Synthesis and characterization of Hf2PbC, Zr2PbC and M2SnC (M=Ti, Hf, Nb or Zr)

Predominantly single phase (92–94 vol.%), fully dense samples of Hf2SnC, Zr2SnC, Nb2SnC, Ti2SnC, Hf2PbC and Zr2PbC were fabricated by reactively HIPing the stoichiometric mixture of the corresponding elemental powders in the 1200–1325°C temperature range for 4–48 h. The latter two, fabricated here for the first time, required a further anneal of 48–96 h to increase the volume fraction of ternary phases. Hf2PbC and Zr2PbC are unstable in ambient atmospheres at room temperature. As a family these compounds are good electrical conductors; the lowest and highest values of the electrical conductivities were, respectively, 2.2×106 (Ω.m)−1 for Hf2SnC and 13.4×106 (Ω.m)−1 for Hf2PbC. The Vickers hardness values range from 3 to 4 GPa. All compounds are readily machinable. The Youngʹs moduli of Zr2SnC, Nb2SnC and Hf2SnC are, respectively, 178, 216 and 237 GPa. The thermal coefficients of expansion, TCEʹs, of the ternaries scale with those of the corresponding binaries, and are relatively low for such readily machinable solids. The lowest TCE belonged to Nb2SnC [(7.8±0.2)×10−6 K−1], and the highest to Ti2SnC [(10±0.2)×10−6 K−1]. The TCEʹs of Hf and Zr containing ternaries cluster around (8.2±0.2)×10−6 K−1. All the synthesized ternary carbides were found to dissociate into the transition metal carbide and the A-group element in the 1250–1390 °C temperature range.