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Abstract(s)
O uso de materiais cerâmicos estruturais na indústria aeronáutica ou aeroespacial é fundamental para a resposta a condições de serviço extremas. Componentes sujeitos a temperatura elevada, resistência mecânica elevada e desgaste, como pás de turbinas, escudos térmicos, cones de escape de foguetes, são atualmente fabricados em materiais cerâmicos avançados como nitreto de silício (Si3N4), zirconia estabilizada com yttria (YSZ), ou alumina (Al2O3).
Nos últimos anos a eficiência térmica dos sistemas de propulsão de aeronaves está limitado pela temperatura máxima de operação (T˜ 1200ºC) dos sistemas de revestimentos de barreira térmica (Thermal Barrier Coatings, TBCs). O desenvolvimento de novos materiais cerâmicos para o revestimento das superligas de níquel é imperioso para responder ao aumento da eficiência energética, redução do consumo de combustível e aumento da autonomia das aeronaves.
Recentemente diversos trabalhos têm proposto a composição estequiométrica de zirconato de cálcio (CaZrO3) como uma alternativa viável para ambientes severos sujeitos a temperaturas elevadas, corrosão e desgaste. A sua fusão congruente assegura a estabilidade termodinâmica e inércia química, acresce uma condutividade térmica baixa e um coeficiente de expansão térmica similar ao do substrato metálico (por exemplo uma superliga de níquel). Além disso, as propriedades mecânicas deste composto podem ser melhoradas por solução sólida formando compósitos cerâmicos multifásico CaZrO3-MgO.
Partindo da mistura equimolar de CaZrO3-MgO obteve-se materiais densos de reduzido tamanho de grão através de sinterização controlada em três condições: 1450ºC – 2h, 1450ºC – 3h e 1500ºC – 2h. A microestrutura destes materiais foi caracterizada através de SEM/EDX e as suas propriedades físicas (densidade e porosidade) e mecânicas (compressão diametral, dureza e tenacidade à fratura) foram comparadas entre si e com a literatura.
Os resultados demonstram que uma sinterização a 1500ºC – 2h permite obter materiais densos (~99%), com microestrutura homogénea e propriedades mecânicas similares ou até superiores aos materiais atualmente propostos para TBCs, como por exemplo um Kc de 2,5 MPa.m1/2 (enquanto Si3N4 apresenta 2,0 MPa.m1/2 e Al2O3 indica 2,1 MPa.m1/2). No entanto, os valores de dureza de ~8 GPa são relativamente modestos e a máxima compressão diametral foi de 60 MPa, o que indica um potencial de otimização.
The use of structural ceramic materials in the aeronautical or aerospace industry is critical to work in extreme conditions of service. Components subjected to high temperature, high mechanical resistance and wear, such as turbine blades, thermal shields, rocket exhaust cones, are actually manufactured from advanced ceramic materials such as silicon nitride (Si3N4), yttria stabilized zirconia (YSZ) and alumina (Al2O3). In recent years the thermal efficiency of aircraft propulsion systems is limited by the maximum operating temperature (T˜ 1200°C) of Thermal Barrier Coatings (TBC's) systems. The development of new ceramic materials for the coating of nickel superalloys is imperative to respond to increased energy efficiency, reduced fuel consumption and increased aircraft autonomy. Several studies have proposed the stoichiometric compound of calcium zirconate (CaZrO3) as a viable alternative to improve the thermomechanical performance at high temperature, corrosion and wear. Its congruent fusion ensures thermodynamic stability, chemical inertia, plus low thermal conductivity and a coefficient of thermal expansion similar to that of the metallic substrate (nickel superalloy). In addition, the mechanical properties of this compound can be improved by the solid solution forming CaZrO3-MgO multiphase ceramic composite. In this work the equimolar mixture of CaZrO3-MgO was obtained through dense materials of reduced grain size by rate controlled sintering in three conditions: 1450ºC - 2h, 1450ºC - 3h and 1500ºC - 2h. The microstructure of these materials was characterized by SEM/EDX and their physical properties (density and porosity) and mechanical (diametral compression, hardness and fracture toughness) were compared. The results demonstrate that the sintering at 1500ºC - 2h allows to obtain dense materials (~99%) with mechanical properties similar to or better than other materials currently proposed for TBC's, as example a Kc of 2.5 MPa.m1/2 (reported values for Si3N4 is 2.0 MPa.m1/2 and for Al2O3 it is 2.1 MPa.m1/2). However, the hardness values of ~8 GPa are relatively modest and the maximum diametral compression resistance was 60 MPa, which indicates a potential optimization.
The use of structural ceramic materials in the aeronautical or aerospace industry is critical to work in extreme conditions of service. Components subjected to high temperature, high mechanical resistance and wear, such as turbine blades, thermal shields, rocket exhaust cones, are actually manufactured from advanced ceramic materials such as silicon nitride (Si3N4), yttria stabilized zirconia (YSZ) and alumina (Al2O3). In recent years the thermal efficiency of aircraft propulsion systems is limited by the maximum operating temperature (T˜ 1200°C) of Thermal Barrier Coatings (TBC's) systems. The development of new ceramic materials for the coating of nickel superalloys is imperative to respond to increased energy efficiency, reduced fuel consumption and increased aircraft autonomy. Several studies have proposed the stoichiometric compound of calcium zirconate (CaZrO3) as a viable alternative to improve the thermomechanical performance at high temperature, corrosion and wear. Its congruent fusion ensures thermodynamic stability, chemical inertia, plus low thermal conductivity and a coefficient of thermal expansion similar to that of the metallic substrate (nickel superalloy). In addition, the mechanical properties of this compound can be improved by the solid solution forming CaZrO3-MgO multiphase ceramic composite. In this work the equimolar mixture of CaZrO3-MgO was obtained through dense materials of reduced grain size by rate controlled sintering in three conditions: 1450ºC - 2h, 1450ºC - 3h and 1500ºC - 2h. The microstructure of these materials was characterized by SEM/EDX and their physical properties (density and porosity) and mechanical (diametral compression, hardness and fracture toughness) were compared. The results demonstrate that the sintering at 1500ºC - 2h allows to obtain dense materials (~99%) with mechanical properties similar to or better than other materials currently proposed for TBC's, as example a Kc of 2.5 MPa.m1/2 (reported values for Si3N4 is 2.0 MPa.m1/2 and for Al2O3 it is 2.1 MPa.m1/2). However, the hardness values of ~8 GPa are relatively modest and the maximum diametral compression resistance was 60 MPa, which indicates a potential optimization.
Description
Keywords
Cazro3-Mgo Cerâmica Avançada Multifásica Compressão Diametral Distribuição de Weibull Dureza Vickers Tbcs Tenacidade à Fratura