Improving Spatial Confinement of Anodic Dissolution of Heat-Resistant Chromium−Nickel Alloys during Pulsed Electrochemical Machining

Abstract

Using a microsecond-pulsed current (20 μs) for the high-rate anodic dissolution of heat-resistant chromium−nickel alloys (current density amplitudes up to 100 A/cm2) can enable the improvement of the spatial confinement of anodic dissolution due to the presence of a growing dependence of current efficiency on the current density observed in these conditions. This effect, however, is limited to chromium−nickel steel only, and the duty cycle must be at least 4. We hypothesize that this dependence arises from thermokinetic effects that manifest as a series of interrelated processes with positive feedback: rate of electrochemical reaction (current density)−surface temperature−rate of electrochemical reaction. In certain critical conditions, this relationship results in thermokinetic instability and destruction of passive surface layers.