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Volume 36, Issue 7
Displaying 1-11 of 11 articles from this issue
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Hidenori Kuroki, Motoyoshi Yokoyama1989 Volume 36 Issue 7 Pages 813-818
Published: October 09, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe dimensional change during bonding and the transverse rupture strength of joints of iron powder compacts were investigated. Most compacts were 10 mm regular cubes produced by pressing a reduced-ore powder with 0.7 mass% of zinc stearate as a lubricant under 600 MPa, and sintered and bonded at 1130°C for 35 min in a single cycle heating process in hydrogen. Some were sintered at 1130°C for 60 min before bonding.
During bonding of green compacts on the pressed faces, the shrinkage increased in the pressing direction of bonding, while the expansion increased in the perpendicular one, with increase in the bonding pressure. The joint area and the transverse rupture strength increased with increasing bonding pressure in the low pressure range.
During bonding of green compacts on the side faces, the shrinkage increased in the pressing direction of bonding, while the expansion increased in the perpendicular one, with increase in the bonding pressure. And the width of microcracks perpendicular to the pressing direction which had originally existed in green compacts grew larger. It caused a remarkable expansion in the pressing direction and a decrease of the transverse rupture strength.
During bonding of sintered compacts on the side faces, the microcracks did not grow larger and the transverse rupture strength increased with increase in the bonding pressure.View full abstractDownload PDF (3527K) -
Tadayuki Fujii, Ken-ichi Okamoto1989 Volume 36 Issue 7 Pages 819-823
Published: October 09, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSIn order to understand in detail the secondary recrystallization behaviour of rolled tungsten sheet doped with CaO and/or MgO, the effect of dopants on the secondary grain growth behavior was investigated using EPMA and chemical analyses.
It was found that the doping elements (CaO and/or MgO) play an important role in the grain growth of the hot-rolled tungsten, initially restraining growth in the fine-grained primary recrystallized matrix and subsequently promoting the abnormal grain growth of the secondary grain at higher temperatures. Consequently a large-scale single crystal sheet can easily be obtained from a hot-rolled tungsten sheet doped with CaO and/or MgO. Moreover, the temperature at which secondary recrystallization commences on the hotrolled sheet is strongly dependent on the kinds of dopant and is correspondent to their dissociation temperatures. Chemical and EPMA analyses indicate that the particles consisting of CaO and/or MgO are observed much more frequently at the primary grain boundaries than the matrices and survive at high temperatures just below the secondary recrystallization temperature. Those results may be closely related to the dissociation and dissolution mechanisms of the dopants on the secondary grain growth in the hot-rolled tungsten sheet.View full abstractDownload PDF (1897K) -
Masatomo Kamada, Kunio Hanata, Youichi Tokunaga1989 Volume 36 Issue 7 Pages 824-830
Published: October 09, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe ferritic grains of SUS410L powder compacts with high green density abnormally grew during vacuum sintering at 1250°C. After the sintering, the size of super coarse grains reached to a few millimeter. In the cast and wrought SUS410L steels, the grain growth started as soon as they were held at high temperature, but in sintered steels, there was the incubation period for grain growth.
In order to explain the process of this abnormal grain growth, an expression based on Zener's equation was proposed.
fz=c(p/r'⋅an)
where fz is the restraining force for boundary migration by pore, p is the porosity, r' is the radius of the sphere which has the same volume of actual angular pore, a is the pore shape factor (a≤1) and c and n are the constants. As the sintering proceeds, the fz gradually decreases because the p decreases by densitication, r' increases by Ostwald ripening of pores and a approaches to 1 by spheroidization of pores. Therefore, some grains start to grow against the fz and result in forming the super coarse grains.View full abstractDownload PDF (8120K) -
Shigeru Ito, Kuniaki Miyazaki, Noboru Yoneda, Kazuo Asaka1989 Volume 36 Issue 7 Pages 831-836
Published: October 09, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSFe-SiC composite was prepared by HIP technique. Although iron is easy to react with SiC at high temperature, the reaction was successfully controlled below 6% under the hipping conditions of 800-900°C, 50-200 MPa and 30 min. Furthermore, dense and pore free composites with the compositions of Fe-5 wt%SiC and Fe-25 wt%SiC were obtained at 800 and 900°C, applying 50-200 MPa and 200 MPa, respectively. The reaction layer between Fe and SiC was about 3 μm in thick, according to the EPMA observation of the cross section of the composite. The Fe-SiC composite exhibited an excellent wear resistance, which was improved with hipping pressures.View full abstractDownload PDF (2101K) -
Teruo Takahashi, Yasuhiko Hashimoto, Koichiro Koyama1989 Volume 36 Issue 7 Pages 837-841
Published: October 09, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSTo prepare a TiC-dispersion-strengthened copper, the mixtures of pure electrolytic Cu, pure Ti and graphite powders as starting materials were mechanically alloyed for 72.0 ks in argon atmosphere. The solid solution or ultra fine grained mixture of the Cu-Ti-C system obtained was heat-treated in vacuo in the temperature range of 873-1273 K for 3.6 ks. Very fine TiC particles precipitated by this heat-treatment. The mean particle size of TiC precipitates became slightly larger with the increase of heat-treatment temperature such as 5-10 nm at 1073 K, and 10-30 nm at 1273 K. The TiC-dispersion-strengthened coppers having up to 4.13 vol% TiC did not separate the Cu dhase from the Cu-TiC alloys by the heat-treatment below the temperature of 1273 K. The separation of Cu phase in Cu-10.00 vol%TiC alloy hardly took place by the heat-treatment up to the temperature of 1073 K, so that the TiC-dispersion-strengthened copper was excellent in thermal stability. The hardness values of them after heat-treatment were higher than those of Cu-Al2O3 alloy having the same volume percentage of dispersoid particles.View full abstractDownload PDF (4380K) -
Tetsuo Kato, Katsushi Kusaka1989 Volume 36 Issue 7 Pages 842-847
Published: October 09, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe objective of this work is mainly to elucidate the potential of TiAl type P/M alloys for higher temperature structural applications. TiAl alloys containing B-0.05% or Si-3% were previously reported to have a good combination of mechanical properties at high temperature. Therefore the high temperature oxidation behavior of TiAl alloys containing Si and B was investigated in this study.
The results were summarized as follows:
(1) Oxidation of TiAl type alloys substantially begins at 900°C or less, fairly sensitive to its alloying elements. Its oxidation resistance was increased by Si-addition up to 4.6% and decreased by B-addition of a few hundred ppm.
(2) Si-addition to TiAl alloy leads to less weight gain in the hot air of the range 1000-1100°C, mainly due to the protective alumina-like oxide formed on the surface layer.
(3) Siliconizing using the pack-cementation process improved the oxidation resistance of TiAl alloy by more than five times, probably relevant to the protective effect of stable silicides.View full abstractDownload PDF (4185K) -
Kazuhiko Majima, Kyotaro Amafuji, Shuhei Maeda, Hiroshi Nagai, Keiichi ...1989 Volume 36 Issue 7 Pages 848-852
Published: October 09, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSStatic tensile properties of as HIP'ed Ti-Fe alloys using Hunter process sponge fines or hydride-dehidride Kroll process sponge fines were studied, and metallographic and fractographic observations were also carried out by the back scattered electron image and scanning electron microscope.
Despite the low level of oxygen content, the HIP'ed Ti-4 Fe specimen using Hunter Process sponge fines as titanium source showed poorer ductility than the HIP'ed Ti-4 Fe specimen using hydride-dehydride Kroll process sponge fines of high oxygen content as titanium source, and brittle fracture appearance was observed in a part of the specimen using Hunter process sponge fines.
All of the HIP'ed Ti-(2, 3, 4, 5) Fe specimens using hydride-dehydride Kroll process sponge fines showed the dimple pattern on the fracture surfaces after the tensile test.View full abstractDownload PDF (7102K) -
Kazuhiko Majima, Kyotaro Amafuji, Mistumasa Yamamoto, Hiroshi Nagai, K ...1989 Volume 36 Issue 7 Pages 853-858
Published: October 09, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSIn this experiment, the corrosion behavior of the HIP'ed Ti-4Fe alloy was studied by investigating the polarization curve in the physiological salt solution at 310 K or in 1N-HCl solution at 333 K in comparison with the HIP'ed Ti-6Al-4 V and the HIP'ed Ti-5Al-2.5 Fe alloys which are considered as the promising candidate for the implant material.
All of the three kinds of specimens were not attacked in the physiological salt solution. The Ti-4 Fe specimen was not attacked even in the 1N-HCl solution, while the localized attack was observed on both the Ti-6Al-4 V and Ti-5Al-2.5 Fe specimens. It was recognized by SEM and EPMA that the α grain has been preferentially attacked and Al content decreased in the localized attack region.View full abstractDownload PDF (5174K) -
Tsutomu Yamamoto, Makoto Asano, Kazuo Ueno, Nobuyuki Tamari1989 Volume 36 Issue 7 Pages 859-864
Published: October 09, 1989
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSAl2O3 composites reinforced with (0-40)mass% SiC whisker were prepared at a temperature range 1673 K-2123 K for 3.6 ks under 40 MPa by hot-pressing and the effects of pretreatment process of SiC whisker and SiC whisker content on the mechanical properties of the composites were mainly investigated. The toughening mechanism of Al2O3 by addition of SiC whisker was also discussed.
The results obtained were summarized as follows: The bending strength of the Al2O3-30 mass% SiC whisker composites with SiC whisker pretreated by ultrasonic disperser and filtration was remarkably improved comparing with that of the composites with untreated SiC whisker, then it showing about 1 GPa. The desification temperature to get full density of each composite increased with SiC whisker content. The SiC whisker in the composites was preferentially aligned in normal direction to the hot-pressing axis and the directional dependence of the mechanical properties was observed. The mechanical properties at room temperature and the failure resistance of the composites with pretreated SiC whisker increased with SiC whisker content. The toughening mechanism of Al2O3 by the addition of SiC whisker was considered to be due to the increase of fracture energy generating suppression against crack growth and crack deflection.View full abstractDownload PDF (3067K) -
Fatigue crack growth characteristics and life prediction of Si3N4Makoto Nishi, Kanji Ueda, Tadaaki Sugita1989 Volume 36 Issue 7 Pages 865-869
Published: October 09, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThis paper describes the fatigue crack growth characteristics of Si3N4 in cyclic three point bending test which is required in the reliability evaluation and prediction of the life of ceramic component. Extensive crack growth is observed prior to the final fracture during cyclic loading. It is confirmed that Si3N4 exhibits a linear relationship on logarithmic scale between the fatigue crack growth rate and the stress intensity factor range. Statistical characteristics of the crack growth parameters m, C and fatigue fracture toughness value Kf, are discussed based on goodness-of-fit test for three types of distribution functions of normal, Weibull and Type I extreme value, and these variables are found to fit Weibull distribution best. It is found that the estimated life of Si3N4 components decreases with increasing stress range and initial crack length and with decreasing fracture probability.View full abstractDownload PDF (1558K) -
Nobujiro Tsuchiya, Masahide Fukuda, Tsuyoshi Nakai, Hisashi Suzuki1989 Volume 36 Issue 7 Pages 870-874
Published: October 09, 1989
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe transverse-rupture strength and hardness of WC-βt-16 vol%%Co alloy were mainly studied as a function of βt content (βt=commercially available WC-TiC-TaC triple carbide). Specimens were in vacuum sintered and subsequently HIP-ed at 1623 K.
It was found that the flaky structures enriched with βt appeared generally in the structure of this alloy system and they acted as a fracture source. The structure was caused by the agglomerated flaky powders which developed during ball-milling. The sharp increase in the strength was observed in particular in the alloy having 27-50 vol% βt in carbides, when the alloy with no flaky structure was prepared by an adequate way. The strength and hardness of WC-βt-Co alloy were considered to obey the law of mixture held between WC-Co and βt-Co alloys.View full abstractDownload PDF (3079K)
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