High-Temperature Mechanical Behavior of End-of-Life Cryomilled NiCrAlY Bond Coat Materials

Abstract

Previous work has demonstrated that the lifetime of atmospheric plasma sprayed thermal barrier coating (TBC) systems incorporating cryomilled NiCrAlY bond coats show superior reliability with up to 3 times longer lifetimes compared to conventional ones. These conventional and cryomilled NiCrAlY bond coats at end-of-life (after thermal cycle failure) were studied in detail in the present work with a focus on the mechanical behavior in the temperature range from room temperature to 1273 K (1000 °C). The investigations were carried out using microtensile samples and the DIC technique. It turns out that the low-temperature strength of the cryomilled NiCrAlY bond coat is inferior to that of conventional ones, which might be due to a more pronounced porosity. At higher temperatures (between 1173 K and 1273 K (900 °C and 1000 °C)), the cryomilled bond coat shows almost twice the strength of the conventional bond coat, despite having been exposed to almost 3 times as many thermal cycles. The thermal stability of the nitride dispersoids appears to compensate for the gamma prime dissolution that typically occurs at these elevated temperatures, allowing for strength retention.