High-mass-proportion TiCp/Ti6Al4V titanium matrix composites prepared by directed energy deposition

Abstract

Titanium matrix composites (TMC) have potential applications in the aerospace industry because of their excellent performance. The comprehensive performance of TMC mainly depends on the matrix, reinforcement and interface characteristics. Hence, this study discussed the knowledge of microstructure-property relationships in detail. Crack-free high-mass-proportion TiCp/Ti6Al4Vcomposites were successfully prepared by directed energy deposition (DED). As the TiCp mass fraction increasing from 0 to 50%, the quantity of primary TiC and unmelted TiC (UMT) increased. Meanwhile, the refined α-Ti in the composites had a relatively weak texture. In addition, the interface between primary TiC and α-Ti was a semi-coherent interface, exhibiting a 112-0 α-Ti // [110]TiC, 1-100 α-Ti // 1-11 TiC orientation relationship, which facilitated the heterogeneous nucleation of Ti and improved bonding of primary TiC with the matrix. With the increase in microhardness taking the form of a cubic function, the wear mechanism was found to transform from abrasive wear to slight delamination wear. Due to the fact that both UMT and primary TiC bonded well with Ti64 matrix, they shared partial friction to protect matrix from severe abrasion, resulting in an excellent wear resistance of composites. Moreover, the thermal conductivity of 50% TiCp/Ti6Al4V was 9.063 W∙m-1∙K-1, which was nearly 26.5% higher than that of Ti6Al4V. Owing to the premature cracking of brittle UMT and dendritic TiC, the tensile strength and elongation of the composite with 50% TiCp were 515.5 MPa and 1.83%, which decreased by 45.8% and 78.8%, respectively. Adding a high proportion of TiCp can significantly improve the hardness and wear resistance of TMC, whereas it is detrimental to the tensile performance of TMC. The study have significant implications for the design of novel TMC, particularly for the aerospace industrial applications.