Transient Creep Cavity Growth in Structural Ceramics
A F. Bower, Tze J. Chuang
Long-term service life of a load-bearing ceramic component such as a turbine blade atelevated temperatures is often controlled by the rates of nucleation and growth of creepcavities at grain junctions and interfaces within the microstructure of the material. Inaddition to steady state, the growth of creep cavities during transient creep stage is animportant ingredient in assessing the lifetime of the structural component. In this paper, acavity embryo of Hull-Rimmer type is considered to grow along a bicrystal interface at agiven temperature and subjected to a suddenly enhanced tensile loading remotely applied in adirection normal to the interface. The growth mechanism is based on stress driven atomictransport along high diffusivity path of cavity surfaces and grain boundary. A finiteelement model is constructed to tackle this time-dependent cavity growth problem with complexgeometry of cavity shapes. The solution is given in the form of a movie documenting theevolution of cavity morphology, cavity growth rate, stress and strain fields, grain-boundaryopening displacements, etc. all as a function of real time, for a given set of materialsconstants, applied stress and exposure temperature. The conditions under which a steadystate exists and how long it takes to achieve are also discussed and quantified.