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Introduction

Research in the advanced processing laboratory is generally focused on the creation of new metallic materials and also the development of new production processes by active application of the nonequilibrium state of materials.
New metallic materials which have high performance properties such as strength, toughness, thermoelectric property, corrosion resistance, shape memory effect, hydrogen absorbing property, etc., will be developed by applying new production processes which include electromagnetic process, mechanical alloying, pulsed current sintering, semi-solid forming, cold crucible levitation melting, and so on, and also connecting these processes.

In our laboratory, following research projects are under progress.

1. Ultra-refinement of microstructure of metallic materials by micro-explosion
2. Technology for creating amorphous bulky materials (Harmonized characteristics materials)
3. Clarification of alloying mechanism in the mechanical alloying process and development of powder consolidation techniques
4. Advanced forming process of high corrosion resistance iron base alloy
5. Development of high performance composite materials by advancement of powder forming process and its joining technology
6. Development of performance controlling technology with the transformation of amorphous materials
7. Application of intermetallic materials as environmental materials
8. Net-shaping process of intermetallic materials by supercritical degreasing technology

Staff

Recent research activities

1. New structure refinement process of metallic materials by application of electromagnetic vibrations

The aim of this project is to develop the processing technology for ultra-refinement of the microstructure of metallic materials by taking advantage of the micro-explosion phenomenon. Micro-explosion occurs in a molten metal when micro-cavities made by a strong electromagnetic vibration or an ultrasonic wave are squashed. When a molten metal is solidified in the presence of micro-cavities, the primary crystal is broken into ultra-fine pieces by the shock wave made by micro-explosion and thus the dimension of the final crystals in the solidified metal is greatly reduced. Advanced metals with much better mechanical and functional properties will be created with this technique, which reduces the grain size by one or two orders compared with the present materials.

a: conventional solidification	b: solidification under electromagentic vibration (micro-explosion)
Effect of micro-explosion on the microstructure of primary Si crystals in Al-17mass%Si alloy.

2. Synthesis of fine nonequilibrium powder of magnesium alloy by mechanical alloying process and consolidation of it.

Applications of magnesium alloys are expanding as lightweight metallic materials, but have some problems on strength and corrosion resistance as compared with aluminum alloys. To improve their properties, nonequilibrium powder is synthesized and consolidated by a pulsed current sintering process.
Magnesium is a soft material and it is difficult to synthesize its powder by mechanical alloying process. It has been clarified that the fine powder can be synthesized by addition of boron element. Bulk materials including nonequilibrium phase have been produced by pulsed current sintering of mechanically alloyed powder under a pressure of 500MPa at 423K. This bulky materials of nonequilibrium magnesium alloy have an improved corrosion resistance.

Bulky materials of nonequilibrium magnesium alloy.	X-ray diffraction pattern and thermal analysis curve (DSC) of bulky nonequilibrium magnesium alloy.

3. Preparation of high performance thermoelectric materials

Conventional thermoelectric materials are prepared by using rare metals such as Bi, Te, Pb and so on. They are insuitable for commercial use on the point of resources. So, the intermetallic compound, Mg₂Si which is well known as a thermoelectric material has been tried to be synthesized with rich resources, magnesium and silicon. But magnesium is an active and dangerous element because of easy combustion. This compound has never been developed actively as a thermoelectric material.
Mixture of nonequilibrium magnesium and silicon powders have been synthesized by using a mechanical alloying apparatus under the inert gas atomosphere. This mixture powder has been consolidated under 400MPa by pulsed current sintering process to get nearly Mg₂Si single phase bulk.

Mg2Si thermoelectric material consolidated by pulsed current sintering process.	X-ray diffraction pattern of Mg2Si thermoelectric material consolidated by pulsed current sintering process.

4. Blended elemental powder semisolid forming on intermetallic compounds

The so-called blended elemental powder semisolid forming method is shown in the following figure schematically. Firstly, powders with high and low melting points are mixed primary. Then, the blended mixture is heated up to a slurry state because of lower melting point of the powder,thereafter, the slurry is filled into a metal mold and loaded under pressure to form the green compact. Finally, the compact is alloying heat treated and intermetallic compound part is obtained.

The advantages of the method are as follows:

1. It can facilitate the forming processes of intermetallic compounds which are extremely difficult when using a casting or forging method.
2. Even for high activity metals such as titanium or magnesium, it is possible to form in the air.
3. This is an energy-saving process because of the low forming tempera- ture that is near the lower melting point of the mixed powders.

However, pores are often found in the microstructures of parts fabricated by this method. This problem might be the big researching theme in this field.