基于热加工图的铸态TC18钛合金热变形特征研究（英文）

采用Gleeble-3800热模拟机对铸态TC18钛合金进行高温热压缩变形实验,分析该合金在变形温度1000~1150℃、应变速率0.01~10s~(-1)和变形量为70%条件下流变应力的变化规律。确定TC18钛合金热变形激活能,建立热加工图,并通过组织观察对热加工图进行解释。综合不同应变量下的热加工图,获得了试验参数范围内热变形过程的最佳工艺参数,为铸态TC18钛合金热加工工艺优化提供理论依据。     

基于热加工图的TC18钛合金热变形行为研究

为了研究TC18钛合金相变点附近塑性成形过程中组织变化及金属流动规律,采用金相法测定实验用锻态β转变温度为1 161 K。在TC18钛合金β转变温度±20 k,应变速率0.01~1.00 s-1,最大应变0.7的情况下,对材料进行恒温-恒应变速率热模拟压缩实验。求解不同应变条件下变形速率敏感指数m,能量耗散率因子η及失稳判据ξ等参数。获得了实验情况下真实应力-应变曲线,绘制了TC18钛合金不同应变条件下热加工图,得到了TC18钛合金实验条件下材料的最佳变形区域。     

TC21钛合金热压缩本构方程及热加工图

为准确获得TC21钛合金塑性加工的变形特征和热加工条件，合理设计锻造工艺参数，利用Gleeble-3500热模拟机进行等温恒应变速率热压缩试验，研究了TC21钛合金在变形温度为830～1010℃、应变速率为0.01～10 s^-1条件下的热变形行为，采用Arrhenius双曲线正弦函数推导出TC21钛合金本构方程。并基于动态材料模型(Dynamic Materials Model, DMM)建立了TC21钛合金的热加工图。结果表明，在本试验的变形条件下，该合金的流变应力随着变形温度的降低和应变速率的升高而增大。根据热加工图确定了合金的热加工安全区域为：变形温度为900～940℃、应变速率为0.01～0.05 s^-1和变形温度为970～1010℃、应变速率为0.01～0.08 s^-1。     

铸态T/P91耐热合金钢热加工图与热挤压工艺

利用热力模拟实验研究铸态耐热合金钢T/P91材料在热加工温度范围900~1200℃、应变速率范围0.01~5 s-1、变形量60%、70%下的真应力-应变曲线,并建立铸态T/P91合金钢的热变形本构方程;利用DMM动态材料模型计算出铸态T/P91合金钢在热变形中的耗散因子和流变失稳判据,绘制出热加工图。结果表明,热加工图预测的安全区晶粒组织均匀、组织易出现失稳开裂和组织粗大的缺陷,T/P91合金钢的热加工要避免高温低应变;利用DEFROM-3D软件通过数值模拟研究挤压工艺参数对挤压过程动态再结晶的影响,制定工艺参数为:挤压温度1500~1200℃,挤压比9,挤压速度26~36 mm/s。     

铸态12%Cr马氏体不锈钢的热变形行为与热加工图

利用Gleeble-3180热模拟机对铸态12%wtCr马氏体不锈钢进行了高温热压缩实验,研究了该钢在900~1200℃和0.001~10 s-1条件下的热变形行为,建立了热加工图。分析了工艺参数对铸态12%Cr钢微观组织的影响。结果表明:铸态12%Cr钢的流变应力随变形温度的提高和应变速率的降低而增大。动态再结晶晶粒尺寸与Z参数成反比关系。依据动态材料模型,建立了热加工图,流变失稳区集中在900~1050℃、应变速率大于1 s-1的区域,其微观组织表现为变形带和M/δ相界处的微孔、微裂纹。最佳的热加工工艺参数范围为:1050~1200℃和0.001~0.01 s-1,在稳定变形区,粗大的毫米级的柱状晶会被细化到10~40μm。     

TC18钛合金热压缩本构方程及热加工图

在温度为750～950℃、应变速率为0.01～10 s-1、变形程度为60%的条件下对TC18钛合金的高温流变应力变化规律进行热模拟实验研究。采用Arrhenius双曲正弦函数推导出TC18本构方程。以热模拟压缩实验为基础建立了真应变0.3、0.5时TC18钛合金热加工图。结果表明:TC18钛合金流变应力随着变形温度升高而降低,随着应变速率的升高而升高;在本实验条件下TC18钛合金表现出动态回复和动态再结晶两种软化机制;Arrhenius双曲正弦函数能够很好地描述TC18钛合金本构方程。热加工图结果表明:在真应变为0.3时存在3个非稳定区域,在应变为0.5时存在2个非稳定区域。结合热加工图,较佳的热加工区间在温度为830～920℃,应变速率为0.01～0.32 s-1区域内。     

TA15钛合金热变形本构方程及热加工图

采用Gleeble-3800热模拟试验机对TA15钛合金进行了热压缩,获得了TA15钛合金在750~980℃、应变速率在0.001~1 s~(-1)的应力-应变曲线。基于TA15钛合金的压缩试验数据建立了高温热变形本构方程和热加工图,并结合热加工图分析了TA15钛合金热变形组织,确定了TA15钛合金的合理热加工参数范围。结果表明,TA15钛合金本构方程为双曲正弦函数,可由Z参数表示,其热变形激活能为523.374 k J/mol。TA15钛合金高温热变形最佳工艺参数为变形温度875~980℃和应变速率0.01~0.10 s~(-1)。     

TC4钛合金EB炉扁锭高温压缩变形行为和热加工图

采用Gleeble-3500热/力学模拟试验机对电子束冷床炉(EB炉)熔炼的TC4钛合金扁锭进行高温压缩实验,研究了TC4钛合金扁锭在变形量为40％,温度为1023～1173 K,应变速率为0.001～1 s-1的条件下热压缩变形行为.通过使用双曲正弦形式修正的Arrhenius关系来描述TC4钛合金高温压缩变形时最大变形抗力的本构方程,并绘制出TC4钛合金的加工图.结果 表明,真应力-应变图可以很好地反映TC4钛合金在不同变形条件下的应力状态,且应力值和实验值有较好相关性.基于Prasad判据得到铸态TC4钛合金的热加工图的最佳变形区间为:变形温度为1023～1173 K,应变速率为0.001～0.002 s-1的区域及变形温度为1073～1160K,应变速率为0.316～1 s-1的区域.     

TC18钛合金热加工图构建、分析及有效性验证

基于动态材料模型,建立了TC18钛合金的热加工图,分析了能量耗散率、非稳定参数和热加工图随应变速率、变形温度的变化规律。结果表明,在800—900℃范围内,应变速率对TC18钛合金的热变形能量分配影响较为显著。不同应变下的能量耗散率峰值对应的变形工艺参数均为变形温度800-820℃、应变速率5×10^-41×10^-3s^-1,该参数即为TC18钛合金等温压缩变形的最佳工艺参数范围。随着应变增大,820℃／1×10^-2s^-1附近的非稳定变形区域逐渐缩小,当应变达到0．3时消失;而（860-900）℃／（1～10）s^-1的非稳定区随应变增大而逐渐扩大,并向低温区域扩展。     

TC21合金的热压缩变形行为及变形机理

对TC21合金的热变形行为进行研究,通过对该合金变形过程中应变速率敏感性指数m值、热变形激活能Q、晶粒指数P的计算,得出不同应变速率和温度下m值、Q值和P值的变化规律。在绘制动态DMM模型热加工图的同时构建含位错数量的双相钛合金高温变形机理图。应用热加工图分析TC21合金热变形工艺,确定加工失稳区以及适合加工区域。运用双相钛合金高温变形机理图,根据不同温度下TC21合金柏氏矢量补偿的晶粒尺寸、模量补偿的应力值和位错数量预报该合金的热变形机理。     

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).     

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.     

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.     

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。