Design of Silicide-Strengthened Nb–Si–Cr–(Mo) alloys for additive manufacturing

• Nb-Cr-Si based alloys were designed for additive manufacturing fabrication. • Electron beam weld tracks simulated refined microstructures of AM alloys. • Rapid solidification refined microstructure and stabilized high temperature silicides. • Residual stress increased with weld velocity, causing cracking in more brittle alloys. • One alloy was identified as the most promising candidate for additive manufacturing. Three high–intermetallic volume Nb–Si–Cr–(Mo) alloys were designed using CALPHAD modeling with the goal of identifying high–specific strength, oxidation-resistant alloys that can be additively manufactured using powder bed fusion. The silicides Nb 5 Si 3 and Nb 9 Si 2 Cr 3 were targeted as the primary strengthening phases, and the addition of Cr promoted the NbCr 2 phase. These alloys were cast and surface-processed with electron beam welding at different speeds to simulate additive manufacturing, and the phases and microstructures of both cast and welded regions were characterized. The weld processing was found to produce fine-grained microstructures in each alloy with fine-scale intermetallics uniformly distributed among a body-centered cubic Nb matrix. Microstructural refinement and hardness were found to increase with weld velocity; one alloy reached its highest hardness of approximately 16 GPa before the brittleness at higher velocities became detrimental. One alloy was found to be qualitatively the least brittle while also attaining a hardness of 13 GPa and was therefore identified as a good candidate for additive manufacturing.