Transgranular fracture studies on magnesium oxide bicrystals

Publisher Website
Google Scholar
Abstract
Transgranular cleavage fracture experiments were carried out on MgO bicrystals with various misorientations. Although the general bicrystal must be characterized by five parameters it was.found that only one was needed to describe transgranular cleavage. This parameter is defined as the angle δ between the lines of intersection of each of the two respective cleavage planes and the grain boundary. During transgranular cleavage, steps formed at the boundary increased in height with increasing values of δ. The large steps caused the originally straight and continuous crack front to break into tongue-shaped segments which overlapped one another. For δ>12° reinitiation of the crack front occurred at the grain boundary. Two energy absorbing mechanisms were observed. Both were related to the segmentation of the crack front. They are (a) the increase in area formed by overlapping cracks and (b) plastic deformation that occurred adjacent to the steps. Estimates of the energy absorbed during fracture were found to increase with increasing values of δ. The results are discussed with regard to the grain boundary acting as a barrier to crack propagation.