Effect of boron microalloying on the microstructure, mechanical, and corrosion properties of as-cast biomedical Co-Cr-W-Ni-based alloys

Co-Cr-W-Ni-Mn-B alloys, potentially applicable for implant materials, with boron contents of 0, 0.01, and 0.05 wt% were prepared by arc melting in an argon atmosphere. The influence of B content on the as-cast microstructure, mechanical, and corrosion properties was investigated. The as-cast state revealed dendritic structure, with the length of dendritic arm-spacing decreasing with increasing boron contents. The addition of boron led to the emergence of M5B3-type precipitates at the interdendritic boundaries within the matrix, which consisted of the gamma and epsilon phases. The alloy with 0.01 wt% B exhibited increased ultimate-tensile-strength and plastic elongation of 17% and 36% higher than those of the boron-free alloy, respectively. The corrosion rate of the Co-Cr-W-Ni-Mn alloy in Hanks' solution has dropped drastically by 850% with a minor B addition of 0.05 wt%. The improved mechanical and corrosion properties were attributed to the refined dendritic structure and formation of boride (M5B3-type) precipitates.