Modification Of Mechanical Properties Of Tzp Ceramics By Ceramic And Metallic Inclusions
Zbigniew Pędzich Akademia Górniczo-Hutnicza, Wydział Inżynierii Materiałowej i Ceramiki, Katedra Ceramiki Specjalnej, al. Mickiewicza 30, 30-059 Kraków
Annals 1 No. 2, 2001 pages 147-150
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abstract The paper summarises investigation on selected inclusion influence on properties of particulate composites with TZP matrix. As an inclusions carbide (WC, NbC, TaC) and metallic phases (Ni, W, Mo) were used. Two grades of carbide inclusion size were applied (see Table I). Composite powders were prepared by attrition mixing of zirconia and carbide or metallic powders. The other way of TZP/metal composite powder preparation was hydrogen reduction of the mixture of zirconia and adequate metal oxide powders (see Table 1). Composite powders and reference zirconia sample were hot-pressed under 25 MPa at 1500ºC with 1 h soaking time. The densities of sintered bodies, their hardness, fracture toughness, bending strength and wear susceptibility were investigated. All the experimental data was collected at Table 2. The coarse (gruby) carbide inclusions increase hardness more effectively than the thin (drobny) ones. Reverse phenomenon takes place in connection with fracture toughness improvement. In this case thin inclusions are more effective. The increase of bending strength was observed only in the composite with thin WC additives. In this system the lowest wear susceptibility was detected. Addition of the metallic phases lead to fracture toughness improvement. It is worth to notice that the TZP/Ni composite shows the worse mechanical properties. Nickel is the only one amoung used additives, which has higher than zirconia coefficient of thermal expansion (αNi > αZrO2). It leads to comprehensive stresses in the zirconia matrix. Such a situation should be profitable for mechanical properties of the composite. The other used additives have coefficient α lower than zirconia what results in tensile stresses in the matrix. But these composites show better mechanical properties than TZP/Ni. The crack paths through the composite were investigated (see Fig 1). In all composite systems crack path is similar. One could observe crack deflection, branching or sometimes bridging. Crack never comes through inclusions. If amount and size of inclusions are similar, decisive influence on composite properties has most probably the matrix-inclusion interface strength. The presented paper indicates that properties of the TZP could be improved by incorporation small amount of the carbide or metallic phases.