A Nb521 alloy processed by selective laser melting: Microstructure and tensile properties

Additive manufacturing is capable of achieving sophisticated geometries not attainable through conventional methods and it is especially attractive to fabricate conventionally hard-to-process Nb alloys via additive manufacturing for aerospace applications. In this study, a Nb521 (Nb-5W-2Zr-1Zr) alloy with relative density of 99.0% was successfully processed by Selective Laser Melting (SLM). The SLM processed microstructure was characterized, showing high dislocation density, dislocation cell structure and a large population of low-angle grain boundaries. Nano-dispersoids of ZrO2 were found in the as-built microstructure whereas carbides were absent. Tensile testing was carried out at room temperature and 1200 degrees C. The strengths of the SLM processed Nb521 were comparable or higher than those of the conventionally processed counterparts reported in literature at both room temperature and 1200 degrees C, while the ductility was significantly lower due to high dislocation density, porosity and oxide dispersoids. The results of the present study are evidence to the feasibility of fabricating Nb521 by SLM and provide insights into the relationship between the SLM processed microstructures and the mechanical properties of Nb alloys.