In-situ synthesis of functionally graded TiN/pure Ti composites via reactive atmosphere additive manufacturing

This study employs an innovative gas–liquid in-situ reaction approach combined with laser powder bed fusion (LPBF) technology to fabricate pure titanium matrix functionally graded composite materials (FGMs) under a progressively decreasing nitrogen (N 2 ) atmosphere. Consequently, the TiN reinforcement was successfully synthesized within a pure Ti matrix, leading to the fabrication of TiN-reinforced titanium matrix FGMs with well-defined gradient features and minimal defects. Furthermore, the continuous decrease in N 2 concentration along the LPBF construction direction leads to a corresponding reduction in both the volume fraction and particle width of in-situ formed TiN reinforcement. As a result, a continuously graded microstructure evolves, characterized by the progressive refinement of the α'-Ti phase and prior β grain from the top to the bottom of the fabricated FGMs. This graded microstructure, in turn, gives rise to smooth gradients in microhardness and wear resistance, which stem from the synergistic effects of nitrogen solid solution strengthening, the variation in content and size of TiN reinforcement, and the refinement strengthening of the matrix grain.