TRIBOMECHANICAL PROPERTIES OF ION-IMPLANTATION-SYNTHESIZED BN FILMS AND THEIR DEPENDENCE ON TI-6A1-4V SUBSTRATE HARDNESS

The tribomechanical properties (i.e. Knoop microhardness, friction coe fficients and wear) of boron nitride films synthesized by ion implanta tion are studied. Boron was evaporated by electron beam heating and de posited as 1000 Angstrom films onto polished Ti-6Al-4V cylindrical sub strates (where the composition is in approximate weight per cent). The films were then bombarded with 50 keV N-2(+) ions to a dose of 3 x 10 (17) N-2(+) cm(-2) at 450 and 600 degrees C implantation temperatures for which we previously reported the formation of hexagonal boron nitr ide. Knoop microhardness measurements indicate that the films are rath er soft with friction coefficients of the order of 0.1 when sliding ag ainst an AISI 52100 steel ball. When the boron-coated Ti-6Al-4V sample s were first hardened with 100 keV N+ ions to a dose of 10(17) Nf cm(- 2) and then implanted with 50 keV N-2+ ions to a dose of 3 x 10(17) N- 2(+) cm(-2). Knoop microhardness increases of 52% and 37% relative to the untreated Ti-6Al-4V substrate were obtained while the sliding fric tion coefficients dropped to 0.06 and 0.08 for the 450 degrees C and 6 00 degrees C implantation temperatures respectively. These results sho w that multienergy ion implantation can be used to obtain low friction tribological systems in agreement with the adhesion theory of frictio n.