Inconel 718 superalloy was fabricated by selective laser melting (SLM) and subsequently subjected to different heat treatments. Microstructure evolution was examined by X-ray diffraction, optical ...microscopy, scanning and transmission electron microscopies. In the horizontal section (normal to the building direction) of the as-built sample, columnar and cellular sub-structures formed in the overlapping area, while only cellular sub-structures existed in the central fusion area. Columnar structures were observed in the vertical section (parallel to the building direction). In the as-built condition, austenite γ and Laves phases predominated, almost to the exclusion of all other phases. When treated by the direct double aging (DA) process, δ-Ni3Nb phases precipitated mainly in the interdendritic regions where Nb preferentially segregated. Homogenization plus double aging (HA), and solution plus double aging (SA) treatments significantly eliminated microsegregation and Laves phases owing to the diffusion of Nb and Ti to the γ matrix. The δ phase dissolved in the HA-treated sample but precipitated in the SA-treated sample. The γ′-Ni3(Al,Ti) phase was prone to precipitate when treated by HA, while γ″-Ni3Nb phase tended to precipitate in the SA sample. Due to the precipitation of the higher fraction of the major strengthening γ″ phases, the SA sample showed the highest hardness value among the as-built, DA, HA, and SA samples. The morphology, distribution and crystallography of precipitates and their formation mechanisms are discussed and analyzed.
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•Heat treatments affected the precipitation behaviors of γ′, γ″ and δ phases.•The orientation relationships of γ′, γ″ with γ, and of δ with γ were observed.•The hardness increased as the volume fraction of γ″ increased.
Weyl (WSMs) evolve from Dirac semimetals in the presence of broken time-reversal symmetry (TRS) or space-inversion symmetry. The WSM phases in TaAs-class materials and photonic crystals are due to ...the loss of space-inversion symmetry. For TRS-breaking WSMs, despite numerous theoretical and experimental efforts, few examples have been reported. In this Article, we report a new type of magnetic semimetal Sr1-y Mn1-z Sb2 (y, z < 0.1) with nearly massless relativistic fermion behaviour (m∗ = 0.04 - 0.05m0 , where m0 is the free-electron mass). This material exhibits a ferromagnetic order for 304 K < T < 565 K, but a canted antiferromagnetic order with a ferromagnetic component for T < 304 K. The combination of relativistic fermion behaviour and ferromagnetism in Sr1-y Mn1-z Sb2 offers a rare opportunity to investigate the interplay between relativistic fermions and spontaneous TRS breaking.
A novel approach to medium-sized cyclic ethers was devised using a Stevens 1,2-shift of a sulfonium ylide derived from a readily accessible six-membered mixed-monothioacetal precursor. The concise ...and efficient transformation offers a surprising degree of chirality transfer with observed retention of stereochemical configuration on the anomeric migrating carbon and has been applied as the key step in an enantioselective formal synthesis of (+)-laurencin.
Horizontal-direction Inconel 718 alloy cylindrical rods were fabricated by selective laser melting (SLM) and subsequently subjected to solution or homogenization plus double aging (SA or HA) ...treatments. Lever arm creep tests were performed with the creep tensile axis perpendicular to the building direction of the samples with a constant stress of 650 MPa at 650 °C. Scanning and transmission microscopy and electron backscatter diffraction were used to clarify the microstructure of the SA and HA samples before and after creep. The experimental results revealed that the average grain sizes of the SA and HA samples were basically the same before creep, and larger γ′ and γ″ strengthening phases existed in the HA sample. The grains tended to grow, and the higher dislocation density within grains and lower local misorientation values close to the grain boundaries occurred in the HA sample during creep, which contributed to the longer creep rupture life in comparison with the SA sample. The fracture surfaces of the SA and HA samples displayed intergranular features, and the creep voids and micro-cracks were formed around the δ or Laves phases at the grain boundaries. The creep fracture mechanism was also discussed.
The complicated structure of the neutron cannot be calculated using first-principles calculations due to the large colour charge of quarks and the self-interaction of gluons. Its simplest structure ...observables are the electromagnetic form factors1, which probe our understanding of the strong interaction. Until now, a small amount of data has been available for the determination of the neutron structure from the time-like kinematical range. Here we present measurements of the Born cross section of electron–positron annihilation reactions into a neutron and anti-neutron pair, and determine the neutron’s effective form factor. The data were recorded with the BESIII experiment at centre-of-mass energies between 2.00 and 3.08 GeV using an integrated luminosity of 647.9 pb−1. Our results improve the statistics on the neutron form factor by more than a factor of 60 over previous measurements, demonstrating that the neutron form factor data from annihilation in the time-like regime is on par with that from electron scattering experiments. The effective form factor of the neutron shows a periodic behaviour, similar to earlier observations of the proton form factor. Future works—both theoretical and experimental—will help illuminate the origin of this oscillation of the electromagnetic structure observables of the nucleon.Form factors encode the structure of nucleons. Measurements from electron–positron annihilation at BESIII reveal an oscillating behaviour of the neutron electromagnetic form factor, and clarify a long-standing photon–nucleon interaction puzzle.
Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically ...generated matter-antimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry
. As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryon-antibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξ
baryon and its antiparticle
Formula: see text, has enabled a direct determination of the weak-phase difference, (ξ
- ξ
) = (1.2 ± 3.4 ± 0.8) × 10
rad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods
. Finally, we provide an independent measurement of the recently debated Λ decay parameter α
(refs.
). The Formula: see text asymmetry is in agreement with and compatible in precision to the most precise previous measurement
.
We study the e^{+}e^{-}→γωJ/ψ process using 11.6 fb^{-1} e^{+}e^{-} annihilation data taken at center-of-mass energies from sqrts=4.008 GeV to 4.600 GeV with the BESIII detector at the BEPCII ...storage ring. The X(3872) resonance is observed for the first time in the ωJ/ψ system with a significance of more than 5σ. The relative decay ratio of X(3872)→ωJ/ψ and π^{+}π^{-}J/ψ is measured to be R=1.6_{-0.3}^{+0.4}±0.2, where the first uncertainty is statistical and the second systematic (the same hereafter). The sqrts-dependent cross section of e^{+}e^{-}→γX(3872) is also measured and investigated, and it can be described by a single Breit-Wigner resonance, referred to as the Y(4200), with a mass of 4200.6_{-13.3}^{+7.9}±3.0 MeV/c^{2} and a width of 115_{-26}^{+38}±12 MeV. In addition, to describe the ωJ/ψ mass distribution above 3.9 GeV/c^{2}, we need at least one additional Breit-Wigner resonance, labeled as X(3915), in the fit. The mass and width of the X(3915) are determined. The resonant parameters of the X(3915) agree with those of the Y(3940) in B→KωJ/ψ and of the X(3915) in γγ→ωJ/ψ observed by the Belle and BABAR experiments within errors.
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