ICMCTF2016 Session B1-3: PVD Coatings and Technologies

Increasingly harsh tribological conditions of many moving mechanical applications are rendering most traditional materials and coatings ineffective and hence the development and uses of more effective tribological coatings have lately become very important. At present, there exist a variety of DLC and novel nano-composite coatings used to combat friction and wear and many others are under development to meet the specific application needs of engines and other lubricated tribological systems [1]. In our laboratory, we have been designing, optimizing, and testing novel tribological coatings for the past two decades with great success and quite recently we pioneered the development of a new class of specialty coatings that can even work even with base lubricating oils. Specifically, these designer coatings are made of catalytically active hard and soft phases (i.e., VN, NbN, MoN and Cu, Ag, Ni, Sn, Sb, etc.) which enable ultra-high hardness, toughness in addition to excellent catalytic responsiveness to the hydrocarbon molecules of such oils. Specifically, when tested in neat or marginally additized oils, these nanocomposite coatings catalytically fragment long-chain hydrocarbon molecules of lubricating oils to produce a carbon-rich boundary film whose structural chemistry is similar to those of DLC which is well known for its superlow friction and wear properties. Overall, comprehensive friction, wear, and scuffing studies in our laboratory have confirmed that these nanocomposite coatings could be extremely useful for a wide range of demanding automotive applications by reducing parasitic friction losses (hence increasing fuel economy) as well as wear and scuffing (hence increasing component durability/reliability).

[1] S-C. Cha and A. Erdemir, eds., “Coating Technology for Vehicle Applications” Springer, New York, 2015.

BN based (c-BN:h-BN-BCN) thin films that are suitable for original product and technology usage through the innovative approaches will be synthesized in order to develop new technology for new boron based products with added-value and strategic importance and to generalize their area of usage. With ulta-high hardness (<40GPa) and high wear resistance, to reach adhesion values (<70N), improved adhesion also exhibits a lower internal stresses as an alternative h-BN and BCN based coating materials have been developed. Pulsed-dc magnetron sputtering technique was used to deposit c-BN based BN thin films by sputtering a boron carbide (B₄C) targets in various combinations of nitrogen and argon plasma. The friction and wear properties of the coatings were investigated for tribological applications. The coated specimens were also characterized by SEM, XPS, Raman spectroscopy and X-ray diffraction techniques. Hardness measurements was performed by micro indentation. Our results suggest that cBN based BN films are the compouns of the c-BN:h-BN-BCN system and the film shows very dense microstructure, high hardness with low CoF and high wear resistance.

Carbon films in different type of binding configurations lead to their applications in a myriad of fields such as optics, biology, tribology and nanomachinery. The amorphous structured carbon films has shown outstanding mechanical properties, while the sp² hybridized nanocrystallites play an important role on the electrical, thermal, and even magnetic behaviors of carbon films. In order to meet the demand for surface conduction and other potential electronic applications, novel type of carbon film is expected with the combination of good mechanical property from amorphous structure and high conductivity from nanocrystallite structure.

In this study, low energy electron irradiation on amorphous carbon film was carried out in electron cyclotron resonance plasma, and the electron energy was less than 100 eV. The structural transition from amorphous to graphene nanocrystallite was observed by transmission electron microscopy. Film conductivity as well as surface morphology was investigated using a conductive atomic force microscopy. The results showed that graphene nanocrystallite with vertically ordered sp² layers were formed in less than 4 nm depth from the film surface after 5 minute electron irradiation. The formation of graphene nanocrystallite notably increased film conductivity by two orders of magnitude, while the surface Ra roughness maintained less than 0.1 nm. The research brought about a novel carbon film with both high electric conductivity and good mechanical strength, which has the potential to serve as interconnection and conductive ultrasmooth coatings.

Diamond-like carbon (DLC) coatings are suitable applicants for cutting tools due to their high hardness, low COF and low wear rate. Doping metals of DLC coatings has been improved tribological properties. In this study, titanium and tantalum doped hydrogeneted DLC films were deposited by closed-field unbalanced magnetron sputtering system onto M2 high speed steels in Ar/N2/C2H2 atmosphere. The friction and wear properties of Ti/Ta-DLC coating were investigated under different tribo-test conditons including in atmoshperic pressure, distilled water, commercial oil and atmosphere of Ar. The coated specimens were characterizied by SEM and X-ray diffraction techniques. The tribological properties of Ti/Ta-DLC were investigated by using pin-on wear test. Hardness measurements was performed by microindendation. Our results suggest that Ti/Ta-doped DLC film shows very dense microstructure, high hardness with low COF and high wear resistance.