基于BP神经网络的BSTMUF601高温合金蠕变本构模型（英文）

通过对BSTMUF601高温合金在1253和1368 K不同载荷下的蠕变试验研究了马弗炉管的真实服役环境下的蠕变行为。基于一种直径修正法近似获得试件的真实应力和应变,通过误差反向传播学习算法的BP神经网络方法逆向标定θ映射法模型参数,建立恒载荷条件下的θ映射蠕变本构模型。结果表明,预测结果与实验结果吻合良好,蠕变初始阶段和稳定阶段的相对最大误差为11.8%,而多元非线性回归的相对最大误差为20.9%,模型计算的表观蠕变应力指数和TEM图像都表明位错攀移是蠕变变形的主导机制,说明BP神经网络方法对BSTMUF601高温合金蠕变本构模型参数识别和预测方面的优势。     

BSTMUF601合金的高温蠕变变形机制

对BSTMUF601合金在不同温度和应力条件下进行了拉伸蠕变实验,获得了该合金的高温蠕变的变形规律,基于此提出了一种新的修正q映射法蠕变本构模型,该模型考虑了蠕变3阶段的蠕变特点.模型预测结果与实验结果吻合较好,平均相对误差为1.86%,相对于没有考虑第2阶段的θ映射法模型和没有考虑第1阶段的修正q映射法模型相对误差分别减少0.10%和6.02%,表明该模型具有较强的适用性,且不降低预测精度.对蠕变和蠕变断裂试样的位错组态和空洞演化进行了显微分析,结果表明,稳态蠕变阶段蠕变应力指数都接近5,合金主要通过位错攀移越过γ′相的方式变形,并未观察到层错和微孪晶存在于γ′相或基体中,蠕变变形机制主要是位错攀移.空洞在晶界上形核,长大连接形成裂纹,在应力集中作用下,裂纹沿晶界扩展,最终导致断裂,蠕变断裂机制主要是晶界断裂.     

基于BP神经网络的GH5188高温合金本构模型

采用Gleeble-3500热模拟试验机对GH5188高温合金试样进行热压缩试验,研究其在应变速率为0.001~0.1s^-1和变形温度在1000~1150℃时的热变形行为;建立了基于BP神经网络的本构模型,并验证了所建本构模型的可靠性,最后基于误差计算分析了BP神经网络本构模型的精度。结果表明,温度和应变速率对GH5188合金流变应力的影响明显,随着压缩温度升高和应变速率降低,GH5188合金流变应力明显减小。经定量误差计算分析,BP神经网络本构模型应力预测偏差值在10%以内的数据点占97.92%,BP神经网络模型能准确地预测GH5188高温合金的高温流变应力。     

基于BP神经网络的Ti3Al基合金本构关系模型的建立

应用THERMECMASTER-Z型热模拟试验机对Ti3Al基合金进行等温恒应变速率压缩试验,在变形温度为950～1350℃、应变速率为0.001～10s-1、最大真应变为1.2下获得流动应力数据。采用流动应力数据,并基于BP神经网络方法,建立了该合金的高温本构关系模型。结果表明,BP神经网络建立的高温本构关系模型具有很高的预测精度,可用于指导Ti3Al基合金热变形过程的有限元模拟和热加工工艺的制定,为本构关系模型的建立提供了一种准确有效的方法。     

B10铜合金高温流变行为及BP神经网络本构模型

利用Gleeble-1500D热模拟机对B10铜合金进行热压缩实验,研究了该合金在高温塑性变形过程中的流变应力行为.实验温度为800～950℃,应变速率为0.1～15s-1.研究结果表明,B10铜合金的流变应力随着变形温度的增加而减小,随着应变速率的增大而增大.基于BP神经网络建立了该合金的本构关系模型,预测值与实验值对比表明BP神经网络具有很高的预测精度,所建立的本构模型平均相对误差在1％以内.该模型能够客观真实地描述B10铜合金的高温塑性变形行为,为该合金热变形分析提供基础.     

HNi55-7-4-2合金高温本构模型修正及变形激活能演化规律

研究了挤压态镍黄铜HNi55-7-4-2合金高温本构模型的修正方法及其变形激活能的演化规律,对HNi55-7-4-2合金进行不同变形温度(873～1073 K)及应变速率(0.01～10 s~(-1))条件下的等温热压缩实验,获取了HNi55-7-4-2合金的流动应力-流动应变曲线。基于材料参数和变形激活能对变形条件的依赖,构建了一种考虑变形条件对材料参数影响的修正本构模型。经验证,修正本构模型能很好地预测HNi55-7-4-2合金的高温流动应力,其预测精度高。在不同变形条件下应用修正本构模型计算变形激活能,变形激活能受到变形温度、应变速率和变形量的综合影响,其变化范围在119.0～173.2 kJ·mol~(-1)之间。此外,变形激活能随着变形温度的增加而降低,随着应变速率的增加先降低后升高。     

TC4钛合金神经网络本构模型及在有限元模拟中应用

利用Zwick/Roell Z100材料试验机,对TC4钛合金进行等温恒应变速率下的单向拉伸试验。基于获得的试验数据,采用BP神经网络技术建立了该合金的高温本构关系模型,并对其预测性能进行分析。基于ABAQUS/Explcit平台进行材料子程序二次开发,将神经网络本构模型嵌入到有限元计算中,实现了TC4钛合金高温变形的数值模拟。结果表明,神经网络本构模型预测精度很高,可以准确地描述TC4钛合金在热态下的动态力学性能。神经网络本构模型应用于有限元模拟可行且有效。     

Laves相NbCr2/Nb两相合金的应变补偿物理本构关系研究

Laves相NbCr2/Nb两相合金因其优良的高温力学性能而具有作为新型高温结构材料应用的潜力；流动应力本构关系反映了合金的热变形行为。本文基于Laves相NbCr2/Nb两相合金在1000-1200℃、0.001-0.1s-1条件下的等温恒应变速率压缩实验数据，首次探讨了该合金在考虑变形温度对合金杨氏模量和自扩散系数影响的应变补偿物理本构关系。结果表明，基于蠕变指数n=5的应变补偿物理本构关系的相关系数R和平均绝对相对误差AARE分别为0.974和59.3%，说明该物理本构模型不适于表征该合金的流动应力行为；而基于蠕变指数n为变量的应变补偿物理本构关系的相关系数R和平均绝对相对误差AARE分别为0.984和10.6%，说明该物理本构模型能满意地表征该合金的流动应力行为，且其对流动应力的预测能力优于传统的Arrhenius本构模型。     

基于BP神经网络Ti600合金本构关系模型的建立

运用Gleeble-1500热模拟机对Ti600合金的圆柱试样进行等温压缩变形试验,以试验所得数据（变形温度800~1100 ℃,应变速率0.01~10 s-1）为基础,基于BP神经网络方法建立了该合金的高温本构关系模型。结果表明：BP神经网络本构关系模型具有很高的预测精度,可以很好地描述Ti600合金在高温变形时各热力学参数之间高度非线性的复杂关系,为本构关系模型的建立提供了一种更加准确有效的方法。     

Ti-6．5Al-3．5Mo-1．5Zr-0．3Si合金本构关系的BP神经网络模型

利用THERMECMASTOR-Z型热力模拟试验机,在变形温度为780～1 080 ℃,应变速率为0.001～70.0 s-1条件下对Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金进行等温恒应变速率压缩试验,获得不同变形温度、不同应变速率和不同真应变下的流动应力数据.结合试验数据和神经网络知识,构建了采用BP算法的人工神经网络,训练结束后的神经网络即成为Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金的一个知识基的本构关系模型.利用所建立的BP网络模型对材料的流动应力进行了预测,发现预测值与试验数据吻合良好,说明该BP网络本构关系模型具有较高的精度,可用于指导Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金热加工工艺的制定.     

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。