Effect of initial microstructure on the properties of K439B nickel-based superalloy during prolonged aging at 800 °C
Zesheng Liu, Chuanwei Li, Anping Dong, Jianfeng Gu
Abstract
This work examined the evolution of microstructure and properties of K439B nickel-based superalloy with various initial microstructure, when subjected to long-term aging at 800 °C for 1000 h. After heat treatment, the average size of the γ′ phase in the air-cooled sample was 150 nm, which increased to 220 nm after long term aging. Conversely, the furnace-cooled sample's initial γ′ phase size of 273 nm expanded to 394 nm over the same period. Initially, the air-cooled sample exhibited a strength of 1151 MPa, while the strength of the furnace-cooled sample is 1114 MPa. Throughout the aging process, the air-cooled samples maintained high strength initially but experienced a reduction in the later stage. In contrast, the furnace-cooled samples showed a rapid decrease in strength, followed by minimal changes. Dislocations predominantly bypasses γ′ precipitates, creating dislocation networks around the γ′ phase, with an increased trend of stacking faults over time.