| 1. |
- Bahr, A., et al.
(författare)
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High-temperature oxidation resistance of ternary and quaternary Cr-(Mo)-Si-B2-z coatings-Influence of Mo addition
- 2023
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 468
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Tidskriftsartikel (refereegranskat)abstract
- The Si-based alloying of transition metal diborides is a promising strategy to improve their limited oxidation resistance in high-temperature environments. In this study, we investigate the oxidation resistance of ternary and quaternary Cr-(Mo)-Si-B2-z coatings sputter-deposited from alloyed CrB2/TMSi2 targets (TM = Cr, Mo). The asdeposited Cr-(Mo)-Si-B2-z coatings are stabilized in the single-phased hexagonal AlB2-structure, except the high-Si containing Cr0.26Mo0.11Si0.24B0.39 presenting amorphous character. The Mo-containing Cr-Mo-Si-B2-z films exhibit relatively high hardness compared to their ternary Cr-Si-B2-z counterparts, obtaining up to 26 GPa due to the formation of (Cr,Mo)B-2 solid solutions. The Si-alloying in ternary and quaternary coatings provides oxidation resistance up to 1200 degrees C, owing to the formation of highly protective double-layered scales consisting of SiO2 with a Cr2O3 layer on top, inhibiting oxygen inward diffusion. The quaternary Cr0.31Mo0.07Si0.15B0.47 coating is distinguished by superior oxidation resistance with lower porosity and void formation compared to the ternary Cr0.37Si0.16B0.47. Mo proved to be the key element for the higher stability and enhanced oxidation resistance due to the evolution of the MoSi2 phase at similar to 600 degrees C. This phase formation controls the Si diffusion and mobility within the microstructure, thus reducing the porosity and governing the Si supply to form SiO2 scale. The quaternary Cr0.31Mo0.07Si0.15B0.47 coating maintained an oxidation resistance up to 30 h at 1200 degrees C by forming a 2.5 mu m dense amorphous Si-based oxide scale with a thin Cr2O3 on top.
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| 2. |
- Bahr, A., et al.
(författare)
-
Non-reactive HiPIMS deposition of NbCx thin films : Effect of the target power density on structure-mechanical properties
- 2022
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 444
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Tidskriftsartikel (refereegranskat)abstract
- The exceptional mechanical properties of transition metal carbide coatings are known to be governed by the carbon content and its morphological distribution. Here, we verify the influence of the target peak power density on the chemical composition, microstructure, and mechanical properties of NbCx coatings grown by non-reactive high-power impulse magnetron sputtering (HiPIMS). By tuning the pulse parameters, the power density can be increased from 0.11 to 1.48 kW/cm2 leading to a decrease in the C/Nb ratio from 1.52 to 0.99 within the films - proven by combined elastic backscattering and time-of-flight elastic recoil detection analysis. This decrease in the C/Nb ratio is accompanied by microstructural changes from nanocomposite morphologies with an average grain size of 6.6 +/- 2.5 nm at 0.13 kW/cm2 into more columnar structures with an average column width of 65.2 +/- 18.7 nm at 1.48 kW/cm2. Independent from the C/Nb ratio, all films exhibit a single face-centered cubic structure. The mechanical properties correlate with the enhanced growth behavior dominated by ions at higher peak power densities and the varied C/Nb ratios. A maximum in hardness and fracture toughness of H = 38.7 +/- 3.6 GPa and KIc = 2.78 +/- 0.13 MPa center dot m1/2 (at 3.2 GPa residual compressive stress), is obtained for the nearly stoichiometric NbC coating exhibiting C/Nb ratio of 1.06.
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| 3. |
- Glechner, T., et al.
(författare)
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Influence of the non-metal species on the oxidation kinetics of Hf, HfN, HfC, and HfB2 coatings
- 2021
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 211
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the non-metal species on the oxidation resistance of transition metal ceramic based thin films is still unclear. For this purpose, we thoroughly investigated the oxide scale formation of a metal (Hf), carbide (HFC0.96), nitride (HfB1.5), and boride (HfB2.3) coating grown by physical vapor deposition. The non-metal species decisively affect the onset temperature of oxidation, ranging between 550 degrees C for HfC0.96 to 840 degrees C for HfN1.5. HfB2.3 and HfN1.5 obtain the slowest oxide scale kinetic following a parabolic law with k(p) values of 4.97.10(-10) and 5.66.10(-11) kg(2) m(-4) s(-1) at 840 degrees C, respectively. A characteristic feature for the oxide scale on Hf coatings, is a columnar morphology and a substantial oxygen inward diffusion. HfC0.96 reveals an ineffective oxycarbide based scale, whereas HfN(1.5 )features a scale with globular HfO2 grains. HfB(2.3 )exhibits a layered scale with a porous boron rich region on top, followed by a highly dense and crystalline HfO2 beneath. Furthermore, HfB(2.3 )presents a hardness of 47.7 +/- 2.7 GPa next to an exceptional low inward diffusion of oxygen during oxidation. This study showcases the strong influence of the non-metallic bonding partner despite the same metallic basis, as well as the huge potential for HfB2 based coatings also for oxidative environments.
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| 4. |
- Riedl, H., et al.
(författare)
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Influence of carbon deficiency on phase formation of super-hard TaCy thin films
- 2018
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Ingår i: Scripta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6462 .- 1872-8456. ; 149, s. 150-154
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Glechner, T., et al.
(författare)
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Correlation between fracture characteristics and valence electron concentration of sputtered Hf-C-N based thin films
- 2020
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 399
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Tidskriftsartikel (refereegranskat)abstract
- Hard protective coating materials based on transition metal nitrides and carbides typically suffer from limited fracture tolerance. To further tune these properties non-metal alloying - substituting C with N - has been proven favorable for magnetron sputtered Hf-C-N based thin films. A theoretically predicted increase in valence electron concentration (from 8.0 to 9.0 e/f.u. from Hf-C to Hf-N) through nitrogen alloying lead to an increase in fracture toughness (K-IC obtained during in-situ SEM cantilever bending) from 1.89 +/- 0.15 to 2.33 +/- 0.18 MPa.m(1/2) for Hf0.43C0.57 to Hf0.35C0.30N0.35, respectively. The hardness remains close to the super-hard regime with values of 37.8 +/- 2.1 to 39.9 +/- 2.7 GPa for these specific compositions. Already the addition of small amounts of nitrogen, while sputtering a ceramic Hf-C target, leads to a drastic increase of nitrogen on the non-metallic sublattice for fcc single phased structured HfC1-xNx films, where x = N/(C + N). The here obtained results also provide experimental proof for the correlation between fracture characteristics and valence electron concentration.
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| 6. |
- Glechner, T., et al.
(författare)
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Tuning structure and mechanical properties of Ta-C coatings by N-alloying and vacancy population
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Lasfargues, H., et al.
(författare)
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Non-reactively sputtered ultra-high temperature Hf-C and Ta-C coatings
- 2017
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 309, s. 436-444
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Tidskriftsartikel (refereegranskat)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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