Cr-Ge-Si Alloys for High-Temperature Structural Applications: Microstructural Evolution

A. Soleimani-Dorcheh, M.C. Galetz

The microstructural evolution of Cr-Si1−x -Ge x (0 < x < 15 at. pct) alloys was studied (in annealed state). The quasi-isothermal section of the ternary diagram was assessed by quantitative EPMA analysis. Morphology, phase formation, chemical distribution, and indentation hardness of the alloys were investigated as a function of Ge/Si ratio. The microstructure of all studied alloys consisted of Crss solid solution and A15 Cr3X intermetallic phases. Substitution of Si by Ge strongly altered the microstructure by transforming the morphology from a lamellar eutectic Cr-Cr3Si system toward a peritectic one with dispersed Crss phase in A15 matrix. EPMA chemical distribution maps and X-ray diffraction results prove the mutual solubility of Si and Ge in A15 phase by forming Cr3(Si,Ge) as a complex A15 structure with Cr3(Si1−x Ge x ) composition. Precipitates of the intermetallic phase within the Crss phase was observed in Ge-alloyed samples. Indentation hardness results showed that upon Si-Ge substitution the hardness of both phases was reduced. However, Si substitution by Ge had a stronger influence on the hardness of the solid solution phase than on the intermetallic phase.

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