Effects of nano-graphite content on the characteristics of spark plasma sintered ZrB^sub 2^–SiC composites

In this study, ZrB2–25 vol% SiC composite containing 0, 2.5, 5, 7.5 and 10 wt% graphite nano-flakes were prepared by spark plasma sintering (SPS) process at 1900 °C for 7 min under 40 MPa. The fabricated composite samples were compared to examine the influences of nano-graphite content on the densif...

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Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2018-02, Vol.716, p.99
Main Authors: Asl, Mehdi Shahedi, Zamharir, Mehran Jaberi, Ahmadi, Zohre, Parvizi, Soroush
Format: Article
Language:English
Subjects:
Boron carbide
Composite materials
Crack bridging
Densification
Flakes
Fracture toughness
Grain size
Graphite
Mechanical properties
Microstructure
Plasma sintering
Refractory materials
Silicon carbide
Spark plasma sintering
Studies
Ultrahigh temperature
Zirconium carbide
Zirconium compounds
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Summary:In this study, ZrB2–25 vol% SiC composite containing 0, 2.5, 5, 7.5 and 10 wt% graphite nano-flakes were prepared by spark plasma sintering (SPS) process at 1900 °C for 7 min under 40 MPa. The fabricated composite samples were compared to examine the influences of nano-graphite content on the densification, microstructure and mechanical properties of ZrB2–SiC-based ultrahigh temperature ceramics. Fully dense composites were obtained by adding 0–5 wt% nano-graphite, but higher amounts of additive led to a small drop in the sintered density. The growth of ZrB2 grains was moderately hindered by adding nano-graphite but independent of its content. The hardness linearly decreased from 19.5 for the graphite-free ceramic to 12.1 GPa for the sample doped with 10 wt% nano-graphite. Addition of graphite nano-flakes increased the fracture toughness of composites as a value of 8.2 MPa m½ was achieved by adding 7.5 wt% nano-graphite, twice higher than that measured for the graphite-free sample (4.3 MPa m½). The in-situ formation of ZrC and B4C nano-particles as well as the presence of unreacted graphite nano-flakes led to a remarkable enhancement in fracture toughness through activating several toughening mechanisms such as crack deflection, crack bridging, crack branching and graphite pullout.
ISSN:0921-5093
1873-4936