Lattice distortion releasing local surface strain on high-entropy alloys

High-entropy alloys(HEAs)have the potential to be a paradigm-shift for rational catalyst discovery but this new type of alloy requires a completely new approach to predict the surface reactivity.In addition to the ligand effect perturbing the surface–adsorbate bond,the random configuration of elements in the surface will also induce local strain effects due to the varying radii of neighboring atoms.Accurate modelling of HEA surface reactivity requires an estimate of this effect:To what degree is the adsorption of intermediates on these lattice distorted atomic environments affected by local strain?In this study,more than 3,500 density functional theory(DFT)calculated adsorption energies of*OH and*O adsorbed on the HEAs IrPdPtRhRu and AgAuCuPdPt are statistically analyzed with respect to the lattice constants of the alloys and the surfaces of each individual binding site.It is found that the inherent distortion of the lattice structure in HEAs releases the local strain effect on the adsorption energy as the atomic environment surrounding the binding atom(s)settles into a relaxed structure.This is even observed to be true for clusters of atoms of which the sizes deviate significantly from the atomic environment in which they are embedded.This elucidates an important aspect of binding site interaction with the neighboring atoms and thus constitutes a step towards a more accurate theoretical model of estimating the reactivity of HEA surfaces.

Residual strain evaluation of curved surface by grating-transferring technique and GPA

This paper investigates an advanced grating-transferring technique combined with geometric phase analysis (GPA) for residual strain evaluation of curved surface.A standard holographic grating is first transferred to a pre-produced epoxy resin film and then consolidated to a test region of curved surface.With a rubber mold and silicone rubber the deformed grating is replicated to a sheet metal after hole-drilling for release of residual stress.After that the grating is transferred from the sheet metal to the glass plate,which would be served as an analyzer grating (specimen grating).By GPA the local strain distributions related to the phase difference between the reference grating and analyzer grating for the released stress can be evaluated.A validation test has been conducted on the weld joint of a stainless steel tube and the obtained results demonstrate the ability of the method in measuring the residual strain of curved surface.

Scanning tunneling microscopy study of surface reconstruction induced by N adsorption on Cu(100) surface

The reconstructed structure of Cu （100） surface induced by atomic N adsorption is studied by using scanning tunneling microscopy （STM）. The 2D structure of copper boundary between neighbouring N covered islands is found to be sensitive to the growth conditions, e.g. N＋ bombardment time and annealing temperature. The copper boundary experiences a transition from nano-scale stripe to nano-particle when the substrate is continuously annealed at 623~K for a longer time. A well-defined copper-stripe network can be achieved by precisely controlling the growth conditions, which highlights the possibility of producing new templates for nanofabrication.

On the homogenization of metal matrix composites using strain gradient plasticity

The homogenized response of metal matrix composites（MMC） is studied using strain gradient plasticity.The material model employed is a rate independent formulation of energetic strain gradient plasticity at the micro scale and conventional rate independent plasticity at the macro scale. Free energy inside the micro structure is included due to the elastic strains and plastic strain gradients. A unit cell containing a circular elastic fiber is analyzed under macroscopic simple shear in addition to transverse and longitudinal loading. The analyses are carried out under generalized plane strain condition. Micro-macro homogenization is performed observing the Hill-Mandel energy condition,and overall loading is considered such that the homogenized higher order terms vanish. The results highlight the intrinsic size-effects as well as the effect of fiber volume fraction on the overall response curves, plastic strain distributions and homogenized yield surfaces under different loading conditions. It is concluded that composites with smaller reinforcement size have larger initial yield surfaces and furthermore,they exhibit more kinematic hardening.

Effect of Surface State on Nodular Corrosion Resistance of Zircaloy-4 Alloy

The effect of surface state on the nodular corrosion resistance of Zircaloy-4 alloy was investigated in super- heated steam at 500 ℃/10.3 MPa by autoclave tests. The microstructures of oxide films on the corroded specimens were observed by TEM and SEM. The results indicate that surface strained layer delays the appearance of nodular spots on the specimen surfaces and improves the nodular corrosion resistance. The columnar grains orientation of the oxide films formed on the specimens with surface strained layer was more consistent than that on the specimens without surface strained layer when a comparison was made on the same orientation of the grain surfaces. Such a kind of oxide micro- structure formed on the specimens with surface strained layer can hinder the diffusion of oxygen ions along the grain boundaries and delay the growth of oxide films, therefore retard the formation process of nodular spots. This indicates that the microstructure of the initial oxide films has an important influence on the subsequent growth of the oxide films.

N_(2)photofixation promoted by in situ photoinduced dynamic iodine vacancies at step edge in Bi_(5)O_(7)I nanotubes

Heterogeneous photosynthesis is a promising route for sustainable ammonia production,which can utilize renewable energy and water as the hydrogen source under ambient condition.In this study,a series of Bi_(5)O_(7)I(BOI)nanosheets and nanotubes are synthesized,the surface tensile strain is formed by curling the nanosheets into nanotubes to tune the concentration and location of dynamic vacancies.Scanning transmission electron microscopy(STEM)with spherical aberration correction confirms the presence of intrinsic areal defects on the surface of the BOI nanotube resulted from surface tensile strain.The presence of areal defects lowers the formation energy of I vacancies(IV)at step edge site,thus the IV with higher concentration would be favorably generated under visible light.Rapid scan in situ Fourier transform infrared(FT-IR)analysis in the aqueous media reveals that the IV promotes photocatalytic N_(2) activation and reduction,proceeds through an associative alternating mechanism.Specially,after turning off the light,the surface vacancy sites can be reoccupied by I−ions,which enables the protection and regeneration of photocatalyst surface in an aerobic and dark environment.This work provides an innovative strategy to tune concentration and location of dynamic surface vacancies on photocatalysts by building surface tensile strain for advancing sustainable ammonia production.