Zekun Yu,Chao Zhou,Kuo Bao,Zhaoqing Wang,Pinwen Zhu,Qiang Tao,Tian Cui
The interactions between the carbon skeleton and metal atoms in binary transition metal carbides are of particular interest for industrial applications involving advanced physics and chemistry, especially in magnetoelectric functional materials and cemented carbides. Cr and carbon BTMCs are a series of intermetallic compounds with specific chemical formulas that share certain unique characteristics. In this study, we used polycrystalline powders of chromium and carbon as precursors and synthesised single-phase bulk Cr7C3 (orthorhombic, space group: Pnma) with high density and good crystallinity using a high-temperature and high-pressure quenching method (HTHPQM). We studied the material properties and electronic structures of Cr7C3 with both experimental measurements and density functional theory ab intio simulations and found that Cr7C3 is a conductor with an electrical conductivity (2.32 × 10−3 Ω m), relatively high compaction (97.2%), excellent thermostability (oxidation at 1175 K), and a magnetic phase transition from paramagnetism to soft ferromagnetism around 50 K, and the electromagnetic properties are chiefly due to the abundance of the 3d electrons of Cr, and the orbital hybridisation between C and Cr with their 2p and 3d electrons is the reason for the crystal structure and high thermostability. Therefore, the synthesised Cr7C3 is a multifunctional material with promising application prospects, and HPHTQM is a simple and effective method for preparing samples.
Graphite flakes (Gf) were coated with Cr7C3 by salt bathing coating, and the Cr7C3 coated Gf reinforced Al matrix composites were prepared by gas pressure infiltration. Surface morphology of uncoated and Cr7C3 coated Gf, the interfacial characteristics of Cr7C3 coated Gf/Al composites were observed by SEM. Surface of Cr7C3 coated Gf is smooth without defects, the Cr7C3 coating effectively improved the wettability. When volume fraction of Gf is below 50%, the experimental value of thermal conductivity (TC) is basically consistent with the calculated value of the EMA model. When volume fraction of Gf is over 50%, the growth of deviates from the EMA model curve. Coefficient of thermal expansion (CTE) of composite was predicted by Kerner model and Orientation Disc model, because Kerner model does not consider the anisotropy of Gf and inaccurately predict the change of CTE. However, the Orientation Disc model can predict the change of CTE better, but there is certainly deviation.
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