Junichi Shimomura

Auger electron spectroscopy of boron nitride in hot-rolled graphitized steel sheet

The distribution of elements in graphitized steel sheet was examined by Auger electron spectroscopy. The microstructure showed pronounced stringers of graphite with an area 6 μm x 15 μm parallel to the rolling direction of the hot-rolled steel sheet after graphitization annealing at 933 K for 36 ks. Boron nitride (BN) precipitates were rarely detected in the graphite in polished specimens, but they were found on the graphite surface in specimens subjected to in situ Ar + ion sputtering. Anger electron spectroscopy colour mapping images showed stringers of BN precipitates in the area 2 μm x 0.5 μm parallel to the rolling direction at the interior of the graphite in the steeL The image was considered to present the first observation of BN precipitates in graphite. High-energy resolution Auger spectra obtained from the area of BN precipitation coincided well with spectra of hexagonal BN (h-BN), even in fine structures of B KLL and N KLL Auger transitions. It was deduced that h-BN precipitates exist inside the graphite and act as sites for the nucleation of graphitization. The distribution of h-BN precipitation in the graphite suggests that h-BN precipitates are formed at the unrecrystallized austenite grain boundaries during hot rolling.

Magnetic properties and the grain boundary structure of Mn-Zn ferrites with the addition of Nb2O5

Abstract The effects of the addition of Nb 2 O 5 on the power losses in manganese-zinc ferrites have been investigated by measuring the magnetic properties and observing the grain boundary structures. The addition of Nb decreases the initial permeability and raises the resonance frequency. Power losses were analyzed as the sum of the contributions of hysteresis loss, eddy current loss and residual loss. The hysteresis and eddy current losses were reduced by about 10% by the addition of Nb below 200 kHz, in spite of the smaller magnetic permeability. These losses are thought to originate from the additive effect of Nb atoms, which are enriched in grain boundaries to form a high-resistivity layer and prevent Ca and Si atoms being incorporated with the spinel lattice. The residual losses were greatly reduced by the addition of Nb at higher frequencies. The origin of the difference in the residual losses is discussed.

State analysis of electrolytic chromate film by XPS and SXS

Abstract The chemical state of Cr in the interior and on the surface of silica-free and silica-added electrolytic chromate and that at the interface between the chromate films and electrogalvanized (EG) steel sheet were quantitatively investigated by SXS and XPS. Specimens for the interface analysis were prepared by dissolving the Zn coating in mercury after adhering stainless steel sheets to the films. The Cr 3+ ( Cr 3+ + Cr 6+ ) ratio (Cr3+ ratio) of the interface was substantially the same as that of the interior, and that of the surface was 20% lower than that of the interior. Addition of silica to the film does not affect the chemical state of Cr. The Cr3+ ratio of the interface as well as the surface increased with the increase in the insoluble Cr3+ ratio obtained by an immersion test in boiling water, indicating that Cr3+ is insoluble in water. The surface of the chromate film was Cr6+-rich and the interior of the film is Cr6+-poor, which is attributed to the fact that Cr6+ is easily reduced to Cr3+ during chromate formation at the interface between the chromate bath and EG surface.

Analytical electron microscopy of corrosion-resistant Nd-(Fe, Co, Ni, Ti)-B magnets

Abstract The microstructures of cast ingot, annealed ingots and sintered bodies of Nd 15 (Fe 0.585 Co 0.3 Ni 0.1 Ti 0.015 ) 77 B 8 alloy were investigated with analytical electron microscopes to clarify the changes of the phases with successive processing. Five phases were identified in the specimens, namely Nd 2 (Fe 0.6 Co 0.3 Ni 0.1 ) 14 B, Nd(Fe 1− x−y Co x Ni y ) 4 B, Nd(Ni 1− x Co x ), Nd(Fe 1− x−y Co x Ni y ) 2 and TiB 2 . In addition, (Nd 1− y TM y ) 2 O 3 (TM  Fe, Ni, Co) phase was also identified in the sintered specimen. An Nd-rich phase was not observed in the present specimens. The phases, except the main magnetic phase (Nd 2 TM 14 B), were different in crystal structure from those in ternary Nd-Fe-B magnets. The majority of NdTM 4 B dissolved to supply B atoms to TiB 2 during the sintering. Some of the Nd(Ni 1− x Co x ) phase reacted with O atoms absorbed during the milling and/or sintering process, and formed Nd 1− y TM y ) 2 O 3 precipitate during the sintering. The remaining Nd(Ni 1− x Co x ) phase precipitated as thin precipitates at grain boundaries. It is suggested that the phases enriched with Ni and the absence of the Nd-rich phase give rise to the high corrosion resistance of Nd-(Fe, Co, Ni, Ti)-B magnets.