Environmental barrier coatings (EBCs) are critical for protecting ceramic matrix composites in gas turbine engines. However, their effectiveness can be compromised by blistering when exposed to molten silicate deposits. This study investigates the mechanisms driving blistering in hafnia/hafnon EBCs through numerical modelling. Two potential mechanisms are explored: one driven by partial dissolution of the parent phases into the melt followed by crystallization into the other phase (hafnia to hafnon or vice-versa) and another driven by partial dissolution and reprecipitation into the same phase via Ostwald ripening. Models for both mechanisms make use of the observations that melt ingress and macroscopic blistering are decoupled in time, with melt ingress occurring relatively rapidly along grain triple junctions and blistering occurring later through a slower process of melt spreading, dissolution and crystallization or reprecipitation. A finite element model incorporating randomly shaped grains and cohesive grain boundaries is developed to simulate these two mechanisms. Phase transformation-driven cracking is found to produce minimal damage and negligible changes in pellet thickness, inconsistent with experimental observations. In contrast, the Ostwald ripening mechanism generates damage patterns and pellet thickness increases closely resembling experimental blistering observations, even though the ripening process produces only modest stresses. Combined effects of phase transformation and Ostwald ripening show no significant synergy. These findings suggest Ostwald ripening as the dominant mechanism responsible for blistering in hafnia/hafnon EBCs exposed to molten silicate deposits. The study provides valuable insights into EBC failure modes and offers a framework for investigations of similar phenomena in other coating systems.

中文翻译：

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暴露于熔融硅酸盐沉积物中的 hafnia/hafnon 复合材料起泡


环境阻隔涂层 （EBC） 对于保护燃气涡轮发动机中的陶瓷基复合材料至关重要。然而，当暴露于熔融硅酸盐沉积物中时，它们的有效性可能会因起泡而受到影响。本研究通过数值建模调查了 hafnia/hafnon EBC 中导致水泡的机制。探讨了两种可能的机制：一种是由母相部分溶解到熔体中，然后结晶到另一相（哈夫尼亚到哈夫农，反之亦然），另一种是由部分溶解并通过 Ostwald 成熟重新沉淀到同一相驱动的。这两种机制的模型都利用了熔体进入和宏观起泡在时间上解耦的观察结果，熔体进入沿晶粒三连接发生得相对较快，而起泡则通过较慢的熔体扩散、溶解和结晶或再沉淀过程发生。开发了一种包含随机形状晶粒和内聚晶界的有限元模型来模拟这两种机制。发现相变驱动的开裂产生的损伤最小，球团厚度的变化可以忽略不计，这与实验观察结果不一致。相比之下，Ostwald 成熟机制会产生损伤模式，颗粒厚度增加，这与实验起泡观察非常相似，即使成熟过程只产生适度的应力。相变和 Ostwald 成熟的综合效应没有显示出显着的协同作用。这些发现表明，Ostwald 成熟是导致暴露于熔融硅酸盐沉积物的 hafnia/hafnon EBC 起泡的主要机制。 该研究为 EBC 失效模式提供了有价值的见解，并为研究其他涂层系统中的类似现象提供了一个框架。