Crack suppression in LPBF-processed W-ta-C alloys: Synergistic roles of alloying and HIP-induced self-healing

Tungsten (W) is a critical material for plasma-facing components in nuclear fusion reactors due to its excellent properties in extreme environment. Research on W and W alloys via Laser Powder Bed Fusion (LPBF) has received widespread attention because of high-degree freedom and integrated forming. However, fabricating crack-free W and W alloys via LPBF remains a challenge, primarily due to the high residual stresses during LPBF, weak connections at high-angle grain boundaries, and limited plastic deformation capacity because of the intrinsic brittleness of W. In this study, W-Ta-C alloys were fabricated by incorporating TaC into pure W via LPBF in situ alloying, to investigate the effects of TaC on microstructure evolution, crack suppression and crack healing. The addition of TaC induced eutectic reaction, promoted grain refinement and decreased the Peierls-Nabarro stress for dislocation motion, thereby suppressing crack nucleation and propagation. Furthermore, a strategy to reduce the crack density through a self-healing mechanism was developed, which is achieved by dissolution and reprecipitation of carbides during hot isostatic pressing (HIP). After HIP treatment, most cracks were healed, resulting in an 88 % reduction in crack density compared to as-printed samples, ultimately achieving nearly crack-free LPBF-fabricated W alloy.