Comparative Analysis of Three Constitutive Models and Microstructure Characteristics of Nb521 during Hot Deformation

Abstract

This study presents an exploration of the flow stress constitutive model and the deformation mechanism of Nb521, both critical for its practical application. Hot-compression experiments were performed on Nb521 at temperatures ranging from 1523 K to 1723 K and strain rates ranging from 0.01 to 10 s−1. In addition, the microstructure evolution was concurrently studied through scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The stress–strain behaviour of Nb521 was assessed, leading to the development of three constitutive models: the Johnson–Cook model, the modified Johnson–Cook model and the Arrhenius model. In the course of the deformation process, it is consistently observed that the hardening effect surpasses the softening effect during the plastic phase, with no observable occurrence of a steady-state phase. The modified Johnson–Cook model offers superior predictive accuracy. Both grain elongation and torsion are the main deformation mechanisms of Nb521 and specific texture forms during stretching. This study also reveals that fractures at both room temperature and high temperatures are brittle in nature. The elucidation of the constitutive model and underlying deformation mechanisms in this study offers indispensable insights into the hot-deformation behaviour of Nb521.