FRICTION AND WEAR PERFORMANCE OF ION-BEAM-DEPOSITED DIAMOND-LIKE CARBON-FILMS ON STEEL SUBSTRATES

In this study, we investigated the friction and wear performance of io n-beam-deposited diamond-like carbon (DLC) films (1.5 mu m thick) on A ISI 440C steel substrates. Furthermore, we performed a series of long- duration wear tests under 5, 10 and 20 N loads to assess the load-bear ing capacity and durability limits of these films under each load. Tes ts were performed on a ball-on-disk machine in open air at room temper ature, about 22 +/- 1 degrees C, and humidity, about 30% +/- 5%. For t he test conditions explored, we found that (1) the steady state fricti on coefficients of pairs without a DLC film were in the range 0.7-0.9 and the average wear rates of 440C balls (9.55 mm in diameter) sliding against uncoated 440C disks were on the order of 10(-5) mm(3) N-1 m(- 1), depending on contact load; (2) DLC films reduced the steady state friction coefficients of test pairs by factors of 6-8, and the wear ra tes of pins by factors of 500-2000; (3) the wear of disks coated with a DLC film was virtually unmeasurable whereas the wear of uncoated dis ks was guile substantial; (4) the DLC films were able to endure the ra nge of loads, 5-20 N, without delamination, and to last over 1 000 000 cycles before wearing out. During long-duration wear tests, the frict ion coefficients were initially on the order of 0.15, but decreased to some low values of 0.05-0.07 after sliding for 15-25 km, depending on the load, and remained low until wearing out. This low friction regim e was correlated with the formation of a carbon-rich transfer film on the wear scar of 440C balls. Microlaser Raman spectroscopy and scannin g electron microscopy were used to examine the structure and chemistry of worn surfaces and to elucidate the wear- and friction-reducing mec hanisms of the DLC film.