ASTM B764 – Standard Test Method for Simultaneous Thickness and Electrode Potential Determination of Individual Layers in Multilayer Nickel Deposit (STEP Test)
Significance and Use
4.1 The ability of a multilayer nickel deposit to enhance corrosion resistance is a function of the difference in the electrode potentials of the nickel layers (as measured individually at a fixed current density in a given electrolyte versus a reference electrode) and the thicknesses of the layers. The potential differences must be sufficient to cause the bright nickel or top layer to corrode preferentially and sacrificially with respect to the semi-bright nickel layer beneath it.
4.2 This test procedure allows the measurement of these potential differences directly on an electroplated part rather than on separate foil specimens in such a way that time determines the thickness of each layer, while the potential difference between nickel layers is an indication of the corrosion resistance of the total nickel deposit.
4.3 The interpretation and evaluation of the results of this test should be by agreement between the purchaser and the manufacturer.
NOTE 1: This test may be used as a quality assurance test of the multilayer nickel coatings applied in production. 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.
1.1 This test method closely estimates the thickness of individual layers of a multilayer nickel electrodeposit and the potential differences between the individual layers while being anodically stripped at constant current density.2,3
1.2 This test method does not cover deposit systems other than multilayer electroplated nickel deposits.