Fatigue crack growth in Ti-6Al-4V specimens produced by Laser Powder Bed Fusion and submitted to Hot Isostatic Pressing

Abstract

The fatigue crack growth (FCGR) behaviour of titanium alloy Ti-6Al-4V submitted to Hot Isostatic Pressing through CT specimens manufactured by Laser Powder Bed Fusion (LPBF) is analysed. Both the crack growth under constant amplitude loading and the transient crack growth behaviour after the application of overloads or underloads were studied. The effect of the mean stress and the transient delay behaviour were studied using the crack closure parameter. The HIP treatment showed an increment in the FCGR strength increasing the fatigue threshold, the critical stress intensity factor and the FCGR resistance. Crack closure induced by plasticity for the stress ratio R = 0 was observed and for R = 0.4 no crack closure was detected. The applied overloads caused a FCGR retardation due to the increase of crack closure effect induced by plasticity resulting from the overloads while for underloads application no change in the FCGR behaviour and crack closure levels was observed. The overloads applied with 100% intensity for R = 0.4 achieved a high level of plasticity in the crack tip leading to higher crack retardation and superior transient period due to a higher zone affected by the overloads.