Measurement On Residual Stress Of Thermal Barrier Coatings And Effect Of Pre-treatment On Thermal Grown Oxides

Thermal barrier coatings (TBCs) are commonly used to improve the reliabilityand durability of hot section components as well as enhance the engine performanceand the efficiency of aero-engines and gas turbines. And TBCs can be applied to thecombustion chamber of diesel engine insulated by ceramic coatings—Low HeatRejection (LHR) Engine. In this paper, high velocity oxy-fuel (HVOF) spraying andair plasma spraying (APS) were used to prepare the CoNiCrAlY bond coat (BC) and8YSZ top coat (TC) respectively.After a vacuum heat treament (1050℃,4h) and subsequent oxidation ageing(950℃,1000℃,1100℃), the growth of thermally grown oxides (TGO) at theinterfaces of both TC/BC and BC/Substrate, phase transformation process andresidual stress were studied by using scanning electron microscope, energy-dispersiveX-ray spectroscopy and Cr3+luminescence spectra. Meanwhile, the mathematicalmodel of the residual stress of TGO was established, and the result showed that themacroscopic stress was compressive stress and decreased slightly with the thickeningof TGO. Subsequently, the stresses in TGO experienced different oxidation time weredetected by using Raman spectral techniques. It could be shown that thetransformation of transient θ-Al2O3into stable-Al2O3occurred according to theweakening of the characteristic peak of θ-Al2O3.The control of the Al2O3phase transformation can have significant effects on thesubsequent isothermal oxidation during the earlier stage of isothermal oxidation. Theformation of (Al, Cr)2O3oxide sub-layer originated from the textured and larger grainof-Al2O3can influence the potential TBCs’ lifetime. Additionally, the potentiallonger oxidation lifetime of TBCs that subjected to the appropriate vacuum heatpre-treatment can be attributed to the larger absorptive energy of the TGO area priorto its fully microcrack imperfection propagation. Most importantly, TBCsdelamination was determined by the steady-state energy release rate in ceramictopcoat and TGO, the TGO and the interface, as well as the formation anddevelopment of the microstructure and composition of imperfections in the vicinity ofthe interface.