A gradient nanostructured (GNS) surface layer was generated in a dual-phase Cu-Ag alloy by means of surface mechanical grinding treatment at liquid nitrogen temperature. With a decreasing depth in ...the surface layer, the coarse-grained microstructure of Cu matrix and Ag precipitates gradually converts into a nanolaminated structure of Ag- and Cu-rich phases with simultaneous chemical mixing, and finally forms a homogeneous single-phase supersaturated solid solution (SSS) nanostructure. Accordingly, a dislocation-mediated transportation mechanism was proposed to dominate the chemical mixing of Ag and Cu atoms, i.e., dislocations interacting with solution atoms penetrate the Cu/Ag interface and glide in the neighboring solvent-phase lamella.
•A gradient nanostructured (GNS) surface layer was generated in a dual-phase Cu-Ag alloy.•Intermixing of Cu- and Ag-rich phases simultaneously occurs in the GNS surface layer.•A dislocation-mediated transportation mechanism was proposed to dominate the chemical mixing of Ag and Cu atoms.
When either electron or hole doped at concentrations x approximately 0.1, the LaFeAsO family displays remarkably high temperature superconductivity with Tc up to 55 K. In the most energetically ...stable Q-->M=(pi,pi,0) antiferromagnetic (AFM) phase comprised of tetragonal-symmetry breaking alternating chains of aligned spins, there is a deep pseudogap in the Fe 3d states centered at the Fermi energy arising from light carriers (m* approximately 0.25-0.33), and very strong magnetophonon coupling is uncovered. Doping (of either sign) beyond x approximately 0.08 results in heavy carriers per Fe (by roughly an order of magnitude) with a large Fermi surface. Calculated Fe-Fe transverse exchange couplings Jij(R) reveal that exchange coupling is strongly dependent on both the AFM symmetry and on the Fe-As distance.
In this study, we identified the ZmCLA4 gene, which is responsible for the qLA4-1 associated with leaf angle, by positional cloning, and parsed the genetic mechanism.
A novel two-step intercritical annealing process was designed for an ultra-low carbon medium manganese steel plate. Excellent mechanical properties with yield strength of 590MPa, tensile strength of ...840MPa, total elongation of 28.5% and high impact energy of 106J at −80°C were obtained. The microstructure comprised of ultra-fine grained ferrite and retained austenite together with a small amount of martensite after the two-step intercritical annealing. Both lath-like and blocky retained austenite with volume fraction of ~25% and relatively poor stability were obtained. The submicron-sized lath-like retained austenite exhibited Nishiyama-Wassermann (N-W) orientation relationship with the neighboring martensitic ferrite lath. The fine grain size played a crucial role in stabilizing austenite during phase transformation by significantly lowering Ms temperature and increasing the elastic strain energy. The overall stability of retained austenite during deformation was considered to be mainly governed by the chemical composition of the studied steel. The mechanism of toughening was elucidated. The superior low-temperature toughness was associated with TRIP effect of metastable retained austenite, which relieved the local stress concentration, enhanced the ability to plastic deformation and delayed the initiation and propagation of microcracks.
Three different grain structures of low-carbon medium-manganese steel were prepared through appropriate controlled rolling process. The laminated microstructure with a strong //rolling direction (RD) ...fiber texture was characterized by ultra-fine elongated ferrite, retained austenite and martensite phase arranged alternately along the RD. The steel with equiaxed grain structure exhibited a relatively low tensile strength of 960MPa and an extremely poor low-temperature toughness of ~ 8J at −196°C. An enhanced upper shelf energy (> 450J) and low-temperature toughness (~ 105J at −196°C), as well as an improved tensile strength (1145MPa) was obtained in the steel with laminated microstructure. The laminated microstructure enabled the steel to be significantly stronger and tougher along the RD, which contributed to the high tensile strength to some extent. It is concluded that the combined effect of the ultra-fine elongated laminated microstructure, the possible interface decohesion and the existence of numerous {001} cleavage planes resulted in the occurrence of delamination. The delamination fracture enhanced the upper shelf energy mainly by promoting crack branching along the RD and thus suppressing crack propagation along the v-notch direction, which finally resulted in greater plastic deformation and significant increase in absorbed energy. Besides delamination toughening, transformation-induced plasticity (TRIP) effect of metastable retained austenite is believed to be responsible for the high cryogenic toughness, which can release stress concentration of crack tips and thus blunting cracks propagation.
We investigate here the correlation between deformation behavior and retained austenite characteristics in a medium-Mn transformation-induced plasticity (TRIP) steel. The sample was characterized by ...a dual-phase microstructure consisting of ultra-fine grained ferrite and retained austenite with relatively high mechanical stability after annealing at 700°C for 5h. Both lath-like and blocky (granular) retained austenite with volume fraction of 38.7% and relatively inhomogeneous grain size was obtained. The tensile specimen exhibited outstanding mechanical properties with yield strength of 745MPa, tensile strength of 1005MPa and total elongation of 46%, as well as a distinctive work hardening behavior. The in-depth investigation on deformation behavior demonstrated that the transformation mechanism of retained austenite during deformation was strain-induced and the yielding behavior was controlled mainly by the deformation of soft ferrite phase. As to the multi-peak work hardening behavior, it is believed to be attributed to the inhomogeneous and discontinuous occurrence of TRIP effect, which resulted from the inhomogeneous stability of retained austenite. Moreover, the orientation of retained austenite (Schmid factors) was proved an important factor in determining the mechanical stability of retained austenite upon deformation, in addition to the heterogeneity of grain size. These two factors together resulted in the inhomogeneous stability of retained austenite.
Strain concentration at grain boundaries and grain boundary microstructure in cold worked Alloy 600 were characterized. Excluding the annealing twin boundaries, the base and 20% cold worked alloys ...exhibited higher random grain boundary fractions than the 8% and 40% cold worked alloys. An increased low angle boundaries and decreased annealing twins were observed with deformation. The 20% cold worked alloy displayed a maximum strain concentration at grain boundaries. The stress corrosion cracking growth in cold worked Alloy 600 in high temperature water showed a strong correlation with the strain concentration at grain boundaries.
Simultaneous improvement in yield strength, ductility and impact toughness has always been a challenge for structural steels. In the attempt to achieve this goal, we proposed a ...Cu-precipitation-strengthened low-carbon medium-Mn steel in the present study. Upon aging at 600 °C for 1 h, a considerable amount of Cu-rich precipitates with average radius of 6.3 nm was uniformly distributed in the tempered martensitic matrix. An ultra-high yield strength, therefore, was attained by the strong interaction of Cu-rich precipitates with dislocations. In addition to the precipitation strengthening effect, the introduction of Cu also dramatically promoted the dissolution of cementite particles and formation of retained austenite at triple junctions or other high-angle grain boundaries. Compositional analysis of cementite and retained austenite was conducted by atom probe tomography. Austenite formation removed Mn segregation from the grain boundaries, consumed brittle cementite particles, and hence eliminated intergranular fracture, leading to a remarkable improvement in toughness. Moreover, a volume fraction of 23.2% retained austenite with appropriate mechanical stability also enabled the steel to be more ductile. The optimal mechanical properties, yield strength of 1005 MPa, tensile strength of 1070 MPa, total elongation of 24.3% and room temperature impact energy of ~ 73 J were obtained, through the cumulative contribution of Cu-rich precipitates and retained austenite.
A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines ...from six 2.9 GW(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10(-3) eV(2)<|Δm(41)(2) |< 0.3 eV(2) range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin(2) 2θ(14) cover the 10(-3) eV(2) ≲ |Δm(41)(2)| ≲ 0.1 eV(2) region, which was largely unexplored.
Stem cells were characterized by their stemness: self-renewal and pluripotency. Mesenchymal stem cells (MSCs) are a unique type of adult stem cells that have been proven to be involved in tissue ...repair, immunoloregulation and tumorigenesis. Irradiation is a well-known factor that leads to functional obstacle in stem cells. However, the mechanism of stemness maintenance in human MSCs exposed to irradiation remains unknown. We demonstrated that irradiation could induce reactive oxygen species (ROS) accumulation that resulted in DNA damage and stemness injury in MSCs. Autophagy induced by starvation or rapamycin can reduce ROS accumulation-associated DNA damage and maintain stemness in MSCs. Further, inhibition of autophagy leads to augment of ROS accumulation and DNA damage, which results in the loss of stemness in MSCs. Our results indicate that autophagy may have an important role in protecting stemness of MSCs from irradiation injury.
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