Mehran Golizadeh

Bio: Mehran Golizadeh is an academic researcher from University of Leoben. The author has contributed to research in topics: Cathode & Coating. The author has an hindex of 4, co-authored 8 publications receiving 42 citations. Previous affiliations of Mehran Golizadeh include National University of Science and Technology.

Microstructure, mechanical, and tribological properties of Ag-free and Ag-doped VCN coatings

Abstract: The aim of this work was a comparative study of the structure, mechanical, and tribological properties of VCN and VCN-Ag coatings. The VCN coatings were deposited by magnetron sputtering of V and C targets either in a gaseous mixture of Ar + 15%N2 or in pure nitrogen. Silver was added into such coatings by simultaneous sputtering of metallic Ag target using an additional ion source. Microstructure and elemental composition of the coatings were studied by means of X-ray diffraction, transmission and scanning electron microscopy, atomic force microscopy, energy-dispersive spectroscopy, and Raman spectroscopy. The coatings were evaluated in terms of their mechanical properties, adhesion strength, intrinsic stress, fracture toughness, room-temperature friction coefficient, as well as wear resistance and fatigue strength. Incorporation of as much as 10–11 at.% Ag was found to cause significant changes in the coating structure and properties: (i) the columnar morphology changes to equiaxial one; (ii) the coating hardness and Young's modulus decrease from 22 to 26 to 15–17 GPa and from 260 to 270 to 220 GPa, respectively; (iii) the friction coefficient and wear rate increased slightly from 0.4–0.47 to 0.51–0.53 and from 1.5–1.6 × 10− 7 to 8.2–13.3 × 10− 7 mm3/Nm, respectively; (iv) the compressive stress decreased from 1.6 to 0.3–0.5 GPa. The Ag-doped VCN coatings withstood high elastic and plastic deformation during scratching with increasing load up to 50 N without adhesive failure and applied load as high as 1000 N for 105 cycles during dynamic impact tests without brittle fracture.

Insights into surface modification and erosion of multi-element arc cathodes using a novel multilayer cathode design

Abstract: Nowadays, multi-element cathodes are frequently employed to grow multi-element thin films and coatings using cathodic arc deposition processes. During cathode erosion, the cathode spot sequentially ignites on the cathode surface and imposes melting–solidification cycles that lead to material intermixing and the formation of a modified layer on the cathode surface. To allow us to study these surface modifications, a 10 μm thick Mo/Al multilayer coating was sputter-deposited onto a standard Ti arc cathode. This cathode was eroded by a dc steered arc discharge for a short duration enabling the observation of single craters formed by type 1 and 2 cathode spots. Furthermore, separated clusters of overlapping craters and a fully eroded surface caused by different stages of erosion were differentiated when scanning the erosion track in the lateral direction. Cross sections of single craters were prepared by focused ion beam techniques while metallographic methods were applied to obtain cross sections of overlapping craters and the modified layer. The layers of the multilayer coating acted as trace markers providing new insights into the material intermixing within craters, the material displacements during crater formation, the plasma pressure acting on the craters, and the temperature gradient (heat-affected zone) below the craters. The observations are discussed within the framework of established arc crater formation models.

Multilayer SiBCN/TiAlSiCN and AlOx/TiAlSiCN coatings with high thermal stability and oxidation resistance

Abstract: In this work we utilized a multilayer approach to achieve extremely high thermal stability and oxidation resistance without compromising the coating hardness. Multilayer SiBCN/TiAlSiCN and AlOx/TiAlSiCN coatings were deposited by magnetron sputtering of TiAlSiCN target and ion sputtering of either SiBC or Al2O3 targets. To investigate thermal stability and oxidation resistance, samples were annealed in vacuum at 1000, 1300, and 1400 °C and in air at 1000 and 1100 °C for 1 h. After vacuum annealing at 1300 °C, the AlOx/TiAlSiCN coatings lost multilayer structure due to crystallization of AlOx layers and significant grain growth within the TiAlSiCN layers, which was accompanied by Si loss, and h-AlN precipitation. In contrast, the SiBCN/TiAlSiCN samples annealed at 1300 °C completely preserved their multilayer structure. After 1400 °C, recrystallization of the SiBCN/TiAlSiCN coating was only observed to occur in several upper layers, whereas other part of the coating retained its initial microstructure. Hardness of the SiBCN/TiAlSiCN and AlOx/TiAlSiCN coatings increased from 34 and 24 GPa to 40 and 30 GPa at 1000 °C and then decreased to 27 and 15 GPa at 1300 °C, respectively. The incorporation of AlOx and SiBCN interlayers into the TiAlSiCN coatings was shown to significantly improve their oxidation resistance. After 1100 °C, the AlOх/TiAlSiCN coatings were only partially oxidized (about 35% of the total coating thickness). Lowermost layers in the SiBCN/TiAlSiCN coatings after annealing at 1100 °C were not affected by oxidation as well. Finally, mechanism and kinetics of oxidation are discussed.

Erosion and cathodic arc plasma of Nb-Al cathodes: composite versus intermetallic

Abstract: Author(s): Zohrer, S; Golizadeh, M; Koutna, N; Holec, D; Anders, A; Franz, R | Abstract: Many properties of cathodic arcs from single-element cathodes show a correlation to the cohesive energy of the cathode material. For example, the burning voltage, the erosion rate, or, to a lesser extent, plasma properties like electron temperatures or average ion energy and charge states. For multi-element cathodes, various phases with different cohesive energies can initially be present in the cathode, or form due to arc exposure, complicating the evaluation of such correlations. To test the influence of morphology and phase composition of multi-element cathodes on cathodic arc properties, a Nb-Al cathode model system was used that includes: pure Nb and Al cathodes; intermetallic Nb3Al, Nb2Al and NbAl3 cathodes; and three composite Nb-Al cathodes with atomic ratios corresponding to the stoichiometric ratios of the intermetallic phases. Pulsed cathodic arc plasmas from these cathodes were examined using a mass-per-charge and energy-per-charge analyzer, showing that charge-state-resolved ion energy distributions of plasmas from the intermetallic and corresponding composite cathodes are nearly identical. An examination of converted layers of eroded cathodes using x-ray diffraction and scanning electron microscopy indicates the formation of a surface layer with similar phase composition for intermetallic and their corresponding composite cathode types. The average arc voltages do not follow the trend of cohesive energies of Nb, Al and intermetallic Nb-Al phases, which have been calculated using density functional theory. Possible reasons for this effect are discussed based on the current knowledge of multi-element arc cathodes and their arc plasma available in literature.

Cathode spot behavior in nitrogen and oxygen gaseous atmospheres and concomitant cathode surface modifications

Abstract: The cathode spot behavior influences the arc plasma chemistry and film growth conditions during reactive cathodic arc deposition of nitride and oxide films. Cathode spots can be studied using their characteristic craters left behind on the cathode surface. The multilayer cathode design used in this study reveals temporal and spatial progress of cathode spots by enabling three-dimensional visualization of the craters. The surface nitridation or oxidation of the cathode, also known as cathode poisoning, was found to give rise to a repeated switching between cathode spots of type 1 and 2. The surface oxide layers, however, more significantly promote the ignition of type 1 spots due to their thermodynamically privileged formation and/or their more favorable physical properties building up a stronger electric field within the insulating layer. The crater depths and their contribution to the surface modification of multilayered cathodes are discussed in detail. These results may contribute to a better understanding of macroparticle generation and arc plasma properties in cathodic arc deposition processes.

High-Entropy Alloys as a Platform for Catalysis: Progress, Challenges, and Opportunities

Abstract: High-entropy alloys (HEAs), which are defined as near-equimolar alloys of five or more elements, are attracting ever increasing attention because of the unique properties in a variety of applicatio...

Characteristics and Wear Mechanisms of TiAlN-Based Coatings for Machining Applications: A Comprehensive Review

Abstract: The machining process is still a very relevant process in today’s industry, being used to produce high quality parts for multiple industry sectors The machining processes are heavily researched, with the focus on the improvement of these processes One of these process improvements was the creation and implementation of tool coatings in various machining operations These coatings improved overall process productivity and tool-life, with new coatings being developed for various machining applications TiAlN coatings are still very present in today’s industry, being used due to its incredible wear behavior at high machining speeds, high mechanical properties, having a high-thermal stability and high corrosion resistance even at high machining temperatures Novel TiAlN-based coatings doped with Ru, Mo and Ta are currently under investigation, as they show tremendous potential in terms of mechanical properties and wear behavior improvement With the improvement of deposition technology, recent research seems to focus primarily on the study of nanolayered and nanocomposite TiAlN-based coatings, as the thinner layers improve drastically these coating’s beneficial properties for machining applications In this review, the recent developments of TiAlN-based coatings are going to be presented, analyzed and their mechanical properties and cutting behavior for the turning and milling processes are compared

Microstructure, mechanical, and tribological properties of Ag-free and Ag-doped VCN coatings

Abstract: The aim of this work was a comparative study of the structure, mechanical, and tribological properties of VCN and VCN-Ag coatings. The VCN coatings were deposited by magnetron sputtering of V and C targets either in a gaseous mixture of Ar + 15%N2 or in pure nitrogen. Silver was added into such coatings by simultaneous sputtering of metallic Ag target using an additional ion source. Microstructure and elemental composition of the coatings were studied by means of X-ray diffraction, transmission and scanning electron microscopy, atomic force microscopy, energy-dispersive spectroscopy, and Raman spectroscopy. The coatings were evaluated in terms of their mechanical properties, adhesion strength, intrinsic stress, fracture toughness, room-temperature friction coefficient, as well as wear resistance and fatigue strength. Incorporation of as much as 10–11 at.% Ag was found to cause significant changes in the coating structure and properties: (i) the columnar morphology changes to equiaxial one; (ii) the coating hardness and Young's modulus decrease from 22 to 26 to 15–17 GPa and from 260 to 270 to 220 GPa, respectively; (iii) the friction coefficient and wear rate increased slightly from 0.4–0.47 to 0.51–0.53 and from 1.5–1.6 × 10− 7 to 8.2–13.3 × 10− 7 mm3/Nm, respectively; (iv) the compressive stress decreased from 1.6 to 0.3–0.5 GPa. The Ag-doped VCN coatings withstood high elastic and plastic deformation during scratching with increasing load up to 50 N without adhesive failure and applied load as high as 1000 N for 105 cycles during dynamic impact tests without brittle fracture.