Structure and mechanics of W-DLC coated spur gears

A detailed structural characterization of W-containing diamond-like carbon (W-DLC) coatings deposited on spur gears was carried out with plan-view and cross-section transmission electron microscopy (TEM). W-DLC coated spur gears were tested in a ‘four-square’ gear-testing machine and examined with TEM in both the as-deposited and tested conditions. High-resolution microscopy clearly shows the presence of nanometer scale structural/compositional modulation within the W-DLC coatings and further reveals the existence of a micrometer scale columnar structure and intercolumnar defects within the coating. Defect morphologies were examined and related to failure mechanisms of coated gears.