Modelling hydrogenation during cold dwell fatigue of additively manufactured titanium alloys

Abstract

Titanium alloys are widely employed in aerospace and automotive industries where lightweight applications are required. Additive Manufacturing (AM) processes have been proposed in order to reduce material waste and optimise mechanical properties. In addition, throughout these manufacturing processes and during service life, hydrogen uptake is expected, and the corresponding modification of mechanical properties needs to be modelled. Hydrogenation process including diffusion, trapping and hydride formation in a Ti-6Al-4V alloy during cold dwell fatigue loading, a common failure mode of titanium alloys, is simulated here. All governing equations are implemented in ABAQUS user subroutines. A boundary layer approach is used to simulate how hydrogen redistribution affects hydride kinetics near a blunting crack tip, in which cyclic loading is implemented considering different dwell times. The influence of AM techniques, especially Selective Laser Melting, is expected to promote the increase in martensite phase and microstructure defects due to rapid cooling; thus, the influence of martensite volume fraction and of trapping density on hydrogen redistribution near the crack tip is analysed. The possibility to implement hydrogen and hydride-induced dilatation is also presented, as well as a hydrogen-dependent localised plasticity model. This framework facilitates the prediction of how additive manufacturing processes affect susceptibility to hydrogen embrittlement in Ti-6Al-4V components subjected to dwell fatigue.