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Coatings 2017, 7(8), 110; doi:10.3390/coatings7080110

Phase and Microstructural Correlation of Spark Plasma Sintered HfB2-ZrB2 Based Ultra-High Temperature Ceramic Composites

High Temperature Ceramic Laboratory, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India
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Received: 31 May 2017 / Revised: 7 July 2017 / Accepted: 13 July 2017 / Published: 26 July 2017
(This article belongs to the Special Issue Ultrahigh Temperature Ceramic Coatings and Composites)
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Abstract

The refractory diborides (HfB2 and ZrB2) are considered as promising ultra-high temperature ceramic (UHTCs) where low damage tolerance limits their application for the thermal protection system in re-entry vehicles. In this regard, SiC and CNT have been synergistically added as the sintering aids and toughening agents in the spark plasma sintered (SPS) HfB2-ZrB2 system. Herein, a novel equimolar composition of HfB2 and ZrB2 has shown to form a solid-solution which then allows compositional tailoring of mechanical properties (such as hardness, elastic modulus, and fracture toughness). The hardness of the processed composite is higher than the individual phase hardness up to 1.5 times, insinuating the synergy of SiC and CNT reinforcement in HfB2-ZrB2 composites. The enhanced fracture toughness of CNT reinforced composite (up to a 196% increment) surpassing that of the parent materials (ZrB2/HfB2-SiC) is attributed to the synergy of solid solution formation and enhanced densification (~99.5%). In addition, the reduction in the analytically quantified interfacial residual tensile stress with SiC and CNT reinforcements contribute to the enhancement in the fracture toughness of HfB2-ZrB2-SiC-CNT composites, mandatory for aerospace applications. View Full-Text
Keywords: ultra-high temperature ceramic (UHTC); zirconium diboride (ZrB2); hafnium diboride (HfB2); carbon nanotubes (CNT); spark plasma sintering (SPS); fracture toughness ultra-high temperature ceramic (UHTC); zirconium diboride (ZrB2); hafnium diboride (HfB2); carbon nanotubes (CNT); spark plasma sintering (SPS); fracture toughness
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Nisar, A.; Balani, K. Phase and Microstructural Correlation of Spark Plasma Sintered HfB2-ZrB2 Based Ultra-High Temperature Ceramic Composites. Coatings 2017, 7, 110.

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