In order to study the basic mechanisms of erosion, hardened steel balls were shot into annealed 6061 Al alloy targets at velocity of up to 150 m/sec. The projectiles were collected and examined by a scanning electron microscope combined with energy-dispersive X-ray analyzer and it was found that target material in substantial amounts is adhesively transferred to the projectile. The transferred material forms on the projectile surface a layer the thickness of which increases with increases in impact velocity

Brainard, W. A.

Salik, J.

English

NASA Technical Reports Server

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NASA Techmcal Memorandum 791b5 
ADHESIVE MATERIAL TRANSFER IN 
THE EROS ION OF AN ALUMINUM ALLOY 
Joshua Salik and William A. Brainard 
Lewis Research Center 
Cleveland, Ohio 
May 1979 
I IUIII'I 'IU IIII UIII UIII'I'I' 1'1'1 I'll lUI 
NF00498 
NASA-TM-7916519790019135 
https://ntrs.nasa.gov/search.jsp?R=19790019135 2020-03-21T22:43:22+00:00Z
1 Report No I 2 Government AccesSion No 3 ReCIpient s Catalog No 
NASA TM-79165 
4 Title and Subtitle 5 Report Date 
ADHESIVE MATERIAL TRANSFER IN THE EROSION OF AN May 1979 
AL UMINUM ALLOY 
6 Performing OrganizatIon Code 
7 Author(sl 8 Performing Organization Report No 
Joshua Sahk and W1lham A Bramard E-028 
10 Work Unit No 
9 Performing Organization Name and Address 
NatlOnal Aeronautics and Space Adm1mstratlOn 
LeW1S Research Center 11 Contract or Grant No 
Cleveland, OhlO 44135 
13 Type of Report and Period Covered 
12 Sponsoring Agency Name and Address Techmcal Memorandum 
NatlOnal Aeronautics and Space Adm1mstratlOn 
14 Sponsoring Agency Code 
Washmgton, D. C 20546 
15 Supplementary Notes 
Joshua Sahk, NatlOnal Researcll Councli - NASA Research Assoclate, Wilham A Bramard, 
Lew1s Research Center 
16 Abstract 
In order to study the bas1C mechamsms of eroslOn, hardened steel balls were shot mto annealed 
6061 Al alloy targets at veloclties of up to 150 m/sec. The proJectiles were collected and exam-
med by a scanmng electron mlCroscope combmed w1th energy-d1spers1ve X-ray analyzer and 1t 
was found that target material m substantial amounts 1S adheslVely transferred to the proJectile 
The transferred material forms on the proJectile surface a layer the th1ckness of Wh1Ch m-
creases w1th mcreases m lmpact veloc1ty 
17 Key Words (Suggested by Author(s)) 18 DIStribution Statement 
EroslOn Unclassuled - unhm1ted 
AdheslOn STAR Category 27 
Metal transfer 
19 Security Classlf (of thiS report) 
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20 Security ClasSif (of thIS page) 
121 
No of Pages 122 Price' 
UnCIaSSU1ed UnclaSSU1ed 
For sale by the National Technical Information Service Srrlngfleld Virginia 22161 
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SUMMARY 
A clear discrepancy exists between erosion theones WhICh predict negllgible 
erOSlOn of ductile materIals at normal incidence and the experimental observation 
of substantial erosion under these conditions. In order to account for this discrep-
ancy the possible role of adhesive material transfer as an erosion mechanism was 
studIed. 
Hardened steel balls were shot mto annealed 6061 alummum (AI) alloy targets 
at velocities of up to 150 m/sec. The projectiles were collected and examined by 
a scannmg electron microscope combined with energy-dispersive X-ray analyzer 
and it was found that target material in significant amounts is adhesively trans-
ferred to the proJecttle. The transferred material forms on the projectile surface 
a contmuous layer covering essentially all the area which had been in contact with 
the target. The thlCkness of this layer increases with increasing Impact velOCity. 
It IS thus establIshed that adheSIve material transfer plays a substantlal role 
m eros IOn and should be taken mto account in theoretical treatments of erOSIOn. 
INTRODUCTION 
The erOSlOn of solIds by streams of solid particles has gamed a growmg inter-
est in recent years due to the severe role It plays In aircraft (ref. 1) and in coal 
gaSIfIcation processes (ref. 2). Several theoretical (refs. 3 to 5) as well as numer-
ous experimental (refs. 6 to 14) studies of the mechanisms involved were conducted. 
Two mechanisms were considered for the erosion of ductile materials: a cutting 
wear mechanism associated with forces parallel to the surface under attack (ref. 3) 
and a so-called deformatIOn wear associated with forces normal to the surface 
(ref. 6). 
However, whereas good agreement between theory and expenment has been ob-
tained for erosion at oblique incidence there is a clear discrepancy between the 
theoretical predlCtlOn according to WhICh practically no erosion should occur at 
normal incidence and the experimental results which exhibit substantial erosion 
(c. a., 50% of the maxImum erosion rate obtained at -170 incidence for Al eroded 
by Al203 particles). It seems quite pOSSible, therefore, that some mechanisms 
which are actually mvolved m erosion have been overlooked. 
Adhesl ve material transfer between the incident particle and the surface being 
eroded is a likely mec hanism candidate since many of the conditions that occur in 
sliding mechanlCal contact (i. e., frictional sliding) also exist in erosion contacts, 
namely intimate interfaCIal contact between the impacting particle and the substrate 
due to rupturing of surface films and flowing of material from the impact region. 
The analogy to this in sliding contacts is Junction growth and Bowden and Tabor 
(ref. 15) showed SignIficant adhesion following Junction growth durmg slIding. 
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In order to ascertam the role, if any, of adhesive material transfer in erosion, 
single particle impingement experiments at normal incidence were performed. The 
proJectiles were later collected and examined by scanning electron microscope com-
bined with energy-dispersive X-ray analyzer in order to observe any evidence of 
adhesive material transfer. 
APPARATUS AND PROCEDURE 
The samples used for this study were 37x25x6 millimeter pIeces of Al 6061 alloy 
which had been annealed at 4200 C for 3 hours. The projectiles were AISI 52100 bear-
ing steel balls of 3, 2 millimeter diameter. 
The gun used for shooting the projectiles was of the same desIgn as the one used 
by Hutchings and Winter (ref. 16) with a barrel length of 20.5 centimeters using 
nitrogen as the driving gas and hollow teflon sabots (c. a. 2.7 gram by weight) for 
holding the proJectile. However, unlIke those workers who measured the sabot veloc-
ity assuming it is identical with the projectile velocity, a direct measurement of pro-
Jectile velocity was made here since there were some indications that the projectile 
velocity is in some cases lower than the sabot velocity due probably to frictional and 
other forces between the sabot and proJectile. Two solar cells illummated by 6.3 
volts d. c. bulbs and placed 5 centImeters apart were used for measuring the veloci-
ties. A schematic of the apparatus is shown in figure 1. 
The gun was operated at pressure up to 4. 1 MPa with aluminum rupture dia-
phragms from 0.06 to 0.25 millimeter thickness. Particle velocities ranged from 
85 to 180 meters per second. 
RESULTS AND DISCUSSION 
Figure 2 presents the X-ray emission spectrum obtained from a ball which had 
not been shot at the target. The peaks at 6,4 keY and 7.1 keY are, respectively, 
the Ka and K{31 emission lines of Fe. The peak at 1. 7 keY is the SiKa emIssion 
line. 
Figure 3 is the X-ray emission spectrum obtained from a ball that had been 
shot at the Al target at a speed of 107 m/sec. A peak of 1. 5 keY due to AlKa emis-
sion is clearly observed, indicating transfer of Al from the target to the proJectile. 
However, the amount of material transferred in this case was too small to be ob-
served in the SEM and it was necessary to go to higher Impact velocities in order to 
gain information about the morphology of the transferred material. 
Figure 4(a) is an SEM micrograph of a ball which had been shot at the target at 
a speed of 147 m/sec. It shows that the target material is transferred to the pro-
Jectile in a form of a continuous layer. The overall surface morphology of the ball 
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after impact is schematically illustrated in figure 5 where two regions are shown. 
The upper one which is the one that had been in direct contact with the target during 
impact and is covered wlth a layer of transferred matenal whereas the lower one IS 
that which had not been m contact with the target and it is essentially "clean." The 
covered part also contains occasional c hunks of target material. An example of suc h 
a chunk is shown in fIgure 6 together with the corresponding AlKa emission map. 
Figure 4(c) is the X-ray emission spectrum taken from the area covered by the 
layer of transferred material. It can be seen that this layer is thick enough to 
extinguish the SiKa emisslOn line of the ball material at 1. 7 keY. Also note that 
the FeKa peak at 6.4 keY obtained from the covered area is higher than the one ob-
tained from the "clean" area which is shown in figure 4(b). This is due to the fact 
that the absorption coeffIcient of Al for FeKa radiation which is 252.4 cm-1 (ref. 17) 
is lower than that of Fe for the same radiation which is 560.0 cm-1 (ref. 17). The 
intensity ratio in these two cases was used to estimate the thickness of the layer of 
transferred material and it was found to be of the order of 3 /.Lm. Since this IS a sig-
nifICant amount of material (of the order of 3x10-4 g per particle) it may be inferred 
that adhesive matenal transfer plays a substantial role in the erosion process and 
thus should be taken mto account in any theoretical treatment of erosion. 
Many other features of erosion are still unknown and it is planned to extend this 
work to other materials and different conditions (e. g., oblique incidence) in order 
to gain a better understanding of it. 
CONCLUSIONS 
Adhesive material transfer has been demonstrated to constitute a mechanism of 
erosion of ductlle materials at normal incidence. Smce theones based on cutting 
wear and deformation mechanisms of erosion were unable to explain the occurrence 
of erosion at normal incidence, this finding accounts, at least partially, for the dif-
ference between theoretical and experimental results. 
The material transferred via this mechanism forms on the projectile surface a 
layer the thickness of which increases with the increase of impact velOCity. At an 
impact velocity of 147 m/sec substantial amounts of target material can be removed 
by this mec hanism. 
REFERENCES 
1. Schmitt, G. F., Jr.: Impact Erosion - A Serious Environmental Threat to Air-
crafts and MIssiles. ASME Paper 75-ENAS-45, July 1975. 
2. Mc Gee, J. P., et. al.: Turbine Blade Wear by Coal Ash in Working Fluid at 
12000 F. BM-RI-7255, Bureau of Mines, 1969. 
3. Finnie, I.: Erosion of Surfaces by Solid Particles. Wear, vol. 3, 1960, pp. 87-
103. 
4 
4. Bitter, J. G. A.: A Study of Erosion Phenomena. Pt. I and Pt. II. Wear, 
vol. 6, 1963, pp. 5-21, and 169-190. 
5. Finnie, I.; and McFadden, D. H.: On the Velocity Dependence of the Erosion 
of Ductile Metals by Solid Particles at Low Angles of Incidence. Wear, vol. 48, 
1978, pp. 181-190. 
6. Neilson, J. H.; and Gilchrist, A.: Erosion by a Stream of Solid Parth.Jes. Wear, 
vol. 11) 1968, pp. 111-122. 
7. Tilly, G. P.: Erosion Caused by Airborne Particles. Wear, vol. 14, 1969, 
pp. 63-79. 
8. Goodwin, J. E.; Sage, W.; and Tilly, G. P.: A Study of Erosion by Solid Parti-
cles. Proc. Inst. Mech. Engrs. (London), vol. 184, pt. 1, no. 15, 1970, 
pp. 279-292. 
9. Tilly, G. P.; and Sage, W.: The Interaction of Particle and Material Behavior 
in Erosion Processes. Wear, vol. 16, 1970, pp. 447-465. 
10. Smeltzer, C. E.; et. al.: Mechanisms of Sand and Dust Erosion in Gas Turbine 
Engines. RDR-1625-6, Solar, 1970. (USAA VLABS-TR-70-36, AD-87 6584.) 
11. Sheldon, G. L.; and Kanhere, A.: An Investigation of Impingement Erosion 
Using Single Particles. Wear, vol. 21, 1972, pp. 195-209. 
12. Tilly, G. P.: A Two Stage Mechanism of Ductile Erosion. Wear, vol. 23, 1973, 
pp. 87-96. 
13. Hutchings, I. M.; and Winter, R. E.: Particle Erosion of Ductile Metals: A 
Mechanism of Material Removal. Wear, vol. 27, 1974, pp. 121-128. 
14. Hutchings, I. M.; Winter, R. E.; and Field, J. E.: Solid Particle Erosion of 
Metals: The Removal of Surface Material by Spherical ProJectiles. Proc. 
Roy. Soc. (London), Sere A, vol. 348, no. 1654, Mar. 1976, pp. 379-392. 
15. Bowden, F. P.; and Tabor, D.: The Friction and Lubrication of Solids. Oxford 
University Press, 1958, p. 306. 
16. Hutchings, I. M.; and Winter, R. E.: A Simple Small-Bore Laboratory Gas Gun. 
J. Phys. E. (S.21. lnstrum.), vol. 8, Feb. 1975, pp. 84-86. 
17. Hodgman, C. D., ed.: Handbook of Chemistry and PhYSICS, Thirty-Eighth ed., 
Chemical Rubber Co., 1956, p. 2428. 
2 liter gas 
reservOi r 
Pressure 
gage 
To gas 
cylinder 
Osc III oscope 
i 
e 
Trigger 
Input 
Vertical 
Input 
~.r- Rupture dlaphrams 
:, 
I " 
\ '~Ball 
'I- PTFE sabot 
Firing valve 
Target 
o 0 ~ 
Photo-optical , 
particle velocity Shield 
controls 
Figure 1 - Schematic of single particle Impingement apparatus 
Figure 2. - X-ray emission spectrum from 
a vi rgin ball. 
Figure 3. - X-ray emission spectrum from 
a ball after hitting the target at 107 mlsec. 
Note that the layer of transferred mate-
rial is thin enough for the SiKa peak to 
be observed. 
(a) An SEM micrograph of a ball after 
hitting the target at 180 mlsec. (X65) 
(b) X-ray smission spectrum from upper part of (a). 
(e) X-ray emission spectrum from lower 
part of (a). 
Figure 4. 
Conti n uous layer of 
transferr-ed material 
Region shown 
in figure 4 _/ 
Occasional chunk of 
tra nsferred materia I 
Figure 5_ - Schematic illustration of steel ball surface after impinging 
on annealed 6061 aluminum surface at 180 ~/sec_ 
(a) An SEM micrograph of a chunk of transferred 
target material on the surface of the ball after 
hitting the target at 180 m/sec. (X1500) 
(b) An AIKa X-ray emission map of the region 
shown in (a). 
Figure 6. 
End of Document 


Adhesive material transfer in the erosion of an aluminum alloy

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