Modification of steel and aluminium by pulsed energetic ion beams

The treatment of surfaces and thin layers of material with pulsed high-energy ions is a novel technique developed in Russia, Poland and USA. The advantages of this method, which is comparable with pulsed laser treatment, is the well-defined modification depth because of partial melting with subsequent quenching, the possibility of simultaneous doping and the low treatment costs in comparison with conventional ion-beam treatment. Important results of other groups and our own results are described and discussed. Stainless steel as well as aluminium and aluminium alloys were bombarded with pulses of different ions ranging from 10 ms down to 50 ns width. The energy density was in the region of 0.01-2 J cm(-2). Thus the region where the microstructure of the materials was modified in the solid state was covered up to the melting point. The longer pulses (greater than or equal to 1 ms) were generated with the Heidelberg ion source MUCIS, the short ones (less than or equal to 1 mu s) in collaboration with the Institute of Nuclear Physics in Tomsk, Russia. The resulting microstructure was studied by X-ray diffraction, conversion electrons Mossbauer spectroscopy and atomic force microscopy; the macroscopic properties by hardness measurements and corrosion tests. The most important result was the proof that aluminium and stainless steel can be nitrided at low temperatures by pulsed nitrogen beams with ms pulse width. In addition, it was shown that various phase transitions occurred in stainless steel after ms- and ns-pulsed ion bombardment. This has consequences for the hardness of the material. For aluminium-based materials the hardness and pitting resistance could be improved. (C) 1999 Elsevier Science S.A. All rights reserved.