The structure and tribomechanical properties of a Ti-Al-Si-Cu-C-N gradient layer coating

To adapt coatings to various operating conditions, identify factors and mechanisms for improving the properties of the coatings, it is necessary to search for new compositions, structures of the layers of multilayer coatings and their combinations. In this regard, this paper examines the features of the structural state and tribomechanical properties of a gradient layer coating featuring the Ti-Al-Si-Cu-C-N system formed by the layers of α-Ti, TiAlSiCuN and TiC/a-C. The initial stages of titanium sublayer and TiAlSiCuN layer growth are established to include the enrichment of the titanium composition by iron and oxygen that leads to the formation of a highly dispersed nanocrystalline state, whereas for the TiAlSiCuN layer, an excess of metallic elements (≈65 at.%) and doping with oxygen (≈10 at.%) determines the amorphization of the structure. The study of the stress state of the coating layers shows that the stress level in the TiC crystals of the TiC/a-C layer amounts to E/40, while in the coherently diffracting domains (CDDs) of the TiAlSiCuN layer that reaches E/60 (where E is the Young's modulus of the layers). Increased indentation depth of the TiC/a-C layer was found to improve its hardness from 13 up to 22 GPa at an indentation depth being several-fold smaller than the layer thickness. The zones of intense wear of the TiAlSiCuN layer structure are also studied. The columnar grains demonstrate that the decrease of the CDD dimensions down to 3 nm and the drop of the residual stresses down to E/80 are accompanied by increasing disorientation of the crystal lattice , hence the grains accumulate deformation with the formation more stable defect structure . It is shown that the friction surface morphology represented by scratches of various size, delaminations or formation of massive lamellae of an oxidized steel counterbody and chips of worn coating and thin iron oxide films evidence of adhesive and abrasive wear of the friction pair . • Amorphization of the TiAlSiCuN layer was observed at high concentrations of Ti, Al, Si, and O. • High level of local stresses in the layer TiC/a-C layer was found. • An increase in properties with indentation depth was noted for the TiC/a-C layer. • An increase of a crystallinity and oxide particles with test temperature was shown. • A less stressed defect microstructure of columnar grains in tribotracks was found.