Long crack growth behavior of implant material Ti–5Al–2.5Fe in air and simulated body environment related to microstructure

The fatigue crack propagation behavior of Ti–5Al–2.5Fe with various microstructures for biomedical applications was investigated in air and in a simulated body environment, Ringerʹs solution, in comparison with that of Ti–6Al–4V ELI and that of SUS 316L stainless steel. The crack propagation rate, da/dN, of Ti–5Al–2.5Fe in the case of each microstructure is greater than that of the Widmanstätten α structure in Ti–6Al–4V ELI in air whereas da/dN of Ti–5Al–2.5Fe is nearly equal to that of the equiaxed α structure in Ti–6Al–4V ELI in air when da/dN is plotted versus the nominal cyclic stress intensity factor range, ΔK. da/dN of the equiaxed α structure and that of the Widmanstätten α structure in Ti–5Al–2.5Fe are nearly the same in air when da/dN is plotted versus ΔK. da/dN of Ti–5Al–2.5Fe is nearly equal to that of SUS 316L stainless steel in the Paris Law region, whereas da/dN of Ti–5Al–2.5Fe is greater than that of SUS 316L stainless steel in the threshold region in air, when da/dN is plotted versus ΔK. da/dN of Ti–5Al–2.5Fe or Ti–6Al–4V ELI is nearly the same in air and in Ringerʹs solution when da/dN is plotted versus the effective cyclic stress intensity factor range, ΔKeff, whereas da/dN of Ti–5Al–2.5Fe or Ti–6Al–4V ELI is greater in Ringerʹs solution than in air when da/dN is plotted versus ΔK.