Deformation, damage and fracture behaviours of TWIP steels based on CZM-CPFEM at high temperature

Abstract

Grain boundaries (GBs) are the most vulnerable areas of metals during high temperature forming and processing where microcracks are highly likely to affect their macroscopic properties, resulting in fracture and ultimately reduced service life. In order to investigate the mechanisms of micro- and nano-scale damage evolution, microcrack initiation and propagation, GBs must be included as a crucial consideration in the theoretical and modelling solutions. Thus, to accurately illustrate the influence mechanisms of GBs on the mechanical behaviours, the cohesive zone model (CZM) considering GB damage evolution and the crystal plasticity finite element model (CPFEM) coupling slip and twinning inside the grain, were combined to propose a micromechanical mechanism of TWIP steels, which is applicable to predict the strengthening, damage and fracture of TWIP steels under high temperature. The CZM-CPFE method was confirmed by in situ SEM experiments at 750 ℃. The representative volume elements (RVEs) are constructed to predict the high temperature deformation behaviour of TWIP steels with different grain sizes and initial microdefects to obtain the influence of different initial states on the high temperature deformation behaviour, which can provide the solid theoretical basis for the subsequent manufacturing and forming processes of TWIP steel sheets. This work not only fills the gap in theoretical modelling of TWIP steels in the field of hot processing and manufacturing, but also provides some research approaches and analysis strategies for the GB damage behaviour of polycrystalline materials at high temperatures.