High-temperature oxidation behavior in YSZ coated Cr2AlC and CoNiCrAlY substrates

Abstract

Yttria-stabilized zirconia (YSZ) was applied as a ceramic top coat on the Cr2AlC and CoNiCrAlY substrates using atmospheric plasma spray (APS) deposition technique and the high-temperature oxidation behavior of these coating systems examined at 1100 °C. The high-temperature performance of coated samples was studied using techniques such as scanning electron microscopy (SEM) to observe the microstructure, energy dispersive spectroscopy (EDS), elemental mapping, and X-ray diffraction (XRD) analysis to examine the phase composition before and after oxidation tests. According to the results, the high-temperature oxidation resistance of Cr2AlC/YSZ was much better than CoNiCrAlY/YSZ. In Cr2AlC/YSZ system, the thermally grown oxide (TGO) formed by the outward diffusion of aluminum and inward diffusion of oxygen. In this system, the thickness of TGO was about 7.6 μm after 350 h and crack nucleated due to the formation of a porous Cr7C3 layer. In CoNiCrAlY/YSZ samples, TGO consisted of Al2O3 and spinel oxides and the thickness of TGO increased up to approximately 5.3 μm after 150 h of oxidation test (failure time). The better oxidation behavior of Cr2AlC/YSZ can be attributed to the decrement of internal stresses due to the lower mismatch of CTE values between this substrate and the TGO layer.