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Kudamatsu, Japan

Morino K.,Tokuyama College of Technology | Kawagoishi N.,Kagoshima University | Yamane K.,Kohan Kogyo Ltd. | Fukada K.,Kohan Kogyo Ltd.
Key Engineering Materials | Year: 2010

In order to investigate the effect of nitriding on the crack initiation and propagation behavior of Ni-base super alloy, Alloy 718, rotating bending fatigue tests were carried out until 108 cycles at room temperature. By nitriding at 500? for 12h, compound layer of about 5μm in thickness was formed and the initiation of a fatigue crack was strongly suppressed causing the increase in fatigue strength. A crack initiated in brittle manner at the compound layer in all of fractures. However the crack propagated in ductile manner controlled by the property of the base alloy. That is, there is no or little influence of nitriding on the crack growth rate of the alloy. © (2010) Trans Tech Publications, Switzerland. Source


Yamane K.,Kohan Kogyo Ltd. | Morino K.,Tokuyama College of Technology | Kawagoishi N.,Kagoshima University | Fukada K.,Kohan Kogyo Ltd.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2010

Effect of radical nitriding on fatigue strength of Alloy 718 was investigated at room temperature and 500°C under push-pull loading. Nitrided alloy used was with compound layer of 4/mi. Fatigue strength was increased at room temperature by nitriding, though there was no or little difference in fatigue strengths between aged alloy and nitrided one at 500°C. All of fracture occurred from specimen surface in both alloys at room temperature. On the other hand, fracture origins were specimen surface at high stress levels and subsurface at low stress levels in both alloys at 500°C. Surface crack in the aged alloy initiated in ductile manner and the one in nitrided alloy was in brittle manner. The increase in fatigue strength at room temperature was mainly caused by the suppression of crack initiation by compound layer. The reasons for the change in fracture origin from specimen surface to subsurface at 500°C were the suppressions of crack initiation by compound layer in the nitrided alloy and the one of propagation of small crack by oxide induced crack closure effect in the aged alloy. In both of aged and nitrided alloys, fatigue strength at 50Ot was larger than that at room temperature in high cycle region where subsurface fracture occurred. © 2010 The Society of Materials Science,. Source


Yamane K.,Kohan Kogyo Ltd. | Morino K.,Tokuyama College of Technology | Fukada K.,Kohan Kogyo Ltd. | Kawagoishi N.,Kagoshima University
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2010

In order to improve the wear and fatigue properties, radical nitriding was applied to Ni-base superalloy, Alloy 718, which is difficult to nitride at low temperature because of its stable passive film. Nitriding conditions selected were at 500°C∼570°C and for 10h∼20h in consideration of practical application. Compound layers formed by these nitriding conditions were 4μm∼10μm in thickness. By nitriding at higher temperature and for longer time, base alloy was softened, though the thickness of compound layer was increased. Wear properties were improved by the nitriding at both of room temperature and 500°C, especially at room temperature. The improvement of wear properties was caused by surface hardening. Moreover, fatigue strength at room temperature increased. The increase in fatigue strength was mainly caused by suppression of fatigue crack initiation due to compound layer. © 2010 The Society of Materials Science,. Source


Itaya T.,National College of Technology, Suzuka College | Ishida K.,Tokuyama College of Technology | Kubota Y.,Kohan Kogyo Ltd. | Tanaka A.,National Institute of Technology, Ube College | Takehira N.,Tokuyama College of Technology
Progress In Electromagnetics Research M | Year: 2016

To visualize eddy current distribution (ECD) of an arbitrarily shaped coil arranged parallel to a moving conductor slab, an exact theoretical solution is derived using an analytical method based on the double Fourier transform method. The arbitrarily shaped coil is regarded as a plane coil of a single turn, and both DC and AC excitation currents can be applied. Furthermore, ECD charts are obtained when the conductor slab is moving. We calculate some examples with respect to a circular coil, rectangular coil, and triangular coil and show the effect of coil excitation frequency and speed of the conductor on ECDs. Results show that the eddy current generated in the moving conductor slab is composed of current induced by the excitation frequency and conductor speed. © 2016, Electromagnetics Academy. All rights reserved. Source


Yamane K.,Kohan Kogyo Ltd. | Kawagoishi N.,Kagoshima University | Maeda Y.,Kagoshima University | Morino K.,Tokuyama College of Technology | And 2 more authors.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2010

In order to investigate the effect of surface treatment on fatigue properties of martensitic type stainless steel, SUS420J2, rotating bending fatigue tests were carried out using the steels surface-treated by three kinds of conditions. The surface treatments tested were CrN coating, radical nitriding and duplex treatment of CrN coating after the radical nitriding, and the results were discussed in comparison with those of quenched and tempered steel. Fatigue strengths were markedly increased by CrN coating, nitriding and duplex treatment. However, there was no or little effect of CrN coating to nitrided steel on the fatigue strength. Surface fracture yielded in quenched and tempered and CrN coated steels, while fractures occurred from inclusions at the subsurface of specimens in nitrided and duplex treated steels. The growth of an internal crack was suppressed at the boundary of fish eye to the direction to specimen surface by the nitriding in nitrided and duplex treated steels. The ligaments between the fish eye boundary and specimen surface showed a brittle fracture in both steels, especially in duplex treated steel there was a few steps on the ligament meaning the coalescence of cracks initiated from droplets at specimen surface and inclusion in subsurface, independently. © 2010 The Society of Materials Science, Japan. Source

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