The role of Ex-situ 0.5wt.% B4C reinforcement and later formed In–situ TiC and TiBw on microstructural evolution of Ti-10Mo mixed powder alloy

In titanium-molybdenum composites reinforced with boron carbide particles, which are produced by spark plasma sintering method, the reaction between the matrix and reinforcement particles can lead to the formation of TiB + TiC hybrid composition. On the other hand, the crystal structure of titanium-molybdenum alloys is strongly depend on the amount of molybdenum added and according to the results obtained in previous researches, it has been determined that in order to achieve a uniform distribution of alpha + beta dual phase structure and optimal mechanical properties, at least 10% of molybdenum should be added to titanium. Therefore, the main purpose of this research, is evaluating the effect of adding 0.5% of boron carbide to the Ti-10Mo mixed powder, SPSed at various sintering temperature on densification, enhancing Mo diffusion in Ti (which leads to microstructural evolution to β and α+β), and the formation of in-situ hybrid reinforcement.  

In this research, Ti–10 wt.% Mo–0.5 wt.% B4C composite samples was consolidated in a SPS machine following cold uniaxial precompaction by applying maximum 10 MPa and then SPS in vacuum below 1 Pa at 1150, 1300 and 1450°C with 50°C/min heating rate under 20 MPa pressure. Subsequently at each sintering temperature the applied pressure was increased to 50 MPa and the final holding time at that temperature was 5 min.Microstructural changes and physical and mechanical properties of produced composites were evaluated in order to measure the effect of increasing temperature and determining the mechanism. In addition, to get more information concerning microstructural evolution, qualitative investigations such as phase analysis of sintered samples to know constituents phases, were performed.

The results showed that the density increased with the rising sintering temperature. Also, the reaction between boron carbide particles with the matrix has been encouraged with sintering temperature and led to the formation of TiB and TiC in situ reinforcements. On the other hand, relatively uniform distributed of ex-situ and in-situ reinforcements is important in improved mechanical properties. Here, uniformly distributed Mo particles and their diffusion to matrix is important in better homogenization.