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

Predominantly single phase (92-94 vol.%), fully dense samples of Hf2SnC, Zr 2SnC, Nb2SnC Ti2SnC, Hf2PbC and Zr2PbC were fabricated by reactively HlPing the stoichiometric mixture of the corresponding elemental powders in the 1 20-1325 degreesC temperature range for 4-48 h. The latter two, fabricated h ere for the first time, required a further anneal of 48-96 h to increase th e volume fraction of ternary phases. Hf2PbC and Zr2PbC are unstable in ambi ent atmospheres at room temperature. As a family these compounds are good e lectrical conductors; the lowest and highest values of the electrical condu ctivities were, respectively, 2.2x10(6) (Ohm .m)(-1) for Hf2SnC and 13.4x10 (6) (Ohm .m)(-1) for Hf2PbC. The Vickers hardness values range from 3 to 4 GPa. All compounds are readily machinable. The Young's moduli of Zr2SnC Nb2 SnC and Hf2SnC are. respectively, 178, 216 and 237 GPa. The thermal coeffic ients of expansion, TCE's, of the ternaries scale with those of the corresp onding binaries, and are relatively low for such readily machinable solids. The lowest TCE belonged to Nb2SnC [(7.8+/-0.2)x10(-6) K-1], and the highes t to Ti2SnC [(10+/-0.2)x10(-6) K-1]. The TCE's of Hf and Zr containing tern aries cluster around (8.2+/-0.2)x10(-6) K-1. All the synthesized ternary ca rbides were found to dissociate into the transition metal carbide and the A -group element in the 1250-1390 degreesC temperature range. (C) 2000 Elsevi er Science Ltd. All rights reserved.