挤压态镍基粉末高温合金热变形行为与组织研究

通过Gleeble-3500D热力模拟研究了挤压态镍基粉末高温合金在恒温和恒应变速率条件下的热变形行为和组织特征,变形温度范围为950~1150℃,应变速率范围为0.001~0.5 s-1。通过线性回归分析,获得了挤压态镍基粉末高温合金的本构方程,并求得热变形激活能为338.638 kJ·mol-1。在1050℃以下热压缩变形时,试样容易开裂;而在1050~1150℃的温度范围热压缩变形时,试样不易开裂。挤压态镍基粉末高温合金热压缩变形后发生了完全再结晶,再结晶晶粒尺寸受温度影响显著,在低于1100℃变形时,再结晶晶粒尺寸随变形温度升高稍有增大;而在高于1100℃变形时,再结晶晶粒尺寸随变形温度升高显著增大。该种合金的合理变形参数范围为0.001~0.01 s-1及1050~1100℃。     

Nb-Ti-Al高温合金的再结晶动力学和晶粒长大行为

研究了Nb-Ti-Al高温合金的静态再结晶行为及晶粒长大行为,并通过实验得出了再结晶动力学和晶粒长大方程.结果表明:冷轧变形后,合金在880～1000℃进行退火处理,可获得均匀、细小的晶粒,再结晶晶粒体积分数与退火时间的关系可用Avrami方程进行描述.随着冷轧变形量的增加,再结晶激活能逐渐减小,其范围为274.05 ～ 198.45 kJ/mol.在850 ～1000℃的温度范围内,研究了加热温度和时间对合金晶粒尺寸变化的影响.     

Nimonic 80A镍基高温合金静态再结晶行为

采用Gleeble-1500热模拟实验机对Nimonic 80A高温合金进行了双道次热压缩实验,研究了该合金在变形温度1050~1150℃,应变速率0.01~2.5 s-1,预应变0.08~0.14,不同间隙时间(0.5~5 s)下的静态再结晶行为。得到了Nimonic 80A高温合金不同变形条件下的真应力-应变曲线及变形后奥氏体晶粒组织,分析了变形温度、应变速率和预应变对该合金静态再结晶行为的影响。结果表明:变形温度、应变速率和预应变对Nimonic 80A高温合金的静态再结晶行为有着显著的影响。Nimonic 80A高温合金静态软化分数随着变形温度、应变速率和预应变的增大而增大,且静态再结晶晶粒尺寸随着温度的升高或应变速率的降低而增大。根据实验结果,建立了Nimonic 80A高温合金静态再结晶动力学模型。将静态再结晶动力学模型预测结果和实验结果进行比较,二者吻合良好,表明本文提出的模型可以较为准确的预测Nimonic 80A高温合金静态软化行为。     

基于计算机仿真镍基单晶高温合金再结晶过程分析

再结晶是影响高温合金高温蠕变性能的重要因素.以DD6镍基单晶高温合金为研究对象,建立了再结晶过程中形核生长、储能分布、晶粒长大的数学模型,利用计算机模拟技术分析了材料热处理过程中再结晶的整个过程和动力学曲线.该研究为镍基单晶高温合金生产过程中的蠕变性能优化提供了参考.     

基于计算机仿真镍基单晶高温合金再结晶过程分析（英文）

再结晶是影响高温合金高温蠕变性能的重要因素。以DD6镍基单晶高温合金为研究对象,建立了再结晶过程中形核生长、储能分布、晶粒长大的数学模型,利用计算机模拟技术分析了材料热处理过程中再结晶的整个过程和动力学曲线。该研究为镍基单晶高温合金生产过程中的蠕变性能优化提供了参考。     

新型粉末高温合金静态再结晶退火的试验研究

通过对热等静压态某高温合金冷变形试样在不同温度和不同保温时间段进行再结晶退火试验，结合热力学计算研究了静态再结晶晶粒尺寸的变化规律。结果表明，该合金中r′相的开始固溶温度为1109cC；在1050℃；低于r′相温度再结晶退火，晶粒尺寸随退火时间的延长变化不大；在1150℃或1170cC高于r′相固溶温度区间再结晶退火，晶粒尺寸明显粗化。     

变形镍基高温合金GH4037在固态和半固态下的高温变形行为及组织演变（英文）

镍基高温合金GH4037圆柱形试样以不同的应变速率0.01、0.1和1 s~(-1)在固态温度(1200、1250、1300℃)和半固态温度(1340、1350、1360、1370、1380℃)下进行压缩试验,研究GH4037合金的高温变形行为及组织演变。结果表明,与固态温度相比,半固体温度下的流动应力下降较快。此外,当应变速率为1 s~(-1)时,半固态温度下的流动应力在达到初始峰值应力后继续增大。随着变形温度的升高,初始固相晶粒和再结晶晶粒尺寸增大。在半固态温度下,固相晶粒为等轴晶,液相存在于晶界和晶内。以晶界膨胀为特征的不连续动态再结晶(DDRX)是GH4037合金的主要形核机理。     

定向凝固和单晶高温合金的再结晶

本文系统分析了定向凝固和单晶高温合金再结晶的特点、危害以及影响再结晶的主要因素,阐述了再结晶的物理本质.再结晶行为受合金元素、变形程度、热处理温度及时间、变形速率、变形工艺等的影响.再结晶的物理本质是由铸态γ'相溶解控制的高能态畸变组织向低能态无畸变组织转变的过程.镍基定向凝固高温合金再结晶开始温度在1050℃左右,钴基定向凝固高温合金在1100℃左右.定向凝固和单晶高温合金的动态再结晶行为主要与高温氧污染和自由表面有关.再结晶对高温持久、疲劳性能影响较大,含再结晶层的断口源区表现为沿晶断裂.目前定向凝固构件上的再结晶检测普遍采用金相方法.     

Re和W对铸态镍基单晶高温合金再结晶的影响

对不同Re和W含量的铸态镍基单晶高温合金通过Brinell硬度计压痕变形,分别在1230~1330℃保温1 h,研究了难熔元素Re和W对合金再结晶行为的影响.结果表明,再结晶晶粒在压痕表面形成,并沿枝晶干向内扩展,晶界迁移受到枝晶间粗大g'相和g+g'共晶阻碍.添加Re和W提高了铸态单晶高温合金的g'相溶解温度和g+g'共晶含量,导致单晶高温合金的再结晶温度升高.热处理温度升高,各单晶高温合金的再结晶面积随着枝晶间g'相和共晶含量的减少而增大.相同热处理温度下,由于不同成分单晶高温合金枝晶间粗大g'相和g+g'共晶含量不同,不含难熔元素Re和W的单晶高温合金再结晶面积最大,含Re单晶高温合金的再结晶面积大于含W单晶高温合金,同时添加Re和W的单晶高温合金再结晶面积最小.     

镍基单晶高温合金再结晶过程仿真分析

以DD6镍基单晶高温合金为对象,建立了合金再结晶过程中晶粒形核长大、储能分布的数学模型,利用计算机模拟技术分析了材料热处理过程中再结晶的动力学曲线。模拟结果和文献实验结果具有很高的吻合度,为镍基单晶高温合金蠕变性能的优化提供了参考。     

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。