ABSTRACT
Hard nitride coatings are commonly employed to protect components subjected to friction, whereby such coatings should possess excellent tribomechanical properties in order to endure high stresses and temperatures. In this study, WN/NbN coatings are synthesized by using the cathodic-arc evaporation (CA-PVD) technique at various negative bias voltages in the 50-200 V range. The phase composition, microstructural features, and tribomechanical properties of the multilayers are comprehensively studied. Fabricated coatings have a complex structure of three nanocrystalline phases: ß-W2N, δ-NbN, and ε-NbN. They demonstrate a tendency for (111)-oriented grains to overgrow (200)-oriented grains with increasing coating thickness. All of the data show that a decrease in the fraction of ε-NbN phase and formation of the (111)-textured grains positively impact mechanical properties and wear behavior. Investigation of the room-temperature tribological properties reveals that with an increase in bias voltage from -50 to -200 V, the wear mechanisms change as follows: oxidative â fatigue and oxidative â adhesive and oxidative. Furthermore, WN/NbN coatings demonstrate a high hardness of 33.6-36.6 GPa and a low specific wear rate of (1.9-4.1) × 10-6 mm3/Nm. These results indicate that synthesized multilayers hold promise for tribological applications as wear-resistant coatings.
ABSTRACT
Due to the increased demands for drilling and cutting tools working at extreme machining conditions, protective coatings are extensively utilized to prolong the tool life and eliminate the need for lubricants. The present work reports on the effect of a second MeN (Me = Zr, Cr, Mo, Nb) layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties. The WN/MoN multilayers have not been studied yet, and cathodic-arc physical vapor deposition (CA-PVD) has been used to fabricate studied coating systems for the first time. Moreover, first-principles calculations were performed to gain more insight into the properties of deposited multilayers. Two types of coating microstructure with different kinds of lattices were observed: (i) face-centered cubic (fcc) on fcc-W2N (WN/CrN and WN/ZrN) and (ii) a combination of hexagonal and fcc on fcc-W2N (WN/MoN and WN/NbN). Among the four studied systems, the WN/NbN had superior properties: the lowest specific wear rate (1.7 × 10-6 mm3/Nm) and high hardness (36 GPa) and plasticity index H/E (0.93). Low surface roughness, high elastic strain to failure, Nb2O5 and WO3 tribofilms forming during sliding, ductile behavior of NbN, and nanocomposite structure contributed to high tribological performance. The results indicated the suitability of WN/NbN as a protective coating operating in challenging conditions.
ABSTRACT
Solid-state dewetting (SSD) on patterned substrates is a straightforward method for fabricating ordered arrays of metallic nanoparticles on surfaces. However, a drawback of this procedure is that the patterning of substrates usually requires time-consuming and expensive two-dimensional (2D) fabrication methods. Nanostructured thin films deposited by oblique angle deposition (OAD) present at the surface a form of stochastically arranged periodic bundles of nanocolumns that might act as a patterned template for fabricating arrays of nanoparticles by SSD. In this work, we explore this concept and investigate the effect of three different types of OAD SiO2 thin films on the SSD of Au deposited on their surface. We demonstrate that the size and spatial distribution of the particles can be tailored through the surface morphology of these OAD film substrates. It has been found that the SSD of the evaporated Au layer gives rise to a bimodal size distribution of particles. A majority of them appeared as mesoparticles with sizes â³100 nm and the rest as nanoparticles with â¼10 nm, respectively, located either on top of the nanocolumns following their lateral distribution (i.e., resulting from a patterning effect) or incorporated inside the open mesopores existing among them. Moreover, on the SiO2-OAD thin films where interconnected nanocolumnar bundles arrange in the form of discrete motifs, the patterning effect gave rise to the formation of approximately one Au mesoparticle per motif, which is one of the assets of patterned SSD. The morphological, optical (i.e., plasmon resonance), and crystalline structural characteristics of Au mesoparticles suggest that the interplay between a discontinuous nanocolumnar surface acting as a template and the poor adhesion of Au onto SiO2 are key factors for the observed template effect controlling the SSD on the surface of OAD thin films.
