High-strength and low-weight composite materials or cermets have been prepared by reinforcing an aluminium-base matrix with boron carbide particles or with boron carbide-coated boron fibres [1-3]. In the former case boron carbide (B4C) is the strengthening agent, whereas in the latter the role of B4C coating is to protect the fibres against a too severe attack by aluminium during processing or use of the composites. Recently B4C-coated carbon fibres have been produced on a pilot plant in our laboratory [4, 5]. A general study is now in progress with the aim of employing these treated fibres for the manufacture of aluminium-base matrix composites. The development of such materials and improvement of their performances require, however, a thorough understanding of the metal-carbide interface chemistry and, primarily, a detailed description of the phases likely to be formed by chemical reaction in the A1-B-C system. In a general study on the processing of B4C-A1 cermets, Halverson et al. observed the formation of a new ternary compound, which they called phase X, at every temperature between 800 and 1400 °C [1]. Attempts were made by Sarikaya et al. [6] to characterize that phase by electron diffraction and energy-loss spectroscopy: those authors proposed a hexagonal symmetry with the lattice parameters a 0 = 0.3520 nm and Co = 0.5820 nm and the chemical formula A14BC. This letter reports the composition and lattice parameters of an aluminium-rich borocarbide that was prepared by direct synthesis from the elements and discusses the possible relationship between this compound and the foregoing phase X. Commercial powders of aluminium (purity 99.8 wt %, grain size d < 50 txm, Alfa Ventron), boron (99.4 wt %, d < 250/xm, Alfa Ventron) and carbon (spectrographic grade, d < 25/xm, Le Carbone Lorraine) were ball-mixed in a steel mortar at the atomic ratio AI:B :C = 80:10:10 and cold-pressed under 272 MPa into small rods (dimensions 4 m m x 6 m m x 3 0 m m and weight about 2g). These rods were placed on an alumina boat and heated for 160 h at 1273 K in a closed silica tube under atmospheric-pressure purified argon. Under these conditions the weight losses were <5%. After air-cooling the resultant samples were characterized by X-ray powder diffraction (XRD), using standard Philips equipment: a PW1720 generator, PW1390 channel-control unit and PW1050/25 two-circle goniometer supplied with a step-scanning motor
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Mar 16, 2022
Dina Carbone + 21
Open Access
