Hot deformation behavior of a new tailored cobalt-based superalloy for turbine discs
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Hot deformation behavior of a new tailored cobalt-based superalloy for turbine discs Xiaokang Zhong1,a)
Fusheng Han2,b)
1
Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, China; and University of Science and Technology of China, Hefei, Anhui 230026, China 2 Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, China a) Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] Received: 19 September 2019; accepted: 23 December 2019
Hot deformation behavior of a new tailored cobalt-based superalloy for turbine discs was investigated in the temperature range of 1050–1200 °C and the strain rate range of 0.01–10 s−1. The results show that the flow stress is closely related to the deformation temperature and strain rate, and the flow stress curve of the new tailored alloy belongs to a typical dynamic recrystallization (DRX) type. Microstructure observation reveals that the dominant nucleation mechanism of DRX for the new tailored alloy belongs to discontinuous DRX, while continuous DRX only acts as an assistant nucleation mechanism. The optimum processing parameters of hot working are obtained in the temperature range of 1155–1200 °C and the strain rate range of 0.01–0.1 s−1. The activation energy for the new tailored alloy is determined to be 833.0 kJ/mol, and the relationship between grain size and processing parameters is established by appropriate constitutive equations.
Introduction High-temperature alloys, also known as superalloys, have a large proportion (more than 40%) in the materials used for gas turbines due to their extraordinary comprehensive performances, e.g., mechanical strength, creep properties, fatigue resistance, hightemperature oxidation resistance, and corrosion resistance. Turbine discs, as hot components of the gas turbine, are generally required to endure operating temperatures of below 800 °C and large centrifugal forces at the rim [1]. Up to now, materials appropriate for turbine discs are predominantly polycrystalline Ni-based superalloys, which have an outstanding balance of strength, creep properties, and fatigue resistance because of strengthening from a high volume fraction of the L12 c9 phase coherent with c matrix. These Ni-based discs with the c9 phase content above 40% usually have a narrow temperature range between the c9 solvus and solidus temperature, resulting in a very rapid formation kinetics of the c9 phase [2]. This causes the c9 phase to precipitate during casting, which make the billet undergo cracking in the subsequent thermal forming process. Thus, modern Ni-based discs are almost manufactured by the powder metallurgy (PM) processing route rather than the conventional cast and wrought (C&W) processing route. However, the problem of PM processing route is prefabricating pure alloy
ª Materials Research Society 2020
powders, which need to take complicated procedure and much higher costs. On the
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