Abstract: The hot deformation behaviors of the SJTU-1 alloy, the high-throughput scanned casting Nickel-based superalloy, was investigated by compression test in the temperature range of 900 to 1200 ◦C and strain rate range of 0.1–0.001 s−1 . The hot processing map has been constructed with the instability zone. At the beginning of hot deformation, the flow stress moves rapidly to the peak value with the increased strain rates. Meanwhile, the peak stress is decreased with the increased temperature at the same strain rates. However, the peak stress shows the same tendency with the strain rates at the same temperature. The optimum hot deformation condition was determined in the temperature range of 1000–1075 ◦C, and the strain rate range of 0.005–0.1 s−1 . The microstructure investigation indicates the strain rate significantly affects the characteristics of the microstructure. The deformation constitutive equation has also been discussed as well. Keywords: nickel-based superalloy; high-temperature deformation; investment casting; hot compression test; mechanical properties.
1. Introduction
Nickel-based superalloy is widely used for crucial structural parts of rock engine, turbine blades, cartridge receiver, and other components bearing high-temperature loads for decades due to its outstanding mechanical properties and extraordinary oxidation resistance at temperatures close to 650 ◦C [1–4]. Meanwhile, it is difficult to get a shape transformation due to its stubborn deformation resistance such as high strength, weak thermal diffusivity as well as work hardening behavior at elevated temperature. For the promotion of the fuel efficiency of such significant components, it is urgent to develop novel Ni-based superalloys to sustain hostile environment attacks such as high temperature and high pressure, thus significantly reducing the service life. For the lower cost and higher benefit of the machining and forming, it is in desperate need of a commercial cast-wrought superalloy to withstand high-temperature loads as well as high cyclic loading. SJTU-1 alloy, known as Ni-based superalloy and excavated from 5.2 million components after high throughput component design, was developed because of its exceptional high-temperature strength, toughness, and outstanding resistance to degradation in corrosive or oxidizing environments. Based on the existing composition and properties of the casting alloy, a Nickel-based superalloy named SJTU-1 alloy was excavated from high throughput component design with its exceptional high-temperature strength, good toughness and outstanding resistance to degradation in corrosive or oxidizing environments.
As is known, hot deformation behavior is vital for manufacture when carrying mental production into reality and it is also affected by many factors [5,6]. The mechanism of hot deformation and recrystallization mechanism of different superalloy varies much though the constitutive equations are prevalent to describe the deformation characteristics [7–9]. The Arrhenius model is typical and fluently used to describe the relationship between the flow stress and deformation temperature and strain rate [10–12]. Recent progress in processing maps has enabled researchers to have a better understanding of the mechanism of the hot deformation behavior of a metallic material [13–15]. Zhang and Li [16] put an insight into the hot deformation behavior of In718 during isothermal compression deformation, it was concluded that the peak stress is decreased due to the absence of DRX. Lin et al. [17] studied the effects of WH, DRV, and DRX work hardening (WH), dynamic recrystallization (DRX) and dynamic recovery (DRV) on high-temperature deformation behaviors of a typical Ni-based superalloy and proposed an improved dislocation densitybased model method to quantificationally describe the flow behaviors. Hence, giving a deeper insight into the hot deformation behavior is of great importance and in turn, guiding on the improved castability and moldability with optimized parameters.
Although the above mentioned constitutive models for Ni-based superalloys have aroused extensive interest and fully investigated, the novel high-throughput scanned superalloy has not been studied yet. In this study, a high-throughput scanning method was performed for the material design, and a novel superalloy named SJTU-1 alloy is obtained through an integrated thermodynamic computing platform. Then, the hot compression tests were carried out at different temperatures and strain rates as well. Moreover, the hot deformation constitutive equations, which are based on the modified Arrhenius model with a hyperbolic sine form coupled with the deformation activation energy and the temperature, is fully developed. Furthermore, the hot processing map is built and the optimum processing condition is confirmed. Last but not least, the microstructure of the compressed material is investigated to explore the effects of deformation temperature as well as strain rates on the metallic microstructure evolution.