Investigation on microstructure, mechanical and tribological properties of in-situ (TiB plus TiC)/Ti composite during the electron beam surface melting

The (TiB + TiC)/Ti composite was successfully in-situ synthesized by the electron beam surface melting. The supplied energy input has significant effect on the microstructure evolution and properties of the titanium matrix composites (TMCs). Some aggregations of TiB whiskers around un/semi reacted B4C particles appeared in the TMCs with low energy input, resulting in the deterioration of mechanical performances, especially the wear resistance. The B4C powders fully interact with Ti matrix when the energy input increases. However, TiB whiskers, the in-situ reaction product, grow and coarsen when the energy input continuously increases, which deteriorates the mechanical and tribological properties of the TMCs. The energy input is thereby optimized to be 3.2 J/mm in order to obtain the fine in-situ reinforcements without the un/semi melted B4C particles, exhibiting the highest hardness, elastic modulus and wear resistance. This study unravels the microstructure controlling methods during the electron beam surface melting process and the optimization mechanism of the mechanical and tribological properties, which is of significance for the application of the in-situ ceramics reinforced titanium matrix composites. Overall, the results indicate that the input energy should be controlled to avoid the presence of un/semi reacted B4C and coarse TiB whiskers for the electron beam surface melted TMCs with superior properties.