Comparison between fatigue behavior of some ceramics: a new concept of intrinsic stress-corrosion exponent n0

The fatigue behavior was systematically investigated with three typical ceramic materials, including Y2O3–ZrO2, Si3N4 and a machinable glass–ceramic. Cyclic, static and dynamic fatigue tests were conducted in three environments, i.e., moist air, distilled water and kerosene. The effects of environment and loading condition on fatigue behavior were analyzed. The difference between materials was discussed. Experimental results showed that, for all the three materials, fatigue life under cyclic load was the shortest and a low value of n (fatigue exponent) was obtained. Compared with the other materials, Si3N4 ceramic had a very large n value under static load. Therefore the static fatigue for Si3N4 ceramics may be ignored. Cyclic load decreases the fatigue life of transformation-toughening ceramics (Y–TZP) more seriously, while no remarkable difference was observed between cyclic and static fatigue for original glass of the glass–ceramic. A new idea about the physical meaning of n value and the concept of intrinsic stress-corrosion exponent n0 were introduced. The exponent n can be separated into two terms, i.e., n=n0+nμ, where n0 is a material constant and just related to the most basic properties, such as atom-bonds or crystalline structure, nμ reflects the contribution of microstructure toughening and is very sensitive to environments or loading conditions. This hypothesis can be used to describe and explain the experiment results successfully.