Effect of SiC on Microstructure, Phase Evolution, and Mechanical Properties of Spark-Plasma-Sintered High-Entropy Ceramic Composite

Hanzhu Zhang,Farid Akhtar

doi:10.3390/ceramics3030032

Abstract

Ultra-high temperature ceramic composites have been widely investigated due to their improved sinterability and superior mechanical properties compared to monolithic ceramics. In this work, high-entropy boron-carbide ceramic/SiC composites with different SiC content were synthesized from multicomponent carbides HfC, Mo2C, TaC, TiC, B4C, and SiC in spark plasma sintering (SPS) from 1600 °C to 2000 °C. It was found that the SiC addition tailors the phase formation and mechanical properties of the high-entropy ceramic (HEC) composites. The microhardness and fracture toughness of the HEC composites sintered at 2000 °C were improved from 20.3 GPa and 3.14 MPa·m1/2 to 26.9 GPa and 5.95 MPa·m1/2, with increasing SiC content from HEC-(SiC)0 (0 vol. %) to HEC-(SiC)3.0 (37 vol. %). The addition of SiC (37 vol. %) to the carbide precursors resulted in the formation of two high-entropy ceramic phases with two different crystal structures, face-centered cubic (FCC) structure, and hexagonal structure. The volume fraction ratio between the hexagonal and FCC high-entropy phases increased from 0.36 to 0.76 when SiC volume fraction was increased in the composites from HEC-(SiC)0 to HEC-(SiC)3.0, suggesting the stabilization of the hexagonal high-entropy phase over the FCC phase with SiC addition.

Highlights

High-entropy ceramics (HECs) that are manufactured from multiple ceramic precursors, such as transition metal carbides and borides, have shown great potential to replace conventional ceramic in certain application fields due to their superior properties including excellent mechanical performance, oxidation resistance, and thermal–electrical properties [1,2,3]
The HEC-(SiC)x composite reveals higher densification with increasing SiC content at 1600 ◦ C, with a relative density increasing from 72.5% for HEC-(SiC)0 to 81% for the HEC-(SiC)3.0 composite
As the sintering temperature increases to 1800 ◦ C, the composites containing SiC whiskers show a relative density above 97%, while the HEC-(SiC)0 composite without SiC whiskers shows a comparatively lower relative density of 92%

Summary

Introduction

High-entropy ceramics (HECs) that are manufactured from multiple ceramic precursors, such as transition metal carbides and borides, have shown great potential to replace conventional ceramic in certain application fields due to their superior properties including excellent mechanical performance, oxidation resistance, and thermal–electrical properties [1,2,3]. In the field of refractory HECs, high-entropy carbides and high-entropy borides synthesized from group IV, V, and VI Metal-C and Metal-B ceramics are the most studied systems to date. The synthesized HECs showed simple solid solution structure with the same crystal structure as the constituent ceramic compounds, i.e., face-centered cubic (FCC) B1 structure for the HE-carbides and hexagonal AlB2 structure for the HE-diborides. In the stated crystal structures, the principal metal atoms occupy the cationic sites randomly while the non-metals occupy the anionic sites. Both of the HE-carbides and HE-borides showed enhancement of mechanical properties as compared to monolithic ceramic compounds [2,3].

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Results

Conclusion