ML20214J839

Final Rept on Metallurgical Investigation of Various Defects on Surfaces of Diesel Engine Aluminum-Tin Bearings

ML20214J839
Person / Time
Site:	Fermi
Issue date:	08/31/1986
From:	Buchheit R, Glaeser W Battelle Memorial Institute, COLUMBUS LABORATORIES
To:	DETROIT EDISON CO.
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ML20214J820	List: ML20214J818 ML20214J839
References
NUDOCS 8612010498
Download: ML20214J839 (57)

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A ETALLLEGICAL INVESTIGATION OF YARIOUS gp$. ($1$j,Q;{'-

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DEFECTS ON.TE SLRFACES OF DIESEL EIGIE DEMlk.. !')g@bc @jjj

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FINAL IEPORT F

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A DETALLLEGICAL INVESTIGATION OF VARIOUS DEFECT. S OK.TE SLRFACES OF DIESEL ENGIBE ALLMINLM-TIN BEARINGS l

L DETHDIT EDISON 7

August 31, 1986

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by R. D. Buchheit and W. A. Gla_eser 7

sa m LLE Columbus Division l

505 King Avenue Columbus, Ohio 43201-2693

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l TABLE OF CONTENTS EA98 INTRODUCTION..........................

1 1

SUN 4ARY............................

IDENTIFICATION AND DESCRIPTION OF SAWLES 2

4 4

LABORATORY PROCEDURES.....................

4 Examinations.......................

I 4

Compositional Analyse's LABORATORY RESULTS.......................

5 5

Compositional analyses m

5 Aluminum-Tin Bearings b

Lapping Compound...................

7 Lubricating Otis...................

7 L

Condition of Surface Distress...............

11 p.

Condition of Dull, Rough Surfaces.............

16 Condition of Dull, Smooth Surface.............

30 o^

34 l

Other Surface Conditions.................

h 49 3

DISCUSSION OF RESULTS.....................

l 51

)

CONCLUSIONS..........................

52 RE00NMENDATIONS........................

n I

L LIST OF TABLES i

Table 1.

Identification and Descriptfon of the 16 Aluminum Bearings.......................

3 Table 2.

Emission Spectrograph 1c Analyses of Four Aluminum-Tin Bearings.....................

6

~, - - _. -. - - -, _ - - -, - -. _ _

e LIST OF TAKES (Continued)

P.aen Table 3.

Results of a Standardless Semiquantitative SEM/EDS Analysis of the Lapping Compound 9

Table 4.

Analyses of Lubricating 011s 10 Table 5.

Emission Spectrographic Analyses of Lubricating 011s 10 Table 6.

X-Ray Energy-Dispersive Areal Analyses of Debris Embedded in Scores in the Bearing Surface of Sample llM-8UT 19 Table 7.

X-Ray Energy-Dispersive Spot Analyses of Particles g

Embedded in the Bearing Surfaces of Samples 14M-5UB and 13M-13UB 27 Table 8.

X-Ray Energy-Dispersive Areal Analyses of Deposits on I

the Bearing Surface of Sample 11M-lLB.........

45 b

LIST OF FIGURES Figure 1.

SEM Micrograph of the Timesaver, Green Label, III Fine Lapping Compound...................

8 r

L Figure 2.

Bearing-Surface Condition of Sample 11M-8UT Described 4

As " SURFACE DISTRESS" 12 5

Ffgure 3.

Appearance of Surface Distress in Sample 11M-8UT...

14 Figure 4.

Meta 11ographic Cross Section of Typical Scores that 4

j Show Folded-Dver Edges................

15 3

l Figure 5.

Meta 11ographic Cross Section That Shows Lateral Extrusion of Metal Over the Edge of the Oil Groove 15 1

Figure 6.

Magnetic Particles Found on the Surface of the 011 Groove of Sample 11M-80T 17 l

Figure 7.

Meta 11ographic Cross Section of Debris in a Score As Ob s e rv e d i n th e S EM..................

18 Figure 8.

Bearing-Surface Condition of Sample 14M-50B Described As " Dull Rough Surface"................

20 Figure 9.

Bearing-Surface Condition of Sample 13M-13UB Described As " Dull Rough Surface"................

21 L

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LIST OF FIGREES (Continued)

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Figure 10. Appearance of Dull Rough Surfaces in Samples 14M-52 and 13M-13 2.....................

22 Figure 11. Comparison of the Duil Rough Surfaces of Samples 14W5 W and 13M-13 2.................

24 Figure 12. Nota 11ographic Cross Sections Showing the Profiles of Dull, Rough Surfaces.................

25

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Figure 13. Meta 11ographic Cross Secticns of Particles Embedded in the Bearing Surfaces of Samples 14M-5W and 13M-13 2.......................

26 Figure 14. Dark Deposit Identified by the Arrow in Figure 8 on the Bearing Surface of Sample 14M-SUB.........

28 Figure 15. Meta 11ographic Cross Section of the Dark Deposit on the 29 Bearing Surface of Sample 14M-5DB Figure 16. Bearing-Surface Condition of Sample 14M-SIK Described As " Dull, Smooth Surface" 31

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Figure 17. Bearing-Surface Characteristics Observed in the Regicn of Sample 14M-5UT, Termed Dull, Smooth Surface 3

Figure 18. Meta 11ographic Cross Sections of the Dull, Smooth Bearing Surface of Sample 14M-5UT 35

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Figure 19. Meta 11ographic Cross Section of the Black Deposit in the 011 Groove of Sample 12M-14UB 37 Figure 20. Damage Described As Spalling on An Outside Edge of the 40 Bearing Surface of Sample 12M-lLB Figure 21. Black Deposit Observed on the Bearing Surface of Sample 43 l

11M-1LB........................

i Figure 22. Brownish Deposit on the Bearing Surface of Sample 44 11M-lLB........................

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A ETALLLifEICAL INVESTIGATION OF VARIOUS DEFECTS ON TE SLRFAES OF CIESEL EIGIE ALfmIBRM-TIN BEARIDGS by

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R. D. Buchheit and W. A. Glasser INTMIDUCTION Emergency power is supplied at the Enrico Fermi II Power Plant by 12-cy11nder, Fairbanks-Morse diesel engines. The engines are p

r subjected once each month to surveillance tests that include start-ups from 0 to 900 rpm in less than 10 seconds and loading within about 150 seconds after start-up. At 18-month intervals the engines are run for a period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. During 1985, various surface defects and blemishes I

were observed by Detroit Edison on the surfaces of swisral main and

(

connecting rod bearings of four diesel engines, Nos.. 11, 12, 13, and 14.

The surface conditions of those bearings were of concern to Detroit Edison and Battelle Columbus Division was requested to conduct a metallurgical investigation of the various defects and blemishes that were apparent among 16 different aluminum-ttn bearings.

The purpose of the metallurgical investigation conducted by Battelle was to identify, insofar as possible, the cause(s) and/or 1-source (s) of the cause(s) of the various surface conditions manifested by the bearings.

g This report describes in dotati the materials investigated, the

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procedures employed for the investigation, and the results of the investigation.

l l

SLMNARY Examinations of various bearing-surface conditions observed and described by Detroit Edison on 16 aluminue-tin diesel engine main and connecting rod bearings were performed to identify, insofar as possible, l

the cause(s) and/or source (s) of the cause(s) of those surface conditions. Three surface conditions described as (1) surface distress,

1 2

(2) dull, rough surface, and (3) dull, smooth surface were of primary concern to Detroit Edison. In addition to the bearing surface, samples of used lubricating oil and a sample of lapping compound were investigated.

The surface condition described as " surface distress" was attributed principally to inadequate lubrication of the bearing.

" Dull-rough" and adull-smooth" surface conditions resulted apparently from contamtnat1on by an excessive amount of forefgn particles that rolled j

through the contact zone and embedded in the bearing surfaces. Some embedded particles were found to be fron-rich; those particles were h

believed to be particles of cast iron from the castings of the diesel engines. A significant nuuber of other embedded particles were 1

apparently abrasive particles from the lapping compound.

Other surface conditions wc e believed to be unrelated to the p

operation of the diesel engines. Among those conditions were evidences of chemical attack, stains or discolorations and residue left from the evaporation of liquid flims, and physical damage due to mishandling during installation or removal of the bearings. Those types of conditions were considered to have developed only during times when the engines were idle.

No surface conditions observed were attributable to metallurgical cond,f tions of the aluminue-tin bearings or to unusual i

characteristics of the lubricating oils.

Recommendations were made to minimize the majority of the bearing-surface conditions that were investigated.

L IDENTIFICATI(Mi Als DESCRIPTION W SNFLES The materials furntshed by Detroit Edf son for the investigat1on included 16 different aluminum-tin bearing halves or quarters, 5 samples l.'

of diesel-engine lubricating oil, and a sample of lapping compound that i

is used presumably to lap journal surfaces. The bearings were solid cast I

bearings made of the SAE 770 aluminum-ttn alloy. Table 1 identiftes each of the 16 bearings and their surface conditions as described by Detroit Edison. The surface conditions that were of most concern to Detroit

3 TABLE 1.

IDENTIFICATION AND DESCRIPTION OF THE 16 ALUMINUM BEARINGS Sample Engine Type of SurfaceConditionofConcern(a)

Nunber Number Bearing 4'

11M-1LB 11 Main Corrosion, pitting, stains, polish and yellow oil-groove discolorations

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11M-3UB 11 Main Axial scratches, stain 11M-4UT 11 Main Chamfer ripple 11M-80T 11 Main Surface distress q'

11M-120T(b) jj g,9, '

Dimples 12M-1LB 12 Main Surface spalling, polish, slightly dull 0-w ooth surface 12M-3LB 12 Main Black stains, yellow oil-groove discoloration, dull smooth surface, straight axial score mark across the total bearing surface 12M-3LT 12 Main Black and yellow stains, scratches 12M-5LB 12 Main Waxy substance, polish 12M-14UB(b) 12 Main Black deposit in oil groove 4

13CR-3UB 13 Connect-Bearing fragments ing rod

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13M-130B 13 Main Dull rough surface

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14CR-10B 14 Connect-Stain, dull rough surface ing rod 14M-5UB 14 Main Dull rough surface 14M-5UT 14 Main Dull smooth surface h

14CR-12VT 14 Connect-Embedments, faint stain ing rod l

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(a) The surface conditions listed were described by Detroit Edison, (b) 1/4-sections of the bearing. All other samples were 1/2-sections of the bearing.

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4 Edison were, in the order of decreasing importance, (1) surface distress represented by Sample 11M-8UT, (2) a dull rough surface represented by Samples 13M-13tB and 14M-stb, and (3) a dull smooth surface represented by Sample 14M-5UT. Therefore, the investigation was focused primarily on those three surface conditions.

The 5 samples of lubricating oils included a sample of used oil recovered from each of the four engines and a sample of unused oil. The four used oil samples were identified as EDG No.11, EDG No.12, EDG No. 13, and EDG No. 14, respectively; the unused oil sample was labeled Caprinus R-40 WR 10255.

The sample of lapping compound was labeled TIESAVER, Green Label, III Fine; the compound was a dry, powdery substance with a greenish tint.

h LABORAYtRY PfiO Dt5tES Examinations Visual examinations, low-magnification (up to 30X) steroomicroscopic examinations, microscopic examinations of metallographic cross sections, and scanning-electron-microscopic (SEM) examinations were made of the bearing surfaces. Those examinations were made to characterize the various defects and blemishes described for each b

bearing sample, as well as other features of the bearing surface conditions, and to evaluate the microstructures of the bearings in the defect regions. SEM examinations also were made of the lapping compound.

3 Significant observations that were made during the examinations

[

were documented photographically.

Campositional Analynas Emission spectrograph 1c analyses were made of the lubricating oli samples and of four samples of bearings. The analyses of the bearings were made to check the chemical compositions t. gainst the chemical requirements for the SAE 770 aluminum-tin alloy. Other analyses l

l

5 of the lubricating oils were made to determine the moisture and phosphorus contents, acidity, and the viscosities at 100 F and 210 F.

In addition, attempts were made to collect for analyses insoluble constituents from the oil saeples by centrifugation and filtration, but so little residue was collected that no analyses of insolubles were obtained.

Elemental analyses of various particles embedded in the bearing surfaces and of other foreign surface deposits were performed in the SEM by X-ray energy-dispersive (EDS) analytic techniques. [SEN/EDS analysis is capable of detecting the presence of elements of Atomic Number 11 (sodium) and higher.] In some instar.ces, spot testir.g was used to identify the presence of iron in embedded particles. A spot test was made by placing a drop of 'a saturated solution of copper sulfate slightly acidified with sulfuric acid on the particle. If iron was present, the h

blue color of the solution became pink.

X-ray diffractometry and SEM/EDS were the analytical methods used to determine the composition of the lapping compound.

LABORATORY REStXTS Onnpositional Analyses w

Aluminum Tin Bearings 1

The surface conditions of most concern were represented by Samples 11M-8tTT (surface distress),13M-13UB and 14M-5UB (dull, rough surface, and 14M-SLTT (dull, smooth surface). Therefore, those four bearings were selected for chemical analyses. The results of the emission spectrographic analyses of those four aluminum bearings are presented in Table 2.

Included in Table 2 are the chemical requirements specified for SAE 770 aluminum alloy.

The results of the chemical analyses indicated that all four bearings analyzed satisfied the chemical requirements of SAE 770. The content of tin in each bearing was at the low side of the specified range of 5.5 to 7.0 percent by weight.

6 TABLE 2.

EMISSION SPECTR0 GRAPHIC ANALYSES OF FOUR ALUMINUM-TIN BEARINGS T

Elemental Content, weight percent SAE 770 Sample Number Specified Element 11M-80T 13M-13UB 14M-5UB 14M-5UT AnalysisRange(,)

Si 0.56 0.24 0.33 0.39 0.7 max h

Fe 0.13 0.44 0.24 0.30 0.7 max Cu 1.00 1.02 1.09 1.15 0.7-1.3 I

Mn

<0.05

<0.05

<0.05

<0.05 0.10 max j

Mg

<0.05 0.08

<0.05

<0.05 Ni 0.83 0.93 0.99 0.97 0.7-1.3 Sn 5.83 5.53 5.90 5.61 5.5-7.0 Ti 0.12 O.14 0.13 0.13 O.20 max Zn

<0.05

<0.05

<0.05

<0.05 Cr

<0.05

<0.05

<0.05

<0.05 Pb

<0.05

<0.05

<0.05

<0.05 Zr '

< 0.05

< 0.05

<0.05

< 0.05 Others each

< 0.05

<0.05

<0.05

<0.05 Others total

<0.10

<0.10

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Al Remainder Remainder Remainder Remainder Remainder P

(a) From SAE Str.ndard, Bearing and Bushing A11oys--J460e, for SAE 770 l

Aluminum Ailoy.

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Lapping Onnpound l

A scanning electron micrograph presented in Figure 1 shows that I

the lapping compound consisted principally of angular particles and much smaller irregularly shaped particles that appear white and are lying on the surfaces of the angular particles in Figure 1.

The results of an

[

SEM/EDS analysis of the area of Figure 1 are presented in Table 3.

Those

}

results show that silicon, iron, and lead were the major elements present in the compound. (Oxygen, which has an Atomic Number less than 11, could not be detected by the FEN /EDS that was used.) SEM/EDS spot analyses of the fine white particles indicated that those constituents contained a very high relative concentration of lead; some silicon, iron, and chrtnium also were detected in the white particles. The angular particles were found by spot analyses to contain high relative concentrations of silicon, aluminum, and iron, and low relative concentrations of calcium and magnesium.

The following chemical compounds were identified from the X-ray diffraction pattern as the most probable substances contained in the lapping compound:

Formula Probable ComDound 1'

Pb (CO I IEI Anhydrous lead carbonate p

3 32 2

$10 Silica 3 -

2 A1 (SiO )3 Iron-manganese-aluminum silicate (Fe,Mn)3 2

4 l

The results of the SEM/EDS and X-ray diffraction analyses were f

compatible. Those analyses suggested that the abrasive medium in the h

lapping compound was essentially silica and silicates to which lead carbonate was added for lubricity.

Lubricating Otis The results of the analyses of the lubricating oils are l

presented in Tables 4 and 5.

The phosphorus contents, acidities, l

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250X 58450 FIGURE 1.

SEM MICR0 GRAPH OF THE TIMESAVER, GREEN LABEL, III FINE Lt.PPING COMPOUND i

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J TABLE 3.

RESULTS OF A STAtJDARDLESS SEMIQUANTITATIVE SEM/EDS ANALYSISta) 0F THE LAPPING COMPOUND I

Element Relative Concentration.

Detected weight percent 5.0 Mg I

A1 9.7

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Si 34.9 Pb 19.0 Ti 2.3 I

Cr 2.2 Fe 20.7 e

Ca 6.2 (a) The analysis was of the area shown in Figure 1.

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ANALYSES OF LUBRICATING OILS Oil Percent Total Acid No.,

Viscosity, cs

Water, Sample Phosphorus KOH, mg/g At 100 F At 210 F ppm Caprinus P,-40 0.001 1.35 169.4 15.30 1454 EDG No. 11 0.001 1.60 190.0 14.11 286 h

EDG No. 12 0.003 1.86 190.0 13.92 2748 EDG No. 13 0.003 1.74 218.1 15.19 1219 EDG No. 14

<0.001 1.91 189.0 13.91 814

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TABLE 5.

EMISSION SPECTR0 GRAPHIC ANALYSES OF LUBRICATING OILS 1

i 011 Chemical Elements Detected Sample Major Minor Trace Caprinus R-40 Ca Na A1, Cu, Fe, K, Mg, Mn, Si b

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EDG No. 11 Ca K. Na A1, Cr, Cu, Fe, Mg, Mn, Pb, Si, Sn l

EDG No. 12 Ca Fe, K, Na A1, B, Cr, Cu, Mg, Mn, Pb, Si, Sn EDG No. 13 Ca Fe. Na A1, B, Cr, Cu, K, Mg, Mn, Pb, Si, Sn l

EDG No. 14 Ca Cr, Fe, K, Na A1, B, Cu, Mg, Mn, Ni, Pb, Si, Sn Zn w-

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11 viscosities, and moisture contents are listed in Table 4; semiquantitative elemental contents are listed in Table 5.

The viscosities and acid numbers for the used oils were within acceptable limits. There was no indication of oil breakdown or of excessive oxidation. The water content also was within acceptable limits.

The trace elements detected by emission spectrograph 1c analysis of the lubricating oils are generally of little concern; those elements may be introduced from other wear surfaces and fuel compositions. Trace elements detected in used oils that were not present in the unused oil were chromium, boron, lead, tin, and zinc. Iron, a trace element in the unused oil, was present as a minor element in the used oils from engines From thos~-comparisons, the fron content and the 12, 13, and 14.

e presence of tin was most 10ely evidence of journal and bearing wer.r.

The source of the lead could be wear of other possible lead-base babbitt

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bearings in the engines or the source also may include the lead-rich particles identified in the lapping compound. The chromium possibly could have come from (1) chrome-plated wear surfaces, e.g., piston rings, (2) wear of the journal, if the chromium was present in the composition of the journal, and/or (3) chromium that was detected in the lead-rich particles in the lapping compound.

Other elements such as calcium, sodium, and potassium can be h

related to additives in the oil. Magnesium, manganese, and silicon were present in the unused oil and those elements were probably associated with detergents and antifoam agents. No evidence of abrasive contaminants, such as silica or aluminum silicates were found in the oil samples.

I Condition of Surface Distress h

i The damage to the bearing surface described as " surface distress" was of primary concern to Detroit Edison. The bearing half that exhibited surface distress was Sample 11M-8UT, which is shown in Figure 2.

Surface distress was observed to be a severe condition of deep, circumferential scoring; scores up to depths of 4 mils were l

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FIGURE 2.

BEARING-SURFACE CONDITION OF SAMPLE 11M-8UT DESCRIBED AS " SURFACE DISTRESS" l

The four black marks on the bearing surface should be disregarded; they i;;

were marks used during the investigation.

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15 observed. Figure 2 shows that the damage occurred in the region of maximum load, i.e., the damaged region was centered on the bearing half.

The photomacrograph in Figure Sa shows the appearance of surface distress in more details Figure 3b is an SEM micrograph of a representative portion of the damaged region.

The scoring was least severe near the outside edges of the bearing surface. The bottom surfaces of most of the scores were 1rregular and smooth and the reflectance of those surfaces was relatively bright. This observativ suggested that possible melting and subsequent solidification of very thin surface layers of the bearing alloy occurred due to inadequate lubrication and excessive frictional heating. The edges of most of the scores were apparently folded over. Evidence also was observed of lateral extrusion, i.e., metal-flow over the edges of the oil groove, but not over N o outside edges of the bearing surface.

Figures 4 and 5, which are photomicrographs from a meta 11ographic cross section of the bearing surface, illustrate typical scores with edge fold-l overs and lateral extrusion over the edge of the oil groove, respectively.

L Very few particles were observed embedded in the scored region of the bearing surface. Aluminum, tin, and calcium were detected by SEM/EDS in most of those particles; magnesium also was detected in two other particles. The presence of sulfur, potassium, iron, and nickel was detected by SEM/EDS in one embedded particle. A few spherical embedded particles containing principally iron were found. In addition, two little magnetic spherical particles were discovered lying on the surface of the oil groove. The larger of those two particles was about 15 mils in diameter and it was found by SEM/EDS to contain the following relative l

concentrations of elements:

k Element Weight Percent Silicon 12.2

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l Calcium 58.2 Titanium 13.0 Manganese 3.7 Iron 8.8 Nickel 4.0

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SEM Micrograph FIGURE 3.

APPEARANCE OF SURFACE DISTRESS IN SAMPLE 11M-8UT l

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METALL0 GRAPHIC CROSS SECTION 0F TYPICAL SCORES THAT SHOW FOLDED-0VER EDGES F

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METALL0 GRAPHIC CROSS SECTION THAT SHOWS LATERAL EXTRUSION OF METAL OVER THE EDGE OF THE l

l OIL GROOVE

16 i

The particle, from its appearance shown in Figure 6 and its composition, appeared similar to a splatter of weld-metal slag.

The metallographic cross section of the bearing surface revealed the presence of debris in some of the scores. Debris is evident in the half-circular score shown in F1 pre 4 and also in Figure 7 which illustrates a scored region at higher magnification. The results of SEM/EDS analyses of debrfs at 5 different locations are presented in Table 6.

The debris shown in Figure 7 is Location 1 in Table 6.

The results of the analyses suggest that a significant amount of the debris consists of bearing material (aluminue-tin). The analyses obtained at Location 3 indicated that some debris may be from an aluminum-magnostum alloy or may contain some very fine fragments of lapping abrasive.

Sulfur and, to a lesser extent, chlorine were present in significant concentrations in most of the debris, which was analyzed. The material in the grooves appeared to be compacted debrfs from the bearing material along with remnants of the lubricant and possibly remnants of the lapping compound.

Onndition of Dull, Rough Surfaces Dull, rough bearing surfaces were typified by Samples 14M-5UB and 13M-13tB. Photomacrographs that show the bearing surfaces of those two samples are presented in Figures 8 and 9, respectively; the rough appearance of the surface damage is not evident at the magnification shown. The photomacrographs show that the surface damage on both bearings occurred in the highly loaded region. In addition to the damage in Sample 14M-5UB, an adherent dark deposit also was observed in a region h

on one side of the bearing surface outside of the damaged region; the l

arrow in Figure 8 identifies some of the dark deposit. Other dark deposits also are avident to the left of the arrow near the edge of the wear damage.

The bearing surfaces of both samples exhibited many relatively shallow score and/or machining marks that are evident in Figure 10. In the SEM, examination of the surfaces indicated that they were roughened l

by numerous nicks and gouges produced by angular sharp-edged particles.

This condition was similar to that metallic surface that has been ground with loose abrasive particlu on a lapping wheel wherein the

- ~ ~ - -

17

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'h.h,e,,A

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i 200X 58594 h

a.

Magnetic Particle As Observed in the SEM h..

4*k 1.'C#,.; p,

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1000X 58595 I

b.

Surface of the Particle Above at a i

Higher Magnification i

FIGURE 6.

MAGNETIC PARTICLE FOUND ON THE SURFACE i

0F THE OIL GROOVE OF SAMPLE llM-8UT SEM micrographs.

....~:

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• surface B,

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500X 58685 FIGURE 7.

METALL0 GRAPHIC CROSS SECTION OF DEBRIS IN A

(-

SCORE AS OBSERVED IN THE SEM The analysis of this debris is listed as Location 1 in Table 6.

[

[

[

b i

19 f

t TABLE 6.

X-RAY ENERGY-DISPERSIVE AREAL ANALYSES OF DEBRIS j

[

EMBEDDED IN SCORES IN THE BEARING SURFACE OF SAMPLE 11M-80T Relative Concentration, percent

~

Location Mg Al S

Cl Sn Ca Ti Fe Ni Cu 0.2 2.3 2.6 30.9 61.7 2.3 1

3.0 1.0 0.9 0.9 67.6 9.7 8.8 8.3 2

0.6 3

30.8 56.6 5.9 1.8 2.4 1.9 0.5 1.0 93.5 0.2 0.1 4.7 4

1.9 5.1 26.2 61.0 5.8 L

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Am S3/4X As Received 7M092 FIGURE 8.

BEARING-SURFACE CONDITION OF SAMPLE 14M-5UB DESCRIBED AS " DULL ROUGH SURFACE" Arrow identifies a black surface deposit located outside of the damaged surface.

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s3/4X As Received 7M093 FIGURE 9.

BEARING-SURFACE CONDITION OF SAMPLE 13M-13UB DESCRIBED AS " DULL ROUGH SURFACE" 1

)

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10X As Received 7M102 b,

Sample 13M-13UB FIGURE 10. APPEARANCE OF DULL ROUGH SURFACES IN SAMPLES 14M-5UB AND 13M-13UB

23 particles roll through contact. Typical details of the surface features are shown at higher magnifications in Figure 11. It is evident from a comparison between Figures lla and 11b that the surface of Sample 14M-5 2 was roughened more severely than that of Sample 13M-132. Some foreign particles on the bearing surfaces were observed in the SEM. One of those particles is designated by the arrow in Figure lla; that particle did not l

appear to be deeply embedded.

(

Examinations of the metallographic cross sections of the bearing surfaces showed that the depth of the damage was typically about

{

0.2 mil. Ccessionally, a gouge was observed to be up to 1 mil deep.

Typical surface damage observed in the metallographic cross sections is revealed in Figure 12.

A few embedded p" articles also were observed in the metallographic cross sections. The facets of most of those particles were angled with apparently sharp edges. The size of the particles were usually about 10 microns (0.0004 inches). Typical particles are identified by arrows in the SEM micrographs presented in Figure 13.

The results of SEM/EDS analyses of several embedded particles observed in Samples 14M-5W and 23M-13W are presented in Table 7.

The particle shown in Figure 13a is listed in Table 7 as Particle 4 of Sample 14M-52; similarly, the particle shown in Figure 13b is ' listed as I

Particle 3 of Sample 13M-132. The results of the SEM/EDS analyses suggest that the particles were most likely silicates containing principally magnesium, aluminum, calcium, and iron, except for Particle 3 from Sampie 14M-52, which may have been a particle of silica. Those results suggest that the embeddsd particles were abrasive particles from the lapping compound.

(Compare with the results in Table 3.)

The appearance in the SEM of the adherent dark deposit, which is identified by the arrow in Figure 8, on the bearing surface of Sample 14M-5 2 is shown in Figure 14a and 14b; a metallographic cross section of the deposit is shown in Figure 15. A comparison of Figure 14b with Figure 15 indicates that the dark 4 posit is primarily an agglomeration of fine particles. An SEM/EDS an.fsis of the cross section of the deposit produced the following results:

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1500X As Received 58541 a.

Sample 14M-5UB, Arrow identifies an angular foreign particle on the surface.

s 500X As Received 58551 b.

Sample 13M-13UB

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SEM micrographs.

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7M062 As Polished I

500X a.

Sample 14M-50B V

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.s 500X As Polished 7M052 b.

Sample 13M-13UB FIGURE 12. METALL0 GRAPHIC CROSS SECTIONS SHOWING THE PROFILES OF DULL, ROUGH SURFACES

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7- _.

r 26 4

r a

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1000X 5867?

a.

Particle (Arrow) Observed in Sample 14M-50B

[

(Listed as Particle 4 in Table 7)

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f. '..,,,

.'.c 1000X 58673 b.

Particle (Arrow) Observed in Sample 13M-1303 (Listed as Particle 3 in Table 7)

FIGURE 13, METALL0 GRAPHIC CROSS SECTIONS OF PARTICLES EMBEDDED IN THE BEARING SURFACES OF SAMPLES 14M-50B AND 13M-13UB s

SEM micrographs.

l t

~,

27 TABLE 7.

X-RAY ENERGY-DISPERSIVE SPOT ANALYSES OF PARTICLES EMBEDDED IN THE BEARING SURFACES OF SAMPLES 14M-5UB AND 13M-1308

)

Particle Relative Concentration, percent

. Number Mg Al Si Ca Mn Fe N1 Sample 14M-5UB 21.4 1.0 1

16.2 18.7.

41.8 0.9 2

9.4 22.2 33.2 4.7 1.7 27.8 1.1 2.9 97.1 3

4 10.5 22.4 34.7 4.9 1.0 26.6 Sample 13M-13UB 1

10.8 26.1 41.6 5.4 0.8 15.3 21.6 2

8.8 27.6 37.9 4.1

{,

3 11.2 25.1 42.4 5.7 0.7 14.9 e

_w

_%m-w

28 l

a

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300X As Received 58548 a.

A Large Lump of the Deposit p

.s S

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1000X As Received 58550 b.

Surface of the Deposit Above at a Higher Magnification FIGURE 14. DARK DEPOSIT IDENTIFIED BY THE ARROW IN FIGURE 8 ON THE BEARING SURFACE OF SAMPLE 14M-5UB SEM micrographs.

- - - - -. - - _,,,, _ -, -. - _ - - - - - -, - - --,,_ _-- --,.,._, ~., _, _ _,..,, - _ - -,. - - - - - - - - - - - - -

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%L 500X 58684 FIGURE 15. METALL0 GRAPHIC CROSS SECTION OF THE DARK DEPOSIT ON THE BEARING SURFACE OF SAMPLE 14M-5UB SEM micrograph.

P

+

6

,..,-..c,,

(

e 30 Relative Concentration, percent Element Dark White Particle Detected Deposit in Figure 15 Na 3.5 Mg 23.1 A1 92.1 Si 45.2 S

4.4 Ca 1.3 Mn 1.5 Fe 27.7 Ni 1.3 3

The results of the SEN/EDS analysis indicated that the composition of the white particle, which is evident in the dark deposit shown in Figure 15, was'similar to the composiIions of the embedded particles, listed in 3

Table 7, and thus the particle was probably abrasive from the lapping compound. The bulk of the dark deposit, however, contained only aluminum, sodium, and sulfur in detectable concentrations and may han been remnants of oil sludge. A small amount of corrosion of the bearing surface underneath the dark t:eposit was evident and the corrosive attack can be seen in Figure 15. The sulfur in the dark deposit was possibly the source of the corrosive attack.

Condition of Dull. Smooth Surface Sample 14M-5UT exhibited the bearing-surface condition l

described as a dull, smooth surface. A photomacrograph of Sample 14M-5UT that shows the damaged bearing surface is presented in Figure 16. The b

l damage occurred in the loaded region. Some characteristic features of

?

the bearing surface are revealed at highcr -:":cifications in Figures 17.

Figure 17a shows some relatively deep scores that ended abruptly. The scores were caused by foreign particles that finally embedded in the bearing surface. Several of those foreign particles were relatively large and they were found by SEM/EDS analyses to contain principally iron. An embedded iron-rich particle is identified by the arrow in Figure l?b.

Embedded iron-rich particles generally protruded above the surface of the bearing. As a result, abraded aluminum particles of the bearirm were wiped over the embedded particle and became entrapped on the

r--

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s3/4X As Received 7M103 FIGURE 16. BEARING-SURFACE CONDITION OF SAMPLE 14M-5UT DESCRIBED AS " DULL, SMOOTH SURFACE" The five black marks on the bearing surface should be disregarded; *. hey were i

landmarks used during the investigation.

l l

l I

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32 f

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Relatively Deep Scores That End Abruptly

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50X As Received 7M106 b.

Embedded Iron-Rich Particle (Arrow) and Repeated Dark Chatter Marks Caused by a Rolling Particle FIGURE 17. BEARING-SURFACE CHARACTERISTICS OBSERVED IN THE REGION OF SAMPLE 14M-5UT, TERMED DULL, SMOOTH SURFACE

=.

o 33

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500X As Received 58599 r

c.

Another Embedded Iron-Rich Particle (SEMmicrograph) l L

s g

r

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1000X 58556 d.

Typical Surface Roughened by Sharp Cuts i

and Gouges FIGURE 17.

(Continued)

+ < -.

o 34 trailing end and sides of the embedded particle. The entrapped aluminum debris is evident in Figure 17b as a white zone around most of the iron-rich particle. This phenomenon also is evident in Figure 17c, which is a SEM micrograph of another embedded iron-rich particle. Figure 17b also shows a line of black chatter marks below the embedded iron-rich particle that were indicative of a particle that had rolled or skipped across the bearing surface. Figure 17d reveals characteristics, such as sharp cuts and gouges, of the surface that were sinflar to those of the surface of Samples 14 W5 W and 13M 13 2. (Compare Figure 17d with Figures lla and lib.)

Generally, the damage to the bearing surface of Sample 1445UT appeared to be the same, but not as severe, as was the damage observed in Sample 14M-5LB. However, Wedded iron-rich foreign particles were not apparent in the bearing surface examined in Sample 14M-5UB.

Examinations of a metallographic cross section of Sample 14M-SUT showed that the depth of the bearing-surface damage was typically about 0.2 mil, similar to the depth observed in the dull, rough surface.

A representative example of the damage observed in the cross section is shown in Figure 18a. A cross section of an embedded iron-rich particle is presented in Figure 18b. A few embedded particles, similar to the

{

particle shown in Figure 18c, also were observed in the cross section.

The results of SEM/EDS analyses of those embedded particles indicated that they were similar in composition to the embedded particles found in r

Samples 14M-5UB and 13M-13UB (see Table 7) and were possibly lapping compounds abrastve particles.

1 Other Surface onnditions Sample 125-14LB Sample 12M-14LB was a 1/4-section of the aluminum bearing that

~

exhibited a black deposit on the bottom and partially up the sides of the L)-shaped oil groove. The cut surface that divided the 1/2-section into two 1/4-sections intersected the deposit. The extent of the deposit from that cut surface was about 2 inches in the circumferentir.1 direction.

It l

l

35 I

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500X As Polished 7M056 a.

Typical Bearing-Surface Damage b

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100X As Polished 7M055 1000X As Polished 58670 b.

Embedded Iron-Rich Particle c.

Embedded Foreign Particle (Arrow)

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FIGURE 18. METALL0 GRAPHIC CROSS SECTIONS OF THF DULL, SMOOTH BEARING SURFACE OF SAMPLE 14M-5UT Figure 18c is a SEM micrograph.

[

[

l.

o 36 was presumed that the cut surface bisected the overall extent of the black deposit about equally so that the deposit most likely extended a I

total of about 4 inches. Thus, the location and extent of the deposit suggested that, at some time, a fluid residue settled at the bottom of the oil groove. Subsequently, the liquid phase apparently dried up or evaporated and a black deposit of solid residue was left intact on the surface of the oil groove.

The photomicrograph in Figure 19a shows a cross section of the oil groove and the black deposit that was situated at the bottom and

[

partially up the sides of the oil groove. It is evident from the contour of the oil groove that the aluminum-tin bearing alloy was corroded I

underneath the black deposit. Figure 19b shows the corrosive attack at a i

higher magnification. The appearance of the corroded oil-groove surface in the SEM is shown in Figure 19c. The SEM micrograph reveals clearly that the corrosive attack was confined to the matrix of the aluminum-tin alloy; the constituents, which appear white in Figure 19c, were not attacked. Examinations of the black deposit, both stereoscopically at low magnifications and microscopically at higher magnifications, revealed areas that were translucent and whitish in a dark opaque matrix. The light-gray patches in Figure 19d were translucent and whitish; the black regions in Figure 19d were void of material.

Regions of the deposit identified by A and regions of the If corrosion product identified by B in Figure 19c were analyzed by SEM/EDS.

Regions of the black deposit that were analyzed included both translucent and opaque areas. Aluminum was the only elvent detected by SEM/EDS in the black deposit. Apparently, the aluminum was combined with a light element, such as oxygen, that was not detectable by the SEM/EDS that was i

used for the analysis. Therefore, the black deposit was believed to be aluminum oxide.

l The results of the SEM/EDS analyses of three areas in the corrosion product, such as Region B in Figure 19c, are presented below:

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37 E

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=-.

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10X As Polished 7M030 Black Deposit on the Bottom and Partially t'I a.

J Up the Sides of the Oil Groove L

Black e deposit 7

Bearing 1

" surface d

(

i 0

~

~

g lu o

l hsPolished 7M026 100X 4

Circled Area in (a) Above at a Higher b.

Magnification Showing the Corrosive Attack of the Bearing.arface S

FIGURE 19. METALL0 GRAPHIC CRGSS SECTION OF THE BLACK I

DEPOSIT IN THE OIL GROOVE OF SAMPLE l

12M-14UB

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- = -. - ~ -.., _,, _. _ _ _ _

38 B1ack

" deposit Bearing

" surface i

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Same Region as Shown in (b)

Observed in the SEM e, ; *

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Structure of the Black Deposit FIGURE 19.

(Continued)

i t

39 Element Relative Concentration, percent f

Detected Area 1 Area 2 Area 3 Na 5.3 5.6 2.9 A1 83.6 E.3 86.7 C1 4.2 3.2 1.0 i

3.0 Sn 1.0 Ca Ti 2.5 1.9 Cu 4.4 6.0 5.4

{

The analyses of Areas 1 and 2 were similar; the detection of tin in Area i

3 indicated that an aluminum constituent containing tin was probably within the volume of material that emitted X-rays. The volume of material included in the analyses of Areas 1 and 2 apparantly did not contain any microstructural constituents containing tin. Sodium a.nd chlorine, which were detected in all three areas, suggest that the presence of those elements may have contributed significantly to the corrosion mechanism that occurred.

Sample 1296-11B E

The surface condition of Sample 12WILB was described by

[

Detroit Edison as ' surface spalling, polish, slightly dull, smooth surface". The damage described as surface spalling was observed at the

[_

two outside edges 'of the bearing surface at approximately the center of the high-load-bearing region. The damaged regions at both edges were very similar

'.t appearance. The damaged region at one of the outside edges is shown in Figure 20.

The damage did not have the physical appearance of spalling; no material appeared to be missing. Rather, the surface of the damage was very rough and exhibited numerous small gouges and/or identations. There was no directionality to the damage. Evidence of plastic deformation of

'{

the aluminum on the bearing and chamfer surfaces around the damaged region also was observed. That deformation, in the fom of rumpling, is barely visible in the bearing surface around the damage ahead of the arrow in Figure 20; the defomation is not visible on the chamfer surface in Figure 20. Those characteristics suggested that the two edges

40 1

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5X As Received 7M033 t

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FIGURE 20. DAMAGE DESCRIBED AS SPALLING ON AN OUTSIDE EDGE OF THE BEARING SURFACE OF SAMPLE 12M-lLB l

t t

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o 41 of the bearing surface were dented probably at some time after, not during, service. It is doubtful that the edge damage would affect the performance of the bearing in service.

The polished appearance on the bearing surface was considered to be a normal appearance of the load-bearing region of the bearing.

Sample 11M-4UT Sample 11M-14UT also exhibited damage at the outside edges between the chaefer and bearing surfaces. That damage was described as "chamfor ripple". On one side of the bearing, the damage was evident on both edges cf the chamfer surface. Like Sample 12M-1LB, the damage was confined to an area at appr'ximately the center of the high-load-bearing o

region. The chamfer ripple was visible due to plastic deformation of the surface of the chamfer. The edges of the.chamfor surface were beveled from contact with another object. Apparently, the contact load was high enough to deform the chamfer surface and produce the ripple effect.

Contact of the chamfer-surface edges was apparently made with something on the crankshaft due to thrust-loading on the bearing. The configuration of the crankshaft and the bearing mount should he. examined to see if any contact between the crankshaft and the chamfer edges is possible under a thrust-loading condition.

?..

Sample 115-1LB The surface condition of Sample llM-1LB was described as

" corrosion, pitting, stains, polished, and yellow oil-groove discolorations". Corrosion and stains were the most prevalent conditions observed. Those conditions occurred on the bearing surface on only one side of the oil groove; the bearing surface on the other side of the oil groove exhibited a normal bearing-surface appearance. The areas of corrosion and stains were located towards the two ends of the 1/2-section of the bearing beyond the region of maximum loading on the surface. Many of the areas were distributed in a way that formed a somewhat regular pattern which suggested that evaporation of a liquid film on the surface occurred during idle time. As evaportation progressed, residue and/or c,

o

=

42 corrodents in the liquid apparently concentrated and deposits of residue, stains and/or corrosive attacks apparently occurred from the last pools of liquid that dried up. Some of the areas were black, and others were brownish, in color. The appearance of a black deposit in the SE% which was located near the edge of the oil groove, is shown in Figure 21; Figure 22 reveals the appearance of a brownish deposit. The surfaces j

under those deposits appeared to be attacked by a corrosive environment.

i The corrosion apparently occurred during idle time.

The results of SEM/EDS analyses of the deposits are presented in Table 8.

Included in Table 8 is an analysis of a " clean" region of 4

I the bearing surface. Areas lA and IB in Table 8 were within the region

[

of the black deposit shown in Figure 21a.

(Figure 21b was Area IA.)

I Area 4 in Table 8 was the area shown in Figure 22b. The results do not show significant differences in composition between black and brownish deposits. The presence of zine in the deposits was unexpected and the

[

source of that element was not evident. The results of the analysis of a 3

" clean" region of the bearing surface, which agree well with the compositions of the bearing materials ofvon in Table 2, did net identify zine in the bearing material, nor was it detected in the oil samples, except for a trace amount in Sample EDG 14 (see Table 5).

Sulfur and j

chlorine, which were detected in deposits, can be corrosive to aluminum l

antf those elements. were probably the principal elements associated with j

the corrosive attack underneath the deposits.

h The yellow discolorations in the oil groove were removed by ethyl alcohol; thus, those discolorations war,e probably oil stains.

Sample 110t12tfr This sample was a 1/4-section of a bearing that exhibited a.

surface condition described as " dimples". The dimples were observed to be essentially depressions in the bearing surface. They appeared to be the result of particles, perhaps spheroidal in some cases, or an object (s) with smooth, curved surfaces that were pressed into ti.a surface. No scratches or scoring were associated with the dimple marks.

l It appeared as though the particles or object (s) alternately slid across l

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Black Deposit Located Near the Edge of the Oil Groove r

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..sf f 500X 59379 b.

Same As (a) Above at a Higher Magnification (Area lA in Table 8)

FIGURE 21.

BLACK DEPOSIT OBSERVED ON THE BEARING SURFACE OF SAMPLE llM-lLB SEM micrographs.

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50X 59384 Typical Brownish Deposit a.

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Same As (a) Above at a Highcr Magnification (Area 4 in Table 6) i FIGURE 22. BROWNISH DEPOSIT ON THE BEARING SURFACE OF SAMPLE 11M-1LB SEM micrographs.

. _ u__. &._

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TABLE 8.

X-RAY ENERGY-DISPERSIVE AREAL ANALYSES OF DEPOSITS ON THE BEARING SURFACE OF SAMPLE 11M-1LB T

b Relative Concentration, weight percent Element Clean Area lA, Area 18 Area 2 Area 3 Area 4, gtected Surface Black Black Brownish Black Brownish o

.c A1 90.5 67.0 60.1 65.7 72.0 71.4 2.2 2.3 ~

1.9 1.4 1.9 S

[-

C1 4.7 4.5 4.8 2.9 3.5 Sn 5.9 8.4 12.8 13.4 10.9 9.7 4.5 8.4 4.4 3.2 3.0

{

Ca 1.7 2.0 1.1 0.7 1.1 Ti Fe 0.5 1.1 1.0 1.5 1.2 1.5 Ni 1.4 2.4 1.9 2.7 2.8 2.5 Cu 1.7 2.4 1.0 2.4 2.7 2.5 Zn 5.6 6.1 2.2 2.3 2.9

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46 the surface and indented several times. The dimples most likely did not occur in service; they might have occurred during removal of the bearing.

Sample 14(m 12tfr i

The surface condition of this sample was described as " foreign embedmonts, stains". The embedded particles were similar in appearance to that of the embedded iron-rich particles observed in Sample 14W5UT; 5

subsequent spot tests for iron in the particles were positive. The 5

particles appeared to have been pressed into the surface; there was y

little or no evidence that particles scored the bearing surface before they became sabedded. The particles apparently rolled over the surface and became embedded under pressure. A buildup of aluminum, which most likely occurred in service, was evident around most of the iron-rich particles that gave them the appearance of a " bull's eye".

The y

appearance was similar to that shown in Figure 17b. A few embedded t

particles obviously had " popped out" of the surface. The faint stains associated with the fron-rich particles were apparently a tarnishing or

[

heat-tint effect that probably developed in service.

Sample 11W3tB r

l5 Sample 11M-3tB exhibited a surface condition described as 7

k

" axial scratches, stain". The regions of axial scratches were localized at the outside edges and at the conter of the loaded bearing surface.

The scratches were short, and repetitive scratch patterns often were observed. The individual scratch patterns tended to be a zig-zag pattern, an indication of lateral movement. The axial scratches were j

across circumferential service scratches and, therefore, the axial

[

scratches were not believed to be related to a service phenomenon. The l

axial scratches were probably incurred during removal of the bearing from

~

the engine or during subsequent handling.

Sample 14(B-llm The surface condition described as " stain, dull rough surface" for Sample 14CR-1LB was observed to be very similar to the surface condition of Sample 13M-13tB. Randomly distributed, small embedded

I 6

9 i

47 particles were observed; the particles were probably loose abrasive particles that rolled through contact and ultimately embedded.

One relatively large embedded particle and a few other embedded particles were found to be iron-rich. A very heavy score mark preceded the embedmont of the large particle. Scores made by the small tron-rich particles were not evident. The f ron-rich particles were found principally on one side of the oil groove; the large embedded particle was located near the oil groove.

Sample 1296-3LB The surface condi.tfon of Sample 124-3LB was described as " black stains, yellow oil-groove discoloration, dull smooth surface, straight

(

axial score mark across the total bearing surface". Evidence of rolling-particle damage and embedded particles with and without scoring preceding f

the embedmont were observed. The dull smooth surfat.e condition was similar to that of Sample 14M-5UT, except no embedded iron-rich particles r

were observed.

The axial score mark apparently was present sometime prior to the last time the bearing was in service because metal flow over the edge i.

of the score was observed. The axial score mark vas very deep and it most likely occurred during either installation or removal at some time earlier in its service life, or by mishandling.

The black stain apparently originated from wear debris that ran

[

over the edge of the bearing and dried up; most of the stain was rubbed off with a finger. The black stains and yellost discolorations, which were removed readily with a cotton swab soaked in ethyl alcohol, were most likely oil residues.

l Sample 1296-3LT i

The surfacs condition of Sample 12M-3LT was described as " black and yellow stains, scratches"._ The black and yellow stains were similar to those in Sample 124-3LB described in the previous section; those i

stains were easily removed by swabbing with ethyl alcohol.

i

a The scratches were stellar to the axial scratches in Sample llM-3tB except that lateral movement was not evident. The scratches crossed over service-wear scratches and, therefore, they were introduced in the bearing surface after, and not during, service.

Sample 12W ELB

" Waxy substance, polish" was the description of the surface H

condition of Sample 12M-5LB. A yellow waxy substance was observed on the surface of the oil groove; the substance was removed readily by cwabbing with ethyl alcohol. The yellow substance and stains on this and other bearing samples apparer.tly originated from the lubricant after it evaporated.

The " pol 1sh" appearance of this sample and other bearing samples was typical of the appearance of load-bearing regions of aluminum bearings.

{

Sample 13(R-3tB/Ur r

5-This sample consisted primarily of numerous small fractured bearing frapents. The fracture surfaces of most of the frapents were y

k severely damaged. Examinations of metallographic cross se:tions of fragments revealed the fracture path to be principally along c

interdendritic regions of the cast microstructure that contained aluminum constitutents. The cause of the bearing failure and ultimate j

frapentation of the bearing could not be determined.

Several magnetic fragments were separated from the aluminum l

bearing fragments with a magnet. Most of the magnetic fragments were found to be pieces of cast iron containing flake graphite. Those pieces l

appeared to be fragments from the edge of a machined disk or other curved i

section that was about 60 mils thick. One magnetic piece was apparently steels that piece appeared to be a steel pin or roller from a needle bearing. The steel piece was about 0.46 inch in length and about 1/8 inch in diameter.

i F-"'

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49 l

DISCUSSION OF RESIE.TS The condition, " surface distress", in Sample 11M-8UT was f

interpreted from the results of the examinations to be adhesive-wear j

metal-transfer damage that is usually caused by marginal or inadequate lubrication. When an oil film is not untfonaly established, the surfaces i

of the bearing and shaft rub together and generate frictional heat which k

raises surface temperatures. Ultimately, the temperature becomes high 4

~enough to cause intermittent welding of the metals, and, subsequently, p

transfer of aluminum bearing material to the surface of the shaft.

However, in this investigation the shaft was not available for examination of its surface' to further verify that metal-transfer of l

bearing material occurred. The shaft surface, thus roughened, scores the k

bearing surface and aggravates the condition further. The ridges L

produced in the bearing by high spots on the shaft were apparently flattened out and smeared causing lateral extrusions and probable loss of

[

material by the extrusions tearing off. The relatively smooth bottoms of most wear grooves in the bearing suggested that melting and p

solfdification of thin surface layers of the bearing material may have 4-occurred. This observation indicated that lubrication was probably

).

inadequate and frictional heating was excessive. Figure 4 shows avidence

(

of the extrusion of very thin sections at the edges of grooves and the indication of lateral flow of metal. Figure 7 shows another example of l

extrusion. Such extrusions are charac'; eristic of inadequate lubricant flims which permits metal smearing to occur.

l While solid aluminum-alloy bearings offer advantages in fatigue strength and corrosion resistants, they ara more prone to roughening h

(early stages of seizure) than are babitted multilayer bearings. In periodr. of marginal lubrication, aluminum-alloy particles can transfer to the shaft end serve to cause the observed scoring of the bearing surface.

Foreign debris (such as lapping compounds) can also initiate the process, but few such debris particles were found by the examinations of the surface-distress condition. Multilayer bearings with babbitt overlays

~~~

I, s..e 50 tend to smear during periods of marginal lubrication, but do not transfer and initiate the progressive roughening of the shaft surface and subsequent damage to the bearing surface. For this reason, multilayer bearings with babbitt overlays have better resistance to scoring in periods of marginal lubricattor. than do the solid aluminum alloy bearings.

During future inspections of aluminum-tin bearing surfaces, the i

mating surface of the shaft also should be inspected for evidence of roughening of that surface by metal-transfer and subsequent damage to the bearing surface.

The dull, rough surface condition apparently was caused by q

loose, angular hard particles, larger than the oil film thickness, 4

i passing through the bearing load support zone. The roughened appearance of the bearing surface was the result of myriads of fine scratches and 3

indentations. The scratch profiles indicated scratching by a sharp edge.

f The indentations were caused by angular particles rolling through the contact zone. Some angular particles were found embedded in the bearing

{

material. Based on the results of SEM/EDS analyses, and particle morphology, most of those angular particles appeared to be lapping-

[

compound particles.

The black surface deposits found on the dull, rough surface bearing, Sample 14M-5UB, appeared to be agglomerated bearing wear debris r

i that possibly included lapping compound debris.

The dull, smooth surface c.ondition was apparently caused by particles rolling through the contact zone. This condition was believed g

to be principally an earlier stage of the dull, rough surfaco condition.

[

Embedded angular particles, which were similar to embedded particles in the dull, rough surface, were suspected to be from the lapping compound.

The dull, smooth surface, however, differed from the dull, rough surface by the presence of some embedded particles that were fron-rich. It was I

suspected that the origin of the iron-rich particles was the shaft I

se" face or metal shavings deposited in the crankcase or oil galleries during manufacture of the engine. Since alloying elenents were not found in the embedded particles, it was likely that they were particles of cast iron from the engine castings. The source of those particles may have

1. =~-

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4 51 been machining burrs or wear damage. The embedded iron-rich particles protruded above the bearing surface and appeared to have contacted the shaft surface. This condition can lead to a self-aggravating condition where embedded particles roughen the shaft and the shaft releases work hardened debris which embeds and increases the rate of damage and so on until the oil film is disrupted and bearing failure or surface molting f

occurs.

I Most of the other surface conditions that were examined

}

{'

evaporation of oil films that, in some instances, left deposits of a appeared to be the result of mishandling of the bearings or the corrosive residue on the bearing surfaces. The latter problem is usually avoided by recirculating the lubrication system continuously bhile the engines are in a standby 's'tatus. If the lubricating oils were

(

(

recirculated continuously, thers apparently was a period in the past when

{

recirculation ses interrupted for an extended length of time.

~

(

In general, the bearings examined, except the bearing with

" surface distress", were not in serious condition. However, there were numerous indications of excessive contamination both by ferrous (presumably cast iron) particles and lapping compound. If not corrected, this condition can lead to serious shaft surface damage and subsequent bearing failures.

C N E LilSI mts The results of the metallurgical investi ation of the defects 2

and blemishes on the aluminum-tin bearing sur' faces led to the following conclusions:

e The condition of surface distress was apparently caused by inadequate lubrication and excessive frictional heating that led to adhesive-wear metal-transfer damage to the bearing surface.

e Dull-rough, and dull-smooth surface conditions most likely were caused by an excessive level of contamination by iron-rich particles and lapping compound particles.

3

~

f

... ~

52 Embedded iron-rich particles were apparently cast-iron e

particles from the engine castings.

The bearings, examined in their present stage of bearing-e surface degradation, except that of " surface distress",

were not considered to be significantly damaged and thus not to be in imminent danger of failure, but failures of the bearings would be expected to occur eventually if the apparent level of particulate contamination was allowed to persist.

e No metallurgical conditions of the aluminue tin bearings that contributed to the damage of bearing surfaces were identified.

e No unusual characteristics of the used lubricating oil sampler, were' identified.

RECWSE9EATIstS

{

The following action is suggested to minimize the majority of

[

the diesel engine bearing-surface conditions that were investigated:

(1) Improve the method used to remove lapping compound from L.

the journal surfaces and the general cleanup procedures.

(2) Consider the use of steel-backed trimetal bearings with a babbitt overlay to replace the solid aluminum alloy bearings.

(3) Maintain a continuous recirculating, pressurized l-f lubrication system to prevent corrosion in stagnant areas of the bearings and to assure adequate lubrication during I

rapid start-ups of the diesel engines.

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