CoB-TiB2 crystalline powders: Synthesis, microstructural analysis and their utilization as reinforcement agent

Due to promising mechanical and chemical properties, transition metal borides have attracted attention, and numerous studies have investigated various combinations of transition elements in hopes of acquiring a final product with desired properties combined. In this study, novel low-temperature approach was adopted for the synthesis of cobalt-titanium-boron based crystalline powders. The method was based on the single-step direct reaction of CoCl _2(s), TiCl _4(l) and NaBH _4(s) in a sealed reactor under autogenic pressure. After the reaction of the precursors at 850 °C by using the molar ratios of metal chlorides to NaBH ₄ as 1:3, CoB and TiB ₂ phases were formed in-situ. The subsequent annealing process at 1100 °C achieved a full conversion of metal chlorides to CoB-TiB ₂ composite nanostructures. It was concluded that the binary forms of the borides tend to form as separate phases, which is illustrated in the SEM/EDS analyses with different morphologies. Amorphous boron layer surrounded TiB ₂ particles with an average particle size of 60 nm, whereas the CoB particles formed agglomerates with an average size of 450 nm. The use of synthesized composite powders as reinforcement in metal matrices resulted in enhanced hardness (506 HV) and compressive strength (1682 MPa) of the Ti6Al4V bulk samples.