The corrosion behaviour of a proprietary stainless steel ('Rex 734') was measured under conditions simulating those found in the human body, in order to assess its suitability for use as an orthopaedic implant material. The performance of this alloy was compared to that of another austenitic stainless steel implant alloy, AISI 316S12. A potentiostat, operating under an original system of computer control, was used to obtain corrosion, breakdown and protection potentials, and Dassive corrosion current densities. Testing was carried out in a variety of different solutions, with various material and surface preparation techniques. Corrosion fatigue and fretting experiments were also performed. Electrochemical corrosion measurements indicated that Rex 734 is more resistant to pitting and crevice attack than 316L in isotonic saline solution. Changing the austenitic grain size of both alloys on cold working Rex 734 did not produce any significant changes in corrosion behaviour. Electropolishing reduced the passive corrosion current on both materials. Torsional fatigue strengths of Rex 734 were higher than those of 316L in air, and were reduced by a smaller amount on exposure to physiological solution. Fretting experiments carried out on simulated bone plate and screw assemblies showed that Rex 734 had a higher initial electrochemical corrosion rate when fretting was initiated, but recovered more quickly after prolonged fretting, 316L specimens showed more fretting damage and wear than Rex 734 assemblies, with specimens containing a mixture of alloys having the worst fretting behaviour. Test samples containing welds exhibited electrochemical corrosion characteristics similar to those of unwelded alloy, but had a poorer fatigue performance. In conclusion, Rex 734 was recommended as a direct replacement for 316L in orthopaedic surgery.
|Date of Award||1984|