The effect of load on the structure and wear of friction pair materials (example of low-carbon steel and copper)

The effect of load on the wear of materials of a friction pair consisting of low-carbon steel and copper was studied. The tests were carried out under reciprocating friction. The wear character was determined by electron diffraction analysis of wear particles isolated from the exhaust lubricant. The structure of the surface layers after friction was studied by X-ray diffraction. It was found that increasing the load up to 980 N and the pressure up to 3.3 MPa accordingly led to a sharp change in the wear rate of the copper. At pressures below 3.3 MPa, 'mild' wear of copper was observed, while at 3.3 MPa, 'severe' wear of copper was observed. The phase composition of wear products changed dramatically at that pressure. The wear rate of low-carbon steel did not change abruptly under these friction conditions. The results of X-ray studies of the metals after friction showed that under the given friction conditions, the dimensions of the fragments formed in the surface layers depend on the magnitude of the pressure during friction. With the change in pressure from 0.8 to 3.3 MPa, the average dimensions of the fragments in low-carbon steel decrease from 0.6 to 0.2 μm, and in copper from 0.09 to 0.05 μm. The surface layers of both copper and low-carbon steel specimens are hardened by the formation of a fragmented structure under these friction conditions. It seems likely that a critical fragmented structure is formed in the surface layer of copper under a pressure of 3.3 MPa. In other words, copper exhausts its plasticity margin. This leads to intensive wear of the copper, because of the abrasive action of the low-carbon steel specimens. The ratio of the strength properties of friction pair materials and the magnitude of the working stresses can explain the nature of mild and severe wear and can be used as a criterion of compatibility for such materials.