Molecular dynamics study on the ductile-to-brittle transition in W-Re alloy systems

Ductile-to-brittle transition (DBT) is frequently found in bcc W-based alloy systems, leading to varied fracture toughness at different temperatures. Re is recognized as an effective alloying element for enhancing the mechanical properties of W-based alloys and helium bubble is the major irradiation defect in W-based alloy systems, both of which affect the DBT phenomenon. Herein, molecular dynamics (MD) simulations are utilized to explore the role of Re and helium bubble in controlling the DBT curve in bcc W-based alloy. DBT curves are constructed with mode-I loading of diverse pre-cracked systems at 1-1800 K. In addition, fracture stress is determined based on the concept of critical strain energy release rate, which is echoed with DBT curves. Re's role in reducing fracture stress sensitivity contributes to the decrease in both the DBT temperature (DBTT) and DBT slope. The effect of helium bubbles is the opposite of the effect of Re. The underlying mechanisms are analyzed in relation to the behavior of the crack tips. In addition, the considerably high strain rate applied in MD simulations primarily accounts for the greater DBTT values observed compared to the experimental data. A logarithmic relationship with the strain rate is applied to connect the experimental data and MD results. Overall, this paper can deepen the understanding of the DBT phenomenon of W-based alloy system, improving the material's long-term performance and reliability.