Tatsuya Ohmi

Combustion Synthesis of TiC Particle Dispersed Metal Matrix FGM Composites

FeAl‐TiC and Fe‐TiC pseudo binary FGM composite alloys have been combustion synthesized from mixtures of the elementary powders. When the powder mixture was heated in an argon atmosphere to approximately 900 K, an abrupt increase in temperature was observed, indicating that the combustion synthesis reactions occurred in the powder mixture. XRD analyses revealed that the combustion‐synthesized samples consisted of only FeAl and TiC or only Fe and TiC, depending on the pseudo binary system. SEM observations and EPMA examinations revealed that TiC particles were distributed in FeAl or Fe matrix phases. As the volume fraction of the TiC particles increased from 0.3 to 0.9, the average particle diameter increased from approximately 1 to 7 micro meters and the Vickers hardness of the sample increased from 800 to 2500. This method has been applied to the fabrication of some other ceramic particle dispersed metal matrix composites such as FeAl‐TiB2 and Fe‐TiB2 pseudo binary systems.

Micro-Arc Nitriding of Titanium Surface

When a surface of a titanium disk was melted in an atmosphere of pure nitrogen using a 3D Micro Welder which was designed by the present authors, the surface was nitrided to a depth of 90 to 260μm depending on the arc current of 6 to 24 A. The concentration of nitrogen in the nitrided layer was approximately 50 mol% at the surface, and the concentration decreased as the distance from the surface increased. A TiN layer was formed at the surface, and beneath the TiN layer, a dual phase layer of TiN and α-Ti was formed. Vickers hardness was approximately 1800 in the TiN layer and it varied from 900 to 200 in the dual phase layer as the distance from the surface increased.

Fabrication of Porous Intermetallic Thick Films by Metallic Powder-Liquid Reaction

We introduce the concept of functional microchannel lining. As an example, we describe the composition and structure of a Ni-Al intermetallic layer lining the inner wall of the microchannel produced by a powder-metallurgical process utilizing microscopic reactive infiltration and/or diffusion. The Ni-Al lining layer is a thick film consists of multiple sub-layers and has a peculiar porous structure, in which long and thin micropores had grown along the thickness direction of the film. In our experiment, a nickel-powder compact containing shaped aluminum wire was sintered at temperatures between the melting points of nickel and aluminum. Molten aluminum migrated into the surrounding nickel powder and reacted with nickel, and thus a microchannel and a Ni-Al intermetallic lining layer were produced. In this process, nickel powder composed the device body, and the aluminum wire gave the shape of the microchannel and act as the aluminum source for the lining layer. Metallographical examinations revealed that both aluminum concentration and voidage in the Ni-Al lining layer show a graded distribution along the thickness direction of the layer. Such a porous structure is appropriate for a catalyst support used for high-temperature reactions.

Solidification Structure and Hardness Distribution in Centrifugally Cast Aluminum Alloy Duplex Pipes

The solidification structure and hardness distribution in aluminum alloy duplex pipes produced by a two-step centrifugal casting have been investigated. In this process, two kinds of molten metals, i.e., the first melt and the second melt with a higher liquidus temperature were cast in sequence at a given interval into a rotating mold of a centrifugal caster. An Al-12mass%Si alloy was used for the first melt, and an Al-30mass%Ni or Al-32mass%Si-0.1mass%P alloy was used for the second melt. The second melt was cast after the solidified shell of the first melt had formed. The resultant cast pipes consisted of an outer side layer and a composite layer containing fine primary crystals. The outer side layer was a portion of the solidified shell of the first melt that survived after the contact with the higher-temperature second melt. The composite layer consisted of one or two layer(s). When the volume of the remelted part of the solidified shell was large, all the second melt mixed into the first melt and the resulted mixed melt formed the composite layer. On the other hand, the composite layer formed only from the second melt when the temperature of the solidified shell was low. In the intermediate case, the composite layer consisted of these two types of the layers.

Structure of Ni-Al intermetallic porous thick films produced by microscopic reactive infiltration

A microchanneling process utilizing microscopic reactive infiltration produces microchannels and alloy lining layers in metal bodies. We examined the composition and structure of a Ni-Al intermetallic lining layer with a peculiar porous structure produced by Ni-Al reactive infiltration. The Ni-Al lining layer is a thick film consists of multiple sub-layers and has many micropores. Such a porous structure and the heat resistance of Ni-Al intermetallic compound are appropriate for a catalyst support in high-temperature use. Image analysis and EPMA revealed that both aluminum concentration and voidage in the Ni-Al lining layer show a graded distribution along the thickness direction of the lining layer.

Swirling Jet Mixing of a Bath Covered With a Top Slag Layer

Mixing of a bath by gas injection is widely used in many engineering fields. In particular, molten iron and steel baths are commonly agitated by Ar gas injection for homogenizing temperature and components and for removing non-metallic inclusions and impurities from molten steel1). In recent years it also finds its applications to parlor wastewater and sludge treatments2).