Microstructure and mechanical properties stability of pre-hardening treatment in Al-Cu alloys for pre-hardening forming process

The stability of the microstructure and mechanical properties of the pre-hardened sheets during the pre-hardening forming(PHF)process directly determines the quality of the formed components.The microstructure stability of the pre-hardened sheets was in-vestigated by differential scanning calorimetry(DSC),transmission electron microscopy(TEM),and small angle X-ray scattering(SAXS),while the mechanical properties and formability were analyzed through uniaxial tensile tests and formability tests.The results in-dicate that the mechanical properties of the pre-hardened alloys exhibited negligible changes after experiencing 1-month natural aging(NA).The deviations of ultimate tensile strength(UTS),yield strength(YS),and sheet formability(Erichsen value)are all less than 2%.Also,after different NA time(from 48 h to 1 month)is applied to alloys before pre-hardening treatment,the pre-hardened alloys possess stable microstructure and mechanical properties as well.Interestingly,with the extension of NA time before pre-hardening treatment from 48 h to 1 month,the contribution of NA to the pre-hardening treatment is limited.Only a yield strength increment of 20 MPa is achieved,with no loss in elongation.The limited enhancement is mainly attributed to the fact that only a limited number of clusters are transformed into Guinier-Preston(GP)zones at the early stage of pre-hardening treatment,and the formation ofθ''phase inhibits the nucleation and growth of GP zones as the precipitated phase evolves.

Surface evolution caused by curvature driven forces based on natural exponential pair potential

Based on the natural exponential pair potential, the interaction potential between curved surface body and on surface particle is studied. Firstly, the interaction potential is written as a function of curvatures through the differential geometry. Secondly, idealized numerical experiments are designed to test the accuracy of curvature-based potential. Then, the driving forces induced by curvatures are analyzed, which confirms that micro/nano curved surface body can induce driving forces, curvatures and the gradient of curvatures are the essential elements forming the driving forces. Finally, by combing with the curvature based potential and driving forces, the movements of on surface particles and the evolution of surface morphology of curved surface body are predicted.

Curvature-Driven Forces Based on Natural Exponential Pair Potential at Micro/Nanoscales

The natural exponential potential (Ce^R/λ0) widely exists at micro/nanoscales;this paper studies the interaction potential between a curved-surface body and an outside particle base on the natural exponential potential. Mat hematical derivation proves t hat the int er act ion potential can be expressed as a function of curvatures. Then, idealized numerical experiments are designed to verify the accuracy of the curvature-based potential. The driving forces exerted on the particle are discussed and confirmed to be a function of curvatures and the gradient of curvatures, which may explain some abnormal movements at micro/nanoscales.

Non-epitaxial growth of highly oriented transition metal dichalcogenides with density-controlled twin boundaries

Twin boundaries(TBs)in transition metal dichalcogenides(TMDs)constitute distinctive one dimensional electronic systems,exhibiting intriguing physical and chemical properties that have garnered significant attention in the fields of quantum physics and electrocatalysis.However,the controlled manipula-tion of TBs in terms of density and specific atomic configurations remains a fomidable challenge.In this study,we present a non-epitaxial growth approach that enables the controlled and large scale fabrication of homoge-neous catalytically active TBs in monolayer TMDs on arbitrary substrates.Notably,the density achieved using this strategy is six times higher than that observed in convention chemical vapor deposition(CVD)-grown sam-ples.Through rigorous experimental analysis and multigrain Wulff construc tion simulations,we elucidate theroleof regulating themetal source diffusion process,which serves as the key factor for inducing the self-oriented growth ofTMD grains and the formation of unified TBs.Furthermore,we demonstrate that this novel growth mode can be readily incorporated into the conventional CVD growth method by making a simple modification of the growth tempera-ture profle,thereby offering a universal approach for engineering of grain boundaries in two-dimensional materials.