Most studies on CSSC (cyclic stress-strain curve) have been conducted in the condition of the stress ratio R=−1. There are few reports on the effect of mean stress on CSSC. In this study, the stress-controlled fatigue tests under R=0 and −1 were performed on JIS S25C (AISI 1020), IF steel, A2024-T6, A6061-T6 and Ti-6Al-4V alloys. CSSCs of R=0 and −1 were compared. Creep strain (ratcheting strain) was also measured to investigate dominating mechanism of fatigue life of these alloys. It was found that the effect of mean stress on CSSC was different with each alloy. The dominating mechanism of JIS S25C and IF steel was creep strain. However, the dominating mechanism of A2024-T6 and A6061-T6 was plastic strain amplitude. The dominating mechanism of Ti-6Al-4V alloy was both creep strain and plastic strain amplitude. Thus, fatigue life reduction caused by mean stress in Ti-6Al-4V alloy was remarkably occurred than the other alloys.
In this study, for the purpose of developing the shot peening process obtaining both improving strength and coating with Cu, the behavior of peened surface modification by using hard media containing soft Cu phase was examined. Shot peening was carried out by Cu phase dispersed FeCrBCu media with high hardness of 1220 HV in Vickers hardness. Media particle diameter was under 45 μm. Annealed JIS-SUJ2 steel was used as workpiece. On the peened surface, compressive residual stress was 440 MPa and Vickers hardness increased to 350 HV. By EDX analysis, 29 mass% Cu was detected on the peened surface. Though this value was beyond the solid solution limit in αFe, no peak of the new phase by Cu adhesion was observed in XRD pattern. Furthermore, according to TEM observation near the peened surface, the nano crystalline region of αFe was observed and Cu was detected at this region by EDX analysis. Logarithmic strain near the surface caused by shot peening in this work was estimated at 4.7 calculated from the crystal grain diameter and thickness before and after shot peening, respectively. Therefore, owing to the severe plastic deformation condition of this shot peening, it seems the crystal grain refinement to nano size and super saturated solid solution of Cu in αFe were observed.
Platelet particles of α-Fe2O3 30-50 nm in size were heated in tetra-ethylene glycol to obtain spinel-structured iron oxide particles, which were confirmed by X-ray diffraction. With heating, 100 nm platelets were formed, and the proportion of the 100 nm platelets increased in comparison to 30-50 nm platelets with increasing duration of heating. In all the samples, irrespective of the heating time used during synthesis, the coercive force, which was considered to be dependent on the shape anisotropy of the platelet particles, remained nearly constant at 12.7-13.5 kA/m (160-170 Oe). The saturation magnetization initially increased and then decreased with the heating time and the maximum value observed was 80.5 Am2/kg (80.5 emu/g). The reduction and oxidation were considered to occur simultaneously during the synthesis.
Surface hydrophilicity is considered to have a strong influence on the biological reactions of bone substituting materials. However, the relationship between hydrophilicity and osteoconductivity has not been discussed quantitatively. In this study, Ti substrates were coated with TiO2 having different water contact angles, using anodizing in aqueous solutions containing different types of solute ion, and the quantitative relationship between hydrophilicity and osteoconductivity was investigated. All of the anodized coatings were anatase-type TiO2 with a fine surface roughness. Most of the solute ions were included in the coatings, but they did not influence the hydrophilicity of the anodized coatings. However, the surface hydrophilicity of the anodized coatings depended on the pH of the aqueous solution. The amount of hard tissue formed on TiO2-coated specimens (denoted as RB-I) depended on the water contact angle on their surface. For water contact angle between 20° and 55°, the value of RB-I increased as water contact angle decreased. On the other hand, for water contact angle between 55° and 70°, the value of RB-I increased as water contact angle increased.
The manufacturing technique of steel sheets in the Edo period has been investigated from a Kusazuri armature that is a protector of the waist. The size of the steel sheets is 300 mm by 235-265 mm and 0.6-1.0 mm in thickness. Most of the steel sheets are composed of multiple steels with different carbon contents. The nonmetallic inclusions in the steel sheets are FeO and a few 2FeO•SiO2. Most of the nonmetallic inclusions are finely distributed in the sheets while some lie in lines in parallel to the sheet surface. The nonmetallic inclusions which are arranged in lines were produced during forge welding. From the number of lines, forge welding was performed one to three times. The nonmetallic inclusions are elongated in the side direction of the sheet than the longitudinal direction. This means that a large plate was extended while maintaining the width of 300 mm and was cut to the length of 235-265 mm. The Vickers hardness of the sheets was larger than that of annealed steel sheet in the literature, suggesting that annealing was not performed to the steel sheets after forging. Finally, the steel sheets were shaped and curved slightly.
We have developed Ti-Mg alloy for dental material corrosion-resistant to aqueous fluoride solutions. Ti plates and granular Mg was put in a sealed vessel and heated at 950℃, so Ti plates were exposed in the liquid and the vapor Mg phases. The conditions made Mg diffuse into the Ti plates to produce Ti-Mg alloy. The Ti-Mg alloy produced in the vapor Mg phase for 430 h achieved homogeneous distribution in Mg concentration of 0.2 at%. A Vickers micro hardness increased almost linearly with an increase in the Mg concentration, and the hardness of the homogeneous Ti-0.2 at%Mg was about 1.2 times larger than that of Ti before alloying. It was confirmed that corrosion resistance of Ti in the fluoride solution was improved by alloying with Mg. The method using the vapor Mg phase contributed much more effective improvement of corrosion resistance than that using the liquid phase. The homogeneous Ti-0.2 at%Mg demonstrated a maximum corrosion resistance of all the specimens, by about 80 times to Ti.
The simultaneous deposition of chromium and silicon on stainless steel using a halide-activated diffusion coating process was performed to improve oxidation properties at high temperatures. Conventional procedure in diffusion coating process uses an activator containing fluoride. Fluoride is harmful for the human body and the environment. This experimental object is a development of the fluoride-free activator in diffusion coating of chromizing-siliconizing. In this investigation, Cr-Si intermetallic compound layers were coated on stainless steel by the pack cementation to improve its oxidation resistance and the resulting properties of the obtained coatings were investigated. The pack powders used for the diffusion coating were Cr and Si as diffusion element, Al2O3 as filler, and NH4Cl and CaCl2 as fluoride-free activator or NH4Cl, NaF and AlF3 as fluoride-added activator. The diffusion coating treatment was conducted at 1323 K for 18.0 ks in an Ar atmosphere. After the simultaneous deposition of chromium and silicon on stainless steel, a modified layer was observed on the treated sample surface and fluoride-free activator could also modify the steel surface using pack cementation.