Metal–Organic Framework Hybrid‐Assisted Formation of Co3O4/Co‐Fe Oxide Double‐Shelled Nanoboxes for Enhanced Oxygen Evolution

Rational design of complex metal–organic framework (MOF) hybrid precursors offers a great opportunity to construct various functional nanostructures. Here, a novel MOF‐hybrid‐assisted strategy to synthesize Co₃O₄/Co‐Fe oxide double‐shelled nanoboxes is reported. In the first step, zeolitic imidazolate framework‐67 (ZIF‐67, a Co‐based MOF)/Co‐Fe Prussian blue analogue (PBA) yolk–shell nanocubes are formed via a facile anion‐exchange reaction between ZIF‐67 nanocube precursors and [Fe(CN)₆]^3? ions at room temperature. Subsequently, an annealing treatment is applied to prepare Co₃O₄/Co‐Fe oxide double‐shelled nanoboxes. Owing to the structural and compositional benefits, the as‐derived Co₃O₄/Co‐Fe oxide double‐shelled nanoboxes exhibit enhanced electrocatalytic performance for oxygen evolution reaction in alkaline solution.     

Atomic Structures of Precipitates in Al–Mg–Si Alloys with Small Additions of Other Elements

In Al–Mg–Si alloys, additions of only a few weight percent of Mg and Si enable formation of hardening precipitates during heat treatment. The precipitation is complex and is influenced by chemical compositions and thermo‐mechanical treatment. Structural analysis at the atomic scale has played an important role for understanding the Al–Mg–Si system. This review paper gives a summary of the influence of elements on the precipitate structures of Al–Mg–Si alloys at the atomic scale. The structures are modified by small additions of different elements, but all the encountered precipitates are structurally connected with the Si network, except for the main hardening phase which exhibit a partially discontinuous Si network. The influence of the selected elements (Li, Cu, Zn, Ge, Ag, Ni, Co, and Au) is discussed in detail.

     

Formation of vacancy clusters in deformed thin films of Al–Mg and Al–Cu dilute alloys

In the present study, vacancy clusters in elongated Al–Mg and Al–Cu thin films (Mg/Cu CONCENTRATION=0.05–1.70 at.%) were examined by electron microscopy. No dislocations were observed in these films. In Al–Mg thin films deformed at room temperature, a large number of stacking fault tetrahedra (sft) were observed alongside a few vacancy loops. The opposite was true for Al–Cu thin films, where well-grown loops predominated, and only a few sft were observed. The Al–Cu film results show that the majority of vacancies form loops larger than sft. We also deformed Al–0.05at.% (Mg or Cu) alloys in liquid nitrogen and cold-transferred to an electron microscope. In Al–Mg, a large number of dotted defects (possibly sft) were observed, while very few such defects were observed in Al–Cu. This indicates that loops observed in Al–Cu thin films deformed at room temperature, grew during/after deformation. The likely contribution of strain-induced vacancies in deformed Al thin films to the voiding in VLSI interconnect wires due to electro-migration were discussed.     

Selective Formation of Carbon‐Coated,Metastable Amorphous ZnSnO3 Nanocubes Containing Mesopores for Use as High‐Capacity Lithium‐Ion Battery

Mesoporous and amorphous ZnSnO₃ nanocubes of ～37 nm size coated with a thin porous carbon layer have been prepared using monodisperse ZnSn(OH)₆ as the active precursor and low‐temperature synthesized polydopamine as the carbon precursor. The small single nanocubes cross‐link with each other to form a continuous conductive framework and interconnected porous channels with macropores of 74 nm width. Because of its multi‐featured nanostructure, this material exhibits greatly enhanced integration of reversible alloying/de‐alloying (i.e., transformation of Li_4.4Sn and LiZn to Sn and Zn) and conversion (i.e., oxidation of Sn and Zn to ZnSnO₃) reaction processes with an extremely high capacity of 1060 mA h g^?1 for up to 100 cycles. A high reversible capacity of 650 and 380 mA h g^?1 can also be delivered at rates of 2 and 3 A g^?1, respectively. This excellent electrochemical performance is attributed to the small particle size, well‐developed mesoporosity, the amorphous nature of the ZnSnO₃ and the continuous conductive framework produced by the interconnected carbon layers.     

Formation of intermetallic compounds in the Cr–Al–Si ternary system

The microstructure and composition of binary and ternary intermetallics have been studied in ternary diffusion couples of Cr and an Al–Si eutectic alloy. The ternary intermetallic always formed in the liquid part of the diffusion couple as a dendritic structure. Two intermetallics compounds, CrSi₂ and Cr₅Si₃, of the Cr–Si binary system have been observed. The CrSi₂ intermetallic has a high solubility of up to 20 at.% Al and forms as faceted plates. A number of intermetallics, namely, CrAl₇, Cr₂Al₁₁, CrAl₄, Cr₄Al₉, Cr₅Al₈ and Cr₂Al, of the Cr–Al system have been observed. The solubility of Si varies from as low as 0.8 at.% in Cr₂Al to as high as 9 at.% in Cr₄Al₉. A schematic of the reaction scheme of the Cr–Al–Si system is presented. This has been based on the observed microstructure and composition of phases.     

Structural evolution during mechanical milling and subsequent annealing of Cu–Ni–Al–Co–Cr–Fe–Ti alloys

This study reports the structural evolution of high-entropy alloys from elemental materials to amorphous phases during mechanical alloying, and further, to equilibrium phases during subsequent thermal annealing. Four alloys from quaternary Cu_0.5NiAlCo to septenary Cu_0.5NiAlCoCrFeTi were analyzed. Microstructure examinations reveal that during mechanical alloying, Cu and Ni first formed a solid solution, and then other elements gradually dissolved into the solid solution which was finally transformed into amorphous structures after prolonged milling. During thermal annealing, recovery of the amorphous powders begins at 100 °C, crystallization occurs at 250–280 °C, and precipitation and grain growth of equilibrium phases occur at higher temperatures. The glass transition temperature usually observed in bulk amorphous alloys was not observed in the present amorphous phases. These structural evolution reveal three physical significances for high-entropy alloys: (1) the annealed state of amorphous powders produces simple equilibrium solid solution phases instead of complex phases, confirming the high-entropy effect; (2) amorphization caused by mechanical milling still meets the minimum criterion for amorphization based on topological instability proposed by Egami; and (3) the nonexistence of a glass transition temperature suggests that Inoue's rules for bulk amorphous alloys are still crucial for the existence of glass transition for a high-entropy amorphous alloy.     

Microstructure and creep properties of a cast intermetallic Ti–46Al–2W–0.5Si alloy for gas turbine applications

The microstructure and creep properties including minimum creep rate, time to 1% creep deformation and creep fracture time of a cast TiAl-based alloy with nominal chemical composition Ti–46Al–2W–0.5Si (at.%) were investigated. The creep specimens were prepared from investment-cast plate and two large turbine blades. Constant load creep tests were performed in air at applied stresses ranging from 150 to 400 MPa in the temperature range 973–1073 K. The microstructure of the specimens is characterised by optical, scanning and transmission electron microscopy before and after creep deformation. The minimum creep rate is found to depend strongly on the applied stress and temperature. The power law stress exponent of minimum creep rate is n = 7.3 and the apparent activation energy for creep is Q_a = 427 ± 14 kJ/mol. The initial microstructure of the creep specimen is unstable. The ₂(Ti₃Al)-phase transforms to γ(TiAl)-phase and needle-like B2-precipitates during long-term creep testing at all testing temperatures. At lower applied stresses, the creep specimens fail by the growth and coalescence of cavities and small cracks formed along the γ/₂ interfaces. At the highest applied stresses, the specimens fail by nucleation and propagation of cracks.     

Laser Surface Modification of a Crystalline Al‐Co‐Ce Alloy for Enhanced Corrosion Resistance

The surfaces of Al‐Co‐Ce bulk crystalline alloys have been successfully laser processed resulting in amorphous‐like surface layer formation with enhanced corrosion characteristics. The material system, Al₈₄Co_7.5Ce_8.5, is one of several next generation alloy compositions scientifically designed to form a metallic glass under the proper processing conditions. This material system exhibits both local composition changes and enhanced corrosion resistance in comparison to their native counterparts.     

Comparing characteristics of serrations in Al–Li and Al–Mg alloys

Characteristics of serrations in the flow stress–strain curves of Al–1Mg and Al–2Li alloys, obtained from tensile tests, are analyzed and compared. The analysis includes stress drop, drop time and reload time at various ageing durations of the alloys. Changes in distributions of the stress drops and the drop time with changing the ageing duration differ markedly in Al–2Li from those in Al–1Mg. The mean values and standard deviations of the stress drops and the reload times increase at large deformation in Al–2Li, while they decrease in Al–1Mg. The influence of precipitates on the characteristics of serrations in the Al–Li alloy is identified and the potential effects are discussed.     

Effect of Al2O3 particles on mechanical properties of directionally solidified intermetallic Ti–46Al–2W–0.5Si alloy

The effect of Al₂O₃ particles on microhardness and room-temperature compression properties of directionally solidified (DS) intermetallic Ti–46Al–2W–0.5Si (at.%) alloy was studied. The ingots with various volume fractions of Al₂O₃ particles and mean ₂–₂ interlamellar spacings were prepared by directional solidification at constant growth rates ranging from 2.78×10⁻⁶ to 1.18×10⁻⁴ ms⁻¹ in alumina moulds. The ingots with constant volume fraction of Al₂O₃ particles and various mean interlamellar spacings were prepared by directional solidification at a growth rate of 1.18×10⁻⁴ ms⁻¹ and subsequent solution annealing followed by cooling at constant rates varying between 0.078 and 1.889 K s⁻¹. The mean ₂–₂ interlamellar spacing λ for both DS and heat-treated (HT) ingots decreased with increasing cooling rate according to the relationship λ∝ ^−0.46. In DS ingots, microhardness, ultimate compression strength, yield strength and plastic deformation to fracture increased with increasing cooling rate. In HT ingots, microhardness and yield strength increased and ultimate compression strength and plastic deformation to fracture decreased with increasing cooling rate. The yield stress increased with decreasing interlamellar spacing and increasing volume fraction of Al₂O₃ particles. A linear relationship between the Vickers microhardness and yield stress was found for both DS and HT ingots. A simple model including the effect of interlamellar spacing and increasing volume fraction of Al₂O₃ particles was proposed for the prediction of the yield stress.