Abstract
The low-pressure plasma spray coating process has been established in the field of gas turbines and is used for parts (turbine blades, duct segments, etc.) which are exposed to corrosive gases at high temperatures. Overlay coatings based on the MCrAlY alloy system (M is Ni, Co or Fe) are commonly employed as oxidation- and corrosion-resistant coatings. Mechanical properties, such as high-cycle fatigue lives, of CoCrAlY, NiCrAlY and CoNiCrAlY coated systems were investigated at high-temperature as compared with the uncoated substrate such as conventional IN738LC, unidirectional solidified CM247LC and single crystal CMSX-2.
High-cycle fatigue properties of the MCrAlY coated superalloys at high-temperature (IN738LC : 1123 K, CM247LC, CMSX-2: 1173 K) showed inferior performance in comparison with the uncoated results. It was because that the high-cycle fatigue cracks initiated at interface defects, such as pores and grit residues, between the coating and the substrate in any cases. The high-cycle fatigue crack could be observed to grow into the MCrAlY coating, and then into the substrate. It seems to be impossible to evaluate the high-cycle fatigue lives of the MCrAlY coated superalloys at high-temperature by using the uncoated results.
