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ASTM B 764-94 (Reapproved 2003) Standard Test Method for Simultaneous Thickness and Electrochemical Determination of Individual Layers in Multilayer Nickel Deposits (STEP Test) This test method closely estimates the thickness of individual layers of a multilayer nickel deposit and the electrochemical potential difference between the individual layers while anodically stripped at constant current density. Significance and use 1) The ability of a multilayer nickel deposit to enhance corrosion resistance is a function of the electrochemical potential difference between the layers (as measured individually at a fixed current in a given electrolyte versus a reference electrode) and the thickness of the layers. The potential difference must be sufficient to cause the bright nickel or top layer to corrode preferentially and sacrificially with respect to the semibright layer beneath it. 2) This test procedure allows the measurement of these potential difference directly on an electroplated part rather than on separate foil specimens in such a way that time determined the thickness of each layer, while the potential difference between nickel layers is an indication of the corrosion resistance of the total nickel deposit. 3) The interpretation and evaluation of the results of this test will be by agreement between purchaser and CHEMIONIC. Note: This test may be used to help predetermine the corrosion resistance of the multilayer nickel coating in production that are subjected to other corrosion media. It should be understood that due to many factors that influence the progress of corrosion during actual use of the part, the performance of different multilayer nickel deposits in the test cannot be taken as an absolute indicator of the relative corrosion resistance of these deposits in service.
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