Weibull modulus of the particulate composites with tzp ceramics matrix
Zbigniew Pędzich Akademia Górniczo-Hutnicza, Wydział Inżynierii Materiałowej i Ceramiki, al. Mickiewicza 30, 30-059 Kraków
Annals 2 No. 3, 2002 pages 38-41
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abstract The paper presents results of investigation on influence of inclusion dispersion on Weibull modulus of particulate composite in TZP/WC system. Two grades of carbide inclusion size were applied (Table 1). Composite powders were prepared by attrition mixing of zirconia and carbide powders. The amount of WC phase introduced to the matrix was 10 vol. % in each case. Composites and zirconia powders were hot-pressed under 25 MPa in argon atmosphere at 1500ºC with 1 h soaking time. Also, the reference zirconia sample sintered in air was prepared. The densities of sintered bodies (ρ), their hardness (HV), fracture toughness (KIc), bending strength (σ ) and Weibull modulus (m) were investigated. The microstructure of sintered bodies was examined with both, scanning and transmission electron microscopy. The experimental data was collected at Tables 2 and 3. All investigated bodies were well densified. Composites were harder than TZP materials and showed increased fracture toughness. The measured value of KIc parameter is higher for composite with fine carbide inclusion (WC-2). The increase of bending strength (σ ) was observed only in the composite with WC-2 additives. In the system TZP/WC-1 distinct decrease of σ was observed. The value of Weibull modulus for air-sintered zirconia was 22. That is typical for this type of material. Hot-pressing increased the m value to 30, most probably due to less grain growth in these sintering conditions (Table 3). The introduction of WC inclusions decreased the values of Weibull parameter when compared to the „pure” TZP material. This decrease is especially significant for composite with coarse (WC-1) grains (m = 5). The m value calculated for composite with fine inclusions (WC-2) was = 18. This fact could be explained by possibility of creation large agglomerates of carbide particles in TZP/WC-1 composite (Fig. 1a). Such agglomeration could be a result of a method of composite constituents homogenisation. Attrition milling was no effective enough. Presence of large agglomerates and weak adhesion of carbide-carbide boundaries produced large flaws in composite microstructure. They caused such significant decrease of flexural strength and Weibull modulus. In TZP/WC-2 materials was easier to avoid such distinct agglomeration (Fig. 1b).