THE EFFECT OF MICROSTRUCTURES OF SIALON C ERAMICS ON FATIGUE PROPERTIES AT ROOM-TEMPERATURE

The effect of microstructure on the fatigue behavior at room temperatu re in air was studied using sialon ceramics with different microstruct ures prepared by selecting starting raw materials and sintering condit ions. Dynamic, static and cyclic fatigue tests were carried out on smo oth specimens by the 3-point bending method, Oxide content in the inte rgranular phase and grain size affectted the dynamic fatigue behavior. Remarkable slow crack growth attributable to the stress corrosion by humidity in air was observed in the sample with elongated grains, In s tatic fatigue tests, the observed lifetime of each sample was in agree ment with that predicted from dynamic fatigue properties, and the crac k propagated through the intergranular phase. The acceleration of fati gue was observed under cyclic loading. The accelerative effects on cyc lic fatigue was significant in the sample with coarse grains, Sialon c eramics with elongated grains prepared by HIP showed both high fractur e toughness and high strength, but the fatigue parameter ''n'' was low and the acceleration of fatigue under cyclic loading was significant because of its coarse grains.