Heat-Resistant Cr-Alloys Strengthened by Intermetallics—Microstructure, Oxidation and Creep

A two phase alloy of Cr, bcc, solid solution matrix strengthened by a Cr₃Si, A15 ordered, intermetallic phase was investigated with the goal of achieving an alloy with properties "Beyond Nickel-Based Superalloys". In comparison to the commonly used Ni-base superalloys, these Cr-Si alloys may enable higher working temperatures and lower densities slightly above 7 g cm^-3. In addition, Cr is the only refractory metal which intrinsically builds an oxide scale suitable for protecting the alloy from oxidation. Si improves the oxide scale formation even further as well as a high temperature strength by precipitation of an intermetallic phase Cr₃Si. We observed that the addition of further alloying elements such as Mo, Ge, and Pt leads to an improvement in creep properties (Mo), oxidation resistance (Ge), and nitridation resistance (Pt) by maintaining the two-phase microstructure. Creep tests were conducted at temperatures at 980°C and higher and reveal promising results. The microstructures, scales, and reaction products were investigated by XRD, SEM, EPMA and Image Analysis.