纳米-相变陶瓷复合材料的有效刚度

含纳米纤维和相变粒子的陶瓷复合材料具有较大的断裂韧性和较高的塑性形变行为,其组织结构以含纳米纤维的棒状复合体为基体,并在棒状复合体周围分布有少量的可产生相变的二相粒子.本文在Mori-Tanaka方法和有效自洽法的基础上提出复合材料刚度预报的随机二相胞元法.首先应用Mori-Tanaka方法计算出棒状复合体的刚度,考虑棒状复合体方位的随机性,根据复相陶瓷基体的应变均值,计算出复合材料基体的有效弹性模量和泊松比,复相陶瓷材料基体为各向同性体.最后将相变粒子看作夹杂在基体中的颗粒,计算出陶瓷复合材料的等效刚度.复相陶瓷的弹性模量随二相组元体积分数的增加而下降且略低于用混合律求解的结果,说明纳米纤维和相变粒子之间的相互作用降低了弹性模量:复相陶瓷的泊松比随二相组元体积分数的增加而下降且略高于用混合律求解的结果,说明纳米纤维和相变粒子之间的相互作用提高了泊松比.     

纳米共晶晶须复相陶瓷的刚度预报

用SHS技术制备的纳米共晶晶须复相陶瓷具有较大的断裂韧性和较高的塑性形变行为,其组织结构以纳米共晶晶须为基体.运用Mori-Tanaka方法研究了复合共晶晶须的等效本征应变,并得到了复合共晶晶须的应力应变关系.通过应力应变关系计算出复合共晶晶须的刚度,复合共晶晶须为横观各向同性,具有5个独立的弹性常数.根据复相陶瓷的应变均值,考虑复合共晶晶须方位的随机性,计算出材料的有效弹性模量和泊松比,复相陶瓷材料为各向同性体.     

纳米/微米Al2O3-ZrO2复相陶瓷SHS制备与显微结构

通过在(CrO3 Al)燃烧体系添加ZrO2(4molY2O3)组元，利用SHS技术可以制备具有亚共晶、共晶和过共晶成分的Al2O3-ZrO2复相陶瓷。复相陶瓷基体组织主要由层片状和纤维状共晶组织所构成。在亚共晶成分复相陶瓷中，纤维状共晶组织体积分数较高，ZrO2纤维直径已达到纳米／微米尺度；在过共晶复相陶瓷中，层片状共晶组织体积分数较高，Al2O3-ZrO2两相层片间距基本在亚微米范围内。基于燃烧合成与凝固理论分析可认为，本试验所获得的复相：陶瓷是通过SHS原位结晶及在大过冷条件下、熔体发生共生共晶反应生成的。所以在本试验条件下，只有亚共晶成分的复相陶瓷才易获得ZrO2相纤维直径在纳米／微米级尺度上的1—3复合的Al2O3-ZrO2纳米／微米晶内型复相陶瓷。     

纳米/微米Al_2O_3-ZrO_2复相陶瓷SHS制备与显微结构

通过在(CrO3+Al)燃烧体系添加ZrO2(4molY2O3)组元,利用SHS技术可以制备具有亚共晶、共晶和过共晶成分的Al2O3 ZrO2复相陶瓷。复相陶瓷基体组织主要由层片状和纤维状共晶组织所构成。在亚共晶成分复相陶瓷中,纤维状共晶组织体积分数较高,ZrO2纤维直径已达到纳米/微米尺度;在过共晶复相陶瓷中,层片状共晶组织体积分数较高,Al2O3 ZrO2两相层片间距基本在亚微米范围内。基于燃烧合成与凝固理论分析可认为,本试验所获得的复相陶瓷是通过SHS原位结晶及在大过冷条件下、熔体发生共生共晶反应生成的。所以在本试验条件下,只有亚共晶成分的复相陶瓷才易获得ZrO2相纤维直径在纳米/微米级尺度上的1 3复合的Al2O3 ZrO2纳米/微米晶内型复相陶瓷。     

纳米陶瓷材料弹性模量的尺度效应

针对纳米陶瓷的界面现象，在三相模型基础上，考虑纳米晶粒与界面相的相互作用，将其改进为复合材料刚度预报的四相模型法，根据有效自恰方法推导出纳米晶粒与界面相内的有效应力，进而得到柔度增量的隐性表达式，再利用相互作用直推法，得到纳米陶瓷材料的柔度增量的显性形式，它具有：1）简单的解析形式；2）适合任何形状的纳米晶粒；3）适合各向同性和各向异性纳米晶粒；4）将复合材料的弹性性能与纳米晶粒尺寸联系起来。结果表明：当纳米晶粒尺寸小于50nm时，纳米陶瓷材料的弹性模量随纳米晶粒尺寸的减小而下降，当纳米晶粒尺寸超过50nm以后，纳米陶瓷材料的弹性模量基本保持不变。     

Al2O3/ZrO2纳米/微米结构自生复相陶瓷组织与性能

通过在铝热剂中添加质量分数为25%的ZrO2(4Y)粉末,借助SHS原位合成技术,快速、直接地制备出t-ZrO2纳米/微米纤维为第2相、Al2O3为基体的晶内型结构复相陶瓷,研究其微观结构、合成机理与力学性能.研究得出,该复相陶瓷是高温陶瓷熔体在SHS所造成的大过冷条件下发生共生共晶反应生成的,SEM与XRD分析表明t-ZrO2相所具有的应力诱发相变增韧机制非常微弱,裂纹扩展主要受纳米/微米晶内型结构控制,从而呈现出强烈的裂纹偏转韧化机制.     

横向压缩载荷下CF/Al复合材料微观损伤演化与断裂力学行为

针对真空压力浸渗制备的单向碳纤维增强铝基复合材料(CF/Al复合材料),采用细观力学数值模拟和实验相结合的手段研究了其在横向压缩载荷下的损伤演化与断裂力学行为,并分析了界面结合性能和纤维体积分数对复合材料横向压缩力学性能的影响。结果表明:基于纤维对角正方形分布RVE建立的细观力学有限元模型,可以较好地计算预测复合材料横向压缩变形力学行为。压缩变形初期界面首先发生损伤和失效现象,进而诱发界面附近基体合金的局部损伤;随压缩应变增加,界面和基体损伤逐渐发展并导致纤维的失效,复合材料横向压缩断口呈现出界面脱粘和纤维断裂共存的微观形貌。复合材料横向压缩弹性模量和极限强度随着界面强度增大而增大,而受界面刚度的影响较小;在相同界面性能条件下,复合材料横向压缩极限强度和弹性模量均随纤维体积分数的增大而减小。     

原位生长纳微米纤维自增韧复相陶瓷显微结构与不同尺度多级增韧

通过将ZrO2微米粉末引入铝热剂中,借助铝热燃烧、陶瓷/金属液相分离及共晶反应中的晶体原位生长,制备出原位生长纳微米纤维自增韧Al2O3/ZrO2陶瓷复合材料.研究表明,陶瓷基体主要由以单晶t-ZrO2纳微米纤维为第二相、单晶α-Al2O3为基体且长径比为8.0～16的棒晶构成,并且在棒晶边界上还分布着α-Al2O3片晶、ZrO2微米粒子及Cr金属颗粒.力学性能测试得出,陶瓷的弯曲强度、弹性模量及断裂韧性分别达到1168MPa、410GPa与12.6 MPa·m0.5;裂纹扩展路径观察发现,陶瓷增韧是通过裂纹偏转增韧、纳微米纤维增韧、α-Al2O3片晶的裂纹桥接增韧、延性相增韧及应力诱发相变增韧不同尺度四级增韧机制的协同作用予以实现.     

电脉冲烧结法制备形状记忆合金颗粒弥散基复合材料

最近的一些研究，有将形状记忆合金纤维和颗粒嵌埋或弥散到金属或高分子材料基体中，利用形状记忆合金的相变造成的应力场抑制裂纹的扩展的新方法。即将基体中的弥散粒子或纤维进行形状记忆处理，使复合材料中产生残余应力场，或者在使用中通过变形材料的裂纹尖端附近的诱发相变产主应力场。在以形状记忆合金粒子弥散分布的场合，主要考虑下述的裂纹扩展抑制机制： （ｌ）弥散粒子周围裂纹围绕的应力缓和效应。在大多数粒子弥散材料中都是这种机制，与粒子的大小和体积分数有关。 （２）弥散材料烧结时因热应力在粒子周围产生残余压应力的效…     

原位生长纳微米纤维自增韧复相陶瓷显微结构与不同尺度多级增韧

通过将ZrO2微米粉末引入铝热剂中,借助铝热燃烧、陶瓷/金属液相分离及共晶反应中的晶体原位生长,制备出原位生长纳微米纤维自增韧Al2O3/ZrO2陶瓷复合材料.研究表明,陶瓷基体主要由以单晶t-ZrO2纳微米纤维为第二相、单晶α-Al2O3为基体且长径比为8.0～16的棒晶构成,并且在棒晶边界上还分布着α-Al2O3片晶、ZrO2微米粒子及Cr金属颗粒.力学性能测试得出,陶瓷的弯曲强度、弹性模量及断裂韧性分别达到1168MPa、410GPa与12.6 MPa·m0.5;裂纹扩展路径观察发现,陶瓷增韧是通过裂纹偏转增韧、纳微米纤维增韧、α-Al2O3片晶的裂纹桥接增韧、延性相增韧及应力诱发相变增韧不同尺度四级增韧机制的协同作用予以实现.     

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。