Profile of implanted nitrogen ions in Al alloy for mold materials

Nitrogen ions were implanted into an aluminum alloy (Al-7Si) for casting mo ld materials by plasma-based ion implantation to enhance wear resistance an d hardness of the target. A negative high-voltage pulse of 10 kV with a pul se width of 10 mus and repetition rate of 100 Hz was applied to the target immersed in the nitrogen plasma produced by filament discharge. Auger elect ron spectroscopy (AES) analysis indicated that the depth profile of implant ed nitrogen had two peaks, corresponding to N+ and N-2(+) ions, for short i mplantation times less than approximately 30 min. For implantation times lo nger than 30 min, however, the two peaks merged with each other. The AES an alysis also indicated the formation of AIN by implantation of nitrogen ions . The AlN was formed in the surface region within the nitrogen ion range. A wear-resistance test by the ball-on-disc method showed that nitrogen ion i mplantation resulted in a reduction of the friction coefficient from 0.6 to 0.1 and the wear resistance was increased by one order of magnitude. It wa s also found that nitrogen ion implantation enhances the hydrophilic proper ties. (C) 2001 Published by Elsevier Science B.V. All rights reserved.