Ultra-Rapid Crystal Growth of Textured SiC Using Flash Spark Plasma Sintering Route

Salvatore Grasso,Adam Tudball,Shi-Hoon Choi,Mike Reece,Theo Saunders,Eun-Young Kim,Min Yu

doi:10.1021/acs.cgd.6b00099

Salvatore Grasso, Adam Tudball + Show 5 more

Open Access

https://doi.org/10.1021/acs.cgd.6b00099

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Abstract

A novel processing route that induces simultaneous densification and texturing of SiC ceramics by Flash Spark Plasma Sintering (FSPS) is reported. Unlike hot forging (which produces texturing in a direction orthogonal to the load as a result of plastic deformation), FSPS produced texturing parallel to the pressing direction. The texturing was driven by a thermal gradient generated within the sample along its axial direction due to the higher electrical resistivity of SiC compared to the pressing graphite punch (the sample midthickness was hotter than the surfaces in contact with the graphite punches). In FSPSed SiC samples, the microstructure consisted of large SiC plate-like elongated crystals (thickness between 40 and 100 μm, width up to 500 μm) with their c-axis (slow growth direction) orthogonal to the Physical Vapor Transport (PVT) direction. The mechanisms producing densification and texture were studied for SiC with and without boron carbide sintering additives. In order to achieve a dense and text...

Highlights

Flash Sintering (FS)[1] produces concentrated heating, which allows energy saving and time efficient densification of ceramics compared to more conventional sintering techniques
The Flash Spark Plasma Sintering (FSPS) setup (Φ 20 mm) employed 3 layers of graphite felt surrounding the precompacted sample. This setup allowed preheating and consequent flash sintering of the pure β-SiC sample. This configuration allowed (a) sample heating by current flowing through graphite felt, at low temperature when the sample was still too resistive; and (b) above a certain temperature when the sample resistance falls below that of graphite felt, the current could instead flow through the sample, providing self-Joule heating leading to thermal runaway of the sample
The results reveal that FSPS processing produces anisotropic grain growth through the Physical Vapor Transport (PVT) process and surface energetics of the SiC platelets

Summary

Introduction

Flash Sintering (FS)[1] produces concentrated heating, which allows energy saving and time efficient densification of ceramics compared to more conventional sintering techniques. Apart from being a tool to densify materials, might be exploited to engineer microstructures. In this respect, the rapidity of the FS process (order of 104 °C/min) allows new temperature profiles which might suppress atomic diffusion,[4] resulting in thermodynamically metastable materials and microstructures. Another work mentioning texture induced by FS processing has been reported by Jha et al.[13] on titania. According to their results, texturing appeared as a reversible effect which was maintained only while the electric field was turned on. In our view, the change in relative XRD peak intensity, used to qualify the degree of texturing by Jha et al, should be attributed to additional field effects, such as electrochemical reduction (or other effects) rather than texturing

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