Phase equilibrium studies of Mo-Y2O3-ZrO2-Zr at 1200 ℃ for developing Y-Zr-O complex oxide dispersion-strengthened Mo alloys

Abstract

Phase equilibria of the Mo-Y2O3-ZrO2-Zr section in the Mo-Y-Zr-O system at 1200 ℃ were studied for developing nanostructured Y-Zr-O complex oxide dispersion-strengthened Mo alloys and understanding the formation behavior of oxides. The evolution of intermetallic Mo2Zr and the powder composition of this Mo alloy during mechanical alloying (MA) were revealed. The results showed that the Mo-Y2O3-Zr section was confirmed by four kinds of two-phase regions (Mo) + αY2O3 and (βZr) + αY2O3 and three-phase regions (Mo) + αY2O3 + Mo2Zr and (βZr) + αY2O3 + Mo2Zr. These three-phase equilibria were associated with the four-phase equilibria of (Mo) + αY2O3 + Mo2Zr + (αZr) with a high concentration of O in (αZr). During MA, Mo2Zr was dissolved in the Mo matrix, and the introduced excess O and ZrO2 contaminants shifted alloy composition from Mo-Y2O3-Zr to Mo-Y2O3-ZrO2. The Mo-Y2O3-ZrO2 section was characterized by six kinds of two-phase regions Mo + βZrO2, Mo + γZrO2, Mo + Zr3Y4O12, and Mo + αY2O3, three-phase regions Mo + βZrO2 + γZrO2 and Mo + γZrO2 + Zr3Y4O12. The established Mo-Y2O3-ZrO2-Zr phase diagram suggests that the presence of excess Zr and insufficient O can bring about the formation of brittle Mo2Zr and Zr phase, and the Y/Zr ratio strongly determines the type of Y-Zr-O precipitates in Mo alloys.