| AVS 55th International Symposium & Exhibition | |
| Advanced Surface Engineering | Wednesday Sessions |
| Session SE+NC-WeA |
| Session: | Hard and Nanocomposite Coatings: Synthesis, Structure, and Properties II |
| Presenter: | J.P. Riviere, University of Poitiers, France |
| Authors: | J.P. Riviere, University of Poitiers, France A. Akbari, Sahand University of Technology, Iran C. Templier, University of Poitiers, France |
| Correspondent: | Click to Email |
Superhard nanocomposite coatings represent an important class of new materials with enhanced mechanical properties. The synthesis of these coatings has been principally obtained by both techniques: plasma-assisted chemical vapour deposition or reactive magnetron sputtering. It appears that dual ion beam assisted deposition could be also an effective tool for tailoring the structure and properties of nanocomposite coatings because it permits independent control of the process variables such as particle nature, energy, flux. A particular important effect of the bombardment of a growing film with energetic ions is the enhanced adatom mobility which plays an important role in the renucleation of nanograins and on the formation of the percolation network of the intergranular phase We have investigated the formation of hard nanocomposite coatings with improved toughness consisting of TiN nanograins embedded in a soft metallic intergranular phase of Ni using reactive ion beam assisted deposition. A composite Ti-Ni target was sputtered with 1.2 keV Ar+ ions and the growing films were simultaneously bombarded with a mixture of 50 eV Ar++N2++N+ ions. The chemical composition was deduced from RBS analysis and a N/Ti ratio of ~ 0.85 independent of the Ni content was determined. Phases, grain size, and texture of the coatings were investigated by XRD and HRTEM. In the composition range 0-22,5 at% Ni, δ-TiN is the only crystalline phase and Ni appears as an X Ray amorphous phase. The hardness increases up to a maximum of 41 Gpa at 6 at.% Ni which corresponds to a TiN crystallite size of ~ 8 nm and a Ni intergranular phase thickness of roughly 1 monolayer. Stress analysis was performed by XRD using the crystallite group method (CGM) developed for textured materials and coatings. It is shown that the hardness enhancement in TiN-Ni nanocomposite coatings is not correlated with residual stresses, but rather with the intrinsic nanostructure. An important improvement in wear resistance is observed however the highest wear resistance is obtained for the coatings exhibiting the highest toughness and not the highest hardness. These results show the beneficial influence of the ductile metallic amorphous intergranular phase on the mechanical behaviour of nanocomposite coatings.