预应变对TA2纯钛板室温滞后回弹的影响

为探明室温下不同预应变对TA2钛板滞后回弹的影响,采用万能试验机进行了不同预应变的滞后回弹实验。预应变分别取自均匀塑性变形区、分散性失稳区以及集中性失稳区。拉伸变形组织采用光镜和透射电镜进行表征。结果表明,TA2钛板卸载后的滞后回弹效应明显,均匀变形区和失稳区的滞后回弹应变(TDSS)累积值随预应变的提高分别以不同的指数规律增长。组织分析表明,孪晶数量与TDSS变化规律相关;失稳区的加载历史对TDSS和弛豫饱和时间tIP产生了一定影响。     

预应变对TA2钛板室温滞后回弹的影响

为探明室温下不同预应变对TA2钛板滞后回弹的影响,采用万能试验机进行了不同预应变的滞后回弹实验。预应变分别取自均匀塑性变形区、分散性失稳区以及集中性失稳区。拉伸变形组织采用OM和TEM进行表征。结果表明,TA2钛板卸载后的滞后回弹效应明显,均匀变形区和失稳区的滞后回弹应变(TDSS)累积值随预应变的提高分别以不同的指数规律增长。组织分析表明,孪晶数量与TDSS变化规律相关;失稳区的加载历史对TDSS和弛豫饱和时间tIP产生了一定影响。     

一种基于黏弹性理论预测DP600钢板滞后回弹的新模型

通过加载不同预应变和保压时间获得了DP600钢板的室温滞后回弹响应.基于黏弹性理论,采用309 MPa恒应力室温蠕变实验,获得了预测滞后回弹过程的蠕变柔量函数.基于DP600钢板室温弹性和塑性加载响应,修正了线黏弹性本构方程的积分下限,将柔量函数与修正的应力率函数进行卷积,获得了影响滞后回弹过程的加载历史效应.再将加载历史应变波形与卸载脉冲叠加,获得不同预变形量的滞后回弹应变预测值.结果表明,滞后回弹初期应变率较高,之后应变率逐渐降低;随着预应变的增加,滞后回弹应变的绝对值逐渐递增,并且滞后回弹占总回弹比例逐渐增加;滞后回弹预测方向与瞬时回弹方向相同,与加载方向相反;相同时间段内,蠕变回弹应变比滞后回弹应变明显降低,与滞后回弹实验相比,蠕变恒应力与蠕变回弹应变的比值随预应变的变化规律呈现出良好的线性关系;基于黏弹性理论的修正模型所得到的预测值接近实验测量值,并能够较好地反映实验变化规律.     

TC4 ELI钛合金包申格效应试验研究

为研究TC4 ELI钛合金常温下循环加载的包申格效应,进行了单轴拉伸-压缩的循环加载试验,获得了TC4 ELI循环加载的应力应变曲线,并通过计算获得了表征钛合金包申格效应的参数,包括包申格应变β、包申格应力参数和包申格能量参数。试验结果表明包申格应变及包申格应力参数随预应变量增大而近似线性增加,包申格能量参数变化不大且反向屈服应力随预应变量增加而大幅降低。     

TC18钛合金相变点区域动态再结晶模型的建立

为了研究TC18钛合金在β转变点附近区域热变形过程中的动态再结晶行为以及微观组织变化规律,利用热模拟设备Gleeble 1500对TC18钛合金β转变点附近的应力-应变曲线进行了测定,并采用金相显微镜对TC18钛合金高温压缩变形后的显微组织进行观察。采用六次多项式拟合方式对TC18钛合金应力-应变曲线进行光顺,然后结合加工硬化率曲线与材料应力-应变曲线确定材料不同情况下的临界应变ε_c、峰值应变ε_p以及稳态应变ε_s,并建立基于Zener-Hollomon参数的数学模型。应用Kopp模型建立TC18钛合金在β转变点附近区域的动态再结晶体积分数模型,并根据金相分析结果建立TC18钛合金的动态再结晶晶粒尺寸模型。     

高应变率下TC4-DT钛合金的动态力学性能及塑性本构关系

为研究TC4-DT钛合金的动态力学性能及其本构关系,在1000~8000 s-1应变率范围内,利用分离式Hopkinson压杆试验装置对该材料进行动态压缩试验,得到高应变率下的真实应力-应变曲线。结果表明:高应变率时TC4-DT钛合金材料存在应变率增强、增塑以及应变强化效应,其流变应力表现出较强的应变率敏感性。通过微观组织观察,发现高应变率变形时出现绝热剪切带是材料流变应力急剧减小的主要原因。改进Johnson-Cook本构模型中的温度项,利用试验数据对TC4-DT钛合金在高应变率下的动态塑性本构关系进行拟合,得到室温下该材料的动态塑性本构方程,模型计算结果和试验结果证明该模型可以更好地预测TC4-DT钛合金高应变率下的塑性流变应力。     

热变形过程中TC21钛合金的微观组织演变

研究了TC21钛合金在不同应变速率和变形温度下的微观组织变化。结果表明,应变速率相对较低或者变形温度相对较低时,TC21钛合金才可以发生再结晶现象。     

考虑应变率效应的轻量化座钣有限元分析（英文）

室温条件下,采用Instron实验机和分离式Hopkinson压杆(SHPB)实验装置对TC4钛合金进行压缩实验,得到了不同应变率下的真应力-真应变曲线。通过对应力-应变曲线拟合分析,建立了TC4钛合金的Johnson-Cook(JC)本构模型。基于该本构模型,采用ABAQUS/Explicit对TC4钛合金高应变率下的冲击压缩实验进行了数值模拟,通过实验结果与仿真数据的对比分析,验证了该本构模型参数的合理性。为实现迫击炮轻量化的目标,设计了一种新型轻量化TC4钛合金质迫击炮座钣。通过建立冲击载荷下迫击炮座钣的有限元模型,考虑材料的应变率效应,对座钣的强度和刚度进行了分析,得到了座钣的应力和位移的变化规律。     

置氢TC16钛合金微观组织与变形行为

通过置氢处理得到不同氢含量的TC16钛合金,采用连续升温法研究了氢含量对TC16钛合金相转变温度的影响,利用光学显微镜研究了置氢TC16钛合金的微观组织,应用准静态压缩试验研究了置氢TC16钛合金的变形行为,通过磁脉冲冷镦试验研究了高应变速率下合金的变形行为。结果表明,TC16钛合金相变温度随氢含量的增加而单调递减,当氢含量达到0.30wt.%时,相变温度大约下降150℃;置氢TC16钛合金微观组织发生变化,低氢时出现了马氏体组织,高氢时主要由等轴β相组织构成;置氢TC16钛合金的应变速率敏感性增加,随着变形速率的提高,其变形性能得到改善,在高应变速率条件下压缩变形极限大于86%,通过冷镦试验制备了表面完好的托板螺母,对变形行为进行了验证。     

考虑应变率效应的新型轻量化迫击炮座钣有限元分析

室温条件下,采用INSTRON实验机和分离式Hopkinson压杆(SHPB)实验装置对TC4钛合金进行压缩实验,得到了不同应变率下的真应力-真应变曲线。通过对应力-应变曲线拟合分析,建立了TC4钛合金的Johnson-Cook(JC)本构模型。基于该本构模型,采用ABAQUS对TC4钛合金高应变率下的冲击压缩实验进行了数值模拟,通过实验结果与仿真数据的对比分析,验证了该本构模型参数的正确性。为实现迫击炮轻量化的目标,设计了一种新型轻量化钛合金质迫击炮座钣。通过建立冲击载荷下迫击炮座钣的有限元模型,考虑材料的应变率效应,对座钣的强度和刚度进行了分析,得到了座钣的应力和位移的变化规律。本文的研究结果为迫击炮座钣及其它装备结构的轻量化设计与开发提供了借鉴。     

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。