Stains on the shell of non-coating rolling stock tend to be conspicuous when compared with rolling stock coated with paint. In some cases these stains sticking to metallic surface remain unremoved in a simple water washing process. In this investigation, an attempt was made to clarify the mechanism of stains. At first, the contents of stains on the non-coating rolling stock shell was examined and it was found that stains principally consisted of iron rust and iron compounds supposed to be the wearing powder of wheel and rail. From this finding, the method of accelerated staining with iron filings was developed. The stains of shell were reproduced on dry and wet cyclic environment tests after iron filings on the test specimen. For cleaning of these stains, normal and high viscosity cleansers were compared. The high viscosity one showed a good result for removing stains.
In this paper, the influences of fatigue frequency and hydrogen content in material were investigated for the crack propagation at 0.5 stress ratio using a low alloy steel by cyclic stress in an overprotective environment. The six frequencies between 10Hz and 0.05Hz, and three hydrogen contents were used as the experimental conditions. Three stages divided by crack propagation behavior existed in the relationship between the stress intensity factor and the crack propagation rate. The lower the frequency was, the higher the crack propagation was at the higher stress intensity factor. The crack propagation rate was constant at Stage II. The relationship between crack propagation rate at the Stage II and frequency was expressed as (da/dN)II=1.4×10-7×f-0.763. It was supposed that the cause of the Stage II was due to the lack of hydrogen to crack tip through diffusion. The hydrogen diffusion rate was of the order of 10-7m/s. The hydrogen content enhanced the crack propagation rate at 1Hz. The Paris Law in hydrogen embrittlement environment at 1Hz was expressed as a function of hydrogen content, which was da/dN=C(ΔK)m where C=1.72×10-10×(10-5.6CH), m=3.05+4.74CH, CH: Hydrogen content in material.
The effects of carbon dioxide on corrosion rate, polarization curve and hydrogen content have been investigated for carbon steels in acetate solutions and sodium carbonate solution with a pH range of 2 to 9 at 313K under carbon dioxide and nitrogen atmospheres. In the acidic solutions less than pH4 both general corrosion and hydrogen content are accerated by the existence of carbon dioxide. In the solutions more than pH7 little corrosion is observed with or without carbon dioxide, where as hydrogen content is detected only at the existence of carbon dioxide. The anodic and cathodic polarization curves with or without carbon dioxide show that their reaction overpotentials are affected by carbon dioxide, effect of which changes depending upon pH. The results obtained are qualitatively explained in terms of the formation of iron carbonate, the adsorption of carbonate ions and so on.
The inside corrosion of automotive mufflers collected in North America way investigated. Aluminized steel corroded severely by automotive exhaust gas condensates. The morphology of the corrosion of aluminized steel was a pit with a diameter of a couple of millimeters and Al coating remained around the pit. This pit-shaped corrosion is characteristic of the inside corrosion of aluminized steel and causes large corrosion depth. Low-Cr steels (type 409: 11%Cr-0.2%Ti, type 410L: 13%Cr-0.01%C) sustained a large number of pits, while high-Cr stainless steel (type 430J1L: 19%Cr-0.5%Cu-0.5%Nb) corroded slightly. The corrosion resistance of these materials was studied with a newly developed condensate corrosion test method which simulates the inside corrosion of automotive mufflers, especially the pit-shaped corrosion of aluminized steel. The life of the materials was estimated by extreme value analysis of the maximum corrosion depth obtained by the new test. The life of type 409 steel was 3.3 times as long as that of aluminized steel and the life of type 436 stainless steel (18%Cr-1%Mo-0.3%Ti) was 1.7 times as long as that of type 409 steel.
The high strength and stiffness, lightness and low coefficient of thermal expansion make metal matrix compositions attractive materials for a diverse range of applications including aerospace, automotive, medical and sports equipment. In this study, the mechanical properties and corrosion behavior of whisker reinforced pure aluminum matrix composites produced by powder metallurgy technique were investigated by measurement of tensile and electrochemical properties in conjunction with their microstructures. The tensile strength and elongation of the composites reinforced with Al borate and TiO2 whiskers were nearly equal to those of SiC whisker reinforced composite. The reactivities of Al borate and SiC whiskers with pure Al were lower than that of TiO2 whiskers. The interfacial reactants act as anchors to enhance the cohesive force between matrix and fillers. The oxides whisker reinforced composites had more noble pitting potential compared to SiC whisker. Especially, TiO2 indicated the most noble pitting potential. On the corroded surface of TiO2 whisker reinforced composite, some precipitation products were found in the vicinity of whiskers. This is explained by the fact that the reactivity of whiskers with pure aluminum is different for the each combination. Therefore, the susceptibility of pitting corrosion depends on the formation ability of galvanic couple.
To develop a material for single layer warm damper of superconducting generator, the influence of alloy elements such as Cu, Al, Ti, C and Zr on strength and toughness in precipitation hardening Ni-Cu-Al alloys was studied. In Ni-11%Cu-4.3%Al type alloys, the combined addition of Ti and C decreases γ' particle diameter and distance between particles. 0.2% proof stress of the alloys is increased by the combined addtion of Ti and C. In Ni-Cu-Al alloys, precipitation of γ' at grain boundaries is promoted by increasing Cu, Al, Ti and C. γ' at grain boudaries embrittles the alloys. In Ni-11%Cu-4.3%Al-0.4%Ti-0.15%C alloy, precipitation of γ' at grain boundaries is suppressed by adding a small amount of Zr and toughness of the alloy is improved. An adequate composition of Ni-Cu-Al alloy for single layer warm damper is approximately Ni-11%Cu-4.0%Al-0.3%Ti-0.13%C-0.03%Zr in terms of mechanical and electromagnetic properties.
A computer-aided interactive system for coating design has been developed, which enables to conveniently analyze the reaction diffusion of bonded materials. The object of this study is to examine the overlay coating of MCrAlY alloy sprayed by a low-pressure-plasma spray (LPPS) process for protection against high-temperature corrosion and oxidation in the field of gas turbine components. However, the reaction diffusion behavior at the interface between the MCrAlY coating and the substrate, which gives an important effect on coating degradation, has not always been clarified. Three kinds of substrate, such as equiaxis IN738LC, directional solidified CM247LC and single-crystal CMSX-2, and the low-pressure-plasma sprayed CoCrAlY coating are selected for the experiments. The experimental results showed that the reaction diffusion layers consisted of aluminum compound layer and CoAl decrease layer. It also indicated that the diffusion thickness changed according to the parabolic time dependence. The reaction diffusion rates of the CM247LC and CMSX-2 were faster than the IN738LC. It was also clear from the simulation analysis that the diffusion distance during heating process should not be ignored in the total diffusion distance.
This paper presents analytical solutions for 3-dimensional anisotropic bi-material problems with line source of heat considering arbitrary directions of the principal axes of elasticity, heat conductivity and thermal expansion. Mechanical and thermal interface conditions treated here are general ones such as perfect bonding, perfect sliding and so on as particular cases. In the last part of this paper, several numerical examples and the effects of anisotropy and their inclinations are shown by many graphical representations.
The effect of transverse shear deformation induced by interlaminar stress on the in-plane behavior of angle-ply laminates is investigated. A laminate model is developed by incorporating the transverse deformation of interlayers. A linear shear slip theory is employed to describe the relation between interlaminar stress and the transverse shear deformation of the interlayer. The classical lamination theory based on a perfect bonding assumption is elaborated by allowing for interlayer shear slip. The resulting theory is applied to a series of angle-ply laminates tubes. It was observed that the transverse shear deformation affects significantly the mechanical behavior of the angle-ply laminates, especially for the laminates with weak interface bonding.
Rotating bending fatigue tests have been carried out notched commercially pure titanium specimens pre-strained by 0% and 10% in tension. The result of fatigue tests shows that the pre-strained titanium has long fatigue life compared to the annealed one in the range of finite life. Conversely, the fatigue limit of the pre-strained one decreases by 12%. The notch sensitivity of the annealed specimen is very low, although it increases due to pre-straining. No non-propagating macrocrack is observed, but some microscopic non-propagating cracks are observed on a sharp notch with a radius of 0.25mm. The crack initiation behavior was investigated through successive observations. On the surface of the annealed specimen, multiple microcracks initiate along slip bands within multiple grains in contact at a notch, and join together to grow beyond grain boundaries. On the other hand, for the pre-strained one, microcracks initiate along the boundaries of deformation twins within a single grain, joining to become a main crack leading to a final fracture.
Corrosion fatigue tests in 3% NaCl aqueous solution have been conducted on a low carbon steel, S10C, a stainless steel, SUS304, and an aluminum alloy, A2024-T4, in order to clarify their crack initiation behavior from corrosion pits. The size of corrosion pits at which crack was generated was plotted on a log-normal probability paper. It was found that the size of corrosion pits increased with decreasing stress level. The stress intensity factor of a corrosion pit at which crack initiation occurred was calculated by regarding the corrosion pit as a crack. The results were plotted on a log-normal probability paper, indicating that the stress intensity factor increased with increasing stress level in S10C and A2024-T4, but it was irrespective of stress level in SUS304. The stress intensity values obtained ranged 0.51-2.33MPa√m in S10C, 0.37-1.40MPa√m in SUS304 and 0.21-1.21MPa√m in A2024-T4.
The bearing used for the axle of Shinkansen train and the #6206 bearing were subjected to a fatigue test, and the V(z) curves were measured by a scanning acoustic microscope. Discussions are made on the detection of bearing damage in terms of residual stress, half-value breadth of X-ray diffraction, by comparing the results of hardness test and metallographic observation (SEM, TEM). The conclusions are as following; (1) The variation in sound velocity of elastic surface waves in the measured V(z) curve can be applied for estimation of bearing damage due to fatigue. (2) When the increase in dislocation is limited, the sound velocity of elastic surface waves corresponds to the variations in residual stress and half-value breadth very well. But when the dislocation increases and a cell structure is formed, the sound velocity tends to drop gradually. (3) When thermal deformation and large stress develop, the sound velocity of elastic surface wave becomes lower regardless of presence of residual stress.