Modeling molten droplet spreading and infiltration into non-isothermal thermal barrier coatings

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

“…10,30 Modeling of CMAS penetration into columnar YSZ by Munuhe et al indicated that penetration occurred faster for the coarser microstructure even without apatite formation. 25 However, that is contrary to what is observed in this study and a study by Morelli et al on CMAS on YSZ. Although there is dissolution of YSZ occurring at the surface of the SG and LG samples, there is no transformational reaction to form a protective layer that would arrest further infiltration.…”

“…Essentially, the rate of infiltration can be outpaced by either the rate of glass deposited onto the surface, the rate of lateral agglomeration of the glass on the surface, or the rate of transformative reaction at the surface. [25][26][27] Subsequently, these rates can be affected by temperature, CMAS particle size, and microstructure (e.g., grain size, grain shape, and surface features). This is supported by work done by Clark et al on the effect of surface temperature of a TBC on the adhesion of CMAS deposited through use of a burner rig.…”

“…However, as initial CMAS infiltration is usually fast, a comparative thickness is likely achieved within minutes for the static regime. 18,21,25 This necessarily implies that the static methods will always portray the worst-case scenarios observed in the dynamic regime. In the static regime, the ADS concentration, which is usually considered the concentration in air, is already at the density of the glass but positioned on the surface.…”

“…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.…”

“…Modeling by Munuhe et al on the infiltration of CMAS into columnar yttria stabilized zirconia (YSZ) revealed a dependency on the coarseness of the microstructure for the infiltration depth. 25 Additionally, the modeling implied that the starting thickness of the CMAS may not affect the ultimate infiltration depth. However, the data in the DEvAC chart would imply that ADS concentration and consequently the areal density/aspect ratio do influence the rate of ingress.…”