PHYSICOCHEMICAL AND TRIBOLOGICAL CHARACTERIZATION OF TITANIUM OR TITANIUM PLUS CARBON IMPLANTED AISI-M2 STEEL

AISI M2 steel samples were implanted with 110 keV titanium ions at fluences ranging from 5 x 10(16) to 4 x 10(17) Ti cm-2. Titanium plus carbon dual implantation was also studied. Titanium distribution profiles were determined using the (Ti(p,gamma)V)-Ti-48-V-49 resonant nuclear reaction. The incorporation of carbon and oxygen from residual gases was studied as a function of titanium fluence and residual pressure using nuclear backscattering spectrometry at 5.7 and 7.5 MeV He+ ion energies respectively. A competition phenomenon between carbon and oxygen incorporation is pointed out. Analysis of the phases formed was performed using conversion electron Mossbauer spectroscopy. Fe(Ti) solid solution, a-FexTi100-x and superficial a-Fe-Ti-C amorphous phases were identified. Tribological tests involving a ball (Al2O3 or 52100) and disc contact were performed to characterize the friction behaviour of the implanted surface. It is shown that titanium or titanium plus carbon implantation leads to a reduction in the friction coefficient. The wear tracks and debris were examined using scanning electron microscopy and electron microprobe cartography. For the two types of balls a reduction in the wear track width was observed together with oxidation of the wear debris. The tribological improvement observed depends not only on the presence of the superficial a-Fe-Ti-C amorphous layer but also on the surface chemical reaction during the wear process.