Microstructural and hardness investigation in laser surface remelted refractory high-entropy alloys

Refractory high-entropy alloys (RHEAs) (Ti41V27Hf16Nb16 and Ti41V27Hf13Nb13Mo6) were treated by laser surface remelting. After laser scanning on the as-cast alloy, surface grains and epitaxially grown grains in the remelted zone exhibit competitive growth relationships, depending on heat transfer conditions. We discovered that the inward growth of surface grains and the upward growth of columnar grains proceed concurrently until they converge to establish the grain boundary. The epitaxial grains generated by rapid solidification consist of refined dendritic cells with element segregation. Additionally, the hardness increment of the remelted zone compared to base metal was attributed to cellular structure rather than conventional grain refinement. Furthermore, adding Mo to the TiVHfNb system led to a solid solution hardening effect and enhanced hardness. These microstructural modifications and improved hardness indicate that laser surface treatment can effectively tailor the mechanical properties of structural materials.