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

抄録

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.