Effect of C addition on microstructure and mechanical properties of laser micro-alloying Ti-Al-V-C titanium matrix composites

Most research activities involving the in-situ synthesis of TiC reinforced titanium matrix composites (TMCs) using laser additive manufacturing (LAM) focus on Ti and C interactions; however, interactions between other elements within the same context remain unexplored. This work details the design of a novel laser processing experiment called the laser micro-alloying (LMA) for depositing the Ti-Al-V-xC (0 ≤ x ≤ 1.0, wt.%) alloys, which was then used to elucidate the solid solution relationships between C, Al, and V in various matrices and the effect of C on the TiC in-situ precipitation behavior. The effect of C addition on the matrix microstructure was also elucidated to determine the alloying mechanism. It was confirmed that the solid solubility of C in the matrix decreases as Al and V contents increase. The TiC precipitation increases with increasing C content in the Ti alloy matrix, while the TiC morphologies in the samples evolved from feathery to clavate, then dendritic. It was noted that 0.12 wt.% C addition in Ti-4Al-3V resulted in a significant decrease in prior β grain size and α laths' width, while further increasing C content had a negligible effect. Also, solid solution strengthening of C and continuous precipitation of TiC increased the indentation hardness, elastic modulus, and yield strength, with the increase being most significant when the C content is 0.12 wt.%. The work will lay a foundation for designing optimized TMCs used for LAM and other laser processing techniques.