Fretting fatigue behaviors of Ti-6Al-4V ELI and Ti-6Al-7Nb for biomedical applications

Effects of fretting on fatigue of Ti-6Al-4V ELI and Ti-6Al-7Nb with equiaxed alpha microstructure as biomaterials are investigated in present work. The testing was conducted in air at room temperature feet under conditions of frequency, f, =10, stress rate, R, =0.1, and a normal clamping pressure of about 30MP, using dogbone-shaped specimens and bridge-type pads with flat. The fretting-fatigue limits of the alloys are dramatically lower than their plain-fatigue limits. The contact areas are fretted heavily, and every scar consists of a stick region in the middle and two slip regions beside. Lots of surface cracks exist in the fretted areas. The dramatic reduction of fatigue life is ascribed to the increased stress intensity factor of the crack in early stage due to the cooperative action of alternating bulk stress, frictional force and normal stress under fretting condition. The fracture features and the angle of the crack propagation to the specimen surface of fretting fatigue are different from those of plain fatigue.