Grain morphology evolution mechanism of titanium alloy by the combination of pulsed arc and solution element during wire arc additive manufacturing

Abstract

Coarse columnar grains formed during titanium alloy additive manufacturing (AM) are generally regarded as unfavorable, which trend to cause solidification defects and mechanical property anisotropy. Achieving the columnar to equiaxed transition (CET) of grain structures has been a great challenge, especially for wire arc additive manufacturing (WAAM) with the highly localized heat input and large temperature gradient. The interdependence model is widely used to explain and predict the grain size and evolution during the welding or AM process. However, the thermal undercooling and the molten pool flow which were neglect in its assumption have been found to have obvious effects on the grain morphology evolution. In this work, different deposition experiments with the combination of growth restricting solutes (boron), nucleant particles (La2O3), and pulsed arc were employed to investigate these intrinsic factors which are often neglected how to influence the grain morphology.