プラズマ溶射セラミックス被覆ステンレス鋼の生理食塩水中における疲労挙動

Abstract

To evaluate the potential of prosthetic application, the SUS316L stainless steel rod specimen coated with plasma-sprayed Al2O3 deposits has been fatigued in a physiological saline solution (0.9% NaCl solution). Fatigue tests were conducted in push-pull loading under the stress ratio of R=-1 and frequency of 2Hz. In the Al2O3 sprayed specimen, fatigue cracks preferentially originated from craters which were formed on the surface of substrate metal by grit blasting, and extended into the bulk of substrate metal. It was considered that a main fatigue crack had grown into plasma-sprayed coating when the coating was unable to accommodate its deformability to the largest displacement of crack opening at the substrate metal surface. It is said that the plasma-sprayed coating can keep the substrate metal from corrosive attack during the initial growth stage of fatigue crack subsequent to its initiation. Microfractography showed that the stage IIb in the fatigue crack growth rate diagram, characterized by more than 50 percent fatigue striation mode in the fraction of fracture surface, appeared in the higher region of ΔK values for the Al2O3 sprayed specimen. The crack growth rate in the stage IIb was lower in the Al2O3 sprayed specimen than in the non-sprayed one. This was thought to be responsible for the prolongation of fatigue life in the Al2O3 sprayed specimen.