Solution-Precipitation Model for Creep

For ceramics with secondary glassy phases, the accommodation processes are governed by these phases in different ways  

In this case, the secondary phases melt at temperatures lower than the matrix and, provided that the crystals are at least partially soluble in the glassy phase, creep may take place by 

This model postulates that the glassy phase in compression can support normal stresses because of the existence of islands that avoid the complete squeezing of the intergranular liquid. However, it has been shown that these islands are not necessary for the grain boundaries to support normal stresses. Several modifications of this first model have been created and revised [9]. 

An important modification of the Raj and Chyung [80] model was made by Wakai [81], who assumed that the solution and precipitation took place at steps (kinks) formed at the grain boundaries. It was proposed that the solution-precipitation process involved the movement of these steps, and the strain rate was therefore related to the step velocity and density, with an expression analogous to Orowan s equation for dislocation movement  

Three different situations were analyzed by Wakai for the density of steps  

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