Simultaneous enhancement of room and high-temperature mechanical properties of Ti6Al4V composite via prealloyed nano-TiB and silicide nanoprecipitates

Multiscale in-situ reinforcements could enable simultaneous enhancement of room and high temperature mechanical properties of titanium matrix composites (TMCs). In particular, knowing the precipitation of alloying elements during sintering and heat treatment is of great importance for manipulating the mechanical performance of TMCs. Here, the precipitation behavior of Si in Ti6Al4V (Ti64) matrix composites and the synergistic strengthening effect of Ti₅Si₃ nanoparticles together with TiB whiskers on the tensile property and fracture behavior at room and high temperatures have been studied by plasma spark sintering. Different from conventional sintering process used mixed powders as feedstock, Ti64-TiBw composite powders and Si powders were used to prepare Ti64-TiBw+xSi composites (x = 0, 0.5, 1.0, 1.5 wt%) with a homogeneous distribution of both reinforcements. The precipitation and distribution of nanoscale silicides was investigated in a temperature range of 1100–1300 ℃. It is found that the optimal silicon content is about 1.0 wt% which results in enhancement of ultimate tensile strength (∼1134–1256 MPa) and ductility (∼8.4–10.5 %) of as-sintered composites at room temperature since the formation of preferred Ti₅Si₃ nanoparticles along the matrix/TiBw interfaces. In contrast, the sample with 1.5 wt% Si displays higher thermal stability and a minimal reduction of yield strength of 750–499 MPa as the temperature increases from 550 to 650 ℃. The combined analysis on microstructure and fractography by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) further reveals the formation details of Ti₅Si₃ nanoparticles and the synergistic strengthening mechanism.