Laser powder bed fusion of a Nb-based refractory alloy: Microstructure and tensile properties

In this study, Nb521 (Nb–5W–2Mo–1Zr) parts were successfully fabricated by laser powder bed fusion (LPBF) using quasi-spherical hydride-dehydride (HDH) powders modified by jet milling. The relative density of the LPBF made (LPBFed) Nb521 parts is 98.8 ± 0.2%, which were subsequently subjected to hot isostatic pressing (HIP) to achieve almost full densification. Nanoscale ZrO2 precipitates were found in the LPBFed parts and those after HIP (HIPed), showing semi-coherent with the matrix. The precipitation behavior is strongly related to the melt pool solidification process during LPBF in terms of thermal distribution and solidification rate. The LPBFed Nb521 parts after HIP presented sound tensile properties with the fracture strength of 678.7 ± 1.1 MPa and elongation of 5.91 ± 0.32%. The precipitated nanoscale ZrO2 underwent plastic deformation after tension, exhibiting the stress-induced tetragonal-to-monoclinic phase transformation and shearing by dislocations. This work presents the LPBFed Nb521 alloy with promising performance by employing low-cost jet-milled HDH powders.