Effects of annealing on microstructure, mechanical and electrical properties of AlCrCuFeMnTi high entropy alloy

The multi-component A1CrCuFeMnTi high entropy alloy was prepared using a vacuum arc melting process. Serial annealing processes were subsequently performed at 590 ℃, 750 ℃, 955 ℃ and 1 100 ℃ respectively with a holding time of 4 h at each temperature. The effects of annealing on microstructure, mechanical and electrical properties of as-cast alloy were investigated by using differential thermal analysis （DTA）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results show that two C14 hexagonal structures remain unchanged after annealing the as-cast A1CrCuFeMnTi alloy specimens being heated to 1 100℃. Both annealed and as-cast microstructures show typical cast-dendrite morphology and similar elemental segregation. The hardness of alloys declines as the annealing temperature increases while the strength of as-cast alloy improves obviously by the annealing treatment. The electrical conductivities of annealed and as-cast alloys are influenced by the distribution of interdendrite re~ions which is rich in Cu element.     

Tensile and compression properties of Zr-based bulk amorphous alloy at different temperatures

Since the discovery of the Au-Si metallic amorphous alloy ribbon in 1960 by Duwez and co-workers[1] by rapid quenching, rapid developments have been obtained on the preparation of the amorphous alloy with the rapid quenching technique. However, from 1960 to 1989, the amorphous alloy could be only produced into forms of ribbon, flake, wire and powder due to the limitation of the cooling rate (>105 K/s). In the late 1980s, the Inoue group at Tohoku University in Sendai, Japan, investigated th…     

Effect of low temperature aging on microstructure and mechanical properties of super-high strength aluminum alloy

The effects of heat treatment on the microstructure and mechanical properties of two alloys, namely Al- 12.2%Zn-2.48%Cu-2.0%Mg-0.15%Zr-0. 166%Ag（alloy 1）, and Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr（alloy 2） were investigated. The results show that low temperature aging after promotive solution treatment can increase elongation without the loss of strength for the studied alloys. The optimum aging treatment （T6） for alloy 1 and alloy 2 is 100 ℃/80 h and 100 ℃/48 h, respectively. Compared with other heat treatment alloys, alloy 1 and alloy 2 show super-high tensile strength up to 753 MPa and 788 MPa, remaining 9.3% and 9.7% elongation under T6 condition, respectively. During aging, trace addition of Ag enhances the formations of GP zone and metastable phase, and stabilizes GP zone and metastable phase to a higher temperature. Trace addition of Ag prolongs the aging time of reaching the peak strength and delays over-aging condition of the alloy. However, trace addition of Ag promotes the formation of coarse constituent in the alloy and consumes hardening alloying elements of Zn and Mg. Moreover, the addition of the transition element Zr in 7000 series super-high alloy forms incoherent Al3 Zr dispersoid which can serve as nucleation sites for nonuniform precipitation of η phase during aging process. The higher the aging temperature, the greater the tendency for nonuniform precipitation of η phase.     

Effect of annealing on microstructure and properties of Si_3N_4-AlN composite ceramics

Aiming at developing novel microwave-transparent ceramics with low dielectric loss,high thermal conductivity and high strength,Si3N4-AlN(30%,mass fraction) composite ceramics with La2O3 as sintering additive were prepared by hot-pressing at 1 800 °C and subsequently annealed at 1 450 °C and 1 850 °C for 2 h and 4 h,respectively.The materials were characterized by XRD and SEM.The effect of annealing process on the phase composition,sintering performance,microstructure,bending strength,dielectric loss and the...     

Effects of Annealing Process on Crystallization and Low Temperature Resistance Properties of PP-R Composites

The effects of the annealing process on the mechanical properties and crystallization behaviors of polypropylene random copolymer(PP-R) composites were investigated using differential scanning calorimetry(DSC), wide-angle X-ray diffraction(WAXD), and dynamic mechanical analysis(DMA), and scanning electron microscopy(SEM). The experimental results indicated that the annealing process significantly influenced the comprehensive properties of PP-R composites. At temperatures below 23 ℃, the impact strength of the PP-R composites annealed at 120 ℃ for 6 h was relatively high at 74.73 k J/m~2, which was 16.8% higher than that of the samples annealed at 80 ℃ for 6 h. At low temperatures(-30-0 ℃), the impact strength ranged from approximately 13.31 k J/m~2 to 54.4 k J/m~2. In addition, the annealing process conducted at 120 ℃ for 6 h improved the crystalline structure and low-temperature toughness of the PP-R composites and induced α-form to β-form crystal transformation. The work provides a possible method to reinforce and toughen the semicrystalline polymer at low temperatures(-30-0 ℃) by annealing.     

Microstructure and flow stress of Mg-12Gd-3Y-0.5Zr magnesium alloy

The microstructure and flow stress of the Mg-12Gd-3Y-0.5Zr magnesium alloy was investigated by compression test at temperatures ranging from 350 to 500 ℃ and the strain rates ranging from 0.01 to 20 s-1. The flow stress of the magnesium alloy increased with strain rate and decreased with deformation temperature. Flow stress can be expressed in terms of the Zener-Hollomon parameter Z, which describes the combined influence of the strain rate and temperature using an Arrhenius function.The values of the deformation activation energy were estimated to be 245.9 and 171.5 kJ/mol at deformation temperatures below 400 ℃ and above 400 ℃, respectively. Two constitutive equations were developed to quantify the effect of the deformation conditions on the flow stress of the magnesium alloy. The effects of deformation temperature and strain rate on the microstructure of the magnesium alloy were also examined and quantified by measuring the volume fraction of dynamically recrystallized grain Xd. Xd increased with increasing of deformation temperature. When the deformation temperature was below 475 ℃, Xd decreased with strain rate until it reached 0.15 s-1, then it increased again. When the deformation temperature was above 475 ℃, Xd increased with strain rate.     

Study on BaTiO<Subscript>3</Subscript> films prepared by AC power microarc oxidation

BaTiO₃ films were prepared by microarc oxidation (MAO) with an in-house built alternating current (AC) power supply in Ba(OH)₂ solution in this study. The surface morphology, combinability with the substrate and phase composition of the films were investigated by XRD, SEM and TEM. The BaTiO₃ films were annealed at a temperature range of 900 to 1200°C and phase compositions were tested thereafter. The results showed that the BaTiO₃ films were mainly composed of the primitive hexagonal phase with relatively small amount of tetragonal and amorphous phases. Moreover, the amount of amorphous phase decreased with the time of annealing. The transformation of BaTiO₃ from hexagonal structure to tetragonal stucture became obvious until the annealing temperature reached 1200°C. The film consisted mainly of BaTiO₃ tetragonal structure with ferroelectric property. The influence of annealing on surface morphology and mechanism of phase transformation of the films were also discussed. Supported by Guangdong Natural Science Foundation (Grant No. 0500649)     

Martensitic transformation fcc(γ)→hcp(ε)

Criteria of the thermoelastic martensitic transformation are suggested, on the basis of which the martensitic transformation fcc(γ)→hcp(ε) in Fe-Mn-Si based alloys is classified as a semi-thermoelastic transformation In contrast with the martensitic transformation fcc(γ)→bct(bcc)α' in iron-based alloys, the thermoelastic transformation in Cu-based alloys and the t→m transformation in ceramics containing ZrO2, in γ→ε of Fe-Mn-Si, the strengthening and grain size of the parent phase will not markedly affecl the Ms and the internal friction peak indicating the martensitic Transformation does not correspond to a significant lowering of the elastic modulus, implying that the nucleation of ε-martensite may occur directly through the stacking fault and may not strongly depend on soft mode. A comparison between the thermal and stress induced ε martensites is made and a brief discussion is given.     

Microstructure and mechanical properties of Al-Zn-Cu-Mg-Sc-Zr alloy after retrogression and re-aging treatments

The mechanical properties and stress corrosion cracking (SCC) resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstructure and mechanical properties on aging parameters was evaluated by tensile test, hardness test and conductivity measurement. The results show that for the alloys with retrogression and re-aging treatment (RRA), the conductivity increases with the retrogression time and temperature, while the tensile strength decreases. The transmission electron microscopy (TEM) results show that the precipitates η(MgZn₂) at grain boundary aggregate apparently with retrogression time and the precipitates inside the matrix exhibit the similar distribution to T6 temper, which comprises fine GP zones, large η′(MgZn₂) and η(MgZn₂) phases. According to the mechanical properties and microstructure observations, the optimal RRA regime is recommended to be 120 °C, 24 h + 180 °C, 30 min + 120 °C, 24 h. The strength level of the alloy after the optimum RRA treatment is similar to that in T6 condition and the SCC resistance is improved obviously in contrast to T6 condition.     

Microstructures and optical properties of solgel derived Ba0.9Sr0.1TiO3 thin films formed by different annealing process

We investigated the effect of annealing process on microstructures and optical properties of the sol-gel derived Ba_0.9Sr_0.1TiO₃ (BST) films. The BST films, fabricated by layer-by-layer high-temperature (? 650 °C) annealing process, had laminated structures consisting of alternating dense and porous BST layers, and exhibited excellent optical performance as Bragg reflectors. The Bragg reflection characteristic can be enhanced with increasing annealing temperature. Those BST films fabricated at temperatures lower than 650°C displayed uniform cross-sectional morphologies even treated at a higher temperature. The difference in the microstructures of the BST thin films was also discussed.     

The stamping formability of AZ31 magnesium alloy sheet improved by equal-channel angular pressing

Equal channel angular pressing (ECAP) processing and annealing were applied to the AZ31 magnesium alloy sheets to evaluate the potential improvement in the mechanical properties and formability. The ECAP experiment was conducted at 300 °C in a die having an included angle of 90° between two channels by the B_CZ route with the sheets rotated by 90° about the normal axis of plate plane. The tensile tests and conical cup tests were conducted at various temperatures from 20 to 250 °C. The experimental results indicated that improving the working temperatures could lead to the soft in the material and the enhancement of ductility. Comparatively, the ECAPed AZ31 alloy sheets showed the lower yield strength and smaller conical cup value (CCV) than the unECAPed counterpart in the room temperature. The difference in yield strength between them became small in the elevated temperature, but the ECAPed samples still had the smaller CCV value, implying the improved formability. The texture of the AZ31 alloy sheets could be modified by ECAP and the decrease in the yield strength and more uniform deformation realized in the material, so the formability of AZ31 alloy sheets was improved.     

Influence of annealing temperature on the properties of TiO2 films annealed by ex situ and in situ TEM

TiO₂ thin films were deposited on quartz substrates by DC reactive magnetron sputtering of a pure Ti target in Ar/O₂ plasma at room temperature. The TiO₂ films were annealed at different temperatures ranging from 300 to 800 °C in a tube furnace under flowing oxygen gas for half an hour each. The effect of annealing temperatures on the structure, optical properties, and morphologies were presented and discussed by using X-ray diffraction, optical absorption spectrum, and atomic force microscope. The films show the presence of diffraction peaks from the (101), (004), (200) and (105) lattice planes of the anatase TiO₂ lattice. The direct band gap of the annealed films decreases with the increase of annealing temperature. While, the roughness of the films increases with the increases of annealing temperature, and some significant roughness changes of the TiO₂ film surfaces were observed after the annealing temperature reached 800 °C. Moreover, the influences of annealing on the microstructures of the TiO₂ film were investigated also by in situ observation in transmission electron microscope.     

Microstructure,martensitic transformation and shape memory effect of polycrystalline Cu-Al-Mn-Fe alloys

In this study, two Cu-Al-Mn-Fe polycrystalline alloys were prepared, and their microstructure, reversible martensitic transformation, mechanical properties and shape memory effects were investigated. The results show that the reversible martensitic transformation temperatures of the studied alloys are between room temperature and 373 K, which are suitable for practical applications. Two typed martensites of 18R and 2H coexist both in two alloys. The bcc β(FeAl) nanoparticles are Fe-rich, Mnrich and Cu-poor, whereas the martensite is Cu-rich, Fe-poor and Mn-poor. The size of nanoparticles ranges from tens to hundreds of nanometers. Full shape recovery property is displayed in Cu-12.9Al-4.5Mn-2.6Fe alloy all the time while applying different deformation from 5% to 8%. The maximum recoverable strain is up to 4.4% with a recovery rate of 100%.     

Microstructural features and properties of high-hardness and heat-resistant dispersion strengthened copper by reaction milling

The oxide dispersion strengthened copper alloys are attractive due to their excellent combination of thermal and electrical conductivities,high-temperature strength and microstructure stability.To date,the state-of-art to fabrication of them was the internal oxidation (IO) process.In this paper,alumina dispersion strengthened copper (ADSC) powders of nominal composition of Cu-2.5 vol%Al2O3 were produced by reaction milling (RM) process which was an in-situ gas-solid reaction process.The bulk ADSC alloys for electrical and mechanical properties investigation were obtained by sintering and thereafter hot extrusion.After the hot consolidation processes,the fully densified powder compacts can be obtained.The single γ-Al2O3 phase and profile broaden effects are evident in accordance with the results of X-ray diffraction (XRD);the HRB hardness of the ADSC can be as high as 95;the outcomes should be attributed to the pinning effect of nano γ-Al2O3 on dislocations and grain boundaries in the copper matrix.The electrical conductivity of the ADSC alloy is 55%IACS (International Annealing Copper Standard).The room temperature hardness of the hot consolidated material was approximately maintained after annealing for 1 h at 900 ℃ in hydrogen atmosphere.In terms of the above merits,the RM process to fabricating ADSC alloys is a promising method to improve heat resistance,hardness,electrical conductivity and wear resistance properties etc.     

Influence of surface finish and annealing treatment on oxidation behavior of Ti-48Al-8Cr-2Ag alloy

The effect of surface finish and annealing treatment on the oxidation behavior of Ti-48Al-8Cr-2Ag (molar fraction, %) alloy was investigated at 900 and 1 000 °C, respectively in air. Thermal gravimetric analysis (TGA) was conducted for the characterization of oxidation kinetics. The microstructures of oxide scales were studied by scanning electron microscopy (SEM) and transmission election microscopy (TEM) techniques. Unfavorable effect of the annealing treatment on the oxidation behavior of the coating was also investigated. The results indicate that the oxidation behavior of the alloy is influenced by surface finish and annealing treatment. The oxidation rate of ground sample is lower than that of the polished alloy at 1 000 °C in air. The former forms a scale of merely Al₂O₃, and the latter forms a scale of the mixture of Al₂O₃ and TiO₂. Annealing can improve the formation of TiO₂. Foundation item: Project(2007430028) supported by the Science and Technique Foundation of Henan Educational Committee, China     

Influence of Temperature on Electrochemical Performances of Rare Earth Based Hydrogen Storage Material

1 IntroductionRare earth-based hydrogenstorage alloys ofAB5typehave beenthe most major electrode material for small-sizeNi/MHbatteries because of their high discharge capacity,superior highrate capability andfavorable ratio of pricetoperformance. But their electrochemical performances be-come worse when the alloys are applied to large-size Ni/MHbatteries of electric vehicles .Thisfact may be due tothe rising of temperature inside the large batteries causedbythe high electric current of char…     

Preparation and properties of FeZrB amorphous-nanocrystalline soft magnetic alloy

Fe₆₈Zr₂₀B₁₂ amorphous alloy was prepared by mechanical alloying(MA) method and annealed at different temperatures. Microstructures and magnetic properties of Fe₆₈Zr₂₀B₁₂ alloys as-milled and annealed at 693, 843, 943 and 993 K were studied. The raw powders(Fe, Zr, B) formed b. c. c. α-Fe solid solution at early stages of MA and then transformed into amorphous alloy. Grain size(D) of Fe₆₈Zr₂₀B₁₂ alloys increases with increasing annealing temperature and keeps at nanometer level. The specific saturation magnetization(σ _s ) increases with increasing annealing temperature from 300 K to 943 K, and then decreases with annealing temperature at 993 K because of the precipitation of Fe₃B.     

Nucleation barrier of fcc(γ)→hcp(ε) martensitic transformation in Fe-based alloys

Based on the dislocation theory and Olson's stacking fault model, a model describing the nucleation of an hcp(ε) martensite embryo at low-angle grain boundary is proposed with the influence of external stress field taken into account. The dependences of temperature (T), shear stress (τ) and dislocation density at grain boundary on the martensite nucleation in FeMnSi based alloy, as an example, are numerically simulated. It has been shown that there exist the subcritical and critical embryos during the course of ε-phase nucleation. The free energy difference between them is just the energy barrier of embryo growth. Depending on T and τ. the characteristic embryo sizes may vary in wide ranges and decreases with increasing σ and decreasing T. The energy condition of martensitic transformation at M _s and critical shear stress (τ_c) is discussed from the viewpoint of kinetics and thus the TEM observed result that stacking fault energy is not zero at M _s temperature is reasonably explained. Besides, it is predicted that the high dislocation density at grain boundary can promote the nucleation of fcc→hcp transformation in Fe-based alloys.     

Point-piezomagnetic properties of the FeCuNbSiB alloy strips

The piezomagnetic properties of rapidly quenched Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy strips were investigated in as-quenched state and after annealing for 2 h in vacuum in the temperature range of 100–300 °C. The impedance of amorphous strips increases with frequency, and sensitively decreases with stress increasing, especially in the frequency range of 10–100 MHz. The impedance increases approximately linearly with frequency below the critical frequency, but begins to decrease non-linearly with frequency above the critical frequency. The higher the point compressive stress is, the smaller the critical frequency will be. The stability of piezomagnetic properties is very excellent. The impedance of amorphous strips after annealing, especially at 300 °C, decreases very strongly. The impedance and the absolute values of the sensitive degree of couple layers’ amorphous strips are lower than those of single layer strips. Funded by the National Natural Science Foundation of China (No. 0576014)     

Effect of dy on structure and magnetic properties of CoPt alloys

The effects of Dy on the microstructure and magnetic properties of Dy _x Co_50?x Pt₅₀ alloys were investigated. The XRD results indicate that all the alloys homogenized at 1000 °C contain only a single A1 (fcc) phase, while the alloys annealed at 675 °C consist of a hard-magnetic face-centered-tetragonal (fct) phase and a magnetically soft face-centered-cube (fcc) phase. Maximum values for the coercivity H _c and remanence ratio m _r were achieved in Dy_0.4Co_49.6Pt₅₀ alloys annealed at 675 °C for 80 min. For the series of Dy _x Co_50?x Pt₅₀ alloys annealed at 675 °C for 60 min, H _c decreases monotonically with increasing Dy concentration, but m _r is first enhanced and then weakened.