The microstructure evolution mechanism of TiC/Ti6Al4V composites fabricated by ultrasonic energy field-assisted laser melting deposition

Laser melting deposition (LMD) of TiC/Ti6Al4V composites frequently exhibits suboptimal mechanical properties due to the uneven distribution of undissolved TiC particles and the formation of large-sized chain-like eutectic TiC. To solve these problems, an ultrasonic energy field was applied synchronously during LMD in this study. Combined finite element simulations and experimental results indicated that ultrasonic vibration enhanced melt pool flow, reduced peak temperature and thermal gradient, promoted a more uniform temperature distribution, and slowed solidification rate, resulting in the phenomena that the undissolved TiC particles were more uniformly dispersed, and the chain-like eutectic TiC was effectively refined into granular structures. As the ultrasonic amplitude increased, both the quantity and uniformity of granular eutectic TiC improved further. Consequently, the tensile strength increased from 1150 MPa (as-built) to 1369 MPa (100 % ultrasonic), while the fracture strain rised from 1.2 % to 2.0 %. The slight increase of fracture strain could be attributed to the inherent brittleness of TiC, which limited the extent of elongation improvement. Concurrently, the hardness improved from 391.7 HV_0.2 to 407.0 HV_0.2, indicating that comprehensive mechanical properties of the composites could be increased under the action of the ultrasonic energy field. This study establishes a theoretical foundation for utilizing external energy fields to regulate the microstructure and performance of additive manufactured metal matrix composites.