Nanostructuring of Nb-Si-Cr Alloys by Electron Beam Melting to Improve the Mechanical Properties and the Oxidation Behavior

Materials processed by additive manufacturing often exhibit a very fine-scaled microstructures due to high cooling rates in the process. In this study, single-layer surface electron beam melting is used to create very high cooling rates similar to additive manufacturing processes to investigate the resulting microstructure. In the case of Nb-Si-Cr in-situ composites, a nano-scaled eutectic microstructure is beneficial for improving the mechanical and oxidational properties. Fast solidification results in the formation of supersaturated phases of Nb-ss and Cr2Nb with phase diameters down to 10 nm as well as in the stabilization of the metastable Nb-9(Cr,Si)(5) phase at room temperature. After processing with different solidification rates, the decomposition of the Nb-9(Cr,Si)(5) phase has been studied in detail with atom probe microscopy. The stabilization of mixed silicide phases by electron beam melting shows a new pathway for improving hardness and enhancing oxidation resistance of nanostructured eutectic in-situ composites, by which the inherent weaknesses of Nb-Si-Cr can be overcome without further alloying elements. [GRAPHICS]