High Wear Resistance of Magnetron Sputtered Cr 80 Si 20 N Nanocomposite Coatings: Almost Independent of Hardness

Hardness has been popularly considered as an essential factor defining the wear resistance of hard coatings. Here, we report magnetron sputtered Cr 80 Si 20 N nanocomposite coatings, of widely varied packing densities, that exhibited identical specific wear rates, while the hardness changed over a wide range (from ~12 to ~36 GPa). All the Cr 80 Si 20 N coatings were free of extended and uninterrupted columnar boundaries, and retained low specific wear rates in the ball-on-plate sliding tests against Al 2 O 3 counterpart with a normal load of 5 N (less than 3.0 × 10 −16 m 3 /N m under ambient condition and less than 2.0 × 10 −15 m 3 /N m under 3.5 wt% NaCl solution, respectively). Post examination reveals extensive interruption or termination of cracks in the wear tracks of the under-dense coatings, indicative of extrinsic toughening mechanisms by effective relief of local contact stress. Our results suggest that a critical role of toughening rather than hardening, played in enhancing the wear resistance of hard coatings, and thus would pave a way to develop highly wear-resistant coatings with a low hardness.