Papers by Keyword: Superalloy 718

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Authors: Y. Wang, Wen Zhu Shao, Liang Zhen, L. Lin, Xin Mei Zhang
Abstract: Hot compression tests at different temperatures and strain rates were performed on superalloy 718 annealed at 1100 °C for 30 min as well as 950 °C for 30 min in order to investigate the effect of the original microstructure on the hot deformation behavior. The results show that the δ phase precipitated on the grain boundaries of superalloy 718 prior to hot deformation leads to a decrease of the flow stress, which can be attributed to the drop of the matrix strength. The activation energy (Q) for hot deformation of the fine-grained material with δ phase on the grain boundaries is determined to be 381 kJ/mol, which is much lower than that of the coarse-grained material without δ phase (472 kJ/mol). It is suggested that the initial δ phase precipitated on the grain boundaries of the annealed material affect the thermal activation process of hot deformation for superalloy 718, resulting in the decrease of activation energy.
Authors: T.S.A. Rosa, A.F. Ribeiro, Luiz Henrique de Almeida, Dílson S. dos Santos
Abstract: In some applications involving aggressive environments, common in oil and gas industries, superalloys 718 may suffer hydrogen embrittlement, resulting in degradation of mechanical properties. The aim of this work is to study the interaction of hydrogen with different microstructures in a 1 mm thick plate, annealed and age hardened superalloy 718. In this way, the effects of hydrogen interaction on microstructure were studied via thermal programmed desorption (TPD), tensile tests and scanning electron microscopy (SEM). Samples were studied in as-received, artificially aged and overaged conditions. Hydrogenated samples submitted to tensile tests presented ductility loss when compared to hydrogen free samples, showing the hydrogen embrittlement sensitivity of this alloy. The influence of  phase precipitation on hydrogen diffusivity, as a result of aging treatment, was also discussed in this work.
Authors: Young Seok Song, M.R. Lee, Jeong Tae Kim
Abstract: To check long term degradation behavior of hydraulic forged superalloy 718 during exposure at high temperature, an Alloy 718 ingot with a diameter of 400mm was manufactured by the vacuum melting process, VIM followed by VAR. The ingot was broken down for uniform microstructure and mechanical properties by a controlled cogging process using a hydraulic press. To investigate long term degradation behavior of impact properties and hardness, the specimens were exposed to 600oC, 650oC and 700oC for holding times up to 12,112 hours. Impact energy absorption tests were performed at room temperature. The fractured area and the microstructure of the impact specimens were observed by OEM and SEM and Brinell hardness tests were also performed. The changes of impact energy and hardness are remarkably different for each temperature condition. The results suggest that the impact properties and hardness of Ni based superalloy 718 is strongly related to temperature and time during high temperature exposure.
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