Published papers

© 2018 The Japan Institute of Metals and Materials. In this study, a diffusion layer of Cr was formed on the surface of a carbon steel by atmospheric-controlled induction heating fine particle peening (AIH-FPP) treatment, followed by coating of a diamond-like carbon (DLC) film in an attempt to provide a less expensive and facile method for the production of DLC-coated steels with superior adhesion to conventional methods. Frictional wear tests and indentation tests with Vickers indenter were conducted on these DLC-coated steel specimens, and adhesion to the substrate was investigated experimentally. It was revealed that the formation of a Cr diffused layer on the surface of the substrate by AIH-FPP treatment significantly improved the adhesion of the DLC film to the substrate under a sliding load and a large plastic deformation. In addition, frictional wear tests revealed that the thickness of the Cr diffused layer formed by AIH-FPP treatment has a significant influence on the adhesion of the DLC film to the substrate. A thicker Cr diffused layer with a thickness of about 100 µm imparted better adhesion of the DLC film to the base material, and the superior friction and wear characteristics of the DLC film were sustained up to 49000 wear cycles while the specimens with a Cr diffused layer thickness of about 40 µm and without a Cr diffused layer maintained low friction coefficients up to 36000 and 8000 wear cycles, respectively. These results suggest that the proposed film forming method with a Cr diffused layer formed by AIH-FPP treatment is superior to the conventional method and is very efficient as a technique to improve the adhesion of DLC films to a carbon steel substrate.

© 2017 Atmospheric-controlled induction-heating fine particle peening (AIH-FPP) using Cr and Mo shot particles in a N2 atmosphere was introduced to improve the electrochemical characteristics of AISI 316 austenitic stainless steel. The surface microstructure of the AIH-FPP-treated specimen was characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). AIH-FPP can be used to form transferred and diffused layers of shot particles on the surface of austenitic stainless steel. The thickness of the diffusion layers of Cr shot particles tended to increase with the heating time in the AIH-FPP process, whereas the Cr concentration at the surface tended to decrease. Electrochemical polarization tests were performed in 3 wt% NaCl + H2SO4 and 20 wt% NaCl environments at 343 K using a three-electrode electrochemical cell connected to a computer driven potentiostat to examine the corrosion resistance of austenitic stainless steel treated with AIH-FPP. The pitting potential of the AIH-FPP-treated specimen was higher than that of the untreated specimen. In particular, there was clear improvement in the pitting potential of austenitic stainless steel by AIH-FPP with Cr shot particles following peening with Mo shot particles. AIH-FPP using Cr and Mo shot particles in a N2 atmosphere is an effective method of improving the electrochemical characteristics of austenitic stainless steel.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. In this paper, we study a process for modifying the surface microtopography of the Ti oxide layer using a nanosecond-pulsed laser (NPL). Even now, the mechanism by which hydroxyl groups are generated on the titanium surface treated by NPL is not clear. Hence, we evaluated the surface properties of the NPL defocus distances on pure titanium surfaces, and investigated the relationship between the generation of hydroxyapatites/cell viability and the titanium surface characteristics. The NPL defocus distance was varied from 0 to 4 mm. Defocus distances of 0 and 2 mm generated microtopographical features on the titanium surface, and the resulting surfaces exhibited a greater density of OH groups than the surface treated with a defocus distance of 4 mm. The surfaces treated using defocus distances of 0 and 2 mm were found to be coated with microspherical hydroxyapatite composed of coexisting plate- and needle-like crystals after immersion in simulated body fluid, and alkaline phosphatase activity assays indicated improved cell compatibility. The improvements in biocompatibility and cell compatibility were due to the pocket-like microtopographical structures formed along the processing trace. These pockets contained a large amount of OH groups, and promoted the growth of hydroxyapatite. [Figure not available: see fulltext.].

© 2019 A modified surface layer was fabricated on Ti–6Al–4V samples by gliding arc discharge plasma assisted with an oxygen jet gas under atmospheric conditions. The oxidation reaction on the sample surface was promoted by active species with strong oxidising performance, such as oxygen and hydroxyl radicals. An amorphous titanium oxide layer was detected on the generated surface. The oxygen diffusion layer penetrated the substrate to an approximate depth of 500 nm. The generated surface exhibited higher biological cell adhesiveness and a lower elution amount of metal ions than the untreated sample surface.

Gas blow induction heating (GBIH) nitriding was carried out for Ti–6Al–4V alloy at different temperatures, and its effect on surface characteristics, wear resistance and fatigue properties was investigated. The microstructures of the specimen surface were characterized using optical microscopy, laser microscopy, X-ray diffraction, micro-Vickers hardness tester, and nano-indentation tester. It was found that the surface characteristics of titanium alloy varied with increasing the treatment temperature of GBIH-nitriding. In this study, a nitrogen diffusion layer was formed on the titanium alloy surface GBIH-nitrided at 1073 ​K. A nitrogen compound layer and diffusion layer were created at the treatment temperature of 1173 ​K, which suppressed the wear loss to under one tenth that of the substrate. In order to examine the fatigue properties of the treated alloy, fatigue tests under four-point bending were performed. The fatigue strength of the Ti–6Al–4V alloy GBIH-nitrided at 1173 ​K was 234 ​MPa lower than that of the mirror-polished alloy. The decrease in the fatigue strength is due to the formation of the compound layer with a Young's modulus approximately twice that of the substrate, and the grain coarsening from 7 ​μm to 300 ​μm. The results indicate that a thick nitrided layer with high hardness and the close Young's modulus to the substrate improved the fatigue strength of the Ti–6Al–4V alloy.

© 2020, Fuji Technology Press. All rights reserved. Titanium alloys are widely used for the hard tissue substitute implants. However, it is necessary to improve interfacial biocompatibility to reduce adhesion period. For improvement of biocompatibility of Ti-6Al-4V ELI alloys, texture and chemical composition on contact part with biological tissue play very important roles. In this research, micro texture was generated on the Ti-6Al-4V ELI alloy surfaces utilizing laser irradiation, in order to improve biocompatibility. The biocompatibility was evaluated by osteoblast cell culture assays. The results indicated the surface having micro texture improve biocompatibility as com-pared with untreated surface. This was considered in order the fact that the formed modified surface had hydrophilicity, thereby improving the cell compatibility, and the cell adhesion due to the complicated shape. In addition, mist of glycerophosphoric acid calcium aqueous solution was applied on the laser irradiated area. As result, micro texture including Ca and P elements was generated on the Ti-6Al-4V ELI alloy surfaces. When laser was irradiated, glycerophosphoric acid calcium aqueous solution was applied as mist flowed on the test pieces as droplet. The velocity of droplet fluid was relatively fast, so that laser irradiation was unhindered access to the surface of test pieces and the treatment was stable. In order to estimate biocompatibility, culture assays using osteoblast cells were conducted on the treated surface having micro texture including Ca and P elements. As results, it was clearly that biocompatibility of the specimen treated by laser with glycerophosphoric acid calcium aqueous solution mist more improved than either untreated specimen or treated specimen soaked in glycerophos-phoric acid calcium aqueous solution.

© 2018 The Japan Institute of Metals and Materials New biomaterials were fabricated by sintering powders of commercially pure titanium（CP-Ti）and partially-stabilized zirconia （PSZ）. The Ti/PSZ composites with different mass fraction of PSZ were consolidated by spark plasma sintering（SPS）at 1173 K and 1373 K. The microstructures of composites were characterized using a scanning electron microscope（SEM）, an energy dispersive X-ray spectrometer（EDS）, X-ray photoelectron spectroscopy（XPS）and an X-ray diffraction（XRD）. Vickers hardness tests, reciprocating wear tests, fracture toughness measurements, cell culture tests and electrochemical polarization tests were conducted to discuss their capability for biomaterials as a slide member. The composites with high wear resistance were achieved by sintering at 1373 K with high mass fraction of PSZ; however, fracture toughness showed low value. In contrast, the composites sintered at relatively low temperature of 1173 K with low mass fraction of PSZ showed high wear resistance and fracture toughness. Furthermore, electrochemical characteristics and biocompatibility of composites sintered at 1173 K tended to improve as the mass fraction of PSZ decreased.

In order to increase the surface hardness and improve the tribological properties of stainless steel, Fe–Al intermetallic compound layers were created by atmospheric-controlled induction-heating fine particle peening (AIH-FPP). The surface microstructure of the stainless steel treated with AIH-FPP was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and micro-Vickers hardness testing. In addition, the tribological properties were investigated by reciprocating ball-on-disk wear tests. When high-speed steel particles coated with thin aluminum layers were used as the shot particles, Fe–Al intermetallic compound layers were formed at the surfaces of the stainless steel with increased heating time during AIH-FPP. This is because aluminum was transferred from the shot particles, and the temperature at the treated surface increased as a result of a combustion synthesis reaction. When the heating temperature after FPP was increased, the transferred aluminum and nitrogen in the atmosphere reacted, which resulted in the formation of aluminum nitrides in addition to Fe–Al intermetallic compounds. The tribological properties of the stainless steel were improved by AIH-FPP since high-hardness layers were created. The results indicate that the formation of an Fe–Al intermetallic compound layer with high hardness by AIH-FPP is effective for modifying the tribological properties of the stainless steel within a relatively short span of time.

In order to fabricate a titanium alloy with superior wear resistance and fatigue strength, fine particle peening (FPP) was introduced as a post-treatment after gas blow induction heating (GBIH) nitriding. The surface characteristics of the treated alloy were examined using X-ray diffraction, scanning electron microscopy, laser microscopy and a micro-Vickers hardness tester. GBIH nitriding and post-treatment with FPP formed nitrided layers with high hardness and compressive residual stress at the surface of the alloy within a short period of time. This is due to the diffusion of nitrogen atoms during GBIH nitriding and plastic deformation of the surface layer during FPP. Reciprocating ball-on-disk wear tests were performed to investigate the wear resistance of the surface-treated alloy. The wear resistance of the titanium alloy was improved by the proposed surface treatment compared with samples that were only polished or FPP-treated. This is due to the presence of a nitrogen compound layer with high hardness at the surface. The abrasiveness toward the wear test counter material was also decreased by the combined surface treatment.

Hyperthermia has been studied as a noninvasive cancer treatment. Cancer cells show stronger thermal cytotoxicity than normal cells, which is exploited in hyperthermia. However, the absence of methods evaluating the thermal cytotoxicity in cells prevents the development of hyperthermia. To investigate the thermal cytotoxicity, culture temperature should be regulated. We, thus, developed a culture system regulating culture temperature immediately and accurately by employing metallic culture vessels. Michigan Cancer Foundation-7 cells and normal human dermal fibroblasts were used for models of cancer and normal cells. The findings showed cancer cells showed stronger thermal cytotoxicity than normal cells, which is quantitatively different from previous reports. This difference might be due to regulated culture temperature. The thermal stimulus condition (43 °C/30 min) was, further, focused for assays. The mRNA expression involving apoptosis changed dramatically in cancer cells, indicating the strong apoptotic trend. In contrast, the mRNA expression of heat shock protein (HSP) of normal cells upon the thermal stimulus was stronger than cancer cells. Furthermore, exclusively in normal cells, HSP localization to nucleus was confirmed. These movement of HSP confer thermotolerance to cells, which is consistent with the different thermal cytotoxicity between cancer and normal cells. In summary, our developed system can be used to develop hyperthermia treatment.

Titanium alloys are widely used for the hard tissue substitute implants. However, it is necessary to improve interfacial biocompatibility for reduce adhesion period. For improvement of biocompatibility of titanium alloys, texture and chemical composition on contact part with biological tissue play very important roles. In this research, mist of glycerophosphoric acid calcium aqueous solution was applied on the laser irradiated area. As result, micro texture including Ca and P elements was generated on the Ti-6Al-4V-ELI alloys surfaces. When laser was irradiated, glycerophosphoric acid calcium aqueous solution applied as mist flowed on the test pieces as droplet. The velocity of droplet fluid was relatively fast, so that laser irradiation was unhindered access to the surface of specimens and the treatment was stable. In order to estimate biocompatibility of treated surfaces having micro texture with Ca and P element, culture assays using osteoblast cells were conducted. As result, it was clearly that biocompatibility of the specimen treated by laser with glycerophosphoric acid calcium aqueous solution mist more improved than treated specimen soaked in glycerophosphoric acid calcium aqueous solution.

© 2020 Society of Materials Science Japan. All rights reserved. In this study, a rapid oxynitriding technique based on induction heating was developed for the titanium alloy Ti-6Al-4V, and its effects on surface characteristics of the alloy were investigated. The surface microstructures of the alloy were characterized by employing a scanning electron microscope, electron back-scatter diffraction, X-ray diffraction and nano-indentation tests. Induction-heating in air for 60 s caused the formation of a hardened layer on the Ti-6Al-4V alloy surface, which can be attributed to the diffusion of oxygen and nitrogen atoms. When water quenching was performed after heating, transformation to an acicular martensitic α’ phase occurred, resulting in increased in substrate hardness. However, cracks were initiated at the surface of the oxynitrided alloy. The cracks were eliminated through fine particle bombarding treatment, whereas the hardened layer formed by the oxynitriding treatment remained. The obtained results thus indicate that the oxynitriding technique developed in this study can enhance the wear resistance and tensile strength of the Ti-6Al-4V alloy within a short period of time.