Microstructure and oxidation resistant of Si–NbSi2 coating on Nb substrate at 800°C and 1000°C

Abstract

The Si–NbSi2 composite coating with a smooth surface was successfully prepared on Nb substrate by hot dip silicon-plating (HDS) technology. The composite coating is composed of Si outer layer, NbSi2 interlayer and Nb5Si3 interfacial layer. And the average surface roughness (RSa) and specific surface area growth rate (Sdr) are only 0.275 μm and 2.85%, respectively. The cyclic oxidation test shows that the Si–NbSi2 composite coating has a very excellent oxidative resistance after oxidation at 800 °C for different times. After oxidation for 40 h, the Δm/S and oxide layer thickness of the coating are only 3.72 mg/cm2 and 8 μm, respectively. After oxidation at 1000 °C for 20 h, the coating surface is almost completely covered by a dense SiO2 layer, the Δm/S and oxide layer thickness of the coating are 7.28 mg/cm2 and 15 μm, respectively. The Si–NbSi2 composite coating presents good self-healing ability and excellent oxidation resistance, which can significantly prolong the service life of bare Nb in oxidation environment.