Calcia–magnesia–alumina–silicate (CMAS) attack mechanisms and roadmap towards Sandphobic thermal and environmental barrier coatings

Abstract

This review critically examines the current understanding of calcia-magnesia-aluminasilicate (CMAS) degradation mechanisms and mitigation approaches in thermal and environmental barrier coatings. First, the review introduces case studies of field returned engine components exposed to CMAS attack, followed by fundamental aspects of CMASinduced degradation. Understanding CMAS adhesion, infiltration, spallation mechanics, and thermochemical attack mechanisms is crucial to designing materials approaches to mitigate CMAS attack. CMAS mitigation strategies have focused on reactive approaches aimed at crystallising molten CMAS at the earliest stage possible to inhibit infiltration. Promising approaches are presented, starting with fundamental reaction kinetics studies, followed by the effects of microstructure in actual coatings systems. Salient results on coating systems tested in various burner rigs and a full engine test are presented to benchmark the success of various mitigation strategies. Lastly, several key future research areas are presented in order to provide a roadmap towards 'sandphobic' thermal and environmental barrier systems.

Effect of test parameters in the exposure of Ca–Mg–Al–silicate on yttria stabilized zirconia

“…The rate of infiltration in Regime 3 is again affected by microstructure, but the effect is compounded by the initial shape of the glass on the surface and likely the areal density as well. 25,28,29 Although many previous studies have examined the effect of composition and temperature on CMAS reaction, the CMAS loading amount can vary and there are only a few that investigate the effect of grain size on CMAS infiltration. 10,30 As the grain size can vary largely between coatings due to processing and property concerns, it is also important to look at the grain size effect on CMAS infiltration.…”

“…For CMAS, this density is ∼2.6 × 10 6 mg/m 3 , which is marked in Figure 1A by the vertical red dashed line. The rate of infiltration in Regime 3 is again affected by microstructure, but the effect is compounded by the initial shape of the glass on the surface and likely the areal density as well 25,28,29 …”

Theory and simulation of electrokinetic fluctuations in electrolyte solutions at the mesoscale

“…Electrolyte solutions, consisting of a polarized solvent and ionic species, are extremely important in a wide range of fields, including chemical physics, biology and geochemistry (Guglielmi et al 2013;Molina-Osorio et al 2020). They are also of interest in engineering physics, such as aggregation and dispersion of charged liquid particles (Boutsikakis et al 2020;Nieto et al 2021) present in aerospace systems. Despite a long history of electrolyte solution studies, there are still important open questions associated with fluctuations and correlations of electrolyte bulk solutions (Donev et al 2019a).…”

“…2020; Nieto et al. 2021) present in aerospace systems. Despite a long history of electrolyte solution studies, there are still important open questions associated with fluctuations and correlations of electrolyte bulk solutions (Donev et al.…”

Theory and simulation of electrokinetic fluctuations in electrolyte solutions at the mesoscale

“…Electrolyte solutions, consisting of a polarized solvent and ionic species, are extremely important in a wide range of fields including chemical physics, biology, and geochemistry (Guglielmi et al 2013;Molina-Osorio et al 2020). They are also of interest in engineering physics, such as aggregation and dispersion of charged liquid particles (Boutsikakis et al 2020;Nieto et al 2020) present in aerospace systems. Despite a long history of electrolyte solution studies, there are still important open questions associated with 2 M. Deng, F. Tushar, L. Bravo, A. Ghoshal, G. Karniadakis and Z. Li fluctuations and correlations of electrolyte bulk solutions (Donev et al 2019).…”