| 1. |
- Fritze, Stefan, et al.
(författare)
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Magnetron sputtering of carbon supersaturated tungsten films-A chemical approach to increase strength
- 2021
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten (W)-based materials attract significant attention due to their superior mechanical properties. Here, we present a chemical approach based on the addition of carbon (C) for increased strength via the combination of three strengthening mechanisms in W thin films. W:C thin films with C concentrations up to-4 at.% were deposited by magnetron sputtering. All films exhibit a body-centred-cubic structure with strong texture and columnar growth behaviour. X-ray and electron diffraction measurements suggest the formation of supersaturated W:C solid solution phases. The addition of C reduced the average column width from-133 nm for W to-20 nm for the film containing-4 at.% C. The column refinement is explained by a mechanism where C acts as re-nucleation sites. The W film is-13 GPa hard, while the W:C films achieve a peak hardness of-24 GPa. The W:C films are-11 GPa harder than the W film, which is explained by a combination of grain refinement strengthening, solid solution strengthening and increased dislocation density. Additional micropillar compression tests showed that the flow stress increased upon C addition, from-3.8 to-8.3 GPa and no brittle fracture was observed.
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| 2. |
- Kaplan, Maciej, 1991-, et al.
(författare)
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Combinatorial design of amorphous TaNiSiC thin films with enhanced hardness, thermal stability, and corrosion resistance
- 2022
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 220
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous TaNiSiC and TaNiC films (with varying Ta/Ni and Si/C ratios) were deposited using combinatorial magnetron sputtering. The TaNiSiC films remained X-ray amorphous after four hour-long annealings up to 700 °C, while TaNiC alloys with high Ni and C contents crystallized. These differences were attributed to a strong driving force for separation of Ni and C in TaNiC, whereas the addition of Si, due to its solubility in the other elements, reduced the elemental segregation in TaNiSiC. The as-deposited TaNiSiC films exhibited hardnesses of 9–12 GPa. Annealing led to an increase in hardness by 2–4 GPa, due to decreases in average atomic distance, as evidenced by X-ray diffraction measurements. Potentiodynamic polarizations from –0.7 to +1.5 V vs. Ag/AgCl (3 M NaCl) in 10 mM sodium borate showed lower current densities by up to 2 orders of magnitude with increasing Ta content (28–52 at.%). Changes in Si/C content (7–13 at.% Si) had no effect. However, optical microscopy showed that TaNiSiC films with high Si/low C contents (13/10 at.%) suffered much less localized etching compared to TaNiC films. Thus, Si had a significant role in increasing the mechanical strength, corrosion resistance, and thermal stability of the TaNiSiC films.
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| 3. |
- Srinath, Aishwarya, 1991-, et al.
(författare)
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An investigation of the corrosion resistances of magnetron sputtered TaW-rich, Nb-rich, and multicomponent CrNbTaTiW alloys
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The corrosion resistances of magnetron sputtered nearequimolar, TaW-rich, and Nb-rich CrNbTiTaW alloys, with and without 8 at.% carbon, were studied in aqueous chloride-containing environments. Electrochemical tests and scanning electron images showed that all the CrNbTaTiW alloys were highly corrosion resistant in 1.0 M HCl. The results conclusively showed that passivated nearequimolar CrNbTaTiW coatings have comparable corrosion performances to passivated Nb- and TaW-rich alloys in 0.01 M HCl + 0.1 M NaCl. Carbon affected the rate of surface repassivation in polarisation measurements of the films whose oxide had been partially reduced, but had a minor influenceon the corrosion resistances once a mature oxide was formed. No conclusive relationships between microstructure and corrosion resistance were established. The comparable corrosion resistances of the multicomponent CrNbTiTaW, Nb-rich and TaW-rich alloys were attributed to the presence of extremely stable surface oxides of Nb and Ta which prevented losses of Ti and Cr. The near surface regions of all the alloys before and after corrosion appeared to be depleted in W compared to the bulk.
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| 4. |
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| 5. |
- Srinath, Aishwarya, et al.
(författare)
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Influence of the nitrogen content on the corrosion resistances of multicomponent AlCrNbYZrN coatings
- 2021
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 188
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the relationship between the nitrogen content and the corrosion resistances of non-equimolar multicomponent AlCrNbYZrN films (N = 13-49 at.%) is probed. While there was no linear relationship between nitrogen content and corrosion resistance, the results clearly show that the corrosion resistances of the films were instead determined by their nitrogen-induced porosities i.e. the less porous the sample, the higher the corrosion resistance. The 23, 30 and 37 at.% N samples were denser while the 13 at.% N sample was porous and the 49 at.% N film had an underdense nanocrystalline columnar cross section permitting the ingress of electrolyte.
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| 6. |
- Srinath, Aishwarya
(författare)
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Investigations of the corrosion resistances of magnetron sputtered multicomponent materials : A study on high entropy alloys, high entropy sublattice ceramics, and metallic glasses
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The corrosion resistances of sputter deposited AlCrNbYZrN, CrNbTiTaWC and TaNiSiC alloys were assessed in acidic and alkaline environments. Compositionally complex alloying strategies, and whether they produced coatings with superior corrosion resistances, were explored. Another priority was to determine if the formation of a random solid solution was necessary for the design of corrosion resistant multicomponent alloys. The results showed that successful surface passivation/oxidation was the key factor determining corrosion resistance. The corrosion resistance was maximised when coating porosity was minimised, spontaneously passivating elements were used, and the oxide solubility in the electrolyte was low. The benefits of multicomponent alloying were demonstrated through the protective effect of oxides of more stable elements (Cr, Nb, Ta) reducing the loss of less corrosion resistant elements (Al, Ti). The supersaturation of nitrogen, carbon and/or silicon affected coating morphologies, surface repassivation rates, and even directly corrosion resistances, e.g. when silicon oxides were formed on TaNiSiC films.The N content (0-50 at.% N) in AlCrNbYZrN films affected the film porosity, the absence of which led to high corrosion resistances in 1.0 M HCl. The formation of a single phase did not govern the corrosion resistances. It was more important that the coatings were dense, as this permitted the formation of an impervious passive layer. The addition of 8 at.% C to nearequimolar CrNbTiTaW alloys affected surface repassivation rates of films whose oxide had been partially removed by chronoamperometry in a 1.0 M HCl electrolyte. However, the effect of carbon on the corrosion properties was minor. A comparison of the nearequimolar CrNbTiTaW, Nb and TaW alloys with their native oxides revealed comparable corrosion resistances in 0.01 M HCl + 0.1 M NaCl. The nearequimolar CrNbTiTaW, Nb, and TaW alloys also showed no evidence of pitting in 1.0 M HCl. The high corrosion resistances in CrNbTiTaW alloys was due to the presence of extremely stable surface oxides abundant in Cr, Nb, and Ta. TaNiSiC films with Si contents above 12 at.%, and C contents lower than 11 at.% showed high corrosion resistances in 10 mM sodium borate due to the formation of silicon oxides, even after three polarisations from −0.7 to +1.5 V vs. Ag/AgCl (3 M NaCl) and 50+ hours of immersion. Microscopy of the Si-rich TaNiSiC film showed negligible differences in surface condition before and after corrosion in sodium borate, while films with lower Si contents or higher Ta contents were more severely corroded.
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| 7. |
- Srinath, Aishwarya, et al.
(författare)
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Near-surface analysis of magnetron sputtered AlCrNbYZrNx high entropy materials resolved by HAXPES
- 2024
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Hard X-ray photoelectron spectroscopy (HAXPES) was used to perform a non-destructive depth profile of AlCrNbYZrNx (x = 0 to ∼50 at.%) thin films. The outermost native oxide of the pristine thin films contained the highest coordination oxides of every metal. Substoichiometric oxides or oxynitrides were found underneath. After exposure to 1.0 M HCl, increases in the most highly coordinated oxides of Cr, Nb, and Al in films with up to 37 at.% N were observed, suggesting that the low coordination oxides and oxynitrides in the subsurface had been further oxidised and were intermediary compounds in the passivation process. Al and Y oxides were lost to the HCl electrolyte, in agreement with their respective Pourbaix diagrams. The film with 49 at.% N showed little to no change in the data due to its high porosity which led to the oxide being detected at all probed depths. The metal core level spectra revealed a preferential order in which nitrogen bonded with the different metals. Nitrogen interacted first with Y, then Zr, then Al and Nb, and lastly Cr as the nitrogen content was increased.
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| 8. |
- von Fieant, Kristina, et al.
(författare)
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Multi-component (Al,Cr,Nb,Y,Zr)N thin films by reactive magnetron sputter deposition for increased hardness and corrosion resistance
- 2020
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 693
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Tidskriftsartikel (refereegranskat)abstract
- Multi-component nitride thin films in the Al-Cr-Nb-Y-Zr system with non-equimolar composition have been deposited by reactive dc magnetron sputtering. The substrate temperature and substrate bias have been varied, from room temperature to 700 degrees C and from 0 to -200 V respectively. The relationship between these varied growth conditions on the structure, morphology, mechanical and corrosion properties of the films have been probed. All films consisted of a single solid solution with a NaCl-type structure, as shown by X-ray diffraction. However, elemental energy dispersive spectroscopy maps, obtained in the scanning transmission electron microscope, indicated that there could be partial segregation of Al, Cr and Y atoms within the grains. The microstructure of the films became denser, more fine-grained and smoother as the bias and temperature were increased. Nanoindentation showed that the hardness of the films increased with both bias and temperature, reaching a maximum of 27 +/- 2 GPa. The corrosion resistance of the films, studied by performing potentiodynamic polarisation curves in 1 M HCl, was also found to be improved when compared to a commercially available hyper-duplex stainless steel and a ternary reference (Nb,Zr)N thin film as well.
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