Abstract
The structural and/or functional design of multiphase ceramics, along with their processing, are timely research topics in the area of field-assisted sintering techniques, such as spark plasma sintering, especially for systems containing both electrically insulating and conductive phases. In the present study, spark plasma sintering of Si3N4–TiN composites was investigated by changing the TiN particle size and electrical current waveform. Their combined effects on both the densification behavior and α-to-β phase conversion of the Si3N4 matrix was studied and compared by means of a thermodynamic approach and dilatometric measurements. Through the control of TiN phase characteristics and heating mode, double-layered Si3N4-based components were also prepared using a one-step spark plasma sintering process, which was compared with conventional hot-pressing. It was shown that the size of the conductive TiN phase has a significant influence on the particle rearrangement, with the formation of a liquid phase, and the solution–diffusion–precipitation process, through the field-induced local heating and electrowetting mechanisms. Moreover, the contribution of current pulsing to the densification and α-to-β conversion of the layered Si3N4-based components was mostly dependent upon the particle size distribution and content of the TiN phase, indicating that the electric-field effect is dependent upon current path.
Highlights
Based on conventional pressure-assisted sintering techniques, spark plasma sintering (SPS) has been developed with the purpose of fully densifying materials, such as nitride and carbide ceramics, that are predominantly covalently bonded and have low atomic self-diffusion [1,2,3]
For composites composites containing the micron-sized TiN as the conductive second phase, the curves under both containing the micron-sized TiN as the conductive second phase, the curves under both applied current applied current waveforms present evidence of two convoluted peaks, which are associated with the waveforms present evidence of two convoluted peaks, which are associated with the two important two important stages of liquid phase sintering (LPS), namely the α-Si3N4 particle rearrangement by liquid flow
SPS experiments were conducted on the electrical-current-assisted liquid-phase sintering of Si3 N4 –TiN composites, controlling both the TiN particle size and current pulsing mode
Summary
Based on conventional pressure-assisted sintering techniques, spark plasma sintering (SPS) has been developed with the purpose of fully densifying materials, such as nitride and carbide ceramics, that are predominantly covalently bonded and have low atomic self-diffusion [1,2,3]. By optimizing sintered densities, a predictable and effective control of the phase composition and microstructure of the processed materials would be significant benefits expected when using this economical sintering method [4,5,6]. Unlike oxide ceramics, those based on nitrides and carbides are routinely consolidated using liquid phase sintering (LPS). As the liquid phase forms during heating of a powder mixture, a series of concomitant effects will contribute to the densification and microstructure development. A challenging question that draws considerable attention from researchers
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