Phase-equilibria investigation of the Dy-Mo-Si ternary system at 1173 K (900 °C)

Abstract The phase equilibria of the Dy-Mo-Si ternary system at 1173 K (900 °C) was experimentally determined in the entire concentration range by using x-ray powder diffraction (XRPD), scanning electron microscope equipped with energy dispersive spectrometer (SEM-EDS), and differential scanning calorimetry (DSC). The results show that there are 13 single-phase regions, 24 two-phase regions, and 12 three-phase regions in the studied isothermal section. Nine binary compounds, i.e., α-MoSi2, Mo5Si3, Mo3Si, α-DySi2, β-DySi1.67, Dy3Si4, DySi, Dy5Si4, and Dy5Si3 and one ternary compound Dy2Mo3Si4 were confirmed to exist at this temperature. The highest solubilities of Dy in Mo3Si and Mo in β-DySi1.67 are both determined to be less than 1 at.%. While the solubilities of Dy in (Mo), Mo5Si3, and α-MoSi2 and Mo in (α-Dy), α-DySi2, Dy3Si4, DySi, Dy5Si4, and Dy5Si3 and Si in (α-Dy) and (Mo) are about 1–6.8 at.%. Combining both DSC analysis and XRPD results, it is concluded that the polymorphic transformation of α-DySi2↔β-DySi2 does not occur in the range of 573 K (300 °C) to 1323 K (1050 °C). DySi2 phase exists as α-DySi2 within the temperature range. β-DySi2 is a metastable phase that exists in higher temperatures.