Product Code: ICA13_1406

Direct Metal Deposition of Titanium Matrix Composites: Optimization of the Process and Microstructural Analysis
Authors:
Sebastien Pouzet, laboratoire PIMM; PARIS USA
Patrice Peyre, Laboratoire PIMM; Paris France
O. Castelnau, Laboratoire PIMM; Paris France
C. Gorny, Laboratoire PIMM; Paris France
C. Colin, Centre des Materiaux; Evry France
Presented at ICALEO 2013

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. The direct metal deposition (DMD) laser technique appears to be a flexible technique for generating rather complex 3D shapes.
Considering a Ti-6Al-4V titanium matrix, and 10 wt. % TiC reinforcements with different powder sizes, TMC's have been manufactured on simple walls, using the DMD laser technique, in order to find out optimal process conditions and optimal powder preparation to ensure sound microstructures in terms of particle size, homogeneity and coherency of particle-matrix interfaces. Microstructural investigations on cross-sections and longitudinal sections have been performed using optical microscopy, SEM, EDS analysis, EBSD maps and micro-hardness tests.
Preliminary DMD trials, using (Ti-6Al-4V + 10 wt. % TiC) powder blends, approximately 50 µm diameter grain sizes, Yb:YAG laser conditions in the 400-600 W current wave regime, have provoked a full dissolution of TiC particles, and the crystallization of large TiC dendrites, with a rather homogeneous distribution, and no specific crystallographic orientation with the titanium matrix. However, such microstructures were shown to be detrimental for mechanical properties of final DMD structures, during conventional tensile tests.
More recent additional tests, using finer TiC particles (around 2 µm), and specific powder blend preparations have shown homogeneously distributed reinforcements in the final microstructure which appears to be attractive for oncoming mechanical investigations.
Last, the quality of surface finish, using a 3D profilometer, has also been addressed as a major contributor to the global properties of the manufactured TMC's. It was clearly 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.