Nitridation of Al–6%Cu alloy by RF plasma process

Aluminum–6 wt.%copper alloys were plasma nitrided by using inductively coupled RF plasma process of N2–H2 admixture gases. Pre-sputtering of sample by argon plasma was carried out prior to the nitriding in order to eliminate the surface oxide film. The process parameters including time (9–36 h), temperature (room–350 °C) , and negative bias of the substrates (0–250 V) were varied. To explore the surface properties induced by plasma, glancing incident-angle X-ray diffraction (GIXD), X-ray photoelectron spectroscopy, optical microscope (XPS), and atomic force microscopy (AFM) were used. Results exhibit the formation of hexagonal aluminum nitride. Significant increases of surface hardness are observed after treatment after plasma nitriding. Longer nitriding time and higher substrate temperature increase the amount of AlN formation. The applied bias voltage also affects surface roughness of the samples. The surface roughness is slightly more pronounced when the bias is increased, for instance, the average roughness (Ra) of aluminum–6 wt.%copper alloy increase from 3.74 nm to 4.5 nm when bias elevate from 150 to 250 V.