Highly adherent tungsten-containing diamond-like carbon (W-DLC) coating on a NiTi shape memory alloy under 10% tensile strain

Highly adherent tungsten-containing diamond-like carbon coating (W-DLC) was investigated. Two types of W-DLC coating are deposited onto a mirror-polished SMA substrate by PECVD and co-sputtering of the tungsten metal target. A DLC coating is also investigated for comparison. Uniaxial tensile tests are performed for these three types of coating and the peeled-off area is estimated visually. The best adherence was achieved with a WD40 film and the peeled-off area was estimated to be ~ 1% even after 10% tensile strain was applied to the coating. To evaluate the adhesive strength, scratching tests were carried out and, of the three, WD40 showed the highest adhesive strength. The higher adhesive strength of the DLC coating results from a reduction in internal stress and a lowering of coating hardness by the introduction of additional elements.