文摘
Oxidation-resistant ZrSi2–NbSi2 bilayer coatings were prepared on an Nb–Ti–Si–Cr based ultrahigh temperature alloy using a two-step (first sputtering Zr film, and then Si–Y co-deposition) process. The coatings prepared with different Zr film thicknesses possess a similar structure, consisting of a ZrSi2 outer layer, a (Nb,X)Si2 (X represents Ti, Cr and Hf) middle layer and a (Ti,Nb)5Si4 inner layer. The higher co-deposition temperature (Si–Y co-deposition at 1350 °C) would cause cracks at the interfaces between the constituent layers of the coatings. The coated specimens possess much lower mass gains than the base alloy after exposure of same static oxidation times at 1250 °C. After oxidation, a dense scale consisting of a mixture of SiO2, ZrSiO4, ZrO2, Al2O3, TiO2 and Cr2O3 formed, which could protect the specimen from oxidation at least for 100 h at 1250 °C in air. Keywords Nb–Ti–Si–Cr based ultrahigh temperature alloy ZrSi2–NbSi2 bilayer coating Oxidation resistance Scale formation mechanism