Microstructure growth behavior and its evolution mechanism during laser additive manufacture of in-situ reinforced (TiB+TiC)/Ti composite

The in-situ (TiB + TiC) reinforced Ti matrix composites with novel microstructures were successfully prepared by laser additive manufacture in this paper. The phase identification, surface morphologies, microstructure growth and its evolution mechanism, and microhardness of B4C/Ti composite under variable laser power were systematically analyzed. The results revealed that the in-situ TiC+TiB reinforcements generated surrounding the incorporated B4C particles and the pro-eutectic TiB phases precipitated from the molten liquid. Under the activities of a large laser power penetrated into powder-bed, the top surface morphology appeared to be smooth, due to the sufficient convections within pool and neighboring tracks. The laser power significantly influenced the microstructure growth within molten pool. As increasing the laser power, the in-situ whisker-like TiB and granular TiC phases were evidently grew and coarsened, ascribed to the sufficient energy and considerable diffusion of B and C elements. The high microhardness of approximate 577.1 HV0.2 was obtained at a relatively low laser power, attributing to the enhancement of fine TiB and TiC reinforcements. Furthermore, the evolution mechanism of microstructure within molten pool was concluded, as well.