Investigation of phase formations and mechanical properties in the binary systems of Ti–TiB₂, Ti–TiN and ternary system of Ti–TiB₂–TiN

Abstract

The effect of TiB₂ and TiN contents on the phase formations and their mechanical properties in the binary systems of Ti–TiB₂ and Ti–TiN, and in the ternary system of Ti–TiB₂–TiN was investigated. In the binary systems, TiB₂ and TiN addition improved the hardness of Ti but reduced its bending strength. In the ternary system of Ti–TiB₂–TiN, the addition of TiB₂–TiN mixture to Ti further improved the hardness to around Hv = 10.0 GPa compared to 7.0 GPa in the binary systems, but it did not improve the bending strength. The increase of hardness in the binary system of Ti–TiB₂ was mainly attributed to the formation of TiB (or non-stoichiometric solid solution of TiB_1−x) and to remaining TiB₂ in samples with high TiB₂ contents. The reduction of bending strength, however, was attributed to the disappearance of metallic Ti, to the formation of TiB_1−x, and to porous structure in samples with high TiB₂ contents. The increase of hardness in the binary system of Ti–TiN was attributed mainly to the formation of non-stoichiometric solid solution of TiN_1−x. The reduction of bending strength was attributed to the large crystal growth of flake like structure of TiN_1−x. The further improvement of hardness in the ternary system of 80Ti–20(TiB₂–TiN) was attributed to the formation of fine crystals of TiB (or TiB_1−x) within the flake like structure of N-diffused α(Ti) crystal phase. The reduction of bending strength is mainly attributed to the large growth of flake like structure of N-diffused α(Ti) crystal phase.