or

rotating contact and the effects of lubricants, lubricant additives, bearing

materials etc. on those processes. Tne characterization of the wear particles

and wearing surfaces should aid in the establishment of the interrelationships

between wear particle shape, size, size distribution, chemical compositions,

metallurgical structure, and surface damage prior to failure.

17. KEY VORDS (six to twelve entries; alphabetical order, capttalise only the first letter of the first key word unlema « proper name; separated by semicolons

)

Bearings; electron diffraction; electron microscopy; gears; lubrication; particles;

wear

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HNCL ASSIFIED

21. NO. OF PAGES

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22. Price

USCOWM-DC 29042-P74