The role of changes in hardness of subsurfaces, transfer particles and wear particles in initial-steady wear transition

After some sliding distance of initial wear of metals, the wear mode transforms to the steady state with a lower wear rate than in initial wear. The mechanism of the transition has been investigated in this study with special attention on the changes in hardness in the transfer particles, the wear particles and the subsurfaces of sliding materials. Ni, Cu and Al pins were under sliding contact with identical disks in an oxygen of 1.0×105 Pa and in a vacuum of 1.6×10−4 Pa. The transversal cross-sections of the transfer particles and the subsurfaces of both sliding specimens, together with the cross-sections of the wear particles were prepared for the Vickersʹ hardness test. The initial-steady wear transition appeared in the rubbings of Ni/Ni and Cu/Cu in the vacuum, and of Al/Al in oxygen. In these cases, the subsurface of the disk was made almost as hard as the transfer particles and the wear particles. The little difference in hardness among the interfacial materials prevents the transfer from the sliding surface to the transfer particle, which results in the transition to lower wear mode.