Takekazu Nagae

Mechanical properties of a ZrC-dispersed Mo alloy processed by mechanical alloying and spark plasma sintering

A ZrC particle-dispersed Mo processed by mechanical alloying showed much higher strength than a recrystallized pure Mo at room temperature and showed a large elongation of 180% at 1970 K. These excellent properties of the particle-dispersed Mo are attributed to a very small grain size of 3 μm.

Electron Beam Surface Modification of Cobalt Chrome Molybdenum Alloy Formed by a Laminate Molding Method

We used electron beam irradiation on a laminate molded Co-Cr-Mo bulk alloy to reduce the surface roughness and increase hardness. The accelerating voltage and beam current were 40 kV and 0.5~5.0 mA, respectively. Irradiation time for each dot was 0.1 ms and the distance between dots (dot pitch) was either 0.2 or 0.4 mm, which corresponded to a scanning speed of 200 or 400 mm/s, respectively. The roughness value, Ra, decreased to 0.3~0.45 m for a beam current of 1 mA and a dot pitch of 0.02 mm. The coarse grains present in the base alloy were refined to sizes of less than 1m by rapid solidification. An increase in the Knoop hardness from 470 HK for the base metal to about 550 HK was achieved by this technique.

PULSE CURRENT PRESSURE SINTERING OF AL/AL 2 O 3 FUNCTIONALLY GRADED MATERIAL

To fabricate densified Al/Al 2 O 3 functionally graded materials (FGM) on hardness and thermal expansion, a pulse current pressure sintering process was employed. This FGM consists of an aluminum layer, an α-Al 2 O 3 layer and seven intermediate layers between the two outermost layers. Aluminum and Al(OH) 3 powders were used as starting materials. Al(OH) 3 powder transformed into several types of Al 2 O 3 after the sintering process. The hardness of the intermediate layers gradually increased in proportion to the volume fraction of γ-Al 2 O 3 . The top layer, which consists of a-Al 2 O 3 , was about 1000 HV on average and 1500 HV at the surface.

PULSED ELECTRIC-CURRENT PRESS BONDING OF ALUMINUM ALLOY TO STAINLESS STEEL

A Pulsed Electric-Current Press (PECP) bonding process which is a new joining process using a spark plasma sintering apparatus was applied for dissimilar material joining between Al-Mg alloy (JIS A5056) and austenitic stainless steel (JIS SUS304) at the bonding temperatures of 673 to 773K with the holding times up to 1.8ks. The bonding pressures were 49 and 80MPa. No obvious reaction layer in the bonding interface was detected by at 673K. A small amount of FeAl 3 was formed as an intermetallic compound at the bonding interface at 723K, and Fe 2 Al 5 became appeared in the reaction layer as well as FeAl 3 over 748K. The thickness of the reaction layer increased with increasing the holding temperature and time. The tensile strengths of the joints at 673K with pressure of 80MPa showed the highest values, 140MPa. The tensile strength of joints decreased with increasing the thickness of the reaction layer.

Surface Modification of Cobalt Chrome Molybdenum Cast Alloy by Electron Beam Irradiation

We irradiated the surface of a Co-Cr-Mo cast alloy plate with an electron beam in order to increase the surface hardness. An accelerating voltage of 40 kV and a current of 1~10 mA of the irradiated electron beam were used. The irradiation time for a single dot was 0.1 ms and the distance between dots (dot pitch) was 0.2 mm, corresponding to a scanning speed of 200 mm/s. A fine cellular structure was obtained by irradiating a low current electron beam. When a high current electron beam (more than 8 mA) was used for the irradiation, fine granular carbides were synthesized. The Vickers hardness of the base metal of 410 HV was increased to about 480~530 HV by the electron beam irradiation.

Deformation Characteristics in AlphaType Brass Worked by Torsion

In present work, bar samples of pure copper and Cu-Zn alpha single phase alloys setting 20mm in diameter and 150mm in length processed by torsion in the rotation speed to 1rpm every 60° twist angles. Then, deformed samples were researched microstructure and their characteristics. Microstructures of non-deformation samples were isometric, however, deformed samples streaky. Elements of bar drawn 10×10mm mesh were developed parallelogram. It was trend angle of between stretchable direction in microstructures and torsion axis increased more torsion angles. It was coincident with between the angle and deformed direction of microstructures. Shear strain was calculated by twist angle by theoretical formula. Their value corresponded rough with measurement from mesh variation. Pure copper and Cu-Zn alpha phase alloys were similar deformation microstructure, but fracture twist angle in copper was more than Cu-Zn alloys, and it was trend fracture angle had decreased as concentration of Zn increased. This trend was difference of fracture elongation obtained in tensile test.

Detection and Identification of the Latent Microorganisms in the Corrosion Layers of Ancient Bronze Mirrors

On an ancient bronze mirror, we carried out a scanning electron microscopic (SEM) examination of fractured corrosion layers, a biological microscopic observation of a gram-stained sample and DNA analyses of the samples removed from corroded sites. From these scientific and technical researches, we obtained the following results. Fine particles about 2 μm in length were confirmed in the corrosion layer by the SEM observation. Microorganisms of the same size were observed in the gram-stained sample removed from the corrosion layer through a biological microscope. From these results, fine particles observed under the SEM should be considered as microorganisms. A lot of fine particles were confirmed especially in the corroded sites by the SEM observation. So (certain kinds of) microorganisms may have played a role in the corrosion (deterioration) of the ancient bronze mirrors while the mirrors were buried in soil. From the base sequences obtained by DGGE analysis, two kinds of microorganisms were confirmed to exist in the corrosion layer of the ancient bronze mirror. One is 97.4% homologous to the 16S rDNA of the uncultured bacterium (Accession number: AY 053488). It was also highly homologous to the sequence derived from the 16S rDNA of the Xanthomonadaceae family such as Stenotrophomonas and Xanthomona. That is, the sequence is derived from a strain belonging to the Xanthomonadaceae family. The other base sequence is 97.4% homologous to the 16S rDNA of the Bacteroidales order such as uncultured Bacteroidales bacterium (Accession number: AY 859647). That is, the sequence is derived from a strain belonging to the Bacteroidales order. Genes of microorganisms, presumed to belong to the Acetobacter, Gluconacetobacter genuses and Fe(III)-reducing bacterium, Shewanella algae were detected from the base sequence analysis by cloning. From the results above, microbial activity is assumed to be high around the ancient bronze mirrors. The corrosion mechanism of bronze mirrors seems complicated, but a several types of microbes which possibly corrode bronze mirrors were verified.

Materials Investigation and Study on the Production Techniques of Chinese Ancient Iron Mirrors

The number of ancient iron mirrors excavated in China is far smaller than those of ancient bronze mirrors. Fortunately, we were honored to have a chance to analyze some of the rare ancient iron mirrors excavated in China. Un-corroded parts were subjected to a structural observation under an optical microscope and a chemical composition analysis with EPMA (Electron Probe Micro Analyzer). Based on the results, the production techniques of the ancient iron mirrors were discussed. The results were as follows. 1. The iron mirror produced during the later Han Period showed a mixture of ferrite and pearlite particles. The possibility that the iron mirror was made by forging small pieces of pig iron, which process accompanied decarburization, can be inferred. Traces of silicon and phosphorous were found as impurities in the uncorroded alloy. 2. The iron mirror excavated from the tomb of the Sui period showed the structure of single-phase ferrite. It is inferred to be made by forging wrought iron which had been decarburized enough. Traces of silicon, phosphorous and sulfur were found as impurities in the uncorroded alloy.

Formation and Magnetic Properties of Fe-6.5% Si-Oxides Composite Powders by Mechanical Alloying

SYNOPSIS Fe-Si-ZrO2 composite powders were prepared by mechanical alloying using vibrating ball mill under Ar atmosphere. The magnetic properties and thermal stability for Fe-Si-Zr02 composite powders were investigated by mesns of VSM, DSC and X-ray diffraction. The addition of Si increased the coercivities, He for Fe-ZrO2 composite powders as much as 130-150% of those for the powders without Si against expectation. On the other hand, X-ray diffraction patterns for annealed sample showed that the addition of Si supress the precipitation of ZrO2 from Fe matrix and the coarsening of crystallite size. These results are thought to be due to the lameller structure of Si in Fe matrix.