外加压应力对纯Ni在800℃空气中氧化行为的影响

Effect of compressive stress on oxidation behavior of pure nickel at 800℃ in air

采用热重(TGA)方法测定纯Ni在800℃无应力及外加压应力为10和20MPa时的氧化动力学曲线,通过扫描电镜观察有无压应力作用下的氧化膜表面和截面形貌,分析压应力作用下氧化动力学的变化和氧化膜的失效形式,从金属空位扩散的角度讨论压应力对纯Ni高温氧化行为的影响。结果表明:纯Ni在800℃时氧化,外加压应力增大其氧化速率,这是由于外加压应力对氧化膜结构的影响造成的;无压应力作用时,氧化膜为脊状氧化物;而在压应力作用下,氧化膜由粒状NiO组成,这增大晶界扩散的短路扩散;且压应力促进空位在氧化膜/金属界面的聚集、粗化,弱化界面,改变氧化膜的失效形式。

The effect of compressive stress on the oxidation behavior of pure nickel was investigated by thermogravimetric analysis（TGA）.Compressive samples were subjected to stresses of 10 and 20 MPa and the oxidation behavior was studied at 800 ℃ in air.The surface and cross section morphologies of the oxidized coating were analyzed by SEM.The change of oxidation kinetic and the failure form of the coatings under compressive stress were analyzed.The effect of compressive stress on the oxidation behavior of pure nickel at high temperature was discussed.The results show that the compressive stress increases the oxidation rate,which is attributed to the effect of compressive stress on the oxidized coating microstructure.Compared with the formation of ridge-like oxide,the compressive stress deduces the formation of particles oxide of NiO,which increases the short-circuit paths for diffusion.In addition,the compressive stresses induce vacancies coalescence at oxide-metal interface and cavities development,thus the strength of oxide-metal interface is weakened,and the failure form of the oxidized coating is changed.