The creep behavior of 200-nm thick gold films was investigated by plane-strain bulge testing between 23 and 100 °C. The polycrystalline gold films were produced by thermal evaporation and their columnar microstructure was stabilized by a preliminary heat treatment at 120 °C. The creep tests were performed at constant stress values between 80 and 300 MPa over 12 h, using a custom-built bulge tester. The stress exponent calculated from the creep data decreased from 4.3 to 2.8 between 23 and 100 °C, suggesting a possible transition in deformation mechanisms. The stress exponent and activation energy measured around room temperature point toward the climb of dislocations at grain boundaries being the rate-limiting deformation mechanism. Above 75 °C, scanning electron microscope inspections of tested membranes suggest an increased contribution of diffusion and of grain-boundary mediated deformation, as evidenced by the formation of grooves along grain boundaries. This is presumably the reason for the decrease of the apparent stress exponent and sudden increase of the apparent activation energy.

Kevlar (polyparaphenylene terephthalamide) and PBDT (poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide))-derivatives have very similar chemical structures with aromatic rings. In this study, thermal conductivities of their single chains were calculated using molecular dynamics simulations. Chain rotation was found to be the key to reducing the thermal conductivity. By introducing a new chain rotation factor (CRF), we can easily quantify chain rotation level of single-chain polymers. We demonstrated that thermal conductivity decreases as the CRF increases. We performed further calculations on phonon properties and unveiled that the small thermal conductivity led by large chain rotation can be attributed to reduced phonon group velocities and shortened phonon mean free paths. Insights obtained in this study can be used for tuning thermal conductivity of various polymers and facilitating their various applications including thermal energy conversion and management.

Here we report a facile and mild synthesis of the sulfonated graphene (PSS-RGO) catalysts by in situ polymerization of sodium p-styrenesulfonate. Graphene sheets can be used as the flat backbones to graft abundant sulfonate groups on both sides. The PSS-RGO catalysts were characterized by 1H Nuclear Magnetic Resonance (1H NMR), energy dispersive spectrometer, Raman spectroscopy, X-ray photoelectron spectroscopy, and so on. The catalytic properties of the PSS-RGO catalysts for the hydrolysis of ethyl acetate and the esterification of acetic acid with ethanol were evaluated, showing that the as-made PSS-RGO catalysts were active for both probe reactions. The possible deactivation mechanism involved in the surface catalysis of the graphene-based acid catalysts has been addressed.

The strong interactions between Mg and Ni/NiH4 are attributed to harsh operating conditions and difficulties for H2 release, restricting the practical applications of the Mg-based hydrides. In this study, a new method of interstitial nonmetals co-doping was proposed to reduce the strong interactions. The calculation results showed that the method of interstitial nonmetals co-doping causes a more significant reduction in the thermal stability of Mg-based hydrides, as compared with the methods of either single transition metal or nonmetal doping. To determine the influence mechanism, a theoretical study was conducted based on the first-principles calculations. The computations demonstrated that the criss-cross action between B–Ni and N–Mg bonds weakens the bonding effects between Mg and Ni/NiH4. Besides, the mutual interactions between nonmetals and H atoms could weaken Ni–H bonding effects and stimulate the breaking of stable NiH4 clusters, thereby facilitating the release of H2 from the hydride.

Highly porous alumina-based oxides, γ-Al2O3, SiO2–Al2O3, and TiO2–Al2O3 were synthesized by a modified sol–gel method. Polivinylpyrrolidone was used as the pore expanding agent, whereas cetyltrimethylammonium bromide was used as the template in the presence of alkoxide inorganic precursors. Both as-synthesized and calcined solids were used as catalysts for esterification of glycerol with acetic acid (EG). The XRD and SEM-EDS measurements demonstrated that the Si-containing solids are amorphous while those containing Ti are semicrystalline with the latter composed of TiO2 rutile, TiO2 anatase, and γ-Al2O3 phases. All solids possessed ordered porous structures comprising of micro- and mesoporosity, with interconnectivity between these pores of different length scales. The high acidity of γ-Al2O3 and TiO2–Al2O3 materials resulted in good catalytic performances in the EG. Porosity of the solids plays a secondary role in determining the catalytic activity. Under the same conditions, the as-synthesized solids exhibited slightly lower catalytic performances compared to that of the calcined ones.

We investigated the connectivity of high-energy random grain boundaries through fractal analyses of specimens with different grain boundary (GB) microstructures in BFe10-1-1 copper–nickel alloy. It was found that the profile of maximum random boundary network possesses a fractal nature and more than one fractal dimension can exist. The fraction of special boundaries and grain size homogeneity can play an important role on GB character distribution. Here, GB microstructures are combined with quantitative materials structure–property relationship models to predict intergranular corrosion properties. The experimental results are accurately consistent with the theoretical predictions.

The microstructure and oxidation behavior at high temperatures ranging from 900 °C to 1100 °C of equiatomic CrMoNbTaV high-entropy alloy produced by vacuum arc melting were investigated. The phase component, microstructure, and microhardness of the alloy were examined by using X-ray diffraction, scanning electron microscopy equipped with an energy-dispersive X-ray spectroscope, and Vickers hardness tests, respectively. The as-cast alloy consists of a single body-centered cubic (BCC) refractory metal solid solution due to the high mixing entropy effect and exhibits a dendritic microstructure. The alloy has a very high microhardness value of 923 HV due to the strong solid solution strengthening effect. The average microhardness in interdendrites (950 HV) was higher than that in dendrites (896 HV) because of composition segregation. The oxidation kinetic curves of the alloy after exposure to air at 900 and 1000 °C follow the pseudo-parabolic rate law, while the mass gain increases first and then decreases at 1100 °C. The thickness of the oxide layer increases with the increasing of oxidation time. The long rod-shaped oxidation products are composed of Nb2O5, NbO2, CrTaO4, CrNbO4, Ta9VO25, Nb9VO25, and TaO after oxidation at 900 and 1000 °C for 25 h. The oxides of CrTaO4 and CrNbO4 disappear as the oxidation temperature elevated to 1100 °C.

A bulk NbCr2 Laves phase matrix composite toughened with ductile Cr phase has been fabricated by spark plasma sintering (SPS) using pre-alloyed NbCr2 and Cr powders. The sintering behaviour and phase morphological evolution of the sintered alloy were investigated. The results show that a series of microstructure evolutions along the sintering temperature occurred: elongated Cr phase with uniform dispersion of fine NbCr2 and Cr phase → coarse Cr phase with matured fine NbCr2 and Cr → coarse Cr and Nb phases with lamellar eutectics. The microstructural evolution and phase transformation along the sintering temperature are analyzed by considering the inhomogenous temperature distribution and the accelerated atomic diffusion due to the pulsed electric current applied during SPS. The room temperature fracture toughness of the sintered samples is expected to be markedly improved due to the absence of lamellar or the occurrence of ductile Cr and Nb phases.

Reduced graphene oxide (RGO) and its composites have a great potential for their applications in optoelectronic devices. In particular, small molecules can be used for tailoring optoelectronic properties of RGO. Here, we report the fabrication of a hybrid RGO/tetrasulfonate salt of the copper phthalocyanine (RGO/TSCuPc) nanocomposite phototransistor. The device shows p-type transistor behavior in the dark which changes to ambipolar behavior at the lower light intensity, and then shows a complete n-type property at the higher light intensity. The photoresponsivity of the device can be tuned by gate voltages, and the best photoresponsivity is recorded to be as high as ∼4.6 A/W for positive gate voltage and ∼6.3 A/W with a negative sign for negative gate voltage under solar light irradiation. The observations suggest that the photogenerated free electrons of TSCuPc molecules can be injected efficiently onto RGO sheets, resulting in increases in electron conduction and hole quenching.

The phase transition behavior of [011]- and [001]-oriented 0.24PIN–0.43PMN–0.33PT single crystals was investigated through dielectric measurement in the process of heating and direct current (DC) bias. The phase transformation sequence in the [011]-oriented crystals is rhombohedral (R) → monoclinic (MB) → orthorhombic (O) → monoclinic (MC) → tetragonal (T) → cubic (C). The phase transition temperatures of R to MB$\left( {{{\rm{T}}_{{\rm{R}} - {{\rm{M}}_{\rm{B}}}}}} \right)$ and MB to O $\left( {{{\rm{T}}_{{{\rm{M}}_{\rm{B}}} - {\rm{O}}}}} \right)$ decrease; meanwhile, the transition temperatures of O to MC$\left( {{{\rm{T}}_{{\rm{O}} - {{\rm{M}}_{\rm{C}}}}}} \right)$ phase, MC to T $\left( {{{\rm{T}}_{{{\rm{M}}_{\rm{C}}} - {\rm{T}}}}} \right)$ phase, and T to C (TT–C) phase increase with the increase of DC bias. The phase transformation sequence in the [001]-oriented crystals is R → T → C. As DC bias increases, the transition temperature TR–T of R to T phase declines and the transition temperature TT–C rises. Intermediate phases MB, O, and MC are only found in the [011]-oriented crystal. The phase transition characteristics of the [011]-oriented crystals are rather more complex than those along [001] direction. The micro–macro domain transition at Tf is related to crystal orientation and DC bias voltage. The phase diagram in terms of temperature and bias voltage is established for [011]- and [001]-oriented 0.24PIN–0.43PMN–0.33PT crystals. The DC bias dependent dielectric properties and phase transition characteristics are also compared with the crystals along [111] direction.

This article showcases details on enumerative information of dissimilar aluminum (Al) to steel welds manufactured using different friction-based welding processes with an emphasis on the description of the manufacturing process, influence of parameters, microstructural variations, formation of intermetallic compounds (IMCs), and variations in mechanical properties. Friction-based welding processes such as friction welding, friction stir welding, hybrid friction stir welding, friction stir spot welding, friction stir spot fusion welding, friction stir scribe welding, friction stir brazing, friction melt bonding, friction stir dovetailing, friction bit joining, friction stir extrusion, and friction stir assisted diffusion welding are analyzed for the formation of dissimilar Al–steel joints. It can be summarized that friction-based joining processes have great potential to obtain sound Al–steel joints. The amount of frictional heat applied decides the type and volume fraction of IMCs that subsequently affects mechanical joint properties. Process variations and novel process parameters can enhance joint properties.

The dynamic response of structured materials, such as regular lattices, is nontrivial partly due to the interaction of mechanical waves throughout the structure and free surfaces as the material is dynamically compressed. The existence of an elastic precursor wave in additively manufactured lattices was recently shown to match theoretical predictions and simulation results. Following up on this work, we have investigated the behavior of the elastic precursor with propagation distance, impact speed, and impact material. Through a series of gas gun experiments coupled to X-ray phase contrast imaging measurements and complementary simulations, the elastic precursor wavespeed appears to be nearly independent of impact speed and impact material. We observed evidence for the sustained elastic wave propagation through many unit cells at four significantly different impact conditions. We compared these results with direct numerical simulations of the experiments and found good agreement.

To systematically investigate the influence of electrolyte substrates on Sr-segregation and SrSO4 formation in (LaSr)(CoFe)O3 (LSCF) cathodes in solid oxide fuel cells, model thin films were grown on Gd-doped ceria (GDC) and on Y-doped BaZrO3 (BZY) electrolytes by pulsed laser deposition and heat treated at 800–1000 °C in synthetic air with a trace amount of SO2. A severe SrSO4 formation was observed in LSCF on GDC as compared with the BZY, especially at low temperature. The difference in Sr-segregation and SrSO4 formation on the LSCF was discussed in relation to Sr diffusion and related elemental redistribution across the interfaces.

The growth advantage of twinned dendrites over regular columnar ones was systematically investigated during Bridgman solidification. An experimental approach was designed and the results indicated that the strong twin growth advantage lost its efficiency in the coexisting microstructure containing both twinned and regular dendrites at a low growth rate of 10 μm/s. The twin growth advantage derives from three essential components: the lateral twin propagation perpendicular to twin plane (Rx), the propagation parallel to twin plane (Ry), and the dendrite tip growth (Rz). The lateral extension component Rx played a vital role and would be limited at a low rate. Meanwhile, the tip undercooling of the twinned dendrite was estimated based on its plate-like growth morphology. Furthermore, the competitive growth between twinned dendrites was investigated in different feathery grains. When the included angle between twin planes was relatively large, the lateral twin propagation would keep down the in-plane twin propagation.

Despite lower hardness, stiffness, and resistance to harsh environments, heavy metallic parts and soft polymer-based composites are often preferred to ceramics because they offer higher resilience. By contrast, highly mineralized biomaterials combine these properties through hierarchical and heterogeneous architecture. Reproducing these internal designs into synthetic highly mineralized materials would therefore widen their range of application. To this aim, external fields have been used to control the orientation and position of microparticles and build complex architectures. This approach is compatible with most manufacturing processes and provides large flexibility in design. Here, I present an overview of these processes and describe how they can augment the properties of the materials produced. Theoretical and experimental descriptions are detailed to determine the strengths and limitations of each technique. With this knowledge, potential areas of improvement and future research directions will lead to the creation of highly mineralized materials with unprecedented functionalities.

For thixoforming, it is necessary to have a good microstructure of fine, uniform, and globular grains in a semisolid range. In this study, the nano-Al2O3(Al2O3np)/Al7075 composites with a high solid fraction were fabricated by specially made Al2O3np containing Mg powders and semisolid ultrasonic vibration (SSUV) process. The influence of SSUV technology on primary α-Al grain and second phase in the composites was investigated. Microstructural studies revealed that a good semisolid slurry with an average grain size of 73 μm, a shape factor of 0.84, and a solid fraction of 0.715 could be obtained. Also, it could be shown that SSUV affected largely the size and type of the second phase as well as growth and nucleation of the primary α-Al grain. TEM analysis revealed that there are well-defined crystallographic orientation relationships between the second phases and α-Al, suggesting enhanced heterogeneous nucleation in Al7075 alloys. Moreover, mechanisms involved in the development of microstructure were discussed.