Papers by Author: Masato Enomoto

Abstract: The nucleation of bcc ferrite precipitates at austenite grain corners in a Co-15Fe alloy was studied by serial sectioning coupled with electron backscatter diffraction (EBSD) analysis. Grain corners were identified by recombination of triple points and triangular annihilation, whereas quite a few precipitates were surrounded by more than four matrix grains when twins were counted as individual grains. More than 40% of corners composed all of high angle grain boundaries were vacant at an undercooling of ~60°C from the g/(a+g) phase boundary. All the precipitates had K-S or N-W orientation relationship with at least one grain and a larger proportion of them had the OR with two and three grains. For half of vacant corners a hypothetical precipitate could have the OR with more than one grain. It is likely that not only the misorientations among the matrix grains, but also the orientations of the grain boundary planes have a major influence on nucleation potency even at grain corners.

Abstract: The characteristics and the mechanism of ferrite transformation in alloy steels which contain a carbide-forming element have attracted considerable attention for past decades. Since it is reported that the nucleation and growth of ferrite in Fe-C base alloys is accelerated by high magnetic field, the influence of a magnetic field of 12 Tesla on ferrite transformation was studied in a Fe-C- Mo alloy. Whereas a significant amount of expedition was observed at lower temperatures, the principal features of ferrite transformation, namely, a marked retardation of transformation at intermediate temperatures and premature cessation of transformation before it reaches the final equilibrium amount below the bay temperature were essentially retained. In contrast, the influence of magnetic field was much less at higher temperatures. These results are discussed in terms of the influence of magnetic field on the phase equilibrium and coupled-solute drag effects on the migration a/g phase boundary.

Abstract: This study aims to analyze the potential of grain boundary corners (GBCs) as nucleation sites of bcc precipitates in an fcc matrix. By combined serial sectioning and electron backscatter diffraction analysis, the crystallography of GBCs and GBC precipitates was analyzed in a Co-Fe alloy.

Abstract: A calculation of the interface energy for the Ni-Al binary alloy, including the inter-phase boundary (IPB) energy and the anti-phase boundary (APB) energy, has been performed using the Cluster Variation Method (CVM) with the tetrahedron approximation within the temperature range of 600°C~1300°C. The calculated IPB energies range between 8 and 13 mJ/m2, while the APB energies range between 24 and 46 mJ/m2. Additionally, the dependence of the average composition and the order parameter on distance with the compositionally diffuse interfacial regions has been computed. The calculation also shows the width of the diffuse IPB increases with the temperature linearly.