Microstructure evolution and underlying thermal behavior of high-content TiC reinforced titanium matrix composites fabricated by laser directed energy deposition

Abstract

Titanium matrix composites (TMCs) with high-content TiC have a wide prospect in the aerospace industry due to their high strength, hardness, and wear resistance. The comprehensive properties of TMCs are mainly determined by the morphology and distribution of TiC reinforcements. Hence, the effects of laser directed energy deposition (LDED) process parameters on the TiC morphology and the properties of TMCs were discussed in detail by simulations and experiments in this study. A finite element model was established by ANSYS APDL to explain the complicated phenomena during LDED of high-content TiC (60 wt%) reinforced Ti6Al4V composites. The effects of process parameters on the temperature field and grain solidification behavior were studied. As the scan speed increased, the maximum temperature gradient (G)·solidification rate (R) value increased from 6.2 × 103 to 1.4 × 104 °C/s, which caused the size of TiC to decrease gradually. The maximum G/R value decreased from 1285.5 to 491.9 °C·s/mm2, resulting in the morphology of TiC changing from dendritic to granular grains. 60 wt% TiC/Ti6Al4V composites free of pores and cracks were successfully fabricated by LDED. It was found that the TMCs were nearly dense (99.48%) with uniform dispersed TiC. Irregular-shape TiC particles were melted and then precipitated in the form of submicron lamellar and granular phases, which was consistent with simulations. At the optimized parameter, TMCs with an average hardness of 549.0 HV0.5 were obtained, and the wear resistance of this sample was improved by 53% compared to LDED-processed Ti6Al4V.