锻态TB6钛合金的热变形行为和热加工图

采用Gleeble热模拟试验机,对锻态TB6钛合金在变形温度660~1050℃,应变速率0.001~0.1s-1的条件下进行等温恒应变速率压缩试验,研究了TB6钛合金的高温压缩变形行为。基于Prasad判据绘制了该合金的热加工图,结合变形微观显微组织分析,确定了该合金在(α+β)两相区至β相区的最佳工艺参数。结果表明:当应变速率0.01~0.1s-1,变形温度980℃时,其变形机制为动态回复,失稳现象不明显。最终确定了应变速率为0.001~0.1 s-1,变形温度为815℃左右,为该合金的最佳热加工工艺参数。     

基于Murty判据的TB8钛合金加工图及变形区分析

采用Gleeble3500对TB8钛合金进行等温恒应变速率热模拟压缩试验,研究该合金在温度750~900℃、应变速率0.001~10 s-1热变形参数范围内基于Murty判据的加工图,并分析TB8钛合金的热变形行为。结果表明:TB8钛合金的失稳变形区为:温度750~780℃,应变速率0.03~10 s-1;温度780~900℃,0.35~10 s-1,发生失稳变形后的组织特征为局部流动及β相晶粒的不均匀变形。较佳的稳定变形区为:温度815~885℃、应变速率0.03~0.1 s-1,发生稳定变形后的组织为动态再结晶后的等轴组织。结合预测的稳定变形区及显微组织特征可知,在单相区850℃变形时,0.1 s-1作为动态回复及动态再结晶的临界应变速率。     

锻态TB9钛合金高温压缩行为数值模型研究

在Gleeble 3500热模拟试验机上对锻态TB9钛合金在变形温度1 003~1 103 K、变形速率1~0.001 s-1进行了等温压缩变形处理。基于真应力-应变曲线建立了锻态TB9钛合金高温变形稳态流变方程。结果表明,TB9钛合金的峰值应力随变形温度的提高和应变速率的减小而降低,达到峰值应力后,在加工硬化和流变软化共同作用下进入稳态流变阶段;获得了锻态TB9钛合金高温变形的本构方程。     

基于加工图技术的铸态TB6钛合金锻造工艺优化

在Thermecmaster-Z型热模拟实验机上对铸态TB6钛合金在800~1150℃、0.001~10 s-1变形参数范围内进行了等温恒应变速率压缩实验,根据实验数据采用基于Murty准则的加工图技术对该合金的锻造工艺进行了优化,并结合显微组织观察研究了该合金的变形机制。结果表明,在低温区的较佳变形参数为800~950℃、0.001~0.01 s-1,其变形机制为大晶粒超塑性;在高温区的较佳变形参数为1020~1080℃、0.001~0.006 s-1,其变形机制为动态再结晶。失稳区出现在800~890℃、0.01~10 s-1的低温区和975~1120℃、3.162~10 s-1的高温区域,在流变失稳区会出现晶界裂纹。     

铸态TB6钛合金β相区热变形行为的研究

采用Thermecmastor-Z型热模拟试验机对铸态TB6钛合金在真应变为0.92、变形温度为950～1100℃、应变速率为0.001～10 s-1的条件下进行等温恒应变速率压缩试验,研究了该合金在β单相区的热变形行为及变形机制.结果表明,该合金的流动应力曲线主要呈流动震荡和流动软化两种特征.在0.001～0.01 s-1时,流动曲线呈小幅度流动震荡;而在10 s-1时,流动曲线呈大幅度流动震荡;在0.1～1 s-1时,流动曲线呈流动软化特征.通过微观组织观察可知:当应变速率为0.001 s-1时的变形机制为动态再结晶;在0.01～1 s-1时的变形机制主要为动态回复;在10 s-1时的变形机制为局部流动.从细化组织和降低变形抗力方面考虑,应变速率以不超过0.1 s-1为宜.     

TB17钛合金热压缩流变应力分析及本构方程

使用Gleeble-3500热模拟试验机在变形温度为800~1000℃、应变速率0.001~10 s~(-1)以及真应变为1.2的条件下对TB17钛合金进行热变形行为研究。根据热压缩数据,分析真应力-真应变曲线,计算TB17钛合金变形激活能,并建立了TB17钛合金应力-应变本构模型,对金相组织进行分析,并进行了本构模型的验证。结果表明,TB17钛合金在热压缩变形过程中,出现动态回复和动态再结晶现象,在低应变速率0.001和0.01 s~(-1)下,以动态再结晶为主要软化机制,在高应变速率1和10 s~(-1)下主要以动态回复为软化机制;流变应力随应变速率的下降和变形温度的升高而降低;峰值应力计算值和实验值的平均误差为6.5%,表明该模型有很高的精确度。研究为TB17钛合金塑性加工过程的模拟和控制提供了参考。     

基于BP神经网络的TB8钛合金流变应力预测模型

利用人工神经网络(ANN)模型来建立钛合金本构关系以及TB8钛合金热压缩试验数据,采用误差反向传播(Error Back-Propagation Networks)算法模拟了流变应力。结果表明:TB8钛合金在较宽泛温度948~1073K,应变速率在0.001~10s-1含有两个节点数为18的隐含层BP神经网络模型,这为研究TB8钛合金高温塑性变形行为提供了依据。对不同相区不同变形机制的TB8钛合金应力应变行为进行精确表征,训练阶段,最大绝对相对误差3.78%。在验证阶段,最大绝对相对误差4.06%,且大部分相对误差点分布在±2%的范围内,实现了较高的精度。     

TC4钛合金热变形行为研究及本构模型

利用Gleeble-3500热模拟试验机进行等温恒应变速率热压缩实验,研究了TC4钛合金在温度800~950℃、应变速率0.001~10s-1条件下的流动软化行为。研究发现随变形温度降低和应变速率增大TC4钛合金的流动软化程度增大,且800~850℃、应变速率1~10s-1变形时的流动软化主要是塑形流动失稳引起的,温度900~950℃、应变速率0.001~0.1s-1条件变形时,流动软化主要是片状α相的等轴化引起的。引入应变对材料常数α、n、A和Q的影响,建立了考虑应变的TC4钛合金Arrhenius本构方程,建立的本构模型精度较好,在800℃、850℃和10s-1条件以及在900℃、950℃和0.1s-1条件下,模型平均绝对误差分别为4.2%和4.3%。TC4钛合金的平均变形激活能为403kJ/mol,平均应变速率敏感指数为0.26。     

铸态TB6钛合金热变形过程中应力诱发马氏体相变

对铸态TB6钛合金进行了恒应变速率热模拟压缩试验（变形温度为800~1150 ℃、应变速率为0.001~10 s-1）,研究了合金微观组织演变和应力诱导马氏体（SIM）相变。结果表明,该合金在热变形过程中出现了具有枝晶形态的正交结构SIM。SIM在β晶内和晶界形核。应变速率和变形温度控制合金成分均匀性和内应力,是SIM析出量的主要影响因素。不同应变速率的SIM析出量与变形温度范围有关。SIM析出量较高变形条件为：在800~900 ℃时应变速率为0.1 s-1,900~1000 ℃时应变速率为0.01和1 s-1,在1000 ℃以上时应变速率为1 s-1。在变形温度925 ℃、应变速率1 s-1时SIM析出量达最大化为50%。     

基于BP神经网络的TB17钛合金热变形行为研究

利用Gleeble-3500热模拟试验机,在变形温度为800～1 000℃,应变速率为0.001～10s-1条件下对TB17钛合金进行等温恒应变速率压缩试验,获得不同参数下合金的流动应力数据。通过金相组织观察,研究了热变形过程中的合金组织的变化规律。建立了具有BP算法的人工神经网络,利用所建立的BP网络模型对TB17钛合金的流动应力进行预测,发现预测值与试验值符合较好,验证了该BP网络本构关系模型的准确性。     

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.     

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.