Resistência ao choque térmico de carbeto de silício sinterizado via fase líquida

Abstract

The behavior of ceramic materials towards thermal shock resistance is a topic of great interest, due to applications in which the reliability against sudden temperature variations is required. In this thesis, it was studied how the variation in the proportion of Y 2 O 3 :Al 2 O 3 additives and different parameters on the processing of liquid phase sintered silicon carbide may influence thermal shock resistance of this material. Samples were prepared with molar composition 90%SiC+10%Y 2 O 3 :Al 2 O 3 , by varying oxides molar proportion between 2:1 and 1:4, with and without previous reaction of the additives. Mixtures were compacted and sintered in a resistive graphite furnace at 1750, 1850 and 1950°C, and by hot pressing at 1750 and 1850°C, and evaluated for densification. After analysis of the first results, pressureless sintering and the mixtures with proportions of 1:3 and 1:4 of previously reacted Y 2 O 3 :Al 2 O 3 were selected for the study of thermal shock resistance. Thermal cycles were performed by heating at temperatures of 600, 750 and 900°C and sudden cooling in water at room temperature. The evaluation of samples regarding thermal shock resistance was conducted by determination of elasticity modulus, porosity, flexural strength and microstructural analysis of the cracks. The samples sintered at 1950°C temperature are those that exhibit the best performance in relation to thermal shock resistance, while the variation in the proportions Y 2 O 3 :Al 2 O 3 from 1:3 to 1:4 do not significantly change this property. Under the conditions used, the maximum temperature for liquid phase sintered SiC application must be limited to 750°C, which allows its use as a component of heat exchanges, bearings, pump bearings, gas turbines and sensors of automotive and aeronautical engines.