FRICTION AND WEAR OF NITROGEN-IMPLANTED GLASSY-CARBON

Scratch friction and wear behavior of a glassy carbon (GC) implanted w ith a high dose of nitrogen as studied when in contact with a steel ba h and with diamond indenter. A sliding velocity of V=0.2 mm s(-1) and loads from 0.5 to 4 N during 50-300 cycles were applied in laboratory air (humidity similar to 50%). Smoother and more closely compacted sur faces than in the virgin state were obtained at doses of 1 x 10(16)-1 x 10(17) ions cm(-2) but surfaces became heavily blistered at higher i on dose levels (1-1.5 x 10(18) ions cm(-2)). It was shown that the enh ancement of wear resistance is associated with the amorphization of th e implanted layer, which leads to a rise in strength of implanted GC a nd to a decrease in the rate of crack propagation in a hostile environ ment. Crescent-shaped cracks were observed on the surface of virgin. G C subjected to friction with a steel ball. At higher doses of implanta tion, steel wear particles adhered to the rough blistered surface in c ontact with the steel ball, and bubbles burst Following contact with t he diamond indenter. The implant dosage needed for maximum wear resist ance was found to be in the vicinity of 1 x 10(16) ions cm(-2). The in fluence of the gradual change in the bonding mode with the of implanta tion dosage (from sp(2), characteristic for graphite and GC, to sp(3), characteristic for diamond) on the tribological properties of the car bon materials is discussed. The synergetic influence of implantation a nd environmental humidity was adduced to explain the observed behavior of GC in friction and wear.