Mechanical properties improvement related to the isothermal holding time in Si3N4 ceramics sintered with an alternative additive |
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Authors: | C Santos K Strecker S A Baldacim O M M Silva C R M da Silva |
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Affiliation: | a FAENQUIL-DEMAR, Polo Urbo-Industrial, Gleba AI-6, s/n, cep. 12600-000, Lorena, SP, Brazil;b CTA-IAE, Pça. Marechal do Ar Eduardo Gomes, 50, cep. 12228-904 S. J., Campos, SP, Brazil |
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Abstract: | In the present work, the influence of the isothermal holding time on the physical (relative density and mass loss), chemical (α–β transformation and intergranular phase crystallization) and mechanical (hardness and fracture toughness) properties of Si3N4 ceramics with Al2O3 and CTR2O3 as additives has been studied. CTR2O3 is a natural rare earth oxide mixture, produced at DEMAR-FAENQUIL from the mineral xenotime, consisting mainly of Y2O3, Yb2O3, Er2O3 and Dy2O3. The increase in hardness and fracture toughness with increasing duration of isothermal sintering is discussed in regard of densification, α–β Si3N4 phase transformation and microstructure. The microstructural variations were decisive for the increase of fracture toughness, because larger grains (>4 μm) with higher aspect ratios (>6) developed during increased sinter periods, enhancing crack deflection and crack-bridging mechanism. In this way longer isothermal holding times contribute to the improvement of the physical and mechanical properties of silicon nitride based ceramics. |
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Keywords: | Si3N4 processing Isothermal holding time Microstructure Densification α – β transformation Fracture toughness |
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