Phase transformation of a CuZnAl alloy during friction

Changes in compositions and microstructures in the surface layer of a Cu-Zn -Al shape memory alloy during friction were investigated by means of scanni ng electron microscopy, electron probe microanalysis (EPMA), X-ray diffract ion, and transmission electron microscopy, It has been found that in fricti on, single M18R martensite beta' transforms into alpha + beta, with the sha pe and distribution of the new phases varying,vith the conditions of fricti on. In mild friction, Zn and Al diffuse over short distances along the slid ing direction, resulting in a structure in which needlelike beta and alpha alternate along the sliding surface. In severe friction, where higher surfa ce temperatures and temperature gradients are expected, Zn and Al make long -distance uphill diffusion from inside toward the surface. Consequently, Zn and Al are concentrated on the surface and depleted in the subsurface, and the phase layers present from the outmost surface inward are beta, alpha, alpha + beta, cross-martensite, and the matrix.