Non-equilibrium Heat Treatment Research Articles

Crystallographic Orientation Relationship between α and β Phases during Non-Equilibrium Heat Treatment of Cu-37 wt. % Zn Alloy

The crystallographic orientation relationship between α and β phases during the non-equilibrium heat treatment of a Cu-37 wt. % Zn alloy was investigated. With this aim, Cu-37 wt. % Zn alloy plates with a thickness of 2 mm were heated at 810 °C for 1 h and then were quenched in water. The microstructure and texture of heat-treated samples were analyzed using optical microscopy and electron backscattered diffraction. By this non-equilibrium heat treatment, β phase was formed on both the grain boundaries and grain interiors. In addition, the Σ3 twin boundaries acted as preferred areas for α→β transformation. The orientation imaging microscopy results revealed a Kurdjumov–Sachs (K–S) orientation relationship between α and β phases. Furthermore, the details of microstructural evolution and texture analysis were discussed.

Developing α/β Laminar Composite Structure in CuZn Alloy by Heat Treatment and Submerged Friction Stir Processing

A laminar composite structure was developed in a CuZn alloy plate by non-equilibrium heat treatment and subsequent submerged friction stir processing. For this aim, Cu-37 wt.% Zn alloy was initially heat treated to produce a double phase structure. Then, the double phase plate was friction stir processed in underwater media at room temperature. The microstructure and mechanical properties of the samples were analyzed using optical microscopy and tensile test. During heat treatment, the large α grains containing annealing twins converted to a double phase structure with β grains on the α grain boundaries. Heat treatment caused an increase in ultimate tensile strength from 240 MPa to 275 MPa, and a reduction in elongation from 67 to 49%. After friction stir processing, the ultimate tensile strength and elongation were obtained as 380 MPa and 48%, respectively. This desirable mechanical property was achieved due to the formation of a novel composite structure containing parallel ultra-fine grained β layers between dynamically recrystallized α layers.

Synthesis of rattle-structured CuCo2O4 nanospheres with tunable sizes based on heterogeneous contraction and their ultrahigh performance toward ammonia borane hydrolysis

Micro/nano-materials with rattle-type structures are attractive because of their unique physicochemical properties and extensive applications. In this study, well-defined rattle-type CuCo2O4 nanospheres were fabricated by heterogeneous contraction caused by non-equilibrium heat treatment with the assistance of an RF (resorcinol formaldehyde) resin colloidal sphere hard template. The sizes of CuCo2O4 nanospheres could be tuned by varying the amount of NH3·H2O used during template synthesis. The possible formation mechanism of rattle-type CuCo2O4 nanospheres was also proposed. When used in ammonia borane hydrolysis, rattle-type CuCo2O4 nanospheres exhibited ultrahigh activity with a turnover frequency of 104.0 min−1, which is one of the highest activities of non-noble-metal based catalysts, and is even higher than many noble-metal-based catalysts. This research provides valuable insights into the development of robust catalysts for ammonia borane hydrolysis. In addition, the synthetic method presented in this work can be easily extended to prepare other oxide composites with rattle structures.

A Novel Approach to Structure Modification of Brasses by Combination of Non-equilibrium Heat Treatment and Friction Stir Processing

A non-equilibrium heat treatment was used to produce secondary phase (β) in the single phase brass (α), which caused the modification of the grain structure and mechanical properties after friction stir processing. For this aim, the single phase brass plate containing 37 wt pct Zn was heated at 810 °C for 1 hour, and then quenched in water, which caused the formation of non-equilibrium secondary β phase. After the non-equilibrium heat treatment, bead on plate friction stir processing was employed. The origin of the modification by β phase was studied using high resolution electron backscattered diffraction and transmission electron microscopy. The results showed that the average grain size, yield strength, and strain-hardening exponent were changed, respectively, from 4.8 µm, 166 MPa and 0.28 to 2.1 µm, 213 MPa and 0.25 in the presence of β phase. The β phase promoted the discontinuous dynamic recrystallization by particle-stimulated nucleation mechanism, and then transformed to α resulting in a finer microstructure with more random texture. In addition, the nanometer-sized β particles were retained at the grain boundaries, which reduced their mobility and hence the grain growth was inhibited.

Facile synthesis of homogeneous core-shell Co3O4 mesoporous nanospheres as high performance electrode materials for supercapacitor

Homogeneous core-shell Co3O4 mesoporous nanospheres are successfully fabricated by virtue of a solvothermal method and subsequent rapid calcination treatment. Note that the solid precursor nanospheres turn into homogeneous core-shell Co3O4 nanostructure only after 10 min of calcination. The stacking density of sub-nanoparticles and the thickness of the Co3O4 shell can be well adjusted by altering the annealing time. A formation mechanism based on a thermally driven contraction process caused by non-equilibrium heat treatment is proposed. The tunable mesoporous and core-shell structure can effectively facilitate the ions and electrons transportation and meanwhile accommodate the strain of oxide electrode upon cycling. Consequently, the optimal core-shell Co3O4 electrode exhibits a high specific capacitance of 837.7 F g−1 at 1 A g−1 and good capacitance retention of 87.0% after 2000 cycles at a high current density of 5 A g−1. More importantly, it possesses an excellent rate capability with high capacitance retention of 93.6% when the current density raises from 1 to 10 A g−1. Besides, an asymmetric supercapacitor (ASC) is constructed using the core-shell Co3O4 nanospheres as positive electrode and graphene aerogel as negative electrode. The ASC delivers a high specific capacitance of 101.4 F g−1 at 1 A g−1 and an energy density of 35.8 Wh kg−1 at a power density of 797.4 W kg−1. Moreover, the assembled ASC displays a good cycling stability with 88.2% capacitance retention after 2000 cycles at 1 A g−1. All of these results make the homogeneous core-shell Co3O4 mesoporous nanostructure a promising electrode for high-performance supercapacitors.

Fabrication of CeO2-MO x (M = Cu, Co, Ni) composite yolk-shell nanospheres with enhanced catalytic properties for CO oxidation.

CeO2–MOx (M = Cu, Co, Ni) composite yolk–shell nanospheres with uniform size were fabricated by a general wet-chemical approach. It involved a non-equilibrium heat-treatment of Ce coordination polymer colloidal spheres (Ce-CPCSs) with a proper heating rate to produce CeO2 yolk–shell nanospheres, followed by a solvothermal treatment of as-synthesized CeO2 with M(CH3COO)2 in ethanol solution. During the solvothermal process, highly dispersed MOx species were decorated on the surface of CeO2 yolk–shell nanospheres to form CeO2–MOx composites. As a CO oxidation catalyst, the CeO2–MOx composite yolk–shell nanospheres showed strikingly higher catalytic activity than naked CeO2 due to the strong synergistic interaction at the interface sites between MOx and CeO2. Cycling tests demonstrate the good cycle stability of these yolk–shell nanospheres. The initial concentration of M(CH3COO)2·xH2O in the synthesis process played a significant role in catalytic performance for CO oxidation. Impressively, complete CO conversion as reached at a relatively low temperature of 145 °C over the CeO2–CuOx-2 sample. Furthermore, the CeO2–CuOx catalyst is more active than the CeO2–CoOx and CeO2–NiO catalysts, indicating that the catalytic activity is correlates with the metal oxide. Additionally, this versatile synthesis approach can be expected to create other ceria-based composite oxide systems with various structures for a broad range of technical applications.

Fabrication of double-shelled Fe2O3/CeO2 boxes from CeO2-modified Prussian blue and their enhanced performances for CO removal and water treatment

Multiple components and well-defined complex nanostructures may synergistically enhance the performance and application of composite materials. Herein, hierarchical double-shelled Fe2O3/CeO2 microboxes, with the robust Fe2O3 hollow microcubes inside and CeO2 shell outside, were fabricated by a facile wet chemical process, which involved the decoration of Fe4[Fe(CN)6]3 microcubes with CeO2 nanoparticles, followed by the thermal decomposition of this precursor in air. The non-equilibrium heat treatment induced heterogeneous contraction process during the calcination of the Fe4[Fe(CN)6]3/CeO2 precursor in air, which is responsible for the formation of the unique hollow structures. The pre-deposited CeO2 nanoparticles acted as stabilizer for the exterior surface of Fe4[Fe(CN)6]3 cubes, and consequently played a crucial role in the formation of the unique hollow structures. The CeO2 molar concentration of the resultant products could be tailored by simply varying the feeding amount of Ce(NO3)3. As a CO oxidation catalyst, the as-prepared Fe2O3/CeO2 microboxes displayed higher catalytic activity in comparison with both CeO2 particles and Fe2O3 cubes owing to the high specific surface area and the synergetic interaction between Fe2O3 and CeO2. More importantly, the catalytic performance is closely associated with the component ratio between Fe2O3 and CeO2. In addition, the Fe2O3/CeO2 microboxes also exhibited significant adsorption capacity of Congo red, implying their potential application in water treatment.

Core–shell CeO2 micro/nanospheres prepared by microwave-assisted solvothermal process as high-stability anodes for Li-ion batteries

Core–shell CeO2 micro/nanospheres are prepared via microwave-assisted solvothermal process followed by calcination in air. The reaction time is only 30 min. Structure information, phase, and morphologies of the as-synthesized powder are characterized by X-ray diffraction (XRD), scan electron microscope (SEM), and transmission electron microscope (TEM), respectively. The heterogeneous contraction originated from the non-equilibrium heat treatment may be responsible for the formation of core-shelled structure. Charge–discharge test and electrochemical impedance spectroscopy (EIS) are carried out by using the as-prepared CeO2 as an anode material for lithium-ion batteries. When tested in 0.01–1.5 V at 0.2 mA cm−2, the initial discharge capacity is 454.2 mAh g−1 and stabilized reversibly at about 327.0 mAh g−1 after 100 cycles. The special core–shell micro/nanostructure is more capable of buffering the volume change, resulting in enhanced electrochemical performances. This exploring about the core–shell micro/nanomaterial may direct a new generation electrode material of Li-ion batteries.

Fabrication of Magnetic Fe3O4 Nanotubes by Electrospinning

Abstract Ferroferric oxide nanotubes were prepared by calcining and reducing the composite nanofiber precursors fabricated by electrospinning. Influences of the electrospun parameters (PVA concentration of solution, applied voltage and collector distance) on the preparation of the composite nanofiber precursors were discussed. The structural properties of the obtained nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation mechanism of the Fe3O4 nanotubes was investigated through the nonequilibrium heat-treatment procedure. Furthermore, the magnetic property of Fe3O4 was measured using a vibrating sample magnetometer. Results reveal that the tubes show a uniform and continuous morphology, whose outer and inner diameters are about 100 nm and 50 nm, respectively. Fe3O4 possesses saturation magnetization (Ms) of 54.2 A·m2/kg, coercivity (Hc) of 215×79.6 A/m and remanent magnetization (Mr) of 12.8 A·m2/kg, respectively.

Facile synthesis of Mn–Co oxide nanospheres with controllable interior structures and their catalytic properties for methane combustion

Uniform Mn–Co mixed oxide solid, hollow and yolk–shell nanospheres with nanometer-sized building blocks have been successfully fabricated by heat-treatment of their Mn–Co alkoxyacetate precursors at a proper ramping rate. The formation of the hollow and yolk–shell structures during the thermal decomposition is mainly based on the heterogeneous contraction caused by non-equilibrium heat treatment. In virtue of the unique structural features, the resultant Mn–Co oxide nanospheres with different interiors were used as catalysts in CH4 combustion, and showed an excellent catalytic activity. Catalytic results suggest that the (Co,Mn)(Co,Mn)2O4 yolk–shell nanospheres show relatively higher activity.

Effects of atoleine on preparation and thermal behaviors of TiO2 gel microspheres fabricated via oil-in-water emulsions

Titanium dioxide (TiO2) gel microspheres were successfully synthesized by sol–gel process in oil-in-water emulsion, and the effects of atoleine on the morphology and thermal behaviors of the microspheres were investigated. Atoleine has no obvious effect on the morphology of the TiO2 gel microspheres. The resulting particles show spherical structure and are suspended without coagulation. However, the additive atoleine changes the thermal behaviors of microspheres, and also alters the interior structures of the microspheres after non-equilibrium heat-treatment. The core–shell structure of microspheres begin to form at the temperature between 600 and 700°C, which is attributed to the formation of rigid outer part from high crystalline and contraction of inner part in sequent calcination. The addition of 3 and 20wt.% atoleine hinders the crystallization of the microspheres at the temperature of below 600°C and leads to a solid structure instead of core–shell structure obtained with small amounts of additive atoleine (0 and 1wt.%).

Simple synthesis of yolk-shelled ZnCo2O4 microspheres towards enhancing the electrochemical performance of lithium-ion batteries in conjunction with a sodium carboxymethyl cellulose binder

Mixed metal oxides have been attracting more and more attention recently because of their advantages and superiorities, which can improve the electrochemical performance of single metal oxides. These advantages include structural stability, good electronic conductivity, and reversible capacity. In this work, uniform yolk-shelled ZnCo2O4 microspheres were synthesized by pyrolysis of ZnCo-glycolate microsphere precursors which were prepared via a simple refluxing route without any precipitant or surfactant. The formation process of the yolk-shelled microsphere structure during the thermal decomposition of ZnCo-glycolate is discussed, which is mainly based on the heterogeneous contraction caused by non-equilibrium heat treatment. The performances of the as-prepared ZnCo2O4 electrodes using sodium carboxylmethyl cellulose (CMC) and poly-vinylidene fluoride (PVDF) as binders are also compared. Constant current and rate charge–discharge testing results demonstrated that the ZnCo2O4 electrodes using CMC as the binder had better performance than those using PVDF as the binder. It was worth pointing out that the electrode using CMC as the binder nicely yields a discharge capacity of 331 mA h g−1 after 500 cycles at a current density of 1000 mA g−1, which is close to the theoretical value of graphite (371 mA h g−1). Furthermore, the obtained synthetic insights on the complex hollow structures will be of benefit to the design of other anode materials for lithium ion batteries.

A facile route to synthesize multiporous MnCo2O4 and CoMn2O4 spinel quasi-hollow spheres with improved lithium storage properties

A facile and general way for the synthesis of porous and hollow complex oxides is highly desirable owing to their significant applications for energy storage and other fields. In this contribution, uniform Mn(0.33)Co(0.67)CO(3) and Co(0.33)Mn(0.67)CO(3) microspheres are firstly fabricated solvothermally just by tuning the molar ratio of Mn and Co. Subsequently, the growth of multiporous MnCo(2)O(4) and CoMn(2)O(4) quasi-hollow microspheres by topotactic chemical transformation from the corresponding precursors are realized through a non-equilibrium heat treatment process. Topotactic conversion further demonstrated that the much larger CoMn(2)O(4) pores than those of MnCo(2)O(4) are possibly due to the longer transfer distance of ions. When evaluated as anode materials for LIBs (lithium ion batteries), after 25 cycles at a current density of 200 mA g(-1), the resultant MnCo(2)O(4) and CoMn(2)O(4) quasi-hollow microspheres possessed reversible capacities of 755 and 706 mA h g(-1), respectively. In particular, the MnCo(2)O(4) samples could deliver a reversible capacity as high as 610 mA h g(-1) even at a higher current density of 400 mA g(-1) with excellent electrochemical stability after 100 cycles of testing, indicating its potential application in LIBs. We believe that such good performance results from the appropriate pore size and quasi-hollow nature of MnCo(2)O(4) microspheres, which can effectively buffer the large volume variation of anodes based on the conversion reaction during Li(+) insertion/extraction. The present strategy is simple but very effective, and due to its versatility, it can be extended to other binary, even ternary complex metal oxides with high-performance in LIBs.

Martensitic transformation behaviour of non-equilibrium heat treated Ni50·9Ti49·1 alloys

Ni50·9Ti49·1 specimens were heat treated using a thermal simulator. The martensitic transformation behaviours of selected areas of the thermal simulating treated specimens were studied with resistivity temperature measurements. In the thermal simulating process specimens were heated by a large electric current to a given peak temperature (400, 500, 600, 800, 900 or 1100°C respectively) and immediately water cooled to room temperature. As the two ends of a NiTi alloy specimen were fixed in copper jigs, unequal heat treatment effect areas were formed in the specimen segments near its two ends. In the unequal area of an 800°C thermal simulating treated sample, a wide transformation temperature range phenomena appeared. The experimental results indicate that non-equilibrium heat treatment proves to be an effective method to fabricate transformation temperature gradient shape memory materials.

Oriented Contraction: A Facile Nonequilibrium Heat-Treatment Approach for Fabrication of Maghemite Fiber-in-Tube and Tube-in-Tube Nanostructures

We present a simple and effective nonequilibrium heat-treatment approach that allows for the facile fabrication of maghemite (γ-Fe(2)O(3)) fiber-in-tube and tube-in-tube nanostructures by heat-treating electrospun precursor fibers composed of polyvinylpyrrolidone (PVP) and iron citrate with a carefully devised heating rate (R). In this nonequilibrium heat-treatment procedure, R can be easily utilized to tune the temperature gradient established in the inner portion of the fibers and the difference between the cohesive force and the adhesive force at the interface layer between the inner gel and the dense rigid shell generated in situ by a high R. Therefore, the contraction direction of the precursor nanofibers and the final morphology of the resultant γ-Fe(2)O(3) fibers ranging from a simple tube to a fiber in tube to a tube in tube are realized for control. The nonequilibrium heat-treatment approach reported here can be readily extended to the fabrication of other materials with controllable interior structures by fast heating their corresponding gel precursors, which may be fabricated on the basis of electrospinning techniques and others. The resultant γ-Fe(2)O(3) fiber-in-tube and tube-in-tube nanostructures may have important applications in a number of areas, such as magnetic separable catalysts or catalyst supporting materials, sensors, absorbents, microreactors, and so forth, because of their structural characteristics and good magnetic properties.

Microstructural Evolution during the Novel Quenching and Partitioning (Q&P) Heat Treatment of Steel

The novel non-equilibrium heat treatment procedure known as Quenching and Partitioning (Q&P) may offer the prospect of higher strength steel products with enhanced formability based upon martensitic microstructures containing controlled quantities of carbon-enriched retained austenite. The Q&P process requires an interrupted quench and isothermal annealing (partitioning) step at intermediate temperatures, whereby untransformed austenite can be thermodynamically stabilised by carbon migration from supersaturated martensite regions. The concept is comparable to that producing carbide-free bainite, for example, in TRIP-assisted steel, although Q&P allows separation of the ferrite formation and austenite enrichment stages of the process. However, although the Q&P concept is readily understood, evolution of the microstructure during interrupted quenching and partitioning has been inferred indirectly from dilatometer studies and metallographic examination after final quenching to room temperature. Consequently, a model alloy was developed in which the sequential steps of heat treatment could be separated for direct inspection by conventional metallography, X-ray diffraction and neutron diffraction techniques.

Martensitic steels with carbide free microstructures containing retained austenite

The concept of employing martensitic microstructures containing controlled quantities of carbon enriched retained austenite as a new route to high tonnage steels with improved properties is developed through an introduction to the novel non-equilibrium heat treatment procedure which has become known as quenching and partitioning (Q&P). This builds upon the earlier development of steels containing carbide free bainite and retained austenite, enabled by alloying with Si to suppress carbide precipitation, embracing a philosophy to produce refined ferritic microstructures by transformation to acicular forms, with the ferrite protected from the more damaging effects of carbon, which is partitioned to the austenite phase where it acts as a chemical stabiliser. This route offers enhanced strength from the martensite structure along with the promise of new properties from the behaviour of the retained austenite phase which could potentially contain a very high controlled concentration of carbon.

Preparation of hollow spheres with controllable interior structures by heterogeneous contraction

We present a simple and effective heterogeneous contraction method to fabricate hollow spheres with controllable interior structures (ranging from solid, simple hollow to core-in-hollow-wall, double-wall hollow and core-in-double-hollow-wall spheres) by a non-equilibrium heat-treatment process of gel precursors with a high heating rate.

Heat Treatment and Interface Effects on the Mechanical Behavior of SiC-Particle Reinforced Aluminium Matrix Composites

Abstract The interface plays a vital role in composites. Strengthening behavior of SiC-particle reinforced aluminium matrix composites relies on load transfer behavior across the interface, whereas toughness is influenced by crack deflection at the boundary between matrix and reinforcement and ductility is affected by relaxation of peak stresses near the interface. In general, metal matrix composites often behave asymmetrically in tension and in compression and have higher ultimate tensile strength, yet lower proportional limits, than monolithic alloys. Such behavior of composites lies with the factors governing matrix plasticity, which can be divided into two areas: those affecting the stress rate of the matrix, and those which alter the flow properties of the matrix through changes in microstructure induced by inclusion of the reinforcement. This work focuses on the characterization of the mechanical response of the interface to stresses arising from an applied load in SiC-particle reinforced aluminium matrix composites. The composites have been studied in the as-received (T1) and in the T6 and modified T6 (HT1) conditions. In the nonequilibrium heat treatment processing of the composites, nonequilibrium segregation arises due to imbalances in point defect concentrations set up around interfaces. Mechanical properties, including microhardness and stress-strain behavior, of aluminum matrix composites containing various percentages of SiC particulate reinforcement have been investigated. The elastic modulus, the yield/tensile strengths, and ductility of the composites were controlled primarily by the volume percentage of SiC reinforcement, the temper condition, and the precipitation hardening.

Influence of Processing Conditions on the Micro-Mechanical Properties of Particulate-Reinforced Aluminium Matrix Composites

During processing, metal matrix attempts to deform and this deformation plays the key role in the microstructural events of segregation and precipitation at the matrix-reinforcement interface. The important aspect of this behaviour is to identify the strengthening micro-characteristics which enhance the material's interphasial reactions in order to improve the bonding properties of the matrix-reinforcement interface. This work focuses on the non-equilibrium segregation which arises due to imbalances in point defect concentrations set up around interfaces during non-equilibrium heat treatment processing of SiC particle reinforced aluminium matrix composites. The important factors affecting the heat treatment process are the temperature, the cooling rate, the concentration of solute atoms and the binding energy between solute atoms and vacancies. Aluminium – silicon – magnesium alloy matrix reinforced with varying amounts of silicon carbide particles were used in this study. Samples in the as-received and heat treated condition were examined by microstructural and microhardness analyses. Based on the analysis, it has been observed that the macroscopic mechanical behaviour of the composite is influenced by several factors including the manufacturing process, the processing conditions, the inter-particle distance, as well as the mean size and the percentage of reinforcement.