Nitriding of Aluminium Alloy in Nitrogen and Nitrogen-Helium Mixture Using 100 Hz-Pulsed DC Glow Discharge

<正> Nitriding of aluminium alloy (AlFe1.8Zn0.8) in nitrogen and nitrogen-helium mixturewas carried out by using 100 Hz-pulsed DC glow discharge. Samples are treated for differentdurations, namely 4 h, 8 h and 12 h, in nitrogen plasma as well as in a mixture of nitrogenheliumplasma for the same processing duration of 4 h. All nitriding treatments are carried out atan input power of 100 W, filling pressure of 1 mbar and substrates temperature of 250℃. X-raydiffraction （XRD） results show an expansion in lattice spacing and consequently shift of diffractionpeaks towards lower angle with the addition of helium in nitrogen plasma. Surface morphology ofthe treated sample is investigated by scanning electron microscopy （SEM） and energy dispersiveX-ray analysis （EDX）. Vickers micro-hardness testing results show increases in surface hardnesswith processing duration as well as with the addition of helium in nitrogen plasmas. This increaseof surface hardness may be attributed to the diffusion of nitrogen content in the surface layergenerating internal stresses. It is observed that the addition of helium positively affects thenitriding of samples.