Effect of annealing on the cohesion, adhesion, and tribological behavior of amorphous silicon-containing diamond-like carbon (Si-DLC) coatings on steel

Amorphous silicon-containing diamond-like carbon (Si-DLC) coatings were dep osited by Arf ion beam-assisted physical vapor deposition of tetraphenyl-te tramethyl-trisiloxane (704 Dow Coming diffusion pump oil) on AISI 4340 low alloy and 440 C high alloy steel specimens, as well as on thin wafers of th e same compositions, in order to evaluate residual stresses within the coat ings. During annealing in an argon atmosphere at 200 degrees C for up to 30 min, the residual compressive stress, attributed to hydrogen entrapment du ring deposition, gradually changed to tensile due to loss of hydrogen, and the rate of stress increase decreased with increasing annealing time. The c ohesion and adhesion failure loads of the coatings decreased with annealing time, as did the friction coefficient between the coating and a diamond st ylus. The specific wear rate: measured by pin-on-disk tribometry, increased with annealing time. These properties are affected not only by the change in residual stress state during annealing, but most likely also by devitrif ication and the accompanying grain growth. If these effects are neglected, then the properties may be correlated directly with residual stresses in th e coating.