Mechanical properties and low-temperature aging of tetragonal zirconia polycrystals processed by hot isostatic pressing
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H. Balmori-Ramı´rez and D. Jaramillo-Vigueras Department of Metallurgical Engineering, Escuela Superior de Ingeniería Química e Industrias Extractivas (ESIQIE), Instituto Polite´cnico Nacional, A.P. 75-872, Mexico City 07300, Mexico
T. Iga Ceramic Science Department, National Industrial Research Institute of Nagoya, Nagoya 462, Japan
G.A. Schneider Technical University Hamburg-Harburg, Advanced Ceramics Group, D-21073, Hamburg, Germany (Received 10 January 2003; accepted 11 July 2003)
The influence of grain size and density of yttria-tetragonal zirconia polycrystals (Y-TZPs) ceramics on mechanical properties and on low-temperature aging degradation (LTD) in air and in hot water was investigated. A TZP powder containing 3 mol% Y2O3 was consolidated by slip casting and densified by the sintering/hot isostatic pressing (HIP) method. Only the presintered samples that contained less than 0.15% open porosity reached near full density after HIP. The best conditions to reach full density were found to be attained by presintering and HIP both at 1400 °C. At these conditions, some of the best mechanical properties such as modulus of rupture and Weibull modulus reached 1397 ± 153 MPa and, 10.6, respectively. These values were clearly higher than those obtained from sintered bodies and samples hot isostatically pressed at 1600 °C. Aging degradation of 3Y-TZP materials can be avoided through microstructural design. Fully dense materials with a critical grain size 99.9%) after HIP at 1400 °C. Further comments on the reduction in density or damage of the samples presintered at 1300 °C and hot isostatically pressed at the given temperatures are as follows. In samples having open porosity, the Ar gas used to pressurize during HIP penetrates the pores and impedes densification. In the worst case, samples
III. RESULTS AND DISCUSSION
In the following sections, we report the results and discussion of microstructure and mechanical properties as well as the low-temperature degradation for the sintered samples. For microstructure, we emphasize density, porosity, phase identification, grain size, and size of defects observed on the surface of the sintered samples while in the section on mechanical properties, H, E, and KIC are reported. In the third section, the low-temperature degradation of the characterized samples in air and in water is discussed. A. Microstructure of the samples after sintering or HIP
FIG. 1. Variation of density and porosity of as-cast 3Y-TZP as a function of sintering temperature (䉲, density; 䊐, open porosity; 䊊, closed porosity). TABLE II. Density and porosity after HIP.
1. Density and porosity
Starting with the as-cast samples, which had a relative green density of 47.55%, the sintering behavior is presented in the form of a curve showing the variation of the relative density as a function of the sintering temperature in Fig. 1. Also in this figure, the variation of the open and closed porosity with sintering temperature is presented. The density increases continuously as the sintering temperature increases.
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