Effect of TiC particle size on the microstructure and tensile properties of TiCp/Ti6Al4V composites fabricated by laser melting deposition

Abstract

TiC particle (TiCp) reinforced Ti6Al4V (TiCp/Ti6Al4V) titanium matrix composites with coated powders (TiC: <10 μm) and small-sized (TiC: 25–45 μm), medium-sized (TiC: 45–75 μm) and large-sized (TiC: 75–100 μm) mixed powders were produced by laser melting deposition (LMD). The influence of TiC particle size on the microstructure and tensile properties of composites was researched. The granular and chain shaped eutectic in-situ TiC phases distributed homogeneously in the composites with coated powders. Besides the eutectic TiC phases, the unmelted TiC particles existed in composites with mixed powders. The number of granular eutectic TiC phases reduced when the TiC particles size increased. The formation mechanism of the microstructure of composites was discussed in depth. The tensile properties of composites with small-sized and medium-sized mixed powders were similar, which were better than those of composites with large-sized mixed powders but were worse than those of composites with coated powders. Compared with that of composites with large-sized mixed powders, the tensile strength (1231.3 MPa) and elongation (2.12%) of composites with coated powders were improved by nearly 4.6% and 259.3%, respectively. This was attributed to the existence of more granular eutectic TiC phases that were difficult to crack, the homogeneous distribution of eutectic TiC phases and the strong bonding of the interfaces between eutectic TiC phases and matrix. The premature damage of the larger unmelted TiC particles during the LMD process or at the initial stage of plastic deformation and the decohesion of the interface between larger TiC particle and matrix deteriorated the tensile properties of the composites fabricated with large-sized mixed powders. The fracture mechanism of composites with coated powders was controlled by eutectic TiC phases cracking followed by ductile damage of matrix. However, the fracture mechanism of composites with mixed powders was controlled by unmelted TiC particles cracking followed by eutectic TiC phases cracking and then by ductile damage of matrix.