Search

The correlation between preparation conditions and microstructure as well as magnetic properties were studied for Sm(Co 0.665 Fe 0.25 Cu 0.06 Zr 0.025 ) 7 magnets. Increase of sintering temperature from 1468 to 1493 K promotes the amalgamation of small grains into big ones, resulting in an enlargement of average grain size from 10 to 25 μm and diffusion of Cu from inner grains to Cu-lean grain boundaries. As a result, the demagnetization curve squareness of the magnets improves substantially, leading to a remarkable enhancement of the maximum energy product from 21.3 to 27.1 MGOe. The coercivity of the magnets drops from 25.3 to 16.0 kOe at the same time, which was verified by the increase of the average domain width from 1.1 μm in small grains to 2.5 μm in big grains. It is therefore concluded that tuning of the preparation conditions causes a more homogeneous distribution of Cu, which is crucial for the improvement of magnetic properties. [ABSTRACT FROM AUTHOR]

SiC f /C/Mo/Ti 2 AlNb composites were prepared by foil-fiber-foil (FFF) method and are used as model system to study the effect of solution-ageing treatments on the interface and mechanical properties of SiC fiber-reinforced TiAl-matrix composites. By contrast, SiC f /C/Ti 2 AlNb composites were prepared and heat treated under the same process parameters. The interfacial microstructures of the as-prepared and heat treated composites were investigated by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Tensile strength tests of the composites were carried out at room temperature. So the effect of C/Mo duplex coated SiC fibers on the microstructure and tensile behavior of the composites was studied. The results reveal that the interfacial thermal stability and integrity of the SiC f /C/Mo/Ti 2 AlNb composites are much better than those of the SiC f /C/Ti 2 AlNb composites, as the C/Mo duplex coating can reduce the formation of brittle α 2 -phase and relieve the interfacial thermal residual stresses in SiC f /Ti 2 AlNb composites compared with C single coating. After the 1080 °C/1 h/850 °C/20 h heat treatment, the matrix of the SiC f /C/Mo/Ti 2 AlNb composite transformed into mainly B2+O homogenous mixture and a small amount of α 2 phase, and the tensile strength of the composite was tested, which shows that the tensile properties of the composite was maintained after the solution-ageing treatment. [ABSTRACT FROM AUTHOR]

Abstract It is rather difficult for Ti alloy welds to be superplastic formed due to their low superplasticity and high flow stress. In this study, the Ti-6Al-4V alloy after hydrogenation with 0.2 wt% hydrogen was subjected to friction stir welding (FSW). The superplastic behavior of the FSW joint was investigated. The stir zone with a fine lamellar microstructure exhibited a largest elongation of 660% at 825 °C and 3 × 10−3 s−1. Besides, the stir zone showed a similar superplasticity of close to 600% to the base material at 825 °C, 3 × 10−4−1 × 10−3 s−1. It is the first report on the superplasticity of FSW Ti alloy joints with hydrogenation. Compared to the FSW Ti-6Al-4V alloy joint without hydrogenation, the hydrogenated FSW joint showed superior superplastic properties, including a high elongation, less than a half flow stress and lower superplastic temperature. These superior superplastic properties were mainly attributed to the globularization of the lamellar microstructure and the high fraction of β phase induced by the hydrogen element. This study provides an effective way to reduce the difficulty of practical superplastic forming for Ti alloy welds, although a dehydrogenation process is still needed to avoid hydrogen embrittlement. Graphical abstract Image 1 Highlights • It is the first time to report the superplastic behavior of hydrogenated friction stir welded Ti alloy joints. • A largest elongation of 660% was achieved at 825 °C, 3 × 10−3 s−1. • The similar superplasticity of ∼600% was achieved for the stir zone and base material at 825 °C, 3 × 10−4-1 × 10−3 s−1. • Hydrogenation largely reduced the flow stress and the optimum superplastic temperature of the joint. • The superior superplastic properties were attributed to the globularization of the lamellae and a large fraction of β phase. [ABSTRACT FROM AUTHOR]

Grain boundary (GB) engineering via alloying opens a pathway to design the interfaces in alloys for tuning their mechanical properties, thus it is quite critical to determine the optimum addition of alloying element. Here, we prepared immiscible Cu-Cr alloyed thin films by non-equilibrium magnetron sputtering deposition to study Cr alloying effects on the microstructure and mechanical properties of Cu thin films. It is found that Cr doping can notably refine the grains and promote the formation of fully nanotwinned columnar grains at low Cr volume concentrations (≤∼3.7 at.%) associated with the average GB Cr concentrations ≤ ∼15 at.%, beyond which the formation of nanotwins is significantly suppressed. The role of Cr atoms/clusters played in the twinning process is rationalized in terms of dislocation rebound-promotion mechanism. Importantly, a maximum hardness is discovered at the optimum Cr addition of ∼2.0 at.%. The Cr concentration-dependent hardness of Cu-Cr alloyed films was quantified by a combined strengthening model. The achievement of the maximum hardness was related to the greatest GB solute segregation-induced strength contribution. It is further uncovered that the Cu-Cr system exhibits strain rate sensitivity (SRS, m ) monotonically reduced with increasing the Cr concentration, ranging from a positive m of 0.0314 (for pure Cu) to a negative m of −0.0245, which is attributed to a competition between the dislocation-boundary interactions (increasing m ) and the dislocation-solute atoms interactions (decreasing m ). These findings provide valuable insights into tuning the composition of alloyed thin films to achieve optimized mechanical performance. [ABSTRACT FROM AUTHOR]

Tuning the microstructure to optimize the mechanical performance of nanocrystalline Cu thin films via the alloying strategy is quite important for their application in microdevices. In this work, we prepared nanocrystalline miscible Cu-Ti and immiscible Cu-Mo alloyed thin films to investigate alloying effects on the microstructure and mechanical properties of Cu thin films in terms of mixing enthalpies. It is found that the dopants of both Ti and Mo can notably refine the grains, and in particular promote the formation of nanotwins below a critical content of solute, beyond which the formation of nanotwins is notably suppressed. The nonmonotonic solute concentration-dependent twinning behavior observed in Cu-Ti and Cu-Mo alloyed thin films is explained by the coupling effects between grain size and grain boundary segregated dopants that affects the stimulated slip process of partials. The increased hardness of both Cu-Ti and Cu-Mo systems with increasing the solute contents are quantitatively explained by combining several strengthening mechanisms, including solid solution strengthening, grain/twin boundary (GB/TB) strengthening, solute segregation-induced strengthening. It unexpectedly appears that with increasing the solute contents, the Cu-Ti system exhibits monotonically reduced positive strain rate sensitivity (SRS, m ), whereas the Cu-Mo system manifests almost constant negative SRS. The fundamental difference in SRS m between Cu-Ti and Cu-Mo is rationalized in terms of the interactions between solute atomic clusters and dislocations based on the cross-core diffusion mechanism. [ABSTRACT FROM AUTHOR]

The magnetron sputtering technique was employed to prepare Zr-alloyed Cu thin films with Zr addition ranging from 0 to 7.0 at.%. Microstructure evolution with Zr doping was characterized by using the transmission electron microscope and atom probe tomography. Plastic deformation characteristics (hardness, strain rate sensitivity and activation volume) of the Cu-Zr alloyed films were examined by using nanoindentation testing. Significant Zr doping effects on the microstructure were clearly uncovered that (i) the Zr segregated at grain boundaries and tuned the grain boundary structure. With increasing the Zr addition, CuZr amorphous particles at grain boundaries (3.0 at.% Zr) and even three dimensional CuZr amorphous grain boundary network (7.0 at.% Zr) were formed; (ii) the grains (size and morphology) and nanotwins were notably influenced by the Zr doping. In particular, the nanotwin thickness was reduced from ∼25 nm in the pure Cu film down to ∼5 nm in the Cu-Zr alloyed films. Accompanied with the microstructure evolution, the Cu-Zr thin films displayed hardness and strain rate sensitivity highly sensitive to the Zr doping, i.e. , hardness increasing while strain rate sensitivity decreasing with raising the Zr addition. The strengthening and deformation mechanisms were discussed in terms of the microstructure-property relationship. Three regimes were divided within the studied Zr doping range: grain/nanotwin boundary-dominated strengthening mechanism in the regime I of pure Cu film, dislocation nucleation-controlled nanotwin softening mechanism in the regime II of Zr addition ≤3.0 at.%, and intergranular amorphous layer-mediated strengthening mechanism in the regime III of Zr addition up to 7.0 at.%. In addition, the reduction in strain rate sensitivity with Zr doping was quantitatively described by adopting a model that involves the thermally activated partials depinning mechanism based on the effective dislocation segment length. [ABSTRACT FROM AUTHOR]

Highlights: [•] Poly(St-AA)/Fe3O4 microspheres were prepared via miniemulsion copolymerization. [•] The effect of crosslinker on the final particle morphology was studied. [•] The adsorbed weight of BSA at different adsorption time and pH were investigated. [•] The adsorbed weight of BSA was increased with the content of AA. [Copyright &y& Elsevier]

Abstract: SiCp/Mg–Zn–Ca composite fabricated by stir casting was extruded at three different temperatures. Firstly, hot extrusion significantly improved particle distribution and refined the grains of the matrix. Even, nano-grains were observed in the composite extruded at 250°C. Secondly, extrusion evidently refined the size of the second phases, but also changed the distribution of the second phases. Extrusion temperatures obviously affected the size and distribution of the second phases. Thirdly, the interface between SiCp and matrix was also modified by hot extrusion. Finally, all as-extruded composites possessed good mechanical properties. Below 150°C, the UTS was very high in the extruded composites, but their strengths decreased sharply above 150°C. [Copyright &y& Elsevier]

Abstract: The microstructure and magnetic properties have been investigated systematically for Sn1−x Mn x O2 (0≤ x ≤7%) nanoparticles synthesized by chemical co-precipitation method. The X-ray diffraction reveals that all samples are pure rutile-type tetragonal phase and the cell parameters a and c decrease monotonously with the increase of Mn content, indicated that Mn ions substitute into the lattice of SnO2. X-ray photoelectron suggests that Mn ions behave as the mixture state of Mn3+ and Mn4+ in samples. Magnetic investigations demonstrate that magnetic properties strongly depend on both the sintering temperature and doping content. No ferromagnetism is observed for samples sintered at high temperature (T S =800°C), irrespective of the doping content. In contrast, the samples sintered at low temperature (T S =450°C) possess room temperature ferromagnetism when the doping content is below 5%. A plausible explanation of the magnetic properties is presented in terms of bound magnetic polaron model. [Copyright &y& Elsevier]

High entropy alloys (HEAs) have attracted extensive attention due to their excellent properties in harsh environments. In this work, we prepare HEA/Cu (HEA = FeCoCrNi) nanotwinned nanolaminates (NTNLs) with equal individual layer thickness (h) and study the He-ion irradiation effects on their deformation behavior and mechanical properties. With decreasing h the microstructure of HEA/Cu NTNLs transits from the nanolayered structure with nanotwins confined in the isolated layers at large h ≥ 25 nm to the columnar grained single crystal-like structure with nanotwins penetrated across the coherent layer interface(s) at small h < 25 nm. Compared with the as-deposited HEA/Cu NTNLs showing notable detwinning behavior, in particular at small h , the nanotwins in irradiated samples are difficult to detwin owing to the He defects pinning effect on twin boundaries. It appears that both as-deposited and irradiated HEA/Cu NTNLs manifest the trend of "smaller is stronger". Unlike the reported monotonically increased/reduced irradiation hardening with h in conventional bimetal nanolaminates, a minimum irradiation hardening occurs in the present HEA/Cu NTNLs. Unexpectedly, the as-deposited HEA/Cu NTNLs manifest positive reduced strain rate sensitivity (SRS) m with decreasing h , while their irradiated siblings exhibit the transition from positive to negative SRS m. The size-dependent mechanical properties of HEA/Cu NTNLs are rationalized by the partial-based mechanism in combination with the stability of nanotwins. • Nanotwins disappear in deformed Cu/HEA NTNLs but are stabilized by He+ irradiation. • Irradiated Cu/HEA NTNLs manifest a unusually non-monotonic irradiation hardening. • As-deposited Cu/HEA NTNLs show unusually reduced SRS as decreasing layer thickness h. • Irradiated Cu/HEA NTNLs show the positive-to-negative SRS transition as decreasing h. [ABSTRACT FROM AUTHOR]