La和Hf对CoNiCrAl合金涂层高温氧化行为的影响

来源期刊：金属学报2011年第6期

论文作者：宋鹏 陆建生 张德丰 吕建国 李德江

文章页码：655 - 662

关键词：CoNiCrAl合金； La； Hf； 高温氧化； 生长机制

Key words：CoNiCrAl alloy； La； Hf； high temperature oxidation； growth mechanism

摘    要：对单一添加及同时添加La和Hf的CoNiCrAl合金进行真空高温氧化处理,研究单一添加与同时添加La和Hf对合金表面氧化物生长机制和黏结性能的影响.结果表明:表面抛光的合金在1100℃氧化时,同时添加La和Hf使CoNiCrAl合金在其表面形成了连续均匀的Al₂O₃,并且具有较好的黏结性能.通过¹⁸O追踪原子氧化发现CoNiCrAlLa,CoNiCrAlHf和CoNiCrAlLaHf合金的Al₂O₃生长均为O^2-内扩散为主的生长机制,同时伴随少量的金属离子外扩散.单一添加La和Hf,形成的Al₂O₃表面富集Cr,Co和Ni等,且随Al₂O₃深度增加而逐渐降低,这些元素促使Al₂O₃表面形成Ni(Co)Al₂O₄,从而降低Al₂O₃的黏结性能.同时添加La和Hf,没有改变O^-2内扩散为主的生长机制,但Hf能够阻碍La在氧化物/合金界面的富集,减少Ni(Co)Al₂O₄形成,同时合金表面局部内氧化的钉扎效应提高了Al₂O₃的黏结性能.

Abstract: CoNiCrAl alloys are widely used as bond coats for thermal barrier coating (TBC) at high operating temperature for energy conversion systems,especially turbine.However,the effect of reactive element (RE) on the oxidation behavior of CoNiCrAl alloys is still not uniform,thereby limiting the usage of the alloys.To study the effect of co-doped RE,the polished cast CoNiCrAlLa, CoNiCrAlHf and CoNiCrAlLaHf alloys were oxidized at 1100℃ in vacuum.Growth kinetics and adherence of oxide scales formed on above alloys were studied through comparing mass dynamics curves and tracer oxidation of the alloys.SEM,TG and XRD as well as secondary neutrals mass spectrometry (SNMS) were employed to study the microstructure and growth mechanism of the oxide layers.The results showed that a protective Al₂O₃ scale formed on the surface of CoNiCrAlLaHf alloy, and the Al₂O₃ scale showed a good adherence due to a pinning effect of the internal oxidation and less Ni(Co)Al₂O₄ formation.The Hf could suppress La enrichment at the oxide/alloy interface for the co-doped alloy.Oxygen inwards-diffusion along the oxide,which mainly controlled oxide scale growth, was observed when these three alloys oxidized in the atmospheres including tracer ¹⁸O.Enrichment of Cr,Co and Ni occurred at the outer part of oxide scale,and then decreased to a low level within the oxide layer.These Cr,Co and Ni enrichments could promote the Ni(Co)Al₂O₄ formation at the top of oxide scale for the single-doped alloys,which was detrimental to Al₂O₃ adherence properties.