Phase Transformation and Crack Growth in Yttria-Stabilized Zirconia

7 Phase Transformation and Crack Growth in Yttria-Stabilized Zirconia 

By assuming that the rate of crack growth is controlled by the rate of tetragonal-to-monochnic phase transformation, a kinetic model was proposed as an analogue to that for martensitic transformation. Only the final form of the model is given here specific details of its formulation may be found in [9]. In this model, the rate 

The various material-related terms in Eqn. (8.23) are considered to be internal variables. Because their expected dependence on composition and microstructure (i.e., on the concentration of yttria and volume fraction of the tetragonal phase), they are to be viewed as random variables. The rate constant Aou, is expected to depend on the mechanism for the enhanced tetragonal-to-monoclinic phase transformation by water, perhaps the replacement of Zr-O-Zr bonds by OH bonding, and needs to be better understood and quantified. 

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