Papers by Author: Daisuke Yonekura

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Authors: Satoshi Fukui, Riichi Murakami, Daisuke Yonekura
Abstract: Four point bending fatigue tests were carried out using martensitic stainless steel with TiN film deposited at five different deposition rates by dynamic ion mixing process in order to investigate the influence of deposition rate on the fatigue strength. As a result, the fatigue limit clearly increased by the deposition at appropriate conditions. However, the deposition by other conditions resulted in the degradation of fatigue strength. This is caused by the decrease of threshold stress intensity factor after TiN deposition and the difference of defect distribution in the film. In addition, the crack propagation rate was increased in low stress intensity factor range by the deposition of TiN film.
1875
Authors: Hiroshi Yamakawa, Nu Yan, Daisuke Yonekura, Riichi Murakami
Abstract: The design of small-sized single pass boilers is usually based on the construction code for small-sized boilers, in Japan. Design methods in this construction code and other country codes have not been clearly defined, although most of small-sized boiler’s headers are constructed from two concentric circular shells and cover plates. Therefore, Finite Element Analysis (FEA) with a PC and measurement by strain gauges are mainly used in strength design of these boilers. A T type welded joint of SS400 was adopted for the header of small-sized single pass boilers was studied. The stress concentration was evaluated by the FEA, and S-N curves were re-drawn using maximum elastic stress, Ktσmax.
2057
Authors: Riichi Murakami, Katsuhiro Fujikawa, Daisuke Yonekura
Abstract: Stainless steel is widely used as a corrosion-resistant material. However, stainless steel corrodes at high temperature (573 K ~) due to the oxidization and grain boundary corrosion. To delay the oxidation at high temperature, coating of gas barrier film will be useful method. The purpose of this study is to improve the corrosion-resistant of SUS304 at high temperature by coating transparent SiOxNy film which has gas barrier properties. In addition, the influence of inlet gas mass flow rate ratio (N2/Ar+N2) on the oxidation properties at 773 K was examined. The SiOxNy films were deposited onto polished SUS304 by unbalanced dc magnetron sputtering apparatus. To examine the oxygen transmission rate (OTR) of SiOxNy films, PET was also used as substrate. The results showed that good OTR was obtained for N2/Ar+N2 < 0.12 on PET substrate. The similar tendency was obtained for SUS304 deposited film heated up to 773 K.
1879
Authors: Daisuke Yonekura, Huriyzju Fukuda, Riichi Murakami
Abstract: Three point bending fatigue tests were carried out to investigate the influence of bias voltage on fatigue behavior of medium carbon steel with chromium nitride film. The substrate material of the specimens was JIS S45C medium carbon steel. The chromium nitride films were coated at two different bias voltages (VB = -20V, -300V) for fatigue test by arc ion plating method. As a result, the fatigue limit was improved by coating at low bias voltage, while the fatigue limit of high bias voltage samples decreased by coating. In order to clarify the difference between high and low bias voltages, the tensile test was performed using the coated specimens. For this test, the chromium nitride films were deposited at four different bias voltages. It was found the cracking behavior clearly changed between -40V and -80V. For low bias voltage samples, short cracks were initiated in the films, while the long cracks were initiated at same strain for high bias voltage samples. These differences between low and high bias voltage sample may be due to the elastic modulus of the film and droplets distribution in the film.
275
Authors: Daisuke Yonekura, Yuta Fujie, Hayato Nishii, Hiroshi Yamakawa, Riichi Murakami
Abstract: Tension-tension fatigue tests were performed to examine the influence of post drawing heat treatment on the fatigue properties of drawn specific steel tube (STB340) for small-sized single pass boiler. The untreated, as-drawn and post drawing heat treated series were prepared for fatigue tests. The hardness, grain size and residual stress were measured for each series. As a result, the change of grain size and residual stress was small after post heat treatment. The drawn series was softened by post heat treatment but the hardness was still higher than untreated samples. The fatigue strength of the as-drawn and the post drawing heat treated series was higher than that of untreated series. In addition, the difference of endurance limit was small between as-drawn and post drawing heat treated series.
109
Authors: Daisuke Yonekura, Tomoyuki Ishikawa, Riichi Murakami
Abstract: Scratch tests were carried out to examine the influence of gas pressure during ion bombarding on adhesion between CrN coatings and aluminum alloy using nitrogen and argon gas. The critical load clearly increased with increasing the nitrogen gas pressure. However, argon gas pressure hardly affected the critical load. The result of SIMS showed that ion bombardment in nitrogen gas generated high Cr content layer at the aluminum substrate surface and the Cr content increased with increasing the pressure. The ion bombardment in argon gas generated low Cr content surface layer and the pressure hardly affected the critical load. Thus, the high Cr content layer by ion bombardment in the high nitrogen pressure improved adhesion between CrN coatings and aluminum alloy
1887
Authors: Nu Yan, I. Lee, Riichi Murakami, Daisuke Yonekura, J. Sun, Satoshi Fukui
Abstract: The effect of plasma radical nitriding treatment on fatigue properties of SCM435 steel in super long life region was investigated. Fatigue tests were carried out using a dual-spindle rotating bending fatigue-testing machine at room temperature in air for the specimens nitrided at 773 K and 823 K for 3 hrs. The fatigue strength of nitrided specimen was greater than that of un-nitrided specimen and the crack initiation mode changed from the surface cracking of un-nitrided specimen to the subsurface cracking of nitrided specimen. Hardening layer and compressive residual stress were formed by nitriding, which resulted in the improvement of the fatigue strength. The stress intensity factor was calculated using facet area in Fish-eye fracture mode. As a result, the stress intensity factor indicated almost constant value, ~ 3-4 MPa·m1/2, regardless of the number of cycles to failure.
266
Authors: Riichi Murakami, Shinichiro Fukui, Daisuke Yonekura, Cheolmun Yim
Abstract: Boron-doped diamonds were deposited by microwave plasma chemical vapor deposition (MPCVD) method in order to investigate the influence of inlet boron concentration on the film properties. The substrate material of the specimens was pure titanium (99.9 %). Boron source was introduced into the vacuum chamber by bubbling of B2O3, acetone and methanol mixture. Samples were produced with different B2O3 concentrations in mixture (1000 ppm, 5000 ppm, and 10000 ppm). The surface morphology of the samples was observed by scanning electron microscope (SEM). X-ray diffraction was used to identify crystal structures of the films. Secondary ion mass spectroscopy was used to examine the qualitative boron contents in the films. For low B2O3 concentrations in liquid mixture (1000 ppm), the surface morphology of the film showed both micro crystalline diamond and nano crystalline diamond. For medium B2O3 concentrations in liquid mixture (5000 ppm), the surface morphology of the film was also consisted of micro crystalline diamond and nano crystalline diamond. However, the content of micro crystalline diamond decreased in comparison with low B2O3 concentration. For high B2O3 concentration in liquid mixture (10000 ppm), the surface morphology of the film was almost dominated by nano crystalline diamond. Therefore, the crystal size of boron doped diamond decreased with increasing boron concentration. From these results, it appears that boron will restrain the growth of diamond crystal during deposition.
1883
Authors: Yukihiro Tokunaga, Nu Yan, Daisuke Yonekura, Riichi Murakami
Abstract: In order to improve the heat transfer efficiency, the fins are commonly used in the industrial boiler in Japan. In actual application, the thermal fatigue due to the cyclic change of temperature usually occurs in the fins. The thermal fatigue tests were carried out by using the thermal fatigue apparatus designed. The designed testing apparatus can apply thermal load to the fin by giving heating and cooling alternatively. The fatigue cracks can be observed in the vicinity of the toe in the thermal fatigue test. The heat transfer coefficient and the thermal stress were calculated by using Finite Element Analysis (FEA) method. The fatigue experiments of the fins were also conducted using electro-hydraulic servo fatigue test machine in the laboratory. The results of thermal fatigue experiments were discussed by comparing with those of the mechanical fatigue experiments.
315
Authors: Riichi Murakami, Daisuke Yonekura, Daisuke Hagihara, Yun Hae Kim, Kiyomi Hirose
1724
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