首次用高分辨电子显微镜(HREM)对Ni-La_2O_3复合镀——扩散渗铝涂层氧化前后的精细结构进行了研究。发现NiAl相中含有纳米级的La_2O_3质点,Al_2O_3层中“嵌”入La_2O_3微粒(直径<50nm);氧化物层涂层界面存在过渡相。由此认为La_2O_3质点通过影响Al_2O_3层的生长机制而改善涂层的抗氧化性能。
β-NiAl type composite coating with dispersive La_2O_3 particles was prepared by electrodeposition of Ni-La_2O_3 composite on M38 superalloy followed by aluminizing. The fine structure of the coating and its oxide scale was studied by means of highresolution electron microscope(HREM) for the first time. It was found that La_2O_3 particles were distributed in β-NiAl phases of the coating, and that after oxidation at 1273K for 25 hours dispersive or agglomerative La_2O_3 particles with a diameter of 10～50nm were incorporated into the α-Al_2O_3 scale. In addition, an intermediate layer located at the α-Al_2O_3/β-NiAl interface was also observed. The superior oxidation resistance of the coating is believed to be related to effect of La_2O_3 dispersoids on growth mechanism of the oxide scale. A sufficient amount of La_2O_3 dispersoids existing in the vicinity of the oxide/coating interface would act as a barrier blocking the bulk diffusion of Al~(3+) ions which tends to reduce the growth rate of the scale and to improve the oxide scale adhesion. The intermediate layer observed may contribute a beneficial effect to stability of the interface.
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