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

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 nonstoichiometric solid solution of TiB1-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 TiB1-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 TiN1-x. The reduction of bending strength was attributed to the large crystal growth of flake like structure of TiN1-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 TiB1-x) within the flake like structure of N-diffused alpha(Ti) crystal phase. The reduction of bending strength is mainly attributed to the large growth of flake like structure of N-diffused alpha(Ti) crystal phase. (C) 2021 The Ceramic Society of Japan. All rights reserved.