Improvement Of Corrosion Fatigue Strength Research Articles

Nitriding Effect on Corrosion Fatigue Strength of Low Alloy Steel in 1% HCl Aqueous Solution

In this paper the emphasis is focused upon nitriding effect on corrosion fatigue strength of Cr-Mo low alloy steel in 1% HCl aqueous solution.Corrosion fatigue strength enhancement of Cr-Mo low alloy steel by nitriding is discussed on the basis of the corrosion fatigue testing results on gas and ion nitrided Cr-Mo low alloy steel plate specimen with 3.5mm thickness in 1%HCl aqueous solution. It can be concluded that residual compressive stress distributed on the nitrided specimen surface caused improvement of corrosion fatigue strength of Cr-Mo low alloy steel.

Improvement of corrosion fatigue strength of magnesium alloy by multilayer diamond-like carbon coatings

The fatigue behaviour of a wrought magnesium alloy AZ80A coated with multilayer diamond-like carbon (DLC) films with the total thicknesses of 3 μm and 12 μm was studied in laboratory air and distilled water. The effects of the multilayer DLC films on fatigue and corrosion fatigue behaviour were discussed. In laboratory air, the fatigue strengths of the multilayer DLC-coated specimens significantly increased compared with those of the single layer DLC-coated ones with equivalent film thicknesses. Fatigue cracks initiated at the substrate under the defects of the film. Higher fatigue strengths of the multilayer DLC-coated specimens could be attributed to the smaller defect size in the film. However, the single layer films and the multilayer 3 μm DLC film could not improve corrosion fatigue strength in distilled water. The defects were found in the films, through which the corrosive water could reach the substrate. The degradation of fatigue strength under the corrosive environment was not recognized in the multilayer 12 μm DLC-coated specimens, indicating that the thick multilayer DLC coating was effective as a protection film. Through-film thickness defects were successfully removed by the thick multilayer fabrication process.

Effect of thick DLC coating on fatigue behaviour of magnesium alloy in laboratory air and demineralised water

ABSTRACTRotating bending fatigue tests have been performed using Diamond‐like carbon (DLC) coated specimens of a wrought magnesium alloy, AZ80A, in laboratory air and demineralised water and the effect of DLC coating on fatigue and corrosion fatigue behaviour was studied. Three film thicknesses of 3.5 μm, 13 μm, and 25 μm (two‐layer film) were evaluated and particular attention was paid to the role of thick DLC coating. In laboratory air, the fatigue strengths of the DLC‐coated specimens were higher than that of the substrate specimen and increased with increasing film thickness. This was because hard DLC coating with good adhesion suppressed the crack initiation due to cracking of inclusions or cyclic slip deformation on the substrate surface. In demineralised water, the fatigue strength of the 3.5‐μm DLC‐coated specimen was the same as that of the substrate specimen due to the penetration of the water through pre‐existing film defects, while the 13‐μm and 25‐μm DLC‐coated specimens showed increased corrosion fatigue strength with increasing film thickness and also exhibited nearly the same fatigue strength as in laboratory air except for a few premature failed specimens, indicating a potential of thick DLC coating or two‐layer coating for complete improvement of corrosion fatigue strength in aqueous environments.

アルミナ被覆処理ステンレス鋼の生理食塩水中における疲労特性に及ぼすTiアンダーコートの効果

The present investigation was undertaken to examine the effect of Ti undercoating on the corrosion fatigue properties of stainless steel bar coated with plasma-sprayed Al2O3. Corrosion fatigue tests were carried out under push-pull loading at a stress ratio R= -1 and at a frequency of 2 Hz. A physiological saline solution was used as corrosive environment. The fatigue strength of Ti undercoated specimen increased over the whole regime of S-N curve in comparison with that of the annealed substrate metal. Through the longitudinal section observation with a scanning electron microscope, it was revealed that Ti undercoating controlled the infiltration of a physiological saline solution to the substrate surface until 107 cycles. From the measurement of residual stress distribution by X-ray diffractometry along radial axis on the longitudinal section, it was found that the residual stress in the subsurface layer of substrate was changed from the tension to compression along radial axis and undercoat layer had compressive residual stresses in Ti undercoated specimen. In addition, it was clarified from the electrochemical experiments that Ti deposit was slightly nobler than annealed substrate metal. Consequently , it was concluded that the improvement of corrosion fatigue strength of Ti undercoated specimen was chiefly caused by both insulation effect by Ti undercoating and compressive residual stress in the subsurface layer of substrate and undercoat layer.

Effect of Anodic Oxide Film on Fatigue Behaviour of Magnesium Alloys in Laboratory Air and Demineralized Water

This paper describes the effect of anodic oxide film on fatigue behaviour of wrought magnesium alloys. Rotating bending fatigue tests have been performed using smooth specimens with anodic oxide films in laboratory air and demineralized water. Two different anodic oxide films, Mg-Hard and Mg-Light, were evaluated, in which both films had the same thickness of 30 μm, but the former had considerably higher hardness than the latter. In laboratory air, the fatigue strength of the anodized specimens with Mg-Hard was nearly the same as, or slightly higher than, that of the bare or untreated specimens, while the anodized specimens with Mg-Light exhibited higher fatigue strength than the bare specimens. In demineralized water, the fatigue strengths of both anodized specimens were the same as these of the bare specimens, indicating no improvement of corrosion fatigue strength by the anodic oxide films. This was because pores and crackings preexisted within the anodic oxide films acted as penetration path of the solution, thus similar corrosion fatigue process to the bare specimens took place underneath the anodic oxide films.

2305 陽極酸化皮膜を有するマグネシウム合金の大気中および純水中における疲労挙動(S07-1 マグネシウム合金の疲労,S07 構造材料の疲労強度とき裂進展問題)

An experimental study was performed to understand the effect of anodic oxide film on fatigue behaviour of wrought magnesium alloys in laboratory air and demineralized water. Two different films, Mg-Hard and Mg-Light, were evaluated. In laboratory air, the fatigue strength of the anodized specimens with Mg-Hard was nearly the same as that of the bare specimens, while the anodized specimens with Mg-Light exhibited higher fatigue strength than the bare specimens. In demineralized water, the fatigue strengths of both anodized specimens were the same as those of the bare specimens, indicating no improvement of corrosion fatigue strength by the anodic oxide films. This was because pores and crackings preexisted within the films acted as penetration path of the solution, thus similar corrosion fatigue process to the bare specimens took place underneath the films.

210 HVOF法によるWC溶射材の腐食疲労強度の改善(材料力学V)

210 HVOF法によるWC溶射材の腐食疲労強度の改善(材料力学V)

Improvement Of Corrosion Fatigue Strength Of Materials By VariousSurface Treatments.

In this paper it is summarized on improvement of corrosion fatigue strength of materials by various kind of surface trcatrnents mainlv based upon the author's experimental data. It is described on the effect of synthetic resins. thermalsprayed coatings and ion plating on corrosion fatigue strength of structural materials. The emphasis is focussed upon the tar epoxy resin coating for ship structural steels and thermal-sprayed coatings for machne structural steels. The mechanism of the improvement of corrosion fatigue strength of materials by surface coatings are also described. It c'm be concluded that the improvement of corrosion fatigue strength is not effective when an interception effect disappear due to the breakage or degradation of the tar epoxy resin coating. It can also be concluded that the effective thermal-sprayed coating to improve corrosion fatigue strength should be of very low porosity and finnly adhesive to the base metal.

Improvement of Corrosion Fatigue Strength of High Strength Steel by Thermal Sprayed (WC-Cr-Ni) Cermet Coating(Fatigue 3)

Improvement of Corrosion Fatigue Strength of High Strength Steel by Thermal Sprayed (WC-Cr-Ni) Cermet Coating(Fatigue 3)

ＴｉＮ被覆処理鋼の疲労強度特性に及ぼす切欠きの影響

In order to investigate the effect of notch on the fatigue strength of carbon steel coated with TiN thin hard film, cantilever-type rotating-bending fatigue tests were carried out in air and in 3% saline solution by using U-shaped notch round-bar specimens of 0.35% carbon steel coated with TiN by physical vapor deposition (PVD) method. From the experimental results of the fatigue tests in air, an increase in fatigue strength was observed for the TiN-coating specimens, as compared with those without coating. Improvement in fatigue strength depends on the stress concentration factor, and the maximum improvement of 50% was observed on the sharp notched specimen. The endurance limit was defined as the crack initiation limit for the notched specimen with coating, while it was defined as crack growth limit for the notched specimen without coating. It was clear from an elasto-plastic analysis by FEM and the experimental results that a strain at the notch root for crack initiation limit was increased by the existence of hard thin film. From the corrosion fatigue test results, TiN-coating film effectively protects the substrate from the corrosive environment, and then the improvement of corrosion fatigue strength was about 87% for the dull notched specimen, which was the same as that in the smooth specimen.

窒化クロム被覆処理鋼の腐食疲労挙動

Chromium nitride (CrN) has good properties, such as high hardness, good wear resistance, relatively good adhesion of the film and an attractive color, in addition to corrosion resistance. The superior properties of CrN thin film may be useful to surface improvement of metals. In order to investigate the effect of CrN coating on the corrosion fatigue behavior of metals, cantilever-type rotating bending fatigue tests were carried out in 3% saline solution by using the round-bar specimens of 0.37% carbon steel coated with CrN by a physical vapor deposition method. Obvious improvement of corrosion fatigue strength was observed for the CrN coated specimens, as compared with those without coating. Also, it was observed that the improvement of corrosion fatigue strength depended on the thickness of coated film, because small pores and pinholes in the coating were produced during coating process and these defects decreased with increasing film thickness. The quantitative evaluation of defects in the coating film was made from the current density determined by the electrochemical polarization method. The open pores in the coating acted as a small anode area which accelerated the corrosion of base metal, and the corrosion fatigue strength was controlled by the defect size in the coating.

１３Ｃｒステンレス鋼の腐食疲労強度に及ぼす溶射皮膜の影響

In order to clarify the influence of plasma-sprayed coating on the corrosion fatigue strength of 13Cr stainless steel, WC-Co, ZrO2, Cr3C2 and Co-Cr-Ni-W were plasma-sprayed on round bar fatigue test specimens of 13Cr stainless steel. The surface, the cross section of these coatings and the interface between these coatings and base metal were examined by SEM and optical microscope. Rotating corrosion fatigue tests of these coated specimens were conducted in 3% NaCl aqueous solution at a testing speed of 3600rpm.The WC-Co and ZrO2 coatings with low porosity improved corrosion fatigue strength at 107 cycles by about 70 percent. It might be concluded that the effective coating to improve corrosion fatigue strength should be of very low porosity and firmly adhesive to the base metal.On the other hand, no improvement of corrosion fatigue strength was observed by the Cr3C2 and Co-Cr-Ni-W coatings with relatively high porosity. In these specimens, corrosion fatigue cracks initiated from corrosion pits at the surface of the base metal and propagated predominantly through the intergranular path.

炭素鋼の腐食疲労強度に及ぼす窒化チタン被覆の影響

In order to investigate the effect of titanium nitride (TiN) coating on corrosion fatigue behavior of metal, cantilever-type rotating bending corrosion fatigue tests were carried out in 3.0% saline solution by using the round bar specimens of 0.37%C carbon steel, JIS S35C, coated with TiN by the physical vapour deposition (PVD) method or the chemical vapour deposition (CVD) method. From the experimental results, obvious improvement of corrosion fatigue strength was observed in TiN coated specimens, as compared with those without coating. The corrosion fatigue crack propagation rate observed on the surface of coated specimens was equivalent to that without coating. Fracture surface observations with a scanning-electron microscope revealed that the corrosion fatigue crack propagated from small corrosion pits formed at the base metal under the coating layer due to aqueous solution transmitted throughout the small pinhole or flaw of the coating. The causes of the improvement in the corrosion fatigue resistance of TiN coated material were elucidated that the TiN layer does not peel off from the substrate surface owing to its enough adhesion and corrosion resistance of the layer itself is more excellent than that of the substrate metal.