Microstructural evolution and mechanical properties of in-situ as-cast beta titanium matrix composites

The aim of this research is to investigate the effects of B4C additions on microstructure refinement and mechanical properties, due to in-situ formation of TiB and TiC in a matrix of beta titanium by casting process. Researches have been done on the individual effects of TiC and TiB compounds in titanium composites, however, their hybrid effect has been scarcely explored in beta titanium alloys. The effects on lattice parameter were investigated by Rietveld refinement and EDS analysis. The beta lattice parameters increased due reaction between Ti and B4C. DTA analysis revealed the sequence of phase formation on heating and cooling around the melting point, being confirmed by investigation of orientation relationship between phases by EBSD and pole figure analysis. Orientation relationships are {312}TiB//{112}β, {112}TiC//{112}β for the smallest addition of B4C, {113}TiC//{112}β for the remaining composites, and {010}TiB//{011}TiC between the particles. Grain size reduced by half with 0.5% addition of B4C, while 3% addition made grains 25 times smaller than the alloy. Young's modulus and hardness increased with the addition of boron carbide. An analysis of the hardness of the materials was carried out from a nano to a macro scale. The as-cast composite materials have a refined structure with improved mechanical properties in comparison to the commercial alloy. •TiB and TiC in-situ particles are produced after melting, while varying composition.•There is a clear orientation relationship between matrix and coarse precipitates.•Lattice parameter of beta titanium decreases with increase in volume of TiB and TiC.•Addition of 3% of B4C to Beta 21S reduced grain size from 504 μm to up to 18 μm.•Young's modulus and hardness from nano to macro increased with addition of B4C.