A size-dependent constitutive model of bulk metallic glasses in the supercooled liquid region

Abstract

Size effect is of great importance in micro forming processes. In this paper, micro cylinder compression was conducted to investigate the deformation behavior of bulk metallic glasses (BMGs) in supercooled liquid region with different deformation variables including sample size, temperature and strain rate. It was found that the elastic and plastic behaviors of BMGs have a strong dependence on the sample size. The free volume and defect concentration were introduced to explain the size effect. In order to demonstrate the influence of deformation variables on steady stress, elastic modulus and overshoot phenomenon, four size-dependent factors were proposed to construct a size-dependent constitutive model based on the Maxwell-pulse type model previously presented by the authors according to viscosity theory and free volume model. The proposed constitutive model was then adopted in finite element method simulations, and validated by comparing the micro cylinder compression and micro double cup extrusion experimental data with the numerical results. Furthermore, the model provides a new approach to understanding the size-dependent plastic deformation behavior of BMGs.

Review on the Research and Development of Ti-Based Bulk Metallic Glasses

“…According to their experiments, Ti-based BMG samples with a smaller diameter exhibit a larger plasticity, while the strength does not markedly change. Similar results have also been reported in other BMGs [158][159][160][161][162][163]. The size effect has been explained from the viewpoints of free volume content [157,162,163], flaw sensitivity [159], plastic zone [160], and elastic energy dissipation [161].…”

Role of Si Minor Addition on Glass Formation and Flow Stress Characteristics of a Zr-Based Metallic Glass

“…Another study presented a thermodynamically constitutive model of MGs by extending an infinitesimal deformation approach, in which the multiplicative decomposition of deformation gradient and additive decomposition of free energy was considered 22 . Yao et al 23 developed a size-dependent constitutive model of MGs and found that the size effect is a crucial factor in micro forming processes. Being able to apply for MGs, the Zener-Hollomon approach was considered by Yao et al 7 , in which the temperature effects and strain rate alterations are included in the model to evaluate the high temperature tensile deformation process.…”