Microstructure evolution and fracture characteristics of GH4079 superalloy during high-temperature tensile process

Abstract

An investigation of the thermal deformation characteristics and fracture mechanisms of the GH4079 superalloy was conducted through a series of hot tensile experiments conducted across a range of strain rates (from 0.01 s⁻¹ to 1 s⁻¹) and temperatures (from 970 °C to 1160 °C). The impact of MC carbides on the thermal deformation characteristics and dynamic recrystallization (DRX) of GH4079 superalloys, which are known for their challenging deformability, was analyzed to provide insights into enhancing the thermal workability of these formidable superalloys. The results suggest that DRX consistently preferentially occurs near MC carbides. The MC carbide plays a nucleation role in the particle-induced dynamic recrystallization mechanism, as determined via EBSD analysis. In addition, the primary grain boundary is the preferred nucleation site for DRX initiation. The promotion of DRX within the GH4079 alloy is considerably facilitated by the increased stored energy and nucleation site density resulting from the larger and more numerous carbides present at the grain boundaries. Moreover, the presence of carbides leads to uncoordinated deformation of the alloy during tensile deformation, which is also the induction factor of alloy cracking. With increasing strain rates and temperatures, the window of control over the hot deformation structure of the alloy diminishes. During the high-temperature deformation process of the GH4079 alloy, it is necessary to control the temperature within the range of approximately 1120 °C–1140 °C and the strain rate within the range of 0.1 s⁻¹ to 1 s⁻¹ to obtain a fine and uniform grain structure, delay material failure, and thus enhance the thermal processing performance of the material.