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Authors
Abstract(s)
Perante as crescentes demandas energéticas e de recursos, é imperativo desenvolver
turbinas a gás para a indústria aeronáutica cada vez mais eficientes e duráveis. A elevada
eficiência térmica do motor de turbina a gás, devido ao aumento da temperatura de
operação, é possível ser alcançada através da camada cerâmica do sistema revestimento de
barreira térmica, cujo aplica-se sobre os componentes metálicos.
A zircónia estabilizada com ítria (YSZ) é a cerâmica predileta para proteção térmica de
substratos metálicos da turbina a gás, dado que é detentora de baixa condutividade térmica,
coeficiente de expansão térmica similar à superliga de níquel e boa resistência à propagação
do dano. Novas arquiteturas baseadas em YSZ têm sido estudadas, para desenvolver novos
materiais com propriedades superiores. Assim, a presente dissertação consistiu no fabrico
como respetiva caracterização microestrutural, física, mecânica e térmica de sete distintos
compósitos cerâmicos multifásicos que tiveram como base a zircónia pura ZrO2 (fase
monoclínica), 3YSZ (fase tetragonal) e 8YSZ (fase cúbica). Com recurso à metodologia de
experiências com misturas obteve-se a superfície de resposta estimada de cada propriedade,
para qualquer combinação das três matérias-primas.
De acordo com as estimativas, os compósitos detêm resistência à tração superior a 104 MPa,
à exceção dos constituídos somente pela fase cúbica e monoclínica. No que se refere à
tenacidade à fratura, materiais somente com a fase tetragonal e compósitos binários em que
a fase monoclínica está presente atingem aproximadamente de 5 MPa.m1/2
. A presença de
cristais referentes à fase monoclínica é um admirável reforço para a tenacidade à fratura
devido à deflexão de fissuras. A fase cúbica sobrepõe-se quando é desejável alta dureza,
cerca de 11 GPa, e baixa condutividade térmica, inferior a 2 W/m.K.
Faced with growing energy and resource demands, it is imperative to develop increasingly efficient and durable gas turbines for the aeronautical industry. The high thermal efficiency of the gas turbine engine, due to the increase in operating temperature, is possible to achieved through the ceramic layer belonging to the thermal barrier coating system, which is applied over the metal components. Yttria-stabilized zirconia (YSZ) is the favourite ceramic for thermal protection of metal substrates of the gas turbine, since it has low thermal conductivity, thermal expansion coefficient like nickel superalloy and good resistance to propagation damage. New architectures based on YSZ have been studied to develop new materials with superior properties. Thus, the present dissertation consisted in the fabrication as well as the microstructural, physical, mechanical and thermal characterization of seven different multiphase ceramic composites based on pure zirconia ZrO2 (monoclinic phase), 3YSZ (tetragonal phase) and 8YSZ (cubic phase). Using the methodology of experiments with mixtures, the estimated response surface of each property was obtained for any combination of the three raw materials. According to estimates, the composites have a tensile strength above 104 MPa, except for those constituted only by the cubic and monoclinic phase. Regarding fracture toughness, materials with only the tetragonal phase and binary composites in which the monoclinic phase is present reach approximately 5 MPa.m1/2. The presence of monoclinic phase crystals is an admirable reinforcement to fracture toughness due to crack deflection. The cubic phase overlaps when high hardness, around 11 GPa, and low thermal conductivity, less than 2 W/m.K, is desirable.
Faced with growing energy and resource demands, it is imperative to develop increasingly efficient and durable gas turbines for the aeronautical industry. The high thermal efficiency of the gas turbine engine, due to the increase in operating temperature, is possible to achieved through the ceramic layer belonging to the thermal barrier coating system, which is applied over the metal components. Yttria-stabilized zirconia (YSZ) is the favourite ceramic for thermal protection of metal substrates of the gas turbine, since it has low thermal conductivity, thermal expansion coefficient like nickel superalloy and good resistance to propagation damage. New architectures based on YSZ have been studied to develop new materials with superior properties. Thus, the present dissertation consisted in the fabrication as well as the microstructural, physical, mechanical and thermal characterization of seven different multiphase ceramic composites based on pure zirconia ZrO2 (monoclinic phase), 3YSZ (tetragonal phase) and 8YSZ (cubic phase). Using the methodology of experiments with mixtures, the estimated response surface of each property was obtained for any combination of the three raw materials. According to estimates, the composites have a tensile strength above 104 MPa, except for those constituted only by the cubic and monoclinic phase. Regarding fracture toughness, materials with only the tetragonal phase and binary composites in which the monoclinic phase is present reach approximately 5 MPa.m1/2. The presence of monoclinic phase crystals is an admirable reinforcement to fracture toughness due to crack deflection. The cubic phase overlaps when high hardness, around 11 GPa, and low thermal conductivity, less than 2 W/m.K, is desirable.
Description
Keywords
Cúbica Tenacidade à Fratura 3ysz 8ysz Compósitos Cerâmicos Multifásicos Compressão Diametral Distribuição de Weibull Drx Dureza Vickers Experiências com Misturas Monoclínica Sem Superfícies de Resposta Tbc Tetragonal Zro2