Correlating Hot Deformation Parameters with Microstructure Evolution During Thermomechanical Processing of Inconel 718 A
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INCONEL 718 is extensively used in gas turbine engine components because of its excellent mechanical properties and corrosion resistance at elevated temperatures.[1,2] High-temperature properties in this alloy are achieved by precipitation and solid solution hardening.[3,4] The most common precipitates in this alloy are c¢ (Ni3 (Al, Ti)—FCC), c¢¢ (Ni3Nb—BCT) and d (Ni3Nb—orthorhombhic).[5,6] Yuan et al.[7] in their work reported that the presence of c¢/c¢¢ precipitates in the material enhances the peak stress during hot deformation. In contrast, the presence of d precipitates
CHIRAG GUPTA, JYOTI S. JHA, ALANKAR ALANKAR, and SUSHIL MISHRA are with the Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, India. Contact e-mail: [email protected] BHAGYARAJ JAYABALAN is with the Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, India. RAJAT GUJRATI is with the National Centre for Aerospace Innovation and Research, Indian Institute of Technology Bombay, Mumbai, India. Manuscript submitted March 25, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
not only reduces the peak stress but also provides higher softening. Thus, the existence of these precipitates significantly impacts the hot deformation behavior of Inconel 718. Agnoli et al.[8] correlated the stored energy and grain growth mechanism during annealing near sub-solvus temperature (985 C) of Inconel 718. They found that in the absence of stored energy grain size remains stable during annealing, which is controlled by d-phase precipitates. On the other hand, a significant grain growth with bimodal distribution was observed in the specimen subjected to deformation prior to true strain < 0.1, whereas a homogeneous grain growth was observed for true strain > 0.1. Moreover, Azarbarmas et al.[9] in their study demonstrated that high-strain and temperature favor dynamic recrystallization (DRX) whereas a high deformation rate inhibits DRX. In addition, Inconel 718 has low stacking fault energy and therefore, it is susceptible to DRX during the hot working.[10,11] In general, DRX is the major flowsoftening mechanism and it is largely employed to control the microstructure in a wide range of temperatures and strain rates in Inconel 718.[12–14] Hightemperature deformation is a widely used processing methods for forming Inconel 718. However, the deformation process at high temperatures and high strain are likely to produce undesirable manifestations of
microstructure in the form of microvoids at intergranular particles, shear band formation and flow localization etc.[15,16] Therefore, a processing window in terms of strain rate ðe_ Þ and temperature ðTÞ for microstructure control is required. The concept of processing maps has evolved in the last couple of decades relating the processing parameters and the microstructures. Wray[17] firstly formularized the failure mechanism in high-temperature tensile deformation by considering the strain rate vs temperature maps. The comprehensive qu
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