The SUS316L stainless steel rod specimen coated with plasma-sprayed Al 2 O 3 deposits has been fatigued in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of its application to prosthetic implant materials. Push-pull loading fatigue tests were conducted at the stress ratio of R = -1, and at the frequency of 2 Hz. Pure titanium powder was selected for undercoat. Fatigue damage was examined on longitudinal section of the specimen and fracture surface by optical and electron microscopy from the microstructural viewpoints. The plasma spraying of Al 2 O 3 powder has significantly improved fatigue properties of the substrate metal in the longer range of fatigue lives, compared with the results of the non-coated steel specimen. It was found from electrochemical experiments that titanium for undercoat metal has acted as sacrificial anode to protect the substrate metal from corrosive attack and under lower stress amplitudes the plasma sprayed Al 2 O 3 coating kept the solution out at an early stage of fatigue lives. Fatigue cracks preferentially originated from flaws, which had been caused on the substrate metal surface through grit blasting, and extended into the bulk of substrate metal. Fatigue cracks appear not to develop into plasma-sprayed deposits while the deposits could accommodate themselves to the crack opening displacement at the surface of substrate metal. It was understood that the plasma sprayed coating has enhanced fatigue properties in the solution both by keeping the solution out during the early stage of fatigue lives and by electrochemical effects of the undercoat metal when the topcoat was cracked in macroscopic scale.

Fatigue properties of the Al 2 O3 plasma-sprayed SUS316L stainless steel rod specimens coated on different spraying conditions have been studied in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of surgical implant application. Fatigue tests were conducted in push-pull loading at the stress ratio of R = -1, and frequency of 2 Hz. Microstructure related with fatigue damage was examined by SEM and TEM. The fatigue strength of Al 2 O 3 plasma-sprayed metals significantly depended on spraying conditions: the effects of spraying on fatigue strength decreased with increasing the applied stress amplitude. As-blasted specimens were higher in fatigue strength than Al2O3 plasma-sprayed specimens. It was found that the plasma spraying had significant effects on fatigue crack growth behavior in the early stage of crack propagation. Fatigue cracks preferentially originated from dents that had been caused on the substrata metal surface subjected to grit-blasting. These results are discussed with both the compressive residual stresses due to the grit blasting which was carried out prior to plasma spraying and the corrosion-resistance of the alumina deposit.