ABSTRACT
Last, creep, or the slow deformation of a solid subjected to a stress at high temperatures, also occurs in ceramics. A part experiencing creep will either fail, or undergo shape and dimensional changes that, in close-tolerance applications, render the part useless. In general, creep is a convoluted function of stress, time, temperature, grain size and shape, microstructure, volume fraction and the viscosity of any glassy phases at the grain boundaries if present, dislocation mobility. Creep, fatigue and Subcritical crack growth are dangerous because they can result in sudden and catastrophic failure with time. An alternative approach is to design a part to last for a certain lifetime, after which it would be replaced, or at least examined for damage. Materials for aerospace applications can be subdivided into load and non-load bearing. The used of ceramics for the latter is well-established.
