材料期刊网

Microcrystalline Ni-20Cr-3Al coatings were deposited on Ni-20Cr-3Al substrates by unbalanced magnetron-sputter deposition. The grain size of the coatings was varied by using different Ar pressures. Cyclic-oxidation testing was performed at 1100 degrees C, It was found that (1) an external alpha-Al2O3 scale formed on coating A (4.7 mu m thick, 50 nm grain size), (2) an external Cr2O3 scale and internal Al2O3 oxide formed on coating B (14 mu m thick, 500 nm grain size); and (3) an outer layer scale of Cr2O3+NiCr2O4 and interior laver of Al2O3 formed on the as-cast alloy. Extensive spallation of the Cr2O3+NiCr2O4 scale took place on the as-cast alloy, but no obvious spallation occurred on the two coatings. Improvement of the spallation resistance of the scale is explained by effective diffusional creep of the coatings and the micropegging effect of the inward-grown oxides.