Pulse current plasma assisted electrolytic cleaning of AISI 4340 steel

An electrolytic plasma process (EPP) for cleaning AISI 4340 steel was performed in a 10% solution of sodium bicarbonate operated at 70 °C. The effects of the pulse frequency (f) and duty cycle (δ) on the surface morphology, microstructure, mechanical and corrosion properties were investigated. Compared to the conventional DC process, the pulsed EPP cleaning resulted in reduced surface roughness and compressive residual stress at the surface. Minimal reduction in hardness and no reduction in toughness due to hydrogen embrittlement (ASTM F519) were found. At the same time, rotating bending beam fatigue tests indicated a noticeable reduction in fatigue life, which could be offset by a shot peening treatment prior to EPP cleaning at 10 kHz and δ = 0.8. Glow discharge optical emission spectroscopy indicated minimal changes in the surface composition and potentiodynamic corrosion studies revealed a slight ennoblement of the surface attributable to an increased rate of cathodic processes. Optimal process parameters were identified for δ = 0.8 and f = 100–10,000 Hz.