Properties

Thermal shock properties: The strength of the zirconia at cycling temperature is definitely dependent on the microstructure, chemical purities and homogeneity in addition to post deposition treatments. It is further reported in the literature that the erosion resistance depends substantially on the cohesive bonds in the zirconia 3).

Residual stresses in zirconia influence the fatigue strength, fracture toughness and endurance of the material. A balanced process forming minor compressive stresses within the coating is preferable. Such a zirconia coating may exceed 20,000 thermal cycles according to results obtained by NASA.

Plasma spraying of zirconia at low substrate temperature may put the ceramic in tension and relieve residual stresses through microcracking.

The improvement related to transformation has been explained in terms of formation of a microcrack zone in front of the propagating crack. These microcracks form due to the strains associated with the tetragonal to monoclinic transformation.

Thermal shock induced cracking is a common failure mode for ceramics. For heat engine applications, resistance to thermal shock is obviously an important material characteristic. Unfortunately, the ranking of ceramics according to resistance to thermal shock will vary extensively depending on the temperature range of interest, the severity of the thermal shock, the microstructure and the failure criteria.

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