Existing theories of erosion of ductile metals based on cutting and deformation mechanisms predict no material removal at normal incidence which is contradictory to experience. Thus, other mechanisms may be involved. The possible role of adhesive material transfer during erosion is investigated by both single particle impingement experiments and erosion by streams of particles. Examination of the rebounding particles as well as the eroded surface yields evidence of a significant adhesive mechanism for the ductile metals investigated

Brainard, W. A.

Salik, J.

English

NASA Technical Reports Server

NASA Technical Memorandum 81458 
-- , 
(NASA-TM-81458) AN INVESTIGATION INTO THE N80-21489 
ROLE OF ADHESION IN THE EROSION OF DUCTILE 
:METALS (NASA) 20 P HC A02/MF A01 CSCL 11F 
Unclas 
G3/26 46824__~, 
AN INVESTIGATION INTO THE ROLE 
OF ADHESION IN THE EROSION OF 
DUCTILE METALS 
William A. Brainard and Joshua Salik 
Lewis Research Center 
Cleveland, Ohio 
Prepared for the 
Thirty-fifth Annual Meeting of the 
American Society of Lubrication Engineers 
Anaheim, California, May 5-8, 1980 
https://ntrs.nasa.gov/search.jsp?R=19800013003 2020-03-21T18:28:44+00:00Z
AN INVESTIGATION INTO THE ROLE OF ADHESION
 
IN THE EROSION OF DUCTILE METALS
 
William A. Brainard and Joshua Salik
 
NASA Lewis Research Center
 
Cleveland, Ohio 44135
 
ABSTRACT
 
Existing theories of erosion of ductile metals based on cutting
 
and deformation mechanisms predict no material removal at normal
 
incidence which is contradictory to experience. Thus, other mechanisms
 
Co
 
o may be involved. The possible role of adhesive material transfer during
 
erosion is investigated by both single particle impingement experiments
 
and erosion by streams of particles.
 
Examination of the rebounding particles as weli as the eroded
 
surfaces yields evidence of a significant adhesive mechanism for the
 
ductile metals investigated.
 
INTRODUCTION
 
The erosion of materials by streams of solid particles presents
 
serious problems in aircraft (ref. 1) and coal gasification processes 
(ref. 2) and thus has been the subject of growing interest in recent
 
years. Both theoretical (refs. 3 to 5) and experimental (refs. 6 to
 
14) studies aimed at elucidating the mechanisms involved were conduct­
ed. Two types of erosion mechanisms were considered in those studies:
 
a cutting wear mechanism associated with forces parallel to the eroded
 
surface (ref. 3) and a so-called deformation wear mechanism associated
 
with forces normal to the surface (ref. 6). Erosion theories based on
 
those two mechanisms were able to explain some features of the erosion
 
behavior of ductile metals, notably the occurrence of a maximum in the
 
erosion rate at an attack angle of -17° . However, whereas the theory
 
predicts negligible or no erosion of ductile metals at normal incidence,
 
the experimental results show substantial erosion under these condit­
ions, amounting to -50% of the erosion rate at 170 for Al eroded by
 
Al203 particles. Although some authors (refs. 11, 12) have offered ex­
planations for this discrepancy it seems quite possible that some mech­
anisms which are actually involved in erosion have been overlooked.
 
In sliding wear one of the major mechanisms of material removal is
 
adhesive material transfer (ref. 15). Since many of the conditions that
 
occur in sliding, namely intimate interfacial contact between the inter­
acting bodies due to rupture of surface films and flow of material from
 
the contact zone due to compressive stress, also exist in erosion, it
 
is likely that adhesive material transfer is also one of the mechanisms
 
contributing to erosive wear. The objective of the study
 
2 
reported herein was to investigate this possibility. Two types of
 
experiments were conducted - single particle impact experiments and
 
erosion by means of continuous stieams of small particles. 
MATERIALS 
Three types of target materials were used in this study: 6061 Al
 
alloy which had been annealed for 3 hours at 4200 C; ASTM B152-76 copper
 
which had been annealed for 3 hours at 5000 C and ASTM A108 steel to 
which no heat treatment was applied. 
APPARATUS AND PROCEDURE
 
The gun used for the single particle impact experiments was of
 
the same design as the one used by Hutchings and Winter (ref. 16) with
 
a barrel length of 20.5 cm using nitrogen as the driving gas and
 
hollow teflon sabots (c.a. 2.7 grams by weight) for holding the
 
projectile. The projectiles were hardened (62-65 Rc) AISI 52100
 
bearing steelballs of 3.2 mm diameter. Two solar cells placed 5 cm 
apart were used for measuring the projectile velocity. A schematic of
 
the apparatus is shown in Figure 1. The gun was operated at pressures
 
up to 4 M~a with aluminum rupture diaphragms 0.06 to 0.25 mm thick 
resulting in particle velocities from 85 to 180 meters per second.
 
A commercial abrasive blasting unit was used for the study of
 
erosion by streams of particles. The unit used a gas nozzle to
 
accelerate the erodant particles. The eroding particles were glass
 
spheres of 15 Um average diameter and AI203 particles 50 pm in size and
 
of irregular shape. The carrier gas was Argon at 80 psi. Although no
 
measurement .of particle velocity or flow rate was made in this case,
 
3 
there is evidence that the particle velocity was much lower than in the
 
single impact experiments (ref. 17).
 
Following impact the eroding particles or steel spheres were
 
collected and examined in a scanning electron microscope augmented with
 
energy-dispersion x-ray analyzer. The impacted metal surfaces were also
 
examined both optically and in the SEM. 
RESULTS AND DISCUSSION
 
Single Impact Experiments
 
The x-ray emission spectrum obtained from a virgin ball which had
 
not been impacted is shown in Figure 2. The peaks at 6.4 keV and 
7.1 keV are, respectively, the K and K emissions of Fe. The peak 
at 1.7 keV is the Si K a line. Figure 3 shows the x-ray emission 
spectrum of a ball that had been shot at an annealed 6061 Al alloy at a 
speed of 107 m/sec. A peak at 1.5 keV due to Al Ka emission is clearly
a 
seen, indicating transfer of Al from the target onto the projectile. 
However, the amount of material transferred in this case was too small 
to be observed 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 portion of the surface of 
a ball which had been shot at a 6061 target at a speed of 147 m/sec. 
It shows that target material which is transferred to the projectile 
forms a continuous layer on its surface. Figure 4(c) is the x-ray 
emission spectrum taken from the area covered by the layer of transferred 
material. Note that the Fe K peak at 6.4 keV obtained from the 
covered area is higher than the one obtained from the uncovered area 
4
 
which is shown in Figure 4(b). This is due to the fact that most of the 
x-ray emission takes place at some depth underneath the surface and thus 
the x-ray is absorbed on its way out of the sample (ref. 18). Since the 
cm

absorption coefficient of Al 	for Fe Ka radiation which is 252.4 
-1 
a 
(ref. 19) is lower than that 	of Fe for the same radiation, which is
 
560.0 cm - I (ref. 19) the absorption with the Al layer present is smaller 
and 	 thus higher intensity is obtained. Using Lambert's law 
I = 10 exp(-pt) 
where I is the intensity of 	the emitted x-ray, I is its intensityo 
after traversing a layer of thickness t and p is the absorption coef­
ficient, one can use the intensity ratio in these two cases to get a 
rough estimate of the thickness of the Al layer, yielding a value of 
the order of 3 pm. By measuring the diameter and depth of the crater 
formed on the target by the impacting ball, the area of intimate contact 
2 
between the ball and the target was calculated and found to be 0.32 cm 
thus yielding a value of 2.6 	10- 4 gram for the amount of target material
 
-
transferred per particle, i.e. an erosion ratio as high as 2 10 (mass
 
removed/mass impinged). Since this is of the same order of magnitude
 
as the total erosion rate observed for the same conditions, it may be
 
inferred that adhesive material transfer plays an important role in the
 
erosion process and thus should be taken into account in theoretical treat­
ments of erosion.
 
The overall surface morphology of the ball after impact is schemat­
ically 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 with the layer of transferred material and the lower
 
5 
one is that which had not been in contact with the target and is "clean".
 
The covered part also contains occasional chunks of target material. An
 
example of such a chunk is shown in Figure 6, together with the corres­
ponding Al K emission map.
 
Adhesive material transfer is not limited to Al as can be seen from 
Figure 7 which shows the ball surface and the corresponding Cu K map 
obtained from a ball which had been shot at an annealed Cu target into a 
region previously impacted several times. The x-ray map clearly shows a 
rather heavy transferred film of copper onto the steel surface. 
Further evidence of adhesion was obtained from examination of the im­
pacted copper surface. Figure 8 is a micrograph taken from the bottom of
 
a crater formed on an annealed Cu target by the impact of a steel ball at­
140 meters per second, and itcan be readily seen that tensile fracture
 
of target material had taken place. The tensile fracture is a result of
 
adhesion forces between the target and the rebounding particle.
 
Erosion by Continuous Streams of Particles
 
In order to verify the role of adhesive material transfer in more
 
real situations, erosion tests using continuous streams of particles
 
were also conducted. The erodant particles rebounding from the target
 
were collected and examined by means of the energy-dispersive x-ray
 
analyzer. Figure 9 is the x-ray emission spectrum obtained from Al203
 
particles which had been used for the erosion of an annealed Cu target.
 
A peak at 8 keV due to transferred Cu is clearly seen.
 
Another technique employed in this study is ferrography which is
 
used in lubrication research to separate ferromagnetic wear debris from
 
liquid lubricants by means of a magnetic field and provides a means of
 
6 
of observing the shape and size of worn material. Analysis of the wear 
debris has been shown to yield information regarding the mechanisms in­
volved (ref. 20). The method is fast and simple but it is limited to 
the analysis of ferromagnetic materials. ASTM A108 steel samples were 
eroded by glass beads and the used erodant particles were captured. 
These particles were then mixed with a light mineral oil and passed 
through the ferrograph. Figure 10 shows a scanning electron micrograph
 
of the eroded debris together with the corresponding Fe K x-ray emis­
a
 
sion map confirming the occurrence of adhesive material transfer from
 
the target onto the glass bead.
 
CONCLUSIONS 
It has been demonstrated that adhesive material transfer constitutes
 
a mechanism of material removal in the erosion of ductile metals. Since 
erosion theories based on cutting and deforiation mechanisms were unable 
to explain the occurrence of erosion of ductile metals at normal inci­
dence, this finding accounts, as least partially, for the difference be­
tween theoretical and experimental results. 
Adhesively transferred material forms a continuous layer on that
 
part of the impinging particle which was in intimate contact with the 
target. In addition, adhesion forces cause material removal via tensile
 
fracture resulting in chunks of transferred material on the erodant par­
ticles.
 
7
 
REFERENCES
 
1. Schmitt, G. F., Jr., "Impact Erosion - A Serious Environmental
 
Threat to Aircraft and Missiles," ASME Paper 75-ENAS-45 (July 1975).
 
2. McGee, J. P., Goff, G. B., Liberatore, A. J., and Strimbeck, D. C.,
 
"Turbine Blade Wear by Coal Ash in Working Fluid at 12000 F,"
 
Bureau of Mines, BM-RI-7255 (1969).
 
3. Finnie, I., "Erosion of Surfaces by Solid Particles," Wear, 3,
 
pp. 87-103 (1960).
 
4. Bitter, J. G. A., "A Study of Erosion Phenomena. Pt. I and Pt. II,"
 
Wear, 6, Pt. I, pp. 5-21, Pt. II, pp. 169-190 (1963).
 
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, 48, pp. 181-190 (1978).
 
6. Neilson, J. H. and Gilchrist, A., "Erosion by a Stream of Solid
 
Particles," Wear, 11, pp. 111-122 (1968).
 
7. Tilly, G. P., "Erosion Caused by Airborne Particles," Wear, 14,
 
pp. 63-79 (1969).
 
8. Goodwin, J. E., Sage, W., and Tilly, G. P., "A Study of Erosion by
 
Solid Particles," Proc. Inst. Mech. Eng. (London), Part 1, 184, 15,
 
pp. 279-292 (1970).
 
9. Tilly, G. P. and Sage, W., "The Interaction of Particle and Material
 
Behavior in Erosion Processes," Wear, 16, pp. 447-465 (1970).
 
10. 	Smeltzer, C. E., Compton, W. A., Gulden, M. E.,,and McElmury, S. S.,
 
"Mechanisms of Sand and Dust Erosion in Gas Turbine Engines,"
 
Solar, RDR-1625-6 (1970). (USAAVLABS-TR-70-36, AD-876584).
 
11. 	Sheldon, G. L. and Kanhere, A., "An Investigation of Impingement
 
Erosion Using Single Particles," Wear, 21, pp. 195-209 (1972).
 
8 
12. Tilly, G. P., "A Two Stage Mechanism of Ductile Erosion," Wear, 23,
 
pp. 87-96 (1973).
 
13. Hutchings, I. M. and Winter, R. E., "Particle Erosion of Ductile
 
Metals: 	 A Mechanism of Material Removal," Wear, 27, pp. 121-128
 
(1974).
 
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). Ser. A, 348, 1654,
 
pp. 379-392 (1976).
 
15. 	Bowden, F. P. and Tabor, D., The Friction and Lubrication of Solids,
 
Oxford University Press, London (1950), p. 306.
 
16. 	Hutchings, I. M. and Winter, R. E., "A Simple Small-Bore Laboratory
 
Gas Gun," J. Phys. E: Sci. Instrum., 8, pp. 84-86 (1975).
 
17. 	Brainard, W. A. and Salik, J., "A Scanning Electron Microscope Study
 
of the Normal Impingement Erosion of Ductile Metals," NASA TP-1609
 
(1980).
 
18. 	Brandon, D. G., Modern Techniques in Metallography, D. Van Nostrand
 
Co., Princeton, NJ (1966), pp. 138-140.
 
19. 	Hodgman, C. D., Ed., Handbook of Chemistry and Physics, Chemical
 
Rubber Co., Cleveland, Thirty-Eighth Edition (1956), p. 2428.
 
20. Jones, W. R., Jr. and Parker, R, J., "Ferrographic Analysis of Wear
 
Debris Generated in Accelerated Rolling Element Fatigue Tests,"
 
ASLE Trans., 22, pp. 37-45 (1979).
 
9
 
ORLgjhA VAGVI IS OF Ouf x 
OSCILLOSCOPE
 
RUPTURE -VERTICAL INPUT 
DIAPIHRAGMS- TRIGGER /,,GAS _._ INPUT- FTRE
 
RE ER o]
2LR 
 2 LITR GASrTARGET 
~~~"-
 BALL ,
 
PTFE SABOT 
FIRING VALVE SHIELD 
PRESSURE PRESSURE GAGE PHOTO-OPTICAL 
AGE - FILL VALVES PARTICLE VELOCITY 
TO GAS CONTROLS 
CYLINDER 
Figure 1. - Schematic of single particle impingement apparatus. 
Figure 2. - X-ray emission spectrum from a virgin ball. 
oRINAL P~ 
or ?OOR QUALMP 
Figure 3. - X-ray emission spectrum from a ball after 
hitting a 6061 aluminum target at a speed of 107 
m/sec. 
(a) AN SEM MICROGRAPH OF A BALL AFTER HITTING A 
6061 ALUMINUM TARGET AT 180 mlsec. 
Figure 4 
toORIGNALPAO14 
OF POOR Q'tAI 
4b) X-RAY EMISSION SPECTRUM FROM UPPER PART 
OF(A). 
c) X-RAY EMISSION SPECTRUM FROM LOWER PART 
OF (A). 
Figure 4. Concluded. 
CONTINUOUS LAYER OF 
TRANSFERRED 
MATERIAL-- -OCCASIONAL CHUNK 
TRANSFERRED 
',, 
SOF MAERIAL 
SHOWN 
REGION 
INFIG. 4 
Figure 5. - Schematic illustration of steel ball surface after impinging
 
on annealod 6061 aluminum surface at 180 mlsec.
 
(a)AN SEM MICROGRAPH OF A3.2 mm DIAMETER STEEL BALL 
AFTER IMPACT AT 140 m/sec INTO ANNEALED COPPER TAR-
GET PREVIOUSLY IMPACTED 4 TIMES. 
(b)AN Al Ka X-RAY EMISSION MAP OF THE REGION SHOWN IN(A). 
Figure 6. 
O QUALMOF 
(a)AN SEM MICROGRAPH OF ACHUNK OF TRANSFERRED TARGET MA-
TERIAL AFTER HITTING A6061 ALUMINUM TARGET AT 180 mlsec. 
(b)ACu K.X-RAY EMISSION MAP OF THE REGION SHOWN IN (A). 
Fiure 7. 
Figure & - SEM micrographs of a crater inannealed cop­
per surface after impacts by 3.2 mm diameter steel ball 
at 140 m/sec. 
Figure 9. - Energy-dispersive spectrum of A1203 erodant 
particles after impacting against annealed copper. 
OF pOORI Q1JI.TV 
(a)FERROGRAPHIC WEAR DEBRIS OBTAINED FROM THE EROSION OF 
A108 STEEL. 
(b)Fe KaEMISSION MAP OF (A). 
Figure 10. 
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An investigation into the role of adhesion in the erosion of ductile metals

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