ICMCTF2016 Session B4-2: Properties and Characterization of Hard Coatings and Surfaces

Titanium doped tungsten disulphide thin films were deposited using magnetron sputtering, varying the Ti percentage from 0 to 40% in order to observe the influence of the Ti doping on the crystalline structure, superficial, mechanical properties. X-ray diffraction showed a critical super saturation Ti percentage between 20 to 30% with an amorphous WS2 phase and low dimensional Ti segregation in the structure. Different amounts of Ti doped films (0, 10 and 40%) presented typical hexagonal structure of the WS2, however Ti segregation was observed as only low intensity peaks were observed for the 40% Ti doped. Profilometry showed an average thickness of 1.5 μm and intrinsic stress, obtained by the Stoney model, showed a compressive stress decreasing with the increase of Ti%. This effect is produced by segregation of Ti to the grain boundary. Subsequently the effect of different loads in the mechanical properties of the films were studied using instrumented nanoindentation, generating a hardness, elastic moduly and plastic deformation profiles, determining the influence of the substrate on the mechanical properties of the films using the Korsunsky model and evaluating the indentation impression using scanning electron microscopy. The generation of radial cracks was observed, which were associated to delamination and adhesive failures. This procedure allowed the estimation of the adhesion critical load and to determinate the fracture tenacity behavior in the thin film. In addition, the contact stress profile was observed from the Hertzian contact model, using the hardness and the elastic moduli obtained from the Oliver and Pharr model.

The objective of this study was to deposit thick TiZrN coatings on Ti interlayer above 3μm on AISI D2 steel by dc unbalanced magnetron sputtering, performances of the coating were compared with TiZrN coatings without Ti interlayer. In our previous study, both TiN and ZrN coatings were deposited on AISI D2 steel with thickness above 6 m and excellent properties such as hardness, fracture toughness, and low electric resistivity. Compared with TiN or ZrN, TiZrN not only retained low resistivity and warm golden color but also possessed more superior mechanical properties and better corrosion resistance. Compositions of Ti_XZr_1-XN might presented different property, so it was obviously to select one of the composition which possessed higher hardness and fracture toughness. Interlayer also played an important role in the films. Introducing Ti interlayer could improve the films adhesion and corrosion resistance; and release the residual stress of the films which limited films thickness. TiZrN and TiZrN /Ti coatings were prepared. The hardness, adhesion strength and wear resistance were assessed by nano-indentation, scratch test and pin-on-disk test, respectively. The residual stress in the coating was determined by both cos²αsin²ψ X-ray diffraction, and crystal structure was studied by XRD. Microstructure was observed by SEM which correlated to the deposition parameters and coatings properties. Roughness was measured by AFM which also affected coating’s wear rate and adhesion. Based on our approach, we can develop a promising deposition process, which can produce TiZrN/ Ti thick coatings with excellent mechanical properties.

This study evaluates wear properties of PIRAC nitrogen-diffusion treatment, single and multilayered plasma-assisted physical vapour deposition (PAPVD) Ti/TiN-coated and duplex-hybrid PIRAC nitrogen-diffusion treated/PVD-coated Ti-6Al-4V. Nanoscratch testing shows that surface layer failure (at the maximum normal critical load of 450 mN) was observed only for TiN deposited on untreated Ti-6Al-4V - characterised by large instances of delamination - and for the PIRAC nitrogen-diffusion treated alloy. The compound layer formed in the latter is not able to support the indenter passage consequently resulting in tensile fracture and exposure of the underlying bulk metal . Finally, the results presented here show that an appropriate sequential PIRAC nitrogen-diffusion pretreatment (at 800 ˚C for 4 h) in combination with a Ti/TiN multilayered metal/ceramic coating provides superior tribological performance when compared to either PIRAC nitrogen-diffusion alone, PAPVD coated-only substrates or the untreated Ti-alloy substrate.

Diamond coating with sufficient adhesion on WC-Co cutting tools is expected to significantly increase their cutting performance. In order to enhance the coating-substrate interfacial adhesion, Al₂O₃ and Ta mono-interlayer, Al-Al₂O₃, Al-AlN and Al-Ta duplex interlayer systems have been developed in this study. These interlayer materials were prepared using a magnetron sputtering method, and diamond coating were deposited on them using microwave plasma enhanced chemical vapor deposition. Grazing incident X-ray diffraction was carried out to determine the phase components in the Al-Al₂O₃ and Al-AlN interlayers. Raman spectroscopy and scanning electron microscopy were used to evaluate the quality, morphology and microstructure of the deposited diamond coatings. Rockwell C indentation testing was performed to evaluate the adhesion of the coatings. To elucidate the coating failure mechanism, the compositions around the delaminated spots of diamond coatings after indentation were identified by Energy-dispersive X-ray spectroscopy. The results show that continuous diamond coatings were achieved on Al₂O₃, Al-Al₂O₃, Al-AlN and Al-Ta interlayered substrates, whereas a graphite layer was still formed with the Ta monolayer, accompanied by an easy spallation of diamond coatings. The Al interlayer has played an important role in obtaining high purity diamond by in-situ forming an alumina barrier layer. Especially, the diamond coating deposited with an Al-AlN interlayer demonstrates superior interfacial adhesion in comparison with all the other interlayers.