Diamond-like carbon (DLC) films have low friction coefficient against variety of materials and high wear resistance; however, DLCs are often damaged when the DLC film is distorted with deformation of the substrate. Segment-structured DLC (S-DLC) coating has been developed to improve these weak points of DLC films. The S-DLC coating is a technique to separate the DLC film into the small segments. The purpose of this study is to fabricate S-DLC film on stainless steel substrate and functionalize DLC films on the substrate based on S-DLC film. In this study, fluorocarbon polymer embedded segment-structured DLC (FC-S-DLC) film was fabricated by spraying fluorocarbon polymer into the grooves between the DLC segments. The DLC films were deposited by a RF plasma chemical vapor deposition (CVD) method. Evaluations of tribological properties of these high-functional DLC films were performed under plane contact condition by pin-on-disk (PoD) test. As a result, the S-DLC film exhibited better tribological properties than that of continuous DLC film. Furthermore, the FC-S-DLC coating exhibited the most excellent tribological property among all samples and gave high wear resistance and steady friction coefficient to stainless steel substrates at a plane contact pressure of 0.16∼0.24MPa.

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Wear and fretting fatigue are important technological problems in automotive, railway and aerospace fields. The purpose of this study is to find a method of reducing the wear of cast-iron (FCD)/aluminum components, which are often applied to automotives, and thus extend their lifetime. First, a stainless-steel (SUS) shim was designed, which can be inserted between an FCD plate and an aluminum plate. Second, diamond-like carbon (DLC) coatings were applied to the shim inserts to prevent the FCD and aluminum plates from wear. Then, the tribological and fatigue characteristics of the shim were evaluated by a ball-on-disk (BoD) test and a bending fatigue test of up to 1×10⁶ cycles. Each substrate was coated with DLC by Plasma-Based Ion Implantation and Deposition (PBII&D). A unique feature of our shim is that a segment-structured DLC film (S-DLC) is employed as well as a continuous DLC (C-DLC) film. The effect of the DLC coating on reducing the damage to the Al plate was apparent, because the surface roughness of the Al plate abraded with the DLC-coated shim was significantly smaller than that abraded directly with the FCD plate. Moreover, the average damage fraction to the C-DLC coating is approximately 20-fold larger than that to the S-DLC coating. The C-DLC film suffers severe damage near the bolt hole, whereas the S-DLC film suffered almost no damage even after 1×10⁶ bending cycles. In conclusion, an S-DLC-coated SUS shim has a marked effect on reducing the wear of Al/FCD components and improving their lifetime.

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A combustion flame method was used to synthesize diamond films on a Mo substrate. During the cooling process, most diamond films delaminated. From previous work it has been shown that a three-step method using combustion flame was viable to prevent a delamination. But it was not perfect. In order to get a better adhesion of the diamond film, distances of the flame inner cone from the substrate were changed for each step of the three-step method. The first step of the three-step method was set to the distance d=1.5mm, the second step was set to the distance d=2.0mm and the third step was set to the distance d=3.0mm, respectively, with each scratching treatment of #180, 400, 800 and 1500 on the substrate surface. The results showed that the better adhesion of the diamond film was obtained on scratched surfaces at #400, 800 and 1500. An abnormal growth of the film was able to prevent by changing the distances. The inspection by SEM and XRD showed that synthesized films on scratched surfaces at #400, 800 and 1500 by the changing distances were good diamond. It was concluded that the delamination-free diamond film could be realized by changing the distances.

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It is important to prevent from hydrogen embrittlement cracking in the heat-affected zone of welded steels. The hydrogen permeation rate for bulk nickel at high temperatures is higher than that of stainless steel, although the reverse is true at low temperatures. Low carbon stainless 316L steel, which contained 12-15% nickel, was selected as the parent material for welding. We have investigated the affect of nickel near the heat-affected zone by measuring the hydrogen permeation at various temperatures. We performed hydrogen permeation tests into the bead on plate specimens using nickel filler. A stationary hydrogen gas flux through the stainless steel specimen was measured by using an orifice and a quadrupole mass spectrometer (QMS). The partial pressure difference for hydrogen that was applied to the specimen was able to be kept constant by maintaining a constant gas flow rate through the orifice in a low- pressure room. An orifice with a 3 mm diameter maintained stationary steady-state hydrogen gas flux from the specimen at 620K, while a 1.2 mm diameter orifice maintained the steady pressure at 520 K. The hydrogen permeability, K was calculated based on the measured steady-state hydrogen gas fluxes at various temperatures. These results plotted as log K versus 1/T (reciprocal temperature) could not be interpolated linearly. The permeability values of the specimen at 570 K and 520 K were less than interpolated ones between the value at 620 K and the value at 520K of the 316 L stainless steel substrate as received.

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An analytical method is derived for obtaining the finite deformation of 2-D thin curved beams with variable curvatures. The general solutions are expressed by fundamental geometric quantities. As the radius of curvature is given, the fundamental geometric quantities can be calculated to obtain the closed form solutions of the axial force, shear force, bending moment, rotation angle, and deformed and un-deformed displacement fields. The closed-form solutions of the circular, spiral, ellipse, parabola, cycloid, catenary and logarithmic spiral beams under pure bending moment cases and simple circular curved beam under a pair of horizontal forces are presented. The results show the consistency in comparison with ANSYS results.

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In this study, a structural topological shape optimization design via the X-FEM and zero level sets is presented. Displacement fields of two-phase topology optimization problems are defined by a weak discontinuity with bisected supports. In order for X-FEM to appropriately be associated with a classical topology optimization algorithm with density design parameters, the design parameters are transformed into control parameters in X-FEM. Then, all elements including enriched elements near material interfaces, which are searched by the control parameters, contain signed distance functions or level set functions at each node. The nodal signed distance functions are bilinearly interpolated, and then, Gauss point signed distance functions determine material properties at Gauss points, i.e. almost complete voids (0.001) or solids (1). Up-wind scheme is used to update the level set functions including zero level set functions, which describe moving material interfaces, followed by shape sensitivity of optimization problems via level set functions. Numerical applications verify the present method produces superior design solutions like smooth material interfaces through considering both mechanically X-FEM and geometrically level set method in comparisons with jagged optimal density distribution results of classical topology optimization.

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In order to establish an appropriate method for measuring the local hydrogen content distribution around a fatigue crack tip in austenitic stainless steels, secondary ion mass spectrometry (SIMS) and the hydrogen micro-print technique (HMPT) were applied to a fatigue crack in a type 304 stainless steel fatigued in a hydrogen gas environment. The main results in this study are as follows. In the SIMS method, it is visualized that a high content of hydrogen exists in the plastic zone at a fatigue crack tip propagated in hydrogen gas, compared to that on a smooth area fatigued in hydrogen, though there is a measurement error based on false detection due to the edge effect regarding hydrogen in water vapor on the fatigue crack surface. On the other hand, hydrogen in the plastic zone is difficult to detect by HMPT. This is attributed to the difficulty for hydrogen atoms to be emitted from the sample in this case. To detect hydrogen, it is necessary to sputter the atoms forcibly. In addition, it is considered that to analyze the local hydrogen distribution around a fatigue crack tip with SIMS not only qualitatively but also quantitatively, reduction of the false detection due to the edge effect is necessary.

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The relationships between pulse frequency and growth rate and between pulse frequency and hardness were investigated for DLC (diamond-like carbon) films prepared by dc pulse plasma CVD (chemical vapor deposition). This study was focused on considering the overlap of the attenuation curve for the chemical species generated by a certain pulse with that for the species generated by the next pulse during DLC film fabrication. As a first-order approximation, the attenuation curves of all ion and radical species were assumed to follow the formula y=y₀ · exp(-λt), where y_o and λ are coefficients. The relationship between pulse frequency and growth rate was derived and compared with the experimental results. The theoretical curve agrees well with the experimental growth rate, indicating that the above approximation for all ion and radical species is useful for estimating the growth rate of DLC films in dc pulse plasma CVD. Moreover, a pulse frequency that gives the maximum film hardness existed. The higher the pulse frequency becomes, that is, the smaller the nonoverlapping ratio becomes, the greater the contribution of ion species to film fabrication. The hardness of the DLC films is small at low frequencies because insufficient numbers of ion species exist in the plasma. In contrast, the hardness slightly decreases at high frequencies owing to the excessive ion contribution to the growth of DLCs.

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It has been found that the strengthening of sintered Ti-6Al-4V alloy compacts were available by addition of fine Mo powder, because of microstructural modification on the sintered compacts. In this study, the metal injection molding process has been applied to strengthen Ti-6Al-4V alloy compacts by addition of fine Fe or Cr powders. Fe and Cr are the same beta stabilizing element as Mo and are more cost effective powders as compared to Mo powder. The microstructures of sintered compacts were consisted of acicular alpha phases and intergranular beta phases. The tensile strength of sintered compacts was increased with increasing Fe or Cr contents, and the effect of Fe addition for strengthening the sintered compacts was larger than Cr addition. Eventually, the tensile strength of sintered compacts added 2mass% of Fe was improved to be 980MPa with 14.8% of elongation, and the compacts added 4mass% of Cr showed the excellent tensile strength of 1030MPa with 15.1% of elongation.

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