Effects of process parameters on the microstructure and mechanical properties of a laser micro-alloying TiB/Ti-6Al-4V titanium matrix composite

The morphology and distribution of TiB are the key factors contributing to the properties of Boron-added titanium matrix composites (TMCs) with the condition of rapid laser solidification. The processing technology called laser micro-alloying is used to prepare titanium matrix composite material Ti-6Al-4V+0.3 wt%B in this work, and the relationship between various parameters and the microstructure of laser micro-alloying is determined. The Ti-6Al-4V+0.3 wt%B alloy shows three typical distributions of TiB under three different laser power ranges: TiB is enriched along the grain boundary in the low laser power range (500-1000 W), intragranular dispersed TiB in the medium laser power range (1500-3000 W), and TiB with a quasi-continuous network structure in the high laser power range (3500-5000 W). The volume fraction of TiB shows an increasing trend with the increase of the laser power, and three different microstructures significantly affect the microhardness of the alloy. The formation mechanism of typical microstructure is then clarified by combining the phase diagram and the melt pool convection conditions. Both the microstructure-process relationship and the parameters-microhardness relationship of laser micro-alloyed Ti-6Al-4V+0.3 wt%B alloy are also established.