A series of oxidation experiments were carried out on these novel γ/γ′-strengthened cobalt-based alloys of the systems Co–9Al–10W and Co–9Al–10W–0.02X (X = La, Ce, Dy, Y) at 900 °C. The appropriate amounts’ addition of rare earth elements leads to improved oxidation properties at 900 °C, especially La elements show the best oxidation resistance (129.008 mg/cm2). However, the base Co–9Al–10W alloy shows the worst oxidation performance (151.544 mg/cm2). Multilayer oxide layers formed during the oxidation process, the outer were mainly CoO and Co3O4 oxides, and the middle layer contained complex oxides (containing Co, Al, and W). The inner layer consists of little discontinuous oxides, included few Al2O3 oxides. There existed a different crack width and the base alloy had the widest crack. Moreover, there exists a phase transformation (γ/γ′ to γ/Co3W) at the interface between oxide film and substrate.

Material mechanical behavior of tube has an essential influence on cross-sectional deformation of rectangular waveguide tube in rotary draw bending (RDB) process. Thus, taking widely used 3A21 aluminum alloy and H96 brass rectangular tubes as research objects, the cross-sectional deformation of these tubes in RDB with and without mandrel was investigated using the reliable three-dimensional finite element models. The results show that when no mandrel is used, compared with 3A21 tube, the position of wrinkle initiation for H96 tube is closer to the final bending section, and the cross-sectional deformation of H96 tube along bending direction is more homogeneous. When a mandrel is used, in bending process, the cross-sectional deformation of 3A21 tube in mandrel support zone (MSZ) is in coincidence with that of H96 tube, and the deformation of 3A21 tube is larger in transition zone (TZ) while smaller in no mandrel affect zone (NMAZ) than that of H96 tube. In retracting mandrel or springback process, the cross-sectional deformation of 3A21 tube in MSZ and TZ is constantly larger than that of H96 tube, while in NMAZ, the deformation of both tubes reverses.

The article focuses on the fatigue performance after a moderate heat treatment of nanocrystalline (nc) nickel, which leads to the formation of a bimodal microstructure in the nc to ultrafine grained (ufg) regime. Electrodeposition was used to produce nc macro nickel samples with grain sizes of about 40 nm for mechanical testing. The thermal stability of the material as well as the influence on the mechanical properties and the fatigue crack propagation behavior was investigated. The results of tensile and fatigue tests are discussed in respect to the chosen production method and boundary conditions. In this context, the influence of the bath additives used during the plating process was investigated and rated as the major challenge for a further improvement of the thermal stability and mechanical properties of the material. Finally, a co-deposition of nickel and metal oxides with enhanced thermal stability is presented.

Composite copper oxide–copper bromide films were electrodeposited on gas diffusion layer (GDL) supports under controlled potential from aqueous copper salt solutions in the presence of a complexing/surfactant agent such as lactate. The solution pH was adjusted to target simultaneous deposition of cubic nanostructures composed of copper, oxygen, and bromine elements. The film composition and morphology were carefully tuned for enhanced electrochemical conversion of CO2 to hydrocarbons. Hydrocarbon products, predominantly ethylene and minor amounts of methane, ethane, and propylene were observed along with inevitable H2 co-generation. Importantly, CO gas was not detected during CO2 electrolyses. Low temperatures (3–5 °C) enhanced the conversion of CO intermediate to C2H4. The durability and electroactivity of these composite films were maintained for extended periods (up to 10 h) of CO2 electrolysis by periodic in situ application of anodic pulses to regenerate the cathode surface.

YCrO3 (YCO) perovskite has been originally reported to be a biferroic with antiferromagnetic and ferroelectric (FE) properties, in which the origin of FE in YCO remains ambiguous. However, further studies reveal the presence of a global orthorhombic Pnma structure with a local structural heterogeneity. In this study, we discuss the high temperature phonon modes and their inter-relation to local structural distortions in YCO perovskite through Raman spectroscopy experiments and density functional theory (DFT) calculations. We observe that the Raman active B3g(3) out of phase scissor mode (SM) disappears above the dielectric transition temperature (T c) commensurate with the local structural distortions. DFT calculations show that the transformation of a room temperature Y-cation distorted orthorhombic structure to a perfect orthorhombic structure above the dielectric transition temperature in which the Y cation is undisplaced could lead to the conversion of SM with symmetry B3g to Raman inactive B1u mode.

Zinc oxide (ZnO) layers and nanowires were grown by chemical vapor deposition (CVD) using methane (CH4) as reducing agent. Compared to conventional CVD processes, which commonly use graphite powder to reduce the ZnO powder source material, this low-cost method allows an improved controllability of the growth processes. Specifically, the consumption of the source material–a commercially available ZnO powder–can be controlled in a very precise way by varying the flow of the reducing CH4 or the re-oxidizing O2. Using this parameter, the growth can be switched between ZnO layers and nanostructures. High-quality ZnO layers have been grown on gallium nitride (GaN) substrates and on c-plane sapphire with an intermediate aluminum nitride (AlN) nucleation layer. By adjusting the growth conditions accordingly, ZnO nanowires were also grown with this method catalyst-free using a- and c-plane sapphire with ZnO nucleation layer as a substrate. The optical properties of the nanowires were investigated by low-temperature photoluminescence (PL) and compared to samples grown by conventional carbo-thermal CVD.

A cost-effective and highly efficient method was proposed for preparing reduced graphene (rEG) by modified Hummers approach. The influence of ratio of KMnO4 to graphite, oxidation time and oxidation temperature on oxidative degree of graphite oxide (GO) was investigated by x-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The thermal exfoliated graphene (EG) was characterized with transmission electron microscopy (TEM), FTIR, Raman spectrum and Brunauer–Emmett–Teller (BET) method. The EG was treated for 4 h at 800 °C with H2/Ar mixed atmosphere (15/85, v%) to remove the residual functional groups. The characterization of x-ray photoelectron spectroscopy (XPS) showed that rEG contains less functional groups than EG, which shows the C/O ratio increased from 10.6 (EG) to 34.71 (rEG). The results indicate that treating EG with a mixed H2/Ar atmosphere (15/85, v%) remarkably removes residual functional groups of EG, supplying a simple and feasible approach with large scale production of reduced graphene.

This study investigated the effects of 1 wt% SiC nanoparticles addition on the microstructures and mechanical properties of Mg9Al–1Si (wt%) alloy subjected to equal channel angular pressing (ECAP). Results showed that addition of SiC nanoparticles could refine matrix grain, Mg17Al12 and Mg2Si phase of as-cast alloy, but the Mg17Al12 phase still exhibited network structure and the morphology of Mg2Si phase was still Chinese-script type. During the ECAP process, network Mg17Al12 and Chinese-script shaped Mg2Si phases were partially broken down into fine particles (∼10 µm) and much finer particles (∼2 µm) respectively. In particular, these Mg17Al12 and Mg2Si particles were uniform distribution in ECAPed Mg9Al–1Si–1SiC composite. The well-distributed particles and the existence of SiC nanoparticles could promote the formation of fine DRXed grains through enhanced grain boundary pinning. During tensile testing at room temperature, ECAPed Mg9Al–1Si–1SiC composite exhibit optimal mechanical properties, the ultimate tensile strength and elongation to failure were reached to 255 MPa and 7.9%, respectively. Furthermore, at elevated temperature of 150 °C, the tensile strength and elongation to failure were considerably increased compared to an ECAPed, SiC-free Mg9Al–1Si alloy.

Boron nitride nanotube (BNNT) reinforced titanium (Ti) matrix composites were prepared using the cold press-and-sinter method. In the composite sintered at 800 °C for 1 h, BNNTs were homogeneously distributed in the Ti matrix and restricted the growth of Ti grains. The compressive strength of the as-sintered Ti–4 vol% BNNT composite achieved 985 MPa at room temperature versus 678 MPa without the BNNT reinforcements. The highest compressive strength of 277 MPa at 500 °C was obtained from the Ti–5 vol% BNNT composite. When sintered at 1000 °C, chemical reactions occurred between Ti and BNNTs leading to the formation of the interfacial TiB phase, which serves as a strong binding between BNNTs and the Ti matrix. The reinforcements were attributed by a mixture of BNNTs and TiB after sintering at 1000 °C for 3 h. However, no BNNT was observed in the microstructure after sintering at 1100 °C for 3 h due to complete transformation into TiB whiskers.

Microstructural and morphological features of the layers forming integrated PTB7/PC71BM organic solar cells with Ca/Al cathode are studied. The effects of vacuum treatment on properties and durability were addressed using complementary approaches: time-resolved experiments revealing the structural evolution of the active layers under illumination were conducted combining the in situ energy dispersive X-ray diffraction (EDXD) technique with atomic force microscopy (AFM); space-resolved characterization of the integrated devices was possible via high resolution X-ray diffraction, using a nano-focused synchrotron radiation X-ray beam to discriminate the device components. Active layers surface morphology is stable under illumination and PC71BM structural properties remain unaltered. PTB7 undergoes crystallinity depletion, mainly at the active layer/cathode interface. This effect is actually inhibited in the device submitted to vacuum treatment, proving that this procedure induces stabilization at the cathode’s buried interface, as verified by fourier transform infrared (FTIR) spectroscopy. Importantly, the protective role of the vacuum treatment results in a significant photovoltaic durability enhancement.

Thermoelectric properties of oxygen-deficient filled strontium barium niobates (SBN, Sr x Ba6−x Nb10O30−δ) in the composition range from the barium end member to a Sr:Ba ratio of 80:20 were investigated. The electrical conductivity, Seebeck coefficients, and power factors for ceramic samples annealed at 1300–1310 °C for 30 h under forming gas (∼10−16 pO2 atm) were evaluated from ∼350 to 970 K. The conduction mechanism in the filled SBNs was found to be similar to that of the heavily-reduced unfilled SBNs reported in literature. However, relative to the unfilled counterparts heat-treated at 10−16 atm pO2, larger power factors were observed in the filled SBNs. The thermoelectric performance of these filled SBNs was composition-sensitive; lower Sr contents showed higher electrical conductivities, and power factors. Electron diffraction and Hall experiments suggest that both mobility and carrier concentration are enhanced with decreasing Sr. For ceramic samples, the highest power factors achievable were found for low Sr, heavily-reduced filled compositions.

MgO/Cu composites containing a 1.0% volume fraction of MgO particles were prepared by internal oxidation and powder metallurgy, respectively. The interfacial bonding state between the MgO particles and Cu matrix was characterized by scanning electron microscopy and transmission electron microscopy. The effect of the MgOp/Cu interfacial bonding state on the arc erosion resistance of the MgO/Cu composites was investigated, and the arc erosion resistance was examined using a JF04C electrical composite testing system. The results indicate that the 1.0 vol% MgO/Cu composite with a semicoherent MgOp/Cu interface experiences a lower arc erosion rate and smaller fluctuations of arcing energy than those of the 1.0 vol% MgO/Cu composite with an incoherent MgOp/Cu interface. Erosion morphology observations further indicate that a solid to liquid phase transformation occurs under arcing and MgO particles dispersed in the molten copper both prevent the copper matrix from splashing and enhance the arc erosion resistance of the MgO/Cu composites. While the shallow electric erosion pits are distributed uniformly on the arc surface of the MgO/Cu composites with a semicoherent interface, the MgO/Cu composite with an incoherent interface has deep and uneven pits on its arc surface, characterized by large electric erosion molten droplets.

The effect of Cr fibers on the deformation of directionally solidified NiAl–Cr eutectics, prepared at three different solidification speeds affecting the fiber diameter and fiber spacing, was studied at varying length scales using different micromechanical testing techniques. In situ tensile tests in a scanning electron microscope of individual Cr fibers showed high strength accompanied by ductile behavior. Comparative microcompression tests on single-phase NiAl pillars and NiAl pillars containing a single fiber showed that the pillars with the single fiber were marginally weaker than the single-phase pillars for similar pillar diameters. Composite pillars with multiple fibers exhibited an increase of 0.2% offset strength values with increasing solidification speed. Transmission electron microscopy of the composite pillars containing a single fiber after deformation revealed significant dislocation activity both in the fiber and the matrix. It is argued that the interface between the fiber and matrix acts as dislocation source promoting plastic deformation of the brittle NiAl matrix.

This study examined the effects of a variety of metallurgical factors on the electrochemical corrosion behavior of superaustenitic stainless steel welds. First, the effects of the sigma (σ)-phase on the corrosion behavior were studied by means of a three-dimensional-atom probe. Cr and Mo depletion areas formed around the σ-phases which are precipitated in the interdendritic area were clearly observed. Second, the effects of oxide inclusion on the pitting corrosion of the steel welds were analyzed. The utilization of high resolution transmission electron microscope clearly demonstrated that the thickness and Cr content of the passive film formed on the steel surface decreased significantly with decreasing distance to the oxide inclusion, resulting in a deterioration of the corrosion resistance. Third, the effects of alloying elements, Cu and Al, were evaluated using an electrochemical polarization technique. This confirmed that Cu has a detrimental effect on the resistance to localized corrosion of the steel. The addition of Al up to 0.25 wt% had no significant effects on corrosion resistance in a chloride environment despite the presence of an Al-based oxide layer (Al2O3) on the outermost surface.

Nanocrystalline bulk materials (also called nanograined materials) are intrinsically unstable due to the excess grain boundary (GB) free energies. Dopants designed to segregate to boundaries have been proposed to lower excess GB energies, increasing stability against coarsening and enabling nanostructure features to survive high temperature processing and operational environments. It has been theoretically proposed that the GB energy of a material can eventually become zero as a function of dopant concentration, signifying negligible driving force for growth—an infinitely stable nanomaterial. In this work we use ultrasensitive microcalorimetry to experimentally measure the absolute GB energy of gadolinium-doped nanocrystalline zirconia as a function of grain size and show that the energy can indeed reach a quasi-zero energy state (∼0.05 J/m2) when a critical GB dopant enrichment is achieved. This thermodynamic condition leads to unprecedented coarsening resistance, but is a temperature dependent function; since increasing temperatures deplete the GB as the dopant dissolves back in the crystalline bulk.

The dissimilar MIG welding of Mg alloy and ultra-high strength steel was investigated. The results indicated that the Mg-steel joints had characteristics of welding-brazing and included weld zone, bond zone, and interface zone. The weld zone with an equiaxed grain structure mainly consisted of α-Mg and α-Mg + β-Mg17Al12 phases when AZ31 and AZ61 filler metals were used respectively. The interface zone presents a double-layer structures: the AlFe3 layer at steel side and the Mg(Fe, Al)O4 + Mg3.1Al0.9 layer at Mg side, and their evolution process has been summarized. The joint strength was improved obviously at the heat input of 1987–2100 J/cm due to eliminating incomplete joining defects and cracks in the interface zone. With AZ61 filler metal, the weld Al content was 6.24%, the joint strength was elevated from 174 MPa for AZ31 filler metal to 201 MPa (83.8% of Mg alloy base metal), which is related to the increased Al promoting the interface reaction.

The aging behavior of precipitation hardenable 17-4 PH stainless steel is studied by analyzing the changes in microstrain, crystallite size, and dislocation density derived from the modified Williamson–Hall (mWH) method and the Fourier analysis of XRD profiles. Aging treatment of this steel at 380, 430, and 480 °C for 0.5, 1, and 3 h durations leads to changes in the microstrain due to precipitation and substructural changes caused by dislocation annihilation. The microstrain estimated from the mWH method is dominated by the precipitate-induced effects. The influence of precipitates and dislocations on the mean squared strain 〈ε2(L)〉 are separated by fitting the variation of 〈ε2(L)〉 with an expression P0 + P1/L + P2/L2, where the parameter (P0)0.5 and P1 are shown to be related to the precipitate-induced and dislocation density-induced microstrain, respectively. The study shows that the XRD profile analysis can be used to separate the combined effects of precipitation and dislocation annihilation.

Zr–Co–Al alloys possess prospects of wide applications in the field of nuclear reactor cladding materials and biomedical materials. (Zr0.5Co0.5)100−x Al x (x = 1, 2, 3 at.%) alloys were prepared by the water-cooling copper mold suction casting technique, and the microstructure and compression mechanical properties of the alloys were investigated. The results showed that the as-cast Zr–Co–Al alloys mainly consisted of the B2 ZrCo phase with columnar or equiaxed grains and a small quantity of intermetallic compounds, i.e., Co2Zr and Zr2Co. The yield strength of Zr–Co–Al alloys increased with increasing Al content, but the plasticity decreased at the same time. The as-cast Zr49.5Co49.5Al1 alloy attained the highest ultimate compression strength up to 2.57 ± 0.02 GPa and the largest compression strain up to ∼54.7%. The B2 to B33 martensitic transformation that occurred during the deformation process was investigated using high resolution transmission electron microscopy. It was concluded that the enhanced plasticity of Zr49.5Co49.5Al1 alloy can be attributed to the transformation induced plasticity associated with the deformation-induced martensitic transformation.

The ferritic steel 16Mo3 coated with the nickel-base alloy IN625mod by high-velocity oxy-fuel (HVOF) spraying was investigated under uniaxial and biaxial fatigue loading at 200 and 500 °C. Furthermore, bulk HVOF-sprayed specimens of the coating material IN625mod were also investigated under uniaxial isothermal fatigue loading at 200 and 500 °C. Moreover, the thermo-mechanical fatigue behavior of 16Mo3 was studied under in-phase (IP) and out-of-phase (OP) loading between 200 and 500 °C. The fatigue lives of the bulk coating and the compound material are presented. In particular, the thermo-mechanical OP loading leads to a strong reduction of the lifetimes compared to the IP loading. A conservative estimation of the fatigue lives of the thermo-mechanical loading can be given by isothermal tests at 500 °C. The comparison of the uniaxial loading with the biaxial loading cases shows reasonable coincidence by using the distortion energy hypothesis according to von Mises.

Two series of lithium iron phosphate (LiFePO4) nanocomposites are prepared by a solvothermal method coupled with high temperature calcination using mononuclear and binuclear metal hexaaminophthalocyanines as modulatory additives, respectively. Physical and electrochemical performances of the composites as cathode materials of lithium-ion batteries are characterized by inductively coupled plasma (ICP), X-ray diffraction (XRD), infrared (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical techniques. The results indicate that the as-synthesized samples modified with binuclear metal phthalocyanines can improve electrochemical properties of LiFePO4 (LFP) for lithium-ion batteries. The composite using binuclear manganese hexaaminophthalocyanine as additive can achieve the highest initial specific discharge capacity of 152.3 mAh/g at 0.1 C, higher than that of ones modified with the corresponding mononuclear phthalocyanine 143.0 mAh/g. Furthermore, the most excellent product exhibits a pretty good capacity retention of 93.0% after 50 cycles at 0.1 C, cycling stability, and low charge transfer resistance of 58.7 Ω.