AD-753 018

CERAMIC GAS BEARING MATERIAL EVALUATION

John T. McCabe, et al

Mechanical Technology, Incorporated

Prepared for:

Office of Naval Research

9 September 1972

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Natios" Tochuicl l•aiu SeieU. S. DEPARTMENT OF COMMERCE5285 Port Royal Road, Springfield Va. 22151

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MTI 72TR40

TECHNICAL REPORT

CERAIC GAS BEARING MATERIAL EVALUATION

Prepared Under

ONR Contract N00014-72-C-0083

September 1972

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MECHANICAL TECHNOLOGY INCORPORATED968 Albany-Shaker RoadLatham, New York 12110

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Mechanical Technology Incorporated Unclassified& 968 Albany-S',aker Road

Latham, New York 12110 N/AII

CERAMIC GAS BEARING MATERIAL EVALUATION

4 to %) C • "Il V 1 i 4 fl Fll % e• n (T pe ,I# rp wr•If *1 ... /I " dof-) •

Technical Report 7 April 1972 - 9 September 1972

John T. McCabePeter R. AlbrechtEugene F. Finkin

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September 9, 1912 ' i 3*. e"CN 10-4( ' -ii ,. ,. *,1 iq.,. ORI ItAT OI-l TotMlI. fI,

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Office of Naval ResearchDepartment of the NavyWashington, D.C.

Flat washer specimens were experimentally tested under conditions simulating start-

stop ani continuous rubbing contact of a gas-lubricated thrust bearing. Minimum i

surface damage with a constant and low value of the friction coefficient were cri't:if

for judging superior performance. The materials tested consisted of conventional

I plasma-sprayed substrates(used as reference materials), solid silicon nitride, beryl-

Hium oxide, and beryllium both coated and uncoated.

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D D FO4m 1 4 7 3 (PAfF UnclassifiedS/N 0101.807.6801cutlv C|ss~lsltl

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KEY LINK A LINK 6 LINK C----NO L It WY TROLE WY TROLEt

Bearing material evaluation

Gas be.aringsCe ramic materialsStart-stop tests

Continuous sliding tests

Friction

Wear

Surface damage

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• DD , Nov eel473 (BAC)u. .. d--- --DDAGE ,1 4 Unclassified(AE )Security

Clzshifiation

NO. MTI 72TR40

DATE: September 1972

TECHNICAL REPORT

AuIh#(s)J.T. McCabe, P. lbrh E.F. Finkin

Approved /'John M. McGrew

Approved

Prepared for

Office of Naval ResearchDepartment of the Navy

Washington, D.C.

Prepared under

ONR Contract N00014-72-C-0083

Reproduction In Whole er in Part is Permitted

jor any purpose of the U.S. Government

ASTI

MECHANICAL TECHNOLOGY INCORPORATED, III I

9. A.BANY - S.AKE ROAD-LAi.. .. -WAHAM -PHOW 735-0922 .V -(Z--

. .. .. .. ..

MTI 72TR40

TECHNICAL REPORT

CERAMIC GAS BEARING HATERIAL EVALUATION

prepared for

Office of Naval ResearchDepartment of the Navy

Washington, D.C.

prepared under

ONR Contract N00014-72-C-0083

prepared by

J. T. McCabeP. Albrecht

E. F. Finkin

September 1972

MECHANICAL TECHNOLOGY INCORPORATED

968 Albany-ShAker Road, Latham, New York 12110 Telephone 518-785-2320

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FOREWORD

This report was prepared for the Office of Naval Research under Contract No.

N00014-72-C-0083 by the Friction and Wear Section of Mechanical Technology

Incorporated Tribology Center. Mr. Stan Doroff managed the program for the 4Office of Naval Research, and Dr. Eugene F. Finkin supervised virtually all

of the program for MTI. S.F. Murray, Peter Albrecht, and Mike Grettern were

principal contributors to the MTI effort. Dr. Peter Gielisse of the Univer-

sity of Rhode Island supplied the silicon nitride test specimens under a

separate ONR contract. Partial support for this effort was supplied by the

Naval Material Command, Strategic Systems Project Office (NSP 23).

preceding Pap blank

Vi/

TABLE OF CONTENTS

Page

ABSTRACT iii

FOREWORD iv

1.0 INTRODUCTION 1

2.0 SUMMARY 3

3.0 CONCLUSIONS AND RECOMMENDATIONS 4

4.v METHOD OF TESTING AND RESULTS 5

4.1 Test Rig Description------------------------- ------ - 5

4.2 Test Description ------------------------------------- 5

4.3 Physical Properties of the Test Specimens -------------- 7

4.4 Discussion and Results 7

5.0 REFERENCES 13

-1-

1.0 INTRODUCTION

Gas bearings and other applications requiring materials capable of surviving

unlubricated, high-speed rubbing contact have led to technology programs, such

as the present, in which the principal effort was focused on ceramic materials.

The goal of the present program was to compare variations of ceramic materials

and to determine the character of a material combination with the following

properties:

* Sufficiently low coefficient of friction to permit dry

starting of a gas bearing without hydrostatic jacking

and with a minimum of torque.

Sufficient consistency of the friction coefficient to

provide restart reliability.

* Sufficiently insignificant surface damage during high-

speed rubbing contact to provide long life.

Start-stop and continuous rubbing experimental tests were employed to deter-

mine the change in friction coefficient, surface roughness, and specimen weiF:•t

loss due to rubbing contact at different loads and surface finishes. In all

cases the rotating and stationary specimens were two flat washers with a one-

inch O.D. and a one-half-inch I.D.

The thrust washer test rig used in the program has been employed as a materials

screening device since 1963 and a considerable body of data, showing good field

correlation in gas bearing gyros, has been generated in the interim period.

This study adds three new candidate matetials to the data library.

The exact relationships amoung material properties, fabrication method and ap-

plication requirements have not been established. The coordinated development

with the University of Rhode Island to sort out these variables is the first

step towards bridging this gap.

Many factors enter into the selection of the optimum material for a gas bear-

ing application: material cost, availability, creep resistance, thermal

-2-

coefficient of expansion, thermal conductivity, resistance to wear, spalling

and galling, corrosion resistance, and others.

The importance of some of these factors depends on the particular application.

For instance, a material combination may be quite satisfactory from a surface

damage view point, but might be judged unsatisfactory if the heat transfer

characteristics of the materials lead to excessive bearing surface distortion.

It is not realistic to expect a single material combination to be an optimum

for all applications, thus the intent of this report is to broaden the data

which gas bearing designers need to select materials that are optimum for each

particular application. In addition, it is hoped that the information con-

tained herein will also help to identify some of the material requirements

that are fundamental to all gas bearing applications.

.11i

-3-

2.0 SUMMARY

Ceramic materials were subjected to start-stop and continuous rubbing tests

which simulated potential operating conditions of a flat, gas-lubricated

thrust bearing. Plasma-sprayed chrome oxide versus itself was used as a ref-

erence because this surface coating has performed successfully in many gas

bearing applications and considerable test data is available in the literature

(Ref. 1,2). The other materials tested were silicon nitride, beryllium oxide,

beryllium, and beryllium coated with chrome oxide and aluminum oxide.

Silicon nitride, versus itself, proved to be a very promising combination be-

cause surface damage was minimal. The friction coefficient, ranging between

0.2 and 0.3, was lower than the reference specimens and remained relatively

constant through both types of tests. However, further evaluation of this

material is necessary because an unidentified white, wear-related debris formed

on some of the test specimens and these specimens performed poorly. The sil-

icon nitride was hot pressed at the University of Rhode Island from power

supplied by the Norton Company.

There were indications that beryllium oxide versus itself was also a good

material combination, principally because the average friction coefficient

for all tests was about 0.2. However, some tests showed an exceptionally

low friction coefficient suggesting the presence of a surface contaminant

(Ref. 1,2). Also, virtually all specimens gained weight during testing

which could be eliminated by heating. In addition, the beryllium oxide con-

tinuous rubbing tests showed a trend towards increasing friction with increas-

ing load. Thus, more controlled tests are needed to evaluate this material.

The test specimens were machined for Thermalox 995 stock.

A satisfactory way of plasma spraying beryllium ox4'ie with ceramic coatings

could not be found.

In gene:ral, metals sprayed with chrome oxide showed lower coefficients of

friction than aluminum oxide and chrome carbide in start-stop tests; but all

test combinations of aluminum oxide and chrome carbide showed high friction,

heavy wear, or both during continuous rubbing tests.

-4-

3.0 CONCLUSIONS AND RECOMMENDATIONS

0 Coated metals appear to be suitable materials for gas bearing start-stop

requirements if friction coefficients between 0.2 and 0.3 are tolerable.

More development work is needed to improve the continuous rubbing performance

of coated metals.Tests accomplished under this program indicate solid Si 3 N4 can provide an

excellent bearing surface for applications where continuous rubbing is

encountered if the Si 3 N4 is processed to avoid the formation of a white

debris that is wear-related and synonymous with poor friction characteris-

tics.

Some tests with solid beryllium oxide indicated this material to be very

suitable, from a friction standpoint, for applications where the rubbing

pressure is nominally 4 psi or less. This material also warrants further

study to verify its characteristics because some tests indicated a low

friction coefficient while others did not.

0 It is essential to identify a white debris which is sometimes formed on

the Si 3 N4 . The formation of this material on an actual gyro bearing would

certainly result in increased and erratic torque.

0 Suitable cleaning techniques must be developed for beryllium oxide. It

seems very unlikely that the low friction values which were measured with this

this material are characteristic of the valueo that would be obtained with

clean materials.

More effort should be placed on evaluating the effect of operating varia-bles, such as humidity and temperature, on sliding behavior. These varia-

bles have been shown to be major factors in determining the performance of

solid A12 03 versus itself and may also be important with these other materi-

als. It has been e::ablished that the sliding chrome oxide is not affected

by temperature or the type of environmental gas, but nothing is reallyknown about Si 3 N4 or beryllium oxide.

-5-

4.0 M9THOD OF TESTING AND RESULTS

4.1 Test Rig Description

The MTI flat thrust washer test facilities were used for this study. This rig

has been used often in the past because it offers a simple and inexpensive way

to screen gas bearing material candidates.

Figure 1 shows a schematic of the test rig with the important components iden-

tified. The rotating specimen is held in the bottom fixture which is rotated

via a motor-driven V-belt. Speed changes are accomplished by changing the

ratio of the pulley diameters. The stationary specimen is held in a vertical

spindle floated in an externally-pressurized gas bearing. Bearing friction

torque is monitored by strain gages mounted on cantilevered torque arms and

the spindle is constrained from rotation by pins which extend from the spindle

and contact the torque arms.

4.2 Test Description

Start-stop and continuous rubbing tests were conducted for each material com-

bination. The start-stop tests consisted of 1,000 starts and stops from 575

rpm under a load of 3.2 psi. Friction measurements were taken every 100 cycles

and the roughness of the mating surfaces was measured by a Talysurf before and

after each test. The specimens were cleaned in a Soxhlet extractor and then

weighed before each test. The weight was again measured after testing.

The continuous sliding tests were performed at 575 rpm under a series of loads

for each set of specimens. The speed was selected for convenience and to cor-

respond to that used in previous tests. Each set was cleaned, weighed, and

Talysurfed prior to testing. A complete test consisted of four 15-minute

sliding periods at load levels of 2.1, 3.2, 4.8, and 6.4 psi. According to

current design practice, this load range covers light loading, 2 to 3 psi,

moderate loading 3 to 5 psi, and heavy loading, greater than 5 psi. The sur-

face roughness was measured, they were Talysurfed again after each period at

a specific load level, and reweighed after each complete test. Rubbing fric-

tion was monitored on startup and after two, five, and fifteen-minute time

intervals. The specimens used in the start-stop tests were not used in the

continuous rubbing tests.

-, ,++ o -.. -.+ -= ,- ..

-6-I S

r

TORQUE ARM

* ITORQUE PN

xT. PRESS.

GS BEARINGI, I SPINDLE

STATIONARYISPECIMEN -- '- •

ROTATING DRIVSPECIMENDIV +

MOTORBALL BEARING-._,SPINDLE

Fig. I Schematic of Thrust Washer Test Machine

,IT1-711S 'I'

ii ~-7-1

4.3 Physical Properties of the Test Specimens

BeO Be Si 3 N4

Thermal Conductivity, Btu/ft-*F-hr 152 84.4 8

Density, #/in3 .108 .067 .113

Thermal Expansion, in/iu-°F 3.16 x 10-6 6.45 x 10-6 1.7 x 10-6

Modulus of Elasticity, psi 50 x 106 42 x 106 43 x 106

Poisson's Ratio .35 .024 - .030 -

Crystal Structure HCP* HCP* HCP*

4.4 Discussion and Results

The effectiveness of several candidates for gas bearing were evaluated in athrust washer test by comparing the sliding performance of these materials

with that of plasma-sprayed chrome oxide (Cr 203 ). Both the start-3top and

continuous rubbing tests were made in air with a relative humidity of 30 per-

cent and an ambiert temperature of 73*F. The combinations of materials tested

are shown in Table 1, and the test results are given in Tables 2 and 3.

The silicon nitride specimens were supplied to MTI by Dr. Peter Gielisse of

the University of Rhode Island, under Office of Naval Research Contract No.

N00014-68-0008. The specimens were returned to the University of Rhode

Island where they are currently being inspected in an attempt to identify a

white debris that formed on about 20 perceL.. of the specimens after testing

and also, to look for a relation between surface damage and material process-

ing method. A report on these findings is anticipated in the near future.

In general, solid silicon nitride mated against itself was a very promising

combination. In the majority of tests the friction measured was lower than

the reference chrome oxide, and the surface appearance of the Si 3N4 and

Cr2 03 showed negligible wear or surface damage. However, in 20 percent of

the tests a white, semi-plastic, non-crystalline debris was found smeared on

the surface of the silicon nitride specimen after the test. This phenomenon

had been observed before in the past with Si 3N4 specimens manufactured inEngland by another process (Ref. 2). Normally, self-mated silicon

nitride appears to have a coefficient of friction between 0.2 and 0.3.

*Hexagonal, close packed

* -\ ~~Tw Lr-

- .-l

TABLE 1I8MATERIAL COMBINATIONS USED IN TESTS

Rotating Specimen Vs. Stationary Specimen

Cr203 Cr203*SCr 3 C2 A12 03"*rs3C* (solid)

sAi3 (solid)

BeO (solid) BeO (solid)

A1203 (on Be) A1203 (on Be)Cr2 03 " (on Be) Cr2 03 " (on Be)

Cr2 03 (on Be) Be (solid)

Cr203 (on Be) BeO (solid)

Plasma-sprayed coating.

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TABLE 2

CERAMIC GAS BEARING HATERSUMMARY OF CONTINUOt

mlateral$ and a •ptlet . go. Weight Loeo (arms) Surface .ougi.... (mir¢olm•cbe CIA) Coofficteot of n

(See notes set".) ( - for Weight CGin]) iatltg Statioiary 3abbin Pressure * 2.1 pat 1 3.2 psi I

Teet me. ataltlq Iitala7ury wiilncn Staieonary Ilaer. After ISAW.t After Stcr 2 m1n. min. I) min. I start 2 mil. 3 min. 11 Kim. sitamrt

3(1) 11034 S(M) 8133N. a() .0096 .0008 13.2 iS 13 .26 .33 .46 .*8 .4 .6 .43(s) . (AV .65

4 u1s3 3(0) 11)Z 4 a(m) .0001 .00C4 14 2.1) 14 7.1) .16 .17 .19 .20 .13 .11 .11 .19-.23 .16-..)

6 Sim, LSL(C) H3014 L5L(D) .0002 . .0002 20 4.13 14 S.9 .5 .5 .4 .4 .5..54 .44 .41-.54 .37 .64..-7

9 $1)34 00(l) W 1)3i 00(1) .0097 .0064 Is 12 14 30 .44- .S6 .41..i .43-.46 .44-.•. .21 .27-.29 .26 .26 .3..))to "A~ll wo(¢ $I,*,l DG( .1054 .039D 15 4..12 14 6.11 .6,3.3 .22 .2 .2 .23.-34 .20-,31 ,.18-30 .16-.23 .22..119

1) le, Dil.(l) $yl DiOL(F) .0O0S .0009 9 9 6 2 .J&-.2 .)4..32 .24-.92 .38-.58 .27..38 .32..S9 .24.-24 .28..•. .31-.UI

14 S1)3'. DOsLG) $1334 DIL(m) - .0002 .0004 2 .-6 5.) 4.4.5 .10 .10 .12 .12 .12-.16 .12-.15 .l..14 .12-.14 .14-.26

I7 Sitie R(A) 6i1)3 R(A) .0141 .0002 2.1 1.2 1.8 .A.-.1 .11 .it .11 .11 .14..19 .11. L . .1-.13 .12-.25

1o 512304 a(c) Sy19 5l0) - .0006 .0002 3. 1.2-I 1.2 .. 1.0 .1l*.16 .15-.16 .15-.17 . . 22-.6 .23-.24 .21-.25 .24-.38 .24-.20

TIM() M5IAI II.0 N4 6 .O 37 - .0013 .001) 1.3.2 2 .7.. 1.3-2.4 .3 .475 .820 .780 .10 .130 .1 .480 .0)) .254

T )(A TD(A)30 6o 20 .Io 21 - .0010 .010 .7-1.4 .8-1.3 .1-1.4 1-.I,4 .153 .3)) .17 .19S .115 .126 .161 .167 .1415(3|) 'ilts)

31 Bo0 44 Soo 47 .0002 .005 2.1.57 1.3-..8 2.7-4.0 1.0.3.7 .129 .122 .126 .126 .089 .098 .069 .042 .182

TM0() T0($) 1 I32 No 32 So0 3) - .C002 - .41 •-.4.6 2.2.4.9 .4.S.1 3.7.2 .238 .9 1 .27i .215 .314 .331 .340 .237 .190

33 CrUP2 om 6. 9 r 0on .00I1 - .0020 4-9 2-7.4 3.710.3 3.7 .1t4 .25S .47S .615 1 .2.24 .424 .343 .49%

34 Alto, on 6. 14 A120 3 "m a 17 . .00." - .0019 4.9 4.3-7.6 3.14 4.2-6.4 .143 .171 .197 .2.) .075 .097 .1t .12 .237

31 cr202 "m 6.e 1 6. 2 .0022 .0017 2.4-4.2 4.2.16 0.8-1.2 10-18 .S44 .176 .4)8 .510 $20 .44b .13 .49) .2'0

10(A) ,1, 4S .0

34 C•0• on 12 It 0 2o - .0024 - .0006 .4-3.2 .7-2.6 .6-2.0 1.4.-.6 .51 .51 .227 .:27 .435 .435 .435 .10S .423

MA) -37 ecO$ am so 1) Bo o ..0024 .0016 .1.2.4. 1.42.6 .3.1.4 .4-.6 .272 Wb04 .272 .324 .296 .398 .0•0 .60) .474

36 1 8.0 29 6.0 4) .O01 . .0193 .86-,6 .7-1.) .5-1.) .6-1.1 .102 .100 .11) .113 .088 .104 .121 .121 .156

(1) Code got 1394 Iaclumm:

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(1) co"* tog IS peie ns I

1T - 21Memie 9. SPI Dla o aomlty11To *bolmem M99, Dr*.r Paneltry(A) - A 14..4b, 2.3 nm(3) - I 1•lo.. 6-10 roo

(c) - C 11.4.4. 2060 cman

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F71

TABLE 2

CERAMIC GAS BEARING MATERIAL EVALUATIONSUMMARY OF CONTINUOUS TESTS

l) Srface Zos.ghess (alcrertuche CIA) Ceffifllt of Irittiov

gotlos Istationary JbbbI5.1.4e4 f re *- 2.1 pst 3.2 pat 4.8 pot 0.4 poi

Before After Beore . After Start 2 mi.. 5 in. 15 "1.. start 2 oil.. 3 Him. O3WNi. start 2 Nis. 3 Rio. ismsI. hnec 2 wisl. Is mi. 15 I..13.3 15 t) .24 .33 ,'s .4 .48 .. (* * *3 , .4f .43 .7(a .W3 .42 (

3Sttrk-.lp. (b)cyi eu4

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20 4.13 14 3.9 .5 .3 .4 .4 .1-.34 .48 .41..$ .37 .. 4..78 .-.. 4 .14..49 .a*.W48 .53.77 4.S-.68 .3-.. .34-•41 SorfUot. polished after tonel

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is 4.12 . 4.11 .26..)) .22 .2 .7 .23-.34 .20..3t .1g.630 .16-.23 .22-.38 .20-..3 .20-.22 .2--.23 '.11-.43 .22-.33 .25-.20 26-..28 Hodersto Stck-atip, fvore• d

9 4 2 38-..: .34..82 .24-.92 .38.•-5 .27..)8 .32-.S9 .241..28 .2S-.34 .53..62 .29..47 29-.M ? .27-.3 .18-.3•6 .11..27.t 3 .27-.32 amro iost of * hlI.t* debris3.4 3.3 4-.4 .10 .t0 .12 .11 .16.tl .IZ..11 .14..t4 .12..14 .14..21 .14 .a8. .1 .13..17 .13..l -.13 .1l-.1, .2..l3 = $loss) wsar rises

2.1 1.2 1.8 .. 1.1 . 0l .-: I .'I .l•4.-9 .tl.112 .l1o.12 .1.-13 .12..2s .3I .10 .10 .13..1$ .04.-17 .06-.15 .1-.168 Occtosioal period. of sthic.4

. 1 .2-1.) 1.2 .8-1.0 .1t..th .1t..16 .15..17 .15..17 .22-.36 .21..24 .23..2S .24-.38 .24..26 .l6..19 .15-.10 .15..17 .24•3.0 .13 .12..19 .13-.2 Sooth rme.

i*3-2.2 1..°- 1.3-2.4 .5 .47 .820 .700 .810 .130 .116 .480 .733 .2M1 .292 .02 .22 .72 4 .320 .740 .800 Periods of high ati. C-slIp

.7-.1& .3.1.) .-. 1.4 l.-.l. .133 .153 .17 .195 .115 .125 .161 .167 .14 .217 .247 .232 .29 .49A .382 .372 veere titck-slip with 4.4 p 1

2.3.? 1.3-5.8 2.2.4.0 1.0.3.7 .129 .22 .126 .12'. .089 .093 .089 .082 I.182 .175 .307 .287 .W4 4 .462 .46 8 0A Periods of 6tiChs3 k sollp wih4..•... .4-h.5 3.7-.2. .238 .281 .274 .2.)9 .3t4 .331 .340 .337 .190 .303 .421 .133 .218 .341 .442 i.490 Soo4•et, sttck~5ltp with 4.8 •

49 27.8 3.7-10.3 3-7 .. 4 1 .25 .473 .518 .4 .4 .424 .31 .4•9 . 45 .447 .53. .3?1 99 .418 .24 3 j .i49 Severe se tick-slip with 3.2

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.4-3.2 .7-2.8 .- O2.0 1.4.1.8 .S1 .51 .32? .327 .433 .4)3 .43S .308 .423 .526 .333 .473 .427 .434 .483 1.644 Stick-slip with 6.4 psi rums

.4.30. - ~ - - - .-0 .4- S- -i .4- -.463_.1.2.4 1.4.2.8 .3.3.4 j.4-81 .272 .304 .272 .124 38 .9 40 .0 44 .8 11 .7 .44 .3 .373 * .550 Pertiodsof slil.lp with..- 1.4 .7.5.1 .. 1.3j .h-1.t .102 .100 .113 .113 .08 1.10 .121 .I21 .158 .219 .20S .198 .140 .172 .143 .148 4 e sl!ght veer rlr 4 #o5; 1

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i -9-

STERIAL EVALUATIONINUOUS TESTS

SITI..of retail"s

4.8 pal 6.4 psi

Itmt 2 uis. 6 me. 16U5t. $test 2 at,. Is Kim. is pus. Iesooka

.66 .2(a .27- ( .49 .6 o .72 .S .42 ()Slttcko.lip. (b)Cyclic stick-slip; white doerts ftensd after two with 3.2 pst.

.16-.17 .21 .23 .25 .196.23 .10-.24 .18-.24 .23.29 $tick-soip (olight to mnderate) Secreaaed to a ximum at 4bout 6 mti. with 6.4 pst test.

.64-.78 1..66 .344 , 6W .46-.63 .52-..7 .4-648 .36-.5 .34.41 Surfaces polishe" after test, no white debris.

.3-•.3 .27..32 .27-.34 .37..47 .3-52 .34W.43 .39-.54 .38-.4$ Stickt.lip except is the r.. with 3.2 pat ruhbtng pr-s-ro.

.22-N .20-21 .20-22 .30-.23 .11-.43 .22-33. .23-.28 .2h628 Moderate stitk-slip. sevre at start of 5.4 pet test.

.33-.62 .24•-. .2M .32 .2T-o36 .18-o34 .A1..27 .16-.25 .27-.32 rg amont of white debris deposited to surface after teot.

.16..26 I . 18-.21 .13-.17 1. 15 .A2-.13 .12-.13 .12-.13 r glossy war rings appeared after 4.S pit r•n.

.12-25 .I10 .10 .10 .13-13 .04-.17 .06-°15 .11-.18 Occasional polods of eticksitip; spoctlwn A chipped soar odso after 4A psi "a.

.24-28 .16-.19 .15-..t .13-o.17 .24-.30 .13 .12.i9 .13-.2 Smooth Mo.

.234 .292 .272 .220 .766 .820 .740 .680 Periods of %tSh stick-slip and wear rings visible on both eurfacis ftom 4.8 pal run on.

.18 .217 .24? .232 .29 .404 .362 .372 Seoer. ,tiok-.lip with 6.4 pst ruo; no vistbl we.. ar. ks.

.182 .175 .307 .287 .614 .442 .448 .480 Periods of stick.slip ctth 6.4 psi run; slight dark war rino on #46. no visible do"&* on #47.

.10 . .61 .11 .218 .24 .42 .40 Soewer. .11thsip with 4.8 ps:; cyclic stick-stip with 6.4 pt; wear rinse on both outfaces.

.4%9 .447 .435 .467 .5;7 .414 .443 °443 Sere cth-slip with 3.2 psI; fairl7 smooth with other r"ne. wear ring. on both surfaces.

.237 .279 .321 .36 .620 .J71 .397 .138 2-paie. 817 chipp"d before test; monoth run.

.730 m.h6 .693 .693 .999 .972 .845 .8i1 Coating to pcdetrio aflot rme with 2.1 pot; severe stickhs-lip; 307 war ringo on both surfaces. ohite on 01i.

.423 .62 .36 6 .473 .627 .654 .661 .S Stick-slip with 6.4 psi runo; any wear rings on both surfaces.

.474 .684 .511 .474 .463 .436 .573 1.560 Period. of otihk-slip with rues of 3.2 psi and 4.8 pst. Slight w.ar rro e #44; very noticeot. t on 13.

.158 .219 I.20 .196 .140 .172 .16) .It j One slight wear ring 4s , visible mekst on 029. Very smooth rue.

~13

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TAB

CERAMIC GAS BEARINGSUMMARY OF ST,

Rubbing Pres

Materials and Specimen No.(,) (ki6ht loss, Bram(6

) Surface RoughnessWegtLsga icroinches, CIA Break-away Coeffici•

Rotat Ing Stationary Soo I0NG

Test No. Rotating Stationary Rotating Stationary Before After Before lAfter Start Cycles Cycles

AM Cr203 5 Cr 2 0 3 3 .0004 .0009 10 8 10 8 0.39 0.48 0.50

3(1) Cr3C2 9 Al 2 0 3 6 0 - .0013 2 2 12 16 .22 .2-.62 .65

I S33N4 B-A $14A B-3 0 - G01l 15 1 14 .5 .1-.5 .I-5

2 S3N4 B-C Si 3 N4 B-D .0002 0 12 20 14 18 .3 .25 .25

5 Si3N4 LBL-A S13N4 LBL-B 0 .0001 16 12 14.2 8.3 .5 .5 .13

7 S13N4 DG-A S13N4 DG-B .00045 0 13 26 14 28 .55 .4 .4'

8 Si3N4 DG-C Si 3 N4 DG-0 - .0002 .0001 15 7-12 14 5.12 (5) (5) (5) C11 S04 DB-A Si 3 N4 DB-B .0313 .0010 18 - 22 .42 .54 .30

12 Si3N4 DB-C St33N4 DB-D - .0006 - .0007 8 3-7 5.5 25-5 .15 .56 .39

is $t3N4 Y-E S13N4 Y-F .0002 .0002 1.5 9 1.5 10 .66 .3-.54 .26

16 t YG i 3 4 ti-H - .0014 - .0186 1.2 1.0 .8 .6 .385-.86 .215 .170

Tt(A) TR(A)19 eO 41 BeO 42 - .0018 - .0017 1-2 1.2-1.4 1-2 1.2-1.4 (5) (5) (5)

TD(A) TD(A)20B4 0 25 8.0 26 - .0007 - .0003 .8-1.4 1.-1.8 1.4-.24 1.2-1.4 (5) (5) (5) (

TR(B) TR(B)

21(4) B&O 48 B.O 49 - .0017 - .0023 8 6 6 4 (5) (5) (5)

TD(B) TD(B) I224 BO 34 Bo0 35 - .0015 - .0004 4-6 2-4 5-6 4.5 (5) (5) (5) (23 Cr 2 03 on Be 4 Cr 20 3 on Be 5 - .0010 - .0009 4-6 3-4 4-5 4-5 (5) (5) (5) (

24 A1 2 03 on Be 14 A12 0 3 on Be 15 - .0020 - .0017 11-14 9-13 8-16 8.14 (5) (5) (5) (

25 Cr 2 0 3 on Be(C) 6 Be(A) 1 .0006 .0035 4-5.5 - 1 12-22 (5) (5) (5) (TD(A)

26(4) Cr 2 0 3 on Be(C) 7 BeO 23 .0088 - .0189 2-5 2-3 1-2 1-2 (5) (5) (5) (

27 Cr 2 0 3 on Be(C) 8 B.O 39 - .0013 - .0001 3-6 1-3 1-2 (5) (5) (5)(4 R(A) TD(A)

28 340 40 8.O 24 - .0017 - .0014 1-2 1-1.8 1-2 .6-1.6 (5) (5) (5)

Notes

(1) Reference specimen; plasma sprayed on 410 S.S. (4) Code for eO Specimens: (6)

(2) Averaged over readings at 100, 300, 500, 600, 700, 800, TR - Thermolox 995 Regular Porosity900, and 1000 start-stop cycles. TD - Thermolox 995 Draper Porosity

(3) (A) - A Finish 2-3 ras(3) Code fr Specimens (B) - B Finish 8-10 rma

Black 30 Nicroinches Rotary: B-A, B-B, B-C, B-d (C) - C Finish 20-60 rmsLight Blue 30 Nicroinches Surface: LBL-A, LBL-B -fDark Green 15-20 Microincbes Surface: DG-A, DG-B, DG-C, IG-D (5) Break-away Coefficients of Frmction notDark Blue 8 Microinches Surface: D0-A, DB-B, DB-C, DB-D doeectably different from runn.ngYellow 1-2 9icroinches: Y-E, Y-F, Y-G, Y-H coefficient of friction.

..........

TABLE 3

CERAMIC GAS BEARING MATERIAL EVALUATIONSUMMARY OF START-STOP TESTS

Rubbing Pressure a 3.2 psi

loss mcroiches CI Break-away Coefficient of Friction IRunning Coefficient of Friction

lotsti g Stationary 500 1000 (2) Avg. Change 500 1000 (2IAvg. Changestationary Beforet After Before After Start Cycles Cycles Average Per Cycle Start Cycle. Cycle /rg.

2 Par Cycle

.0009 10 8 10 8 0.39 0.48 0.50 .47 9.32 x 10'4

0.32 0.48 0.40 .39 7.86 x 10"4 Oscillating.

.0013 2 2 12 16 .22 .2-.62 .65 .50 9.9 x 10.4 .18 .62 .65 .50 10 x 10'4 Severe stick-slip.

.0011 15 14 14 18 .5 .1-.5 .1-.5 .35 7. x 10' .42 .12 .22 .19 3.87 x 10' Stick-slip; both surfacc12 20 14 18 .3 .25 .25 .26 5.125x 10' .3 .25 .25 .26 5.125 x 10' No stick-slip; edge of

.0001 16 12 14.2 8.3 .5 .5 .13 .38 7.6 x lO"- .35 .32 .13 .28 5.675 x 10- S rTsces p. Ished.13 26 14 28 .55 .4 .4 .42 8.45 x 10" .4 .4 .4 .38 7.55 x 10.4 Waite debiu iL thv e wear

.0001 15 7-12 14 5-12 (5) (5) (5) (5) (5) .13 .16 .18 .16 3.145 x 10'4 A few spots were pollshe44 .4 Large ,.uantities of whit

.0010 - 18 - 22 .42 .54 .30 .425 8.5 x 10' .30 .36 .30 .31 6.2 x 10 to weight measurement).

8.0007 3-7 5.5 25-5 .15 .56 .39 .47 9.4 x 10" .15 .56 .39 .47 9.4 x 10.4 White debris showed up a

.0002 1.5 9 1.5 10 .66 .3-.54 .26 .43 8.6 x 10'3 .40 .37 .26 .32 6.5 x 10" Severe stick-slip; stab

.0186 1.2 1.0 .8 .8 .385-.86 .215 .170 .26 5.28 x 10'4 .385-.86 .215 .170 .26 5.28 x 10" Surfaces highly spolis

.0017 1-2 1.2-1.4 1-2 1.2-1.4 (5) (5) (5) (5) (5) .3 .11 .13 .14 2.75 x 10' Scratches on surfaces

.0003 .8-1.4 1.-1.8 1.4-.24 1.2-1.4 (5) (5) (5) (5) (5) .07 .09 .07 .08 1.6 x 10 . Glossy surfaces with a

- .0023 8 6 6 4 (5) (5) (5) (5) (5) .138 .253 .324 .236 4.27 x 10" Surfaces appeared dull

- .0004 4-6 2-4 5-6 4-5 (5) (5) (5) (5) (5) .176 .310 .280 .26 5.2 x 104 Dull surfaces before te.0009 4-6 3-4 4-5 4-5 (5) '5. (5) (5) (5) .127 .138 .148 .147 2.95 x 10' Partial wear rings slig

- .0017 11-14 9-13 8-16 8-14 (5) (5) (5) (5) (5) .18 .30 .31 .285 5.69 x 10"4 A number of mall polio

.0035 4-5.5 - 1 12-22 (5) (5) (5) (5) (5) .41 .83 .82 .66 13.2 x 10" Very noticeable surface

ispecimens.- .0189 2-5 2-3 1-2 1-2 (5) (5) (5) (5) (5) .23 .33 .29 .32 6.36 x 10O

4 Wear marks appeared on

- .0001 3.6 3-4 1-3 1.2 (5) (5) (5) (5) (5) .32 .23 .21 .24 4.8 x 10' Wear marks appeared befafter test.

1-2 1-1.8 -2 .-. 6 1(5) 1(5) 1(5) (5) (5) Erratic Repeated erratic readings

(4) Code for WaO Specimens: (6) Negative sign indicates gain in weight.

TR - Thermolox 995 Regular PorosityTO - Theruolox 995 Draper PorosityT(A) A Finish 2-3 rus(B) - B Finish 8-10 ras(C) - C Finish 20-60 rus

C, D0-D (5) BreaI.-awy Coefficients of Friction not

W8-D detectably different from runningcoefficient of friction.

t

-10-

•3

MATERIAL EVALUATIONPART-STOP TESTS

sure - 3.2 psi

PI of Friction bioning Coefficient of friction

(2) A"g. Change 500 1000 (2)"'s Changeorae Per Cycle Start Cvcles Cycle _rg. , Per Cycle Remarks.4]

.47 9.32 x 10'4 0.32 Q.48 0.40 .39 7.86 x 10'4 Oscillating.

9.9 a 10"4 .18 .62 .65 .50 10 x 10. Severe stick-slip.

35 7. x l0e4 .42 .12 .22 .19 3.87 x 10"4 Stick-slip; both surfaces scored.

.26 5,13 x l104 .3 .25 .25 .26 5.125 i 10'4 No stirk-slip; edge of washers polished.

.38 7.6 x 10.4 .35 .32 .13 .28 5.675 x 10"4 Surfaces polished.

.42 8.45 a 10.4 .4 .4 .4 .38 7.55 x 10°4 White debris in the wear t:acks (removed before weighing).

(5) (5) .13 .16 .19 .16 3.145 A few spots were polished..4 .4 Large -uantities of white debris on surface (not cleaned prior

.425 8.5 a 104 .30 .36 .30 .31 6.2 a 10 to weight measurement). One heavy scratch on specimen A.

.47 9.4 x 10.4 .15 .56 .39 .47 9.4 x 10"4 White debris showed up slightly in both specimens.

.43 8.6 lo0-3 .40 .37 1.26 .32 6.5 x 10"4 Severe stick-slip; stabilized out after 500 cycles to no stick-slip.

.2u 5.28 x 10"4 .385..86 .215 .170 .26 5.28 x 10'4 Surfaces highly spolished and shiny.

(5) (5) .3 .11 i ' .14 2.75 x 10'4 Scratches on surfaces before teat; polished and glos*., after test.I4

(5) (5) .07 .09 .07 .08 1.6 x 10.4 Glossy surfaces with sone rings formed from ame.zing..

(5) (5) .138 .253 .324 .236 4.27 a j, ; .urface appeared dull before ane after test; no scratches or blemishes.

(5) (5) , 76 .310 .280 .26 5.2 x 10'4 Dull surfaces before test; specimen #34 .. pwared glossy after test.

(5) (5) .127 .138 .148 .147 2.95 x 10'4 Partial wear rings slightly visible; no vijible scratches.

(5) (5) .18 .30 .31 .285 5.69 x 10-4 A nuaber of small polished patches appeared ifter test.

() (5) .41 .83 .82 .66 13.2 x 10.4 Very noticeable surface .lmage to both specs.; whie wear rings on coatedspecimens.

(5) (5) .23 .33 .29 .32 6.36 x 10 Wear mar.s appeared on bo'h t rfs...

(5) (5) .32 .23 .21 .24 4.8 x 10- Wear marks appeared before and after test. Very light wear rings appearedafter test.

(5 ' (5) ( Erratic Repeated erratic readings on friction cueffivients.

Negative sign indicates gain in weight.

SIo. 56

III

I1•-13565

[---

When higher friction values were measured, they were t-nerally associated with

the presence of this white wear product.

Attempts to relate the effect of surface roughness to tte sliding performance

of Si 3N4 were disappointing since the roughness of the -ýst specimens did not

have enough variation. The centerline average of the spcirmens before testing

ranged from one to eighteen microinches. Negl.ecting the. ipecimens with white

wear debris, there stems to be a very slight increase in `riction as the CLA

roughness increases up to about 15 microinches. Above thi 4 there seems to be

a sharp increase in friction. Unfortunately, there were fe4 samples with

roughness above 15 microinches and even those were shown to• have widely

scattered coefficients of friction. No significant trend cct.ld be discerned

in the variation of the coefficient of friction of silicon niitride as a func-

tion of stress.

Beryllium oxide sliding against itself appeared to be an effective combination,

but the friction values in many cases are so low that it is very likely that

the surfaces were contaminated. The possibility of some reaction product being

formed between the solvent used to clean the specimens and the BeO surface is

a potential source of this contaminacion. The combination of very low friction

and a polishing effect, such as was observed in the start-stop test numbers

19 and 22, generally points to the presence of a reactive film on the surfaces.

The beryllium oxide combinations showed a definite trend toward increas'ng

friction with increasing load. No pattern of frictional variation with changes

in the surface roughness of the BeO could be detected, at least in this range

of surface roughnesses (- 1-6 microinches).

Comparisons between the regular porosity BeO and the Draper porosity material

J do not indicate any strong trends. In some of the tests, such as test numbersS30 and 32 under continuous sliding conditions, or test number 26 of the start-

stop series, the Draper porosity specimens showed much higher wear than the

regular porosity BeO. However, because of the possibility of contaminating

films being present, it is difficult to interpret these results as being due

to the effect of porosity. Of the other combinations, Cr2 03 coated beryllium

versus BeO did not show any particdIlr promise. Cr3C2 versus A1203 resulted

-12- Ain some surface damage to the A120.3 during the start-stop test. Al2 03 versus

A120 3 gave low friction, but moderate wear. Past experience (Ref. 2) has

shown that this combination is very sensitive to humidity effects, and in dry J

environments or at higher temperature levels sudden increases in friction and

surface damage should be anticipated, especially at higher stress levels.

Finally, when Cr20 3-coated beryllium was mated with plain beryllium, consider-able damage was incurred on both specimens.

In the continuous rubbing tests all of tl'e sliding surfaces, except for the

chrome oxide versus beryllium, showed improved surface finishes after the

sliding tests had been concluded.

'31

*1

T7 TOM 77

-13-

5.0 REFERENCES1. Peterson, M.B. and Murray, S.F., "A Review of Material and Lubricant for

Gas-Lubricated Gyro Bearings," MTI Report MTI 63TR30 prepared for Bureau

of Naval Weapons, Department of the Navy, NObs88615(FBM), June 1963.

2. Murray, S.F. and Peterson, M.B., "The Selection and Evaluation of Materialsand Lubricant Films for Gas-Lubricated Gyro Bearinga," MTI Report MTI64TR1 prepared for Director, Special Projects Office SP-24, N0bs88615(FBM),January 1964.

3. Waldron, W.D., Young, W.E., and Curwen, P.W., "An Investigation of AirBearings for Gas Turbine Engines," MTI Report MTI 71TR23 prepared forU.S. Army Air Mobility Research an4 Development Laboratory, Ft. Eustis,USAAMRDL Technical Report 71-59, December 1971.

I

• €I

LI•1

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