In this paper, a non-destructive method for evaluation of a CoNiCrAlY coating applied to gas turbine blades has been studied. The specimens from cast Ni-base superalloy IN738LC were coated with Co–34Ni–18.6Cr–8.7Al–0.5Y by low pressure plasma spray (LPPS) technique. The XRD peaks indicated that CoNiCrAlY coatings are composed of β-NiAl and γ-Co (Ni, Cr) matrix with small amounts of Al 2 O 3 and γ′-Ni 3 Al. The surfaces of the coated specimens were covered with thin salt mixture of Na 2 SO 4 + l0 wt% NaCl. Afterward, the specimens were maintained at 850 °C for 24 h, cooled to room temperature (as one cycle) and then reintroduced in the furnace. The magnetic susceptibility of coating, as one of the magnetic properties, was periodically determined after each cycle. The results showed that the magnetic susceptibility of Co–34Ni–18.6Cr–8.7Al–0.5Y coating is related to the phase compositions and microstructures. The magnetic susceptibility typically increases with depletion of β-NiAl phase and decrease in the coating thickness during cyclic oxidation and hot corrosion. Therefore, measurement of magnetic susceptibility can be employed as a non-destructive test (NDT) method to estimate the thickness or residual lifetime of CoNiCrAlY coatings.

中文翻译：

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CoNiCrAlY涂层在循环氧化和热腐蚀下的磁性能变化

在本文中，研究了一种用于评估应用于燃气轮机叶片的 CoNiCrAlY 涂层的无损方法。来自铸造镍基高温合金 IN738LC 的试样通过低压等离子喷涂 (LPPS) 技术涂覆有 Co-34Ni-18.6Cr-8.7Al-0.5Y。XRD 峰表明CoNiCrAlY 涂层由β-NiAl 和γ-Co (Ni, Cr) 基体与少量Al 2 O 3 和γ'-Ni 3 Al 组成。涂覆样品的表面覆盖有Na 2 SO 4 + 10wt% NaCl的薄盐混合物。之后，将试样在 850 °C 下保持 24 小时，冷却至室温（作为一个循环），然后重新放入炉中。涂层的磁化率作为磁性特性之一，在每个循环后定期测定。结果表明Co-34Ni-18.6Cr-8.7Al-0的磁化率。5Y涂层与相组成和微观结构有关。在循环氧化和热腐蚀过程中，磁化率通常随着 β-NiAl 相的消耗和涂层厚度的减少而增加。因此，磁化率的测量可以作为一种无损测试 (NDT) 方法来估计 CoNiCrAlY 涂层的厚度或剩余寿命。