Plasma electrolytic polishing of nitrided steel under force convection condition

Abstract

The effect of plasma electrolytic polishing in an ammonium chloride electrolyte under force convection condition on the characteristics of medium carbon steel after anodic plasma electrolytic nitriding was investigated. The morphology of the steel surface was studied using a metallographic microscope. The phase composition of the surface layers was studied using an X-ray diffractometer. Treatment specimens were tested under dry friction conditions with a counter body made of bearing steel. Corrosion studies were performed using potentiodynamic polarization curves in a 3.5 % sodium chloride solution. Nitriding increased the surface hardness up to 1130 HV due to the formation of a nitride-martensite layer with an outer oxide layer. After polishing of the nitrided surface, the loose outer part of the oxide layer containing microcracks and pores is removed, surface lightening has occurred. The reduction of the wear rate of 45-fold and the corrosion current density of 4.8-fold of nitrided steel by plasma polishing without changing the structure of the diffusion layers was shown.