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1. Corrosion behavior of an in situ consolidated nanocrystalline Al-V alloy

   https://doi.org/10.1038/s41529-022-00225-5  

   Witharamage, C. S. ; Christudasjustus, J. ; Smith, J. ; Gao, W. ; Gupta, R. K. ( February 2022 , npj Materials Degradation)

   Supersaturated solid solutions of Al and corrosion-resistant alloying elements (M: V, Mo, Cr, Ti, Nb), produced by non-equilibrium processing techniques, have been reported to exhibit high corrosion resistance and strength. The corrosion mechanism for such improved corrosion performance has not been well understood. We present a fundamental understanding of the role of V in corrosion of an Al-V alloy, which will provide a theoretical background for developing corrosion-resistant Al alloys. High-energy ball milling of the elemental powder of Al and V produced an in situ consolidated Al-V alloy, which exhibited high solid solubility of V. The corrosion resistance of Al-V alloy was significantly higher than that of pure Al, which was attributed to the (1) enrichment of V at the passive film/substrate interface, (2) incorporation of V into the passive film, and (3) deposition of V on the iron-containing cathodic particles and therefore, retardation of cathodic reaction.
2. Swelling as a stabilizing mechanism in irradiated thin films: III. Effect on critical angle in a composite model

   https://doi.org/10.1088/1361-648X/acd31b  

   Evans, Tyler ; Norris, Scott ( May 2023 , Journal of Physics: Condensed Matter)

   Ion-beam irradiation of an amorphizable material such as Si or Ge may lead to spontaneous pattern formation, rather than flat surfaces, for irradiation beyond some critical angle against the surface normal. It is observed experimentally that this critical angle varies according to many factors, including beam energy, ion species and target material. However, many theoretical analyses predict a critical angle${\theta }_{\mathrm{c}}$of 45^∘independent of energy, ion and target, disagreeing with experiment. Previous work on this topic has suggested that isotropic swelling due to ion-irradiation may act as a stabilization mechanism, potentially offering a theoretical explanation for the elevated value of${\theta }_{\mathrm{c}}$in Ge compared to Si for the same projectiles. In the present work, we consider a composite model of stress-free strain and isotropic swelling with a generalized treatment of stress modification along idealized ion tracks. We obtain a highly-general linear stability result with a careful treatment of arbitrary spatial variation functions for each of the stress-free strain-rate tensor, a source of deviatoric stress modification, and isotropic swelling, a source of isotropic stress. Comparison with experimental stress measurements suggests that the presence of angle-independent isotropic stress may not be a strong influence on${\theta }_{\mathrm{c}}$more »href='cmacd31bieqn3.gif' type='simple'/>for the 250 eV Ar${}^{+}\to$Si system. At the same time, plausible parameter values suggest that the swelling mechanism may, indeed, be important for irradiated Ge. As secondary results, we show the unexpected importance for${\theta }_{\mathrm{c}}$of the relationship between free and amorphous-crystalline interfaces in the thin film model. We also show that under simple idealizations used elsewhere, spatial variation of stress may not contribute to${\theta }_{\mathrm{c}}$selection. These findings prompt modeling refinements which will be the focus of future work.

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3. Combinatorial measurement of critical cooling rates in aluminum-base metallic glass forming alloys

   https://doi.org/10.1038/s41598-021-83384-w  

   Liu, Naijia ; Ma, Tianxing ; Liao, Chaoqun ; Liu, Guannan ; Mota, Rodrigo Miguel Ojeda ; Liu, Jingbei ; Sohn, Sungwoo ; Kube, Sebastian ; Zhao, Shaofan ; Singer, Jonathan P. ; et al ( February 2021 , Scientific Reports)

   Direct measurement of critical cooling rates has been challenging and only determined for a minute fraction of the reported metallic glass forming alloys. Here, we report a method that directly measures critical cooling rate of thin film metallic glass forming alloys in a combinatorial fashion. Based on a universal heating architecture using indirect laser heating and a microstructure analysis this method offers itself as a rapid screening technique to quantify glass forming ability. We use this method to identify glass forming alloys and study the composition effect on the critical cooling rate in the Al–Ni–Ge system where we identified Al₅₁Ge₃₅Ni₁₄as the best glass forming composition with a critical cooling rate of 10⁴ K/s.
4. Unraveling the role of tungsten as a minor alloying element in the oxidation NiCr alloys

   https://doi.org/10.1038/s41529-022-00265-x  

   Volders, Cameron ; Angelici, Valentina Avincola ; Waluyo, Iradwikanari ; Hunt, Adrian ; Árnadóttir, Líney ; Reinke, Petra ( December 2022 , npj Materials Degradation)

   Abstract Ni-based superalloys offer a unique combination of mechanical properties, corrosion resistance and high temperature performance. Near ambient pressure X-ray photoelectron spectroscopy was used to study in operando the initial steps of oxidation for Ni-5Cr, Ni-15Cr, Ni-30Cr and Ni-15Cr-6W at 500 °C, p(O 2 )=10 −6 mbar. The comparison of oxide evolution for these alloys quantifies the outsized impact of W in promoting chromia formation. For the binary alloys an increase in chromia due to Cr-surface enrichment is followed by NiO nucleation and growth thus seeding a dual-layer structure. The addition of W (Ni-15Cr-6W) shifts the reaction pathways towards chromia thus enhancing oxide quality. Density functional theory calculations confirm that W atoms adjacent to Cr create highly favorable oxygen adsorption sites. The addition of W supercharges the reactivity of Cr with oxygen essentially funneling oxygen atoms into Cr sites. The experimental results are discussed in the context of surface composition, chemistry, reactant fluxes, and microstructure.
5. Influence of chemical heterogeneity and microstructure on the corrosion resistance of biodegradable WE43 magnesium alloys

   https://doi.org/10.1039/c9tb00388f  

   Mraied, Hesham ; Wang, Wenbo ; Cai, Wenjun ( October 2019 , Journal of Materials Chemistry B)

   Magnesium–yttrium-rare earth element alloys such as WE43 are potential candidates for future bioabsorbable orthopedic implant materials due to their biocompatibility, mechanical properties similar to human bone, and the ability to completely degrade in vivo . Unfortunately, the high corrosion rate of WE43 Mg alloys in physiological environments and subsequent loss of structural integrity limit the wide applications of these materials. In this study, the effect of chemical heterogeneity and microstructure on the corrosion resistance of two alloys with different metallurgical states was investigated: cast (as in traditional preparation) and as-deposited produced by magnetron sputtering. The corrosion behavior was studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests in blood bank buffered saline solution. It was found that the as-deposited alloy showed more than one order of magnitude reduction in corrosion current density compared to the cast alloy, owing to the elimination of micro-galvanic coupling between the Mg matrix and the precipitates. The microstructure and formation mechanism of corrosion products formed on both alloys were discussed based on immersion tests and direct measurements of X-ray photoelectron spectrometry (XPS) and cross-sectional transmission electron microscopy (TEM) analysis.