Studies on the Improvement of High-Temperature Corrosion Resistance of Ni_3Al Base Alloys

制备了Ni_3Al、Ni_3Al-0.1B和Ni_3Al-1b-0.42Hf样品，并进行了以下表面处理：(1)用CO_2激光进行激光上光，(2)在极低氧压下或在氢气中进行退火，(3)采用离子束技术进行表面处理。每次处理后，样品在1100~1400K的大气压下进行纯氧氧化，并对处理前后的样品和在特定条件下氧化后的样品进行金相分析。490~2000W的激光表面处理表明，随着激光功率的增加，形成更具保护性的氧化铝膜，从而提高了抗氧化性。这可能是由于处理过程中的细化作用，促进了Al的扩散，在真空中退火形成了较薄的Al_2O_3氧化膜，对抑制后续氧化起到了很好的保护作用。氢气气氛中的热处理结果与真空中的结果非常相似，在样品表面注入镁或钽离子可以在氧化初期形成具有很强保护性的Al_2O_3膜，而不消耗基合金中的镍。合金的离子混合处理形成了含硅的表面层。该处理还促进了极具保护性的Al_2O_3膜的生长。离子束增强沉积形成的0.5微米厚的Cr2N膜和1微米厚的Si3N4膜显著降低了氧化速率。

Ni_3Al, Ni_3Al-0.1B, and Ni_3Al-1b-0.42Hf specimens were prepared and then subjected to the following surface treatments.(1) laser glazing using a CO_2 laser,(2) annealing under a very low oxygen pressure or in hydrogen, and(3) surface treatments using ion beam techniquesAfter each treatment the specimens were oxidized in a flow of purified oxygen under atmospheric pressure in a temperature range 1100 to 1400 K. Metallographic examinations were carried out for the specimens before and after the treatment and also after the oxidation under specified conditions.The laser surface treatments at the powers of 490 to 2000 W showed that the increase in the laser power resulted in the formation of more protective alumina scales leading to enhanced oxidation resistance. This was considered to be due to the grain refining effect brought about by the treatment which would have enhanced the diffusion of Al.The annealing in a vacuum resulted in the formation of thin Al_2O_3 scales, which were very protective to suppress the subsequent oxidation. The annealing in hydrogen atmosphere showed very similar results as those for the annealing in the vacuum.Implantation of Mg or Ta ions to the specimen surfaces resulted in the formation of very protective Al_2O_3 scales during the initial periods of oxidation without consuming Ni of the base alloy. The ion mixing treatment of the alloy formed a surface layer containing Si. This treatment also enhanced the growth of very protective of Al_2O_3 scales. A Cr_2N film of 0.5 micron meter thickness and a Si_3N_4 film of (1 micron meter) formed by ion beam enhanced deposition decreased the oxidation rate significantly.