TC18钛合金高温变形行为与加工图

采用Gleeble1500热模拟机进行了热压缩试验,研究了TC18钛合金在温度700～950℃,应变速率0.001～10s-1条件下的高温压缩变形行为,并根据应力-应变曲线建立了合金的加工图.研究结果表明:合金在两相区温度变形,应力-应变曲线呈现流变软化特征;而在单相温度区和高应变速率下,合金表现出间断的屈服现象.合金适宜的加工条件为T=700～850℃,(ε)=0.01～0.001s-1与T=850～900℃,(ε)=1～10s-1.合金热加工失稳区为T=700～750℃,应变速率为0.1～10s-1区域.     

热等静压态TC4钛合金高温变形行为研究

在不同变形温度(T=850～1050℃)和不同应变速率(ε觶=0.001～5s~(-1))下采用Gleeble~(-1)500D热模拟试验机对热等静压态TC4钛合金进行了高温热压缩试验,分析了真应力-真应变曲线特征及热变形参数对显微组织的影响,建立适用于热等静压态TC4钛合金高温流动行为的Arrhenius方程及DMM(动态材料模型)加工图。结果表明:峰值应力随应变速率的增大及变形温度的降低而增大;显微组织随变形温度升高发生马氏体相变,随应变速率增大,β相析出次生α'相,且T=900℃、ε觶=0.01s~(-1)时获得(α+β)双态组织,表明该条件能够改善材料加工性能。误差分析表明,峰值应力计算值与试验值平均相对误差绝对值仅6.77%,证明建立的本构方程能够准确预测材料高温变形时的流动应力。加工图分析表明材料流动失稳区为T=850～950℃、ε觶0.6 s~(-1),最佳加工区间为T=850～950℃、ε觶=0.01～0.1s~(-1)。     

TA7钛合金板材高温拉伸变形

利用Gleeble-1500D热模拟试验机对板厚为4 mm的TA7 ELI材料在变形温度为800、850、900、950和1000℃,应变速率为0.01 s~(-1)和0.001 s~(-1)下进行高温拉伸实验,获得材料发生超塑性变形的温度区间和应变速率范围。采用炉中高温拉伸实验对Gleeble实验结果进行验证。得出在950～1000℃范围内,应变速率低于0.001s~(-1)时,TA7 ELI钛合金高温拉伸会出现超塑性变形。伸长率最高可达260%。在应变速率0.001 s~(-1)、800℃时,TA7钛合金的断口组织中有动态再结晶现象。1000℃时,断口出现较为粗大的层片状α组织和明显的晶粒长大现象。m和n值都随着温度的升高而增大,在950℃时到达最大值。硬化现象能够有效的抑制颈缩,变形温度为950℃时,材料的硬化和软化达到较好的平衡,易获得较大的伸长率。     

TA10钛合金高温流变行为及拉伸性能

利用Gleeble-1500D热模拟试验机对TA10钛合金在变形温度为800~1050℃,应变速率为0.01~5 s-1条件下进行拉伸变形,研究合金的流变应力及显微组织,分析其高温拉伸性能。结果表明:变形温度为800~900℃时,流变曲线有明显的应力峰值,软化机制主要是动态再结晶;而变形温度为1000~1050℃时,流变曲线没有明显的应力峰值,软化机制为动态回复;而当变形温度为800℃时,TA10钛合金的应变速率越高动态再结晶的进行程度越低;以(α+β/β)相变点为界,在相变点以下的温度区间,随着变形温度的升高,TA10钛合金的强度和塑性下降;在相变点以上的温度区间,TA10钛合金的强度下降,塑性上升;而在相变点的过渡区间,强度上升,塑性下降。当应变速率一定时,TA10钛合金在温度为800℃时能够获得强度和塑性的较好匹配。     

基于响应面法的TA5钛合金工艺参数优化

在变形温度为850～1050℃、应变速率为0.001～10s-1和最大下压量为60%的条件下,采用Gleeble-3800热模拟试验机对TA5钛合金进行等温恒应变速率压缩试验。基于实验数据,分析TA5钛合金的流变应力曲线,计算出不同工艺参数下的材料参数（变形激活能、Z参数以及功率耗散系数）,建立了基于响应面法的工艺参数和材料参数的预测模型,最后对响应面模型进行多目标可视化优化,得到优化后的工艺参数。结果表明：TA5钛合金的流变应力具有负温度相关性和正应变速率敏感性。基于响应面法所建立的预测模型具有较高精度,且优化后的加工参数范围为850～990℃/0.004～0.15 s-1。经组织验证,该区域主要的变形机制为动态回复和动态再结晶。     

0Cr11Ni2MoVNb钢连续冷却热压缩特性研究

采用Gleeble 3500研究了0Cr11Ni2MoVNb钢在变形速率0.01s-1,温度为1100℃～850℃时的连续冷却热压缩特性,结果表明,加热一次压缩0Cr11Ni2MoVNb钢在950℃变形抗力增加幅度加大,即终锻温度或终轧温度不应低于950℃;加热一次热变形压缩没有发现动态再结晶,加热两次及三次后变形有动态再结晶出现,出现再结晶的温度区间为1000℃～1050℃.     

FGH4096粉末高温合金的热变形行为

对FGH4096合金进行了变形温度1050～1140℃,应变速率0.001～2s-1的热压缩实验。分析了合金的流变行为,构建了Arrhenius型本构方程,得到合金的热变形激活能为870.785kJ/mol。并建立了能够准确描述热加工过程中能量耗散情况和预测变形失稳的热加工图。结果表明:能量耗散与动态再结晶和晶粒长大有关,在变形温度Td为1050～1070℃,应变速率ε为0.001～0.01s-1范围内,峰值耗散率为61%(1050℃,0.001s-1),此区域易形成"项链"组织,很多晶粒处于形核阶段;在Td为1100～1140℃,ε为0.001～0.01s-1范围内,能量耗散峰值达50%(1110℃,0.001s-1),此时,晶界迁移显著,再结晶晶粒明显长大;在Td为1070～1100℃,ε为0.01～0.1s-1范围内,能量耗散率大于39%左右,再结晶完全、晶粒细小。Td为1060～1100℃,ε为0.5～2s-1时,合金落入流变失稳区,能量耗散率达到最小值,局部变形严重是造成流变失稳的重要原因。     

铸态TC21钛合金高温变形行为研究

以铸态TC21钛合金为研究对象,在Gleeble3500热模拟试验机上对TC21钛合金在开坯温度1000～1150℃、应变速率0.01～10 s-1的高温变形行为进行了研究.结果表明,铸态TC21钛合金流动应力随应变速率的提高和温度的降低而升高,具有温度和应变速率敏感性;β区变形激活能为196.277 kJ/mol,变形机制以动态回复为主;低应变速率下(ε≤0.1 s-1),流变曲线呈稳态流动特征,拉长的β晶粒晶界呈锯齿状,晶界处发生连续再结晶;高应变速率下(ε≥1 s-1),拉长的β晶粒晶界平直,为典型动态同复;高应变速率且温度相对较低(ε=10 s-1,T≤1150℃)时,流变曲线呈流动软化特征,原因是局部温升效应及局部塑性流动.     

Cu-Cr-Zr-Y合金动态再结晶临界机制

利用Gleeble-1500D热模拟试验机,采用高温等温压缩试验,对Cu-0.4Cr-0.15Zr-0.04Y合金在应变速率为0.001~10 s-1、变形温度为650~850℃、最大变形程度为50%条件下的动态再结晶行为以及组织转变进行了研究。利用加工硬化率和应变(θ-ε)的关系曲线确定了该合金发生动态再结晶的形变条件为T≥750℃,应变速率小于0.1 s-1;根据θ-σ模型,确立了合金变形特征参数之间的关系:σc/σp=0.86,εc/εp=0.30;同时建立了合金变形特征参数与Z参数的关系:εp=2.61×10-3Z0.14,εc=7.83×10-4Z0.14。Cu-0.4Cr-0.15Zr-0.04Y合金在热变形过程中的动态再结晶机制受变形温度和应变速率的控制。当温度达到850℃,应变速率为0.001 s-1时,合金发生完全的动态再结晶。     

0Cr11Ni2MoVNb钢高温压缩变形的流变应力

采用Gleeble-2000热模拟试验机对OCr11Ni2MoVNb马氏体热强钢在不同变形温度(950～1160℃)及不同变形速率(0.01～10 s-1)的高温压缩变形的流变应力进行了研究.结果表明,当应变速率低于0.1 s-1且温度高于1000℃时,OCr11Ni2MoVNb钢出现动态再结晶,其热变形激活能Q=461.568 kJ/mol,高温压缩变形时Z参数和流变应力方程分别为Z=εexp(55516.959/T)=5.654×1013exp(0.075σp),σp=13.4131nε 7.447×1051/T-422.214.     

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。