Creep Fracture in Ceramics

With kind permission of John Wiley and Sons 

In Chap. 6, creep was discussed in general, but a considerable portion of the chapter was devoted to creep fracture and creep rupture, so these will not be reviewed here. However, since various additives do influence the basic properties of materials (e.g., second phases, fibers, whiskers), to complete this discussion on creep phenomena in ceramics, an example follows of the effect of whiskers in a 

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R. L. Tsai and R. Raj, Creep Fracture in Ceramics Containing Small Amounts of a Liquid Phase, Acta Metall., 30,1043-1058 (1982). 

Cavitation is the formation of cavities. This phenomenon has been found to take place in ceramics containing a glass phase. The final creep fracture in this case results from the accumulation of cavities. The factors controlling this kind of creep are the microstructure, volume of glass phase, temperature, and applied stress. These factors give rise to bulk and localized damage. 

In this paper, the importance of particle and whisker reinforcement to creep and creep rupture behavior of ceramics is discussed. Particle and whisker additions generally increase both the fracture toughness and creep resistance of structural ceramics. These additions also act as nucleation sites for cavities. Cavities form preferentially in tensile specimens. This results in a creep asymmetry, in which composites creep faster in tension than in compression. As a consequence of cavitation, the stress exponent for creep in tension 6-10,... 

T.-J. Chuang, D. F. Carroll, and S. M. Wiederhom Creep Rupture of a Metal-Ceramic Particulate Composite, Seventh International Conference on Fracture, in Advances in Fracture Research, Vol. 4, eds., K. Salama, K. Ravi-Chandler, D. M. R. Taplin, and P. Rama Rao, Pergamon Press, New York, NY, 1989, pp. 2965-2976. 

The mechanisms responsible for fracture in structural ceramics at elevated temperatures have been reviewed [154]. Sensitivity to flaws or microstructural inhomogeneities which nucleate microcracks are among the failure mechanisms. The flaws which control failure under creep conditions are different from those responsible for fast fracture at room temperature. A common feature is the development of cracks through gradual damage accumulation, depend on the microstructure. The role of cracks in the deformation and fracture behavior of polycrystalline structural ceramics have been reviewed [155]. 

Creep deformation in 2-D ceramic composites is a complex phenomenon with deformation possible in the matrix, the woven fabric, the fibers, and the interface layers. Analysis of the data and of the fracture surfaces in these aeep tests does not clearly indicate what... 

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