Improving ductility by coherent nanoprecipitates in medium entropy alloy

Controlling precipitates in spatial density and size distribution is essential for tailoring the microstructure and mechanical properties through precipitation hardening. We herein obtained heterogeneous grain structures with coherent L12 nanoprecipitates in (CrCoNi)94Al4Ti2 medium entropy alloy (MEA) by annealing and aging. Additional pre-aging leads to a high spatial density and more random distribution nucleation sites of the coherent L12 nanoprecipitates. The preaging doubled the ductility without apparently sacrificing the strength. Transmission electron microscopy (TEM) revealed that, in pre-aged MEA, finely dispersed L12 nanoprecipitates with higher spatial density were sheared by dislocation, promoting planar slips, which favors geometrically necessary dislocations (GNDs) piling up to increased hetero-deformation-induced (HDI) stress and work-hardening. Stacking faults, Lomer-Cottrell locks, and 9R structures were formed in aged and pre-aged MEA after tensile deformation. The formation of these defects enormously enhanced strain hardening by blocking dislocation movements and accumulating dislocations. Moreover, a higher frequency of interactions between defects and coherent L12 nanoprecipitates can be observed in the pre-aged MEA due to the more randomly distributed L12 nanoprecipitates, substantially increasing ductility. This work demonstrates a new route to achieving a super strength-ductility combination of single-phase FCC high entropy alloys by nanoscale coherent precipitation strengthening

Enhanced strength-ductility synergy in a gradient hetero-structured CrCoNi medium-entropy alloy

A CrCoNi medium-entropy alloy (MEA) with gradient hetero-structure (GHS) composing of gradient nanostructured surface layer and hetero-structured matrix was prepared via a two-step process: pre-cold rolling (CR) deformation and subsequent annealing followed by surface mechanical grinding treatment (SMGT) and secondary annealing. The GHS CrCoNi exhibits an excellent synergy of strength and ductility, as evidenced by a yield strength of approximately 1.2 GPa and a uniform elongation of about 20%. The GHS displays a pronounced hetero-deformation induced (HDI) hardening effect, whereby the central layer (CL) and surface layer (SL) undergo local strain hardening in a mutually compatible manner. This process facilitates the multiplication and accumulation of geometrically necessary dislocations (GNDs) at intra- and inter-layer hetero-interfaces and also activates the deformation faulting and twinning in both CL and SL, thus enhancing the overall mechanical response. The interlayer compatible deformation observed in the GHS significantly bolsters the sustainability of strain hardening at the microscopic scale. This effect is of significant importance in redistributing stress and strain more rationally across the entire GHS sample, effectively reducing the risk of localized deformation failures. This study offers insight into the correlation between macroscopic strain hardening and micromechanical behavior in gradient-/hetero-structured materials

Determination of the number of ψ(3686) events taken at BESIII

The number of ψ(3686) events collected by the BESIII detector during the 2021 run period is determined to be (2259.3±11.1)×106 by counting inclusive ψ(3686) hadronic events. The uncertainty is systematic and the statistical uncertainty is negligible. Meanwhile, the numbers of ψ(3686) events collected during the 2009 and 2012 run periods are updated to be (107.7±0.6)×106 and (345.4±2.6)×106, respectively. Both numbers are consistent with the previous measurements within one standard deviation. The total number of ψ(3686) events in the three data samples is (2712.4±14.3)×10^

Measurement of integrated luminosity of data collected at 3.773 GeV by BESIII from 2021 to 2024

We present a measurement of the integrated luminosity e+e- of collision data collected by the BESIII detector at the BEPCII collider at a center-of-mass energy of Ecm = 3.773 GeV. The integrated luminosities of the datasets taken from December 2021 to June 2022, from November 2022 to June 2023, and from October 2023 to February 2024 were determined to be 4.995±0.019 fb-1, 8.157±0.031 fb-1, and 4.191±0.016 fb-1, respectively, by analyzing large angle Bhabha scattering events. The uncertainties are dominated by systematic effects, and the statistical uncertainties are negligible. Our results provide essential input for future analyses and precision measurements