Microstructural characterization of as-cast and homogenized 2D70 aluminum alloy

The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as-cast 2D70 aluminum alloy mainly consists of the dendritic network of aluminum solid solution and intermetallic compounds (Al₂CuMg, Al₂Cu, Al₉FeNi, Cu₂FeAl₇, and Al₇Cu₄Ni). After conventional homogenization, Al/Al₂CuMg eutectic phases are dissolved into the matrix, and a small amount of high melting-point eutectic Al/Al₂Cu phases exist in the matrix, resulting in an increase in the starting melting temperature. Under double homogenization, the high melting point Al/Al₂Cu phases are dissolved, and no obvious change is observed for the size and morphology of Al₉FeNi, Cu₂FeAl₇, and Al₇CuaNi compounds.     

Microstructure and texture evolution of TRC A8006 alloy by homogenization

The microstructure and texture evolution of twin-roll cast A8006 alloy by homogenization were characterized using scanning and transmission electron microscopy, and the microhardness was tested as well. According to the relationship between dendritic arm spacing and cooling rate the cooling rate of the as-cast twin-roll cast A8006 sheet of 6 mm in thickness was estimated as 1.48×103 K·s?1. It is found that the grains and the nanostructural precipitates of the twin-roll cast sheet become coarser after homogenization at 580℃ for 4 h in comparison with those after homogenization at 500℃ for 8 h. The textures formed after cold rolling and became weaker during homogenization. The increase in hardness of the as-cast twin-roll cast sheets is related to the supersaturated α-Al solid solution and fine microstructure, but the decrease in hardness after homogenization can be attributed to the coarsening of grains and Al₆Fe(Mn) precipitates.     

Sintering mechanism of Cu-9Al alloy prepared from elemental powders

The sintering behavior of Cu-9Al alloys prepared from die pressing of elemental powders was investigated. The experimental results and kinetic analysis showed the formation of three consecutive layers of Al₂Cu, Al₄Cu₉, and AlCu phases, with Al₂Cu appearing first in the initial solid phase sintering stage. A liquid phase formed in the intermediate stage, resulting from the eutectic reaction between Al and Al₂Cu phases at 500 °C, which is 47 °C lower than the equilibrium reaction temperature. Swelling occurred when the liquid phase infiltrated the gaps between the copper particles, leaving pores at the original sites of Al particles and Al₂Cu. In the final stage of sintering, the Al-rich phases (Al₂Cu and AlCu) transformed to Al-poor phases (Al₄Cu₉ and α-Cu) in the temperature range of 500–565 °C. Al₄Cu₉ and α-Cu then transformed to AlCu₃ (β) above the eutectoid reaction temperature (565 °C), whereas AlCu₃ transformed to α-Cu and eutectoid phases (α-Cu + Al₄Cu₉) during cooling. The pure copper transformed to AlCu₃, and the pore volume decreased at 1000 °C. The microstructure study helps manipulate precisely the sintering process of Cu-Al alloys and optimize the microstructure with a high dimensional accuracy.     

Effect of sintering temperature on phase evolution of Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) bulk amorphous composites synthesized via mechanical alloying and spark plasma sintering

Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) amorphous powders were synthesized by mechanical alloying for 200 h. Subsequent consolidation was performed via spark plasma sintering in the temperature range of 250 ℃ to 500 ℃ at the pressure of 500 MPa. The role of viscous flow on densification was investigated by studying the viscosity change of the amorphous phase at different consolidation temperatures. The decrease in viscosity at higher sintering temperatures resulted in better particle bonding and densification of consolidated samples. The formation of only FCC Al was observed in the consolidated samples at sintering temperatures ≤ 300 ℃ and the intermetallic phases formed at temperatures ≥ 400 ℃. The mechanical properties of the bulk samples were measured by Vickers microhardness and nanoindentation tests. The testing results showed that the average values of microhardness, nanohardness and elastic modulus of the sample consolidated at 500 ℃ were 3.06 ± 0.14 GPa,4.85 ± 1.14 GPa and 89.53 ± 9.25 GPa, respectively. The increase in hardness and elastic modulus of the higher temperature consolidated samples is attributed to the improvement in particle bonding, densification and distribution of various hard intermetallic phases in the amorphous matrix.     

Effect of heat treatment on microstructures and properties of a novel Al-Zn-Mg-Cu alloy for oil drilling

In view of the special requirements for strength, heat resistance and corrosion resistance of Al-Zn-Mg-Cu alloy for oil drilling, the Al-6.2 Zn-2.5 Mg-1.6 Cu alloy was prepared by increasing Cu content on basis of Russian Series 1953 alloy. The effect of heat treatment on the microstructures and properties of the alloy was characterized by optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscope(TEM), and investigated by tensile test at room temperature, thermal exposure test and corrosion test. The results show that the strength after T6 aging treatment exhibit a decrease trend as an increase of the solution temperature from465 °C to 480 °C. After the solution treated by the rate of 470 °C/1 h, second phases dissolve into the matrix very well and the strength property reaches optimum. The alloy has better comprehensive properties treated by a solution treatment of 470 °C/1 h and then followed by an aging treatment of 120 °C/24 h + 170 °C/1 h + 120 °C/24 h. Under the aging state, the precipitated phases inside the grains are suitable in size, while on the grain boundary distribute discontinuously and the precipitate-free zone is obvious. Besides, the alloy still maintain high tensile properties. The yield strength, tensile strength and elongation are 650 MPa, 686 MPa,12.0%, respectively. The yield strength retention after heat exposure is 92%. The alloy has good corrosion resistance and the exfoliation corrosion degree. The average corrosion rate in the H_2S and CO_2 environment is 0.0024 mm/a, which is far less than the required 0.12 mm/a. It is insensitive to H_2S and CO_2 environments.     

Al-Cu-Mn合金铸锭均匀化工艺及组织性能分析

采用光学金相显微镜、扫描电子显微镜及能谱分析、电导率等检测手段,对铸态和均匀化态的2219合金微观组织、第二相分布及电导率进行研究分析。结果表明,2219合金铸态组织存在着枝晶偏析,在晶界上聚集大量的Al₂Cu相,并有长条状的脆性相Al₇Cu₂（Fe、Mn）穿插在晶界上。经525 ℃均匀化处理22 h后,晶界上Al₂Cu相回溶到基体中,枝晶网络被破坏,枝晶偏析消除,Cu元素从晶界到晶内的分布趋于平稳;处于亚稳态的溶质原子从过饱和固溶体中析出,在晶内呈细小、弥散地分布,基体溶质原子固溶度降低,电子散射作用减弱,电导率提高10 %IACS。     

Zr-pillared montmoril lonite supported cobalt nanoparticles for Fischer – Tropsch synthesis

In this article Fischer–Tropsch(FT) synthesis was studied over cobalt nanoparticles supported on modifed Montmorillonite(Zr-PILC).Co-loaded/Zr-PILC catalysts were synthesized by hydrothermal methods and were characterized by XRD,XRF,BET,H2-TPR,TGA and SEM techniques.FT reactions were carried out in fxed bed microreactor(T 225 1C,260 1C and 275 1C,P 1,5 and 10 bars).The FT-products obtained over Co-loaded/Zr-PILC catalysts showed increased selectivity of C2–C12hydrocarbons and decreased selectivity towards CH4and higher molecular weight hydrocarbons(C21) at a TOS of 2–30 h as compared to the Co-loaded/NaMMT catalysts.With increase in reaction temperature from225 1C to 275 1C,CO-conversion and CH4selectivity increases while that of C5+hydrocarbons decreases.Decrease in CH4selectivity while increase in C5+hydrocarbons and CO-conversion were observed on increasing the pressure of reaction.     

La2O3–Al2O3 –SiO2 glass-infiltrated 3Y-TZP all-ceramic composite for the dental restora tive application

The 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) powder had three particle size distributions, while the fine one was lower than 100 nm. The 3Y-TZP compact was prepared by dry-pressing under pressures ranged from 10 to 30 MPa and then presintered at 1250°C for 2 h. The matrix dry-pressed under the pressure of 20 MPa had a porosity of 16.7% and could be easily processed by computer aided design and computer aided manufacturing (CAD/CAM), and which had been infiltrated by the La2O3–Al2O3–SiO2 glass at 1200°C for 4 h. The flexural strength and fracture toughness of the composite were 710.7 MPa and 6.51 MPa m^1/2, respectively. The low shrinkage (0.3%) of the composite can satisfy the net-shape fabrication standard. XRD results illustrated that zirconia in the La2O3–Al2O3–SiO2 glass-infiltrated 3Y-TZP all-ceramic composite was mainly in the tetragonal phase. SEM and EDS results indicated that the pores of the matrix were almost filled by the La2O3–Al2O3 –SiO2 glass     

Microstructure, mechanical and thermo-physical properties of hot-pressed Al2O3-GdAlO3-ZrO2 ceramics with eutectic composition

A low cost chemical co-precipitation method was employed to fabricate nanoscale Al_2O_3-GdAlO_3-ZrO_2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20-200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from θ-Al_2O_3 to α-Al_2O_3 and a thermal decomposition from Gd_3 Al_5O_(12)(GdAG) to GdAlO_3 and α-Al_2O_3 occurred in sequence. A calcination temperature of 1300 ℃ was needed for the crystallization of α-Al_2 O_3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al_2O_3-GdAlO_3-ZrO_2 ceramic hot-pressed at 1500 ℃ exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m~(1/2). The ceramic had a thermal conductivity of 1.9 W m K~(-1) at 1200 ℃ and a thermal expansion coefficient of 9.49 ×10~(-6) K~(-1) at 1100 ℃.     

Bulk Al-Al3Zr composite prepared by mechanical alloying and hot extrusion for high-temperature applications

Bulk Al/Al₃Zr composite was prepared by a combination of mechanical alloying (MA) and hot extrusion processes. Elemental Al and Zr powders were milled for up to 10 h and heat treated at 600℃ for 1 h to form stable Al₃Zr. The prepared Al₃Zr powder was then mixed with the pure Al powder to produce an Al-Al₃Zr composite. The composite powder was finally consolidated by hot extrusion at 550℃. The mechanical properties of consolidated samples were evaluated by hardness and tension tests at room and elevated temperatures. The results show that annealing of the 10-h-milled powder at 600℃ for 1 h led to the formation of a stable Al₃Zr phase. Differential scanning calorimetry (DSC) results confirmed that the formation of Al₃Zr began with the nucleation of a metastable phase, which subsequently transformed to the stable tetragonal Al₃Zr structure. The tension yield strength of the Al-10wt%Al₃Zr composite was determined to be 103 MPa, which is approximately twice that for pure Al (53 MPa). The yield stress of the Al/Al₃Zr composite at 300℃ is just 10% lower than that at room temperature, which demonstrates the strong potential for the prepared composite to be used in high-temperature structural applications.     

Effect of the microstructure of Al 7050-T7451 on anodic oxide formation in sulfuric acid

The effect of the microstructure of an Al 7050-T7451 substrate on the anodic oxide formation in sulfuric acid was studied in this article. The microstructure of the substrate was assessed by optical microscope (OM) and transmission electron microscope (TEM). The surface and cross-section morphologies of the oxide films were examined by scanning electron microscope (SEM). The chemical composition of intermetallic particles in the alloys and films was investigated using energy dispersive spectroscope (EDS). The roles of intermetallic phases and grain or subgrain boundaries on the oxide film formation were researched using the potentiodynamic and potentiostatic polarization technique in sulfuric acid solution. The results show that the transition of coarse intermetallic particles or grain (subgrain) boundaries at the surface of Al alloys can be characterized by potentiodynamic polarization curves. The surface and cross-section micrographs of the anodic layer seem to preserve the microstructure of the substrate. Large cavities in the anodic films are caused by the preferential dissolution of coarse AItCuMg particles and the entrance of Cu-rich remnants into the electrolyte during anodizing. The Al₇Cu₂Fe particles tend to be occluded in the oxide layer or lose from the oxide surface because of peripheral trenching. Small pores in the films are induced by the dissolution of precipitates in grain or subgrain boundaries. The film surface of recrystallized grain bodies is smooth and homogeneous.     

Novel approaches to produce Al2O3– TiC/TiCN– Fecomposite powders directly from ilmenite

Al2O3 –TiC/TiCN–Fe composite powders were successfully prepared directly from ilmenite at 1300–1400℃.The effects of Al/C ratio,sintering atmosphere,and reaction temperature and time on the reaction products were investigated.Results showed that the nitrogen atmosphere was bene cial to the reduction of ilmenite and the formation of Al2O3 –TiC/TiCN–Fe composite powders.When the reaction temperature was between 600 and 1100℃,the intermediate products,TiO2,Ti3O5 and Ti4O7 were found,which changed to TiC or TiCN at higher temperature.Al/C ratio was found to affect the reaction process and synthesis products.When Al addition was 0.5 mol,the Al2O3 phase did not appear.The content of carbon in TiCN rose when the reaction temperature was increased.     

Effect of CuO addition on the sintering temperature and microwave dielectric properties of CaSiO3– Al2O3 ceramics

CuO-doped CaSiO3–1 wt% Al2O3 ceramics were synthesized via a traditional solid-state reaction method, and their sintering behavior,microstructure and microwave dielectric properties were investigated. The results showed that appropriate CuO addition could accelerate the sintering process and assist the densification of CaSiO3–1 wt% Al2O3 ceramics, which could effectively lower the densification temperature from1250 1C to 1050 1C. However, the addition of CuO undermined the microwave dielectric properties. The optimal amount of CuO addition was found to be 0.8 wt%, and the derived CaSiO3–Al2O3ceramic sintered at 1100 1C presented good microwave dielectric properties of εr?7.27,Q f?16,850 GHz and τf? 39.53 ppm/1C, which is much better than those of pure CaSiO3 ceramic sintered at 1340oC(Q f?13,109 GHz).The chemical compatibility of the above ceramic with 30 Pd/70 Ag during the cofiring process has also been investigated, and the result showed that there was no chemical reaction between palladium–silver alloys and ceramics.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

MgCo2-D2 and MgCoNi-D2 systems synthesized at high pressures and interaction mechanism during the HDDR processing

MgCo_2 and MgNiCo crystallize with hexagonal Laves type intermetallic structures of the C14 type and do not form hydrides at ambient hydrogen pressures. However, applying high hydrogen pressures in the GPa range forces the hydrogen absorption and leads to the formation of multi-phase compositions, which contain approximately 2.5 atoms H per formula unit of MgCo_2 or MgNiCo and remain thermally stable under normal conditions.The hydrogenation of MgCo_2 resulted in its decomposition to a ternary Mg_2CoD_5 deuteride and metallic cobalt. Phase-structural transformations accompanying the vacuum desorption of deuterium in the temperature range of 27–500 °C were studied using in situ neutron powder diffraction. The investigation showed a complete recovery of the initial MgCo_2 intermetallic via a Hydrogenation-Disproportionation-Desorption-Recombination process. At 300°C, the Mg_2CoD_5 deuteride first decomposed to elementary Mg and hexagonal Co. At 400°C, a MgCo phase was formed by interaction between Mg and Co. At the highest processing temperature of 500°C, a solid-state interaction of MgCo and Co resulted in the recovery of the initial MgCo_2.The interaction of MgNiCo with deuterium under the synthesis conditions of 2.8 GPa and 200 °C proceeded in a more complex way. A very stable ternary deuteride MgNi_2D_3 was leached away while Co was separated in the form of Mg_2CoD_5 and the remaining nickel formed a solid solution with Co with the approximate composition Ni_(0.7)Co_(0.3).The thermal desorption of deuterium from MgCo_2D_(2.5) and from MgNiCoD_(2.5) has been studied by Thermal Desorption Spectroscopy with deuterium released into a closed volume. The observed effects nicely correlate with changes in the phase structural composition of the hydrides formed.MgCo_2 is a new example of the hydrogen storage alloy, in which a successful HDDR processing results in the reversible formation of the initial intermetallic at much lower temperatures than in the equilibrium phase diagram of the Mg-Co system.     

Mechanical and wear properties of Al-Al3Mg2 nanocomposites prepared by mechanical milling and hot pressing

β-Al₃Mg₂ intermetallic was used as a reinforcing agent to improve the mechanical properties of an aluminum matrix. Different amounts of Al₃Mg₂ nanoparticles (ranging from 0wt% to 20wt%) were milled with aluminum powders in a planetary ball mill for 10 h. Consolidation was conducted by uniaxial pressing at 400°C under a pressure of 600 MPa for 2 h. Microstructural characterization confirms the uniform distribution of Al₃Mg₂ nanoparticles within the matrix. The effects of nano-sized Al₃Mg₂ content on the wear and mechanical properties of the composites were also investigated. The results show that as the Al₃Mg₂ content increases to higher levels, the hardness, compressive strength, and wear resistance of the nanocomposites increase significantly, whereas the relative density and ductility decrease. Scanning electron microscopy (SEM) analysis of worn surfaces reveals that a transition in wear mechanisms occurs from delamination to abrasive wear by the addition of Al₃Mg₂ nanoparticles to the matrix.     

Highly effective La-deficient La_(1-x)Ce_xMnO_3 mixed oxides for the complete oxidation of methane

La-deficient La_(1-x)Ce_xMnO_3 mixed oxides, obtained by selective dissolution in 1 M nitric acid, were employed in methane complete oxidation. The majority of the La cations in these perovskites were removed, resulting in increased specific surface areas, better reducibility and greater activity. Incorporation of a small amount of Ce stabilized the structure and a perovskite phase persisted in La-deficient La_(1-x)Ce_xMnO_3 mixed oxides after 12 h of acid dissolution. La_(0.95)Ce_(0.05)MnO_3 after the acid treatment exhibited satisfactory catalytic activity, with T50 and T90 values of 365 and 459℃, respectively, which was even comparable to that previously reported 1% Pd/Al_2O_3 catalysts. And it showed excellent long-term activity even in the presence of CO_2 and H_2O.     

Dissolution characteristics of sericite in chalcopyrite bioleaching and its effect on copper extraction

The effects of sericite particle size, rotation speed, and leaching temperature on sericite dissolution and copper extraction in a chalcopyrite bioleaching system were examined. Finer particles, appropriate temperature and rotation speed for Acidithiobacillus ferrooxidans resulted in a higher Al3+ dissolution concentration. The Al3+ dissolution concentration reached its highest concentration of 38.66 mg/L after 48-d leaching when the sericite particle size, temperature, and rotation speed were -43 μm, 30℃, and 160 r/min, respectively. Meanwhile, the sericite particle size, rotation speed, and temperature can affect copper extraction. The copper extraction rate is higher when the sericite particle size is finer. An appropriately high temperature is favorable for copper leaching. The dissolution of sericite fitted the shrinking core model, 1-(2/3)α-(1-α)2/3=k₁t, which indicates that internal diffusion is the decision step controlling the overall reaction rate in the leaching process. Scanning electron microscopy analysis showed small precipitates covered on the surface of sericite after leaching, which increased the diffusion resistance of the leaching solution and dissolved ions.     

Effects of aging treatment on the microstructure and superelasticity of columnar-grained Cu<Subscript>71</Subscript>Al<Subscript>18</Subscript>Mn<Subscript>11</Subscript> shape memory alloy

The effect of aging treatment on the superelasticity and martensitic transformation critical stress in columnar-grained Cu₇₁Al₁₈Mn₁₁ shape memory alloy (SMA) at the temperature ranging from 250°C to 400°C was investigated. The microstructure evolution during the aging treatment was characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results show that the plate-like bainite precipitates distribute homogeneously within austenitic grains and at grain boundaries. The volume fraction of bainite increases with the increase in aging temperature and aging time, which substantially improves the martensitic transformation critical stress of the alloy, whereas the bainite only slightly affects the superelasticity. This behavior is attributed to a coherent relationship between the bainite and the austenite, as well as to the bainite and the martensite exhibiting the same crystal structure. The variations of the martensitic transformation critical stress and the superelasticity of columnar-grained Cu₇₁Al₁₈Mn₁₁ SMA with aging temperature and aging time are described by the Austin–Rickett equation, where the activation energy of bainite precipitation is 77.2 kJ·mol?1. Finally, a columnar-grained Cu₇₁Al₁₈Mn₁₁ SMA with both excellent superelasticity (5%–9%) and high martensitic transformation critical stress (443–677 MPa) is obtained through the application of the appropriate aging treatments.     

Preparation and catalytic effect of porous Co3O4 on the hydrogen storage properties of a Li-B-N-H system

A porous Co_3O_4 with a particle size of 1–3 μm was successfully prepared by heating Co-based metal organic frameworks MOF-74(Co) up to 500 °C in air atmospheric conditions. The as-prepared porous Co_3O_4 significantly reduced the dehydrogenation temperatures of the LiBH_4-2LiNH_2 system and improved the purity of the released hydrogen. The LiBH_4-2LiNH_2-0.05/3Co_3O_4 sample started to release hydrogen at 140 °C and released hydrogen levels of approximately 9.7 wt% at 225 °C. The end temperature for hydrogen release was lowered by 125 °C relative to that of the pristine sample. Structural analyses revealed that the as-prepared porous Co_3O_4 is in-situ reduced to metallic Co, which functions as an active catalyst, reducing the kinetic barriers and lowering the dehydrogenation temperatures of the LiBH_4-2LiNH_2 system. More importantly, the porous Co_3O_4-containing sample exhibited partially improved reversibility for hydrogen storage in the LiBH_4-2LiNH_2 system.     

Minor-alloyed Cu-Ni-Si alloys with high hardness and electric conductivity designed by a cluster formula approach

Cu-Ni-Si alloys are widely used due to their good electrical conductivities in combination with high strength and hardness. In the present work, minor-alloying with M =(Cr, Fe, Mo, Zr) was conducted for the objective of further improving their hardness while maintaining their conductivity level. A cluster-plus-glue-atom model was introduced to design the compositions of M-alloyed Cu-Ni-Si alloys, in which an ideal composition formula[(Ni,Si,M)-Cu_(12)]Cu_3(molar proportion) was proposed. To guarantee the complete precipitation of solute elements in fine δ-Ni_2 Si precipitates, the atomic ratio of(Ni,M)/Si was set as 2/1. Thus the designed alloy series of Cu_(93.75)(Ni/Zr)_(3.75)Si_(2.08)(Cr/Fe/Mo)_(0.42)(at%) were arc-melted into ingots under argon atmosphere, and solidsolutioned at 950 ℃ for 1 h plus water quenching and then aged at 450 ℃ for different hours. The experimental results showed that these designed alloys exhibit high hardness(HV 1.7 GPa) and good electrical conductivities(≥ 35% IACS). Specifically, the quinary Cu_(93.75)Ni_(3.54)Si_(2.08)(Cr/Fe)_(0.42)Zr_(0.21) alloys(Cu-3.32 Ni-0.93 Si-0.37(Cr/Fe)-0.30 Zr wt%) possess both a high hardness with HV = 2.5-2.7 GPa, comparable to the highstrength KLFA85 alloy(Cu-3.2 Ni-0.7 Si-1.1 Zn wt%,HV= 2.548 GPa),and a good electrical conductivity(35-36% IACS).