Development, microstructural and mechanical caracterization of SiC ceramics with alumina and rare earth oxides additions / Desenvolvimento, caracterização microestrutural e mecânica de cerâmicas de SiC aditivadas com alumina e óxidos de terras raras

AUTOR(ES)

Miriam Kasumi Hwang

DATA DE PUBLICAÇÃO

2006

RESUMO

In this work, the mechanical properties are determined at room temperature (hardness and fracture toughness) and high temperatures (compressive creep) of SiC ceramic samples with alumina (Al2O3) and rare earth oxides (REO) additions. The REO is obtained by REC (rare earth concentrate - Nuclemon) calcinations, which contains 76 wt % of yttria (Al2O3). Three compositions have been studied: A90 (90 wt% SiC, 5 wt% Al2O3 and 5 wt% REO), A80 (80 wt% SiC, 10 wt% Al2O3 and 10 wt% REO) and A70 (70 wt% SiC, 20 wt% Al2O3 and 10 wt% REO). The powder mixtures were milled, sieved and compacted. The compacted samples were cold pressed and sintered at 2000°C and hot-pressed at 1800°C. Some parameters of mechanical properties were determined at room temperature (Vickers surface hardness and fracture toughness) and high temperatures (deformation rate, activation energy and stress exponent). They were also characterized by X-ray diffraction, electron scanning and transmission microscopy. Compressive creep study was carried out on samples with the best room temperature properties (A90), under stress up 150 to 300 MPa and temperatures of 1300, 1350 and 1400°C, during 72 hours. Some creep tests were also performed on A70 samples, to compare different compositions. Theses samples have been analyzed in relation to the strain rate, activation energy and stress exponent. The A90 sample has shown better results in the creep parameters. The microstructure and phases are investigated on the sample surface after the creep. The oxidation and secondary phase have influenced the creep parameters. The possible active creep mechanisms in this system are diffusion, grain boundary sliding and cavitation.

ASSUNTO(S)

materials physics alumina microestrutura metais de terra rara fluência silicon carbide mechanical properties propriedade mecânica creep microstructure sinterização via fase liquida alumina liquid fhase sintering fisica de materiais carbeto de silício rare earth metals

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