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Volume 76, Issue 12
Displaying 1-5 of 5 articles from this issue
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Regular Article
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Etsuo Takeuchi, Masao Hayakawa, Saburo Matsuoka2012 Volume 76 Issue 12 Pages 647-652
Published: 2012
Released on J-STAGE: December 01, 2012
JOURNAL FREE ACCESSCarbon steels with high resistance to hydrogen-assisted fatigue crack growth were successfully produced by addition of a carbide forming element and refinement of ferrite grain size. In carbon steels containing vanadium (V), titanium (Ti) or niobium (Nb), fine carbide (VC, TiC or NbC) precipitation and the refinement of grain size below 1 μm was achieved by caliber rolling at 833 K. In standard JIS-S45C carbon steel, hydrogen charging increased the fatigue crack growth rate to about 25 times that of non-charged steel. In contrast, for carbon steels containing carbide forming elements, the hydrogen-assisted fatigue crack growth was either absent or at most two times as fast as that of non-charged steels.
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Naohito Morita, Noriharu Yodoshi, Rui Yamada, Akira Kawasaki2012 Volume 76 Issue 12 Pages 653-660
Published: 2012
Released on J-STAGE: December 01, 2012
JOURNAL FREE ACCESSIn a previous paper we reported that slightly pressurized liquid phase sintering permits to fabricate fully dense Fe-based metallic glass composites, that the phase content of dual phase structure can be controlled by pressure squeezing of the liquid phase, and that the fracture strength increases with an increase in solid phase volume fraction. Throughout the process the pore shape at the contact of the particles, and accordingly the shape of the liquid phase at the particle contacts, were found to keep a cusp-shaped morphology, which implies and guarantees a complete penetration of the molten alloy into the pore space. In the present study, a model experiment was employed using a mono-sized spherical Fe-based metallic glassy powder to show an advantage of the present process for the fully dense composite structure and for the control of the composition of the two phase structure. Two types of experiments were conducted; one is pressure infiltration in which hot pressed solid skeleton was impregnated with a molten alloy, and the other is a squeezing liquid phase sintering, in which a mixture of the solid metallic glass powder and a liquid-phase alloy powder was hot pressed to control the relative density and the content of the liquid phase by squeezing out the molten alloy. The squeezing liquid phase sintering was found to give fully dense compacts, compared to the solid sintering of the metallic glass powder, which gives the relative density of 97.5% at most. An incomplete penetration of molten alloy into the dense preform and also the formation of peripheral pores near the die wall in the case of the infiltration process are discussed.
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Toshifumi Yamamoto, Yohei Katayama, Masanori Suzuki, Shigeru Katsuyama ...2012 Volume 76 Issue 12 Pages 661-668
Published: 2012
Released on J-STAGE: December 01, 2012
JOURNAL FREE ACCESSIt has been found that metals and semiconductors with high surface asperity readily absorb sunlight. In our previous work, iron and copper substrates with porous surface layers were prepared by redox treatment. The metal substrates with porous surface layers absorbed more light of ultraviolet-visible-infrared wavelength than those with flat surfaces. In the present study, we attempt to enhance the light absorption properties of ceramic materials made from blast furnace slag, using needle-shaped hydrate crystals formed on the surface of the slag compact by hydrothermal reaction. Under the hydrothermal conditions used, blast furnace slag particles react with highly pressurized water to form a hydrate glass phase containing H2O, and form needle- or plate-shaped hydrate crystals such as Tobermorite (5CaO•6SiO2•5H2O) between original slag particles and on the surface of the slag compact. The slag compact with needle-like crystals on its surface absorbed ultraviolet-visible-infrared light more poorly than that with a flat surface. However, after the surface of slag compact was coated with metal, the sample with needle- or plate-shaped hydrate crystals on its surface absorbed light significantly better than that with a flat surface, exceeding 90% over ultraviolet-visible-infrared wavelengths.
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Yohei Sakakibara, Kyohei Nomura, Keiji Kubushiro, Hiroki Yoshizawa2012 Volume 76 Issue 12 Pages 669-676
Published: 2012
Released on J-STAGE: December 01, 2012
JOURNAL FREE ACCESSMisorientation in austenitic stainless steels (Type316NG, Type304NG, KASUS304J1HTB) and nickel base alloy (Alloy690TT) was measured by Electron back scatter diffraction (EBSD). Kernel Average Misoirientation (KAM) values were calculated for each material and their calculated pitch dependency were consistent with the theory in the range of smaller plastic strain and the shorter calculated pitch. However, constant β, which is plastic strain and measured pitch dependency in KAM values for Alloy690TT was lower than those for austenitic stainless steels. For the misorientation gradient scatters in austenitic stainless steels, on the other hand, the gradient doesn't scatter in Alloy690TT. It suggests that continuous precipitates on grain boundary in Alloy690TT make grains uniformly when plastic strain was applied. Grain Orientation Spread (GOS) that is one of calculation methods of EBSD was also calculated and the plastic strain dependency was confirmed. Constant β derived from the dependency of GOS shows the approximately same values in austenitic stainless steels and Alloy690TT.
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Ken Takata, Jun Takahashi, Makoto Saga, Kohsaku Ushioda, Akira Hibino, ...2012 Volume 76 Issue 12 Pages 677-683
Published: 2012
Released on J-STAGE: December 01, 2012
JOURNAL FREE ACCESSThe change of the state of Mg-Si cluster with aging time at 303 K and 323 K after pre-aging at 363 K was studied by means of tensile test focusing on yield stress, 3DAP (3 Dimensional Atom Probe) and DSC (Differential Scanning Calorimetry) measurement. Mg-Si clusters formed during isothermal aging at the temperature of 363 K after solution treatment were different from the ones formed at the temperatures of 303 K and 323 K. During aging at 303 K and 323 K following pre-aging at 363 K, the cluster that was once formed at 363 K grew in size together with the new nucleation of another type of cluster formed at 303 K and 323 K. The increment of yield stress with aging time at 303 K and 323 K after pre-aging at 363 K was greater than the one without pre-aging at 363 K. This was considered to stem from the fact that the cluster formed during pre-aging at 363 K further grows during aging at 303 K and 323 K but at the same time the another type of cluster is supposed to newly nucleate and grow at 303 K or 323 K after pre-aging, both of which are inferred to contribute to the larger increase in yield strength.
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