MICROSTRUCTURE AND TRIBOLOGY OF NITROGEN-IMPLANTED MOLYBDENUM AND TUNGSTEN

The microstructure, microhardness, wear and friction of nitrogen impla nted (100-300 keV, (0.75-10) X 10(17) cm-2) Mo and W were investigated . Using X-ray diffraction the formation of alpha-phase, cubic subnitri des (Mo2N, MoN(x), W2N) and hexagonal nitride (W2N, WN) as a function of the implant dose has been observed. The microhardness (HV 0.005) of implanted Mo and W shows a significant increase. Tribological tests w ere performed using an oscillating ball-on-disk tester (where the ball material was cemented carbide). Implanted Mo exhibits wear rates orde rs of magnitude smaller than those of unimplanted samples. The wear re duction is mainly due to a transition from severe adhesive wear to mil d oxidative wear. Concurrently the coefficient of friction of Mo again st cemented carbide is reduced from 0.75 to < 0.10. For W the effect o f N implantation onto the wear rate is less pronounced than for Mo.