This paper examines the oxidation behavior of thin specimens of cast NiCoCrAlY alloys at 1150 \(^\circ {\rm C}\) through successive stages, from \({\rm Al}_2{\rm O}_3\) growth to complete alloy conversion to oxide. Five alloy compositions were used, with varying fractions and compositions of \(\gamma\) and \(\beta\). The time evolution of the alloy composition during \({\rm Al}_2{\rm O}_3\) growth was simulated using the DICTRA module of Thermo-Calc and calculated analytically in the approximation of flat profiles. Simulated and experimental profiles were found to be in good agreement, indicating that the phase equilibrium and mass balance were correctly reproduced in the simulations. Local variations of alloy composition were observed in thinner specimens and found to be comparable with the variations expected from the uncertainty on the initial specimen thickness. The variations observed in the time-to-\({\rm Al}_2{\rm O}_3\) failure were greater than expected on this basis, suggesting that additional sources of variability were in effect. Alumina failure was followed by the growth of a \({\rm Cr}_2{\rm O}_3\) layer at the alloy–scale interface. Similarly, Cr consumption eventually led to \({\rm Cr}_2{\rm O}_3\) failure, and Ni- and Co-containing spinel oxide formed, converting the \({\rm Cr}_2{\rm O}_3\) at the alloy–scale interface and the \({\rm Al}_2{\rm O}_3\) at the scale–gas interface. The remaining NiCo alloy was then converted to (Ni,Co)O. This sequence occurred without abrupt increase in the mass gain, due to the continued presence of the remnant \({\rm Al}_2{\rm O}_3\) layer, and to the small amount of metal left to oxidize when the (Ni,Co)O eventually broke through the scale. The evolution of the scale composition throughout the oxidation stages is discussed based on an analysis of the thermodynamic conditions at the alloy–scale interface.

本文通过从\({\rm Al}_2{\rm O}_3\)生长到1150 \(^\circ {\rm C}\) 的连续阶段检查了铸造 NiCoCrAlY 合金薄试样的氧化行为。 合金完全转化为氧化物。使用了五种合金成分，具有不同的分数和成分\(\gamma\)和\(\beta\)。\({\rm Al}_2{\rm O}_3\)期间合金成分的时间演变使用 Thermo-Calc 的 DICTRA 模块模拟生长，并在近似平面轮廓中进行分析计算。发现模拟曲线和实验曲线非常吻合，表明在模拟中正确再现了相平衡和质量平衡。在较薄的试样中观察到合金成分的局部变化，发现与初始试样厚度的不确定性所预期的变化相当。在此基础上观察到的\({\rm Al}_2{\rm O}_3\)失效时间的变化大于预期，表明额外的变异源在起作用。氧化铝失效之后是\({\rm Cr}_2{\rm O}_3\)合金-尺度界面处的层。类似地，铬消费最终导致\（{\ RM的Cr} _2 {\ RMö} _3 \）故障，并且Ni基和含Co的尖晶石氧化物形成，转换\（{\ RM的Cr} _2 {\ RMÓ }_3\)在合金-尺度界面和\({\rm Al}_2{\rm O}_3\)在尺度-气体界面。然后将剩余的 NiCo 合金转化为 (Ni,Co)O。由于残余物\({\rm Al}_2{\rm O}_3\)的持续存在，该序列发生时质量增益没有突然增加层，当 (Ni,Co)O 最终突破氧化皮时，剩下的少量金属会被氧化。基于对合金-氧化皮界面处的热力学条件的分析，讨论了整个氧化阶段氧化皮成分的演变。