Shape change of liquid B2O3 particles dispersed in copper crystals during high-temperature deformation

Copper single crystals and bicrystals containing B2O3 particles were tensile tested at high temperatures, where B2O3 becomes liquid. The shape change of the liquid B2O3 particles in the matrix and on grain boundaries under high-temperature deformation was studied. In the Cu–B2O3 single crystal, the spherical liquid B2O3 particles became ellipsoidal as the strain rate was increased. The shape change depended also on the size of the liquid B2O3 particle. The smaller the particle size was, less of a shape change occurred. This is due to diffusional relaxation. On the other hand, in the bicrystal, grain-boundary sliding caused shear deformation of the liquid B2O3 particles on the grain boundary. The shear deformation accompanied by grain-boundary migration and dragging of particles led to an increase in the area fraction of liquid B2O3 on the grain boundary, which was supposed to cause embrittlement of the grain boundary.