WEAR OF STEELS IMPLANTED WITH OXYGEN OR ALUMINUM IONS IN AIR, OXYGEN AND NITROGEN

The wear resistance of the martensitic steels AISI 52100 and 440B improved by a factor of more than two by implantation of aluminium ions, and by up to two orders of magnitude after implantation of oxygen ions or co-implantation of aluminium and oxygen ions when tested with a ball-on-disc tribometer in air. Wear tests of oxygen-implanted samples in dry oxygen and dry nitrogen proved the importance of air humidity for the tribo-oxidation of iron. The wear behaviour of the co-implanted samples was less determined by air humidity than that of the oxygen-implanted samples. Instead, the wear reduction of the co-implanted samples depended on the oxygen content of the test atmosphere. Measurements of the microhardness indicated the formation of iron oxides after oxygen implantation and of aluminium oxides after co-implantation. The wear particles formed on AISI 52100 in air contained FeOOH before implantation and both FeOOH and Fe2O3 after all types of ion implantation, as determined by infrared spectroscopy. Concentration profiles by secondary ion mass spectroscopy (SIMS) showed a maximum of 60 at% oxygen after oxygen implantation and of 24 at% aluminium and 21 at% oxygen after co-implantation. Surface analysis of oxygen-implanted samples by X-ray photoelectron spectroscopy (XPS) showed the formation of Fe2O3 and Cr2O3 on the wear tracks. No changes in the microstructure were found by transmission electron microscopy (TEM).