Potentiometric evaluation of substrate oxidation and coating porosity

摘要

A fast, nondestructive, and easy to perform method of Potentiometric Evaluation of Substrate Oxidation ("PESO") is provided. A coated part to be analyzed is placed in contact with an electrolytic solution having a pH adjusted to provide an optimum oxide dissolution rate. The open circuit potential of the part is monitored as the substrate oxide dissolves in the electrolytic solution. The voltage typically changes as a function of time during oxide dissolution. When oxide dissolution is complete, the voltage reaches a steady value associated with active dissolution of the substrate metal and reduction processes on the coating. The electrolytic solution can be flowed or agitated to reduce concentration polarization, provide more meaningful voltage measurements, and minimize the time required for analysis. The time required to reach a steady-state voltage provides a measure of the amount of substrate oxide within pores in the coating. The final steady-state voltage level provides a measure of the relative areas of the coating and the exposed substrate, which relates to the porosity of the coating. The method is useful for evaluating the quality of coated parts by providing a quantitative measure of both substrate oxidation and coating porosity.