1986 Volume 94 Issue 1088 Pages 432-439
The fatigue behavior of 3mol% Y2O3-partially stabilized zirconia with average grain size of 0.4μm (Z3Y-I) and 1.0μm (Z3Y-II) was studied by measuring their strength as a function of stressing rate (dynamic fatigue) and time to failure under constant stress (static fatigue). The crack growth parameter (N) measured by the dynamic fatigue technique at 20°C was 40.8 and there was no difference between the fracture stress-stressing rate relationship of Z3Y-I and that of Z3Y-II. The N value of Z3Y-I at 250°C was 50.5 and the fracture stress-stressing rate relationship was similar to that of Z3Y-I and Z3Y-II at ambient temperature. On the other hand, the N value of Z3Y-II at 250°C was 10.2 and it was found that the fatigue resistance of Z3Y-II decreased markedly at 250°C in comparison with that at ambient temperature. Average lifetime of Z3Y-I and Z3Y-II predicted from dynamic fatigue data at 20°C was about 12 years at the applied stress of 600MPa and about 20, 000 years at 500MPa, and lifetime of Z3Y-I at 250°C was 114 days at 600MPa and 3, 000 years at 500MPa. It was found that it is possibile to use Z3Y-I and Z3Y-II below the applied stress of 600MPa at 20°C and Z3Y-I below 500MPa at 250°C over a long period of time. On the other hand, the lifetime of Z3Y-II at 250°C was about 8 minutes at 500MPa, and even if applied stress was lowered to 200MPa, the lifetime merely extended to 4.7 months. The average lifetime of Z3Y-II measured by the static fatigue technique at 250°C was 4 to 6 times the liftime predicted from dynamic fatigue data, and the N value obtained from static fatigue data was 10.7 and it was considered that its value is the same as that from dynamic fatigue. The fracture surface of Z3Y-I and Z3Y-II tested by dynamic fatigue technique at 20°C and that of Z3Y-I at 250°C showed a smooth region near the fracture origin and was followed by a rougher area being spread in a radial manner from the fracture origin. Their fracture surface features were similar to those of the typical fracture surface observed in many ceramics. The fracture surface of Z3Y-II tested at a higher stressing rate at 250°C was similar to that in ambient temperature, too. However, if the stressing rate was lowered to 0.301MPa/s, fatigue fracture surface was observed at the fracture origin, and it was followed by a smooth region and rougher area. The fracture surface of Z3Y-II tested by the static fatigue technique at 250°C showed fatigue fracture surface near tensile surface and its zone size increased with decreasing applied stress and increasing time to failure.
