Plasma nitriding process design in duralumin alloys

Abstract

High density plasma nitriding was proposed as an effective surface treatment for duralumin alloys. This process has a capability to control the RF- and DC-plasmas independently for nitriding. Different from the conventional nitriding processes, the matching between input and output powers is automatically adjusted with the shorter response time less than 1 ms. Plasma diagnosis was instrumented to search for optimum processing condition to plasma nitriding of the duralumin alloys, type A2011 or Al-Cu alloys. RF-voltage, DC bias, carrier gas pressure and nitrogen-hydrogen gas flow ratio were determined to maximize the peak intensities of activated nitrogen atoms and NH radicals in the spectroscopic measurement. In the case of plasma nitriding where the RF-voltage was 250 V, the DC-bias, -350 V, the pressure, 75 Pa and the gas flow-rate ratio, 80 ml/min to 20ml/min the surface hardness of nitrided A2011 alloy sample increased up to 800 Hv even for 14.4 ks at 723 K.