DEVELOPPEMENT D'UN FOUR MICRO-ONDES MONOMODE ET FRITTAGE DE POUDRES CERAMIQUE ET METALLIQUE

A single-mode microwave cavity was developed to study the sintering of ceramic and metallic powders. In this TE10p cavity, the electromagnetic pattern is controlled and the materials can be heated up under either predominant electric or magnetic field. Samples can be microwave-sintered directly or with a cylindrical SiC susceptor. The temperature was measured by an infrared camera. A new microwave heating procedure was proposed to control a thermal cycle. Comparatives studies between microwave and conventional sintering processes were achieved on ceramic and metallic powders. Microwave sintering of yttria-doped zirconia at 25°C/min heating rate led to a shift of the densification curve, an enhancement of the kinetics of densification during the initial and intermediate stages and a restricted grain growth. A submicronic nickel powder can be only sintered by plasma-induced heating under predominant electric field.Un four micro-ondes à cavité monomode a été développé afin d'étudier le frittage de poudres céramiques et métalliques. Dans cette cavité TE10p, la distribution du champ électromagnétique est maîtrisée et les matériaux peuvent être chauffés en champ soit électrique soit magnétique prépondérant. Le chauffage micro-onde peut être direct ou hybride (avec suscepteur). La température est mesurée par une caméra infrarouge. Un pilotage en température original a été mis au point. Des études comparatives entre les frittages micro-ondes et conventionnel ont porté sur une poudre céramique et une poudre métallique. Pour la zircone yttriée avec une vitesse de chauffage de 25°C/min, le chauffage micro-ondes décale d'une centaine de degrés les courbes de densification, accélère les cinétiques pendant les premiers stades et permet de limiter la croissance granulaire. Pour une poudre de nickel submicronique un frittage n'a été observé qu'en champ électrique dominant et en présence d'un plasma

DEVELOPPEMENT D'UN FOUR MICRO-ONDES MONOMODE ET FRITTAGE DE POUDRES CERAMIQUE ET METALLIQUE

A single-mode microwave cavity was developed to study the sintering of ceramic and metallic powders. In this TE10p cavity, the electromagnetic pattern is controlled and the materials can be heated up under either predominant electric or magnetic field. Samples can be microwave-sintered directly or with a cylindrical SiC susceptor. The temperature was measured by an infrared camera. A new microwave heating procedure was proposed to control a thermal cycle. Comparatives studies between microwave and conventional sintering processes were achieved on ceramic and metallic powders. Microwave sintering of yttria-doped zirconia at 25°C/min heating rate led to a shift of the densification curve, an enhancement of the kinetics of densification during the initial and intermediate stages and a restricted grain growth. A submicronic nickel powder can be only sintered by plasma-induced heating under predominant electric field.Un four micro-ondes à cavité monomode a été développé afin d'étudier le frittage de poudres céramiques et métalliques. Dans cette cavité TE10p, la distribution du champ électromagnétique est maîtrisée et les matériaux peuvent être chauffés en champ soit électrique soit magnétique prépondérant. Le chauffage micro-onde peut être direct ou hybride (avec suscepteur). La température est mesurée par une caméra infrarouge. Un pilotage en température original a été mis au point. Des études comparatives entre les frittages micro-ondes et conventionnel ont porté sur une poudre céramique et une poudre métallique. Pour la zircone yttriée avec une vitesse de chauffage de 25°C/min, le chauffage micro-ondes décale d'une centaine de degrés les courbes de densification, accélère les cinétiques pendant les premiers stades et permet de limiter la croissance granulaire. Pour une poudre de nickel submicronique un frittage n'a été observé qu'en champ électrique dominant et en présence d'un plasma

Densification and microstructure evolution of Y-Tetragonal Zirconia Polycrystal powder during direct and hybrid microwave sintering in a single-mode cavity

International audienceThe densification and microstructure changes of 2 mol% yttria-stabilized zirconia nanopowder have been investigated during direct and hybrid microwave sintering. Microwave heating tests were achieved in a resonant single-mode cavity at 2.45 GHz and a cylindrical SiC susceptor was used for hybrid sintering experiments. Constant heating rate runs (25 degrees C/min) were controlled by adjusting the position of a sliding piston at constant forward microwave power. The temperature on the upper surface of the specimen was measured with an infrared camera. The final densities and the microstructures observed by SEM were compared to those of conventionally sintered materials. Homogeneous microstructures have been obtained by hybrid heating whereas direct microwave heating led to rather heterogeneous microstructures due to thermal gradients. Nevertheless, microwave-sintered materials always exhibited higher final densities for a given sintering temperature. This significant enhancement of the densification process was particularly observed in the intermediate sintering stage (1200-1350 degrees C range). Besides, grain growth was found to be mainly influenced by the sintering temperature rather than by the heating mode

All-Materials-Inclusive Flash Spark Plasma Sintering

Abstract A new flash (ultra-rapid) spark plasma sintering method applicable to various materials systems, regardless of their electrical resistivity, is developed. A number of powders ranging from metals to electrically insulative ceramics have been successfully densified resulting in homogeneous microstructures within sintering times of 8–35 s. A finite element simulation reveals that the developed method, providing an extraordinary fast and homogeneous heating concentrated in the sample’s volume and punches, is applicable to all the different samples tested. The utilized uniquely controllable flash phenomenon is enabled by the combination of the electric current concentration around the sample and the confinement of the heat generated in this area by the lateral thermal contact resistance. The presented new method allows: extending flash sintering to nearly all materials, controlling sample shape by an added graphite die, and an energy efficient mass production of small and intermediate size objects. This approach represents also a potential venue for future investigations of flash sintering of complex shapes