Strengthening/softening effects of vacancies on twinning deformation in zirconium

Duo to the low thermal neutron capture cross-section and high corrosion resistance to water and steam at high temperatures, zirconium alloys were used as fuel cladding in light water reactors. In this work, the effects of vacancies on { 10 1 ¯ 2 } twin boundary (TB) migration were studied by molecular dynamics (MD) simulations in zirconium at different temperatures. The simulation results indicate that vacancies have a softening effect on TB migration at low temperatures < 300 K. At high temperatures >300 K, vacancies have a strengthening effect on TB migration. By mechanism analysis, we found that those vacancies in coherent positions on TB have a softening effect, while those in incoherent positions have a strengthening effect on TB migration. As the temperature increases, the vacancies in coherent positions migrate to the incoherent positions, and as a result, the softening effect at low temperatures turns into a strengthening effect at high temperatures. This work provides new insights into understanding the irradiation effects on the mechanical property of zirconium and its alloys.