ASTM F746-04 (R2021) pdf free download.Standard Test Method for Pitting or Crevice Corrosion of Metallic Surgical Implant Materials.
1.1 This test method covers the determination of resistance to either pitting or crevice corrosion of metals and alloys from which surgical implants will he produced. It is a modified version of an established test2 and is used as a screening test to rank surgical implant alloys in order of their resistance to localized corrosion.
1.2 This test method applies only to passive metals and alloys. Nonpassive alloys (other than noble alloys) arc susceptible to general corrosion and are not normally suitable for implant use.
1.3 This test method is intended for use as a laboratory screening Lest for metals and alloys which undergo pitting or crevice corrosion, or both.
1 .4 The values stated in either SI units or inch-pound units are to he regarded separately as standard. The values stated in each system may not he exact equivalents: therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
3. Summary of Test Method
3.1 A cylindrical specimen fitted with an inert tapered collar is immersed in a phosphate buffered saline electrolyte at 37 °C for I h to establish a corrosion potential. Pitting (or crevice corrosion) is then stimulated by potenliostatically polanzing the specimen to a potential much more noble than the corrosion potential. Stimulation of pitting (or crevice corrosion) will be marked by a large and generally increasing polarizing current.
3.2 Immediately after the stimulation step. the potential is decreased as rapidly as possible to one of several preselected potentials at, or more noble than, the corrosion potential. If the alloy is susceptible to pitting (or crevice corrosion) at the preselected potential. the polarizing current will remain at relatively high values and will fluctuate or increase with time. A post-test examination of the metal specimen establishes whether localized corrosion has occurred by pitting of the exposed surface or by preferential attack at the crevice formed by the tapered collar, or both.
3.3 If the pit (or crevice) surface repassivates at the preselected potential and localized corrosion is halted, the polarizing current will drop to values typical for passive surfaces and the current will decrease continuously. The parameter of interest, the critical potential for pitting (or crevice corrosion), is defined as the highest (most noble) preselected potential at which pit (or crevice) surfaces repassivate after the stimulation step.
4. Significance and Use
4.1 This test method is designed solely for determining comparative laboratory indices of performance. The results may be used for ranking alloys in order of increasing resistance to pitting and crevice corrosion under the specific conditions of this method. It should be noted that the method is intentionally designed to reach conditions that are sufficiently severe to cause breakdown of at least one alloy (Type 316 L stainless steel) currently considered acceptable for surgical implant use, and that those alloys which suffer pitting or crevice corrosion during the more severe portions of the test do not necessarily suffer localized corrosion when placed within the human body as a surgical implant.ASTM F746 pdf download.