Ti-6Al-4Fe-0.5Si 합금에서 Ti-Si 석출과 베타상의 방위관계

This study examined the effect of Si addition in (α+β) Ti alloy on the phase stability about the Ti silicide precipitation from b matrix. The changes in the volume fraction and shape of precipitates with different Si contents were correlated with the tensile properties of the present alloys based on the detailed TEM micrographic observation. In Ti-6Al-4Fe-0.5Si alloy, the precipitates with rectangular or round shape were found at inter-grain of α/β interface and intra-grain of β phase. The precipitates were generally known as Ti5Si₃ with enough stabilizing thermo-mechanically. However, in this study, a new type silicide of Ti_(5)Si₄was mostly observed in the as-cast specimens, representing the metastable or unstable state phase thermo-mechanically compared to Ti_(5)Si₃. It was consistent with the phase transformation processes of TiSi₂TiSiTi_(5)Si₄Ti5Si₃ in the ternary alloy system of Ti-Al-Si. The improvement of mechanical properties including high temperature ones was to be induced by the fine precipitation of Ti silicides such as Ti5Si₄ and Ti5Si₃ in the ductile matrix of b phase. The precipitates of Ti_(5)Si₄ (P1) and Ti_(5)Si₃ (P2) have a coherent relationship with bcc β matrix of (200)_(β) //(220)_(P1) //(2111)_(P2) and (011)_(β) //(001)_(P1)//(0110)_(P2).