Secondary precipitation behavior of silicides and enhancement of mechanical properties of Nb-silicide-based alloy by in-situ remelting electron beam powder bed fusion

Nb-silicide-based alloys are promising ultrahigh-temperature structural materials for aerospace applications. However, conventional electron beam powder bed fusion (EB-PBF) typically leads to insufficient silicide precipitation, resulting in unsatisfactory high-temperature mechanical properties. In this study, crack-free Nb-16Si-10Ti-10Zr-3Cr-3Al-3Hf (at%) specimens with dimensions of 80×20×35 mm 3 were successfully fabricated by EB-PBF using an in-situ remelting strategy. During the in-situ remelting EB-PBF process, each layer was scanned twice to impose an in-situ heat treatment effect during forming, which effectively broadened the heat-affected zones and promoted the secondary precipitation of silicides. Consequently, the silicide fraction increased from 10% to 17.3% with only a 4.69% extension in processing time. At 1250 °C, the yield strength and ultimate tensile strength were remarkably enhanced by 328% and 223%, respectively. The superior high-temperature strength is attributed to the combined effects of precipitation strengthening and an inferred mixed dislocation strengthening, involving both dislocation cutting and bypassing mechanisms. This in-situ remelting EB-PBF procecss enables outstanding elevated-temperature tensile properties in as-built Nb-silicide alloys without additional post-heat treatments, significantly improving the feasibility of additive manufacturing for complex high-temperature Nb-silicide components.