高碳珠光体钢挤压变形过程中的组织演变

在试验温度为650℃的情况下,对原始材料组织为层片状高碳珠光体的T8钢进行等通道角多道次挤压变形,同时根据AFM、TEM和SEM表征了材料在挤压变形过程中其渗碳体片层的组织演变过程。结果表明,层片状渗碳体有较强的塑性变形性能,通过产生扭折、断裂及弯曲等方式来缓和塑性变形所带来的剧烈影响;从二维角度观察到的变形过程及结果与从三维立体角度观察的相吻合。     

过共析珠光体钢在冷轧过程中的组织演变

用SEM、TEM和XRD等方法研究了过共析珠光体钢在冷轧变形过程中的组织演变情况.结果表明:变形珠光体组织不均匀,主要由不规则弯曲片层、带有剪切带的粗大片层以及精细片层组成,随着变形量的增加,精细片层比例增大,渗碳体片层严重塑性变形的同时发生部分溶解,铁素体点阵常数也随之增大.     

ECAP温变形制备亚微晶钢中渗碳体变形特征

采用透射和扫描电子显微镜研究了ECAP变形中渗碳体的变形特征。结果表明:片状渗碳体相主要以弯曲变形、剪切变形、拉伸变形、扭折变形和剪断变形5种方式协调ECAP剧烈塑性变形,这表明在本实验ECAP纯剪切变形条件下钢中硬而脆的渗碳体相具有良好的塑性变形能力。渗碳体片层的变形方式主要是取决于渗碳体所处的应力状态,而渗碳体所处的应力状态是与渗碳体的片层取向和片层厚度密切相关,其中渗碳体的片层厚度起决定性作用。     

共析珠光体钢在冷轧过程中的组织变化

用SEM、TEM及XRD等方法研究了共析钢中珠光体经40％-90％的冷轧变形后所产生的显微组织变化．接渗碳体形态特点,变形珠光体组织可分为以下3种类型：(1)不规则弯曲片层型,即变形后的渗碳体与轧制面呈大角度偏离且不规则弯曲的珠光体．(2)带有剪切带的粗大片层型,即被渗碳体剪切带分开且变形轻微的珠光体．(3)精细片层型,即与轧制方向平行排列、片间距细小且渗碳体严重变形的珠光体．精细片层区域的比例随着轧制压下率的提高而增大．此外,重度冷轧变形还引起渗碳体严重塑性变形和部分溶解．     

共析珠光体钢激光冲击处理后的组织演变

采用SEM、TEM及显微硬度等方法研究了原始组织为层片状珠光体的共析钢激光冲击处理后的组织演变与硬度变化规律.结果表明:单道次激光冲击即可实现共析钢表层铁素体晶粒超细化,等轴铁素体晶粒尺寸约为0.8 μm;激光冲击产生的冲击波诱发材料表层产生高应变速率的塑性变形,渗碳体层片具有较好的塑性变形能力,冲击波中心区域渗碳体层片球化完全,渗碳体颗粒粒径约为50 nm,而冲击波边缘区域渗碳体层片主要发生弯曲、扭折和断裂;塑性变形导致大量位错的产生使得冲击波中心区域材料表层的硬度相比冲击前提高约20%左右.     

温压缩变形过程中渗碳体的球化行为

在Gleeble-3500热模拟试验机上对原始组织为层片状珠光体的高碳钢进行温度为640～700℃、应变速率0-01～10s-1,最大真应变为1的温压缩变形.采用扫描电镜研究了该过程中渗碳体片层的组织演变情况,并用DEFORM-3D软件模拟了温变形过程中试样内部等效应变的分布情况.结果表明,温压缩变形过程中存在着形变不均匀性,使得试样心部和边缘组织形态有明显差异,随着应变速率的降低,边缘层片状珠光体组织球化为粒状珠光体;在变形过程中珠光体组织主要发生渗碳体片层的球化,随着应变量、应变速率以及变形温度的增加,渗碳体球化率明显增大.     

共析钢的过冷奥氏体动态相变和组织超细化

通过在Gleeble-1500热模拟试验机上进行单轴热压缩实验,研究了共析钢中过冷奥氏体在A1-Ar1之间变形时的组织演变,探讨了共析钢中复相组织球化超细化的机理.结果表明:随着应变量的增加,片层珠光体在原始奥氏体晶界形成的铁素体生长前沿形核长大,并向原始奥氏体晶内推进,直至相变完成.片层珠光体生成后继续变形,发生渗碳体的溶断和球化,及铁素体的动态回复再结晶等轴化等过程.渗碳体的球化有两种机制,其一是由于Gibbs-Thomson效应,珠光体中片层状渗碳体发生溶断和球化,生成的大颗粒渗碳体主要分布在铁素体晶界;其二是纳米级渗碳体粒子伴随铁素体动态再结晶在晶内重新析出.实验证实,在合适的变形工艺条件下可以得到亚微米级铁素体与亚微米、纳米级颗粒状渗碳体的双相组织.     

剧烈冷拉珠光体钢丝的组织性能演变及其对退火工艺的影响

研究了剧烈冷拉SWRH72B钢丝的组织演变及大变形量对珠光体钢丝球化退火的影响.结果表明,钢丝的抗拉强度和维氏硬度都随真应变的增大呈线性趋势提高;渗碳体片层随真应变的增大逐渐减薄.纵截面渗碳体片层最终趋向沿拉拔轴向排列,横截面珠光体片层发生了剧烈的弯曲和扭转.变形量较大时,渗碳体大量溶解.在不同温度对冷拉钢丝进行球化退火处理,发现随着真应变的增大,有效地降低了钢丝球化退火温度.缩短了球化退火时间.提高了球化均匀度.     

珠光体组织的形变、裂纹形核与扩展微观过程的动态研究

用扫描电镜对含碳量为0.15,0.47和0.79wt-％的三种碳素钢进行了拉伸试验,观察了珠光体组织形变与断裂的动态过程。结果表明,15和45号钢形变主要在铁素体中进行,珠光体可发生剪切形变与旋转等现象。裂纹主要在夹杂物界面、珠光体与铁素体两相界面上产生,最后的断裂遵循延性断裂机制;对于完全是片层珠光体组织的T8钢,渗碳体片层表现出一定程度的塑性变形能力,并随片层间距的减小变形能力增强。对于细片层组织,应变分布比较均匀,变形范围比较广泛,渗碳体片层可产生滑移和弯曲,断裂方式表现出延性断裂特征;在粗珠光体中,应变分布很不均匀,变形主要集中在强烈剪切变形带中进行,裂纹形核主要是渗碳体片层沿剪切形变带开裂的结果,断裂方式表现出脆性断裂特征。用位错塞积模型讨论了珠光体组织的脆性开裂现象。     

AN IN S ITU STUDY OF CRACK NUCLEATION AND PROPAGATION IN PEARLITE DURING DEFORMATION

用扫描电镜对含碳量为0.15,0.47和0.79wt-％的三种碳素钢进行了拉伸试验,观察了珠光体组织形变与断裂的动态过程。结果表明,15和45号钢形变主要在铁素体中进行,珠光体可发生剪切形变与旋转等现象。裂纹主要在夹杂物界面、珠光体与铁素体两相界面上产生,最后的断裂遵循延性断裂机制;对于完全是片层珠光体组织的T8钢,渗碳体片层表现出一定程度的塑性变形能力,并随片层间距的减小变形能力增强。对于细片层组织,应变分布比较均匀,变形范围比较广泛,渗碳体片层可产生滑移和弯曲,断裂方式表现出延性断裂特征;在粗珠光体中,应变分布很不均匀,变形主要集中在强烈剪切变形带中进行,裂纹形核主要是渗碳体片层沿剪切形变带开裂的结果,断裂方式表现出脆性断裂特征。 用位错塞积模型讨论了珠光体组织的脆性开裂现象。     

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。