From eutectic to peritectic: Effect of Ge on morphology, structure, and coarsening of Cr-Cr3Si alloys

Intermetallics 93 (2018), 201-208, DOI: 10.1016/j.intermet.2017.11.020

The influence of germanium on microstructure, crystallography, and thermal stability of the eutectic Cr-Cr₃Si alloy was investigated. Fine eutectic microstructures could be preserved but slightly degenerated when up to 2 at.% Si was substituted by Ge. A transition from eutectic to peritectic microstructure composed of primary dendrites and A15 Cr₃Si matrix was observed when higher amounts of Ge were added. X-ray diffraction results showed no limit for substitution of Si and Ge in the studied composition range. The lattice parameter of both Cr solid-solution and A15 silicide increased with increasing the Ge/Si ratio. A macro was developed for the ImageJ program to automate the quantitative microstructural image analysis. Results showed that Ge addition increases the A15 phase fraction of the two-phase alloys. Microstructural investigations on annealed alloys at 1350 °C demonstrated that the coarsening of both binary Cr-Cr₃Si and ternary Cr-Cr₃(Si, Ge) is interface-controlled. Although Ge addition to the eutectic alloy offered an isotropic microstructure, it decreased the thermal stability by degeneration of the lamellar structure.