Consolidating and Deforming SiC Nanoceramics Via Dynamic Grain Sliding

Abstract

The effort of grain refinement to achieve SiC nanoceramics has been driven by the expectation of the radical improvement of the mechanical performances and the superplasticity with decreasing grain size. [1,2] It requires the minimization of grain growth during sintering, i.e. to establish the optimized sintering condition where the grain-boundary migration is suppressed while the grain-boundary diffusion is stimulated. In principle, two approaches, namely solid-state sintering and liquid-phase sintering, have been adopted to densify SiC ceramics, with the major densification mechanism being identified as the grain-boundary diffusion enhanced by the segregated doping elements, e.g. boron, [3] and, respectively, by the liquid phase formed in grain-boundaries. [4] The densification is enhanced by the application of an external mechanical pressure, either uniaxial or isostatic. [3,5] It may be further enhanced by involving a disorder-order phase transformation, [6] by involving a suitable liquid that facilitates the solution-reprecipitation of the major phase, [7] or by allowing deformation to occur during densification, i.e. sinter forging. [5] So far, nanoceramics of SiC, as it is generally defined as ceramics consisting of grains less than 100 nm, have been prepared both by solid-state sintering and by liquid-phase sintering of nano-powders. [3][4][5][6]8] Their record superplastic deformation strain rate is in the order of 1 × 10 -5 /s above 1600°C and of 1 × 10 -4 /s at 1700°C for solid-state sintered and liquidphase sintered SiC nanoceramics, respectively. [3,4] These deformation strain rates are far too low for the potential application of plastic forming of complex shaped ceramic components at elevated temperatures. It appears that the achievable low deformation strain rate is yet an obstacle for densification, which yields the formation of a fraction of undesirable larger pores in the size range of 1-3 lm even under hot-pressing conditions. [5] In order to assure full densification, therefore, either time-consuming and/or more complicated sintering approaches, e.g. high pressure hot isostatic pressing, [3] pre-sintering plus sinter forging, [5] or two-step liquid-phase sintering, [8] have to be employed.A recent progress in achieving high deformation strain rate is to process materials by spark plasma sintering ® . Due to the very efficient heating and the influence of the electrical current/field on mass transport deformation strain rates in the order of 1 × [**] This work was partially supported by the Swedish Research Council through grant 621-2005-6290. We thank Prof. M. Nygren for valuable discussions. Fig. 1. Normalized shrinkage (a) and shrinkage rate (b) recorded during SPS processing of SiC nanoceramics. The applied heating rate is 100°C/min.

Combustion Synthesis of Nanosized β-SiC Powder on a Large Scale

“…Silicon carbide (SiC) ceramics have been widely studied for tribological and structural applications, such as abrasives, refractories, bearings, valves, and seals, because of their high Young's modulus and hardness, excellent oxidation and corrosion durability, high strength at elevated temperatures, and good thermal shock resistance. , Consolidated SiC ceramics are usually prepared by various sintering techniques including liquid-phase sintering, hot-pressing, and spark plasma sintering. − In these sintering processes, both densification behavior and microstructure development depend on the quality of the starting powders. The properties and fabrication costs of the final SiC ceramic components are determined to a large extent by the SiC powders used as raw materials.…”

“…1,2 Consolidated SiC ceramics are usually prepared by various sintering techniques including liquid-phase sintering, hot-pressing, and spark plasma sintering. [3][4][5][6][7] In these sintering processes, both densification behavior and microstructure development depend on the quality of the starting powders. The properties and fabrication costs of the final SiC ceramic components are determined to a large extent by the SiC powders used as raw materials.…”

Combustion Synthesis of Ceramic Powders with Controlled Grain Morphologies

“…SiC ceramics are widely studied for tribological and structural applications, such as abrasives, refractories, bearings, valves, and seals, because of its high elastic modulus and hardness, excellent oxidation and corrosion durability, high strength at elevated temperatures, and good thermal shock resistance. Consolidated SiC ceramics are usually prepared by sintering techniques including liquid-phase sintering, hot-pressing, and spark plasma sintering [9][10][11][12]. In these sintering processes, both densification kinetics and microstructure evolution strongly depend on the quality of starting powders.…”

3D Visualization of Morphological Evolution of Large Defects during Spark Plasma Sintering of Alumina Granules

“…[22] In contrast, it is advantageous to use granules for making complex-shaped components by SPS. [23] Granules have been sometimes used for SPS of alumina, [24,25] zirconia, [26,27] monolithic SiC ceramic, [28,29] magnesium aluminate spinel, [30] carbon nanotube (CNT)-incorporated aluminazirconia composite, [31] quasi-crystalline materials, [32] and microporous alumina. [33] We aim to present a model experiment for understanding the shrinkage of defects in SPS of granules.…”