Effect of Presputtering on Plasma Ion Nitriding of Aluminium Substrates

The relative effect of the presputtering treatment on the formation of AlN on Al substrates by ion plasma nitriding is investigated. In particular, presputtering time and temperature are considered. Samples of a commercial 7022-T6 Al alloy were nitrided in a two step process consisting of a presputtering stage in which time and temperature were varied and a nitriding stage carried out in the same conditions for all samples. The treated samples were characterised by optical and scanning electron microscopy and energy dispersive X-ray microanalysis, by glancing angle X-ray diffraction and by X-ray photoelectron spectroscopy. An optimal sputtering time was found for the production of thick, uniform AlN layers on the substrates. A higher presputtering temperature resulted in a shorter optimal presputtering time.