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Damage process of permalloy during repeated frictional contact
Wear, I.21 (1988)
37
37 - 40
DAMAGE PROCESS OF PERMALLOY DURING REPEATED FRICTIONAL CONTACT HIROSHI FURUICHI Department of Mechanical Engineering, Kofu 400 (Japan) (Received November 11,1986;
Faculty of Engineering,
Yamanashi University,
revised April 7, 1987; accepted July 9, 1987)
Summary Microscopic observations of the damage process of Permalloy were made during repeated unidirectional dry frictional sliding. The observations revealed a layer, near the friction surface, of adhered flattened debris whose thickness was over 100 pm and whose hardness was extraordinarily high (the highest hardness was 666 HV). Sometimes, along the traces of the debris boundaries, rows of voids were observed. These voids often become connected and form grooves; they also can be the cause of debris. This is the damage process.
1. Introduction Magnetic materials have been used as tape recorder heads and in similar applications. Accordingly, damage caused by repeated unidirectional sliding is an important problem from the viewpoint of strength. There are, however, surprisingly few reports on the primitive observation of the damage process of magnetic materials. The main purpose of this paper is, therefore, to present the microscopic damage process of Permalloy, as an example of a magnetic material, with appropriate discussion.
2. Experimental details Both the specimens (20 mm X 8 mm X 1 mm) and the sliders (20 mm X 9 mm X 1 mm) were finished with emery papers, from rough to fine. After that, they were annealed at 1420 K for 10.8 ks (3 h) in hydrogen and furnace cooled to 870 K and again they were cooled to room temperature at a rate of about 100 K s-i. 0043-1648/88/$3.50
@ Elsevier Sequoia/Printed
in The Netherlands
38 ‘1
Fig. 1. Schematic diagram of the device used for repeated unidirectional 1, slider; 2, specimen; 3, spring.
dry sliding:
Before sliding, they were sufficiently electropolished in order to exclude the effect of machining and polishing. The specimens underwent sliding friction using the apparatus shown in Fig. 1, under dry conditions and unid~ection~ly. The contact area was 8 mm X 1 mm, the pressure was 23.8 MPa or 8.7 MPa, the sliding speed was 31.8 mm s-‘, the sliding distance per cycle was 19.4 mm and the frequency was 18.8 cHz.
3. Results and discussion Figure 2 shows the typical structure of a longitudinal section of a repeatedly and unidirectionally slid specimen. It is seen that below the frictional surface there is a layer of unusual structure where no grain boundaries are visible, The thickness of the layer was over 100 pm. It was observed that, during the repeated sliding, the size and weight of the specimens sometimes increase, in contrast with the almost usual decrease in the size and weight of the sliders, presumably because of debris adhering to the frictional surface, under gravity. It is natural to think that, under high pressure, debris should stick to the frictional surface, under gravity, during repeated dry frictional contact. Figure 3 shows the typical appearance of a surface which has undergone repeated sliding friction. Something like flattened debris can be seen. From the above-mentioned facts, it may be said that the layer appeared because of the pile-up of adhered debris. It is necessary to add that exfoliation of debris from the layer occasionally occurred (Fig. 4).
39
Fig. 2. Microstructure cycles).
of a longitudinal section of a friction specimen (23.8 MPa, 5000
Fig. 3. Scanning electron micrograph showing adhered flattened debris on the friction surface of a specimen (8.7 MPa, 15 000 cycles).
Fig. 4. Scanning electron micrograph showing exfoliation surface of a specimen (23.8 MPa, 5000 cycles).
of debris from the friction
Fig. 5. Scanning electron micrograph showing rows of voids along the adhered flattened debris boundaries on a specimen (8.7 MPa, 15 000 cycles).
The highest and the mean hardness of the layer were 666 HV and 540 WV in the case of 23.8 MPa and 584 HV and 479 HV in the case of 8.7 MPa respectively; these values are much higher than that after ordinary very severe cold working (358 WV in the case of severe cold rolling). It was impossible to find any difference in the appearance of the layers under the two different pressures. Layers having the above-mentioned features were observed in other metals and alloys [l - 3 1.
40
As seen in Fig. 5, rows of voids arrange themselves along traces of the adhered and elongated debris boundaries; there are many traces of adhered and elongated debris boundaries where no voids can be seen. These voids sometimes became interconnected and formed grooves that may cause cracks, as seen in Fig. 2. Again, debris can be generated by these grooves. This is the damage process during repeated frictional sliding. The mechanism of void formation is not clear. There is a possibility, however, that the faults at the traces of the debris boundaries grew by consuming vacancies formed during the repeated sliding [ 3,4 1.
4. Conclusions The damage process of Permalloy, during repeated unidirectional dry sliding with a Permalloy slider, was studied microscopically. The pressure was 23.8 MPa or 8.7 MPa, the sliding speed was 31.8 mm s-l, the sliding distance per cycle was 19.4 mm and the frequency was 18.8 CHZ. It was found that sliding generated a layer consisting of adhered flattened debris near the friction surface, The thickness of the layer was over 100 pm and the hardness was exceedingly high, for example, at a pressure of 23.8 MPa, the highest hardness was 666 HV; this value is much higher than that after severe cold roiling (358 HV). It was impossible to find any difference in the appearance of the layer under both pressures. In the layer, it was observed that the voids arranged themselves along the adhered flattened debris boundaries. These voids sometimes became connected and formed grooves. These grooves again can be the cause of debris formation. It may be said, therefore, that the above-mentioned phenomena comprise the damage process.
References 1 H. Furuichi and S. Nakamura, Formation and structure of unusually hard, thick damaged surface layer of copper, 18-8 stainless steel and iron, J. Mater. Sci. Left., 3 (1984) 917 - 920. 2 H. Furuichi and H. Yoshida, The formation of a thick hardened surface layer by repeated frictional contact, Wear, 50 (1987) 357 - 363. 3 H. Yoshida and H. Furuichi, Wear behaviour of a 3% Si steel during repeated frictional contact, Wear, 68 (1981) 219 * 228. 4 N. Ohmae, Analysis of wear using the finite element method, Junkatsu, 29 (1984) 627 - 632.
37
37 - 40
DAMAGE PROCESS OF PERMALLOY DURING REPEATED FRICTIONAL CONTACT HIROSHI FURUICHI Department of Mechanical Engineering, Kofu 400 (Japan) (Received November 11,1986;
Faculty of Engineering,
Yamanashi University,
revised April 7, 1987; accepted July 9, 1987)
Summary Microscopic observations of the damage process of Permalloy were made during repeated unidirectional dry frictional sliding. The observations revealed a layer, near the friction surface, of adhered flattened debris whose thickness was over 100 pm and whose hardness was extraordinarily high (the highest hardness was 666 HV). Sometimes, along the traces of the debris boundaries, rows of voids were observed. These voids often become connected and form grooves; they also can be the cause of debris. This is the damage process.
1. Introduction Magnetic materials have been used as tape recorder heads and in similar applications. Accordingly, damage caused by repeated unidirectional sliding is an important problem from the viewpoint of strength. There are, however, surprisingly few reports on the primitive observation of the damage process of magnetic materials. The main purpose of this paper is, therefore, to present the microscopic damage process of Permalloy, as an example of a magnetic material, with appropriate discussion.
2. Experimental details Both the specimens (20 mm X 8 mm X 1 mm) and the sliders (20 mm X 9 mm X 1 mm) were finished with emery papers, from rough to fine. After that, they were annealed at 1420 K for 10.8 ks (3 h) in hydrogen and furnace cooled to 870 K and again they were cooled to room temperature at a rate of about 100 K s-i. 0043-1648/88/$3.50
@ Elsevier Sequoia/Printed
in The Netherlands
38 ‘1
Fig. 1. Schematic diagram of the device used for repeated unidirectional 1, slider; 2, specimen; 3, spring.
dry sliding:
Before sliding, they were sufficiently electropolished in order to exclude the effect of machining and polishing. The specimens underwent sliding friction using the apparatus shown in Fig. 1, under dry conditions and unid~ection~ly. The contact area was 8 mm X 1 mm, the pressure was 23.8 MPa or 8.7 MPa, the sliding speed was 31.8 mm s-‘, the sliding distance per cycle was 19.4 mm and the frequency was 18.8 cHz.
3. Results and discussion Figure 2 shows the typical structure of a longitudinal section of a repeatedly and unidirectionally slid specimen. It is seen that below the frictional surface there is a layer of unusual structure where no grain boundaries are visible, The thickness of the layer was over 100 pm. It was observed that, during the repeated sliding, the size and weight of the specimens sometimes increase, in contrast with the almost usual decrease in the size and weight of the sliders, presumably because of debris adhering to the frictional surface, under gravity. It is natural to think that, under high pressure, debris should stick to the frictional surface, under gravity, during repeated dry frictional contact. Figure 3 shows the typical appearance of a surface which has undergone repeated sliding friction. Something like flattened debris can be seen. From the above-mentioned facts, it may be said that the layer appeared because of the pile-up of adhered debris. It is necessary to add that exfoliation of debris from the layer occasionally occurred (Fig. 4).
39
Fig. 2. Microstructure cycles).
of a longitudinal section of a friction specimen (23.8 MPa, 5000
Fig. 3. Scanning electron micrograph showing adhered flattened debris on the friction surface of a specimen (8.7 MPa, 15 000 cycles).
Fig. 4. Scanning electron micrograph showing exfoliation surface of a specimen (23.8 MPa, 5000 cycles).
of debris from the friction
Fig. 5. Scanning electron micrograph showing rows of voids along the adhered flattened debris boundaries on a specimen (8.7 MPa, 15 000 cycles).
The highest and the mean hardness of the layer were 666 HV and 540 WV in the case of 23.8 MPa and 584 HV and 479 HV in the case of 8.7 MPa respectively; these values are much higher than that after ordinary very severe cold working (358 WV in the case of severe cold rolling). It was impossible to find any difference in the appearance of the layers under the two different pressures. Layers having the above-mentioned features were observed in other metals and alloys [l - 3 1.
40
As seen in Fig. 5, rows of voids arrange themselves along traces of the adhered and elongated debris boundaries; there are many traces of adhered and elongated debris boundaries where no voids can be seen. These voids sometimes became interconnected and formed grooves that may cause cracks, as seen in Fig. 2. Again, debris can be generated by these grooves. This is the damage process during repeated frictional sliding. The mechanism of void formation is not clear. There is a possibility, however, that the faults at the traces of the debris boundaries grew by consuming vacancies formed during the repeated sliding [ 3,4 1.
4. Conclusions The damage process of Permalloy, during repeated unidirectional dry sliding with a Permalloy slider, was studied microscopically. The pressure was 23.8 MPa or 8.7 MPa, the sliding speed was 31.8 mm s-l, the sliding distance per cycle was 19.4 mm and the frequency was 18.8 CHZ. It was found that sliding generated a layer consisting of adhered flattened debris near the friction surface, The thickness of the layer was over 100 pm and the hardness was exceedingly high, for example, at a pressure of 23.8 MPa, the highest hardness was 666 HV; this value is much higher than that after severe cold roiling (358 HV). It was impossible to find any difference in the appearance of the layer under both pressures. In the layer, it was observed that the voids arranged themselves along the adhered flattened debris boundaries. These voids sometimes became connected and formed grooves. These grooves again can be the cause of debris formation. It may be said, therefore, that the above-mentioned phenomena comprise the damage process.
References 1 H. Furuichi and S. Nakamura, Formation and structure of unusually hard, thick damaged surface layer of copper, 18-8 stainless steel and iron, J. Mater. Sci. Left., 3 (1984) 917 - 920. 2 H. Furuichi and H. Yoshida, The formation of a thick hardened surface layer by repeated frictional contact, Wear, 50 (1987) 357 - 363. 3 H. Yoshida and H. Furuichi, Wear behaviour of a 3% Si steel during repeated frictional contact, Wear, 68 (1981) 219 * 228. 4 N. Ohmae, Analysis of wear using the finite element method, Junkatsu, 29 (1984) 627 - 632.