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

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, CrSi2 and Cr5Si3, of the Cr–Si binary system have been observed. The CrSi2 intermetallic has a high solubility of up to 20 at.% Al and forms as faceted plates. A number of intermetallics, namely, CrAl7, Cr2Al11, CrAl4, Cr4Al9, Cr5Al8 and Cr2Al, of the Cr–Al system have been observed. The solubility of Si varies from as low as 0.8 at.% in Cr2Al to as high as 9 at.% in Cr4Al9. 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.