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In order to improve corrosion resistance of carbon steel by AIH-FPP treatment using Cr/Ni hybridized particles, the specimens was peened in an argon atmosphere , at 1200°C , for 30 s, varying post heating time from 0 s to 300 s. Cr and Ni particles were mixed by means of a planetary ball mill to obtain hybridized particles, and it was used as shot particles. Results showed that changing the post heating time strongly affects the characteristics of modified layer at the specimen surface. Results of EDX analysis showed that the Cr and Ni diffused layer was formed at the post heating time of 300 s. Corrosion tests were performed using a three-electrode electrochemical cell connected to a computer driven potentiostat. The specimens with Cr and Ni diffused layers showed a wide passive region and almost the same pitting corrosion resistance of Stainless Steel (X30Cr13). This is because of the existence of Cr passive films on treated surfaces.

To improve the fatigue properties of structural steel, a novel surface modification process which combines high-frequency induction heating (IH) with fine particle peening (FPP) was developed. IH-FPP treatment was performed on the surface of structural steel specimens (0.45%C) at temperatures from 600 to 750 °C, with peening times of 60 and 120 s. To determine the characteristics of the treated surfaces, the microstructure was observed using an optical microscope and a scanning electron microscope. Vickers hardness and residual stress distributions were also measured. The characteristics of fine-grained microstructures were examined by electron backscatter diffraction. Furthermore, in order to investigate the effect of the grain refinement achieved by IH-FPP treatment, rotational bending fatigue tests were performed on treated specimens. Results showed that IH-FPP treatment created fine-grained microstructures beneath the surfaces of steel samples. The average ferrite grain size was 4.06 μm for a treatment temperature of 700 °C, and finally 0.76 μm for 600 °C . This was due to dynamic recrystallization in the processed region. IH-FPP treated specimens exhibited a higher fatigue strength than untreated specimens. As almost no compressive residual stress was measured in the treated or untreated specimens, the increase in fatigue strength resulting from IH-FPP treatment was due solely to grain refinement.

In order to increase surface hardness of AISI 1045 steel, a new hybrid surface modification; combination of atmospheric-controlled induction-heating fine particle peening (AIH-FPP) and plasma nitriding, was developed. Surface microstructures of plasma nitrided specimens pre-treated with AIH-FPP using Cr shot particles were characterized by an optical microscope, a scanning electron microscope (SEM), an energy dispersive X-ray spectrometer (EDX) and X-ray diffraction analysis (XRD). As results, the nitrided layer was formed at the surface of the specimen with Cr diffused layer induced by AIH-FPP. This nitrided layer showed higher hardness than that of without AIH-FPP specimen. This was because CrN was formed at the surface of the AIH-FPP/Plasma nitriding treated specimen. And, the surface hardness of the nitrided layer tended to increase as the Cr concentration in the surface layer decreased. It was clarified that the pore formation during the AIH-FPP/Plasma nitriding treatment was inhibited by decreasing Cr concentration. These results suggest that the proposed hybrid surface treatment remarkably increases surface hardness of AISI 1045 steel. [doi:10.2320/matertrans.MBW201205]

Basic mechanisms of generating a surface modified layer formed by a previously developed atmospheric controlled IH-FPP system, consisting of induction heating system and fine particle peening system, were investigated. Three types of specimen treated at 900°C in argon with Cr, Al2O3 and Cu shot particles were prepared. Surface microstructures of the treated commercial-grade pure iron were characterized with a scanning electron microscope (SEM), an energy dispersive X-ray spectrometer (EDX) and an X-ray diffraction analysis (XRD). When treatment was carried out using Cr particles, the transferred layer and the diffused layer of the shot-particle element formed at the treated surface. This was because the radius of Cr atom was almost the same as that of the Fe, thus forming a solid solution in the substrate. Conversely, when the treatment was applied using chemically stable Al2O3 particles, a transferred layer only was observed. In the case of Cu particles, adhesion occurred due to the low melting temperature of Cu particles, resulting in the formation of a thick adhesive layer such as that generated by thermal spraying. These results suggest that the characteristics of the modified layer, generated by the atmospheric controlled IH-FPP treatment system, can be controlled by varying the shot particles and other processing parameters.

To evaluate the influence of hybrid surface modification processing on the rolling contact fatigue life, we used a roller pitting test comprising a combination of high strengthening by Super Rapid Induction heating and Quenching (SRIQ) and improvement of the tribological quality by a Diamond Like Carbon (DLC) membrane. The applicability of the process to a small gear was examined. Results show that the rolling contact fatigue life of the SRIQ+DLC specimen was longer than that of SRIQ specimen at all loads. Subsequent SEM observation of fractures showed that many micro-surface cracks and pittings along with pitting caused fracturing of the SRIQ specimen. However, the SRIQ+DLC specimen showed few micro-surface cracks aside from the pitting causing fracture. Many internal cracks were found. Based on these results, we infer that improvement of the rolling contact fatigue life is introduced by retarding of the generation of surface damage attributable to the decrease of tangential stress brought by superior low friction and excellent wear resistance of the DLC membrane. Therefore, SRIQ+DLC compound surface modification, which improves tribological and fatigue properties, is suggested as effective for improving rolling contact fatigue life. Regarding SRIQ, it is possible also for the discharge of carbon dioxide to produce a substantial decrease in comparison to other heat treatment processes. It can contribute also to protection of the terrestrial environment. It might be said that a new hybrid surface modification process has been produced.

A new surface treatment system (IH-FPPsystem) combined with an induction heating and a fine particle peening machine were developed. FPP treatments were carried out on structural steel discs by using Cr shot particle at room temperature, 400°C, 600°C and 900°C. After characterizing the surfaces by SEM, EDX and XRD, corrosion tests were performed by a three electrode method using a computer driven potentiostat. No noticeable differences were observed on the specimen treated at RT, 400°C and 600°C. In the case of the specimen treated at 900°C, however, higher corrosion resistance which is almost the same as FPP treated stainless steel (SUS316L) was observed. This was because Cr diffused layer covered with relatively smooth oxidized surface prevented a corrosion reaction in 3%NaCl environment.

In recent years, with the background of weight saving and downsizing in machines and devices, it is important subject to downscale mechanical parts which are contained in them. So in this study, in order to achieve power transmission parts like a compact gearwheel which indicates high performance properties, hybrid surface modification was performed by combining Super Rapid Induction Heating and Quenching (SRIQ) which creates high fatigue strength and Diamond Like Carbon (DLC) coating which are well known for their high hardness, low friction and excellent wear resistance. And, in order to prevent the base material from decreasing its fatigue strength, DLC was coated by using Unbalanced Magnetron Sputtering (UBMS) method which can coat at low temperature. Rotational bending fatigue tests and friction-wear tests were carried out. It was clear that it is possible to keep high fatigue strength and to create excellent tribological properties at specimen surface by performed hybrid surface modification. Furthermore, it is possible to prevent increase in handling process because tempering process after quenching can be performed by heat process during DLC coating process.

It has been well known that mechanical properties of steels are improved by gain refinement, smaller cementite particle and finely dispersing cementite particle, It is enabled by super rapid induction tempering the the smaller cementite particle and the finely dispersing cementite particle. In this study, mechanical properties of induction quenching and tempering carbon steel using super rapid induction heating system were investigated. Dtail, the effect of quenching time on tensile properties is examined. The quenching time was changed in four steps of 0.44 s (1163 K), 10 s (1233 K) +10 s (1153 K), 20 s (1273 K) and 20 s (1433 K). As a result, it was found that the tensile strength of QT steel indicated an increase tendency with hardness. The yield strength was in proportion to a square root of grain size. However, the ductility improvement effected by super rapid induction quenching was not found, reduction of area did not depend on grain size.

To clarify the effects of Super Rapid Induction Heating and Quenching (SRIHQ) on fatigue properties of Ferritic Ductile Cast Iron (FDI), rotational bending fatigue tests were carried out on specimens treated with four types of heating cycle. Results showed that; (i) the SRIHQ process generated a thin dark gray area around the graphite. This dark area was composed of a martensite structure (ringed martensite). (ii) The ringed martensite generated a compressive residual stress field at the surface hardened layer. Two types of compressive residual stress generative mechanisms were observed. One was a microscopic residual stress generative process due to the formation of ringed martensite and the other was a macroscopic residual stress generative process due to the expansion of the surface hardened layer. (iii) The fatigue strength of SRIHQ treated FDI specimen was higher than that of the untreated one. This was because the compressive residual stress field generated by the ringed martensite suppressed initiation and propagation of fatigue cracks.

This study was conducted to examine how and why a difference of fatigue strengths between unnotched and notched specimens, in terms of maximum stress amplitude at the notch bottom, depends on the change of hardness level in steel. As a result, the local fatigue strength of the notch bottom in the notched specimen became higher than that of the un-notched one with increase of notch sharpness and this was remarkable in high strength steel. This is because the transition of the fatigue fracture mode occurs from a slip induced crack initiation mode to a defect controled one with increasing hardness in steel. In addition, using a new experimental approach combined with a simulation technique based on the concept of risk competition of defects, a computer simulation was conducted on an effect of inclusion on the local fatigue strength at the notch bottom of high strength steel. It was clarified that the difference of fatigue strength between notched and un-notched specimens in high strength steel was caused by the statistical variation of the largest inclusion size contained in the critical volume at the notch bottom.

The effect of short-time duplex heat treatment on the microstructure and mechanical properties of Ti–6Al–4V alloy was investigated. This heat treatment consisted of solution treatment at 1203 K for 60 s and subsequent water-quenching plus aging at 753, 853 and 953 K for 40 s. The yield strength and tensile strength of the alloy were significantly increased by the above heat treatment and their maximum improvement rates reached about 25%. It was thought that this strengthening was caused by the formation of α′ martensite phase with quenching after the short-time solution treatment and the precipitation of fine α phase in the retained β phase during the short-time aging. In spite of the remarkable improvement in the strength, the ductility of the heat-treated materials remained above the level of the non-treated material, most likely because strain-induced martensite transformation occurred in β phase which was retained even after the short-time aging.

The effects of a surface-layer whose Young's modulus is lower than that of the substrate on the fatigue strength were studied. Pure iron plates possessing pure titanium layers on the both sides were prepared as a model material. The formation of the titanium layer remarkably improved the fatigue strength of pure iron. In addition to the fatigue test, we made a calculation of the image stress which acts on a dislocation due to the discontinuity of the elastic constants at the surface and interface. As a result, it was found that the absolute value of image stress in the vicinity of the surface becomes smaller as the elastic modulus of the surface-layer is decreased. From the results of the above experiment and calculation, it was thought that the improvement of the fatigue strength with the formation of the titanium layer was caused by the reduction in the remote applied stress and image stress acting on dislocations near the surface.

It seems to be possible to heat treat the gears having higher fatigue strength with lower distortion by applying newly developed super rapid induction heating and quenching (SRIHQ) technology. In this previous research, rotating bending fatigue properties of S 45 C tempered martensite structure plane specimens heat treated by SRIHQ having shallower hardened layer and higher compressive residual stress were studied, and it was observed that the fatigue strength was not improved due to the fatigue cracks initiation just beneath the shallow hardened layer. In the present research, rotating bending fatigue properties of same specimens with notch (α=2.3) heat treated by SRIHQ were studied. As a result, on the contrary of previous work, much higher fatigue strength was obtained in spite of shallow hardened layer. The compressive residual stress formed at the bottom of notch is extremely high (2000 MPa) due to the effect of stress concentration.

In order to estimate fatigue reliability of super-rapid induction quenched spheroidal graphite cast iron, FCD500, FCD700, the influence of complex surface microstructure on the fatigue strength was examined through fractography. The main results obtained are as follows : (1) Fatigue strength of quenched FCD500 was superior to that of quenched FCD700 in the long-life region (N> 5.0×105), in spite of tensile strength of FCD500 was lower than that of FCD700. (2) Fatigue property of super-rapid induction quenched spheroidal graphite cast iron could be estimated using a concept of "S-N globe". (3) Initial stress intensity factor at crack initiation under the surface of quenched FCD500 was comparable to that of quenched FCD700, therefore the improvement in fatigue strength of FCD500 depended on the crack propagation behavior through the complex surface microstructure, not the crack initiation behavior. (4) The prevention of crack propagation through the complex surface microstructure gave and appearance of high level fatigue reliability of FCD500.

— The factors affecting the fatigue strength of nitrided titanium were clarified. The fatigue strength depended strongly on the fracture strength of the compound layer formed on the surface by nitriding. We found a Hall-Petch relationship between the fatigue strength of nitrided titanium and the grain size. The findings indicated that the reduction in the fatigue strength by nitriding results from both the formation of the compound layer possessing low fracture strength and grain growth occurring from ordinary nitriding. Furthermore, low-temperature nitriding (620°C, 24 h) was proposed to suppress grain growth. This treatment method improved not only the wear resistance and the corrosion resistance but also the fatigue strength of titanium.

This study was conducted to clarify the effect of CO2 laser irradiation on the wear resistance, corrosion resistance and fatigue strength of Ti-6Al-4V alloy. The results are as follows. (1) Laser irradiation results in formation of a hardened case on the titanium alloy because precoated carbon, oxygen and nitrogen existing in the air rapidly diffuse to the inside during the irradiation. The formation of such a hardened case greatly improves the wear and corrosion resistance of the titanium alloy. (2) Laser irradiation results in a marked decrease in the fatigue strength of the titanium alloy. This is caused by (i) cracking on the surface during the irradiation, and (ii) change of the fine equiaxed microstructure to the widmanstatten microstructure.

The purpose of this study was to determine the effect of nitriding, used as a surface-modification method on the fatigue strength of metals. By conducting experiments for evaluation of the factors controlling the fatigue strength of nitrided pure iron and titanium, we obtained the following results. (1) The improvement in the fatigue strength of nitrided pure iron results from the fact that the hardened case existing under the compound layer suppresses the propagation of cracks. However, the fatigue strength of nitrided pure titanium decreases because a crack initiated in the compound layer at a low stress level directly results in the overall fracture of the brittle hardened case. (2) There is a Hall-Petch relationship between grain size and the fatigue strength of nitrided pure iron and titanium. This effect does not influence the fatigue strength of nitrided pure iron because the grains do not grow during nitriding. In contrast, the above effect results in the inferior fatigue strength of nitrided pure titanium because grain growth inevitably occurs during nitriding at high temperatures.

Recently, a new super rapid heating induction hardening technique which uses MICROPULSE SYSTEM has been developed. The new induction hardening technique differs from the former induction hardning in that the new technique is very useful for controlling case-hardened depth exactly, and is attendant on little deformation after hardening.In this study, in order to clarify the fatigue strength of the notched specimens of carbon steel (S45C, α=1.6) whose effective case-hardened depth are about 0.70mm and 0.45mm, uniaxial loading fatigue tests were conducted. It was found that the fatigue strength of the hardened specimens was 670MPa for the hardning depth 0.70mm and 630MPa for the hardening depth 0.45mm. Micro pulse induction hardening improved the fatigue strength about two times higher than that of the S45C base metal. The “Fish-eye” which indicates that fatigue cracks initiated from the inside of a specimen appeared on many fracture surfaces. And the position of the “Fish-eye” coincided nearly with that of the case-hardened depth.

It has always been difficult to perform analysis and characterization of substances in aqueous solution by using infrared (IR) spectrometry. We propose a new method in which ions are concentrated on the attenuated total reflection (ATR) surface of a germanium prism by using an electrophoretic means. The method may provide insolution. These results implied that the dissolved state of sodium decanoate in 0.06 M solution was different from that in 0.02, 0.04, and 0.2 M solutions.

Computer simulations of the dynamics of screw dislocations are performed, using the model in which screw dislocations are piled up against a hard thin layer after their slip movement in a region possessing the distribution of friction stress. The calculation of stress field in the compound layer is performed for various values of slip length and thickness of a thin surface layer in order to discuss the effect of these factors on the fatigue strength of nitrided titanium. The results show that the well-known Hall-Petch-type relation between the fatigue strength and the grain size can be predicted for nitrided titanium through analysis of the proposed model. And the results exhibit that further consideration concerning the role of crack initiation resistance of the compound layer is essential for a better understanding of the influence of the thickness of the surface-hardened layer on the fatigue strength of nitrided titanium.

The formation of ultrafine intermetallic compound particles in the Al-Cu and Al-Ni systems were examined using a plasma jet method. Pre-mixed elemental powders of Al-Cu and Al-Ni of several tens of pm in diameter were subjected into the plasma jet of Ar-N2 working gas. The ultrafine particles thus formed were examined by X-ray, TEM and EPMA. The main results obtained were as follows; (1) Ultrafine intermetallic compound particles of Al2Cu, AlCu, Al4Cu9 and AlCu3 in the Al-Cu system and Al3Ni, Al3Ni2, AINi and AlNi3 in the Al-Ni system were produced in the present plasma jet method. (2) All the intermetallic compound particles were spherical with the diameter ranging from 1Onm to 100nm. (3) The intermetallic compounds produced were not always with large negative formation energy. Since the cooling rate was relatively fast, the intermetallic compounds which require solid state diffusion at low temperature were not observed. (4) Cu or Ni was richer in the ultrafine particles than that in the source pre-mixed powders. (5) Ultrafine AIN particles were observed when the source pre-mixed powder was Al rich. Such AIN were considered to be produced by the reaction of vapor or liquid Al with the nitrogen in the working gas. AIN was eliminated by using the working gas containing a small amount of H2. (6) The composition of ultrafine particles can be controlled close to that of source powder by reducing the amount of flowing working gas.

A study has been conducted on the relationship between the initiation and propagation behavior of a fatigue crack originating at the non metallic inclusion and the fracture-mode transition from a surface to subsurface fracture known as fish eye fracture in high-strength steels. Special attention is paid to the propagation of microcracks originating at each inclusion both on the specimen surface and in the subsurface. The results obtained are summarized as follows. (1) Metallographic observation using SEM revealed that the initiation of microcracks from inclusions occur at numerous inclusions both on the specimen surface and in the subsurface. (2) The initiation of these microcracks from inclusions on the specimen surface occurs at a very early stage in the fatigue cycles. (3)The propagation of a crack initiating from an inclusion on the specimen surface stops at an early stage in the fatigue cycles before failure occurs as a fish eye fracture. (4) These phenomena suggest that there exists a fatigue limit in the surface fracture mode, and that the mechanism of fracture mode transition is associated with the difference in crack propagation behavior of microcracks from inclusions on the specimen surface and in the subsurface.

The application of powder interlayers to solid-state diffusion bonding was investigated. Base materials used in this investigation were pure Cu, Fe and Ni. Interlayer materials were also Cu, Fe and Ni powders. The bonding was carried out by hot pressing at bonding temperatures of 573-973K and bonding pressures of 7 or 100MPa in vacuum. The cross section of the bonded specimens obtained was observed by optical microscope and SEM. The bonding strength of the specimens was measured using a shearing test. The main results obtained were as follows : (1) When the base and powder interlayer materials are the same, the strength of the diffusion bonded powder interlayer samples was higher than that of direct bonded samples. (2)When the base and powder interlayer materials are different, the strength of diffusion bonded powder interlayer samples was found to be high when the two components are well soluble and low when they are not. (3)When the green density of the powder interlayers was low, the bonding strength of the diffusion bonded powder interlayer samples was below that of direct bonded samples, This is thougth to be due to the sintering shrinkage of powder interlayers during bonding.

Metallurgical factors controlling the fatigue properties of gas-nitrided titanium have been studied through some critical experiments concerning the fatigue strength of nitrided pure titanium whose grain size had been changed from 100 μm to 2800 μm through annealing prior to nitriding. The results are summarized as follows. (1) There exists a Hall-Petch-type relationship between the fatigue strength of nitrided pure titanium and its grain size. (2) The fatigue strength of pure titanium is improved by low-temperature nitriding (620°C) where the grain growth can be suppressed. (3) The fatigue strength of nitrided pure titanium decreases with increasing the thickness of compound layer at the specimen surface.

Rotating bending fatigue tests were carried out on quenched and low temperature tempered SAE 9254 spring steels having two kinds of microstructure in which either isolated defects (retained ferrite) or connected defects (proeutectoid ferrite) are dispersed, with a special interest in the transition of surface to subsurface fracture known as "Fish-eye fracture" in high strength steel. Discussions were made of the relationship between the fatigue fracture mode transition and the surface conditions, and also of the role of the microstructure in the formation of the Fish-eye pattern. Results show that (1) the fracture mode transition occurs in the material having isolated defects in the microstructure when a surface fracture mode is prevented by strengthening the surface layer with mechanical polishing and, (2) such a fracture mode transition is associated with the change in fatigue crack initiation process from slip band cracking of surface retained ferrite to cleavage cracking of internal retained ferrite.

An attempt was made to clarify the effect of a surface-hardened layer produced by gas-nitriding (880°C, 24 hours) on the fatigue strength of pure titanium through experiments concerning the fatigue properties of nitrided pure titanium whose surface-hardened layer was removed to a thickness of 12-60μm. The results are summarized as follows : (1) the fatigue strangth of nitrided pure titanium is improved by removing the compound layer, (2) the fatigue strength of nitrided pure titanium can be reduced because the compound layer posesses a very low fracture toughness compared with that of the matrix, and in addition to this, residual compressive stress in the compound layer is cancelled out by tensile stress developed by the stress magnification effect due to a difference of Young's moduli between the marix and the compound layer.

Low cycle fatigue tests were carried out over a wide range of plastic strain levels including an extremely low cycle fatigue (ELCF) regime on ferritic ductile cast iron under push-pull loading conditions. To evaluate the internally accumulated fatigue damage, the measumement of the density of the materials was also taken after a given number of strain cycles. Results show that ( 1 ) in the ELCF regime, the generation and the coalescence of microvoids, which originated from debonding of the graphite-matrix interface inside the material, lead to the final fracture of the specimen ; ( 2 ) in this case, the local density of the specimen, at the region where fatigue damage is concentrated, decreases gradually with strain cycling and its most drastic change occurs at the final stage of fatigue. This drastic decrease in density at that stage is caused by the rapid coalescence of microvoids inside the material.

A Study has been made to clarify the effect of gas-nitriding on the corrosion resistance and the fatigue properties of pure titanium in a hydrochloric environment. The results are summarized as follows : ( 1 ) most of the fatigue life of nitrided pure titanium is spent in the period of the destruction of the TiN layer associated with pit formation due to hydrochloric acid attack ; ( 2 ) the fatigue strength of annealed pure titanium is greatly reduced in a hydrochloric environment because a fatigue crack initiation along the grain boundary is promoted by hydrochloric acid attack.

An attempt was made to clarify the effect of nitriding on the fatigue strength (Nf=107) of pure titanium through some critical experiments concerning the fatigue properties of gas-nitrided pure titanium including a sample with a small artificial surface pit. The results are summarized as follows : (1) The reduction of fatigue strength occurs in the nitrided pure titanium with increase in the thickness of the hardened layer. (2) The small pit (dp-80 μm) has little effect on reducing the fatigue strength of nitrided pure titanium, while such a pit gives a large reduction of the fatigue strength of unnitrided pure titanium. (3) Fractography of the fracture surface of nitrided pure titanium revealed that there exists a microfracture facetlike cleavage at the fatigue crack initiation site beneath the nitrided layer, while a small featureless facet associated with stage-I crack growth can be observed at the fracture edge of an unnitrided pure titanium. (4) The fatigue strength of nitrided pure titanium can be considered as a critical stress at which microcracking of the hardened layer occurs under cyclic loading.

Numerlcal simulations considering spatial and size distributions of nonmetallic inclusions in the material have been carried out for the purpose of initiating a discussion concerning the critical size of the inclusion responsible for the fatigue failure of high-strength steel. Results show that the geometrically largest inclusion within a critical volume of the specimen is not necessarily responsible for the fatigue failure of such material, and that the most dangerous inclusion for fatigue failure is that of the near surface having the largest relative inclusion size calculated from the spatial distribution of inclusions within the critical volume of the specimen.

The rotating bending fatigue test and the measurement of inclusion size distribution in a material using the quantitative metallography technique were carried out on a quenched and tempered SAE9254 steel. The relationship between the size of inclusions which act as nucleation sites for actual fatigue failures and the inclusion size distribution was discussed, and an attempt was also made to estimate the effect of the size distribution of inclusions on the scatter of fatigue lives of the steel. The results obtained were summarised as follows. (1) Almost all the sizes of inclusions, Dfs, which were observed at crack nucleation sites on the fracture surfaces are larger than the maximum size of inclusions, Dic, expected from the inclusion size distribution in the material. indicating that the inclusion which acts as a nucleation site for actual fatigue failure is the largest one in the present microstructure. (2) The scatter of fatigue life is closely related to the inclusion size distribution in the critical volume for fatigue failure and can be estimated using a new parameter of Dfs/Dic.