Formation of intermetallic compounds in the Cr–Al–Si ternary system

Abstract

The microstructure and composition of binary and ternary intermetallics have been studied in ternary diffusion couples of Cr and an Al–Si eutectic alloy. The ternary intermetallic α always formed in the liquid part of the diffusion couple as a dendritic structure. Two intermetallics compounds, CrSi 2 and Cr 5Si 3, of the Cr–Si binary system have been observed. The CrSi 2 intermetallic has a high solubility of up to 20 at.% Al and forms as faceted plates. A number of intermetallics, namely, CrAl 7, Cr 2Al 11, CrAl 4, Cr 4Al 9, Cr 5Al 8 and Cr 2Al, of the Cr–Al system have been observed. The solubility of Si varies from as low as 0.8 at.% in Cr 2Al to as high as 9 at.% in Cr 4Al 9. A schematic of the reaction scheme of the Cr–Al–Si system is presented. This has been based on the observed microstructure and composition of phases.