Mathematical modeling of the hot-deformation behavior of superalloy IN718

Abstract

Isothermal constant-displacement-rate compression tests of superalloy IN718 were conducted using a computer-controlled MTS machine, at temperatures from 960 ЊC to 1040 ЊC, initial strain rates from 0.001 to 1.0 s Ϫ1 , and true strains from 0.105 to 1.204 (corresponding to a relative height reduction from 10 to 70 pct). The flow stress was obtained directly from compression tests using the controlling computer. The grain size was obtained by the intercept method and by comparing microstructures to the ASTM standard grain chart. Based on the results of these tests, a mathematical model showing the hot-deformation behavior of superalloy IN718 was developed in the form of a constitutive equation and a Hall-Petch relationship. Both the flow stress and the grain size calculated from the model were compared to the experimental results. Meanwhile, the effect of hot-deformation parameters such as strain, strain rate, and temperature on the flow stress and on the grain size was analyzed according to the model. It was found that these parameters influenced the flow stress and the grain size. The model developed in this work can be used to explain such effects.

Hot Forging of IN718 with Solution-Treated and Delta-Containing Initial Microstructures

“…2a, b. The overall behavior is in broad agreement with that usually observed for IN718: A distinct peak stress, tending to be more pronounced at higher strain rates, is followed by significant post-peak flow softening that is generally attributed to recrystallization and/or adiabatic heating [6][7][8][9][10]. Since all the flow curves presented here have been corrected for the effect of deformation heating, the observed flow softening must, in this case, be due to the evolving microstructural state of the material.…”

“…Significant research has been directed toward characterizing the precipitation and dissolution kinetics of the d phase in IN718 during heat treatment and aging, e.g., [1][2][3][4][5], and several experimental investigations have explored recrystallization associated with high-temperature compressive flow in solution-treated material, e.g., [6][7][8][9][10], but there has been rather less focus on the specific role of d precipitates during hot deformation. However, it is known that prior aging in the d stability field can have a significant effect on stress-strain response [11,12] and recent studies have highlighted the complexity of the mechanisms involved, including dynamic dissolution and reprecipitation [13], sub-grain formation [14], and platelet spheroidization [15].…”

INCONEL 718 Single and Multipass Modelling of Hot Forging

“…For INCONEL 718, the dynamic recrystallization mechanism was characterized as a discontinuous process (see for instance, Wang et al [2]). Some authors [3][4] report a necklace dynamic recrystallization process, depending on the deformation rate and the temperature compatible with a discontinuous behaviour of the dynamic recrystallization. Recrystallization is characterized by two processes: nucleation and growth.…”

Modelling Microstructural Transformations of Nickel Base Superalloy in 718 During Hot Deformation

“…[1][2][3][4][5][6][7][8][9][10][11][12]), they either fall into the category of being too simplistic and producing only an average grain size and approximate volume fraction recrystallised, or are far too complicated and too computationaly intensive to be used on a daily basis by process engineers. A model is required, therefore, that can be run within a commercially available finite element package, or in tandem with one, that will deliver detailed results, run in a reasonable time, and be simple to use.…”