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- Characterization of a Functionally Gradient Ceramic Based on CaZrO3 – MgOPublication . Babo, Débora Rafaela Telha de; Nunes-Pereira, João; Silva, Pedro D.; Pena, Pilar; Baudin, Carmen; Pereira Silva, AIn the case, where the structure is exposed to severe conditions of operation, such as high strength, wear and high-temperature gradients (e.g. engine components, insulation system, thermal barrier and thermal shield) must be applied. In this work, it was developed and characterized a functional gradient ceramic coating. A ceramic composite based in CaZrO3 – MgO was used in order to design a material with successive layers of molar composition 2:3, 1:1 and 1:3 of CaZrO3:MgO, respectively. A dense material was obtained by sintering assisted reaction (Figure 1). Thermal conductivity at room temperature, hardness, fracture toughness, surface energy, and microstructure were characterized.The results show for monolithic specimens of 2:3 CZ, 1:1 CZ and 1:3 CZ a H of 9,9 GPa, 9,8 GPa and 10,1GPa; a Kc of 1,6 MPa.m1/2, 1,7 MPa.m1/ and 2,1 MPa.m1/2; a k of 0,59 W/mK; 0,76 W/mK and 0,79 W/mK; and a surface energy (SE) of 43,27 mN/m, 51,39 mN/m and 46,55 mN/m, respectively. The functional gradient ceramic shows a H of 10,7 GPa, a Kc of 1,97 MPa.m1/2; a k of 0,82 W/mK and SE of 53,98 mN/m. The individual composition and the functional gradient ceramic show a similar relative density of 4,3 g/cm3 and a porosity of 0,2%. This design methodology has the advantage of allowing the properties of the same material to suit different substrates.
- Development and characterization of ceramic composites based on CaZrO3-MgOPublication . Nunes-Pereira, João; Pena, Pilar; Baudin, Carmen; Pereira Silva, AAdvanced materials for severe environment conditions, such as high temperature, wear and high erosion and corrosion, are of growing interest, namely for transport and energy industries. Particularly, in aerospace industry the increase of working temperature of engines and turbines combined with weight reduction will give rise to higher thrust and lower fuel consumption and consequently less emissions. In this sense, new ceramic multiphasic composites based on calcium zirconate (CaZrO3) and magnesium oxide (MgO) are being proposed with suitable thermal, mechanical and chemical properties for severe conditions application. In the present work, an equimolar composition of CaZrO3-MgO, processed from easily and accessible synthetic raw materials, have been developed and the particle size distribution optimized by milling under controlled conditions. CaZrO3-MgO ceramic composites uniaxially pressed disks have been produced by rate controlled sintering during 2 hours at 1400, 1450 and 1500 ºC, respectively. The physical, microstructural and mechanical properties, have been assessed to evaluate the performance and suitability of the processed materials for high responsibility applications. A homogeneous microstructure was obtained for all sintering temperature samples with porosities ranging between ~10 %, for samples sintered at 1400 ºC, to ~100 % theoretical density for samples sintered at 1500 ºC. Diametral compression strength follows the Weibull distribution with characteristic strengths between ~50 and 170 MPa, Vickers hardness reach values above 8 GPa, while the facture toughness present values between 2 and 3 MPa.m1/2, for 1400 and 1500 ºC respectively. These results show that the ceramic composites based on CaZrO3-MgO sintering at 1500 ºC proved to be a suitable alternative to high responsibility applications.
- Modelling of elastic modulus of CaZrO3-MgO composites using isotropic elastic and anisotropic modelsPublication . Nunes-Pereira, João; Carneiro, Pedro; Maceiras, Alberto; Baudin, Carmen; Pereira Silva, AStarting from synthetic raw materials (CaZrO3 and MgO), microstructural and mechanical properties were optimised in order to obtain dense multiphasic ceramic, then finite element method (FEM) of an equimolar (1:1) CaZrO3-MgO composite was performed in order to obtain the effective elastic modulus. Composite presents two main phases of orthorhombic CaZrO3 (81.5 wt.%) and cubic MgO (18.5 wt.%); For 1500 °C, relative density of 99.9%, characteristic strength of 168 MPa, hardness of 7.8 MPa and toughness of 2.5 MPa.m1/2 were obtained. FEM simulation was performed using two representative volume elements (RVE’s) with edge lengths of 14 μm (933 grains) and 17 μm (1670 grains), using isotropic elastic model, and anisotropic on specific set of crystallographic planes. The results of FEM using isotropic approach for the two RVE’s are perfectly aligned with the experimental (245 GPa), while the anisotropic model shows a difference of 6.5%.