REDUCED WEAR AND CLADDING PERFORMANCES OF SEVERAL MATERIALS BY NITROGEN ION-IMPLANTATION

Ball-on-flat-disc wear and friction measurements have been carried out on different materials implanted with nitrogen ions at an acceleration voltage of 80 kV. The investigated disc substrate materials were aluminum, titanium, AISI 52100 steel, nonhardened, hardened and nitrided AISI 420 steel, AISI 304 steel, molybdenum, hardened AISI 420 steel coated with titanium nitride (PVD) and hardened AISI 420 steel coated with titanium carbide (CVD). All measurements were done under dry sliding conditions. In cases where the sliding ball material consisted of a softer material than the rotating substrate material, the effect of cladding, i.e., transport and bonding of material from the sliding ball on to the substrate surface, could be observed. Surface microhardness values were determined by indentation techniques. The results indicate optimum reductions of wear and cladding performances for all materials studied at nitrogen doses of about 2 x 10(17) atoms/cm2, except for aluminum and titanium which showed improved tribological properties up to doses of 4 x 10(17) atoms/cm2. Reduced friction coefficients and enhanced surface hardnesses could also be found for these optimum doses. The observed improvements of surface characteristics are explained by the combination of different effects such as: (i) increase of surface hardness (formation of nitrides); (ii) inhibition of thick surface oxidation layers during wear; and (iii) reduction of the friction coefficient.