Study of stress-driven cracking behavior and competitive crack growth in functionally graded thermal barrier coatings

Abstract

Thermal barrier coatings' (TBCs) stability and toughness are essential for insulating aero-engine parts. However, during service, the thickness of thermally grown oxide (TGO) will have an impact on the growth of internal vertical and horizontal cracks as well as the cracking and spalling of the coating, which may ultimately fail as a result of the aforementioned factors. The competitive growth of vertical and horizontal fractures in three functional gradient thermal barrier coatings (FG-TBCs) created with varied gradient index P magnitudes is investigated in this study. Gaining a thorough grasp of how competitive growth affects coating failure under various compositional and gradient structural parameters is the goal. Additionally, this work explores the effects of various TGO thicknesses on early crack expansion as well as the stress characteristics within the FG-TBCs. The research takes into account how crack growth changes the stress condition as well as the implications of crack extension rate, route, and form on coating failure. Our results show that the stress step phenomena in the FG-TBCs occurs in various places for various P values. The expansion of cracks in the top coat (TC) is fueled by this stress phase. Furthermore, a greater vertical crack extension length is obtained with a higher P value, with further expansion being prevented by horizontal cracks along the extension path. Notably, thicker TGO coatings change the direction and rate of expansion of cracks, both vertical and horizontal.