Morphological evolution and weak interface development within chemical-vapor-deposited zirconia coating deposited on Hi-Nicalon™ fiber

The phase contents and morphology of a ZrO₂ fiber coating deposited at 1050°C on Hi-Nicalon™ by chemical vapor deposition (CVD) were examined as a function of deposition time from 5-120 min. The morphological evolution in the ZrO₂ coating was correlated to the development of delamination within the ZrO₂ coating. The delamination appears to occur as a result of: (i) continuous formation of tetragonal ZrO₂ nuclei on the deposition surface; (ii) martensitic transformation of the tetragonal phase to a monoclinic phase on reaching a critical grain size; and (iii) development of significant compressive hoop stresses because of the volume dilation associated with the transformation. Our observations suggest that it will be of critical importance to further understand and eventually control the nucleation and grain growth behavior of CVD ZrO₂ and its phase transformation behavior for its potential applications for composites.