| 1. |
- Bahr, Ahmed, et al.
(författare)
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Quaternary diborides-improving the oxidation resistance of TiB2 +/- z coatings by disilicide alloying
- 2023
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Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 11:9, s. 733-741
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Tidskriftsartikel (refereegranskat)abstract
- To overcome the limited oxidation resistance of the emerging class of transition metal borides, we suggest within this study novel quaternary diborides, Ti-TM-Si-B-2 +/- z (TM = Ta, Mo), achieving the compromise between excellent oxidation resistance and requirements of hard coatings. Single-phase AlB2-type structured Ti-TM-Si-B-2 +/- z films (3-5 mu m) are sputter-deposited from TiB2/TMSi2 targets. The Ti-Ta-Si-B-2 +/- z coatings exhibit 36 GPa in hardness, while maintaining strongly retarded oxidation kinetics till 1000 degrees C. Ti-Mo-Si-B-2 +/- z coatings preserve a hardness up to 27 GPa, although outperforming all their counterparts by featuring outstanding oxidation resistance with 440nm oxide scale thickness after 1 h at 1200 degrees C. First report on quaternary Ti-TM-Si-B-2 +/- z coatings stabilized in hexagonal AlB2-prototype structures. These hard coating materials exhibit unprecedented oxidation resistance up to 1200 degrees C due to the formation of Si-rich scales.
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| 2. |
- Chien, Yu-Ping, et al.
(författare)
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Deviations between film and target compositions induced by backscattered Ar during sputtering from M-2-Al-C (M = Cr, Zr, and Hf) composite targets
- 2022
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 446
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Tidskriftsartikel (refereegranskat)abstract
- M-Al-C (M = Cr, Zr, and Hf) thin films are deposited from stoichiometric M2AlC composite targets by direct current magnetron sputtering (DCMS) and high power pulsed magnetron sputtering (HPPMS) in an industrial coater. Using DCMS it is observed that the composition of the Cr-Al-C film is close to stoichiometric, while the Al concentration in the Zr-Al-C and Hf-Al-C films is significantly reduced compared to the Al concentration in the targets. It is evident that the magnitude of the difference in Al concentration between the target and the cor-responding film composition is strongly dependent on the atomic mass of the transition metal. Zr and Hf atoms are 1.8 and 3.4 times heavier than Cr. In HPPMS, the target potential is approximately 1.6 times larger than that in DCMS, which can result in the film compositions deviating even stronger from the target composition as compared to DCMS. The Zr-Al-C thin film deposited by HPPMS exhibits a larger Al-deficiency than the film deposited by DCMS. The energy distributions of backscattered Ar neutrals are simulated by utilizing a two-body collision model and the Transport of Ions in Matter (TRIM) code. Based on the simulation results the experimentally observed Al -deficient film compositions can be readily explained: As the mass of the transition metal in the target is increased, both, energy and flux of the (at the target) reflected Ar is increased causing preferential re-sputtering of Al in the films. As stoichiometric compositions are a prerequisite for the formation of single-phase compound thin films it is evident that composite targets with a transition metal mass-dependent Al-overstoichiometry are required to compensate the Al-loss induced by the energetic Ar neutrals.
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| 3. |
- Halim, Joseph, et al.
(författare)
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Tailored synthesis approach of (Mo2/3Y1/3)(2)AlC i-MAX and its two-dimensional derivative Mo1.33CTz MXene: enhancing the yield, quality, and performance in supercapacitor applications
- 2021
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Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372. ; 13:1, s. 311-319
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Tidskriftsartikel (refereegranskat)abstract
- A vacancy-ordered MXene, Mo1.33CTz, obtained from the selective etching of Al and Sc from the parent i-MAX phase (Mo2/3Sc1/3)(2)AlC has previously shown excellent properties for supercapacitor applications. Attempts to synthesize the same MXene from another precursor, (Mo2/3Y1/3)(2)AlC, have not been able to match its forerunner. Herein, we show that the use of an AlY2.3 alloy instead of elemental Al and Y for the synthesis of (Mo2/3Y1/3)(2)AlC i-MAX, results in a close to 70% increase in sample purity due to the suppression of the main secondary phase, Mo3Al2C. Furthermore, through a modified etching procedure, we obtain a Mo1.33CTz MXene of high structural quality and improve the yield by a factor of 6 compared to our previous efforts. Free-standing films show high volumetric (1308 F cm(-3)) and gravimetric (436 F g(-1)) capacitances and a high stability (98% retention) at the level of, or even beyond, those reported for the Mo1.33CTz MXene produced from the Sc-based i-MAX. These results are of importance for the realization of high quality MXenes through use of more abundant elements (Y vs. Sc), while also reducing waste (impurity) material and facilitating the synthesis of a high-performance material for applications.
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| 4. |
- Hsu, Tun-Wei, 1991-, et al.
(författare)
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Dense and hard TiWC protective coatings grown with tungsten ion irradiation using WC-HiPIMS/TiC-DCMS co-sputtering technique without external heating
- 2023
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 618
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Tidskriftsartikel (refereegranskat)abstract
- Titanium tungsten carbide (TiWC) coatings are deposited by a combined high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) technique. No external heating is applied during deposition phase, instead, the thermally driven adatom mobility is substituted by heavy ion irradiation. DCMS sources equipped with titanium carbide targets provide constant neutral fluxes to establish the predominant coating structures, whereas tungsten carbide target in HiPIMS mode serves as the source of heavy metal-ions. Substrate bias of −60 V is synchronized to W+ ion-rich time domains of HiPIMS pulses to minimize the contribution from working gas ions. The influence of W+ ion flux intensity, controlled by varying peak target current density (JT), on film properties is investigated. X-ray photoelectron spectroscopy reveals the presence of over stoichiometric carbon forming an amorphous phase, the amount of which can be fine-tuned by varying JT. Changes in film composition as a function of JT are explained based on the in-situ ion mass spectroscopy analyses. Dense TiWC coatings by hybrid process exhibit hardness higher than 30 GPa, which are comparable to TiWC films deposited by DCMS with dc substrate bias and external heating. The relative energy consumption in the hybrid process is reduced by 77 % as compared to high-temperature DCMS processing.
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| 5. |
- Hsu, Tun-Wei, 1991-, et al.
(författare)
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Effects of substrate rotation during AlSi-HiPIMS/Ti-DCMS co-sputtering growth of TiAlSiN coatings on phase content, microstructure, and mechanical properties
- 2023
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 453
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Tidskriftsartikel (refereegranskat)abstract
- A combined high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) technique is used to deposit Ti0.6Al0.32Si0.08N films with 1-fold substrate table rotation. Layers are grown at two different substrate-target separations, two different rotational speeds, and with different values of substrate bias. The aim is to study the role of (1) overlap between ion and neutral fluxes generated from HiPIMS and DCMS sources, respectively, and (2) the subplantation range of low-mass ions. Results from X-ray diffractometry highlight the necessity of flux intermixing in the formation of the metastable B1-structured TiAlSiN solid solutions. All films grown at short target-to-substrate distance contain the hexagonal AlN phase, as there is essentially no overlap between HiPIMS and DCMS fluxes, thus the Al+ and Si+ subplantation is very limited. Under conditions of high flux intermixing corresponding to larger target-to-substrate distance, no w-AlN forms irrespective of rotational speed (1 or 3 rpm) and bias amplitude (120 or 480 V), indicating that the role of Al+/Si+ and Ti flux overlap is crucial for the phase formation during film growth by HiPIMS/DCMS with substrate rotation. This conclusion is further supported by the fact that the reduction of the bilayer thickness with increasing the target-to-substrate distance (hence increasing flux overlap) is larger for films grown with higher amplitude of the substrate bias, indicative of more efficient Al+/Si+ subplantation into the c-TiN phase. Single-phase films with the hardness close to that of layers grown with stationary substrate table can be achieved, however, at the expense of higher compressive stress.
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| 6. |
- Hsu, Tun-Wei, 1991-, et al.
(författare)
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Influence of Si content on phase stability and mechanical properties of TiAlSiN films grown by AlSi-HiPIMS/Ti-DCMS co-sputtering
- 2021
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 427
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Tidskriftsartikel (refereegranskat)abstract
- Ti1-x(AlySi1-y)xN coatings covering a wide compositional range, 0.38 < x < 0.76 and 0.68 ≤ y ≤ 1.00, are deposited to investigate the influence of Al+/Si+ ion irradiation on microstructural and mechanical properties. The samples are grown in Ar/N2 atmosphere by the hybrid high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) method with substrate bias synchronized to the Al+/Si+-rich portion of the HiPIMS pulses. Two Ti targets are operated in DCMS mode, while one AlSi target is operated in HiPIMS mode. Four different AlSi target compositions are used: Al1.0Si0.0, Al0.9Si0.1, Al0.8Si0.2, and Al0.6Si0.4. X-ray diffractometry reveals that films without Si (i.e., y = 1.0) have high Al solubility in NaCl-structure, c-TiAlN, up to x ≤ 0.67 no w-AlN is detected. Once Si (y < 1.0) is introduced the Al solubility limit decreases, but remains higher than other PVD techniques, along with grain refinement and the formation of a SiNz rich tissues phase, as shown by transmission electron microscopy. The nanoindentation hardness is high (~ 30 GPa) for all films that do not contain the w-AlN phase. All the coatings have compressive stresses lower than -3 GPa. Interestingly, a range of films with different compositions displayed both high hardness (~ 30 GPa) and low residual stress (σ < 0.5 GPa). Such an unique combination of properties highlights the benefits of using HiPIMS/DCMS configuration with metal-ion-synchronized substrate bias, which utilizes the Al+/Si+ supplantation effect and minimizes the Ar+ incorporation.
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| 7. |
- Janknecht, Rebecca, et al.
(författare)
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A Strategy to Enhance the B-Solubility and Mechanical Properties of Ti-B-N Thin Films
- 2024
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 271
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Tidskriftsartikel (refereegranskat)abstract
- 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–TiB2 or TiN–TiB tie-line influence this B-solubility. The variation between these two tie-lines is realized through non-reactive co-sputtering of a TiN, TiB2, and Ti target. We show that for variations along the TiN–TiB tie-line, even 8.9 at.% B (equivalent to 19.3 at.% non-metal fractions) can fully be incorporated into the fcc-TiNy lattice without forming other B-containing phases. The combination of detailed microstructural characterization through X-ray diffraction and transmission electron microscopy with ab initio calculations of fcc-Ti1-xNBx, fcc-TiN1-xBx, and fcc-TiN1-2xBx solid solutions indicates that B essentially substitutes N.The single-phase fcc-TiB0.17N0.69 (the highest B-containing sample along the TiN–TiB tie-line studied) exhibits the highest hardness H of 37.1±1.9 GPa combined with the highest fracture toughness KIC of 3.0±0.2 MPa·m1/2 among the samples studied. These are markedly above those of B-free TiN0.87 having H = 29.2±2.1 GPa and KIC = 2.7±<0.1 MPa·m1/2.
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| 8. |
- Syed, Bilal, 1977-, et al.
(författare)
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Effect of work function and cohesive energy of the constituent phases of Ti-50 at.% Al cathode during arc deposition of Ti-Al-N coatings
- 2019
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Ingår i: Surface & Coatings Technology. - USA : Elsevier. - 0257-8972 .- 1879-3347. ; 357, s. 393-401
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Tidskriftsartikel (refereegranskat)abstract
- The differences in work function (W.F.) and cohesive energy (C.E.) of the phases constituting the cathode, plays an important role in the formation of the converted layer at its near-surface region during cathodic arc deposition. As a consequence, this also affects the deposition conditions for the coatings. In this study, we explore the effect of W.F. and C.E. of the constituent phases during arc evaporation by utilizing two kinds of customized Ti-50 at.% Al cathodes with different phase compositions. Our results show that during reactive arc evaporation the disparity in W.F. and C.E. among the constituent phases of Ti-50 at.% Al cathodes leads to preferential erosion of the phases with lower W.F. and C.E. The aforementioned preferential erosion begets higher surface roughness on the Ti-50 at.% Al cathode with a wider range of W.F. and C.E. disparity. It is also observed that the thermal conductivity of the Ti-50 at.% Al cathode plays a dominant role in the deposition rate of Ti-Al-N coating. This article also presents how the surface geometry of the cathode in the presence of arc guiding magnetic field significantly influences the microstructure of the deposited coatings.
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| 9. |
- Syed, Bilal, et al.
(författare)
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Morphology and microstructure evolution of Ti-50 at.% Al cathodes during cathodic arc deposition of Ti-Al-N coatings
- 2017
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Ingår i: Journal of Applied Physics. - Melville, New York 11747-4300 : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 121:24
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Tidskriftsartikel (refereegranskat)abstract
- Today's research on the cathodic arc deposition technique and coatings therefrom primarily focuses on the effects of, e.g., nitrogen partial pressure, growth temperature, and substrate bias. Detailed studies on the morphology and structure of the starting material—the cathode—during film growth and its influence on coating properties at different process conditions are rare. This work aims to study the evolution of the converted layer, its morphology, and microstructure, as a function of the cathode material grain size during deposition of Ti-Al-N coatings. The coatings were reactively grown in pure N2discharges from powder metallurgically manufactured Ti-50 at.% Al cathodes with grain size distribution averages close to 1800, 100, 50, and 10 μm, respectively, and characterized with respect to microstructure, composition, and mechanical properties. The results indicate that for the cathode of 1800 μm grain size the disparity in the work function among parent phases plays a dominant role in the pronounced erosion of Al, which yields the coatings rich in macro-particles and of high Al content. We further observed that a reduction in the grain size of Ti-50 at.% Al cathodes to 10 μm provides favorable conditions for self-sustaining reactions between Ti and Al phases upon arcing to form γ phase. The combination of self-sustaining reaction and the arc process not only result in the formation of hole-like and sub-hole features on the converted layer but also generate coatings of high Al content and laden with macro-particles.
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| 10. |
- Thörnberg, Jimmy, et al.
(författare)
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Oxidation resistance and mechanical properties of sputter-deposited Ti0.9Al0.1B2-y thin films
- 2022
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Ingår i: Surface & Coatings Technology. - : Elsevier Science SA. - 0257-8972 .- 1879-3347. ; 442
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Tidskriftsartikel (refereegranskat)abstract
- Direct-current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) were used to deposit understoichiometric Ti(1-x)Al(x)B(2-y )diboride coatings by sputtering from a segmented TiB2-AlB2 target using Ar and Kr as sputtering gas. For films with a fixed Al/(Ti + Al) ratio of x = 0.1 (Ti0.9Al0.1B2-y), the B content was varied with y & ISIN; (0.1, 0.6 and 0.7). For films with a fixed y = 0.7 (Ti1-xAlxB1.3), the Al content was varied with x & ISIN; (0.1, 0.4 and 0.7). Evaluation of the mechanical properties of the Ti1-xAlxB1.3 samples showed a reduction in both hardness and elastic modulus with increasing Al concentration, while the Ti0.9Al0.1B2-y samples showed a hardness increase with decreasing B content. Thus, Ti0.9Al0.1B1.3 films exhibited a superior hardness of 46.2 +/- 1.1 GPa and an elastic modulus of 523 & PLUSMN; 7 GPa, compared to the values for Ti0.9Al0.1B1.4 and Ti0.9Al0.1B1.9, showing a hardness of 44 +/- 1 GPa and 36 +/- 1 GPa, and an elastic modulus of 569 +/- 7 GPa and 493 +/- 6 GPa, respectively. The oxidation behavior of the mechanically most promising Ti0.9Al0.1B2-y sample series was investigated through air-annealing at 600 C for durations from 1 h to 10 h. All films formed a mixed non-conformal Al2O3-TiO2 oxide scale which acts as an inward and outward diffusion barrier, significantly reducing the oxidation rate compared to TiBz films, which form an oxide scale consisting of porous TiO2. The thinnest oxide scale after 10 h was found in the B-deficient samples, Ti0.9Al0.1B1.3 and Ti0.9Al0.1B1.4, at ~200 nm, which is significantly below that for Ti0.9Al0.1B1.9 at 320 nm. The enhanced oxidation resistance of highly understoichiometric films is due to the elimination of the B-rich tissue phase that is present at the grain boundaries for higher B content, where the latter has been shown to enhance the rate of oxidation in borides.
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