Plasma nitriding of Al alloys by DC glow discharge

Substrates of Al alloys 1100 and 2025 were plasma nitrided using a secondary vacuum dc plasma nitriding unit. The influence of process parameters such as, working gas, gas mixture and treatment time on the nitride layer characteristic were examined by ex situ analysis using SEM, EDX, GDS and RBS in order to optimize the plasma nitriding process. Sputtering step was carried out in Ar and H2 (50 : 50) plasma at 400 °C for 50 min. All nitriding treatments were carried at a temperature of 400 °C using 700 V dc voltage. The experimental results showed a dense and continuous AlN layer with thickness about 2.2 μm and nitrogen content about 35–40 at.% for both specimens after 20 h nitriding at pressure of 80 Pa using N2–H24 gas with vol.% of 80/20. The XRD analysis confirmed the presence of AlN phase with a face centered cubic lattice together with fcc metallic Al and aluminum oxide.