A study on the thermal cyclic behavior of thermal barrier coatings with different MCrAlY roughness. (March 2017) - Yuan, Kang
Abstract: Thermal cycling behavior of thermal barrier coatings (TBCs) with different MCrAlY (M for Ni and Co) interface roughness was studied under two thermal cycling simulation conditions, namely thermal shock with short heating time and high cooling rate, and thermal-ageing fatigue with long heating time but low cooling rate. MCrAlY powders with various sizes were used to obtain different bond coat interface roughness for the TBCs. The MCrAlY bond coat (BC) was sprayed by HVOF, APS, or the combination of them, and the top coats (TCs) with different thickness (300 or 1000 μm) were made. It was found that while the coarser MCrAlY powder gave higher BC roughness, the APS spraying provided more micro-roughness. The increased BC roughness was found to improve the thermal cycling resistance of the TBCs under both testing conditions. The failure mechanism of the TBCs with various MCrAlY roughness was investigated by analyzing microstructures and via finite-elemental modeling. Highlights: TBCs were failed via piece-by-piece spallation of topcoat in thermal shock codnition but via peeling of the whole topcoat layer in thermal-ageing failure condition. Increasing the MCrAlY interface roughness improves the TBCs life in both test conditions. Increased MCrAlY roughness transfers fracture of TBCs from ceramic top coat to the MCrAlY interface in thermal shock. Higher MCrAlY roughness promotes larger deformation zone in the MCrAlY which may help to release some stresses in the topcoat.