LONG-TERM CORROSION RESISTANCE OF BIOMEDICAL GRADE-STAINLESS STEEL ISO 5832-1 ('316LVM') UNDER EXTERNAL ANODICELECTRICAL PULSING CONDITIONS

摘要

For medical implant application of metals or alloys, one major prerequisite is the ab-sence of release of metal ions to the surrounding tissue. In the case of stainless steel, this prerequisite can be achieved by modifying the surface by chemical and electrochemical passivation pre-treatments so that the general corrosion-rate will be reduced and pitting corrosion will, not occur. In a first step, the surface of the test specimens (10 mm diam.) were chemically pre-treated with nitric acid using different concentrations and duration. In the second step, the passivation effect was tested by applying voltage-scans reaching from hydrogen to oxygen evolution in a,3-electrode CV-measurement using phosphate buffered saline (PBS) (pf17.4) as electrolyte. It turned out that after the 2nd of a total of five scans all CV-diagrams looked almost the same and the chemical passivation treatment was of minor effect; none of the CV-diagrams showed effects of pitting corrosion. The.third step was to apply ex-ternal electrical anodic pulses (n=5.3x10~6) on the surface of. the specimen (+4.5V, 0.5ms, 740Hz). In the-forth step, the passive behaviour again was tested using the same CV-measurement setup. Again, no. effect of pitting corrosion was seen and in parts of the CV-diagrams the.measured current signal was less than before.