Stress and shape evolution of irregularities in oxide films on elastic–plastic substrates due to thermal cycling and film growth

Numerical simulation of displacement instabilities of surface grooves on an alumina forming alloy during thermal cycling oxidation

“…4, it is apparent that the lateral growth strain varies with TGO thickness. In contrast to other works [1,[4][5][6][7][8], the lateral growth strain of TGO at high temperature exhibits the strong dependence on the thickness of TGO, with the value of lateral growth strain rate decreasing rapidly as TGO thickens. For incorporating this trend into a finite element scheme to simulate reality, the process of TGO growth can be divided into four parts in terms of TGO thickness, that is, TGO thickness from 0 to 4µm with an interval of 1 µm.…”

“…5 illustrates some of new TGO resides between the internal grain boundaries causing it to elongate, while most of TGO prefers to the sites between TGO and substrate, which results in TGO thickening [1][2][3][4][5][6]10]. The TGO formation at elevated temperature was simulated by the two components in the previous studies [2][3][4][5][6][7][8], namely, lateral growth strain and thickening growth strain. The methodology used in these works can simulate displacement instability of TGO based simply on an ideal assumption of material properties and easily confined by the limitation that total TGO thickness is much less than the initial TGO thickness.…”

“…The lateral growth strain was introduced at the high temperature as a necessary condition for the occurrence of displacement instabilities, and it was found that the amplitude of undulation increases with thermal cycles. Ambrico et al [4] further derived analytical results for stress distribution and plastic zone sizes, to pursue for a mechanics-based explanation for the evolution of undulations with thermal cycles. Based on an idealized model the TGO was simulated as an annular domain embedded with the elastic-plastic matrix and it was demonstrated that thermal strain, cyclic reverse yielding and oxide growth are combined together to promote the rapid evolution of displacement instability.…”

A fundamental model of cyclic instabilities in thermal barrier systems

“…Guided by this nding, the following analyses emphasize lateral strains, designated g per cycle (no thickening). This diers from a previous analysis by Ambrico et al (2001), which examined the role of thickening.…”

“…Most relevant are the plastic strains occurring in the bond coat in the vicinity of the imperfections (Ambrico et al, 2001;He et al, 2000He et al, , 2002Karls son and Evans, 2001;Karlsson et al, 2002a, b). These strains have a dominant ra dial component that facilitates the outward (downward) displacement of the instability (Fig.…”