Scratch-wear resistance of nanoscale super thin carbon nitride overcoat evaluated by AFM with a diamond tip

Atomic force microscopy (AFM) was used to investigate the scratch-wear resi stance of ultrathin superhard carbon nitride overcoats of thickness 1, 2, 4 , 6, 8 and 10 nm. When sliding against a diamond tip of radius less than 10 0 nm in the mode of line scratch, the thin overcoats of thickness 1-4 nm ex hibited poor wear resistance, especially at contact pressures larger than 2 5 GPa, with a wear depth of 4 nm or larger and a specific wear rate up to 0 .8 X 10(-4) mm(3)/nm. Non-contact mode imaging of a scratched surface has s hown that a large amount of nanoscale wear debris was formed along the two sides of the scratched grooves, which indicated that the material removal m echanism of such thin overcoats was due to brittle fracture and abrasive we ar, both in the nanoscale. In comparison, the overcoats of thickness 6-10 n m exhibited wear resistance with a specific wear rate less than 0.2 x 10(-4 ) mm(3)/nm. Instead, the least debris was observed on the scratched surface s and only shallow grooves were left after scratching. It means that the gr ooves were formed by both plough and plastic deformation. The micro/nanowea r mechanism and thickness effect of coating on scratch resistance were disc ussed. (C) 2000 Elsevier Science S.A. All rights reserved.