Damage Accumulation Mechanisms in Thermal Barrier Coatings
Damage Accumulation Mechanisms in Thermal Barrier Coatings
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热障涂层中的损伤累积机制
DOI：
10.1115/1.2807004
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Z. Chaudhury
中科院分区：
文献类型：
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作者：
G. Newaz;S. Nusier;Z. Chaudhury
层裂是热障涂层在热载荷和机械载荷作用下的一种主要失效状态。尽管层裂的证据是确凿的，描述破坏条件的力学模型在文献中很普遍，但导致层裂的损伤演化的渐进性质还没有得到充分的解决。本文研究了部分稳定氧化锆热影响区在镍基单晶高温合金RENEN5上的损伤演化。对电子束-等离子体气相沉积(EB-PVD)TBC涂层的纽扣样品进行了热循环。粘结涂层为PtAl。使用的温度范围是200-1177摄氏度。在一系列热循环的情况下，使用显微镜跟踪样品的渐进损伤演化。菲克定律可以描述早期循环中热生长氧化物(TGO)的积聚。然而，在较高的热循环次数下，以微裂纹及其合并的形式出现的损伤会导致TGO失去完整性。因此，氧化动力学和损伤似乎都扮演着重要的角色，因为它与层裂有关。当这些微裂纹聚集在一起形成主要的分层裂纹或层间分离时，涂层屈曲的敏感性增加。分层裂纹最终消耗了TGO层。粘结层和基材的TBC完整性的丧失有助于其在从高温降温过程中的屈曲。我们的估计表明，对于当前的材料系统来说，需要大约16倍于TBC厚度的分层裂纹长度来启动屈曲。渐进微裂纹连接是产生这种临界分层裂纹长度的一种可能机制。在完全层裂之前的试件中发现了屈曲的物理证据。
Spallation is a major failure condition experienced by thermal barrier coatings (TBCs) subjected to thermal and mechanical loads. Although evidence of spallation is substantiated and mechanistic models to describe the failure condition is prevalent in literature, the progressive nature of damage evolution leading to spallation has not been addressed adequately. In this paper, we investigated the damage evolution in partially stabilized zirconia TBC on Nickel-based single crystal superalloy, Rene N5. Thermal cycles were imposed on button specimens with Electron Beam - Plasma Vapor Deposition (EB-PVD) TBC coating. The bond coat was PtAl. The temperature range used was 200–1177C. Progressive damage evolution was tracked using microscopy on samples subjected to a series of thermal cycles. Fick’s law can describe the thermally grown oxide (TGO) buildup for early cycles. However, at higher number of thermal cycles, damage in the form of microcracks and their coalescence results in the loss of integrity of the TGO. Thus, both oxidation kinetics and damage appears to have significant roles to play as it relates to spallation. As these microcracks coalesce to form major delamination cracks or interlayer separation, the susceptibility for coating buckling is increased. The delamination cracks finally consume the TGO layer. The loss of TBC integrity from the bond coat and the substrate facilitates its buckling during cool down from elevated temperature. Our estimations show that a delamination crack length of about sixteen times the TBC thickness is needed for the current material system to initiate buckling. Progressive microcrack linking is a possible mechanism to develop such critical delamination crack lengths. Physical evidence of buckling was found in specimens prior to complete spallation.