高井 健一

Degradation property of aluminum due to hydrogen is studied. Hydrogen is introduced by electrolysis charge in aqueous solution with addition of 0.1 mass % NH4SCN as a hydrogen recombination poison. The amount of hydrogen and its existing state in the material is analyzed by hydrogen desorption curves measured by the thermal desorption spectroscopy. The hydrogen desorption curves of charged aluminum showed two peaks, one at less than 100 °C and the other around 400 °C. The existing state of hydrogen relate to each peaks are identified as weakly trapped solute hydrogen to vacancy and free hydrogen molecule located in cavities that exists in the bulk of the material. Tensile properties are obtained to determine degradation property of the material due to hydrogen. The effect of hydrogen on degradation of charged aluminum is analyzed in terms of interaction between hydrogen and vacancy or dislocation. Solute hydrogen and cavities are found to affect ductility of aluminum, whereas hydrogen molecule in cavities has no effect. © 2008 Materials Research Society.

Hydrogen absorbed during corrosion causes the environmental degradation of mechanical properties. The principal factor causing the degradation was investigated using Inconel 625 as an face-centered-cubic (fcc) metal and pure iron as a body-centered-cubic (bee) metal to clarify the role of hydrogen. When Inconel 625 with zero hydrogen content was subjected to a strain of up to 0.02, the stress was relieved, and the specimens was then charged by hydrogen, the hydrogen content was 20 mass ppm. In contrast, when the Inconel 625 containing hydrogen was subjected to a strain of up to 0.20, the stress was relieved, and the specimen was charged by hydrogen, the hydrogen content was 29 mass ppm. A similar tendency was observed for pure iron. These results suggest that both hydrogen and strain induce the formation of lattice defects in metals. To identify the type of lattice defect causing hydrogen degradation, various mechanical tests were conducted by the slow strain rate technique (SSRT). The ductility did not recover when the Inconel 625 containing hydrogen was subjected to a strain of up to 0.02, the stress was relieved, the specimens was maintained at 30 degrees C to release all the hydrogen, and stress was applied again. In contrast the ductility completely recovered when the Inconel 625 containing hydrogen was subjected to a strain of up to 0.02, the stress was relieved, the specimen was maintained at 200 degrees C to release all the hydrogen, and stress was reapplied. A similar tendency was observed for pure iron. These results suggest that the principal factor causing hydrogen degradation is the formation of vacancies and vacancy clusters induced by hydrogen and strain, since maintaining the specimens at 200 degrees C results in the annihilation of vacancies and vacancy clusters.

We have developed a numerical model to simulate the hydrogen desorption profiles for pure iron and eutectoid steel, which is obtained in thermal desorption analysis (TDA). Our model incorporates the equation of McNabb and Foster without the hydrogen diffusion term combined with the Oriani's local equilibrium theory. It is found that the present numerical model successfully simulates the hydrogen desorption profile both for pure iron and for eutectoid steel. We further verify the model by discussing the trapping site concentration and the effect of hydrogen diffusion.

Hydrogen-fuel-cell vehicles have been developed and the gaseous pressure in the current major storage tanks of the vehicles varies from 35 to 70 MPa because of the demand for the increase in running distance. Hydrogen refueling stations are required to be resistant to 100 MPa hydrogen gas and the alloys used for such stations are required to have an excellent resistance to hydrogen environment embrittlement (HEE). The purposes of the present study are to substitute the high-pressure gaseous charge of hydrogen by electrolysis charge and to evaluate hydrogen degradation susceptibilities for Inconel 625 and SUS 316L in the environments substituted by electrolysis charge. Electrolysis hydrogen was charged to Inconel 625 and SUS 316L at various electrolysis fugacities and gaseous hydrogen was charged from 0.3 to 45 MPa hydrogen gas at 90°C. Hydrogen states and contents were compared using thermal desorption analysis (TDA). Hydrogen degradation susceptibilities were evaluated using the slow strain rate technique (SSRT) at a constant extension rate of 8.6×10-6 /s at room temperature. The fundamental properties of thermal hydrogen desorption for Inconel 625 and SUS 316L were first analyzed to compare the hydrogen states after hydrogen charge by electrolysis and high pressure. The peak temperatures and profiles of hydrogen desorption do not change with charging temperature. When hydrogen is charged by electrolysis and high pressure until hydrogen saturation at 90°C, the peak temperatures and profiles are the same in both environments. This means that hydrogen diffusion during and hydrogen states after hydrogen absorption are independent of charging method in spite of the differences in adsorption and dissociation reaction on the specimen surfaces. Using Sieverts law, the fugacity of electrolysis can transform into gaseous pressure. This indicates that high-pressure hydrogen environments in pipes or other components at hydrogen refueling stations can be substituted by electrolysis charge. Fracture strain in Inconel 625 decreases as hydrogen content charged by electrolysis increases, whereas that in SUS 316L does not change regardless of the hydrogen content of 161.5 mass ppm. Grain boundary fracture is observed on the surface of Inconel 625 absorbing a hydrogen content of 27.5 mass ppm, which corresponds to 59.2 MPa hydrogen gas at R.T using Sieverts law. In contrast, the fracture surfaces of SUS 316L hydrogen-charged at extremely high fugacities remain ductile dimples. Thus, hydrogen degradation susceptibility is much lower for SUS 316L than for Inconel 625. Copyright © 2006 by ASME.

A calcium phosphate compound (Hydroxyapatite) has similar composition and crystal structure to an organism bone. Except an absorbent calcium phosphate compound, the composition that resembled apatite and a deposit having configuration generate it on the surface of apatite ceramic in vivo. In other words apatite ceramics does an organism bone and direct bonding through an apatite deposit without causing negativism. Generally this function is named bioactivity. These functions can inhibit ionic elution, roosting, wear and fretting occurring in metal biomaterial, and be extremely important from a point of view to use in vivo. However, ceramics material is extremely inferior in mechanical properties in comparison with metal material. Therefore, an application to locus accompanied by high load is difficult. It is used as bone filling material such as shank or body of vertebra under the present conditions. In other words low load is applied to locus to be accompanied by. Therefore, static load than cyclic load is important when longterm use was considered. However, bioactivity ability of apatite ceramic material and relation of mechanical properties were not clarified. A fatigue characteristic in consideration of organism environment is particularly unclear. Furthermore, it is necessary to evaluate a fatigue characteristic and crack propagation behavior when micro structure changes by apatite and chemical reaction with body fluid. This study, a static fatigue characteristic of apatite ceramics in simulated body fluid environment was examined.

Biocompatible materials, such as bioactive ceramics and bioactive glasses can be effective in the repair of bone defects during orthopaedics surgery. These materials have been found by observation to exhibit varying degrees of osteoconductive behavior. The hydroxyapatite ceramics and bioactive glass ceramics was known as a highly bioactive ceramics, and replacements of lost bone. However, it is to be inferior to a fracture characteristic in a weak point of apatite ceramics. In the present study, surface structural changes of apatite ceramics with the bioactive function and mechanical property in simulated body fluid were investigated. Sub-micrometer hydroxyapatite ceramics powder was used as starting materials for making hydroxyapatite ceramics. Pressure less sintering was preformed at 1300℃ in O_2 atmosphere using the pre-sintered bodies. Fracture resistance (K_Q) was evaluated by ASTM E399-90 method. And also, fracture resistance tests were performed using compact tension specimens. It has been confirmed by SEM observation, thin-film X-ray diffraction matter and FT-IR reflection spectroscopy that the apatite layer can be reproduced on the surface of the hydroxyapatite ceramic even in a cellular simulated body fluid with ion concentrations nearly equal to those of human blood plasma. As a result, corrosion degradation of hydroxyapatite ceramics were preferentially recognized on hydroxyapatite particle after short time immersion into simulated body fluid. The general tendency of drastic decrease in fracture resistance was recognized in these materials. The fracture resistance of the specimen was found to decrease with increasing corrosion degradation, especially after Sweeks immersion in simulated body fluid. This remarkable degradation in fracture resistance is considered to be caused by crack propagation through corroded pit. However, the specimens after 4weeks immersion into simulated body fluid showed improved fracture resistance compared with those of corroded hydroxyapatite ceramics. There improvements in fracture resistance may be brought about through the mechanics was shown to induce the apatite layer formation on it's surface in some areas between 4 and Sweeks by simulated body fluid.

Metals are by far the oldest materials used in surgical procedures. Titanium alloys are hoped to be used much more for applications as implant materials in the orthopedic and dental medical fields because of their mechanical properties, such as biocompatibility, corrosion resistance and specific strength compared with other metallic implant materials. The performance of any biomedical material is controlled by two characteristics, biofunctionality and biocompatibility. Biofunctionality defines the ability of the device to perform the required function, whereas biocompatibility determines the compatibility of the material with the body. This biocompatibility is improved by coating the surface in contact with living tissues with calcium phosphates, specially hydroxyapatite. Some of the new implants utilize titanium alloys substructure coated with a thin layer of calcium phosphates ceramics, hydroxyapatite, or the plasma spray technique. Hydroxyapatite coating are designed to produce a bioactive surface promoting bone growth and inducing a direct bond between the implant and the hard tissues. The titanium metal also forms the bone like apatite layer on its surface in simulated body fluid, when it has been previously treated with NaOH aqueous solution to form a sodium titanium hydro gel layer on its surface. In the present study, surface structural changes of Ti-6Al-4V alloys with the alkali treatments and mechanical property in simulated body fluid were investigated. Thus it is expected that alkali treated titanium alloys could also form the bone like apatite layer on its surface in the living body and bond to living bone through the apatite layer. Studies have demonstrated that the bone bonding ability of titanium alloys could be evaluated by testing the titanium alloys in a simulated body fluid. In test results of with apatite coating specimens extremely higher fracture strength, compared with monolithic Ti-6Al-4V alloys whose fracture strength was 60MPa・m^<1/2>. For apatite coating Ti-6Al-4V alloys the general tendencies in the fracture strength depending upon apatite coating were understood as follows. With apatite coating Ti-6Al-4V alloys it is recognized that speculated that this tight bond might be attributed to a graded interface structure between the apatite layer and the substrates.

Interaction between fatigue damage and hydrogen is the concern of the present study. The susceptibility of a high-strength martensitic steel to delayed fracture has been examined using as-heat-treated and pre-fatigued specimens. The pre-fatigued specimens showed a tendency to fail earlier, but annealing the pre-fatigued specimens at 200 degreesC recovered nearly all of the delayed fracture life. Production of point defects during fatigue was detected by means of hydrogen thermal desorption analysis (TDA), using hydrogen as a probe of defects. Hydrogen absorption capacity increased in fatigued specimens, but it was reduced to the level of the as-heat-treated specimens when fatigued specimens were annealed at 200 degreesC, implying that increased hydrogen-trapping defects, presumably vacancies, were produced during fatigue. Hydrogen TDA peak profiles showed alterations that imply agglomeration of vacancies associated with an increase in fatigue cycles. The involvement of vacancies created during fatigue in the enhanced delayed fracture is consistent with a model that proposes strain-induced vacancies and their agglomeration are the primary mechanism of hydrogen-related failure. (C) 2002 Elsevier Science B.V. All rights reserved.

Hydrogen in trapping states innocuous to environmental degradation of the mechanical properties of high-strength steels has been separated and extracted using thermal desorption analysis (TDA) and slow strain rate test (SSRT). The high-strength steel occluding only hydrogen desorbed at low temperature (peak 1), as determined by TDA, decreases in maximum stress and plastic elongation with increasing occlusion time of peak 1 hydrogen. Thus the trapping state of peak 1 hydrogen is directly associated with environmental degradation. The trap activation energy for peak 1 hydrogen is 23.4 kJ/mol, so the peak 1 hydrogen corresponds to weaker binding states and diffusible states at room temperature, In contrast, the high-strength steel occluding only hydrogen desorbed at high temperature (peak 2), by TDA, maintains the maximum stress and plastic elongation in spite of an increasing content of peak 2 hydrogen, This result indicates that the peak 2 hydrogen trapping state is innocuous to environmental degradation, even though the steel occludes a large amount of peak 2 hydrogen, The trap activation energy for peak 2 hydrogen is 65.0 kJ/mol, which indicates a stronger binding state and nondiffusibility at room temperature. The trap activation energy :or peak 2 hydrogen suggests that the driving force energy required for stress-induced diffusion during elastic and plastic deformation, and the energy required for hydrogen dragging by dislocation mobility during plastic deformation are lower than the binding energy between hydrogen and trapping sites. The peak 2 hydrogen, therefore, is believed to not accumulate in front of the crack tip and to not cause environmental degradation in spite of being present in amounts as high as 2.9 mass ppm,

The distribution and desorption processes of hydrogen and deuterium have been visualized by secondary ion mass spectrometry (SIMS). The present article deals with four principal points: (1) visualizing the hydrogen distribution, (2) visualizing the hydrogen desorption process from each metallurgical microstructure under various holding times at 25 degreesC, (3) visualizing the hydrogen desorption process during heating, and (4) determining the correspondence between desorption profiles and desorption sites. A spheroidal graphite cast iron specimen was prepared for visualizing hydrogen, since it consists of basic microstructures of steels such as ferrite and pearlite. Hydrogen and deuterium were occluded into the cast iron. The amount of hydrogen and the existing states of hydrogen in the cast iron were analyzed by thermal desorption spectrometry (TDS). The TDS analyses show that the hydrogen desorption has two peaks, namely, the low- and high-temperature peaks corresponding to trap activation energies of 21.6 and 105.8 kJ/mol, respectively. The SIMS analyses of the specimen cooled after heating to 100 degreesC, 200 degreesC, and 300 T reveal that the hydrogen desorbs from the ferrite after heating to 100 degreesC, from the pearlite and the interfaces between the ferrite and the graphite after heating to 200 degreesC, and from the pearlite after heating to 300 degreesC. The graphite remains, trapping hydrogen after heating to 300 degreesC. On the basis of TDS and SIMS results, the relationship between the desorption profile and desorption sites was identified; that is, the low-temperature peak corresponds to ferrite, pearlite, and graphite/ferrite interfaces, while the high-temperature peak corresponds to graphite.

The mechanism for fatigue failure in extremely high cycle fatigue in the regime of N > 10^7 is studied on a bearing steel, JIS SUJ2. Special focus was given to the fracture morphology in the vicinity of fracture origin (subsurface non-metallic inclusion) of a heat treated bearing steel (Specimen QT). The particular morphology looks dark during optical microscopic observation. Specimens with short fatigue life of the order of N_f=10^5 did not have such a dark area, ODA (optically dark area). To investigate the influence of the hydrogen trapped by nonmetallic inclusions on fatigue properties, specimens heat treated in a vacuum followed by quenching and tempering (Specimen VQ) were prepared. Specimens VQ contained 0.07ppm hydrogen as compared to 0.80ppm hydrogen for conventional Specimens QT. Specimens VQ had a slightly smaller ODA than Specimens QT. Hydrogen was detected by a Secondary Ion Mass Spectrometer around the inclusion at fracture origin of Specimens QT and Specimens VQ. Thus, it can be concluded that the formation of ODA is closely related to hydrogen trapped by nonmetallic inclusions. Estimations of fatigue limit by the √areaparameter model based on the original size of inclusions for fatigue limit defined for 10^7 cycles are ,10% unconservative. Considering the size of ODA into fatigue limit estimation, the √area parameter model can predict the mechanical fatigue threshold for small cracks without influence of hydrogen. The mechanism of duplex S-N curve is also discussed.

The susceptibility to hydrogen embrittlement (HE) of martensitic steels has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. The intensity of a desorption-rate peak around 50 degreesC to 200 degreesC increased when the specimen was preloaded and more remarkably so when it was loaded under the presence of hydrogen. The increment appeared initially at the low-temperature region in the original peak. As hydrogen entry proceeded, the increment then appeared at the high-temperature region, while that in the low-temperature region was reduced. The alteration occurred earlier in steels tempered at lower temperatures, with a higher embrittlement susceptibility. A defect acting as the trap of the desorption in the high-temperature region was assigned to large vacancy clusters that have higher binding energies with hydrogen. Deformation-induced generation of vacancies and their clustering have been considered to be promoted by hydrogen and to play a primary role on the HE susceptibility of high-strength steel.

Transparent superhydrophobic thin films with TiO(2) photocatalyst were prepared by utilizing a sublimation material and subsequent coating of a (fluoroalkyl)silane. The transparency of the films decreased with increasing TiO(2) concentration, which was attributed to the size difference of the starting materials. The film with only 2 wt % TiO(2) maintained higher contact angle than the film without TiO(2) after 1800-h outdoor exposure, the accumulation of stain being avoided due to TiO(2) photocatalysis. The films prepared in this study are the first ones that satisfy the requirements of transparency, superhydrophobicity, and long lifetime simultaneously.

We developed a new water repellent coating consisting of PTFE particles dispersed in PVDF resin. This coating exhibited a contact angle of 150 degrees. By ice accreting test, the intensity of reflected microwave on the water-repellent coated plate did not decrease, whereas that on uncoated one decreased.

Thermal desorption spectroscopy (TDS) has been used to reveal the nature of defects acting as trapping sites of hydrogen. Hydrogen was charged to ferritic and eutectoid steels deformed to various degrees and then given annealing treatment. Desorption with a single peak appeared between roam temperature and 600 K from ferritic steels. Under constant hydrogen charging conditions, the amount of desorption increased with strain. However, when the deformed samples were subjected to annealing at temperatures as low as 500 K, the increase of desorbed hydrogen no longer appeared. Vacancy clusters, which themselves annihilate in the course of TDS measurement, are the probable source of hydrogen desorption. When heavy deformation was given to ferritic steels, a two-step decrease of hydrogen desorption took place with increasing annealing temperature, corresponding to annihilation of vacancy clusters and decrease of dislocation density, respectively. The desorption with a single peak has two origins, one due to the annihilation of the trapping sites themselves and the other to desorption from stable sites. For heavily deformed eutectoid steel, an additional desorption peak centered at around 640 K appeared. The peak likely results from deformation-induced defects within the cementite phase or supersaturated carbon in ferrite. Two types of desorption, one due to the annihilation of trapping sites in the course of measurement and the other due to desorption from stable sites, should be discriminated. TDS using hydrogen as a tracer can be applied as a tool to investigate the various defects induced by plastic deformation. (C) 1999 Elsevier Science S.A. All rights reserved.

無線アンテナ等の通信装置に雪氷が付着して通信回線に問題が生じることがある.これを未然に防ぐためにはっ水材料の実用化が期待されている.本論文では, 高性能の塗料型はっ水材料による着雪氷の防止性能, 着氷が電波反射に及ぼす影響の軽減について検討を行った.結果は以下のとおりである.(1)水の接触角が150度, 氷の付着力が0.1kgf・cm^-2の新しいはっ水材料を開発した.(2)このはっ水材料を塗装したアルミニウム板では+1.5℃でも雪が明確な摩擦角を示した.(3)試料に着氷が生じている間, 電波反射には影響がなかった.(4)試料上の着氷が融解する際に, アルミニウム板やエポキシ樹脂を塗装したアルミニウム板では電波の反射強度は減少するが, はっ水材料を塗装したアルミニウム板では反射強度は減少しない.

When snow or ice sticks to radio communications antennas, it sometimes causes signal transmission problems. In many cases, the degree to which snow or ice sticks to antennas is based on the degree of adhesion. We have been developing water-repellent coatings to prevent such adhesive problems. In this paper, the snow adhesive property of these water repellent coatings is experimentally studied. We obtained following results. (1)Much more fallen snow adheres to FRP samples than water-repellent coatings. (2)Much more fallen snow adheres to samples at+1.5 degrees C than at -5 degrees C. (3)Snow naturally falls off of the surface when its weight reaches a certain value. (4)The estimated value of snow falling off consists with experimental value.

Thick snow or ice adhering to the surface of an antenna used for radio communication can impede telecommunication, so methods to reduce the build-up of snow and ice are needed. We have studied the use of water-repellent coatings to prevent snow and Ice sticking, and in this paper, we report our results of tests on ice adhesion and how it is affected by the contact angle, surface roughness and thermodynamics. And we obtained the results as following: (1) A water-repellent coating consisting of PTFE particles dispersed in polyvinylidene fluoride exhibited a contact angle of 150 degrees. (2) Ice adhesion was linearly proportional to the surface free energy of the water-repellent coating. (3) The higher the surface roughness of high wettability materials, the stronger the adhesion. The higher the surface roughness of water-repellent coatings, the weaker the adhesion.

A water-repellent material with a contact angle of more than 150 degrees has been developed. This material is composed of low molecular weight polytetra-fluoroethylene (PTFE) particles and an appropriate binder. The water-repellent properties were found to persist even after exposure to ultraviolet light and water splashing for a time equivalent to 20 years at ambient conditions.

A new type of water repulsive material was found to exhibit contact angles of more than 150 degrees. This particulate material is a composite consisting of low molecular weight PTFE particles dispersed in an appropriate binder. In order to explain the extraordinary wetting properties of these water repulsive particulate composites, their behavior has been analyzed on the basis of the Wenzel equation which takes into consideration surface roughness and the Cassie equation which considers heterogeneous surfaces. The analysis demonstrates that contact angles of 150 degrees are possible and identifies the conditions under which such high contact angles are possible.

Hydrogen and deuterium trapping sites in high-strength steels have been observed by secondary ion mass spectrometry(SIMS). High-strength steels with 1400 MPa tensile strength are stressed and dipped in D2O and 20% NH4SCN solution at 323 K to occlude hydrogen and deuterium. Depth profiles by SIMS show the presence of deuterium, which indicates hydrogen trapping sites occluded during the delayed fracture test. Secondary ion image analysis by SIMS has made it possible to observe hydrogen and deuterium trapping sites in high-strength steels. Hydrogen tends to accumulate at grain boundaries, in segregation bands, and on inclusions. Line scans by SIMS have shown that the accumulation ratios of hydrogen for the grain boundaries, segregation bands of P and inclusions are 7.8, 5.0 and 11.0 times higher than that in the matrix, respectively. Hydrogen trapping sites at the grain boundaries can be observed by measuring within 24 h after the delayed fracture test.