| 1. |
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| 2. |
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| 3. |
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| 4. |
- Zamora, Juan Carlos, et al.
(author)
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Considerations and consequences of allowing DNA sequence data as types of fungal taxa
- 2018
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In: IMA Fungus. - : INT MYCOLOGICAL ASSOC. - 2210-6340 .- 2210-6359. ; 9:1, s. 167-185
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Journal article (peer-reviewed)abstract
- Nomenclatural type definitions are one of the most important concepts in biological nomenclature. Being physical objects that can be re-studied by other researchers, types permanently link taxonomy (an artificial agreement to classify biological diversity) with nomenclature (an artificial agreement to name biological diversity). Two proposals to amend the International Code of Nomenclature for algae, fungi, and plants (ICN), allowing DNA sequences alone (of any region and extent) to serve as types of taxon names for voucherless fungi (mainly putative taxa from environmental DNA sequences), have been submitted to be voted on at the 11th International Mycological Congress (Puerto Rico, July 2018). We consider various genetic processes affecting the distribution of alleles among taxa and find that alleles may not consistently and uniquely represent the species within which they are contained. Should the proposals be accepted, the meaning of nomenclatural types would change in a fundamental way from physical objects as sources of data to the data themselves. Such changes are conducive to irreproducible science, the potential typification on artefactual data, and massive creation of names with low information content, ultimately causing nomenclatural instability and unnecessary work for future researchers that would stall future explorations of fungal diversity. We conclude that the acceptance of DNA sequences alone as types of names of taxa, under the terms used in the current proposals, is unnecessary and would not solve the problem of naming putative taxa known only from DNA sequences in a scientifically defensible way. As an alternative, we highlight the use of formulas for naming putative taxa (candidate taxa) that do not require any modification of the ICN.
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| 5. |
- Fuger, C., et al.
(author)
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Influence of Ta on the oxidation resistance of WB2-z coatings
- 2021
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In: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 864
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Journal article (peer-reviewed)abstract
- Ternary W1-x TaxB2-z is a promising protective coating material possessing enhanced ductile character and phase stability compared to closely related binaries. Here, the oxidation resistance of W1-xTaxB2-z thin films was experimentally investigated at temperatures up to 700 degrees C. Ta alloying in sputter deposited WB2-z coatings led to decelerated oxide scale growth and a changed growth mode from paralinear to a more linear (but retarded) behavior with increasing Ta content. The corresponding rate constants decrease from k(p)* = 6.3.10(-4) mu m(2)/s for WB2-z to k(p)* = 1.1.10(-4) mu m(2)/s for W0.66Ta0.34B2-z as well as k(1) = 2.6.10(-5) mu m/s for TaB2-z, underlined by decreasing scale thicknesses ranging from 1170 nm (WB2-z), over 610 nm (W0.66Ta0.34B2-z) to 320 nm (TaB2-z) after 10 min at 700 degrees C. Dense and adherent scales exhibit an increased tantalum content (columnar oxides), which suppresses the volatile character of tungsten-rich as well as boron oxides, hence being a key-factor for enhanced oxidation resistance. Thus, adding Ta (in the range of x = 0.2-0.3) to a-structured WB2-z does not only positively influence the ductile character and thermal stability but also drastically increases the oxidation resistance.
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| 6. |
- Moraes, V., et al.
(author)
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Substoichiometry and tantalum dependent thermal stability of alpha-structured W-Ta-B thin films
- 2018
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In: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 155, s. 5-10
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Journal article (peer-reviewed)abstract
- Physical vapor deposited (PVD) WB2 thin films crystallize in the alpha-AIB(2)-prototype structure rather than in their thermodynamically stable (omega-W2B5-z-prototype structure. Contrary to the majority of alpha-AlB2-type transition metal diborides (TMB2), alpha-WB2 exhibits a more ductile character. Combining density functional theory and sophisticated experiments, we show that the stability of alpha-WB2 thin films is basically influenced by point defects such as vacancies present in PVD materials. With the help of alpha-TaB2 (one of the most ductile TMB2 with high preference for alpha-AlB2-type), the thermally driven decomposition and phase transformation of alpha-W1-xTaxB2-z to the omega-W2B5-z-type can be shifted to temperatures above 1200 degrees C.
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| 7. |
- Resl, P., et al.
(author)
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Large differences in carbohydrate degradation and transport potential in the genomes of lichen fungal symbionts
- 2022
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13
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Journal article (peer-reviewed)abstract
- Lichen symbioses are thought to be stabilized by the transfer of fixed carbon from a photosynthesizing symbiont to a fungus. In other fungal symbioses, carbohydrate subsidies correlate with reductions in plant cell wall-degrading enzymes, but whether this is true of lichen fungal symbionts (LFSs) is unknown. Here, we predict genes encoding carbohydrate-active enzymes (CAZymes) and sugar transporters in 46 genomes from the Lecanoromycetes, the largest extant clade of LFSs. All LFSs possess a robust CAZyme arsenal including enzymes acting on cellulose and hemicellulose, confirmed by experimental assays. However, the number of genes and predicted functions of CAZymes vary widely, with some fungal symbionts possessing arsenals on par with well-known saprotrophic fungi. These results suggest that stable fungal association with a phototroph does not in itself result in fungal CAZyme loss, and lends support to long-standing hypotheses that some lichens may augment fixed CO2 with carbon from external sources.
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| 8. |
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| 9. |
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| 10. |
- Hahn, R., et al.
(author)
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Unraveling the superlattice effect for hexagonal transition metal diboride coatings
- 2023
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In: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 235
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Journal article (peer-reviewed)abstract
- Superlattice structures enable the simultaneous enhancement in hardness (H) and fracture toughness (KIC) of ceramic-like coatings. While a deeper understanding of this effect has been gained for fcc-structured transition metal nitrides (TMN), hardly any knowledge is available for hexagonal diborides (TMB2). Here we show that superlattices can-similarly to nitrides-increase the hardness and toughness of diboride films. For this purpose, we deposited TiB2/WB2 and TiB2/ZrB2 superlattices with different bilayer periods (?) by non-reactive sputtering. Nanoindentation and in-situ microcantilever bending tests yield a distinct H peak for the TiB2/WB2 system (45.5 & PLUSMN; 1.3 GPa for ? = 6 nm) but no increase in KIC related to a difference in shear moduli (112 GPa). Contrary, the TiB2/ZrB2 system shows no peak in H, but for KIC with 3.70 & PLUSMN; 0.26 MPa & BULL;m1/2 at ? = 4 nm originating from differences in lattice spacing (0.14 & ANGS;), hence causing coherent stresses retarding crack growth.
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| 11. |
- Lasfargues, H., et al.
(author)
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Non-reactively sputtered ultra-high temperature Hf-C and Ta-C coatings
- 2017
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In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 309, s. 436-444
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Journal article (peer-reviewed)abstract
- Transition metal carbides are known for their exceptional thermal stability and mechanical properties, notably governed by the carbon content and the prevalent vacancies on the non-metallic sublattice. However, when using reactive deposition techniques, the formation of amorphous C-containing phases is often observed. Here, we show that non-reactive magnetron sputtering of HfC0.89 or TaC0.92 targets lead to fully crystalline coatings. Their C content depends on the target-to-substrate alignment and globally increases from HfC0.66 to HfC0.76 and from TaC0.69 to TaC0.75 with increasing bias potential from floating to - 100 V, respectively, when using a substrate temperature T-sub of 500 degrees C. Increasing T-sub to 700 degrees C leads to variations from TaC0.71 to TaC0.81. All HfCy films are single-phase face-centered cubic, whereas the TaCy films also contain small fractions of the hexagonal Ta2C phase. The highest hardness and indentation modulus among all coatings studied is obtained for TaC0.75 with H = 41.9 +/- 03 GPa and E = 466.8 +/- 15 GPa. Ab initio calculations predict an easy formation of vacancies on the C-sublattice, especially in the Ta-C system, and a temperature driven stabilization of defected structures at high temperatures, with fewer vacancies on the C sublattice for Hf-C than for Ta-C The predicted phase stability is proven up to 2400 C for both systems by annealing experiments in vacuum.
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| 12. |
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| 13. |
- Mayrhofer, P.H., et al.
(author)
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Spinodal decomposition of cubic Ti1-xAlxN : Comparison between experiments and modeling
- 2007
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In: International Journal of Materials Research. - : Walter de Gruyter GmbH. - 1862-5282 .- 2195-8556. ; 98:11, s. 1054-1059
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Journal article (peer-reviewed)abstract
- Annealing of cubic (c) Ti1-xAlxN, possessing NaCl structure, leads to decomposition into the stable constituents c-TiN and hexagonal (h) AlN (ZnS wurtzite structure) via the formation of metastable C-TiN rich and metastable c-AlN rich phases. In this paper, we describe the influence of sizes of the newly formed particles and strain energy due to their different lattice parameter and elastic constants with respect to the remaining matrix on decomposition processes and energetics. Good agreement between the enthalpy output obtained from differential scanning calorimetry and values derived from ab-initio and continuum mechanical based calculations for the decomposition and transformation processes occurring is obtained. Based on the comparison between experiments including X-ray diffraction and small-angle neutron scattering of annealed samples and modeling we can conclude that spinodal decomposition is present in c-Ti1-xAlxN coatings with x = 0.50 and 0.66, whereas the alloy with x = 0.25 is outside the spinodal. © carl hanser verlag gmbh & co. Kg.
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| 14. |
- Bartosik, M., et al.
(author)
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Interface controlled microstructure evolution in nanolayered thin films
- 2016
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In: Scripta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6462 .- 1872-8456. ; 123, s. 13-16
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Journal article (peer-reviewed)abstract
- X-ray nano-diffraction and transmission electron microscopy were conducted along the thickness of a similar to 4 pm thick CrN/AlN multilayer with continuously increasing AlN layer thicknesses from similar to 1 to 15 nm on similar to 7 nm thick CrN template layers. The experiments reveal coherent growth, large columnar grains extending over several (bi-)layers for thin AlN layer thicknesses below similar to 4 nm. Above similar to 4 nm, the nucleation of the thermodynamically stable wurtzite structured AlN is favored, leading to coherency breakdown and reduction of the overall strains, disrupting the columnar microstructure and limiting the maximum grain size in film growth direction to the layer thickness. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd.
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| 15. |
- Glechner, T., et al.
(author)
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Tuning structure and mechanical properties of Ta-C coatings by N-alloying and vacancy population
- 2018
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
-
Journal article (peer-reviewed)abstract
- Tailoring mechanical properties of transition metal carbides by substituting carbon with nitrogen atoms is a highly interesting approach, as thereby the bonding state changes towards a more metallic like character and thus ductility can be increased. Based on ab initio calculations we could prove experimentally, that up to a nitrogen content of about 68% on the non-metallic sublattice, Ta-C-N crystals prevail a face centered cubic structure for sputter deposited thin films. The cubic structure is partly stabilized by non-metallic as well as Ta vacancies-the latter are decisive for nitrogen rich compositions. With increasing nitrogen content, the originally super-hard fcc-TaC0.71 thin films soften from 40 GPa to 26 GPa for TaC0.33N0.67, accompanied by a decrease of the indentation modulus. With increasing nitrogen on the non-metallic sublattice (hence, decreasing C) the damage tolerance of Ta-C based coatings increases, when characterized after the Pugh and Pettifor criteria. Consequently, varying the non-metallic sublattice population allows for an effective tuning and designing of intrinsic coating properties.
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| 16. |
- Holec, D., et al.
(author)
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Macroscopic elastic properties of textured ZrN-AlN polycrystalline aggregates: From ab initio calculations to grainscale interactions
- 2014
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 90:18, s. 184106-
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Journal article (peer-reviewed)abstract
- Despite the fast development of computational material modeling, the theoretical description of macroscopic elastic properties of textured polycrystalline aggregates starting from basic principles remains a challenging task. In this study we use a supercell-based approach to obtain the elastic properties of a random solid solution cubic Zr1-x Al-x N system as a function of the metallic sublattice composition and texture descriptors. The employed special quasirandom structures are optimized not only with respect to short-range-order parameters, but also to make the three cubic directions [1 0 0], [0 1 0], and [0 0 1] as similar as possible. In this way, only a small spread of elastic constant tensor components is achieved and an optimum trade-off between modeling of chemical disorder and computational limits regarding the supercell size and calculational time is proposed. The single-crystal elastic constants are shown to vary smoothly with composition, yielding x approximate to 0.5 an alloy constitution with an almost isotropic response. Consequently, polycrystals with this composition are suggested to have Youngs modulus independent of the actual microstructure. This is indeed confirmed by explicit calculations of polycrystal elastic properties, both within the isotropic aggregate limit and with fiber textures with various orientations and sharpness. It turns out that for low AlN mole fractions, the spread of the possible Youngs modulus data caused by the texture variation can be larger than 100 GPa. Consequently, our discussion of Youngs modulus data of cubic Zr1-x Al-x N contains also the evaluation of the texture typical for thin films.
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| 17. |
- Hurtado, P., et al.
(author)
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Disentangling functional trait variation and covariation in epiphytic lichens along a continent-wide latitudinal gradient
- 2020
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In: Proceedings of the Royal Society of London. Biological Sciences. - : ROYAL SOC. - 0962-8452 .- 1471-2954. ; 287:1922
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Journal article (peer-reviewed)abstract
- Characterizing functional trait variation and covariation, and its drivers, is critical to understand the response of species to changing environmental conditions. Evolutionary and environmental factors determine how traits vary among and within species at multiple scales. However, disentangling their relative contribution is challenging and a comprehensive trait-environment framework addressing such questions is missing in lichens. We investigated the variation in nine traits related to photosynthetic performance, water use and nutrient acquisition applying phylogenetic comparative analyses in lichen epiphytic communities on beech across Europe. These poikilohydric organisms offer a valuable model owing to their inherent limitations to buffer contrasting environmental conditions. Photobiont type and growth form captured differences in certain physiological traits whose variation was largely determined by evolutionary processes (i.e. phylogenetic history), although the intraspecific component was non-negligible. Seasonal temperature fluctuations also had an impact on trait variation, while nitrogen content depended on photobiont type rather than nitrogen deposition. The inconsistency of trait covariation among and within species prevented establishing major resource use strategies in lichens. However, we did identify a general pattern related to the water-use strategy. Thus, to robustly unveil lichen responses under different climatic scenarios, it is necessary to incorporate both among and within-species trait variation and covariation.
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| 18. |
- Kirnbauer, A., et al.
(author)
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Mechanical properties and thermal stability of reactively sputtered multi-principal-metal Hf-Ta-Ti-V-Zr nitrides
- 2020
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In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 389
-
Journal article (peer-reviewed)abstract
- Crystalline (Hf,Ta,Ti,V,Zr)N nitride thin films, with a high-entropy metal-sublattice, were synthesized at 440 degrees C by reactive magnetron sputtering using an equimolar Hf-Ta-Ti-V-Zr-compound target. The coatings are single-phase fcc structured mono-nitrides for N-2/(Ar + N-2) flow-rate-ratios (f(N2)) between 30 and 45%. For higher f(N2) a small fraction of a second phase (next to the fcc matrix) can be detected by X-ray diffraction (XRD) and selected area electron diffraction (SAED). All coatings studied (prepared with f(N2) between 30 and 60%) show similar chemical compositions and hardness (H) values between 30.0 and 34.0 GPa with indentation moduli of similar to 460 GPa. Atom probe tomography (APT) indicates a homogenous distribution of all elements within our fcc-(Hf,Ta,Ti,V,Zr)N even after vacuum-annealing at 1300 degrees C. While H decreased from 32.5 to 28.1 GPa by this annealing treatment, the coating is still single-phase fcc structured with a defect density (expressed by XRD and SAED features, transmission electron microscopy contrast, and grain sizes) comparable to the as-deposited state. Only after vacuum-annealing at 1500 degrees C, XRD and APT reveal the formation of hexagonal structured (Ta,V)(2)N. The onset of nitrogen-loss - detected by thermogravimetric analysis - is similar to 1350 degrees C. Based on our results we can conclude that the sluggish diffusion within our fcc-(Hf,Ta,Ti,V,Zr)N warrants the single-phase fcc structure up to 1300 degrees C, although ab initio based calculations would suggest the lower-entropy products [fcc-(Hf,Zr)N, fcc-(Ta,V)N, and fcc-TiN] and [fcc-(Hf,Zr)N and fcc-(Ta,Ti,V)N] to be energetically more stable up to 1302 K.
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| 19. |
- Kirnbauer, A., et al.
(author)
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Thermal stability and mechanical properties of sputtered (Hf,Ta,V,W,Zr)-diborides
- 2020
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In: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 200, s. 559-569
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Journal article (peer-reviewed)abstract
- Non-reactive magnetron sputtering of a diboride target composed of HfB2, TaB2, VB2, W2B5, and ZrB2 with equimolar composition leads to the formation of crystalline single-phase solid solution diboride thin films, (Hf,Ta,V,W,Zr)B2, with a high-entropy metal-sublattice. Their growth morphology (dense and fine- fibrous), crystal structure (AlB2-type), as well as mechanical properties (indentation modulus E of ~580 GPa and hardness H of ~45 GPa), and chemical compositions are basically independent of the substrate bias potential applied (varied between -40 and -100 V) during the deposition at 450 °C. Detailed X-ray diffraction (XRD) and atom probe tomography (APT) studies indicate that the (Hf,Ta,V,W,Zr)B2 thin films remain single-phase AlB2-structured (with randomly distributed elements at the metal-sublattice) during vacuum-annealing at temperatures up to 1200 °C. Only when increasing the annealing temperature to 1400 °C, the formation of small orthorhombic structured (V,W)B-based regions can be detected, indicating the onset of decomposition of (Hf,Ta,V,W,Zr)B2 thin films into (Hf,Ta,Zr)B2 and (V,W)B, accompanied by the formation of confined B-rich boundary regions between these phases. After annealing at 1400 °C the hardness is still very high with ~44 GPa, as the volume fraction of the newly formed (V,W)B-rich domains is small and the majority of the coating is still solid-solution (Hf,Ta,V,W,Zr)B2 with severe lattice distortions. Only at even higher Ta of 1500 and 1600 °C, H decreased to ~39 GPa.
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| 20. |
- Klimashin, F. F., et al.
(author)
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Composition driven phase evolution and mechanical properties of Mo-Cr-N hard coatings
- 2015
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 118:2
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Journal article (peer-reviewed)abstract
- Although many research activities concentrate on transition metal nitrides, due to their excellent properties, only little is known about Mo-N based materials. We investigate in detail the influence of Cr on the structural evolution and mechanical properties of Mo-N coatings prepared at different nitrogen partial pressures. The chemical composition as well as the structural development of coatings prepared with N-2-to-total pressure ratios (p(N2)/p(T)) of 0.32 and 0.44 can best be described by the quasi-binary Mo2N-CrN tie line. Mo2N and CrN are face centered cubic (fcc), only that for Mo2N half of the N-sublattice is vacant. Consequently, with increasing Cr content, also the N-sublattice becomes less vacant and the chemical composition of fcc single-phase ternaries can be described as Mo1-xCrxN0.5(1+x). These coatings exhibit an excellent agreement between experimentally and ab initio obtained lattice parameters of fcc Mo1-xCrxN0.5(1+x). When increasing the N-2-to-total pressure ratio to pN(2)/p(T) = 0.69, the N-sublattice is already fully occupied for Cr-additions of x >= 0.4, as suggested by elastic recoil detection analysis and lattice parameter variations. The latter follows the ab initio obtained lattice parameters along the quasi-binary MoN-CrN tie line for x >= 0.5. The single-phase fcc coating with Cr/(Mo+Cr) of x similar to 0.2, prepared with pN(2)/p(T) = 0.32, exhibits the highest hardness of similar to 34 GPa among all coatings studied. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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| 21. |
- Kohlhauser, B., et al.
(author)
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How microalloying of the Al target can improve process and film characteristics of sputtered alumina
- 2020
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In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 393
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Journal article (peer-reviewed)abstract
- The outstanding thermo-mechanical and chemical stability of Al2O3 thin films attracts particular attention in academia and industry. Here we show that alloying of the powder metallurgically prepared Al targets with 2 as well as 5 at.% of Cr, Mo, or W significantly improves the process stability (e.g., reducing arcing events) for Al2O3, allowing their reactive magnetron sputtering in DC mode (substrate temperature was always 360 degrees C). Contrary to these microalloying elements, Nb did not change or improve the process characteristics of the Al target due to the relatively coarse Nb particles (< 125 mu m). Particularly the small (< 10 mu m) and fine-dispersed W particles are very effective in stopping the collision cascades to concentrate them to the near subsurface target-regions. This leads to a shift of the target-poisoning onset from O-2/(Ar + O-2) flow-rate-ratios of about 32 to 52%, specifically when adding 5 at.% to the Al target. Thereby also improved deposition rates are possible. However, detailed X-ray diffraction (XRD) and transmission electron microscopy studies show that only thin films developed from the 2 at.% W alloyed Al target have a nanocrystalline gamma-Al2O3-based structure comparable to those prepared from Al or Cr alloyed Al targets. The films are with 28.3 GPa instead of 26.8 GPa slightly harder when sputtered from Al0.98W0.02 instead of Al targets. Higher W contents (and also Nb) in the target lead to the formation of Al2O3-based films with considerably lower crystalline phase fractions and hardness (similar to 13 GPa). Hardest films, with 30.0 and 29.6 GPa, are obtained when using Al0.98Cr0.02 and Al0.98Cr0.05 targets, respectively. The formation of volatile Mo-oxides during film growth interferes the structure development, leading to rather soft films with 8.0 GPa especially when using the higher Mo alloyed Al0.98Cr0.05 target. Based on our results we can conclude that microalloying the Al targets with small and fine-dispersed Cr or W particles not just improves process stability and deposition rate during reactive sputtering of Al2O3, but also their mechanical thin film properties.
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| 22. |
- Mayrhofer, P.H., et al.
(author)
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Microstructural design of hard coatings
- 2006
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In: Progress in Materials Science. - : Elsevier BV. - 0079-6425 .- 1873-2208. ; 51:8, s. 1032-1114
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Research review (peer-reviewed)abstract
- Microstructural design has attracted increasing interest in modern development of hard coatings for wear-resistant applications. In plasma-assisted vapor deposited thin films, the material's microstructure can be designed during growth or post-deposition annealing treatments. In this review, we demonstrate the correlation between microstructure and mechanical as well as tribological properties of hard ceramic coatings. This is done for single-phase coatings and composition or phase modulated layers. In the latter case, the microstructure can be designed by choice of the deposition technique chosen, understanding the growth processes taking place on a film surface, either by sequential deposition of layers or by taking advantage of newly discovered self-organization processes including segregation effects of the elements. Consequently, the effects of individual microstructural features like grain size, defect density (and hence residual stress), phase arrangements in a one-, two- or three-dimensional manner on the mechanical properties are treated. Here, especially TiN-TiB2 is used as a model system to describe the development of two- and three-dimensional coating nanostructures. Due to their particular structures, such coatings can exhibit superhardness (H = 40 GPa). The microstructural changes of hard ceramic coatings during a post-deposition annealing treatment are discussed in detail. Although the significance of heat treatments to optimize properties (by a well-designed microstructure) for specific applications is recognized in bulk material science, only a few elements have been applied for hard ceramic coatings so far. Due to limited atomic assembly kinetics during the deposition process (e.g., by using a low substrate temperature), defects (point-, line-, and area-defects), supersaturated, and metastable phases can easily be obtained. For example, growth of (Ti,Al)N and Ti(B,N) films can result in the formation of a supersaturated TiN based phase. Such films undergo age hardening processes during post-deposition annealing due to the decomposition of the supersaturated phases into their stable constituents. The review clearly shows that nanostructure dependent hardness increase (compared to hardness of the bulk counterparts) sustains higher annealing temperatures than hardness increase due to an increased density of point- and/or line-defects. Tribological properties of hard thin films can be engineered by adding phases with lubricious properties at operation temperature (either room or elevated temperatures) and prevailing environment. Especially in high speed and dry cutting applications, low-friction and lubricating mechanisms of the thin film itself are required in addition to excellent mechanical properties. © 2006 Elsevier Ltd. All rights reserved.
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| 23. |
- Riedl, H., et al.
(author)
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Influence of carbon deficiency on phase formation of super-hard TaCy thin films
- 2018
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In: Scripta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6462 .- 1872-8456. ; 149, s. 150-154
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Journal article (peer-reviewed)abstract
- Using nonreactive sputter deposition allows the preparation of single-phase fcc structured TaCy thin films over a wide compositional range with y between 0.63 and 1.04. Among this composition range, the C-deficient TaC0.78 exhibits the highest as deposited hardness of 43.4 +/- 0.65 GPa combined with the highest thermal stability. Even after vacuum annealing to 2400 degrees C, no vacancy-ordered or faulted Ta-C based phases can be detected. The stabilization of carbon deficient fcc structured TaCy near y of about 0.75, revealed the decisive character of vacancy engineered thin films materials for ultra-high temperature applications. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 24. |
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| 25. |
- Dalbauer, V, et al.
(author)
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On the phase formation of cathodic arc evaporated Al1-xCrx-based intermetallic coatings and substoichiometric oxides
- 2018
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In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 352, s. 392-398
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Journal article (peer-reviewed)abstract
- The phase evolution of Al1-xCrx-based intermetallic coatings and corresponding substoichiometric oxides grown by cathodic arc evaporation was investigated in order to obtain a better understanding of the relation between oxygen flow rate, Al and Cr content, and structural evolution of the coatings deposited. When using 20 sccm Ar, or 50 sccm O-2, or 100 sccm O-2 per active source (p.a.s.) the cathode reaction zone consists of various intermetallic Al-Cr-compounds, which are in good agreement with the binary Al-Cr phase diagram. This is generally also reflected in the phase composition of the metallic and substoichiometric oxide coatings. The Al-rich compositions, Al0.75Cr0.25 and Al0.70Cr0.30, show a strong tendency for the formation of gamma(1)-Al8Cr5 phases. Mostly, the coating compositions of the metallic constituents of the synthesised intermetallic and substoichiometric oxide coatings deviate from the elemental compositions of the cathode, show enrichment in Cr. This deviation is more pronounced for Cr-rich cathodes using low O-2 flow rates during deposition. The dense columnar structure of the intermetallic coatings (hardness values between 2.5 and 10.2 GPa) turns into a nano-composite-like morphology for depositions with 50 and 100 sccm O-2 p.a.s., which in turn leads to a significant hardness increase up to similar to 24 GPa. Among all coatings investigated, the Cr-rich compositions have higher hardness and denser morphology than the Al-rich layers.
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