Fatigue performance differences between rolled and selective laser melted Ti6Al4V alloys

Abstract

In this work, the performance differences between rolled and selective laser melted (SLM) Ti6Al4V alloys used commonly for orthopedic implants were investigated. By rotation bending fatigue (RBF) and in-situ fatigue tests, the SN curves, crack propagation rate (d a /d N ) curves and cracking behavior of the SLM samples (in 0°, 45° and 90° directions) and rolled samples (fabricated along the rolling and transverse directions (RD and TD)) were compared. Slight fatigue performance distinction was identified for the rolled TD and RD Ti6Al4V samples. However, the building directions exhibited an obvious impact on the SN and d a /d N curves of the SLM Ti6Al4V alloy. The SLM 45° samples revealed excellent crack propagation resistance and the fatigue limit of the SLM 0° samples reached to that of the rolled Ti6Al4V alloy. The fatigue performance difference of the SLM components in different SLM directions can be expected. Moreover, the crack aspect ratios ( a / b ) of the SLM Ti6Al4V alloy were obtained from sample fracture surfaces. The effect of SLM building directions on the a / b values was revealed. Based on the results, the residual fatigue lives of the SLM and rolled Ti6Al4V hip joint prostheses were compared by finite element simulation. The SLM prostheses exhibited excellent fatigue performance and could replace the existing components fabricated by traditional alloys in some fields. • The various material anisotropies were identified for the rolled (RD and TD) and SLM Ti6Al4V (0°, 45° and 90°) samples. • The SLM 0° and 45° samples exhibited excellent fatigue limit and crack propagation resistance, respectively. • The effects of AM directions, sample types and crack depths on the crack aspect ratios of the SLM samples were revealed. • A K IC estimation method was applied for the rolled and SLM Ti6Al4V alloys. The validity of the method was proved. • The residual fatigue lives of SLM Ti6Al4V prostheses were calculated, which exhibited excellent fatigue performance.