Microstructure evolution and oxidation/ablation behaviors of NbSi2/Nb2O5-SiO2/HfC-HfO2 multilayer protective coating at 1200 °C and 1800 °C

In this study, the LPDS-coating charactered by the volcanic-like surface with micropores is synthetized on Nb alloys through halide activated pack cementation (HAPC) combined with a liquid-plasma-assisted particle deposition and sintering (LPDS) technology. Results show that the mass gain of NbSi2/Nb2O5-SiO2/HfC-HfO2 coated sample (6.38 mg/cm2) is only 46% compared to NbSi2 coated sample (13.8 mg/cm2) and holds the lowest oxidation rate (0.367 mg2·cm−4·h−1) during the isothermal oxidation process after 100 h at 1200°C. Besides, this multilayer coating also exhibits an enhanced oxyacetylene ablation resistance (the lowest mass ablation rate of −0.106 mg/s and a linear ablation rate of −0.333 μm/s) compared with NbSi2 coating and NbSi2/Nb2O5-SiO2 coating. Such superior high-temperature oxidation/oxyacetylene ablation resistance of multilayer coating are mainly ascribed to HfC oxygen-consuming phase combined with the oxide scale’s high-temperature stability provided by the HfSiO4-HfO2-SiO2 skeleton.