Improved dislocation density-based models for describing hot deformation behaviors of a Ni-based superalloy
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Dong-Xu Wen, Ming-Song Chen, Yan-Xing Liu, and Xiao-Min Chen School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, Hunan Province, China; and State Key Laboratory of High Performance Complex Manufacturing, Changsha 410083, Hunan Province, China
Xiang Ma SINTEF Materials and Chemistry, Blindern, 0314 Oslo, Norway (Received 19 February 2016; accepted 20 May 2016)
Generally, the obvious work hardening, dynamic recrystallization (DRX), and dynamic recovery behaviors can be found during hot deformation of Ni-based superalloys. In the present study, the classical dislocation density theory is improved by introducing a new dislocation annihilation item to represent the influences of DRX on dislocation density evolution for a Ni-based superalloy. Based on the improved dislocation density theory, the peak strain corresponding to peak stress and the critical strain for initiating DRX can be determined, and the improved DRX kinetics equations and grain size evolution models are developed. The physical framework and algorithmic idea of the improved dislocation density theory are clarified. Moreover, the deformed microstructures are characterized and quantitatively correlated to validate the improved dislocation density theory. It is found that the improved dislocation density-based models can precisely characterize hot deformation and DRX behaviors for the studied superalloy under the tested conditions.
I. INTRODUCTION
In hot forming, metallic materials often undergo severe plastic deformation, which induces the complicated microstructural evolutions, such as phase transformation, dynamic recrystallization (DRX), and dynamic recovery (DRV), etc. The hot deformation behaviors of metallic materials are greatly affected by hot forming conditions, including strain, strain rate, deformation temperature, etc.1,2 Meanwhile, microstructural evolution in metallic materials also exerts considerable impacts on hot deformation behaviors.3–6 Therefore, the interactions between the hot deformation mechanisms and microstructural evolution need to be thoroughly investigated.7–9 Up to now, some suitable models are used to characterize the hot deformation behaviors and microstructural evolution in metallic materials.1,10,11 The phenomenological constitutive models, such as Arrhenius hyperbolic-sine equation and Johnson–Cook model, are often established based on empirical observations.12–17 The material
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected]; [email protected] DOI: 10.1557/jmr.2016.220 J. Mater. Res., 2016
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parameters can be easily calibrated based on experimental data. Meanwhile, the accuracy of phenomenological constitutive model is relatively high at the given tested conditions. However, due to their empirical characteristics and lack of physical mechanism, the phenomenological constitutive models cannot be extrapolated to wide ranges of practice forming conditions. Accounting f
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