Zirconium carbide oxidation: Maltese Cross formation and interface characterization

Oxidation of dense hot pressed ZrC specimens from 10 73 – 1473 K was investigated using an in - situ technique: HT - ESEM. Cuboid specimens were monitored on the surface and on edges and corners durin g oxidation in order to understand the influence of crack formation and propagation on the Maltese c ross shape development of the oxide . The oxidation mechanism comprised three steps: (1) delamination of sample edges , (2) crack formation at corners and (3) crack propagation towards the inner core and formation of microcracks parallel to the interface that increase the accessible surface area followed by a drastic volume expansion . The m icrocrack pattern is found to be repetitive as if a cyclic deb on ding of the interface occurred . Characterization of the interface by TEM and HRTEM revealed the interface between ZrC and ZrO 2 to comprise a 2 μm thick amorphous carbon matrix with ZrO 2 nanocrystals embedded in it