Microstructure and tensile properties of TiCp/Ti6Al4V titanium matrix composites manufactured by laser melting deposition

Abstract

Laser melting deposition (LMD) technique was used to manufacture TiC particle (TiCp) reinforced Ti6Al4V (TiCp/Ti6Al4V) titanium matrix composites with TiC volume fraction ranging from 5% to 30%. The microstructure and tensile properties of as-deposited and heat-treated TiCp/Ti6Al4V composites were studied. Microstructure and tensile properties of TiCp/Ti6Al4V varied as the TiC volume fraction changing. The (i) microstructural evolution of TiCp/Ti6Al4V under different TiC volume fraction and (ii) the effect of heat treatment on modifying microstructure and properties of the composites were researched. Moreover, the strengthening mechanism and fracture mechanism of the composites were discussed. The results showed that composites were composed of α Ti, β Ti, and TiC. The undissolved TiC particles were observed in all the composites. The strip-like eutectic TiC phases were observed in the composites when the volume fraction of TiC was 5%, while many dendritic primary TiC phases existed in the composites when the volume fraction of TiC exceeded 10%. When the heat treatment was held at 950°C for 10h, the basketweave microstructure and partly dissolved off strip-like eutectic TiC phases existed in the composites with 5 vol.% TiC. The strength of the TiCp/Ti6Al4V with 5% TiC volume fraction was improved by nearly 12.3% compared with that of the Ti6Al4V matrix alloys. Compared with that of the as-deposited composites, the ultimate tensile strength of TiCp/Ti6Al4V composites heat-treated at 950°C decreased only from 1225.5MPa to 1202.2MPa. However, the elongation of heat-treated composites increased from 1.31% to 3.95%, which was attributed to the presence of both basketweave microstructure and dissolved off strip-like eutectic TiC. The fracture mechanism of TiCp/Ti6Al4V composites was quasi-cleavage fracture.