In this paper, a novel sintering method is introduced for the forming of microcomponents in which the loose powders were loaded directly into the die, sintered with an external electric field, a thermal field, and an external stress field (called coupled multifields activation), where the fields were generated by a Gleeble thermal simulation instrument. Two kinds of 316L stainless steel powders of different particle sizes (20 and 70 μm) with no binder were sintered with microforming using a multifield coupling method. For particle size of 20 μm, a nearly fully densified microsintered compact (relative density is 99.2%) was manufactured at a relatively low sintering temperature (900 °C) and within a relatively short sintering time (4 min). The fluctuated temperature–time curve reveals that the rapid mass transfer of liquid phase is the dominant densification mechanism in the compacts with a starting particle size of 20 μm.

The effects of hydrogen on the structure of Zr-based bulk metallic glasses were investigated by positron annihilation lifetime spectroscopy. Three lifetime components are identified, indicating the presence of three distinct size ranges for open volume defects in the glass. The concentration of the smallest sites identified as tetrahedral interstitial holes in the densely packed and the intermediate sites identified as flow defects, changes with hydrogen addition. The concentration of tetrahedral interstitial holes in Zr55Cu30Ni5Al10 alloys initially increases with the increase of hydrogen content. When Zr55Cu30Ni5Al10 alloys were prepared in Ar + 10%H2 atmospheres, the concentration of tetrahedral interstitial holes reaches a maximum, which may provide a more dense random-packed structure. For Zr57Al10Cu15.4Ni12.6Nb5alloys, the increase of hydrogen content causes a decrease in the concentration of tetrahedral interstitial holes and an increase in the concentration of flow defects.

We report a family of novel Strontium (Sr)-based bulk metallic glasses (BMGs) with good glass-forming ability and ultralow glass transition temperature (Tg) by strategic composition design. The Sr-based BMGs can be easily formed with wide composition range by a conventional copper mold cast method. The glassy alloys have many unique and diversified properties such as lowest glass transition temperature, ultralow elastic modulus, small value of Poisson’s ratio and fragility, homogeneous flow at room temperature and tunable water degradation behavior. The BMGs with novel physical and chemical properties could have potential applications for biomaterial and micromanufacture, and are model system for studying some fundamental issues such as crystallization, relaxation and deformation in metallic glass.

Copper–zinc alloy (Cu/Zn) powders with different Zn to Cu molar ratios were prepared by the combustion synthesis technique using a CuO + 0.15(C2H4)n + kZn (0.2 ≤ k ≤ 1.6 mol) reactive mixture. Depending on the Zn concentration, the combustion wave developed a temperature between 950 and 1040 °C and passed through the sample with a speed of 0.04–0.08 cm/s, resulting in almost single-stage temperature distributions. Cu/Zn alloy powders with Zn concentrations ranging from 0.5 to 45 wt% were obtained. It was shown that alloy particles become spherical and well dispersed with increasing Zn concentration. Inert dilution test with KCl salt was also performed to determine the influence of temperature degradation in the combustion wave on the morphology and composition of alloy powders.

Cu6Sn5 is a critical intermetallic compound in soldering operations. Conventional equilibrium phase diagrams show that this compound is of either a hexagonal or monoclinic structure at temperatures above and below 186 °C, respectively. Under nonequilibrium conditions, the crystal structure is dependent on composition, temperature, and processing history. The effect of Zn, Au, and In on the hexagonal to monoclinic polymorphic transformation in Cu6Sn5 intermetallics is investigated using variable temperature synchrotron powder x-ray diffraction and differential scanning calorimetry. It is revealed that, as in the case of trace Ni additions, the alloying elements Zn and Au completely stabilize the hexagonal Cu6Sn5 and prevent the phase transformation. In contrast, In additions only partially stabilize the hexagonal Cu6Sn5.

Effects of Ti and Si particle sizes on phase transformations of Ti–Si–Cu system were explored through differential thermal analysis (DTA), x-ray diffraction (XRD), and field emission scanning electron microscope (FESEM). For Ti[15]Si[15]Cu[45] system, fine Ti easily dissolves into Si–Cu liquid to form Ti–Si–Cu liquid at ∼795 °C, which further participates into the reaction of β-Ti and Si to yield abundant quantity of Ti5Si3 at ∼917 °C. For Ti[150]Si[15]Cu[45] system, nonetheless, the reaction of coarse Ti with Si–Cu liquid involves more difficulty in forming the ternary liquid , which is the causal factor for the delay in the formation of Ti5Si3 to ∼948 °C. For Ti[15]Si[150]Cu[45] system, coarse Si results in the formation of insufficient Si–Cu liquid initially, whereas Ti–Cu liquid forms at ∼960 °C instead, which further reacts with coarse Si to form Ti–Si–Cu liquid, and then Ti5Si3is precipitated from the liquid.

Methods for identifying the hardening behavior of solids described by power law through indentation testing have been well developed. However, many important engineering materials deviate from the power law description significantly. After fitting the uniaxial curves of several typical materials, the three-parameter relationship proposed by Voce [E. Voce, J. Inst. Met.74, 537–562 (1948)] is chosen to describe the hardening behavior for its fitting performance and inherent simplicity. Based on the Voce law, an efficient method is formulated to extract the hardening data from a single spherical indentation curve. Improved identifying performance is manifested by applying the method to four metallic materials. It is validated that the present method has the ability to effectively identify the plastic properties of materials through spherical indentation testing.

Electropulsing treatment (EPT) has been first applied to the recrystallization of a refractory metal—tungsten (W). We have three major observations: (i) the recrystallization temperature of a rolled pure W under EPT is ∼900 K higher than its conventional recrystallization temperature (1603 K); (ii) the time required for recrystallization is significantly reduced compared with that of conventional heat treatment (CHT); (iii) the recrystallized grains are also much finer than the ones under CHT. Based on quantitative analysis, we conclude that the huge increase of the recrystallization temperature of the rolled pure W under EPT is due to the high heating rate generated by EPT and high activation energy for vacancy diffusion of W, and the accelerated recrystallization and grain refinement have resulted from the coupling of thermal and electromigration effects of EPT at relatively high temperatures.

Cu–In–Ga precursor thin films were deposited onto soda lime glass by magnetron cosputtering CuIn and CuGa alloy targets. After that, Cu(In,Ga)Se2(CIGSe) absorbers were formed by selenizing those alloy precursors with Se vapor at 550 °C. The influence of the precursor temperature on the properties of CIGSe thin film was investigated. The results show that a lot of pinholes existed in the CIGSe thin film produced by selenizing the Cu–In–Ga alloy precursor, which was sputtering deposited at ambient temperature. After sputtering substrate temperature of 250 °C was applied, pinholes were avoided. The surface roughness of Cu–In–Ga precursor increased with the increase of sputtering substrate temperature. Due to the volume expansion of selenization process, even the precursor with high surface roughness could be converted to smooth and compact CIGSe thin film.

The covalent attachment of cysteamine-functionalized polyaniline (PANI–NH2) nanofibers onto graphene oxide (GO) sheets in an aqueous medium is investigated for the first time. The functionalized PANI is covalently attached onto the GO surface by simple amidation in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide. The technique can be conveniently scaled up for bulk production. The hybrid nanomaterial is easily synthesized, has good thermal stability, and disperses well in a solvent. Characterization techniques (Fourier transform infrared spectroscopy, thermogravimetry analysis, field emission scanning electron microscopy, and transmission electron microscopy) indicate the successful binding of the functionalized PANI nanofibers onto GO.

As anhydrous proton conductive membranes, sulfonated polysulfone (SPSU) and 1H-1,2,3-benzotriazole (BTri) hybrid membranes were prepared. The sulfonation of polysulfone was performed with trimethylsilyl chlorosulfonate, and high degree of sulfonation (134%) was obtained. The polymer electrolyte membranes, SPSU–BTriX, were prepared by blending of 1H-1,2,3-benzotriazole in SPSU. FTIR confirmed the sulfonation of PSU and the ionic interaction between sulfonic acid and benzotriazole units. Thermogravimetric analysis (TGA) analysis showed that the polymer electrolyte membranes are thermally stable up to approximately 200 °C. Scanning electron microscopy analysis indicated the homogeneity of the membranes. The maximum proton conductivity has been measured for SPSU–BTri2 as 3.6 × 10−3S/cm at 150 °C.

Hybrid ultrahigh molecular weight polyethylene–nylon 6–single-wall carbon nanotube fibers were processed using solution spinning method. Elastic properties and normalized velocity ($\root 3 \of \Omega $) of the hybrid fibers were measured before and after strain hardening through repeated loading–unloading cycles. Phenomenal improvement in the properties was found: strength, modulus, and normalizing velocity increased by almost one order of magnitude after strain hardening. Neat and reinforced filaments were characterized through differential scanning calorimetry, Raman spectroscopy, and scanning electron microscope before and after strain hardening. It has been revealed that nylon 6 contributed to the deformation ability of the composite fiber, while carbon nanotubes contributed to the sharing of load as they aligned during extrusion and strain hardening processes. Important morphological features determining the fiber properties were the change in crystallinity and rate of crystallization, formation of microdroplets, interfacial sliding, polymer coating of nanotubes, alignment of polymer fibrils and nanotubes.

To replace ternary polymer with binary polymer, a novel bifunctional comonomer β-methylhydrogen itaconate (MHI) was synthesized to prepare poly(acrylonitrile-co-β-methylhydrogen itaconate) [P(AN-co-MHI)] copolymer used for carbon fiber precursor. The structural evolution and stabilization mechanism of P(AN-co-MHI) and polyacrylonitrile (PAN) during stabilization were studied by Fourier transform infrared spectroscopy, x-ray diffraction, differential scanning calorimetry, thermogravimetry, and kinetic investigation. The activation energy (Ea) of the stabilization reactions were calculated by Kissinger method and Ozawa method. The results show that the P(AN-co-MHI) exhibits a lower stabilization temperature than terpolymers containing similar chemistry component and a significantly improved stabilization performance compared with PAN homopolymer, such as lower cyclization temperature, lower Ea (85.36 kJ/mol), and larger extent of stabilization under the same condition, which is mainly attributed to the initiation of MHI comonomer through an ionic cyclization mechanism. The dehydrogenation of P(AN-co-MHI) is also promoted by the incorporation of comonomer MHI into PAN chains. Simultaneously, the rheological analysis shows that P(AN-co-MHI) possesses better spinnability than PAN, which is beneficial for preparation of high performance carbon fiber.

The numerical approach of Lee et al. [Trans. Korean Soc. Mech. Eng., A28, 816–825 (2004)] to spherical indentation technique for property evaluation of hyperelastic rubber is enhanced. The Yeoh model is adopted as the constitutive form of rubber material because it can express well large deformation and cover various deformation modes with a simple form. We first determine the friction coefficient between a rubber specimen and a spherical indenter in a practical viewpoint and perform finite element simulations for a deeper indentation depth than that selected by Lee et al. [Trans. Korean Soc. Mech. Eng., A28, 816–825 (2004)]. An optimal data acquisition spot is selected, which features sufficiently large strain energy density and negligible frictional effect. We improve then two normalized functions mapping an indentation load–displacement curve onto a strain energy density–invariant curve, the latter of which gives the Yeoh model constants. The enhanced spherical indentation approach successfully produces the rubber material properties with an average error of less than 5%. The validity of our developed approach is verified by experimental evaluation of material properties with three kinds of rubber materials.