The role of adhesion and delamination in the fretting wear of metallic materials

Fretting corrosion is a mild form of wear which is distinguished from unidirectional sliding wear by the small amplitude of movement and the low relative velocity of the surfaces. Macroscopic adhesion occurs in the early stages of the process, and there is evidence of the making and breaking of local welds and a roughening of the surface. Eventually adhesion falls off, the surfaces become smoother and removal of material from the surfaces occurs by delamination. The change-over from adhesion to delamination is a function of the particular material and the nature of the environment. The process is investigated in a number of materials of commercial interest such as mild steel, stainless steel and titanium alloys. The adhesion stage is more pronounced the nobler the metal and the more inert the environment. In systems exhibiting adhesion the number of fretting cycles to develop maximum adhesion corresponds to the number of cycles to initiate a propagating fatigue crack. However, it is thought that fall-off in adhesion is the significant factor.