Estudio de la evolución de esfuerzos residuales debido al ataque de depósitos vítreos (CMAS) en recubrimientos de barrera térmica

Abstract

This work was conceived as an integral project aimed to  understand and tackle thermal barrier coating (TBC) spalling  and delamination phenomena occurring in gas turbines due  to CMAS attack. Such attack is thought to have an influence  on the magnitude of residual stresses in the coating and, in  turn, on the integrity of TBCs. A thermal barrier coating was  manufactured by deposition of two layers of different chemical  composition, i. e., CoNiCrAlY and yttria-stabilized zirconia  (YSZ) on an AISI 304 stainless steel substrate. Both layers  were deposited by employing thermal spraying processes, the  bonding metallic layer (BC) was deposited by employing a HVOF  gun, whereas the ceramic component (TC) by atmospheric  plasma spray (APS). The TBCs were heat treated at 1250 °C,  with CMAS attack by concentration of 10 mg/cm2 for different  soaking times (2, 4 & 6 hours), in order to evaluate CMAS  effect on the magnitude of the state of residual stresses in  the coating. The stress state of the coating was determined  by employing the Modified Layer Removal Method for Duplex  Coatings (MLRMDC). It was noted that longer exposure times  at high temperature resulted in an increase in the state of  residual compressive stress in the TC, due to the effect of  CMAS. Furthermore, it is confirmed that with increasing the  thickness of thermally grown oxide (TGO), the magnitude of the  compressive residual stresses increased.