Rapid fabrication of Nb-Si based alloy by selective laser melting: Microstructure, hardness and initial oxidation behavior

Highlights: • Nb-Si based alloy with a novel refined microstructure was fabricated by selective laser melting (SLM). • The hardness of Nb-Si based alloy by SLM reduced to 542HV_0.1 from 810HV_0.1 after heat treatment at 1500 °C for 4 h. • A layered oxide scale was formed at the initial stage of high temperature oxidation, including a sound SiO₂ layer. Nb-18Si-24Ti-2Cr-2Al-2Hf (at%) alloy was fabricated by selective laser melting (SLM). The microstructure, hardness and oxidation behavior of Nb-Si based alloy via SLM were investigated. Results showed that the relative density of SLM alloy under the optimized processing parameters was 98.27%. The as-built alloy consisted of Nb solid solution (Nbss), αNb₅Si₃, βNb₅Si₃ and Nb₃Si. Sphere shaped Nbss phases with a maximum diameter of 300 nm were obtained. Between the neighbouring Nbss phases distributed the strip shaped α/β Nb₅Si₃ phases. After heat treatment at 1500 °C for 4 h, the Nbss phases interconnected to form a continuous matrix with discontinuous αNb₅Si₃ phases. The average hardness of the SLM parts decreased from 810HV_0.1 to 542HV_0.1 after heat treatment. Compared with the oxide scale on arc-melted alloy, oxide scale formed on SLM-processed after oxidation at 1300 °C for 0.5 h was more compact with fewer holes, combined with the formation of a more continuous SiO₂ layer at the initial oxidation stage. A layer-structured oxide scale model was presented to describe the high-temperature oxidation behavior of Nb-Si based alloy processed by SLM.