Microstructure evolution during isothermal aging for wrought nickel-based superalloy udimet 520+1

Abstract

This paper investigates the evolution of microstructure during isothermal aging at 1173 K in the wrought nickel-based superalloy Udimet 520, after being solution-treated at 1393 K for 4 h, followed by various cooling rates. Age-hardening behavior was observed during isothermal aging for water-quenched (WQ) and air-cooled (AC) specimens after the solution treatment, whereas it could not be detected for a furnace-cooled (FC) specimen. No primary £ A particles were observed in any continuously cooled samples. For the WQ and AC specimens, the size of the secondary £ A precipitates increased during the isothermal aging along the Ostwald ripening and their morphology evolved from spherical to an intermediate shape between spherical and cuboidal. Conversely, the secondary £ A particles exhibited an octodendritic shape for the FC specimen, and the octodendritic character of the secondary £ A particles was emphasized during isothermal aging, resulting in the splitting of the secondary £ A particles. It was found that the splitting of £ A particles occurred during the isothermal aging for Alloy 80A with a lower volume fraction of £A phase around 20%.