Influences of composition and annealing on the martensitic transformation in Ni-Fe-Ga alloys

A series of Ni-Fe-Ga alloys near the prototype Heusler composition (X₂YZ) were prepared through arc-melting suction-casting method. The dependences of the transformation behavior on the alloy composition and annealing treatment were studied in detail by an optical microscope, X-ray diffraction, and differential scanning calorimeters methods. The experimental results show that the martensitic transformation temperatures increase almost linearly with increasing Ni content in all the NiFeGa alloys. Annealing the Ni_55.5Fe₁₈Ga_26.5 alloy at 100?C500 °C for 3 h and at 300 °C for 1?C10 h shifts the martensitic transformation start temperature by almost 20 °C to high temperature. The variations in the martensitic transformation temperatures in these alloys are discussed in terms of structural differences resulting from alloy composition and annealing treatment.     

Effect of homogenization treatment on microstrucmre and properties of Al-Mg-Mn-Sc-Zr alloy

The effect of homogenization on the hardness, tensile properties, electrical conductivity and microstructure of as-cast Al-6Mg-0.4Mn-0.25Sc-0.12Zr alloy was studied. The results show that during homogenization as-cast studied alloy has obviously hardening effect that is similar to aging hardening behavior in traditional Al alloys. The precipitates are mainly Al3（Sc,Zr） and Al6Mn When homogenization temperature increases the hardness peak value is declined and the time corresponding to hardness peak value is shortened. The electrical conductivity of the alloy monotonously increases with increasing homogenization temperature and time. The decomposition of the supersaturated solid solution containing Sc and Zr which is formed during direct chilling casting and the precipitation of Al3（Sc, Zr） cause hardness increasing. The depletion of the matrix solid solubility decreases the ability of electron scattering in the alloy, resulting in the electrical conductivity increased. Tensile property result at hot rolling state shows that the optimal homogenization treatment processing is holding at 300-350℃ for 6-8 h.     

Mechanical properties and microstructure evolution of cold-deformed high-nitrogen nickelfree austenitic stainless steel during annealing

The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 ℃ to 650 ℃ for 90 min and at 550 ℃ for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope (TEM). The steel was strengthened when it got annealed at temperatures ranging from 100 ℃ to 550 ℃, while it was softened when it got annealed at temperatures ranging from 550 ℃ to 650 ℃. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 ℃ for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 ℃ for 90 min, and its scale increased with annealing temperature. Nano-sized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed.     

退火处理对Ti-Zr-Cu-Be块体非晶合金力学性能的影响

采用铜模铸造法制备了直径为2mm的Ti55-xZr10+xBe27.5Cu7.5(x=0,10,20)块体非晶合金,并对其进行等温退火处理.利用X射线衍射(XRD)、扫描电镜(SEM)、差氏扫描量热仪(DSC)及压缩试验等方法研究了非晶合金的相结构、显微组织和热稳定性,以及退火处理对其力学性能的影响.结果表明:该系列合金在553 K及583 K下保温长达5 h时间内依然表现为非晶态.退火处理后,Ti35Zr30Be27.5Cu7.5合金屈服强度、断裂强度均提到了提高,其中在583 K下保温1 h后屈服强度、断裂强度分别达到了1 921、2 169 MPa;其塑性由处理前的3.47%提高到了6.57%.Ti45Zr20Be27.5Cu7.5合金在退火后其力学性能变化不明显.Ti55Zr10Be27.5Cu7.5合金随着退火温度及保温时间的增加其屈服强度、断裂强度及塑性均明显降低.     

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.     

多主元AlFeCuCoNiCrTi1.5合金的研究

多主元高熵合金是一种新型的合金,具有许多优越的性能。通过电弧熔炼法制备了AlFeCuCoNiCrTi1.5高熵合金,并在不同温度下进行退火处理,利用XRD、SEM以及洛氏硬度仪分析了它在不同的退火温度处理后的组织及硬度变化,结果表明随着退火温度的逐渐升高,该合金中的相除了长大其组织结构保持不变,但是其硬度值会越来越高,到了1000℃甚至达到了61.5HRC。另外,利用阳极极化法测试了铸态下AlFeCuCoNiCrTi1.5高熵合金在0.5MH2SO4溶液和1MNaCl溶液中的电化学性能,极化曲线表明,在0.5MH2SO4溶液中的,与304不锈钢相比,该合金具有较低的腐蚀速率;在1MNaCl溶液,该合金的腐蚀速率与304不锈钢相当,但是其耐点蚀的能力要优于304不锈钢。     

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.     

Characterization and Electrochemical Properties of LiMn2O4 Thin Films Prepared by Solution Deposition

1 IntroductionThin-filmlithium-ion batteries have attracted greatattention of researchfor possible use inimplantable medi-cal devices , CMOS-based integrated circuits ,radio fre-quency (RF) identification tags for inventory control andanti-theft protection[1],etc. Li Mn2O4thin films , aspromising cathode materials for thin-filmlithium-ion bat-teries, have been prepared by a few methods such aspulsedlaser deposition[2 ,3],electrospraying[4-9],RF mag-netron sputtering[10], laser ablation[11]…     

Effect of air annealing on the optical electrical and structural properties of In2S3 films

The effect of the annealing temperature T _a on the optical, electrical and structural properties of the In₂S₃ films obtained by the spray pyrolysis method at 350°C substrate temperature was studied. All the In₂S₃ films annealed in the range from 100 to 400°C are polycrystalline with (220) preferential orientation. The resistivity decreases as T _a increases until it reaches a value of 25 Ohm-cm for T _a=400°C. The grain size also increases when T _a increases as observed in data calculated from X-ray measurements. XRD data indicates that samples show microstructural perfection improvement as a function of annealing temperature.     

Influence of annealing on the structure of silica glass

Two types of high-purity synthetic silica glasses were annealed with different processes in precision annealing furnace. The thermal stress and structure of samples were analyzed by two types of stress instruments and Fourier transform infrared spectrometer. After being annealed at 1 070 °C for 6 days and then cooled slowly, optical path difference (OPD) caused by stress in the center and edge of Type III silica glass with a diameter of 150 mm and thickness of 50 mm decreased from 6 to 2 nm/cm. Meanwhile, with the same annealing process, fictive temperature of small-size Type III glass decreased to 939 °C, and structural stability of silica glass was improved. In addition, after being annealed at 1 100 °C for 5 hours and then cooled slowly, internal stress in Type IV silica glass with a thickness of 1 mm was basically eliminated, and its fictive temperature decreased from 1 421 to 966 °C.     

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.     

Mg-Gd-Er-Zn稀土变形镁合金的微观组织与力学性能

为研究Mg-Gd-Er-Zn稀土变形镁合金微观组织与力学性能,通过金属模铸造、固溶处理、热挤压和时效处理工艺过程,制备了Mg-Gd-Er-Zn稀土变形镁合金,并利用金相显微镜(optical microscopy,OM)、X射线衍射仪(Xray diffraction,XRD)、扫描电镜(scanning electron microscopy,SEM)及透射电镜(transmission electron microscopy,TEM)等手段进行表征.结果表明:Mg-Gd-Er-Zn合金的铸态组织主要由α-Mg基体和沿晶界分布的(Mg,Zn)3Gd第2相组成,固溶后生成层片状的长周期堆垛有序(long period stacking ordered,LPSO)结构;经过热挤压变形,合金的晶粒得到显著细化;时效处理过程中,合金中析出纳米级尺寸的β'相.最终时效态合金的室温抗拉强度、屈服强度和伸长率可分别达397.5 MPa、359.0 MPa和6.0%.     

Effect of ECAP on the microstructure and mechanical properties of a high-Mg<Subscript>2</Subscript>Si content Al-Mg-Si alloy

A high-Mg₂Si content Al alloy was extruded by equal channel angular pressing (ECAP) for 8 passes at 250 °C and an ultrafine-grained structure with an average grain size of about 1.5 μm was achieved. The coarse skeleton-shaped Mg₂Si phase presenting in the as-cast alloy are significantly fragmented into fine rod-shaped as well as equiaxed particles mostly less than about 230 nm and become relatively dispersed. The tensile strength 192.8 MPa and the elongation up to 31.3% at ambient temperature are attained in the 8-pass ECAPed alloy versus 163.3 MPa and 9.1% in the as-cast alloy. High-temperature creep test at 250 °C reveals that the ECAPed sample exhibits a high elongation close to 100% at a relatively high creep rate 7.64×10⁻⁵ s⁻¹, compared to the elongation 56% at a low strain rate 1.74×10⁻⁷ s⁻¹ in the as-cast alloy.     

Preparation and characterization of nanocomposite MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

Nanocomposites MgFe₂O₄/SiO₂ were successfully synthesized by the sol-gel method in the presence of N, N-dimethylformamide (DMF). The formation of pure MgFe₂O₄ was confirmed by powder X-ray diffraction (XRD) and electron diffraction. The structural evolution of MgFe₂O₄ nanocrystals was followed by powder X-ray diffraction and IR absorption spectroscopy. The formation of spinel structure of MgFe₂O₄ started at 800 °C, and completed at 900 °C. The transmission electron microscopy (TEM) measurements suggest that the particle sizes increase with the increasing annealing temperature, and the mean particle sizes of the spherical samples annealed at 800 °C, 900 °C and 1 050 °C are ca. 3 nm, 8 nm and 11 nm, respectively. Magnetization measurements at room temperature and 78 K indicate superparamagnetic nature of these MgFe₂O₄ nanocrystals. Funded by the National Natural Science Foundation of China(No. 30771676), the Natural Science Foundation of Jiangsu Province (No. BK20081842), and the Foundation of Nanjing Bureau of Personal for the Returned Overseas Chinese Excellent Scholars     

Fracture toughness of multiphase TiAl-Nb alloy in situ consolidated by spark plasma sintering

A fine-grained TiAl alloy with a composition of Ti-45Al-5Nb-1.5Cr-0.2W (mole fraction, %) with multiphases was prepared by spark plasma sintering (SPS) and heat-treating at 1 100 °C for 48 h. The relationship among sintering temperature, microstructure and fracture toughness were investigated by X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and mechanical testing. The results show that microstructure of the bulk alloy depends on the sintering temperature strongly, and the main phase TiAl and few phases Ti₃Al and niobium solid solution (Nbss) are observed in the SPS bulk samples. In the heat-treatment condition, the lamellar and Nbss phase can provide significant toughening by plastic strengthening, interface decohension, crack branch and crack bridge mechanisms. The fracture mode of the SPS TiAl composite samples is intergranular rupture and cleavage fracture.     

Preparation of TiO<Subscript>2</Subscript> thin film by the LPD method on functionalized organic self-assembled monolayers

In this paper, uniform titania (TiO₂) films have been formed at 50° on silanol SAMs by the liquid-phase deposition (LPD) method at a temperature below 100°C. OTS (Octadecyltrichloro-Silane) self-assembled monolayers (SAMs) on glass wafers were used as substrates for the deposition of titanium dioxide thin films. This functionalized organic surface has shown to be effective for promoting the growth of films from titanic aqueous solutions by the LPD method at a low temperature below 100°C. The crystal phase composition, microstructure and topography of the as-prepared films were characterized by various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results indicate that the as-prepared thin films are purely crystallized anatase TiO₂ constituted by nanorods after being annealed at 500°. The pH values, concentration of reactants, and deposition temperatures play important roles in the growth of TiO₂ thin films. Support by the National Natural Science Foundation of China (Grant No. 50672055) and National Key Technology R&D Program (Grant No. 2006BAF02A28)     

Al-induced Lateral Crystallization of Amorphous Si Thin Films by Microwave Annealing

Al-induced lateral crystallization of amorphous silicon thin films by micr owave annealing is investigated,The erystallized Si films are examined by optical microscopy,Raman spectroscopy ,transimission electron microscopy and transmission electron diffraction micrography.After microwave annealing at 480 ℃ for 50min the amorphous Si is completely cystallized with lagrge grains of main (111) orientation,The rate of lateral crystallization is 0.04μm/min,This process,labeled MILC-MA ,not only lowers the temperature but also reduces the time of crystallization.The crystallization.mechanism during microwave annealing and the electrical properies of polycrystalline Si thin films are analyzed.This MILC-MA process has potentila application in large area electronics.     

Microstructure and RRA treatment of LFEC 7075 aluminum alloy extruded bars

The microstructures after casting and extruding, the mechanical properties and electrical conductivity after RRA treatment of conventional DC casting and low frequency electromagnetic casting (LFEC) 7075 aluminum alloy were investigated. The results showed that finer grains which distributed more homogeneously was obtained in LFEC ingots compared with those conventional DC ingots. The extruded bars of LFEC alloy kept its fine grain features of original as-cast structure. In the RRA treatment, with the extension of second aging time, the tensile strength and hardness of alloy decreased, but the electrical conductivity increased. Meanwhile, as the second aging temperature raised, the phase change rate in precipitation also increased. Under the same conditions, extruded bars of LFEC alloy had better performance than that of conventional DC cast alloy. The optimum RRA heat treatment process was 120 ℃/24 h+180 ℃/30 min+120 ℃/24 h. The LFEC extruded bars acquired tensile strength 676.64 MPa, hardness 198.18, and electrical conductivity 35.7% IACS respectively, which were higher than that in the T6 temper, indicating that a notable RRA response takes place in LFEC extruded bars, whose second-step retrogression time was 30 min, and it was suitable for mass production.     

A high-fe aluminum matrix welding filler metal for hardfacing aluminum-silicon alloys

A high-Fe containing aluminum matrix filler metal for hardfacing aluminum-silicon alloys has been dmeloped by using iron, nickel, and silicon as the major strengthening elements, and by measwing mechanical properties, room temperature and high temperature wear tests, and microstructural analysis. The filler metal,which contains 3.0% - 5.0% Fe and 11.0% - 13.0% Si, exhibits an excellent weldability. The as-cast and as-welded microstructures for the filler metal are of uniformly distribution and its dispersed network of hard phase is enriched with Al-Si-Fe-Ni. The filler metal shows high mechanical properties and wear resistance at both room temperature and high temperatures. The deposited metal has a better resistance to impact wear at 220℃ than that of substrate Al-Si-Mg-Cu piston alloy; at room temperature, the deposited metal has an equivalent resistance to slide wear with lubrication as that of a hyper-eutectic aluminmn-silicon allot with 27% Si and 1% Ni.     

Surface nanocrystallization of magnesium alloy AZ91D by high-energy shot peening

High-energy shot peening (HESP), a method to produce severe plastic deformation by high velocity flying balls, was applied on die cast magnesium alloy AZ91D. Effects of surface nanocrystallization by HESP and heat treatment at different temperatures were investigated. The microstructure evolution was conducted using X-ray diffraction (XRD) and field emission scanning electronic microscopy (FESEM). The hardness was measured by microhardness tester. The experimental results show that surface nanocrystrallization of AZ91D obtained by HESP would lead to the increase of microhardness. Low temperature heated at 100 °C for 1 h do not change the property obviously. However, both the microstructure and microhardness vary greatly after heat treatment at 400 °C for 1 h. Funded by the National Ministry of Education (No.207095) and Beijing Key Laboratory for Corrosion Erosion and Surface Technology