Peter Polcik

Oxidation and diffusion processes during annealing of AlCrVN hard coatings

V-alloyed AlCrN hard coatings were deposited by reactive arc evaporation in an industrial-sized deposition system and subsequently annealed in ambient air at temperatures ranging from 550to700°C in order to study the formation mechanisms of the desired lubricious oxides. The oxidized samples were investigated by means of secondary ion mass spectrometry depth profiling, x-ray diffraction, Raman spectroscopy, and analytical transmission electron microscopy. Vanadium diffusion in the oxidized part of the coating leads to the formation of a V-rich top layer containing AlVO4 and the desired lubricious oxide V2O5 followed by a V-depleted inner oxide layer consisting of a mixed or nanocrystalline (Al,Cr,V)2O3 on top of the intact AlCrVN coating.

Controlling microstructure, preferred orientation, and mechanical properties of Cr-Al-N by bombardment and alloying with Ta

Recent ab initio studies showed that the inherent ductility of cubic structured Cr1−xAlxN coatings (as compared with similar hard coatings) significantly increases when alloyed with Ta. As there is only little experimental and theoretical information available, we have performed a combined experimental and ab initio based study on the influence of Ta additions (0, 2, 6, 12, and 26 at. % on the metal sublattice) on structure and mechanical properties of arc evaporated Cr1−x-yAlxTayN coatings with Al/(Cr + Al) ratios >0.61. With increasing Ta-content, the droplet number density decreases and the coating surface smoothens, which is much more pronounced as with increasing the bias potential from −40 to −120 V. Simultaneously, the columnar structure observed for Ta-free Cr0.37Al0.63N significantly changes into a fine-grained structure (crystallite size ∼5 nm) with clearly reduced columnar character. Increasing the Ta content also favors the formation of a preferred 200 growth orientation resulting in a reducti...

Oxidation behavior and tribological properties of multilayered Ti-Al-N/Mo-Si-B thin films

The impact of highly oxidation resistant Mo1−x−ySixBy on the oxidation resistance and tribological properties of arc evaporated face-centered-cubic Ti0.57Al0.43N is investigated in detail through Mo1−x−ySixBy/Ti0.57Al0.43N and Mo1−x−ySixByN/Ti0.57Al0.43N compound coatings as well as Ti0.57Al0.43N/Mo1−x−ySixBy multilayer coatings. The Ti0.57Al0.43N/Mo0.54Si0.30B0.16 and Ti0.57Al0.43N/Mo0.68Si0.12B0.20 multilayers with bilayer periods of 35 and 70 nm (consisting of 6 and 15 nm thin sputtered Mo0.54Si0.30B0.16 and Mo0.68Si0.12B0.20 layers), respectively, significantly outperform all coatings investigated during 900 °C ambient-air-oxidation treatments. Consequently, the oxidation resistance of the multilayer coatings is higher as compared with their individual layers. Even after 1000 min exposure, only ∼1.0 μm of the Ti0.57Al0.43N/Mo0.68Si0.12B0.20 multilayer is consumed to form a dense adherent and protective oxide scale. The latter is composed of Si-, Al-, Ti-, and Al-rich layered outer oxides preventing th...

Erosion behavior of composite Al-Cr cathodes in cathodic arc plasmas in inert and reactive atmospheres

AlxCr1−x composite cathodes with Al contents of x = 0.75, 0.5, and 0.25 were exposed to cathodic arc plasmas in Ar, N2, and O2 atmospheres and their erosion behavior was studied. Cross-sectional analysis of the elemental distribution of the near-surface zone in the cathodes by scanning electron microscopy revealed the formation of a modified layer for all cathodes and atmospheres. Due to intermixing of Al and Cr in the heat-affected zone, intermetallic Al-Cr phases formed as evidenced by x-ray diffraction analysis. Cathode poisoning effects in the reactive N2 and O2 atmospheres were nonuniform as a result of the applied magnetic field configuration. With the exception of oxide islands on Al-rich cathodes, reactive layers were absent in the circular erosion zone, while nitrides and oxides formed in the less eroded center region of the cathodes.

Generation of super-size macroparticles in a direct current vacuum arc discharge from a Mo-Cu cathode

An inherent property of cathodic arc is the generation of macroparticles, of a typical size ranging from submicrometer up to a few tens of μm. In this work, we have studied macroparticle generation from a Mo0.78Cu0.22 cathode used in a dc vacuum arc discharge, and we present evidence for super-size macroparticles of up to 0.7 mm in diameter. All analyzed particles are found to be rich in Mo (≥98 at. %). The particle generation is studied by visual observation of the cathode surface during arcing, by analysis of composition and geometrical features of the used cathode surface, and by examination of the generated macroparticles with respect to shape and composition. A mechanism for super-size macroparticle generation is suggested based on observed segregated layers of Mo and Cu identified in the topmost part of the cathode surface, likely due to the discrepancy in melting and evaporation temperatures of Mo and Cu. The results are of importance for increasing the fundamental understanding of macroparticle ge...

Magnetic field strength influence on the reactive magnetron sputter deposition of Ta2O5

Reactive magnetron sputtering enables the deposition of various thin films to be used for protective as well as optical and electronic applications. However, progressing target erosion during sputtering results in increased magnetic field strengths at the target surface. Consequently, the glow discharge, the target poisoning, and hence the morphology, crystal structure and stoichiometry of the prepared thin films are influenced. Therefore, these effects were investigated by varying the cathode current Im between 0.50 and 1.00 A, the magnetic � (%)

Element- and charge-state-resolved ion energies in the cathodic arc plasma from composite AlCr cathodes in argon, nitrogen and oxygen atmospheres

The energy distribution functions of ions in the cathodic arc plasma using composite AlCr cathodes were measured as a function of the background gas pressure in the range 0.5 to 3.5 Pa for different cathode compositions and gas atmospheres. The most abundant aluminium ions were Al+ regardless of the background gas species, whereas Cr2+ ions were dominating in Ar and N2 and Cr+ in O2 atmospheres. The energy distributions of the aluminium and chromium ions typically consisted of a high-energy fraction due to acceleration in the expanding plasma plume from the cathode spot and thermalised ions that were subjected to collisions in the plasma cloud. The fraction of the latter increased with increasing background gas pressure. Atomic nitrogen and oxygen ions showed similar energy distributions as the aluminium and chromium ions, whereas the argon and molecular nitrogen and oxygen ions were formed at greater distance from the cathode spot and thus less subject to accelerating gradients. In addition to the positively charged metal and gas ions, negatively charged oxygen and oxygen-containing ions were observed in O2 atmosphere. The obtained results are intended to provide a comprehensive overview of the ion energies and charge states in the arc plasma of AlCr composite cathodes in different gas atmospheres as such plasmas are frequently used to deposit thin films and coatings.

Macroparticle generation in DC arc discharge from a WC cathode

We have studied macroparticle generation from a tungsten carbide cathode used in a dc vacuum arc discharge. Despite a relatively high decomposition/melting point (∼3100 K), there is an intensive generation of visible particles with sizes in the range 20–35 μm. Visual observations during the discharge and scanning electron microscopy of the cathode surface and of collected macroparticles indicate a new mechanism for particle formation and acceleration. Based on the W-C phase diagram, there is an intensive sublimation of carbon from the melt resulting from the cathode spot. The sublimation supports the formation of a sphere, which is accelerated upon an explosion initiated by Joule heating at the critical contact area between the sphere and the cathode body. The explosive nature of the particle acceleration is confirmed by surface features resembling the remains of a splash on the droplet surface.

Combinatorial synthesis of Cr1−xAlxN and Ta1−xAlxN coatings using industrial scale co-sputtering

For a comprehensive understanding of the scientific relations between composition, microstructure and properties of hard coatings usually a multitude of deposition runs is necessary. Within the present work, a combinatorial deposition approach using triangular shaped segmented sputter targets was adapted for an industrial scale sputter system. Owing to the position of the substrates relative to the target segments, a wide range of compositions can be achieved within a single deposition run. To verify this concept, Cr1 − xAlxN reference coatings and Ta1 − xAlxN coatings, each with a base layer of TiAlN (i.e. a bilayer configuration), were synthesised. The effect of the varying chemical compositions on the structure and mechanical as well as tribological properties was investigated. This approach enables to efficiently identify promising coating compositions.

Ab initio studies on the adsorption and implantation of Al and Fe to nitride materials

The formation of transfer material products on coated cutting and forming tools is a major failure mechanism leading to various sorts of wear. To describe the atomistic processes behind the formation of transfer materials, we use ab initio to study the adsorption energy as well as the implantation barrier of Al and Fe atoms for (001)-oriented surfaces of TiN, Ti0.50Al0.50N, Ti0.90Si0.10N, CrN, and Cr0.90Si0.10N. The interactions between additional atoms and nitride-surfaces are described for pure adhesion, considering no additional stresses, and for the implantation barrier. The latter, we simplified to the stress required to implant Al and Fe into sub-surface regions of the nitride material. The adsorption energies exhibit pronounced extrema at high-symmetry positions and are generally highest at nitrogen sites. Here, the binary nitrides are comparable to their ternary counterparts and the average adhesive energy is higher (more negative) on CrN than TiN based systems. Contrary, the implantation barrier ...