ABSTRACT

The microstructure and cyclic oxidation behaviour of Hf and Zr co-doped B2 NiAl single-crystal alloys at 1473 K were investigated. Hf and Zr co-precipitated into one phase during alloy manufacturing. The RE-free single-crystal alloy obtained a double-layered alumina film comprised of outer equiaxed grains and inner columnar grains and exhibited lower oxidation rate than the corresponding poly-crystal alloy, while the co-doped single-crystal alloy displayed higher oxidation rate than the RE-free single-crystal alloy and no synergistic effect was discovered. The effect of Hf and Zr co-doping on the growth behaviour of the alumina film was discussed. It is proposed that the existence of grain boundaries is an important precondition for activating the reactive element effect. The absence of grain boundaries significantly weakened the positive effect of Hf and Zr co-doping and distinctly magnified its negative effect on the cyclic oxidation resistance of the alloy in the meantime.

Highlights

• Cyclic oxidation behaviour of Hf and Zr co-doped NiAl single-crystals is compared.

• The undoped alloy obtains a double-layered alumina film during oxidation.

• The co-doped alloy shows higher alumina film growth rate than the undoped alloy.

• The absence of alloy grain boundaries suppresses the reactive element effect.

中文翻译：

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Hf和Zr共掺杂对热循环氧化镍铝单晶氧化铝膜生长的负面影响

摘要

研究了 Hf 和 Zr 共掺杂 B2 NiAl 单晶合金在 1473 K 下的显微组织和循环氧化行为。在合金制造过程中，Hf 和 Zr 共沉淀为一相。不含稀土的单晶合金获得了由外等轴晶和内柱状晶组成的双层氧化铝膜，氧化速率低于相应的多晶合金，而共掺杂单晶合金的氧化速率较高与不含稀土的单晶合金相比，没有发现协同效应。讨论了Hf和Zr共掺杂对氧化铝薄膜生长行为的影响。提出晶界的存在是激活反应元素效应的重要前提。

强调

• 比较了Hf和Zr共掺杂NiAl单晶的循环氧化行为。

• 未掺杂合金在氧化过程中得到双层氧化铝膜。

• 共掺杂合金显示出比未掺杂合金更高的氧化铝膜生长速率。

• 合金晶界的缺失抑制了反应元素的影响。