Ti_2AlC/TiAl(Nb)复合材料热变形能力

采用Gleeble3500热模拟试验机对Ti2AlC/TiAl(Nb)复合材料进行高温压缩实验,实验温度范围为1000℃～1150℃,应变速率范围为10-3s-1～10-1s-1,工程压缩应变为50%,得到复合材料高温压缩真应力-真应变曲线。结果表明,Ti2AlC/TiAl(Nb)复合材料的高温变形流变应力对温度及应变速率敏感;流变应力随应变速率的增大而增大,随温度的升高而减小,可用位错-颗粒交互作用模型解释复合材料的应力-应变行为;Zenner-Hollomon参数的指数函数能够较好的描述该合金高温变形时的流变应力行为。建立的本构方程为ε=9.31×1011[sinh(0.0044σ)]2.52exp[-366.2/(RT)],其变形激活能为366.2kJ/mol。     

热压缩7075铝合金流变应力特征

采用Gleeble-1500热模拟高温压缩变形试验,研究了7075铝合金高温塑性变形时的流变应力行为.结果表明,应变速率和变形温度的变化影响合金稳态流变应力的大小,在变形温度为350～500℃、应变速率为0.01～1 s^-1的条件下,随变形温度升高,流变应力降低;而随应变速率提高,流变应力增大;应变速率和流变应力之间满足指数关系,温度和流变应力之间满足Arrhenius关系,可用Zener-Hollomon参数描述7075铝合金高温塑性变形时的流变应力行为.     

碳化硼-铝硅复合材料的热压缩流变应力研究

采用Gleeble-1500D热模拟机高温等温压缩试验,研究了新型反应堆中子吸收材料-碳化硼-铝硅复合材料在应变速率为0.1～10s-1、变形温度为300～500℃条件下的流变应力特征.结果表明:该材料在试验条件下压缩变形时均存在稳态流变特征,应变速率和变形温度强烈影响试验材料流变应力;该流变应力随应变速率的提高而增大,随变形温度的升高而降低;采用Zener-Hollomon参数的双曲正弦函数描述该复合材料高温变形的峰值流变应力,获得峰值流变应力解析式,其热变形激活能为236.248 kJ/mol.     

Mg-Gd-Y-Zr镁合金热压缩流变应力的研究

采用恒应变速率高温压缩模拟实验，对Mg-Gd-Y-Zr镁合金在应变速率为0．001～1．0s^-1、变形温度为150～500℃条件下的流变应力行为进行了研究，计算了变形激活能及相应的应力指数，建立了峰值流变应力方程。结果表明：在恒温条件下，合金的流变应力随应变速率的增大而增大；在恒应变速率条件下，合金的流变应力随温度的升高而降低；在350-500℃，0．001～1．s^-1的变形条件下，变形激活能和应力指数分别为2215kJ／mol和368；流变应力方程计算出的峰值应力与真实值基本吻合。     

3003铝合金热变形流变应力特征

采用Gleeble-1500热模拟机进行圆柱体压缩实验．研究了3003铝合金在变形温度为300～500℃、应变速率为0．01～10s^-1、真应变为0～0．8条件下的流变应力特征。结果表明．流变应力随温度升高而降低，随应变速率的提高而增大；在应变速率小于10s^-1。时，3003铝合金首先出现加工硬化，流变应力达到峰值后单调下降，趋于平稳，表现出动态回复的特征；而在应变速率为10s^-1、变形温度在350℃以上时，合金发生了局部动态再结晶；可用Zener-Hollomon参数的双曲正弦形式来描述3003铝合金热压缩变形时的流变应力行为。     

5083铝合金的高温压缩变形行为

在Gleeble-3500热模拟实验机上采用高温压缩实验研究了5083铝合金在变形温度为300～500℃、应变速率为0.01～10 s~(-1)、真应变为0～0.9条件下的热变形行为。对高温压缩实验结果进行分析,修正了实验中由于摩擦和变形热效应引起的流变应力误差,得到5083铝合金修正后的真应力-真应变曲线。结果表明:在高温压缩实验过程中,摩擦和变形热效应产生的温升影响不能忽略,摩擦和温升引起应力变化的最大值分别为31.78、33.66 MPa;5083铝合金修正后的流变应力随变形温度的升高而降低,随应变速率提高而增大;应力峰值出现后,应力逐渐下降,且呈稳定的流变特性。     

BFe30-1-1铜合金热压缩流变应力行为

通过在Gleeble-1500动态热模拟机上进行高温等温压缩试验，研究了BFe30—1—1合金在高温塑性变形过程中的流变应力行为。试验温度为800-950℃，应变速率为0．1-20s^-1.研究结果表明：BFe30-1-1合金的流变应力随变形温度的增加而减小，随应变速率的增大而增大；应变速率越大，流变应力下降越明显；获得了采用Zener-Hollomon参数来描述的BFe30—1—1合金高温变形的流变应力方程，计算获得该合金变形激活能Q为177．62kJ／mol。     

铸造Mg-4Al-2Sn-Y-Nd镁合金的热压缩行为与加工图

利用热压缩实验研究一种新型的具有优异室温塑性的Mg-4Al-2Sn-Y-Nd镁合金的高温流变行为,变形温度为200～400℃,应变速率为1.5×10-3～7.5 s^-1。结果表明：合金的应变速率敏感因子（m）在不同变形温度下均明显小于AZ31镁合金的m值,因此该合金适合在高应变速率下进行热加工。在真应力-应变曲线基础上,建立Mg-4Al-2Sn-Y-Nd 镁合金高温变形的本构方程,并计算得到合金的应力指数为10.33,表明合金在高温下主要的变形机制为位错攀移机制。同时,利用加工图技术确定合金的最佳高温变形加工窗口,即变形温度在350～400℃之间,应变速率在0.01～0.03 s^-1。     

Ti600合金的高温本构方程

采用热模拟压缩试验研究了Ti600合金在变形温度为800～1100℃、应变速率为0．001～10s^-1范围内应力一应变曲线的变化规律。研究结果表明：Ti600高温钛合金热变形的流变应力随温度的升高和应变速率的降低而减小；随着应变的增大，合金的真应力一真应变曲线在经历了明显的加工硬化阶段后达到最大值，然后渐渐出现流变“软化”现象。以经典的双曲正弦形式的模型为基础建立了Ti600合金热变形的本构方程，同时也通过对数据回归处理确定了合金不同温度下的应力指数n、应变激活能Q等数值。     

AZ80变形镁合金高温变形流变应力分析

采用实验法研究了AZ80镁合金高温高应变速率压缩时的流变应力.结果表明,镁合金在200～400℃、应变速率为0.001～10s-1进行高温压缩的情况下,流变应力随应变速率的升高和变形温度的降低而升高,其稳态流变应力同Zencr-Hollomon参数的对数之间呈线性关系.引入Zener-Hollomon参数的指数形式来描述AZ80镁合金热压缩变形时流变应力与变形温度和应变速率之间的关系.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。