热分析在Fe-B合金深过冷凝固过程中的应用

采用熔融玻璃净化与循环过热相结合的深过冷技术,研究了Fe-B共晶合金熔体的深过冷及超过冷凝固组织与冷却曲线的关系.凝固过程的热分析表明,合金熔体冷却曲线的变化体现了熔体的过冷程度,即通过对冷却曲线特征参量的分析能够直接确定深过冷/超过冷凝固组织的获得,而且过冷度与初生相的形核、分布、晶粒大小及共晶组织形貌等凝固特征的对应关系也能够通过冷却曲线反映出来.     

Ag-Cu/Co-Sn共晶合金深过冷快速凝固反常共晶的形成研究

利用熔融玻璃净化循环过热的方法进行了Ag-Cu/Co-Sn共晶合金的深过冷快速凝固实验,并系统研究了熔体过冷度和微量Nb添加对反常共晶形成的影响。结果表明,快速凝固过程中共晶枝晶内部首先重熔形成反常共晶,随着过冷度的增大,共晶相的形貌从蠕虫状转变为球形颗粒,被重熔形成的固相颗粒将作为剩余液相形核生长的基底,Ag-Cu共晶中共晶两相形核具有非互惠性。Co-Sn共晶合金中添加Nb元素后样品内部反常共晶形成的临界过冷度由23 K降低至15 K,而表面组织中过冷度从45 K降低至30 K。由于样品表面与坩埚壁接触有利于结晶潜热消散,反常共晶形成的临界过冷度较高。Ag-Cu共晶合金温度再辉曲线上慢速凝固阶段持续的时间较Co-Sn共晶合金要长。     

深过冷铁钴基块体合金的细晶化研究

采用熔融玻璃净化与循环过热相结合的深过冷技术,对比研究了深过冷凝固和过冷熔体Cu模激冷凝固Fe₄₄Co₄₄Nb₇-B₄Cu₁块体合金的组织特征.结果表明,随过冷度增大,深过冷和深过冷Cu模激冷凝固组织均由最初的发达树枝晶逐渐演变为细小的粒状晶,并且Cu模激冷可显著减小树枝晶向粒状晶转变的临界过冷度.在相同过冷度下,过冷熔体Cu模激冷凝固组织更加细小均匀,其根本原因在于Cu模激冷和熔体深过冷的双重作用不仅提高了熔体的形核率并抑制了晶粒长大,而合金化元素在晶界聚集并不是阻碍晶粒长大的主要原因.     

Cu原子簇触发形核下的深过冷Ag-Ge合金组织演变研究

采用玻璃包覆的方法获得具有较大过冷度的亚共晶、共晶以及过共晶Ag-Ge合金熔体，并通过高能离子束轰击Cu箔产生Cu原子团簇溅射到过冷合金熔体中来触发非均质形核过程。凝固后合金显微组织的分析结果表明：在深过冷合金熔体中引入Cu原子团簇，它对亚共晶、共晶以及过共晶Ag-Ge合金的显微组织演变有着不同的影响效果，分析了显微组织的演变规律与形成机制。     

高密度脉冲电流对Fe-B共晶合金熔体过冷度的影响

采用熔融玻璃净化加循环过热相结合的深过冷技术及高密度脉冲电流作用于金属熔体的方法,研究了Fe-B共晶合金深过冷条件下及脉冲电流作用下的凝固组织。通过DSC方法分析了高密度脉冲电流对Fe-B共晶合金熔体过冷度的影响。结果表明,高密度脉冲电流作用下的凝固组织与深过冷条件下的凝固组织形貌类似,且两种实验条件下获得的过冷度基本相同,证明了脉冲电流可以对金属熔体实现深过冷。     

Al50Si50合金过冷熔体中Si晶体的生长

利用电磁悬浮设备，通过在真空状态下反复加热与冷却处理，获得了Al50Si50(原子分数)合金熔体的深过冷，最大过冷度为320K、观察了不同过冷度下凝固样品小球的表面及其截面深腐蚀后的组织形貌．过冷度较小时，初生相Si为板条状枝晶形貌，并在其中发现了Al的层状沉积；过冷度较大时，初生相Si转变为粒状形貌，共晶体的形貌也随过冷度的增大转变为离异共晶形态．较大过冷度下，微观组织中发现有晶粒细化现象，这与Si晶体生长受溶质的抑制及初生相Si枝晶的断裂有关．     

Fe-Ni-P-B共晶合金的深过冷凝固组织演化

采用玻璃熔覆法使Fe-Ni-P-B共晶合金在不同过冷度条件下凝固,研究了其组织随过冷度的演化规律.结果表明,随着过冷度的增加,凝固组织形态逐渐从棒状规则共晶向不规则的粒状共晶组织转化.当T＜35 K时,棒状规则共晶组织随过冷度增加而逐渐细化;当35 K＜ T＜150 K时,凝固组织由团状非规则共晶与棒状规则共晶构成,且随着过冷度增加非规则共晶逐渐增多,规则共晶组织减少,共晶间距增大;当T＞150K时,获得完全非规则共晶组织.应用Jackson-Hunt共晶生长模型和枝晶熔断理论,对Fe-Ni-P-B共晶合金凝固组织形成机制进行了分析讨论.     

高压凝固ZA43合金的非平衡组织

研究了高压凝固条件下ZA43合金凝固组织的变化。高压凝固ZA43合金的组织明显变细，没有形成粗大的树枝晶，分布随机，形状各异，部分横截面类似于胞晶的粒状结构，共晶相呈均匀细小的蠕虫状结构。高压增加了溶质原子在固溶体中的固溶度，减少了枝晶偏析。讨论了高压对凝固组织的影响。     

DZ125高温合金深过冷凝固组织转变规律

采用熔盐净化剂与循环过热相结合的方法,获得了过冷度高达180 K的DZ125高温合金深过冷熔体,研究了合金深过冷凝固的组织演化过程.结果表明,随着过冷度△T的增大,凝固组织经历3次转变过程:当△T<48 K时,合金的凝固组织为普通树枝晶;当48 K≤△T<85 K时,枝晶因再辉发生熟化和重熔,组织转化为第1类粒状晶;当85 K≤△T<160 K时,再辉所产生的重熔效应大大降低,凝固组织为深过冷树枝晶;当△T≥160 K时,发生枝晶破碎及再结晶,凝固组织转变为第Ⅱ类粒状晶.     

Fe-B共晶合金的净化及超过冷的获得

通过真空熔炼和气体保护,采用熔融玻璃与循环过热相结合的深过冷快速凝固技术,研究了影响富Fe端Fe-B共晶合金熔体净化效果的主要因素,确定了该合金熔体获得超过冷的净化方法,并使Fe83B17共晶合金熔体稳定获得了300-460 K的超过冷度,使Fe80B20过共晶合金熔体的过冷度达到了485 K,从而使Re-B共晶系合金熔体开始形核前的初始过冷度达到了0.3Tm-0.4Tm的水平.通过对冷却曲线的分析,讨论了表征超过冷快速凝固的热力学特征.     

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。