Hidenori Ogawa

Amorphization in iron-carbon systems with transition metals by mechanical alloying

Abstract Mechanical alloying (MA) of elemental powder mixtures of Fe 83− x M x C 17 (M ≡ Cr, Mo or Co) with x = 0–35 was performed using a planetary ball mill, to examine effect of the ternary additions M on amorphization of FeC materials by MA. In the MA processing, the additions Cr and Mo with the high carbide-forming tendency (CFT) in FeC-based systems strongly promoted the amorphization reaction in milled powder products. In contrast, for the case of Co with a lower CFT such a remarkable effect was not observed. These results are interpreted in terms of atomic bonding energies in the ternary FeMC solution and crystal structures of competing stable carbides in the FeMC system. The amorphicity of MA samples was examined by X-ray diffraction, differential scanning calorimetry and electrical resistivity measurements.

Amorphization of Interstitial Elements Containing Iron Materials by Mechanical Alloying

In mechanical alloying (MA) of Fe–C and Fe–N materials with additive elements A such as Nb, Ti, Cr, and Co in an Ar atmosphere using a ball mill, the amorphization of MA powders is most crucially dependent on the interaction parameter WAX (X=C or N) among the several properties of additives A, including their melting points and atomic sizes, and the milling energy supplied to MA materials. The parameter WAX represents the difference between the bonding energies of the atomic A–X pair (UAX) and the Fe–X pair (UFeX) in the Fe–A–X solution, i.e., WAX=UAX-UFeX. Additives such as Cr and Nb with negative WAX values markedly promote the amorphization of MA materials, in contrast to Co or Ni which have positive WAX values. When V–VI group elements with negative and moderate WAX values, such as Nb, Ta, and Cr, are employed as the ternary additives, the amorphization of Fe–C and Fe–N materials is readily attained.