Stainless steels show excellent corrosion resistance, which is lost during
conventional hardening processes at temperatures above 500 degrees C, like
gas or plasma nitriding, to improve the low hardness and to reduce the high
wear rate. For aluminium alloys it is impossible to improve the mechanical
properties by traditional nitriding. Plasma immersion ion implantation (PI
II) of nitrogen is successfully used for hardening both austenitic stainles
s steels and aluminium alloys. Compared to the untreated materials the hard
ness and the wear resistance can be improved significantly. For austenitic
stainless steels an 'expanded austenite' layer of up to several tens of mic
rometer thickness and for aluminium alloys an AlN layer of more than 10-mu
m thickness were formed over a few hours. Corrosion tests showed no or only
small changes in the corrosion behaviour for stainless steel. The AlN laye
r can be used as a supporting layer for the deposition of hard materials li
ke CrN on aluminium alloys. It is shown that the partial pressure of oxygen
in the residual gas in the vacuum chamber plays an important role for the
nitriding of both stainless steel and aluminium alloys. (C) 2000 Elsevier S
cience S.A. All rights reserved.