Determination of the Nb–Cr–Si phase diagram using diffusion multiples

Abstract

A high-efficiency diffusion-multiple approach was employed to determine the phase diagram of the Nb–Cr–Si ternary system which is critical for the design of niobium silicide-based in situ composites. These composites have high potential as a replacement for Ni-base superalloys for jet engine applications. The formation of the Nb(Cr,Si) 2 Laves phase is beneficial to the high oxidation resistance of the composites and the Nb–Cr–Si system serves as the base for understanding the Laves phase formation. The results clearly demonstrate the applicability of the diffusion-multiple approach in determining such complex phase diagrams as Nb–Cr–Si which contains 14 phases. Two isothermal sections at 1000 and 1150 °C were constructed from the results obtained from diffusion multiples using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and electron backscatter diffraction (EBSD). Three ternary compounds, CrNbSi, (Cr,Nb) 6Si 5 and (Cr,Nb) 11Si 8, were observed at both temperatures, and the C14 Laves phase of the Cr–Nb binary system was stabilized by Si to lower temperatures.