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Instantaneous high temperature improved the low-temperature sintering efficiency of the un-doped MgB 2 superconductor, and the MgB 2 was rapidly synthesized at 600 °C for only 2 h. In addition to the refinement of MgO impurity particles, the sudden high temperature induced defects within the MgB 2 grains, e.g. twinning crystal, and the J c performance is therefore significantly enhanced, about 2.2 × 10 3 A·cm − 2 at 4 T for bulk sample. Differed from the two-dimensional nucleation growth mode of the MgB 2 grains in the high-temperature sintered un-doped sample, the low-temperature sintered MgB 2 grains accord with the dislocation growth mechanism, relying on the thermal-stress-triggered twinning crystal. [ABSTRACT FROM AUTHOR]

Sintering temperature plays a vital role in the evolution of phase structure and microstructure in polycrystalline FeSe 0.5 Te 0.5 bulks fabricated by the two-step sintering method, and thus significantly influences their superconducting properties. Elevated sintering temperature (600–700 °C) at second step facilitates the substitution of Te into the superconducting phase, which leads to the increased lattice distortion and thus contributes to the enhancement of superconductivity (the value of T c reaches 15.6 K). At the same time, the accelerated growth of the superconducting grains and the improved homogeneity motivated by elevated sintering temperature serve as the main reason for the sharp superconducting transition. [ABSTRACT FROM AUTHOR]

A significant enhancement of critical current density (J c) was obtained in MgB2 +3wt.% glycine samples with a large amount of MgO. The improvements in J c and in the irreversible magnetic field (H irr) are attributed to the pinning effects of high C-substitution level, nanoscale MgO, and to the even boundaries of small grains. This doping method overcomes the degradation of J c under a low field in previously reported SiC-doped samples. Moreover, the formation of MgO was demonstrated to be the result of the reactions between Mg, CO2 and O2. [ABSTRACT FROM AUTHOR]

Lamellar MgB2 grains were synthesized by Cu-activated sintering at low temperature. We found that the Mg–Cu liquid can provide a constant liquid environment and the formation of lamellar MgB2 grains is attributed to the two-dimensional nucleation and growth mechanism in the liquid–solid interface. According to the analysis on the temperature dependence of resistivity, these lamellar MgB2 grains possess much better grain connectivity than the typical morphology of MgB2 grains synthesized by the traditional solid-state sintering. [Copyright &y& Elsevier]

Multi-doped MgB2 superconductors with excellent critical current density (Jc ) were rapidly synthesized by low-temperature activated sintering with Cu addition as the activator and nano SiC addition as the carbon-based chemical. Combined with microstructure observation and flux pinning force analysis, it is found that the enhancement of Jc (especially at low field) was mainly attributed to the higher density, lower crystallinity and the concentration of Cu activator around the sintered voids. [Copyright &y& Elsevier]

This study proposes a strategy for developing force-data-driven machine learning models to precisely predict defects and their types in friction stir welding (FSW). The characteristics of the three component forces in FSW, including traverse force (F x), lateral force (F y), and plunge force (F Z) are studied. The change in the force wave corresponded well with the variation in the defect. F y a v g had the best correlation with the characteristics of tunnel defects, whereas some other time-frequency features had negligible effects on the defect variation. The machine learning models built with the input of 15 force features could detect defects with an accuracy of 95.8% and classify them into tunnels and porosities with an accuracy of 98.0%. The abnormal increase in F y a v g , caused by the buildup of redundant material transported to the retreating side, was the main characteristic of force change when a defect was formed. [Display omitted] [ABSTRACT FROM AUTHOR]

In order to further refine W particles and improve properties of traditional W-Cu alloys, an innovative freeze-drying and subsequent solid phase sintering technology was employed to fabricate ultrafine W-10/20/30Cu alloys in our work. Compared with W-Cu powder precursors synthesized by traditional technologies, the freeze-dried powders (35 nm) are finer and better dispersed, which possess ultrahigh sintering activity. After solid phase sintering, the relative density of prepared W-Cu alloys is as high as above 98%. Meanwhile, the Cu network possesses complete continuity and the W particles keep ultrafine size (178 nm), which is much smaller than W particles in W-Cu literatures. Compared with other traditional technologies, freeze-dried W-Cu alloys in our work possess the highest hardness (499 HV 0.2), taking into account high thermal conductivity (246.9 W/mk) and electrical conductivity (48.3% IACS), which provides a new insight for the further development of W-Cu alloy industries. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Inconel 718 is a widely used nickel-based superalloy in aircraft engines during the past decades, whose elevated temperature strength derives from disc-shaped gamma double prime (γ″) in three perpendicular variants plus less spherical gamma prime (γ′) precipitates. In present work, we observed an abnormal γ″ variant with tailored orientation and shape in directly aged cold-rolled Inconel 718, creep tests proved its substantial benefits in improving creep resistance at 650 °C superior to commonly perpendicular γ″ variants. The results can provide new insights for processing optimization and second-particle configuration design to maximize the strengthening effect of γ″ phase in 718-type superalloys. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract The heterogeneity of microstructures in heat affect zone of 9Cr-1.5 W heat resistant steel friction stir welding joint was studied, and its influence on the weld creep property was discussed. The inter critical heat affect zone at the advancing side of the weld is found as the most likely area to be failure during creep, owing to the formation of ferrite grains and lath martensite with low carbon content and the coarsening of M 23 C 6 carbides. The as-welded joint exhibits a good creep resistance of 1173.8 h creep rupture time at 600 °C temperature and 200 MPa stress. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

In this work, 316L/CuCrZr functionally graded materials were prepared by laser powder bed fusion. Not only the strong bonding of 316L and CuCrZr was achieved, but more importantly, the grain-size gradients and heterogeneous microstructures were introduced into the samples. The gradient microstructure was characterized by ultrafine equiaxed grains sandwiched between micron-scale columnar grains. The dual-scale heterogeneous microstructure was composed of the BCC α-Fe and FCC ε-Cu phases. This grain size gradient and heterogeneous microstructure ensure that the samples possess high shear and tensile strength. The formation mechanisms of the grain-size gradients and heterogeneous microstructures of the samples were further discussed. The proposed strategy that functionally graded materials with grain size gradients and heterostructures can be fabricated by additive manufacturing may open up a new avenue for materials design. [Display omitted] [ABSTRACT FROM AUTHOR]

WC dispersion-reinforced Cu composites with high thermal stability were fabricated using intermittent electrodeposition and the spark plasma sintering (SPS). WC nanoparticles were dispersed uniformly due to the formation of the Cu cladding WC structures. The pin and impurity drag mechanisms contributed by the dispersed WC impeded the migration of grain boundaries. Based on the kinetic analysis, the improved grain-growth activation energy was observed for 3.0 wt% WC-reinforced Cu (up to 376.4 ± 3.7 kJ/mol), which is over three times higher than that for self-diffusion in pure Cu. The yield strength of this composite increased to 282.9 MPa at 300 °C, which is nine times higher than the value in Cu. This work provides an advanced pathway for designing thermal stable Cu composites for application as heat sinks. [Display omitted] [ABSTRACT FROM AUTHOR]

A new thermo-mechanical treatment strategy is proposed to improve the creep resistance of a recently developed G115 steel. The goal of this strategy is to construct a favourable microstructure with superior thermal stability at high temperatures up to 650 °C. The improved creep strength can be ascribed to the reinforced interactions between dislocations and nano-sized MX and Cu-rich precipitates. Creep analysis suggests that these MX and Cu-rich particles exhibit more important contribution to the creep resistance than the M 23 C 6 carbides. Following this strategy, the creep rupture life of the G115 steel can be significantly prolonged by more than two times. [Display omitted] [ABSTRACT FROM AUTHOR]

A chemical heterogeneity of Mn is introduced into the parent austenite of a Fe-0.2C-2Mn steel. The Mn-rich regions in the parent austenite is substantially stabilized by a promoted C partitioning during the austenite to ferrite transformation, without which these regions cannot be preserved as retained austenite. Following this strategy, a multiphase microstructure is achieved which presents a better combination of strength (ultimate strength of 977 MPa) and ductility (uniform elongation of 17.9%) as compared with that of other Si- or Al-added AHSSs of similar compositions. The results here suggest an alternative, yet a simple route, to acquire retained austenite in advanced high strength steels without the need of Si and Al alloying. [Display omitted] [ABSTRACT FROM AUTHOR]