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An explanation of the relation between wear and material hardness in three-body abrasion
313
Wear, 151 (1991) 313-321
An explanation of the relation between wear and material hardness in three-body abrasion* L. Fang and Q. D. Zhou Xian Jiaotong University Xian (China) Y. J. Li Xian Heat Power Research Institute, Xian (China) (Received June 10, 1991)
Abstract In three-body abrasion the relation between wear weight loss and material hardness is more complicated than in two-body abrasion. In order to explain the relation, short-travel three-body, short-travel two-body and long-travel three-body abrasion tests were done. The results showed that: (1) in three-body abrasion cutting wear and plastic deformation wear coexist; (2) when the material hardness changes, the ratio of cutting wear to plastic deformation wear also changes. On the basis of the test results an expression is proposed whereby the relation between wear and material hardness in three-body abrasion can be satisfactorily explained.
1. Introduction
The phenomenon of surface wear caused by loose abrasives is usually called threebody abrasion. It is a common wear type encountered in industry and agriculture. In order to reduce the wear of equipment and devices, the common practice of material selection is based on the hardness of materials and other parameters such as toughness or cost. In three-body abrasion the movement patterns of abrasives relative to the surfaces is more complicated than in two-body abrasion. The abrasives not only slide but also roll. The scratches caused by the abrasives during sliding can lead to cutting wear. Thus a cutting wear viewpoint of three-body abrasion was proposed [l-3]. The craters caused by abrasives during rolling can lead to plastic deformation wear. Then a viewpoint of plastic deformation wear in three-body abrasion was proposed [4, 51. Larsen-Basse and Premaratne [6] used steel containing 1% C and 1% Cr to do three-body abrasion tests. It was found that when the load was low, the morphology of the worn surface was dominated by craters; but when the load was increased, the surface morphology began to be dominated by scratches. On the basis of the work mentioned above, it is reasonable to expect that during three-body abrasion cutting wear and plastic deformation wear may coexist and the ratio between them can change with changes in test conditions. This is just the point that makes the relation between wear and
*Paper presented at the International Conference on Wear of Materials, Orlando, FL, U.S.A., April 7-11, 1991.
0043-1648/91/$3.50
0 1991 -
Elsevier Sequoia, Lausanne
314
material hardness quite complicated. The following examples are quoted here to show the complexity of this relation. Rabinowicz et al. [l] and Misra and Finnie [4] conducted three-body abrasion tests and showed that the wear resistance of metals and annealed steels increased with increasing hardness almost linearly. The relation obtained by them was similar to that in two-body abrasion. Prasad and Kulkani [7] conducted a three-body abrasion test in a cast iron drum with a carbon steel specimen containing O.l%-1.2% C using silica particles as abrasives. If the test results were treated as a relation between wear weight loss and material hardness as shown in Fig. 1, the curve was V shaped. Prasad and Kulkani found it difficult to explain the relation simply by hardness or structural considerations. They pointed out further that a combined consideration of hardness and toughness was necessary for understanding the relation. Zum Gahr and Doane [S] studied the wet rubber wheel wear and fracture toughness of high chromium cast iron in different states of heat treatment. Their test results are replotted here against material hardness in Fig. 2. The curve is S shaped. Zum Gahr and Doane found that wear cannot be related to fracture toughness. The explanation must be found elsewhere. Impact three-body abrasion testing was done by Ma [9] on a type MLD-10 test machine. A loaded upper specimen was hammered on a rotating lower specimen. Abrasives were fed into the gap between the two specimens to produce three-body abrasion. The details of the test machine can be found in ref. 10. The upper specimens were five martensitic steels with increasing carbon content: 20Cr (0.2% C), 40CrSi (0.4% C), 60Mn (0.6% C), T8 (0.8% C) and TlO (1.0% C). After heat treatment their Vickers hardness was 393, 556, 595, 680 and 726 HV respectively. The lower specimens were steels 20Cr, 40CrSi and TlO; their hardness was 393, 556 and 726 HV respectively. The results are shown in Fig. 3 with the martensitic steels arranged along the abscissa according to their hardness. From the figure it can be seen that the three curves are all S shaped and are quite similar to the curve of Zum Gahr and Doane in the rubber wheel wear test.
I
I
1
50
0 O.l6%C 6
100
I
I
A 0.37%C
0 austenitic
I
I
,
200
400
600
0) 800
300
500
Fig. 1. Weight loss in 120 m of three-body abrasion QJS.Brine11 hardness of ref. 7).
Fig. 2. Effect of hardness on weight loss of white cast irons ref. 8).
700
Hardness
Hardness (BHN)
in three-body
900
(HV50)
of carbon
abrasion
steel
(data
(data
of
315
200
400
Hardness of
Fig. 3. Results
600
800
upper specimens(HV)
of three-body abrasion with impact tester (data of ref. 9).
From the above examples it is clear that the relation between wear and material hardness is complicated. In the present paper an attempt is made to explain the relation by conducting short-travel three-body, short-travel two-body and long-travel three-body abrasion tests. On the basis of the experimental results an appropriate expression is proposed.
2. Experimental
details
2. I. Testers
Short-travel two-body and three-body abrasion tests were done on the tester shown in Fig. 4. A load was applied on the upper specimen by a balance with dead-weights on both ends. A moving plate was driven by a screw which was operated manually. The moving plate pushed the upper specimen a short distance, ranging from 0 to 20 mm. During a test the bottom specimen was put into a slot in the moving plate. Then about 4.5 g of abrasives were uniformly fed onto the bottom specimen and the upper specimen was put lightly on the abrasives. Finally the upper specimen was loaded by the balance and a three-body abrasion test could be started. If an abrasive sheet was glued on the table of the tester, a two-body abrasion test could be performed. The reproducibility error of the tester was 5.6%. The upper specimen was 8X 10x 14 mm3 in size with a nominal contact area of 80 mm*. When a long-travel three-body abrasion test was needed, a pin-disk-type tester was used. A sketch of the tester is shown in Fig. 5. Abrasives were fed continuously under gravity from a vibrating feeder into a gap between the pin and disk, then left the tester. The reproducibility error of the tester was 5.7%. The upper specimen was 8~8.5 X 14 mm3 in size with a nominal contact area of 68 mm*. 2.2. Test materials During all wear tests in both test devices the bottom specimens were pure iron and the upper specimens were pure copper, pure iron, 0.45% C steel, 0.8% C steel and high chromium cast iron. The chemical composition of the high chromium cast iron was 3.40% C, 0.70% Si, 0.33% Mn and 19.1% Cr. Its hardness after quenching and tempering was 60 HRC. The hardnesses of the other materials are given in Table
316
lscreFig.
4. Short-travel
Fig. 5. Principle
TABLE Hardness
of long-travel
abrasion
tester.
three-body
abrasion
tester.
1 of test materials
Pure Cu
Hardness
three-body
72
Pure Fe
103
in three-body
0.45%
abrasion
C steel
0.8%
High
C steel
Annealed
Normalized
Normalized
Quenched
121
168
211
522
Cr Iron
656 (60 HRC)
(BIW
1. The abrasives were 200-315 pm Qinghuangdao silica sand. The shape factor of the abrasives was 0.7865, so they were quite angular. 2.3. Test procedure In order to find the relation between wear and material hardness in three-body abrasion, a long-travel wear test was done using the tester shown in Fig. 5. Before each test a running-in was done on the tester to ensure a consistent surface roughness of all specimens. The travel was 83.2 m and the flow rate of abrasives was 18 g min-‘. The load on the specimen was 9.96 N, producing a nominal pressure of 0.15 MPa. Varying travel wear tests were done in the two devices. In order to find the wear details at the very beginning, the two-body and threebody abrasion tests were carried out in the short-travel wear tester (Fig. 4) using abrasive sheets and loose abrasives respectively. The test load was 11.76 N, producing a nominal pressure of 0.15 MPa, which was the same as in the long-travel test. The travel was 12 mm. During the tests one travel of each specimen produced a very small wear loss. In order to produce a reliable average measurement of wear loss, the tests were done as follows. Twelve specimens were used. At first each of them was subjected to one pass. Then all of them were put together on a balance with a sensitivity of 0.0001 g for weighing. The weight loss obtained was divided by 12 to produce an average wear loss. A wide range of travel distance could be covered by appropriate repeat pass tests.
317 The long-travel three-body abrasion tests in the tester shown in Fig. 5 were carried out to extend the length of travel by increasing the number of disk rotations.
3. Results 3.1. Eflect of material hardness on wear In three-body abrasion the relation between material hardness and wear established by long-travel wear tests in which the lower specimen was pure iron the upper specimens were the materials listed in Table 1. The weight loss of upper specimens V.Y.material hardness is shown in Fig. 6. The curve is S shaped its shape is similar to the curves of Zum Gahr and Doane [S] and Ma [9].
was and the and
3.2. Effect of travel on wear Varying travel wear tests of three-body and two-body abrasion were done to show the patterns of material removal (cutting wear or plastic defo~ation wear) in the three-body abrasion process. Figure 7 is the relation of weight loss vs. travel of annealed 0.45% C steel obtained by a varying travel three-body abrasion test on the long-travel tester. At the beginning the weight loss increases slowly, then quickly and finally reaches a stable stage with a constant wear rate. In order to examine the very beginning of the curve of Fig. 7 up to about 300 mm length of travel, a varying travel wear test was done on the short-travel wear tester by the repeat pass method. The result is shown by the broken line in Fig. 8. The result of another varying travel test on the long-travel wear tester has been shown in Fig. 7. A segment of the curve in Fig. 7 from 200 to 600 mm has been enlarged and drawn in Fig. 8 as a solid straight line which matches the broken line very well. The curve in Fig. 8 can be divided into three zones. It is noted that in zone 3 there is a significant inflection point at A. 350
1
300 250 g .63 gjl $
150 100
E
fl
50 4
200 ~
Y
-5
I~ 21 168 211 522 656 Hardness (BHN)
0
10
20
30
40
Travel (mmf
Fig. 6. Relation of wear weight loss vs. material hardness in long-travel test of three-body abrasion. Fig. 7. Relation of wear weight loss vs. travel in long-travel test of three-body abrasion.
318
x
tong-travel ---short-travel
0
0
200
400
0
600
40
80
120
160
Travel (mm)
Travel (mm)
Fig. 8. Wear weight loss varies with travel at the very beginning for annealed 0.45% C steel in three-body abrasion. Fig. 9. Wear of annealed
weight 0.45%
by cutting
wear
U.V.travel
TKWd
0
Fig.
loss caused C steel.
10. Schematic
diagram
of wear
Fig. 11. Schematic diagram showing VS. travel superimposed from Figs.
in short-travel
two-body
U
weight
loss caused
weight loss caused 9 and 10.
abrasion
tests
TKWd
by plastic by cutting
deformation and
plastic
VS. travel. deformation
wear
The next question under consideration is whether a similar relation exists in the case of two-body abrasion. Figure 9 is the result of a short-travel two-body abrasion test using abrasive sheets with 200-315 pm Qinghuangdao silica sand from the same batch as used for the three-body abrasion tests. The curve goes quickly upward at the beginning of the test, then slowly and finally reaches a stable stage with a constant wear rate. Note that there is no inflection point in Fig. 9 as in Fig. 8. Very likely, in zone 3 of Fig. 8, besides cutting wear (shown in Fig. 9), there is plastic deformation wear. If only plastic deformation and fatigue occur, the wear curve may take the shape shown in Fig. 10. On this curve plastic deformation damage takes place at the begjnning and with increasing length of sliding an accumulation of plastic deformation damage occurs and spalling will eventually take place, resulting in weight loss as shown by the curve in Fig. 10. If both cutting wear and plastic deformation wear occur, the curve of Fig. 9 may be superimposed on the curve of Fig. 10 as shown by the solid curve in Fig. 11. The curves in Figs. 8 and 11 are similar. Here an important conclusion can be drawn, that under the curve in zone 3 of Fig. 8 there must be plastic deformation wear besides cutting wear.
319 3.3. Morphoiogicai
examination
of worn surface
The morphology of a worn surface can indicate directly the pattern of movement of abrasives along the worn surface. In the present paper, with increasing material hardness the number of scratches increases as shown by the microphotographs in Figs. 12-15. Figure 12 shows the surface morphology of the pure iron specimen after the three-body abrasion test. Almost no scratches can be found on the surface. Figure 13 shows the surface morphology of normalized 0.8% C steel with somewhat higher hardness. A few scratches are found. More scratches are seen on the surface of quenched 0.8% C steel with still higher hardness (as shown in Fig. 14). If the hardness of the material is further increased, e.g. high chromium cast iron, many more scratches are present as shown in Fig. 15. Therefore the second important conclusion herewith is drawn, that with increasing material hardness the probability of cutting wear increases and that of plastic deformation wear decreases. This conclusion is useful to the explanation of the relation of material hardness vs. wear.
Fig. 12. Scanning electron body abrasion.
photomicrograph
Fig. 13. Scanning electron photomicrograph steel after three-body abrasion.
Fig. 14. Scanning electron photomicrograph steel after three-body abrasion. Fig. 15. Scanning electron photomicrograph iron after three-body abrasion.
of the surface morphology
of pure iron after three-
of the surface morphology
of the surface
morphology
of the surface morphology
of normalized
0.8% C
of quenched
0.8% C
of high chromium
cast
320
4. Discussion The curve of wear VS. travel (Fig. 8) indicates the coexistence of cutting wear and plastic deformation wear in three-body abrasion. Hence the weight loss in threebody abrasion can be written by the following expression:
w=pw,+
(1 -p)W,
where W is the total wear weight loss, WC is the weight loss caused by cutting, W,, is the weight loss caused by plastic deformation and p is the probability of cutting wear. On the basis of this expression an analysis of the relation of material hardness US. wear can be carried out. The number of scratches increases with increasing material hardness as shown by the microphotographs in Figs. 12-15. Therefore a reasonable assumption can be made here that the probabilityp increases with increasing material hardness. On the other hand, the weight loss caused by cutting wear, WC, decreases with increasing material hardness. These two factors included in the first term of the above expression are shown by the broken lines in Fig. 16. The joint action of these two factors may produce a peak on the curve as shown by the solid line in Fig. 16.
0
Hardness
Fig. 16. Schematic abrasion.
presentation
Fig. 17. Schematic presentation three-body abrasion.
0
Hardness
of cutting wear changes with material of plastic deformation
hardness
in three-body
wear changes with material hardness
in
L
\ \\ \ \ \\ \
\ \ \ ‘,
:__-- pw, /H’
,’
\
‘1 w-PW, ‘\
(1-P)Wd\\\
‘\
\\
‘\
,,k,--,
=:::,
\ PW/
--..
Hardness
_--
0
‘\
I’
$.
’
‘.
“\
‘x
\
\
\\
‘\
‘.
-
\ -‘-\
Hardness
Fig. 18. Schematic presentation of wear weight loss changes with material intensity of cutting; (b) high intensity of cutting.
hardness:
(a) low
321
Kraghelsky [ll] proposed a mathematical model of plastic deformation wear showing that the weight loss W, caused by plastic deformation was inversely proportional to material hardness. Then the second term in the above expression can be expressed by the solid line in Fig. 17. As mentioned above in the expression, the weight loss in three-body abrasion is composed of a cutting wear term and a plastic deformation wear term. Thus Fig. 16 may be superimposed on Fig. 17 and the result may have two forms (Fig. 18). The first one is the case of low intensity of cutting wear as shown by the dotted line pW, in Fig. 18(a) with a low peak. The weight loss decreases with increasing material hardness (see solid line). The curves of Rabinowicz et al. [l] and Misra and Finnie [4] belong to this case. The second one is the case of high intensity of cutting wear as shown by the dotted line pW= in Fig. 18(b) with a high peak. The curve of weight loss W. material hardness is S shaped (see solid line). The curves of Zum Gahr and Doane [S], Ma [9] and the present authors (Fig. 6) belong to this case. The curve of Prasad and Kulkani 171 is only a part of the S-shaped curve of Fig. 18(b).
5. Conclusions
(1) In three-body abrasion of metals cutting wear and plastic deformation wear coexist. The number of scratches increases and the amount of plastic indentation decreases by particle rolling with increasing material hardness. (2) An expression is proposed in the present paper which can explain the relation between wear and material hardness satisfactorily.
References I E. Rabinowicz, L. A. Dunn and P. G. Russel, A study of abrasive wear under three-body conditions, Wear, 4 (1961) 345-355. 2 T. Sasada, M. Oike and N. Emori, Role of ioose abrasive grains interposed between rubbing surfaces in wear of metals, L.ubrication, JSLE, 27 (1982) 922-929 (in Japanese). 3 M. Oike, N. Emori and T. Sasada, Effect of fine particles interposed between sliding surfaces on wear of materials, hoc. Znt. Conf. on Wear of Materids, ASME, New York, 1987, pp. x5-190. 4 A. Misra and I. Finnie, Correlations between two-body and three-body abrasion and erosion of metals, Wear, 68 (1981) 33-39. 5 Y. L. Wang and Z. X. Wang, An analysis of the influence of plastic indentation on three body abrasive wear of metals, Proc. Znt. Co& on Wear of Materials, ASME, New York, 1987, pp. 619626. 6 J. Larsen-Basse and B. Premaratne, Etfect of relative hardness on transitions in abrasive wear mechanisms, Proc. Zni Con$ on Wear ofMatetiis, ASME, New York, 1983, pp. 161-166. 7 N. Prasad and S. D. Kulkani, Relation between microstructure and abrasive wear of plain carbon steels, Wear, 63 (1980) 32!%338. 8 K. H. Zum Gahr and D. V. Doane, Optimizing fracture toughness and abrasion resistance in white cast irons, Metall. Trans. A, II (1980) 613620. 9 Y. P. Ma, Research on three-body abrasion of martensitic steels with an impact tester, Master The.&, Xian Jiaotong University, 1990, (in Chinese). 10 J. M. Tong, Y. Z. Zhou, T. Y. Shen and 11. J. Deng, The influence of retained austenite in high chromium cast iron on impact abrasive wear, Proc. Znt. Con$ on Wear of Materials, ASME, New York, 1989, pp. 65-70. 11 I. V. Kraghelsky, Calculation of wear rate, Trans. ASME, J. Basic Eng., 87 (1965) 785-790.
Wear, 151 (1991) 313-321
An explanation of the relation between wear and material hardness in three-body abrasion* L. Fang and Q. D. Zhou Xian Jiaotong University Xian (China) Y. J. Li Xian Heat Power Research Institute, Xian (China) (Received June 10, 1991)
Abstract In three-body abrasion the relation between wear weight loss and material hardness is more complicated than in two-body abrasion. In order to explain the relation, short-travel three-body, short-travel two-body and long-travel three-body abrasion tests were done. The results showed that: (1) in three-body abrasion cutting wear and plastic deformation wear coexist; (2) when the material hardness changes, the ratio of cutting wear to plastic deformation wear also changes. On the basis of the test results an expression is proposed whereby the relation between wear and material hardness in three-body abrasion can be satisfactorily explained.
1. Introduction
The phenomenon of surface wear caused by loose abrasives is usually called threebody abrasion. It is a common wear type encountered in industry and agriculture. In order to reduce the wear of equipment and devices, the common practice of material selection is based on the hardness of materials and other parameters such as toughness or cost. In three-body abrasion the movement patterns of abrasives relative to the surfaces is more complicated than in two-body abrasion. The abrasives not only slide but also roll. The scratches caused by the abrasives during sliding can lead to cutting wear. Thus a cutting wear viewpoint of three-body abrasion was proposed [l-3]. The craters caused by abrasives during rolling can lead to plastic deformation wear. Then a viewpoint of plastic deformation wear in three-body abrasion was proposed [4, 51. Larsen-Basse and Premaratne [6] used steel containing 1% C and 1% Cr to do three-body abrasion tests. It was found that when the load was low, the morphology of the worn surface was dominated by craters; but when the load was increased, the surface morphology began to be dominated by scratches. On the basis of the work mentioned above, it is reasonable to expect that during three-body abrasion cutting wear and plastic deformation wear may coexist and the ratio between them can change with changes in test conditions. This is just the point that makes the relation between wear and
*Paper presented at the International Conference on Wear of Materials, Orlando, FL, U.S.A., April 7-11, 1991.
0043-1648/91/$3.50
0 1991 -
Elsevier Sequoia, Lausanne
314
material hardness quite complicated. The following examples are quoted here to show the complexity of this relation. Rabinowicz et al. [l] and Misra and Finnie [4] conducted three-body abrasion tests and showed that the wear resistance of metals and annealed steels increased with increasing hardness almost linearly. The relation obtained by them was similar to that in two-body abrasion. Prasad and Kulkani [7] conducted a three-body abrasion test in a cast iron drum with a carbon steel specimen containing O.l%-1.2% C using silica particles as abrasives. If the test results were treated as a relation between wear weight loss and material hardness as shown in Fig. 1, the curve was V shaped. Prasad and Kulkani found it difficult to explain the relation simply by hardness or structural considerations. They pointed out further that a combined consideration of hardness and toughness was necessary for understanding the relation. Zum Gahr and Doane [S] studied the wet rubber wheel wear and fracture toughness of high chromium cast iron in different states of heat treatment. Their test results are replotted here against material hardness in Fig. 2. The curve is S shaped. Zum Gahr and Doane found that wear cannot be related to fracture toughness. The explanation must be found elsewhere. Impact three-body abrasion testing was done by Ma [9] on a type MLD-10 test machine. A loaded upper specimen was hammered on a rotating lower specimen. Abrasives were fed into the gap between the two specimens to produce three-body abrasion. The details of the test machine can be found in ref. 10. The upper specimens were five martensitic steels with increasing carbon content: 20Cr (0.2% C), 40CrSi (0.4% C), 60Mn (0.6% C), T8 (0.8% C) and TlO (1.0% C). After heat treatment their Vickers hardness was 393, 556, 595, 680 and 726 HV respectively. The lower specimens were steels 20Cr, 40CrSi and TlO; their hardness was 393, 556 and 726 HV respectively. The results are shown in Fig. 3 with the martensitic steels arranged along the abscissa according to their hardness. From the figure it can be seen that the three curves are all S shaped and are quite similar to the curve of Zum Gahr and Doane in the rubber wheel wear test.
I
I
1
50
0 O.l6%C 6
100
I
I
A 0.37%C
0 austenitic
I
I
,
200
400
600
0) 800
300
500
Fig. 1. Weight loss in 120 m of three-body abrasion QJS.Brine11 hardness of ref. 7).
Fig. 2. Effect of hardness on weight loss of white cast irons ref. 8).
700
Hardness
Hardness (BHN)
in three-body
900
(HV50)
of carbon
abrasion
steel
(data
(data
of
315
200
400
Hardness of
Fig. 3. Results
600
800
upper specimens(HV)
of three-body abrasion with impact tester (data of ref. 9).
From the above examples it is clear that the relation between wear and material hardness is complicated. In the present paper an attempt is made to explain the relation by conducting short-travel three-body, short-travel two-body and long-travel three-body abrasion tests. On the basis of the experimental results an appropriate expression is proposed.
2. Experimental
details
2. I. Testers
Short-travel two-body and three-body abrasion tests were done on the tester shown in Fig. 4. A load was applied on the upper specimen by a balance with dead-weights on both ends. A moving plate was driven by a screw which was operated manually. The moving plate pushed the upper specimen a short distance, ranging from 0 to 20 mm. During a test the bottom specimen was put into a slot in the moving plate. Then about 4.5 g of abrasives were uniformly fed onto the bottom specimen and the upper specimen was put lightly on the abrasives. Finally the upper specimen was loaded by the balance and a three-body abrasion test could be started. If an abrasive sheet was glued on the table of the tester, a two-body abrasion test could be performed. The reproducibility error of the tester was 5.6%. The upper specimen was 8X 10x 14 mm3 in size with a nominal contact area of 80 mm*. When a long-travel three-body abrasion test was needed, a pin-disk-type tester was used. A sketch of the tester is shown in Fig. 5. Abrasives were fed continuously under gravity from a vibrating feeder into a gap between the pin and disk, then left the tester. The reproducibility error of the tester was 5.7%. The upper specimen was 8~8.5 X 14 mm3 in size with a nominal contact area of 68 mm*. 2.2. Test materials During all wear tests in both test devices the bottom specimens were pure iron and the upper specimens were pure copper, pure iron, 0.45% C steel, 0.8% C steel and high chromium cast iron. The chemical composition of the high chromium cast iron was 3.40% C, 0.70% Si, 0.33% Mn and 19.1% Cr. Its hardness after quenching and tempering was 60 HRC. The hardnesses of the other materials are given in Table
316
lscreFig.
4. Short-travel
Fig. 5. Principle
TABLE Hardness
of long-travel
abrasion
tester.
three-body
abrasion
tester.
1 of test materials
Pure Cu
Hardness
three-body
72
Pure Fe
103
in three-body
0.45%
abrasion
C steel
0.8%
High
C steel
Annealed
Normalized
Normalized
Quenched
121
168
211
522
Cr Iron
656 (60 HRC)
(BIW
1. The abrasives were 200-315 pm Qinghuangdao silica sand. The shape factor of the abrasives was 0.7865, so they were quite angular. 2.3. Test procedure In order to find the relation between wear and material hardness in three-body abrasion, a long-travel wear test was done using the tester shown in Fig. 5. Before each test a running-in was done on the tester to ensure a consistent surface roughness of all specimens. The travel was 83.2 m and the flow rate of abrasives was 18 g min-‘. The load on the specimen was 9.96 N, producing a nominal pressure of 0.15 MPa. Varying travel wear tests were done in the two devices. In order to find the wear details at the very beginning, the two-body and threebody abrasion tests were carried out in the short-travel wear tester (Fig. 4) using abrasive sheets and loose abrasives respectively. The test load was 11.76 N, producing a nominal pressure of 0.15 MPa, which was the same as in the long-travel test. The travel was 12 mm. During the tests one travel of each specimen produced a very small wear loss. In order to produce a reliable average measurement of wear loss, the tests were done as follows. Twelve specimens were used. At first each of them was subjected to one pass. Then all of them were put together on a balance with a sensitivity of 0.0001 g for weighing. The weight loss obtained was divided by 12 to produce an average wear loss. A wide range of travel distance could be covered by appropriate repeat pass tests.
317 The long-travel three-body abrasion tests in the tester shown in Fig. 5 were carried out to extend the length of travel by increasing the number of disk rotations.
3. Results 3.1. Eflect of material hardness on wear In three-body abrasion the relation between material hardness and wear established by long-travel wear tests in which the lower specimen was pure iron the upper specimens were the materials listed in Table 1. The weight loss of upper specimens V.Y.material hardness is shown in Fig. 6. The curve is S shaped its shape is similar to the curves of Zum Gahr and Doane [S] and Ma [9].
was and the and
3.2. Effect of travel on wear Varying travel wear tests of three-body and two-body abrasion were done to show the patterns of material removal (cutting wear or plastic defo~ation wear) in the three-body abrasion process. Figure 7 is the relation of weight loss vs. travel of annealed 0.45% C steel obtained by a varying travel three-body abrasion test on the long-travel tester. At the beginning the weight loss increases slowly, then quickly and finally reaches a stable stage with a constant wear rate. In order to examine the very beginning of the curve of Fig. 7 up to about 300 mm length of travel, a varying travel wear test was done on the short-travel wear tester by the repeat pass method. The result is shown by the broken line in Fig. 8. The result of another varying travel test on the long-travel wear tester has been shown in Fig. 7. A segment of the curve in Fig. 7 from 200 to 600 mm has been enlarged and drawn in Fig. 8 as a solid straight line which matches the broken line very well. The curve in Fig. 8 can be divided into three zones. It is noted that in zone 3 there is a significant inflection point at A. 350
1
300 250 g .63 gjl $
150 100
E
fl
50 4
200 ~
Y
-5
I~ 21 168 211 522 656 Hardness (BHN)
0
10
20
30
40
Travel (mmf
Fig. 6. Relation of wear weight loss vs. material hardness in long-travel test of three-body abrasion. Fig. 7. Relation of wear weight loss vs. travel in long-travel test of three-body abrasion.
318
x
tong-travel ---short-travel
0
0
200
400
0
600
40
80
120
160
Travel (mm)
Travel (mm)
Fig. 8. Wear weight loss varies with travel at the very beginning for annealed 0.45% C steel in three-body abrasion. Fig. 9. Wear of annealed
weight 0.45%
by cutting
wear
U.V.travel
TKWd
0
Fig.
loss caused C steel.
10. Schematic
diagram
of wear
Fig. 11. Schematic diagram showing VS. travel superimposed from Figs.
in short-travel
two-body
U
weight
loss caused
weight loss caused 9 and 10.
abrasion
tests
TKWd
by plastic by cutting
deformation and
plastic
VS. travel. deformation
wear
The next question under consideration is whether a similar relation exists in the case of two-body abrasion. Figure 9 is the result of a short-travel two-body abrasion test using abrasive sheets with 200-315 pm Qinghuangdao silica sand from the same batch as used for the three-body abrasion tests. The curve goes quickly upward at the beginning of the test, then slowly and finally reaches a stable stage with a constant wear rate. Note that there is no inflection point in Fig. 9 as in Fig. 8. Very likely, in zone 3 of Fig. 8, besides cutting wear (shown in Fig. 9), there is plastic deformation wear. If only plastic deformation and fatigue occur, the wear curve may take the shape shown in Fig. 10. On this curve plastic deformation damage takes place at the begjnning and with increasing length of sliding an accumulation of plastic deformation damage occurs and spalling will eventually take place, resulting in weight loss as shown by the curve in Fig. 10. If both cutting wear and plastic deformation wear occur, the curve of Fig. 9 may be superimposed on the curve of Fig. 10 as shown by the solid curve in Fig. 11. The curves in Figs. 8 and 11 are similar. Here an important conclusion can be drawn, that under the curve in zone 3 of Fig. 8 there must be plastic deformation wear besides cutting wear.
319 3.3. Morphoiogicai
examination
of worn surface
The morphology of a worn surface can indicate directly the pattern of movement of abrasives along the worn surface. In the present paper, with increasing material hardness the number of scratches increases as shown by the microphotographs in Figs. 12-15. Figure 12 shows the surface morphology of the pure iron specimen after the three-body abrasion test. Almost no scratches can be found on the surface. Figure 13 shows the surface morphology of normalized 0.8% C steel with somewhat higher hardness. A few scratches are found. More scratches are seen on the surface of quenched 0.8% C steel with still higher hardness (as shown in Fig. 14). If the hardness of the material is further increased, e.g. high chromium cast iron, many more scratches are present as shown in Fig. 15. Therefore the second important conclusion herewith is drawn, that with increasing material hardness the probability of cutting wear increases and that of plastic deformation wear decreases. This conclusion is useful to the explanation of the relation of material hardness vs. wear.
Fig. 12. Scanning electron body abrasion.
photomicrograph
Fig. 13. Scanning electron photomicrograph steel after three-body abrasion.
Fig. 14. Scanning electron photomicrograph steel after three-body abrasion. Fig. 15. Scanning electron photomicrograph iron after three-body abrasion.
of the surface morphology
of pure iron after three-
of the surface morphology
of the surface
morphology
of the surface morphology
of normalized
0.8% C
of quenched
0.8% C
of high chromium
cast
320
4. Discussion The curve of wear VS. travel (Fig. 8) indicates the coexistence of cutting wear and plastic deformation wear in three-body abrasion. Hence the weight loss in threebody abrasion can be written by the following expression:
w=pw,+
(1 -p)W,
where W is the total wear weight loss, WC is the weight loss caused by cutting, W,, is the weight loss caused by plastic deformation and p is the probability of cutting wear. On the basis of this expression an analysis of the relation of material hardness US. wear can be carried out. The number of scratches increases with increasing material hardness as shown by the microphotographs in Figs. 12-15. Therefore a reasonable assumption can be made here that the probabilityp increases with increasing material hardness. On the other hand, the weight loss caused by cutting wear, WC, decreases with increasing material hardness. These two factors included in the first term of the above expression are shown by the broken lines in Fig. 16. The joint action of these two factors may produce a peak on the curve as shown by the solid line in Fig. 16.
0
Hardness
Fig. 16. Schematic abrasion.
presentation
Fig. 17. Schematic presentation three-body abrasion.
0
Hardness
of cutting wear changes with material of plastic deformation
hardness
in three-body
wear changes with material hardness
in
L
\ \\ \ \ \\ \
\ \ \ ‘,
:__-- pw, /H’
,’
\
‘1 w-PW, ‘\
(1-P)Wd\\\
‘\
\\
‘\
,,k,--,
=:::,
\ PW/
--..
Hardness
_--
0
‘\
I’
$.
’
‘.
“\
‘x
\
\
\\
‘\
‘.
-
\ -‘-\
Hardness
Fig. 18. Schematic presentation of wear weight loss changes with material intensity of cutting; (b) high intensity of cutting.
hardness:
(a) low
321
Kraghelsky [ll] proposed a mathematical model of plastic deformation wear showing that the weight loss W, caused by plastic deformation was inversely proportional to material hardness. Then the second term in the above expression can be expressed by the solid line in Fig. 17. As mentioned above in the expression, the weight loss in three-body abrasion is composed of a cutting wear term and a plastic deformation wear term. Thus Fig. 16 may be superimposed on Fig. 17 and the result may have two forms (Fig. 18). The first one is the case of low intensity of cutting wear as shown by the dotted line pW, in Fig. 18(a) with a low peak. The weight loss decreases with increasing material hardness (see solid line). The curves of Rabinowicz et al. [l] and Misra and Finnie [4] belong to this case. The second one is the case of high intensity of cutting wear as shown by the dotted line pW= in Fig. 18(b) with a high peak. The curve of weight loss W. material hardness is S shaped (see solid line). The curves of Zum Gahr and Doane [S], Ma [9] and the present authors (Fig. 6) belong to this case. The curve of Prasad and Kulkani 171 is only a part of the S-shaped curve of Fig. 18(b).
5. Conclusions
(1) In three-body abrasion of metals cutting wear and plastic deformation wear coexist. The number of scratches increases and the amount of plastic indentation decreases by particle rolling with increasing material hardness. (2) An expression is proposed in the present paper which can explain the relation between wear and material hardness satisfactorily.
References I E. Rabinowicz, L. A. Dunn and P. G. Russel, A study of abrasive wear under three-body conditions, Wear, 4 (1961) 345-355. 2 T. Sasada, M. Oike and N. Emori, Role of ioose abrasive grains interposed between rubbing surfaces in wear of metals, L.ubrication, JSLE, 27 (1982) 922-929 (in Japanese). 3 M. Oike, N. Emori and T. Sasada, Effect of fine particles interposed between sliding surfaces on wear of materials, hoc. Znt. Conf. on Wear of Materids, ASME, New York, 1987, pp. x5-190. 4 A. Misra and I. Finnie, Correlations between two-body and three-body abrasion and erosion of metals, Wear, 68 (1981) 33-39. 5 Y. L. Wang and Z. X. Wang, An analysis of the influence of plastic indentation on three body abrasive wear of metals, Proc. Znt. Co& on Wear of Materials, ASME, New York, 1987, pp. 619626. 6 J. Larsen-Basse and B. Premaratne, Etfect of relative hardness on transitions in abrasive wear mechanisms, Proc. Zni Con$ on Wear ofMatetiis, ASME, New York, 1983, pp. 161-166. 7 N. Prasad and S. D. Kulkani, Relation between microstructure and abrasive wear of plain carbon steels, Wear, 63 (1980) 32!%338. 8 K. H. Zum Gahr and D. V. Doane, Optimizing fracture toughness and abrasion resistance in white cast irons, Metall. Trans. A, II (1980) 613620. 9 Y. P. Ma, Research on three-body abrasion of martensitic steels with an impact tester, Master The.&, Xian Jiaotong University, 1990, (in Chinese). 10 J. M. Tong, Y. Z. Zhou, T. Y. Shen and 11. J. Deng, The influence of retained austenite in high chromium cast iron on impact abrasive wear, Proc. Znt. Con$ on Wear of Materials, ASME, New York, 1989, pp. 65-70. 11 I. V. Kraghelsky, Calculation of wear rate, Trans. ASME, J. Basic Eng., 87 (1965) 785-790.