Experimental study on phase relationships in the Co-rich portion of the Co–Ti–Zr system

Abstract

AbstractThe isothermal section at 1 050 °C and the liquidus projection in the Co-rich portion of the ternary Co–Ti–Zr system were determined. The microstructures and solidification paths of the as-cast alloys were established experimentally. The constituent phases and their compositions of both as-cast and heat-treated alloys were investigated by means of optical microscopy, X-ray diffraction and electron probe microanalysis. No ternary compound was observed. For the Co-rich portion of the isothermal section at 1 050 °C, there are four three-phase regions, αCo + TiCo3 + TiCo2 (h), αCo + TiCo2 (h) + (Ti,Zr)Co2 (c), αCo + (Ti,Zr)Co2 (c) + Zr6Co23 and αCo + Zr2Co11 + Zr6Co23. For the investigated liquidus projection, there exist six primary crystallization fields: αCo, TiCo3, TiCo2 (h), (Ti,Zr)Co2 (c), Zr2Co11 and Zr6Co23; three transition invariant reactions, L + αCo → TiCo3 + TiCo2 (h), L + (Ti,Zr)Co2 (c) → αCo + TiCo2 (h), and L + Zr6Co23 → αCo + Zr2Co11; and one eutectic invariant reaction of L → αCo + (Ti,Zr)Co2 (c) + Zr6Co23.