Interfacial fracture mechanisms in solid solution directionally solidified eutectic oxide composites

The interfacial fracture behavior of the solid solution directionally solidified eutectic oxide, Co _1-xNi _xO/ZrO ₂(CaO), is investigated via indentation testing. An abrupt transition from interfacial delamination to interfacial penetration is observed as a function of NiO fraction (x>0.33). The use of a focused ion beam technique is introduced as a means for exploring sub-surface cracking in brittle materials. The sub-surface observations revealed a compositional transition from energy dissipative mechanisms (e.g., delamination, secondary cracking) for cracking to brittle cracking behavior, in the Co _1-xNi _xO phase. It is proposed that the transition in interfacial fracture behavior for the directionally solidified eutectic material is the result of competing dislocation-based crack nucleation mechanisms. The observations and analyses have significant implications for fracture behavior in composites with one phase exhibiting (pseudo-) plastic behavior.