Tetsuichi Motegi

The extraction of Nd from waste Nd–Fe–B alloys by the glass slag method

We report the use of molten slag materials to extract neodymium from waste Nd–Fe–B magnets. X-Ray diffraction and EPMA studies revealed that the Nd–Fe–B alloys produced by the glass slag method using boron trioxide consisted of α-Fe and Fe2B phases. No Nd-containing phase such as the Nd2Fe14B phase and the Nd oxide phase was found in the resultant alloys. The chemical analyses confirmed that the Nd content in the Nd–Fe–B alloys produced by the glass slag method was less than 0.01 wt.% Nd. On the other hand, the slag materials contained a large amount of neodymium. The Nd in the Nd–Fe–B alloys was successfully extracted by the glass slag method using boron trioxide.

Effect of minor elements on grain size of Mg-9%Al alloy

The Influence of minor elements, such as Be. Zr, Fe and Mn. on grain size and grain-refining effect of Mg-9%Al alloy was investigated by use of high-purity Mg-9%Al alloy (high-purity alloy). This high-purity alloy was prepared from distilled pure magnesium and 99.99% commercial aluminum. Given amounts of Be. Zr, Fe and Mn were then added Microscopic examination clarified that these elements have grain coarsening action for natural fine-grained high-purity alloys, and the grain refinement by superheating was possible as long as the alloy grain was coarsened by Fe or Mn addition EPMA analysis revealed the existence of some species of aluminum carbide in high-purity alloy Fe-Al-C-O and Mn-Al-C-O compounds were also obscrved in allovs coarsc-grained by Fe or Mn addition Existence of aluminum carbide and its change were probably associated with the grain size of the Mg-9%Al alloy.

Production of Nd-Fe-B alloys by the glass slag method

The microstructures of the Nd–Fe–B alloy with the stoichiometric composition of Nd2Fe14B produced by the glass slag method were investigated. The Nd–Fe–B melts in the molten slag materials such as lead silicate glass, soda-lime glass, and Pyrex glass experienced a large undercooling over 160 K below solidification. When the Nd–Fe–B melts were solidified either in the molten lead silicate glass or in the molten soda-lime glass, the resultant Nd–Fe–B alloys had coarse dendrites of α-Fe phase together with grains of Nd2F14B. On the other hand, the Nd–Fe–B alloys exhibited columnar dendrite grains of Nd2Fe14B phase when the Nd–Fe–B melts were solidified in the molten Pyrex glass.

Clarification of Grain Refining Mechanisms of Superheat-Treated Mg-Al-Zn Alloy Castings

We performed two experiments to clarify the grain-refining mechanisms of Mg-Al system alloys by superheat treatment of molten alloys. Numerous Al 4 C 3 nucleants were formed in the molten commercial-purity alloy of AZ91 by superheat treatment. The high-purity alloy was made of 99.99% Mg and 99.999% Al. Grain refinement occurred without superheat treatment. A small amount of impurity carbon included in the pure Mg and Al reacted with Al to form Al 4 C 3 compounds. Carbon is an important element for grain refining of commercial-purity AZ91 alloy. Pure carbon powder with an argon gas carrier was therefore blown into the molten AZ91 alloy instead of harmful C 2 Cl 6 . Numerous Al 4 C 3 nucleants were formed in the molten alloy.

Magnetic properties of Nd–Fe binary alloys produced by a metallic mold casting method

Nd–Fe binary alloys with the composition of Fe–23 at. % Nd (∼Nd5Fe17) and Fe–80 at. % Nd (the eutectic composition) were produced by the metallic mold casting method. The microstructures and magnetic properties of the resultant cylindrical specimens with 1–5 mm in diameter and 50 mm in length were investigated. The cylindrical specimens of Fe–23 at. % Nd alloy consisted of Nd and Nd2Fe17 phases together with a small amount of Nd5Fe17 phase. The coercivity of the cylindrical specimens was as low as the original alloy ingot. On the other hand, the cylindrical specimens of Fe–80 at. % Nd alloy consisted mainly of Nd and Nd5Fe17 phases and showed a high coercivity over 5 kOe. It was found that the coercivity was dependent on the grain size of the cylindrical specimens produced by the metallic mold casting method.

Effects of cooling rate on microstructures and magnetic properties of Nd–Fe–B alloys

Abstract The microstructures and magnetic properties of Nd–Fe–B alloys produced by rapid solidification processing techniques were examined by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and in a vibrating sample magnetometer. Two rapid solidification processing techniques, metallic mold casting and melt-spinning, were used to investigate the influences of cooling rates on the microstructure and magnetic properties of the Nd–Fe–B alloys. The Nd–Fe–B alloys had equiaxed Nd 2 Fe 14 B grains together with α-Fe dendrites when produced by the metallic mold casting technique with moderately high cooling rates (3.3×10 2 to 1.2×10 3 K s −1 ). The Nd–Fe–B alloys had fine equiaxed Nd 2 Fe 14 B grains with or without amorphous phase when produced by the melt-spinning technique with high cooling rates (4.3×10 5 K s −1 to 1.5×10 6 K s −1 ). The relationships among the cooling rate, microstructure, and coercivity of the Nd–Fe–B alloys were determined.

Solidification behavior in undercooled Nd–Fe–B alloys

The solidification behavior of Nd–Fe–B undercooled melts with the stoichiometric composition of Nd2Fe14B was studied. The melts experienced a large undercooling of 180 K during static furnace cooling. The resultant alloy ingots consisted of fragmented dendritic iron phase together with the Nd2Fe14B phase. However, quenching the undercooled melts at various undercooling levels significantly changed the resultant microstructures. Nd–Fe–B alloy ingots with columnar Nd2Fe14B phase were obtained by quenching the melts with an undercooling of 50 K.

Influence of mixing in liquid on unidirectional solidification rate in transparent organic alloy

Abstract In the transparent organic crystal known as succinonitrile-acetone binary alloy, transient behavior of unidirectional solidification is directly observed within the range where the planar interface is stable, by means of a microscopic interferometer. Interface morphology and solidification rates are obtained by bright-field observations. Interference fringes are used to determine the gradient of the temperature and of the solute concentration in the liquid ahead of the solid-liquid interface. Although the solidification direction is taken such that the thermal convection is suppressed, experimental data on solidification rates and concentration gradients agree well with numerical values based not on the diffusion-controlled model, but on the boundary layer model which assumes fluid mixing beyond the boundary layer. One of the reasons why fluid mixing occurs is thought to be the thermosolutal convection induced by the concentration gradient built up ahead of the solid-liquid interface. Thickness of the boundary layer estimated from experimental data of solidification rates agrees quantitatively with those obtained from interference fringes and from tracer analysis.

Internal stress superplasticity in anisotropic polycrystalline materials

A theoretical model of internal stress superplasticity is developed in a single-phase polycrystalline material with an anisotropic thermal expansion. Quasi-steady-state creep equation during a thermal cycle is derived quantitatively based on continuum micromechanics. The model assumes that the generated mismatch strain is accommodated simultaneously by the plastic flow of the material. The linear creep deformation, which corresponds to internal stress superplasticity, is obtained at low applied stress region, and the creep rate depends on the crystallographic texture of the material. The validity of the model is experimentally verified using polycrystalline zinc which is a typical metal having large anisotropy in thermal expansion. The calculated strain rates using the texture information and the isothermal creep equation agree quantitatively well with the experimental results. The apparent activation energy of thermal cycling creep reveals 1/n (n: stress exponent of isothermal creep) of that of isothermal creep, which is one of the characteristics of internal stress superplasticity. Except for the factors attributable to the material geometry, the thermal cycling creep equation in the polycrystalline material is identical to that in a metal matrix composite.

Extraction of Rare Earth from La–Ni Alloys by the Glass Slag Method

The use of the glass slag method in the extraction of rare earth from La-Ni alloys was studied. X-ray diffraction and electron probe microanalysis studies revealed that the La-Ni alloys produced by the glass slag method using boron trioxide consisted of Ni and Ni 3 B phases. No La-containing phase such as the LaNi 5 phase and the La oxide phase was found in the resultant alloys. The chemical analyses confirmed that the La content in the alloys produced by the glass slag method was very limited. However, the glass slag materials contained a large amount of lanthanum. The La in the La-Ni alloys was successfully extracted by the glass slag method using boron trioxide.