| 1. |
- Zendejas Medina, León, et al.
(författare)
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Enhancing corrosion resistance, hardness, and crack resistance in magnetron sputtered high entropy CoCrFeMnNi coatings by adding carbon
- 2021
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- This study explores carbon addition as a materials design approach for simultaneously improving the hardness, crack resistance, and corrosion resistance of high entropy thin films. CoCrFeMnNi was selected as a starting point, due to its high concentration of weak carbide formers. The suppression of carbides is crucial to the approach, as carbide formation can decrease both ductility and corrosion resistance. Films with 0, 6, and 11 at.% C were deposited by magnetron co-sputtering, using a graphite target and a sintered compound target. The samples with 0 at.% C crystallized with a mixture of a cubic closed packed (ccp) phase and the intermetallic chi-phase. With 6 and 11 at.% C, the films were amorphous and homogenous down to the nm-scale. The hardness of the films increased from 8 GPa in the carbon-free film to 16 GPa in the film with 11 at.% C. Furthermore, the carbon significantly improved the crack resistance as shown in fragmentation tests, where the crack density was strongly reduced. The changes in mechanical properties were primarily attributed to the shift from crystalline to amorphous. Lastly, the carbon improved the corrosion resistance by a progressive lowering of the corrosion current and the passive current with increasing carbon concentration.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- Voigt, Christian C., et al.
(författare)
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The Impact of Light Pollution on Bats Varies According to Foraging Guild and Habitat Context
- 2021
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Ingår i: BioScience. - : Oxford University Press (OUP). - 0006-3568 .- 1525-3244. ; 71:10, s. 1103-1109
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Forskningsöversikt (refereegranskat)abstract
- We Review How Different Bat Guilds Respond To Artificial Light At Night (Alan) And Assess How The Impacts Can Vary According To Ecological Context. All Studied European Species Respond Negatively To Alan Close To Roosts And Drinking Sites, And The Impacts Occur Across A Wide Range Of Light Colors And Intensities. Most Bat Species Are Sensitive To Alan When Commuting And Foraging. Although Narrow-Space-Foraging Bat Species Consistently Avoid Alan When Foraging, Open And Edge-Space-Foraging Species May Exploit Insects Lured By Alan. Therefore, Alan Acts As An Environmental Filter On Bat Assemblages. Considering The Detrimental Effect Of Alan On Insects, We Conclude That Alan Probably Has Negative Impacts On All Bat Species, Even On Those Foraging At Streetlights. The Sprawl Of Alan May Be A Key Factor Driving The Decline Of Bat Diversity Globally, And The Current Trajectory Of Increasing Alan Is Therefore Of Considerable Concern For Bat Conservation.
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| 5. |
- Zendejas Medina, Léon, et al.
(författare)
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Enhancing the mechanical and electrochemical properties of sputtered CoCrFeMnNi thin films by carbon addition
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- High entropy alloy (HEA) thin films of CrMnFeCoNi are promising materials for polymer electrolyte membrane fuel cells, due to their high fracture resistance and passivation against corrosion. The addition of carbon to HEA films have shown to improve corrosion resistance, hardness and ductility. HEA films with 0%, 6% and 11% amounts of carbon were deposited on Si[100] and polyimide substrates by magnetron co-sputtering using a graphite target and a sintered compound target for this study. Characterization using XRD and TEM showed that the samples were crystalline with a mixture of ccp and α-Mn at 0 at-% C, and underwent amorphization from 6 at-% C. No evidence of either free carbon or a crystalline carbide phase was found, and the films displayed homogenous composition. Nanoindentation measurements on coated Si [100] substrate showed that the hardness of the thin films changed with increasing carbon content. The tensile fragmentation test method was shown to be useful to characterize the strength distribution and fracture energy at crack onset for the present materials. This method revealed fewer cracks at all levels of strain for the carbon containing films compared to the carbon free ones. Consequentially, there was a trend of higher fracture energies by addition of carbon because of a shifting towards of crack onset strain. Electrochemical studies showed that the carbon had a beneficial effect on the passive layer, lowering the corrosion current and the passive current during with increasing carbon.
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