Design and Characterization of Silicide-Strengthened Nb-Si-Cr-(Mo) Alloys for Additive Manufacturing

Three high intermetallic volume Nb-Si-Cr-(Mo) alloys have been designed using CALPHAD modelling with the goal of identifying high specific strength, oxidation resistant alloys which can be additively manufactured using powder bed fusion. Nb₅Si₃ and Nb₉Si₂Cr₃ silicides were targeted as the primary strengthening phases while the addition of Cr promoted the NbCr₂phase. 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 weld regions were characterized. The weld processing was found to produce fine grained microstructures in each alloy and stabilized the high temperature NbCr₂ Laves phase as well as the metastable Nb₉Si₂Cr₃phase, which decomposed in cast samples. Microstructural refinement as well as hardness were found to increase with weld velocity, with one alloy reaching its highest hardness of ~16 GPa before the brittleness at higher velocities became detrimental. The alloy with the lowest intermetallic content was found to be the least brittle while also attaining a hardness of 13GPa and was therefore identified as a good candidate for additive manufacturing.