U-5.7Nb合金绝热剪切带微观组织结构特征

利用SHPB实验装置对U-5.7Nb合金帽型样品在室温下进行动态加载,获得U-5.7Nb合金绝热剪切带,采用激光共聚焦、SEM、纳米压痕以及TEM等测试方法开展了U-5.7Nb合金绝热剪切带内组织结构的研究。U-5.7Nb合金绝热剪切带宽约40μm,且呈现蚀刻"暗带";剪切带内微裂纹的萌生和扩展导致带内"破碎"等轴晶特征组织的出现;剪切带核心区域出现取向高度异性的纳米"晶畴"。剪切带内特殊的组织结构变化导致剪切带硬度与弹性模量的不同变化趋势。     

应变水平对锆合金动载下塑性变形机制的影响

基于实验设计研究了应变参数对锆合金动载下塑性变形机制的影响。通过控制应变速率,采用应变限位环的方法实现了锆合金高应变速率下应变参数的单一分离,应变速率为2300 s~(-1)时,获得了4个不同的应变水平:0.11、0.21、0.30、0.33。基于锆合金高应变速率不同应变下微观组织的表征,预测了应变参数对锆合金动载下塑性变形过程的影响。结果表明:形变带和转变带是锆合金不同应变阶段塑性变形的重要方式,形变带内部由严重变形的晶粒组成,而转变带内部主要由100~300 nm的细小等轴晶粒组成。在变形初始阶段,锆合金变形以柱面滑移和锥面滑移为主,以孪生为辅;随着应变的增加,位错持续增殖,位错的塞积导致应力增加,直至最大抗压强度;当应变达到一个临界值时,形成形变带;随应变继续增加,形变带发生动态再结晶,演化为转变带;应变继续增加,便会在剪切带内部诱发微空洞、微裂纹,直至材料断裂。     

显微组织和应变速率对TC4合金动态力学性能和绝热剪切带的影响

通过热处理成功获得了等轴、片层和双态3种组织结构的TC4合金,并研究了其动态力学性能及变形机制。通过对比硬化-软化转变临界剪切应变率、最大抗剪切强度、萌发绝热剪切带的临界剪切应变速率和承载时间4个指标评估了3种组织合金的动态力学性能。结果表明,片层组织TC4合金具有较高的抗剪切强度和临界剪切应变速率以及最低的绝热剪切敏感性,其动态力学性能最佳。进一步的微观结构分析表明,3种组织合金中所形成的绝热剪切带均为脆性剪切带,且剪切带宽度随剪切应变速率的增大而减小。当剪切应变速率相同时,3种组织合金的剪切带宽度由大到小依次为：片层组织、双态组织、等轴组织。     

高速切削Inconel718绝热剪切带微观特征研究

镍基高温合金Inconel718是多组元复杂合金,在高速切削过程中,切削变形复杂,切削温度高,使得刀具磨损十分严重。因此,通过切削实验获取切屑根进行观察分析,同时结合切削仿真深入研究锯齿形切屑的形成过程中绝热剪切带的微观特征。结果表明:绝热剪切带以两种形式存在,形变带(应变高度集中)和转变带(有高温转变痕迹)。形变带是材料热塑性剪切失稳后形成的一条窄带(其中也有少量动态再结晶),转变带则是发生了组织转变以及动态再结晶形成的。在切削过程中,绝热剪切带上受到大应力、应变的作用,剪切带上的空洞聚合最终导致微裂纹的产生。     

中温变形下TC4合金绝热剪切带研究（英文）

研究了TC4合金在中温变形过程中形成的绝热剪切带,应变速率为50 s-1,变形温度为560~660 oC。结果表明变形温度对绝热剪切带的形成有很大影响。剪切带宽度随着变形温度的升高从85μm增加至140μm。因为发生了加工硬化和绝热剪切带中产生的细晶强化作用,绝热剪切带对应的维氏显微硬度比基体高。讨论了绝热剪切带中微观组织演变规律,大应变以及高温使得绝热剪切带中发生了动态再结晶,形成了等轴的再结晶晶粒,再结晶晶粒尺寸为200 nm左右。本研究中形成的绝热剪切带具有形变剪切带和相变剪切的特点。     

Adiabatic Shear Band of TC4 Alloy during Warm Comp- ression

研究了TC4合金在中温变形过程中形成的绝热剪切带,应变速率为50 s-1,变形温度为560~660 oC。结果表明变形温度对绝热剪切带的形成有很大影响。剪切带宽度随着变形温度的升高从85μm增加至140μm。因为发生了加工硬化和绝热剪切带中产生的细晶强化作用,绝热剪切带对应的维氏显微硬度比基体高。讨论了绝热剪切带中微观组织演变规律,大应变以及高温使得绝热剪切带中发生了动态再结晶,形成了等轴的再结晶晶粒,再结晶晶粒尺寸为200 nm左右。本研究中形成的绝热剪切带具有形变剪切带和相变剪切的特点。     

高应变速率对纯钛塑性变形的影响

利用动态塑性变形(DPD)和准静态压缩变形(QSC)技术对纯钛圆柱样品进行对比压缩试验,研究了不同应变速率下纯钛形变孪晶和微结构演变。结果发现:2种变形方式的变形机制相似,低应变时以形变孪生为主,孪生饱和后转变为位错滑移主导;高应变速率促进了形变孪晶的产生,激发{4211}压缩孪晶的形成,同时使变形机制转变临界应变提前至0.2;纯钛在高应变速率和高应变(ε≥0.6)下出现绝热剪切带(ASB)。     

高应变速率下45钢绝热剪切变形特征

基于退火、正火、调质三种不同热处理状态的45钢的帽型试样强迫剪切实验,在Hopkinson压杆的不同速率加载条件下,利用金相显微镜和扫描电镜测试方法研究了材料绝热剪切的变形特征和敏感性,分析了组织因素对绝热剪切的影响规律。结果表明,材料的组织不同,其绝热剪切变形的特征也不同。45钢正火态、调质态中均出现转变带,其余为形变带。随着加载速率和材料强度的提高,绝热剪切带由形变带变为转变带,剪切带宽度越窄,绝热剪切越敏感。     

钛合金（Ti—17）的动态力学性能和损伤特性

利用分离式Ｈｏｐｋｉｎｓｏｎ压杆冲击加载装置,采用圆柱和锥台两种试样,在高应变速率加载条件下研究Ｔｉ－１７合金的应力应变响应和动态损伤特征实验结果表明,动态屈服应力和断裂应力比静态相应值高宏观损伤对应变速率敏感,而对应力不敏感,出现宏观损伤的临界应变速率．试样微观解剖显示绝热剪切带是材料宏观损伤的先兆,试样主要沿剪切带发生破坏、在垂直加载轴的横截面上,绝热剪切带呈圆弧形,平行加载轴剖面上绝热剪切带沿最大剪切应力方向．锥台试样中绝热剪切带的应变从始点到终点逐渐减小     

不同取向疲劳态铜单晶高速冲击下的绝热剪切带

采用分离式Hopkinson压杆装置（SHPB）和扫描电镜电子通道衬度（SEM—ECC）技术研究了不同取向疲劳态铜单晶高应变率压缩下形成的绝热剪切带（ASB）．实验表明,ASB形成的临界应变与晶体取向有关,接近压缩临界双滑移取向晶体需要的临界应变最小,单滑移和压缩共轭双滑移取向的次之,共面双滑移取向的最大．本实验条件下形成的ASB内部典型的位错组态为位错胞结构,未观察到再结晶现象．根据空间位向,ASB可以分为3类：第1类非常接近铜晶体疲劳时形成的第2类形变带（DBII）平面,其临界应变最小;第2类ASB位向或者比较接近DBII平面或者比较接近第1类形变带（DBI）平面,其临界应变居中;第3类ASB位向与DBI和DBII平面均不接近,其临界应变最大．     

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。