Microstructure modulation and property enhancement via an underwater induction heating treatment strategy for underwater laser-directed energy deposition of Ti-6Al-4V

In this study, an underwater in-situ induction heating treatment (UIHT)was carried out to modulate microstructure and improve the performance of underwater laser-directed energy deposition (ULDED) samples. The results showed that the redistributive behaviour of alloying elements during the UIHT process promoted the α′→α + β transition. Furthermore, the high temperature enabled dislocation motion, and the heterogeneous dislocations cancelled each other out, causing a decrease in the dislocation density. Notably, the changes in mechanical properties were primarily attributed to the changes in α grain size and dislocation density. The decomposition of martensite α′, characterised by a high dislocation density, elevated the likelihood of intergranular slip. The homogeneously dispersed α + β microstructure promoted coordinated deformation during slip, enhancing the ductility of the specimen and reducing the anisotropy of its mechanical properties. This study offers valuable guidelines for microgroup tailoring and property modulation of ULDED-repaired titanium alloys.