Kunio Nagaoka

Solid state amorphization of FeC alloy by mechanical alloying

Abstract Alloys prepared by mechanical alloying four kinds of crystal FeC powder mixtures were examined by X-ray diffraction. The amorphization reaction was confirmed in the case of Fe 75 C 25 at 25.2 × 10 5 s of milling time.

EXAFS study of the solid state amorphization process in an FeC alloy

Abstract The structural changes in an Fe 75 C 25 alloy powder were observed during solid state amorphization by EXAFS. The solution of carbon in iron during mechanical alloying (MA) plays an important role in disordering the crystalline iron lattice and leads to amorphization of the Fe 75 C 25 alloy. The amorphous Fe 75 C 25 alloy prepared by MA has a short range order analogous to the Fe 3 C cementite.

EXAFS study on mechanical deformation for PdSi amorphous alloy

Abstract Extended X-ray absorption fine structure (EXAFS) spectra were measured in situ under several tensile strains to study the atomic-scale process of mechanical deformation in Pd83Si17 amorphous alloy using synchrotron radiation at KEK. With an increase in the tensile strain, the PdSi distance shifts to higher R space with little change in the coordination number while PdPd distance is displaced towards lower R space values with a large reduction in the coordination number. During the unloading process, the values of the PdSi and PdPd distances do not return to their initial values. From these facts, the deformation mechanism is discussed in terms of the atomic-scale structure.

Positron Annihilation in Plastically Deformed Ni-P Amorphous Alloy

The positron life time and the angular correlation of positron annihilation radiation (ACPAR) from a plastically deformed Ni–P amorphous alloys were measured. The counting rate around θ=0 increased, the counting rate around θ=10 mrad decreased and the life time of positron increased, as a result of plastic deformation. It is interpreted that a slight growth of the free volume in the specimen by plastic deformation was detected. “Work softening” behaviour of the amorphous alloy is interpreted by this growth of the free volume.

EXAFS study on solid state amorphization process of NiNb alloy by mechanical alloying

Abstract The main purpose of this work is to investigate the micromechanism of the solid state amorphization of metals by mechanical alloying. The changes of radial distribution functions around the atomic species of a NiNb mixture powder through ball milling were studied by means of EXAFS. The atomic structural change during crystalline to amorphous phase was discussed.

Structural changes in B2 CoZr compound during amorphization process by mechanical milling

Abstract A structural study of the B2 CoZr compound during amorphization reaction by high energy ball milling was done using extended X-ray absorption fine-structure (EXAFS) measurement to discuss the micromechanism of amorphization. The B2 CoZr compound powder was prepared by are melting and annealing. The mechanical milling was done using a vibrating mill. A change in the radial distribution function, provided by the Fourier transform of EXAFS signal, around the Co atom shows that the Zr atom at the first-nearest neighbor around a Co atom is replaced by Co atom at the second-nearest neighbor, simultaneously the crystalline structure disintegrates and the amorphization reaction occurs. When the accumulated strain energy, e.g. the nanocrystal grain boundary energy, is comparable with the difference to drive the crystalline-to-amorphous phase transformation in CoZr, the amorphization reaction starts.

Structural changes in PdSi powder mixtures during amorphization process by mechanical alloying

Abstract The change in atomic arrangement of a PdSi powder mixtures during mechanical alloying (MA) was studied by XAFS and the resulting atomic structure of the PdSi amorphous alloy was compared with that obtained by rapid quenching (RQ). The results suggest that the amorphization proceeds by the forcing of Si atoms into the FCC Pd crystal.