CROSS SECTION CHANGING GROWTH PHENOMENON OF Sn WHISKER IN Sn–3.8Ag–0.7Cu–1.0Er LEAD–FREE SOLDER

在Sn--3.8Ag--0.7Cu无铅钎料中添加质量分数为1%的稀土Er会在其内部形成尺寸较大的稀土相ErSn₃. 暴露于空气中ErSn₃将发生氧化, 同时在其表面会出现Sn晶须的快速生长现象. 室温时效条件下, 在氧化的ErSn₃表面会生长出少量的杆状Sn晶须, Sn晶须的截面尺寸会发生连续变化; 高温时效条件下, 在氧化的ErSn₃表面会生长出大量的针状Sn晶须, Sn晶须的截面尺寸会发生阶梯式变化. 提出了ErSn₃氧化过程中体积应变能是一个变量的模型, 可以解释观察到的现象.     

稀土相ErSn3表面Sn晶须的快速生长

将稀土相ErSn3分别暴露于空气与真空环境中,研究在时效处理过程中ErSn3表面Sn晶须的生长情况。结果表明：大气环境中,在稀土相ErSn3的表面出现了Sn晶须的生长现象,且室温条件下Sn晶须的分布不均,生长速度慢,而高温条件下Sn晶须的分布均匀,生长速度快;真空环境中,在稀土相ErSn3的表面未出现Sn晶须的生长现象。由于在大气环境中稀土相ErSn3发生了氧化,氧原子向ErSn3晶格内部的扩散引起的体积膨胀提供了Sn晶须生长的驱动力,因此,大气环境中在ErSn3的表面会出现Sn晶须的生长现象,而真空环境中则不会出现     

稀土相RE-Sn表面Sn晶须的生长规律

将稀土相CeSn3、LaSn3、(La0.4Ce0.6)Sn3及ErSn3暴露于空气中,研究在时效处理过程中其表面Sn晶须的生长规律。结果表明:室温时效过程中,在稀土相的表面均出现了Sn晶须的生长现象,且稀土相LaSn3的表面倾向于形成包状和扭结状的Sn晶须,稀土相CeSn3和(La0.4Ce0.6)Sn3的表面倾向于形成针状和扭结状的Sn晶须,而稀土相ErSn3的表面倾向于形成大尺寸的杆状和棒状Sn晶须。150℃时效过程中,稀土相CeSn3、LaSn3和(La0.4Ce0.6)Sn3的表面没有出现Sn晶须的生长现象,而稀土相ErSn3的表面出现了大量的小尺寸线状Sn晶须。综上所述,稀土相的氧化倾向决定了其表面Sn晶须的生长规律。     

Sn晶须的形态机制

将稀土相CeSn3与ErSn3暴露于空气中,研究在时效处理过程中稀土相表面Sn晶须的形态机制.结果表明:时效过程中在稀土相表面出现的绝大多数Sn晶须均是具有恒定截面的规则Sn晶须;同时也发现少数特殊形态的不规则Sn晶须,如卷曲状的Sn晶须、变截面的Sn晶须、分枝及搭接的Sn晶须等;由于稀土相的氧化所产生的体积膨胀提供Sn晶须生长的驱动力,而稀土相的氧化极不均匀,因此,认为Sn晶须在生长过程中其根部受力状态的改变是导致特殊形态Sn晶须出现的根本原因.     

SnAgCuCe/Er无铅钎料表面锡晶须的形态及特性

在Sn-3.8Ag-0.7Cu无铅钎料中添加1%(质量分数)的稀土铈或铒会在其内部形成尺寸较大的稀土相CeSn3和ErSn3.暴露于空气中的CeSn<,3和ErSn3将发生氧化,同时在其表面会出现锡晶须的快速生长现象.文中研究了稀土相CeSn3与ErSn3表面锡晶须的生长行为.结果表明,在CeSn3与ErSn3表面形成了大量的传统圆柱状锡晶须,同时,在其表面还出现了一些特殊形态的锡晶须,如带纹状的锡晶须、扭曲状的锡晶须、变截面的锡晶须、锡晶须的分枝、合并及搭接现象等.     

Sn晶须生长的双应力区模型

利用FIB(Focused Ion Beam)将发生氧化的稀土相ErSn3剖开,研究其表面Sn晶须的生长机制。结果表明:时效过程中稀土相ErSn3发生了不均匀氧化,在其内部形成了大量的"快速氧化通道"及"氧化区"。由于在Sn晶须的根部及附近同时存在两个"氧化区",且它们通过"快速氧化通道"相连。因此,提出了Sn晶须生长的"双压应力区"模型,即Sn晶须的生长需要形成两个压应力区,其根部的"低压应力区"将为Sn晶须的形成提供驱动力,而"高压应力区"将为Sn晶须的生长提供Sn原子。     

稀土Y加速Sn晶须生长规律

氧原子向稀土相YSn3晶格内部的扩散使YSn3产生体积膨胀,而周围钎料基体对体积膨胀的抑制作用使其内部产生巨大的压应力,此压应力为Sn晶须的生长提供了驱动力;与此同时,稀土相YSn3氧化过程中释放出的自由Sn原子为Sn晶须的生长提供了生长源.对空气中室温与150℃时效条件下稀土相YSn3表面Sn晶须的生长进行了研究.结果表明,室温时效条件下,稀土相YSn3表面Sn晶须的生长速度缓慢且分布不均;高温时效条件下,稀土相YSn3表面Sn晶须的生长速度较快且巨大的压应力使钎料基体发生了隆起现象.     

稀土相表面特殊形态锡晶须生长现象

在Sn3.8Ag0.7Cu钎料中添加过量的稀土Ce和Er元素会在其内部形成尺寸较大的稀土相CeSn3和ErSn3.将钎料合金Sn3.8Ag0.7Cu1.0Ce/Er的铺展试样沿中心剖开,利用金相水砂纸及专用抛光液抛光后,将制备好的试样在空气中分别进行室温与150℃时效处理.分析了时效处理过程中稀土相CeSn3及ErSn3表面锡晶须的生长行为.结果表明,在稀土相的表面出现了大量规则的针状及线状锡晶须,它们在生长过程中始终保持了恒定的截面.试验中还发现了一些特殊形态的锡晶须,如锡晶须的分枝、合并以及锡晶须的搭接现象.     

Sn晶须形态的研究

添加微量稀土可以有效地改善钎料的综合性能.然而当钎料中添加过量的稀土时,钎料内部会形成体积较大的稀土相.如果将稀土相暴露于空气中,其将发生氧化,氧化产生的压应力将加速稀土相表面Sn晶须的生长.研究了CeSn3与YSn3与ErSr3稀土相表面Sn晶须的生长情况.研究结果表明,稀土相表面出现了Sn晶须的快速生长现象,且试验中发现了一些特殊形态的Sn晶须.     

稀土Ce加速Sn晶须生长的研究

稀土被认为是金属中的"维他命",在钎料中添加微量的稀土Ce可以显著地改善钎料合金的综合性能.然而,当钎料中添加过量的稀土时,将会发现Sn晶须的快速生长现象.结果表明,如果将Sn3.8Ag0.7Cu1.0Ce钎料内部的稀土相暴露于空气中,稀土相将发生氧化而产生体积膨胀,钎料基体对体积膨胀的抑制作用将使稀土相内部产生巨大的压应力从而加速Sn晶须的生长.     

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。