Papers by Author: Toru Shimizu

Abstract: Already, we developed a high porosity alumina foam. However, alumina has high thermal conductivity about 36W/mK at room temperature, and it need to achieve to high porosity to decrease thermal conductivity to for application of refractory bricks. Therefore, high porosity mullite refractory brick is developed using GS (Gelation of Slurry) method that is already developed for production of high porosity metal foam. Appling this method to production of mullite foams, the ceramics foams from 93 to 97% porosity can be produced. Also, their thermal conductivities are proportional to densities and obey to Ashby-Glicksman model. Its thermal conductivity is about 0.07W/mK when density is 0.1 g/cm3. The high porosity mullite foams achieved enough thermal insulating properties for refractory brick.

Abstract: Spherical powders via gas atomization etc. are recommended for use in SLM, however, the spherical powders are expensive and able to make in limited types of metal materials. Using non-spherical powder in SLM are capable of applying SLM to cheap part production and diversify powder materials for SLM. In this paper, to study the feasibility of using Ti6Al4V milled powder via hydride-dehydride method for SLM, characteristics of powders, powder bed performances, and SLM fabricated samples made from gas atomization powder and milled powder were analyzed and compared. The milled powder which added a fumed silica as a lubricant were also analyzed. In the results, flow and packing characteristics of the milled powder are lower than the gas atomized one. The characteristics of the milled powder are improved by adding fumed silica as lubricant, and had comparable characteristics to the gas atomized one. Microstructure of the SLM fabricated samples has a comparable size and morphology regardless of powders. Hardness of the SLM fabricated sample made from milled powder are larger than that of it made from gas atomized powder, owing to solid solution hardening by oxygen.

Abstract: Metal injection molding (MIM) is capable of mass producing intricately shaped components. In recent years, this technology has been adopted in the electronic, computer, aerospace and medical industries. Titanium alloy (Ti6Al4V) is difficult to process because of its reactive nature and primarily because of problems with carbon and oxygen impurities. Even at low concentration, these interstitials can severely degrade the mechanical properties of titanium and its alloys. The main objective of this study is to develop a sintering condition that would eliminate problems with carbon and oxygen contamination and facilitate binder removal, thus enhance the sintering properties. Ti6Al4V with binder formulation consists of polyethylene (PE), paraffin wax (PW), stearic acid (SA) and palm oil derivatives; palm stearin (PS) were mixed homogeneously and injected to produce green compacts. The binders then were removed and sintering of injection molded material was conducted up to 1200 °C in vacuum atmosphere. The parts sintered at 1150 °C for 8 h exhibited among the highest tensile strength of 921.1 MPa while the elongation, density, porosity and hardness was 6.4%, 4.358 g/cm³, 3.16% and 320 HV respectively. This is the advantageous of additional argon flow during debinding , whereas the physical and mechanical properties were improved due to the impurity gas in argon that had strong effects on the aspects of densification and elimination of pores that turn the powder into a dense solid Ti6Al4V.

Abstract: Metal Injection Moulding (MIM) is an efficient method for high volume production of complex shape components from powders. The purpose of this study is to determine the sintering condition of titanium alloy (Ti6Al4V) tensile shape sample. In high temperature, Ti6Al4V will react with oxygen to form of titanium oxide (TiO₂) which present a problem during sintering thus affected the mechanical properties and microstructure. This reaction can be avoided either by introducing argon gases or in vacuum condition. Ti6Al4V with binder formulation consist of polyethylene (PE), paraffin wax (PW), stearic acid (SA) and palm oil derivatives; palm stearin (PS) were mixed homogenously and injected to produce green compact. The binders then are removed and sintered at 1100 °C for 8 h. During sintering, the debound part is heated, thus allowing densification of the powder into a dense solid with the elimination of pores. It was expected that the impurity gas in argon had strong effects on aspects of the densification and properties. Samples of PE/PS formulation with argon added to the sintering atmosphere, experience density of 4.375g/cm₃ and tensile strength stated at 1000.100MPa compared to samples in vacuum condition which do not show any significant increment with density of 3.943g/cm₃ and tensile strength at 325.976MPa. PE/PW/SA samples of vacuum condition also show no improvement in sintered properties. However with additional argon flow the density can reach until 4.359g /cm₃ and 940.823MPa of tensile strength. Ti-alloy sintered in argon exhibited better densification rate than in vacuum with high strength, better elongation and lower porosity. In argon, the powder particles became interconnected signifying densification was achieved due of non-reactive properties of inert gases that prevent undesirable chemical reactions from taking place.

Abstract: Metallic closed cellular materials containing polymer were fabricated by the penetrating polymer into metal foam. The aluminum and stainless steel foams were selected for the metal foam and epoxy resin and polyurethane resin were selected for the penetrated polymer. The many kinds of mechanical properties of this material were measured. The results of the compressive tests show that these materials have different stress-strain curves among the specimens that containing different materials in the cells. Also, this metallic closed cellular materials containing polymer have higher compressive strength, higher Young’s modules, higher energy absorption and higher internal friction than that of metallic closed cellular material without any polymer.

Abstract: Machined AZ31 alloy chips were consolidated by hot-pressing and then hot-extrusion at 300 °C, and their workability was evaluated. The consolidated sample has a fully dense microstructure with fine equiaxed grains. The　compression and backward extrusion tests reveal that the consolidated AZ31 chips have a good workability at above 200°C.　It is said that the recycled AZ31 alloy by hot-extrusion of the chips is suitable for forging materials and the process is useful for the recycling of Mg chips.

Abstract: Site-selective growth of multi-walled carbon nanotubes (MWCNTs) from an iron oxide nanoparticle catalyst patterned by drying-mediated self-assembly technique is present. The ethanol solution of the iron nitrate was employed as catalyst precursor. The catalyst precursor was mounted on silicon wafer by dip-coating. After evaporation of solvent at room temperature, the catalyst pattern formed. The catalyst pattern was employed to synthesize carbon nanotube pattern by chemical vapor deposition of ethanol vapor after oxidation of iron nitrate. The patterned array of MWCNTs was obtained with a dot size of around 5 'm and the distance of about 25 'm. The present method offers a simple and cost-effective method to grow carbon nanotubes with self-assembled patterns.

Abstract: A simple thermal chemical vapor deposition (STCVD) growth technique of multi-walled carbon nanotubes (MWCNTs) is present. Carbon nanotube film was synthesized on the Pt plate substrates by pyrolysis of ethyl alcohol as carbon source at lower reaction temperature at atmospheric pressure by using simple apparatus. The as-synthesized MWCNTs were characterized by both scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The electrical property of an individual MWCNT was evaluated by I-V measurement. The electrical resistance of single MWCNT is about 450 k/ in linear region under bias voltage between 2 to 4 V. It can undergo a large current of 6 2A at 4 V

Abstract: In order to meet the requirements of various applications, considerable efforts have been focused on the new approaches for synthesizing carbon nanotubes. Recently, simple thermal chemical vapor deposition growth technique by pyrolyzing ethyl alcohol has been developed. However, this method needs metallic catalyst. Here, we demonstrate that it is possible to synthesize multi-walled carbon nanotubes without the aid of any catalyst. The as-synthesized products were analyzed by high-resolution transmission electron microscopy (HRTEM). The HRTEM images show that the products are straight multi-walled carbon nanotubes. The synthesis technique of carbon nanotubes is cost-effective because of the catalyst-free process.

Abstract: Already, we are developing the process to produce stainless steel foam over 97% porosity using hydro-gel binder. However, this process is very sensitive process, and foaming condition is affected by the slight deference of heating temperature. Therefore, we tried to improve the process by changing the foaming agent and foaming conditions. By the improvement of the process, the foaming operation becomes stable and finer cell size stainless steel foam can be obtained.