モリブデンと炭素および炭化物との反応

抄録

Diffusion couples of molybdenum with carbon and several carbides, i.e. B₄C, SiC, TiC, and TaC, respectively, were heated for up to 3.6×10⁵ s at various temperatures ranging from 1373 to 2223 K. The couples were then examined for composition, growth rate, structure, and hardness of reaction layers. Main results obtained are as follows:
(1) In the Mo-C system, only Mo₂C layer was formed at below 1873 K, while two sub-layers consisted of Mo₂C and η (MoC_1−x), respectively, were found at above 1873 K. The activation energy for growth of total layer was 374 kJ/mol.
(2) In the Mo-B₄C system, two sub-layers consisted of Mo₂B and MoB, respectively, with dispersed carbon particles were formed.
(3) In the Mo-SiC system, Mo₂C layer, including η (MoC_1−x) phase at high temperature, mixture of Mo₂C and Mo₃Si₂ phases, and Mo₃Si₂ phase in order from the Mo side were formed. The activation energy for growth of total layer was 477 kJ/mol.
(4) In the Mo-TiC system, two kinds of TiC in point of view of free carbon content were used; one is with 0.2% free carbon and the other is with 0.01%. In the Mo-TiC with 0.2% free carbon system, two sub-layers, i.e. relatively thick Mo₂C layer and thin (Ti, Mo)C layer, were formed, while in the Mo-TiC with 0.01% free carbon system two thin sub-layers, Mo₂C and (Ti, Mo)C, were formed; the Mo₂C layer in the latter case was very thin and was not found after short time heating at low temperature. The activation energy for growth of Mo₂C layer in the former system was 393 kJ/mol.
(5) In the Mo-TaC with 0.02% free carbon system, two thin sub-layers, (Mo, Ta)₂C and (Ta, Mo)C, were observed.
(6) TEM studies on the interface between Mo(bcc) and Mo₂C(hcp) showed that there was the following orientation relation, called as the Burgers relation, between these two phases; {110}_Mo\varparallel(0001)_Mo2C, ⟨111⟩_Mo\varparallel⟨11\bar20⟩_Mo2C.