Plasma electrolytic oxidation of brass

Abstract Plasma electrolytic oxidation (PEO) is first reported for the non-valve metal of brass. The surface morphology of the PEO-treated brass has been examined, indicating the formation of a porous layer similar to that of PEO of valve metals. Abundant lines of Cu and Zn in the optical emission spectra (OES) of the PEO plasma confirms the participation of substrate in the oxide formation. Plasma electron temperature has been estimated by two-line method based on species of Cu, Zn and H, respectively, and also the Boltzmann plot with multiple lines of Cu I. The temperature lies between ~4393 and ~6911 K. However, the spectral lines of Cu I in ultraviolet region are found to be not suitable for temperature estimation. The coating contains crystalline phases of CuO, Cu2O and ZnO, as well as amorphous SiO2. Tribological tests show that the wear resistance of the PEO-treated brass is nearly ~16 times that of the uncoated metal. The mechanism of the PEO of brass has also been discussed.