Plasma characterization for nitridation of aluminium alloy using 50 Hz ac discharge

Abstract

A 50 Hz ac abnormal glow discharge is characterized as a function of filling pressure (1–4 mbar) using a Langmuir probe. It is found that electron temperature, electron density and electron energy distribution function decrease with the gas filling pressure. Nitriding of aluminum alloy (Al–Mg₂–Si) is performed for various time durations (3, 6, 9 and 12 h) and pressures (1 and 2 mbar) by keeping the input power (100 W) and substrate temperature (250 °C) constant. To explore the surface properties induced by plasma, X-ray diffractometer, optical micrography, atomic force microscopy and Vickers micro-hardness tester diagnostic techniques are used. Results exhibit the formation of cubic aluminum nitride. A significant increase in surface hardness is observed when samples are exposed at 1 mbar pressure for 12 h of processing time. A rapid decrease in surface hardness values with the imposed load suggests the formation of a thin modified surface layer.

Keywords:

• glow discharge
• gas–solid reactions
• kinetics
• plasma nitriding

Acknowledgements

This work was partially supported by the Department of Physics, GC University, Lahore, Pakistan, and GC University Research Project for year 2007–08. The authors are very thankful to Prof. Dr Shehzad Naseem, Centre for Solid State Physics, University of Punjab, Lahore, Pakistan, for his contribution in this paper for atomic force micrography.