Masahiko Kato

Bio: Masahiko Kato is an academic researcher from Hiroshima University. The author has contributed to research in topics: Delamination & Fatigue limit. The author has an hindex of 12, co-authored 83 publications receiving 451 citations.

Relation between delamination of thin flims and backward deviation of load–displacement curves under repeating nanoindentation

Abstract: The delamination behavior of sputter coated TiN and AlN films have been examined from the load–displacement curves under repeated nanoindentation loading. When the penetration depth is either much larger or much smaller than the film thickness, the curve progresses in forward direction that represents the deformation of the substrate or film. On the other hand, a backward deviation is observed when the penetration depth is comparable with the film thickness. Observation of the indents by a scanning electron microscope (SEM) and an atomic force microscope (AFM) shows that cracking and extrusion of the film occur when the backward deviation appears. It suggests that the partially delaminated film releases the compressive residual stress and causes an upward bending due to the elongation of the delamintated film, which resists the penetration of the indenter in the consecutive cycle.

Observation by atomic force microscope of corrosion product during pitting corrosion on SUS304 stainless steel

Abstract: Using in situ observation by atomic force microscope, it was found that the corrosion product plays an important role on the growth of corrosion pits on SUS304 steel in NaCl solution and the current density for pit growth was much higher than that applied on the entire surface.

Influence of ultraviolet light irradiation on corrosion behavior of weathering steel with and without TiO2-coating in 3 mass% NaCl solution

Abstract: In this study the influence of ultraviolet (UV) light on the corrosion behavior of weathering steel with and without TiO 2 coating has been investigated in 3% NaCl solution, using anodic polarization, dipping and dropping tests. In polarization tests a large negative shift of corrosion potential appeared for the TiO 2 -coated specimen in UV light. The weight loss of the steels with and without TiO 2 film increased under UV light in the dipping test, while they decreased in the dropping test. The rust formed on the weathering steel showed a semiconductor like behavior, similar to that shown by TiO 2 film.

3-Dimensional observation of the interior fracture mechanism and establishment of cumulative fatigue damage evaluation on spot welded joints using 590 MPa-class steel

Abstract: To investigate the fatigue fracture mechanism in spot welded joints using a 590 MPa-class base metal, fatigue tests were conducted under constant loading conditions. In this study, three dimensional observation was made on the propagation behavior of fatigue cracks initiating at the edge of the slit between sheets. Moreover, an evaluation method of the fatigue life was proposed for random loading conditions. Since the mean load obviously affected the fatigue life of the spot welded joints, the proposed evaluation method was applied to account for this load effect. The proposed evaluation method satisfied the application range in the automobile industry. Therefore, it is thought that the proposed method is suitable for practical applications.

Backward deviation and depth recovery of load–displacement curves of amorphous SiC film under repeating nanoindentation

Abstract: The deformation and delamination behaviors of sputtered amorphous SiC film have been studied from the load–displacement curves under repeated nanoindentation loading When the penetration depth is either much larger or much smaller than the film thickness, the curve progresses in forward direction that represents the deformation of the substrate or film On the other hand, when the penetration depth is comparable with the film thickness, large backward deviation and depth recovery around the minimum load are observed Observation of the indents by an atomic force microscope proved that delamination starts from the portions beneath the indenter and progresses towards the shoulder of the indent This behavior is strongly connected with the existing large residual compressive stress in the film The difference in the delamination behaviors between SiC and TiN, AlN films is also discussed

Corrosion resistance of TiO2 films grown on stainless steel by atomic layer deposition

Abstract: Titanium dioxide (TiO2) films have been deposited onto stainless steel substrates using atomic layer deposition (ALD) technique. Composition analysis shows that the films shield the substrates entirely. The TiO2 films are amorphous in structure as characterized by X-ray diffraction. The electrochemical measurements show that the equilibrium corrosion potential positively shifts from − 0.96 eV for bare stainless steel to − 0.63 eV for TiO2 coated stainless steel, and the corrosion current density decreases from 7.0 × 10− 7 A/cm2 to 6.3 × 10− 8 A/cm2. The corrosion resistance obtained by fitting the impedance spectra also reveals that the TiO2 films provide good protection for stainless steel against corrosion in sodium chloride solution. The above results indicate that TiO2 films deposited by ALD are effective in protecting stainless steel from corrosion.

A study on the N-, S- and Cl-modified nano-TiO2 coatings for corrosion protection of stainless steel

Abstract: Nano-titania coatings doped with anions of nitrogen, sulfur and chlorine have been supplied on the surface of 316L stainless steel by a sol–gel process and dip-coating technique. The measurements of XRD, SEM, ATR-IR, Raman and XPS were carried out to characterize the chemical composition and structure for the prepared samples. The corrosion performances of the coating in 0.5 M NaCl were evaluated by electrochemical impedance spectroscopy (EIS) and polarization measurements. According to the measurements of EIS and electrochemical polarization, the N-modified TiO 2 nano-coatings show a highest corrosion resistance among the prepared coatings. It is revealed, from the SEM, XRD and Raman characterizations, that the surface of N-modified TiO 2 nano-coatings are more compact and uniform, relatively well-crystallized and able to act as an optimal barrier layer to metallic substrates. The XPS analysis confirms the presence of low concentration of N element in two forms, atomic β-N (interstitial state) and chemisorbed γ-N 2 on the surface of TiO 2 nano-coatings. It is suggested that the addition of nitrogen is beneficial to improve the compact structure and enhance the hydrophobic property.

Advances in friction stir spot welding

Abstract: Friction stir spot welding (FSSW) is a variation of linear Friction Stir Welding (FSW), which was invented to compete with resistance spot welding (RSW) and riveting of lightweight alloys in the au...

Localized corrosion behaviour of reinforcement steel in simulated concrete pore solution

Abstract: The correlation of localized corrosion behavior and microstructure of reinforcement steel in simulated concrete pore solutions was investigated. The SEM/EDS analysis showed that most of ferrite, minor amount of pearlite and some MnS inclusions existed on the steel surface. The SKPFM results indicated a higher corrosion tendency at the ferrite grain boundaries, pearlite grains and MnS inclusions. The EIS and electrochemical polarization measurements demonstrated the influence of pH and chloride concentration on the corrosion behavior. In situ optical observations and AFM images revealed a detail of the localized corrosion behavior, which was in good agreement with the results from the other measurements.

Self-propagating high temperature combustion synthesis of TiB/Ti composites

Abstract: Dense TiB/Ti composites were fabricated by Self-propagating High Temperature Synthesis connected with Pseudo Hot Isostatic Pressing (SHS/PHIP). T ad s, T c and combustion velocities of the TiB– x Ti system decrease with increasing the amount of Ti. The synthesized TiB–Ti cermets mainly consisted of TiB and Ti phases, but TiB 2 phase existed in some products with lower content of metal. Needle-like, rod-like or plate-like TiB grains formed in the microstructure of synthesized TiB– x Ti composites. The size of the TiB grains decreased with an increasing amount of metal addition. The hardness and relative density of the synthesized materials are all beyond HRA82 and 94%, respectively. The introduction of Ti into TiB– x Ti cermets resulted in a drastic increase in the bending strength, tensile strength, compression strength, fracture toughness and the maximum values were obtained with the addition of 40 wt.%Ti.