Deposition of mirror-like surface finish ultrananocrystalline diamond films on tungsten carbide by optimizing the substrate pretreatment

In this study, we successfully fabricated ultrananocrystalline diamond (UNCD) films on tungsten carbide with mirror-like surface finish (R-a < 40 nm), strong adhesion, and exceptional tribological performance by adopting the optimized two-step pretreatment process. It was found that the ultrasonication in Murakami reagent will substantially increase the substrate surface roughness even with short duration, which is less controllable compared with that of immersion in Murakami reagent. Besides, the surface roughness is strongly affected by acid etching when the substrate is firstly ultrasonicated in Murakami reagent. However, it is much less influenced for the immersion pretreatment. With the UNCD film, a decrease in the surface roughness up to 72% can be realized compared with the as-pretreated substrate. The Rockwell indentation tests demonstrate that the adhesive strength of the UNCD film deposited with the optimized pretreatment is comparable to that of MCD and NCD films as reported in other studies. Ball-on-plate tribotests with Si3N4 counterpart balls reveal that the coefficient of friction (COF) of the UNCD film is 0.07-0.12, which is 76.6% and 41.6% lower compared with that of the MCD and NCD film. The wear rate of the UCND film is 0.708-1.844 x 10(-7) mm(3)/(N.m), close to that of the MCD and NCD film. The results reported in study provide significant insights into the scientific and industrial research of diamond-coated WC-Co cutting tools.