Sub-critical crack propagation in particulate composites with Y-TZP matrix
Zbigniew Pędzich Akademia Górniczo-Hutnicza, Wydział Inżynierii Materiałowej i Ceramiki, Katedra Ceramiki Specjalnej, al. Mickiewicza 30, 30-059 Kraków
Quarterly No. 3, 2005 pages 86-90
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abstract The paper presents the results of investigation on an influence of inclusion type on subcritical crack propagation of hotpressed particulate composites based on 3 mole % yttria - zirconia matrix (TZP). Three composite materials containing 10 volume % of a second phase additive were examined. Tungsten carbide, metallic tungsten and alumina particles were used as additives. All kinds of inclusion have mean grain size about 1 micrometer. Microstructure observations showed some differences between composites. Inclusions in TZP/W and TZP/WC materials were aggregated (Figs 2 and 3), on the contrary in TZP/Al2O3 material, alumina grain were almost perfectly dispersed in the matrix (Fig. 1). Sub-critical crack propagation was investigates using Double Torsion method in static loading mode. Dependence of crack velocity (VI) vs. stress intensity factor (KI) was measured for all composite materials. Diagrams, prepared as a result of these measurements, allowed threshold values of the critical stress intensity factors (KI0) to be establish (see Table 1 and Fig. 10). It was established that independent on the kind of inclusion, all investigated composite materials show increased of KI0 parameter value. Quantitatively the scale of this increase was different for different materials. The most effective improvement was detected in TZP/W system and the smallest KI0 increase was noticed for TZP/Al2O3 material. It could be describe to effective crack deflection by inclusion aggregates in TZP/W and TZP/WC (Figs 5 and 7) and to the presence of plastic deformation in TZP/W material (Fig. 8). Qualitatively, the run of VI ~ KI dependences for all composites were similar. It suggests that phenomena occurred during slow crack propagation did not change, despite of type of chemical bond in inclusion. Key words: composites, sub-critical crack propagation