Solid solution strengthening and deformation behavior of single-phase Cu-base alloys under tribological load

Abstract

The influence of solid solution strengthening on the evolution of the microstructure under cyclic dry sliding is still not fully rationalized. One reason is that alloying needed for solid solution strengthening alters the stacking fault energy at the same time and, hence, the mode of dislocation slip in face-centered cubic metals and alloys. Both aspects determine the details of plastic deformation and, therefore, lead to different results under tribological load. A series of Cu-Mn alloys was investigated in the present study, which exhibit wavy slip mode and an almost constant stacking fault energy over a wide solute concentration range. Solid solution strengthening is the main contribution to the hardness in these alloys. The sole impact of changing strength and hardness on the tribological response along with microstructure evolution during tribological load is assessed. After the reciprocating, tribological loading a linear correlation between the wear track width and hardness could be ascertained. Electron microscopy reveals a horizontal discontinuity of the dislocation structure beneath the surface in all alloys at a similar depth. An evaluation of the Hamiltonian elastic stress field model indicates that the depth of the dislocation feature after one sliding pass correlates with the stress distribution as well as the critical stress for dislocation motion. The subsurface microstructure features a transition from the dislocation feature to subgrain formation after about five to ten cycles. Beyond ten cycles, oxide clusters are formed on the sliding surface and the grains elongate in the sliding direction.