Phase equilibria in the Cr-Si-Ti system below 40 at.% Si

Abstract

Phase transformations in the Cr-Si-Ti ternary system have been studied using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) at silicon content <40 at.%. Partial liquidus and solidus projections and the melting diagram (solidus + liquidus) have been constructed. Some sections as partial isothermal at 1450 and 1150 °C, isopleths at 10 at.% Si and 50 at.% Ti are described. The liquidus surface is characterized by the presence of primary crystallization regions of a solid solution (Cr,βTi) and binary based phases (Cr3Si), (Ti5Si5) and the Laves-phase C14, which is stabilized by additions of silicon, and in the ternary system melts congruently above 1600 °C. The solidus surface is characterized by the presence of three-phase fields: (γTiCr2) + (Cr3Si) + (Cr,βTi), (Ti5Si3) + (γTiCr2) + (βTi,Cr) and (Ti5Si3) + (γTiCr2) + (Cr3Si). The former two regions form invariant four-phase eutectic equilibria L ↔ (βTiCr2) + (Cr3Si) + (Cr,βTi) and L ↔ (Ti5Si3) + (γTiCr2) + (βTi,Cr) at 1534 and 1243 °C, respectively. The maximum of the solidus temperature of about 1580 °C is observed in the field (γTiCr2) + (Cr,βTi). At 1495 °C the solid-state transformation (γTiCr2) + (Cr3Si) ↔ (Ti5Si3) + (Cr,βTi) takes place.