A7075搅拌摩擦焊疲劳裂纹扩展速率试验分析

对航空用铝合金A7075-T651的搅拌摩擦焊接头的母材、焊核区和热影响区的疲劳裂纹扩展速率（da／dN）进行了试验研究。疲劳裂纹扩展试验采用CT（紧凑拉伸）试样,在810 Material Test System试验机上进行。用递增多项式法求得疲劳裂纹扩展速率（da／dN）和（△K）,并分别将母材、焊核区和热影响区同一组试样的（da／dN）和（△K）数据点合在一起进行了整体回归分析。试验中得到了以Paris公式表达的铝合金A7075-T651母材、焊核区、热影响区da／dN与△K的关系式。结果表明,热影响区疲劳裂纹扩展速率高于母材和焊核区,是该合金搅拌摩擦焊接头最薄弱的区域。     

基于两步七点拟合ADB610钢焊接接头疲劳裂纹扩展

在应力比为0.1、恒幅加载载荷下,对低碳贝氏体ADB610钢手工电弧焊焊接接头母材区、热影响区和焊缝区采用CT(紧凑拉伸)试样进行疲劳裂纹扩展试验研究。采用两步七点递增多项式拟合方法计算疲劳裂纹扩展速率(da/dN),并计算应力强度因子范围(ΔK),分别将母材区、热影响区和焊缝区每个试样的(da/dN)和(ΔK)数据进行了回归拟合,得到了以Paris公式表达的ADB610钢母材区、热影响区、焊缝区(da/dN)与(ΔK)的关系式。并将这三区域中多个试样Paris公式中的参数取均值,得到三区域均值裂纹扩展速率表达式。结果表明,在裂纹扩展的初期和中期,母材区的裂纹扩展速率最快,焊缝区的裂纹扩展速率最慢;在裂纹扩展末期,三区域的裂纹扩展快慢相当。     

载荷比对含氢Ti-4Al-2V钛合金疲劳裂纹扩展速率的影响

研究了含氢量为110μgg/和280μg/g的Ti-4Al-2V钛合金在不同载荷比下的疲劳裂纹扩展行为。载荷比降低，da/dN曲线向高△K方向移动，并逐渐不出现疲劳裂纹的近门槛扩展阶段；无论载荷比和含氢量的高低，稳态裂纹扩展区的裂纹扩展行为符合Paris幂律关系，即da/dN=C(△K）^m；含氢量为110μg/g时，载荷比对稳态裂纹扩展区的da/dN没有影响；含氢280μg/g时，载荷比降低，稳态裂纹扩展区的da/dN也降低；载荷比影响裂纹由近门槛扩展区进入稳态裂纹扩展区的应力强度因子范围△Kp和开始失稳扩展的应力强度因子范围△K1H。载荷比越小，△Kp和△K1H越大。     

桥梁钢Q345焊接接头疲劳裂纹扩展速率研究

对桥梁用钢Q345焊接接头疲劳裂纹扩展性能进行了试验研究。测得对接接头的硬度分布,结果表明,焊接接头焊缝中心处的硬度值较低,在热影响区的重结晶区存在硬度最高点,而在部分重结晶区存在硬度最低点,硬度最低点为对接接头的薄弱区。通过疲劳裂纹扩展速率测试,得到其对接接头不同区域的疲劳裂纹扩展a-N曲线以及lg(da/dN)-lgΔK曲线。分析对比对接接头各区域的疲劳裂纹扩展速率lg(da/dN)-lgΔK曲线可知,在同一应力水平下,对接接头不同部位的疲劳裂纹扩展速率不同,热影响区的扩展速率较快,母材次之,焊缝金属最慢。并通过疲劳断口和焊接接头的显微组织,分析了其疲劳裂纹扩展速率不同的原因。     

显微组织对珠光体钢疲劳裂纹扩展速率的影响

用金相显微镜、扫描电镜(SEM)及带有切口的三点弯曲试样研究了显微组织对珠光体钢疲劳裂纹扩展速率的影响。结果表明:共析珠光体钢中的疲劳裂纹扩展速率da/dN取决于珠光体层片间距。细化珠光体层片间距可有效减缓共析珠光体钢中的疲劳裂纹扩展速率,尤其在高应力场强度因子幅值△K作用的情况下;珠光体钢的疲劳裂纹扩展速率与断裂前的△K之间的关系为:da/dN=6.94×10~(-9)(△K)~(2.919) (mm·c~(-1));显微组织中存在一定量的先共析铁素体可显著降低珠光体钢中疲劳裂纹的扩展速率。     

2124铝合金TL取向疲劳裂纹扩展门槛值

用降载法测得了2124铝合金TL取向应力比R=0.1、0.3、0.5、0.7下的疲劳裂纹扩展门槛值,用线性拟合法得到da/dN=C1△Kn1中的C1和n1值,将其带入裂纹扩展速率da/dN-△K表达式中,并按标规定取疲劳裂纹扩展速率(da/dN)=10-7 mm/cycle时的△K值为疲劳裂纹扩展门槛值△Kth,分析了应力比对裂纹扩展门槛值的影响.     

镍基合金K4648焊接接头疲劳裂纹扩展速率的研究

为了对某飞机发动机涡轮导向器叶片修复焊接后的安全性和寿命进行评估,试验研究了导向器叶片用K4648合金TIG焊接头的疲劳裂纹扩展速率(da/dN- △K).分别测得了K4648合金母材、焊缝和热影响区疲劳裂纹扩展速率的表达式,对各区域的显微组织特征进行了观察,并测量了3个区域的硬度.结果表明:裂纹在母材中最容易扩展,在...     

显微组织对Ti-6Al-4V ELI合金疲劳裂纹扩展速率的影响

研究了Ti-6Al-4V ELI合金板材的显微组织对疲劳裂纹扩展速率的影响。用金相显微镜对不同热处理制度下该合金α和β转变组织的变化进行了观察分析。采用MTS-810低周疲劳试验机测试合金的裂纹扩展速率。通过Origin 6.0软件对数据进行处理并绘制裂纹扩展速率（△a／△N）与应力强度因子幅△K的关系曲线。结果表明：在Pairs区范围内，疲劳裂纹扩展速率对双态组织中初生α相含量的多少不敏感，而在近门槛区和快速扩展区，裂纹扩展速率对组织比较敏感；在本实验研究的条件下，细针编织状魏氏组织的da／dN〈平直状片层组织的da／dN〈双态组织的da／dN。     

不同冲击波作用区da/dN下降的机理研究

采用16Mn钢三点弯曲试样,研究了塑性冲击波和弹性冲击波作用区疲劳裂纹扩展速率da/dN的变化结果表明,经过爆炸处理,da/dN在整个冲击波作用区(约100mm)均有明显降低,以塑性冲击波作用区最为明显在整个纯弹性波作用区,如果△K相同,则爆炸处理后的da/dN在不同位置的弹性波作用区基本相同认为冲击波作用下材料具有的裂纹闭合效应使有效应力强度因子△K_(eff)的减小是da/dN下降的主要原因在塑性波冲击区,裂纹闭合主要由裂纹尖端产生的塑性形变和氧化物形成;在弹性波作用区主要由塑性形变和粗糙度产生     

铸造Ti-6Al-4V合金的疲劳性能研究

通过铸造Ti-6Al-4V合金疲劳性能试验,绘制出了铸造Ti-6Al-4V合金在不同应力比下裂纹扩展速率da／dN-△K曲线。根据logda／dN和log△K的拟合曲线方程,计算出Paris公式下材料常数c、n值。经SEM对铸造Ti-6Al-4V疲劳断口进行分析,发现随着应力比R的增大,疲劳条带越宽,裂纹扩展速率越大。     

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.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.