Abstract
In order to create the composite ultrafine particles of metal and ceramics, ultrafine particles (UFP) of Fe-TiN, Ni-TiN and Co-TiN systems were prepared by arc melting, vaporization and deposition of binary Fe-Ti, Ni-Ti and Co-Ti alloys in an atmosphere of a nitrogen-hydrogen mixed gas (“reactive plasma-metal” reaction) at 0.1 MPa pressure. The crystal structure, the chemical composition, the morphology and the specific surface area of obtained UFP were determined by X-ray diffractometry, energ dispersion analysis for X-ray, transmission electron microscopy and the BET method, respectively.
Crystal structures of UFP obtained from Me (Fe, Ni or Co)-Ti parent alloys containing less than about 40-50 at%Ti were found to be a single phase of Me (α-Fe, Ni or β-Co), but in the case of titanium contents higher than about 40-50 at%, the TiN phase (NaCl type structure) was found in UFP. The TiN concentration of the obtained UFP remarkably deviated negatively compared with titanium concentration of the Me-Ti parent alloys over the entire composition range. It agreed very closely with the apparent vapor composition of Me-Ti parent alloys measured by “hydrogen plasma-metal” reaction.
The composite UFP consisting of TiN and Me particles, whose morphlogy were dumbell-like or dice-like particles was found in UFP obtained from the parent alloys containing more than 50 at%Ti. The formation mechanism (LS mechanism) of the composite UFP was presumed as follows: (i) vaporization of Me and Ti into the nitrogen atmosphere, (ii) nucleation of TiN owing to the reaction of Ti vapor with nitrogen, (iii) deposition of a Me-Ti-N melt on the TiN nucleus, (iv) crystallization of TiN on the TiN nucleus from the Me-Ti-N melt, (v) solidification of residual Me-rich melt (composite UFP is formed).
