Comparison of microstructural evolution in laser-deposited and arc-melted in-situ Ti-TiB composites

In-situ Ti-TiB composites have been processed via two different routes: arc by melting elemental Ti and B and by direct laser deposition of a blend of elemental Ti and B powders using the laser-engineered net-shaping (LENS(TM)) process. The conventionally cast composite exhibits a significantly coarser-scale microstructure as compared with the LENS(TM)-deposited composite and consists of primary proeutectic TiB precipitates dispersed in an eutectic matrix. The microstructure of the LENS(TM)-deposited Ti-TiB composite consists of a fine-scale homogeneous dispersion of primary TiB precipitates in an alpha-Ti matrix. In addition, a nanometer-scale dispersion of secondary TiB precipitates is formed in the a matrix. The hardness and modulus of these composites have been measured using nanoindentation techniques. The ability to produce such a fine dispersion of TiB precipitates in near-net-shape, near-full-density Ti-TiB composites processed using LENS(TM) could potentially be highly beneficial from the viewpoint of applicability of these metal-matrix composites.