Effect of Carbon Addition and Mixture Method on the Microstructure and Mechanical Properties of Silicon Carbide.

Zeynep Aygüzer Yaşar,Richard A Haber

doi:10.3390/ma13173768

Zeynep Aygüzer Yaşar, Richard A Haber

Open Access

https://doi.org/10.3390/ma13173768

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Abstract

High dense (>99% density) SiC ceramics were produced with addition of C and B4C by spark plasma sintering method at 1950 °C under 50 MPa applied pressure for 5 min. To remove the oxygen from the SiC, it was essential to add C. Two different mixture method were used, dry mixing (specktromill) and wet mixing (ball milling). The effect of different levels of carbon additive and mixture method on density, microstructure, elastic modulus, polytype of SiC, Vickers hardness, and fracture toughness were examined. Precisely, 1.5 wt.% C addition was sufficient to remove oxide layer from SiC and improve the properties of dense SiC ceramics. The highest hardness and elastic modulus values were 27.96 and 450 GPa, respectively. Results showed that the 4H polytype caused large elongated grains, while the 6H polytype caused small coaxial grains. It has been observed that it was important to remove oxygen to achieve high density and improve properties of SiC. Other key factor was to include sufficient amount of carbon to remove oxide layer. The results showed that excess carbon prevented to achieve high density with high elastic modulus and hardness.

Highlights

Silicon carbide (SiC) is widely used in the defense industry, turbine engines, nozzles, heat conducting tube, and aerospace applications [1,2,3,4,5,6,7]
SiC ceramics can be densify by pressureless sintering, hot pressing (HP), and spark plasma sintering (SPS) with solid state or liquid phase sintering [3,11,20,21,27,33]
With increasing the carbon content from 2.0 to 5.0 wt.%, surplus carbon started appearing on the Fieldemission emissionscanning scanningelectron electron microscope (FESEM) images

Summary

Introduction

Silicon carbide (SiC) is widely used in the defense industry (bulletproof vests), turbine engines, nozzles, heat conducting tube, and aerospace applications [1,2,3,4,5,6,7]. Depending on particle size of powder, moisture in the air and additives, nonoxide high-temperature materials like B4 C, SiC, and TiB2 tend to have oxide layer on their surfaces. This oxide layer inhibits to achieve high density and causes grain coarsening [8,9,29,30,31]. SPS is a quite new technique that allows sintering of materials without exaggerated growth in a short time [3,6,7,15,34,35,36,37]

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