Carbon stabilized Al5Cr3 Re precipitates and ductility enhancement of Cr-based alloys

A new metastable Al5 phase in the Cr-Re system is predicted based on full-potential linear muffin-tin orbital (FLMTO) calculations of its electronic structure and cohesive properties. While Al5Cr3 Re is unstable as a bulk compound, we demonstrate that nonstoichiometry and carbon impurities play a dominant role in stabilizing this phase and may lead to the occurrence of Al5 type particles in Cr-based alloys. Thus, these Al5 precipitates may scavenge carbon impurities and prevent the formation of brittle carbides and, additionally, provide an obstacle for dislocation motion. The formation of small close-packed particles appear to explain the improvement of both ductility and strength and is most likely the mechanism of the 'rhenium effect' in Cr(W, Mo) based alloys. (Author)