Paul H Mayrhofer

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• Univ. Prof. Dr.
• University Professor at TU Wien

Graphene has been suggested as an ultimately thin functional coating for metallurgical alloys such as steels. However, even on pure iron (Fe), the parent phase of steels, growth of high quality graphene films remains largely elusive to date. We here report scalable chemical vapour deposition (CVD) of high quality monolayer graphene films on Fe subs...

Fracture toughness and strength are critical for structural ceramics, which are prone to brittle failure. However, accurately characterizing these properties is challenging, especially for thin films on substrates. In-situ microscopy often fails to resolve crack initiation, while fractured samples provide limited insight into fracture modes and cra...

Though offering unprecedented pathways to molecular dynamics (MD) simulations of technologically-relevant materials and conditions, machine-learning interatomic potentials (MLIPs) are typically trained for ``simple'' materials and properties with minor size effects. Our study of MAB phases (MABs) - alternating transition metal boride (MB) and group...

CrN belongs to a family of transition metal nitrides used as protective coatings. It has an antiferromagnetic (AFM) orthorhombic structure below the Néel temperature (T_N) and adopts paramagnetic (PM) cubic B1 above T_N. In the past, the PM state was often wrongly approximated by a non-magnetic (NM) configuration. First-principles calculations sugg...

The layered character of transition metal diborides (TMB2:s)---with three structure polymorphs representing different stackings of the metallic sublattice---evokes the possibility of activating phase-transformation plasticity via mechanical shear strain. This is critical to overcome the most severe limitation of TMB2:s: their brittleness. To unders...

Diamond-like carbon (DLC) coatings are among the toughest and most effective measures for preventing wear on critical surfaces. Due to its high wear resistance, the deterioration of the protective coating only occurs upon failure. Understanding the events leading to failure and identifying a mild-abrasive wear process is crucial for sustainable app...

Transition metal nitrides are widely used in the hard materials and protective coatings industry, but are limited by their low fracture toughness. Encouraged by previous studies on remarkable simultaneous improvements in strength and ductility through superlattice (SL) architectures, various TiN/MoN SL thin films were developed on (100) MgO substra...

The tribological performance of sputtered (Al,Cr,Nb,Ta,Ti)N, (Hf, Ta, V, W, Zr)B2 , and (Al, Cr, Nb, Ta, Ti)O2 coatings on steel substrates was compared against TiN in dry ball-on-disk and scratch tests in ambient air at 20 °C, 400 °C and 700 °C. The (Al,Cr,Nb,Ta,Ti)N and TiN perform similar in all tests, with (Al,Cr,Nb,Ta,Ti)N showing higher oxida...

The demand for cutting tools drives the quest for advanced hard coatings, emphasizing hardness, thermal stability, toughness, tribological properties, wear, corrosion, and oxidation resistance. Chromium Nitride (CrN) is prized for its exceptional attributes, including hardness, wear and oxidation resistance, and chemical inertness, making it valuab...

The intermetallic transition metal B2‐structured aluminide RuAl is a candidate material for use in various applications, including microelectronics and structural materials under demanding conditions, for example, as oxidation‐ and corrosion‐resistant materials. In contrast to other B2 transition metal aluminides, which usually suffer from brittle...

Transition metal diboride thin films are promising functional materials for their outstanding mechanical properties and thermal stability. By combining experiment and simulations, we discuss angular distribution of the sputtered species, their scattering in the gas phase, re-sputtering and potential evaporation from the grown films for the complex...

The Ti-B-N system offers a wide range of possible meta(stable) phases, making it interesting for science and industry. However, the solubility for B within the face-centered cubic (fcc)-TiN lattice is rather limited and less studied, especially without forming B-rich phases. Therefore, we address how chemistries along the TiN-TiB 2 or TiN-TiB tie-l...

For mechanically dominated load profiles, nitrides are preferred as the base material for structural and functional hard coatings, while oxide-based materials offer better protection against high-temperature corrosion (such as oxidation). Thus, when mechanical and thermal loads are combined, the nitrides used should also have excellent stability ag...

Machine-learning interatomic potentials (MLIPs) offer a powerful avenue for simulations beyond length and timescales of ab initio methods. Their development for investigation of mechanical properties and fracture, however, is far from trivial since extended defects—governing plasticity and crack nucleation in most materials—are too large to be incl...

Your personalized Share Link: https://authors.elsevier.com/c/1ivI3wevWRE5 Metastable (Ti,Al)N thin films with face-centered cubic (fcc) structure are widely applied to protect tools and components used in the machining industry for their high hardness and exceptional thermal stability. Alloying is a simple but powerful strategy to further improve...

To quickly screen for single-phased multi-principal-element materials, a so-called entropy forming ability (EFA) parameter is sometimes used as a descriptor. The larger the EFA, the larger is the propensity to form a single-phase structure. We have investigated this EFA descriptor with atomic relaxations in special-quasi-random structures and disco...

High‐entropy metal sublattice coatings (HESCs) prepared by physical vapor deposition (PVD) have received attention due to their diverse range of properties and applications. One of the most critical requirements for their synthesis is the prediction and control of their widespread properties, and several efforts have been undertaken using various t...

Tailoring vacancies is a feasible way to improve the mechanical properties of ceramics. However, high concentrations of vacancies usually compromise the strength (or hardness). We show that a high elasticity and flexural strength could be achieved simultaneously using a nitride superlattice architecture with disordered anion vacancies up to 50%. En...

Machine-learning interatomic potentials (MLIPs) offer a powerful avenue for simulations beyond length and timescales of ab initio methods. Their development for investigation of mechanical properties and fracture, however, is far from trivial since extended defects -- governing plasticity and crack nucleation in most materials -- are too large to b...

Hard coatings like (Al,Cr)N are commonly used to protect cemented carbide cuttings tools from wear and corrosion. While such coatings increase the tool-lifetime, they also hinder the recycling effort of damaged tools. We report a new recycling strategy for coated cemented carbide tools by applying an interlayer between an arc evaporated Al0.7 Cr0.3...

The near-surface regions of rail wheels experience a complex thermo-mechanical loading, which varies along the location of the tread and causes severe changes to the microstructure. Occasionally, brittle white etching layers (WEL) are formed, representing a high risk of wheel damage. Therefore, we studied the depth-evolution of the surface-near mic...

High entropy alloys (HEAs) have triggered significant scientific interest due to their unusual structural stability combined with excellent mechanical and other functional properties. Recently, the high-entropy concept has also been applied to the field of protective coatings. We use ab initio calculations to provide an unbiased insight into their...

Alloying (Ti,Al)N with Ta, CeSi2 or LaB6 is beneficial for both hardness and thermal stability. Here we show that their different mechanisms allow for a cumulative improve-ment when alloyed together, which is especially pronounced for the oxidation resistance. During isothermal oxidation treatments in ambient air at 900 °C (for up to 25 h), Ti0.44A...

To quickly screen for single-phased multi-principal-element carbides, Sarker, P. et al. (High-entropy high-hardness metal carbides discovered by entropy descriptors. Nature Communications 9, 4980 (2018)) have proposed the so-called entropy forming ability (EFA) as a descriptor. In their experimental validation, the authors found a clear correlation...

Transition metal diborides crystallise in the $\alpha$, $\gamma$, or $\omega$ type structure, in which pure transition metal layers alternate with pure boron layers stacked along the hexagonal [0001] axis. Here we view the prototypes as different stackings of the transition metal planes and suppose they can transform from one into another by a disp...

Detailed investigations of white etching layers (WELs) formed on rails and wheels are of utmost importance to improve railway safety. This calls for lab-generated WELs with well-comparable characteristics to conduct further testing such as in twin-disc experiments. In this work, laser surface treatments were applied on wheel steels to induce therma...

Supersaturated (Ti,Al)N materials with face centered cubic (fcc) structure offer unique combinations of thermal stability and mechanical properties. However, their thermally-induced decomposition processes are crucial for extracting their full potential. Detailed experimental studies by X-ray diffraction and transmission electron microscopy reveal...

The performance of electrochemical capacitors strongly depends on their accessible surface area, chemical stability, and electrical conductivity. Simple columnar and zig-zag γ-Mo2N thin-film electrodes were prepared by magnetron sputtering. The latter is obtained by glancing angle deposition (GLAD), which is known for open porous structures due to...

Diamond-like carbon (DLC) coatings protect engine parts from wear and provide low-friction. Unfortunately, the nature of DLC coatings does not allow progressing wear measurement using conventional methods. Therefore, we applied a radioactive isotope-based wear measurement method (RIC method). A tribometer with oscillating contact and one with slidi...

Transition metal diboride-based thin films are currently receiving strong interest in fundamental and applied research. Multilayer thin films based on transition metal diborides are, however, not yet explored in detail. This study presents results on the constitution and microstructure of multilayer thin films composed of TiB x and the intermetalli...

At present, the theoretical predictions of the mechanical properties of transition-metal nitride (TMN) superlattices (SLs) are primarily based on the intrinsic properties of perfect epitaxial nanolayers. However, due to a lack of understanding of the specific strengthening mechanism, the experimentally determined strength, e.g., hardness, of TMN SL...

The mechanical properties of superlattice (SL) TMN (transition-metal nitrides) coatings with different as-deposited structures are often quite different. These differences in mechanical properties can be attributed to distinct deformation and strengthening mechanisms. Here, we discuss the strengthening mechanisms of single- and poly-crystalline SLs...

Phase stability and mechanical properties of multimetal-boronnitride (Hf,Ta,Ti,V,Zr)-B-N is investigated by ab-initio computations and experimental methods. (Hf,Ta,Ti,V,Zr)-B-N shows a strong energetic preference for the fcc NaCl-type structure over other structures up to a B:N ratio of 3.5. Reactively deposited (Hf,Ta,Ti,V,Zr)-B-N coatings show fo...

The superior mechanical properties and thermal stability of Ti-Al-Si-N coatings have attracted extensive research interests in academia as well as industry. In this study, Ti0.52Al0.48N, Ti0.53Al0.38Si0.09N, Ti0.43Al0.48Si0.09N, and Ti0.48Al0.38Si0.14N coatings are developed by arc-evaporation. This compositional variation allows to study the impac...

The publisher regrets that in the abovementioned article the root symbol in Eq. (16) incorrectly extends over the term −A/B . Eq. (16) has been printed correctly below: The evolution of the particle radius in Fig. 5 that refers to Eq. (16) was obtained with the correct expression.

The low intrinsic fracture toughness of transition metal nitride thin films critically restrains their applicability as protective coatings. We therefore investigate the Ti1-xWxNy system to provide detailed theoretical and experimental insight into simultaneous hardening and toughening effects induced by heavy-element-alloying via an enhanced metal...

γ-TiAl alloys have gained much attention due to their low density, excellent fatigue resistance, and high specific strength at elevated temperatures. Throughout this study, we showcase physical vapor deposited Al-rich γ-TiAl coatings as a considerable solution to extend the durability and longevity of γ-TiAl bulk materials in high temperature regim...

Interfaces between components of a material govern its mechanical strength and fracture resistance. While a great number of interfaces is present in nanolayered materials, such as superlattices, their fundamental role during mechanical loading lacks understanding. Here we combine ab initio and classical molecular dynamics simulations, nanoindentati...

Motivated by density functional theory (DFT)-derived ductility indicators for face centred cubic (fcc, rocksalt) structured TiN/MoN0.5 superlattices and Ti0.5Mo0.5N0.75 solid solutions, TiN/MoNy superlattice (SL) thin films with bilayer periods Λ of 2.4, 3.9, 6.6, 9.9, and 23.0 nm and corresponding solid solutions were developed by DC reactive magn...

Recently, the favorable impact of O-addition on the oxidation resistance, toughness and machining performance of Ti1-xAlxN coatings has attracted a wide range of research interests. We systematically studied the effect of O-addition on structure, mechanical and thermal properties of Ti1-xAlxN coatings by experimental and theoretical methods. The ha...

Diamon-like carbon (DLC) coatings protect engine parts from wear and provide low-friction. Unfortunately, the nature of DLC coatings does not allow progressing wear measurement using conventional methods. Therefore, we applied a radioactive isotope-based wear measurement method (RIC method). A tribometer with oscillating contact and one with slidin...

(Al,Mo,Ta,V,W)-N0.79, -N0.33, and -N0.88O0.12 coatings were sputtered in N2-rich, N2-lean, and N2+O2 containing atmospheres. The face-centered cubic structured coatings feature as-deposited hardness values of 32.3, 39.7, and 34.5 GPa, respectively. The (Al,Mo,Ta,V,W)N0.79 and (Al,Mo,Ta,V,W)N0.33 consist of highly oriented columns, plus some very la...