Direct metal deposition of titanium matrix composites: Optimization of the process and microstructural analysis

Titanium matrix composites (TMC’s) are attractive materials for aeronautical applications because of their superior mechanical performance at high temperature combined to their low density. Due to their critical machinability, the direct metal deposition (DMD) laser technique appears to be a flexible technique for generating rather complex 3D TMC shapes. In this study, considering a Ti-6Al-4V titanium matrix, and TiC reinforcements with different powder sizes, TMC walls have been manufactured, in order to find out optimal DMD conditions and powder preparation to ensure sound microstructures in terms of particle size, homogeneity and particle-matrix interfaces. Microstructural investigations on cross-sections and longitudinal sections have been performed using optical microscopy, SEM, EDS analysis, and micro-hardness tests. Preliminary DMD trials, using (Ti-6Al-4V+10 % TiC) powder blends, and approximately 50 µm diameter grain sizes, have provoked a full dissolution of TiC particles, and the extensive re-crystallization of large TiC dendrites, with a rather homogeneous distribution. However, such microstructures were shown to be detrimental for mechanical properties of DMD structures, during conventional tensile testing. More recent tests, using finer TiC particles (less than 5 µm), and specific powder blend preparations have shown more homogeneously distributed reinforcements in the final microstructure which appear to be attractive for oncoming mechanical investigations. It was also shown that the addition of TiC particles in titanium melt-pools could play a tension-active role, resulting in a large improvement of surface roughness.