Atomistic modeling of the tensile behavior of monoclinic ZrO₂ bicrystal

Molecular dynamics was used to simulate the tensile behavior of monoclinic ZrO₂ bicrystals constructed by fusing two symmetrically tilted single crystals at several temperatures ranging from 300 to 1200 K and then annealing them to 300 K. The average amorphous grain boundary (GB) is about 11 Å thick (approximately twice the average unit-cell dimension). Axial elongation of the typical bicrystal at constant (boundary) velocity leads to failure at a global strain of about 4%, at which the maximum stress (i.e., the tensile strength) is approximately 6 GPa. The failure process is ductile, driven by growth and coalescence of voids in the GB, in contrast with that of the monoclinic single crystal, which undergoes essentially brittle fracture at a tensile stress of around 10 GPa. The tensile strength of the bicrystal is approximately inversely proportional to the thickness of the GB. Decreasing the fusion temperature increases the thickness of the GB and lowers the tensile strength accordingly. The dependence of tensile strength on the loading rate is insignificant for the range of tilt angles and loading conditions examined. The influence of the GB on the small-strain effective elastic response of the bicrystal is also insignificant.