Compression properties and failure mechanisms of laser additively repaired titanium alloys under quasi-static and dynamic loading

Laser directed energy deposition (LDED) garners significant attention for its potential to repair titanium alloy aeronautic equipment, which is vulnerable to damage from high-speed foreign objects. However, the dynamic mechanical behavior and underlying deformation micro-mechanisms of LDED-repaired titanium alloys remain relatively unexplored. In this study, through integrated experimental efforts and theoretical calculations, we systematically investigate the effects of the LDED repair process on the quasi-static and dynamic compression properties of TC4-DT titanium alloy, alongside elucidating the relevant micro-mechanisms governing microstructural evolution. Results show that the yield strength and ultimate compressive strength of the LDEDrepaired titanium alloys increase with the strain rate, indicating significant strain rate sensitivities. Compared to quasi-static compression, dynamic impact results in a notable reduction in strain hardening, accompanied by the occurrence of thermal softening phenomena, primarily attributed to the initiation and propagation of adiabatic shear bands (ASBs). Furthermore, due to the synergistic interplay of rotational dynamic recrystallization, dynamic recrystallization, dislocation glide in pyramidal slip systems, and deformation-induced alpha to beta phase transformation, the grains within the ASBs are substantially refined, forming heterogeneous structures. Under continued loading, the mismatch of various nanocrystals within the ASBs induces the nucleation of microvoids, ultimately resulting in the failure of the specimens.