微量TiC、TiB2引起铝熔体粘度的突变现象

研究了TiC、TiB2两种钛化物对纯铝及亚共晶Al 6 5%Si合金熔体粘度的影响。结果表明,加入少量Al 5Ti 1B或Al 3Ti 0 15C中间合金的铝熔体,其粘度大幅度增加。如在工业纯铝中加入0 3%的Al 5Ti 1B后,其粘度增加了31 83%;在Al 6 5%Si合金熔体中加入0 5%的Al 3Ti 0 15C后,其粘度增加了59 51%。因此,熔体中引入固相粒子是引起熔体粘度增加的原因之一,并在此基础上进行了机理探讨。     

TiAl_3对TiC粒子在铝基体中分布及α(Al)晶粒形核的影响

研究TiC和TiAl_3细化工业纯铝时TiAl_3的存在对TiC在铝基体中分布及α(Al)晶粒形核的影响,分析Al-Ti-C晶粒细化机制.结果表明:TiC单独作为工业纯铝的晶粒细化剂时,大量TiC被α(Al)晶粒推向树枝晶的晶界处,从而限制了TiC的异质形核作用;当TiC和TiAl_3共同作为晶粒细化剂时,在α(Al)晶粒内部出现了大量TiC粒子,大量的TiC粒子成为了α(Al)的结晶核心,并且在TiC颗粒和铝基体的界面处存在"富Ti过渡区";TiAl_3在铝熔体中分解释放出Ti原子并向TiC粒子周围偏聚,形成的"TiC/铝熔体界面富Ti过渡区" 改善了TiC与α(Al)的结构适应性,降低了TiC粒子的表面张力,促进了TiC粒子在铝熔体中的均匀分布,提高了其形核能力.     

TiB2/Al复合材料熔体的粘滞性

通过对TiB:颗粒增强铝基复合材料熔体粘度的系统测量和分析,研究了TiB2颗粒增强铝基复合材料熔体的粘度随温度变化的规律和熔体结构的变化.结果表明TiB2颗粒增强铝基复合材料熔体的粘度随温度的变化呈明显的不连续性,根据粘度的变化可以将熔体状态分为高温区、中温区和低温区,各温区间存在粘度突变温度点.在低温区和中温区之间可能存在着由TiB2引起的熔体结构的变化.     

SiC/Ti-6Al-4V复合材料界面反应的扫描电镜分析

采用扫描电镜分析了国产SiC纤维增强Ti-6Al-4V复合材料的界面反应,发现不带C涂层的SiC纤维与Ti-6Al-4V反应形成TiC和钛的硅化物,带有C涂层的SiC纤维与Ti-6Al-4V反应仅形成TiC。观察表明C涂层的厚度差别较大。     

超重力场反应加工TiB2基凝固陶瓷——Ti-6Al-4V多尺度多层次复合研究

采用超重力场反应加工技术,通过陶瓷-钛合金之间熔化连接与原子互扩散,制备出TiB2基凝固陶瓷—Ti-6Al-4V层状复合材料。XRD、FESEM及EDS分析发现,正是作为陶瓷基体相的TiB2片晶(或板晶)可诱发强烈的自增韧机制,使TiC-TiB2细晶凝固陶瓷具有高的弯曲强度与断裂韧性,并且也正是因在超重力场反应加工引发的热真空环境下钛合金与液态陶瓷发生熔化连接与原子互扩散,进而在凝固后期相继诱发TiB2与Ti液的包晶反应、TiB自钛液的析晶反应及TiB与钛液的共晶反应,最终实现以TiB2、TiB尺寸与分布为特征的陶瓷—钛合金多尺度(微米—亚微米—微纳米)多层次(TiC/TiB2—TiC1-x/TiB/TiB2—TiB2/Ti/TiC1-x/TiB—TiB2/TiC1-x/TiB/Ti—TiB/TiC1-x/Ti—TiC1-x/Ti—Ti)复合。     

TiC颗粒增强钛基复合材料的内应力

利用X射线衍射技术测试了TiC颗粒增强钛基复合材料Ti-6Al-4V 7％TiC(质量分数，下同)(T64)，Ti-3Al-2．5V 7％TiC(T32)和Ti-6Al-2．5Sn-4Zr-0．5Mo-1Nb-0．45Si 3％TiC(T650)的内应力。发现该复合材料在800℃左右存在一个应力性质转变点，即在800℃以上处理，钛基体感生残余拉应力，增强TiC颗粒感生残余压应力；在800℃以下处理，应力性质相反。并且内应力随处理温度升高而增加，由Eshelby模型得出，该转变点和钛合金基体的相变点有关。     

热处理对镀镍后钛基复合材料组织和性能的影响

为了进一步提高(TiC+TiB)/Ti-6Al-4V钛基复合材料的力学性能和物理化学性能,在钛基复合材料表面进行了化学镀镍处理,并通过不同温度的等温热处理,研究了钛基复合材料组织演变和性能的变化。结果发现,化学镀镍后,(TiC+TiB)/Ti-6Al-4V钛基复合材料在高温预扩散过程中,首先在其表层生成NiTi、Ni_3Ti和Ti_2Ni等多种镍钛的化合物;进一步扩散时,表层Ni元素主要沿着相界向内扩散,并随着热处理温度的变化,基体组织形貌和化合物相的种类都出现了变化,基体组织在950℃等温时出现了层片状共析组织,而继续升高温度会造成组织严重粗化,层状组织消失;试样的整体硬度随着热处理温度的升高,呈先下降后上升的趋势。     

Fe对Al-Ti-B和Al-Ti-C中间合金细化纯铝时晶粒形核与生长行为的影响

分别用Al-Ti-B、Al-Ti-C两种中间合金细化不同Fe含量(w(Fe)=0.2%～1.0%)的铝。通过扫描电镜观察异质形核晶粒核心及围绕核心所形成的晕圈,分析晶粒形核及生长过程。结果表明,两种中间合金加入铝熔体后释放出的TiB2和TiC颗粒都能吸附熔体中的Ti,形成围绕TiB2和TiC颗粒的Ti浓度梯度场。围绕TiB2和TiC颗粒团的晕圈形状存在差异:围绕TiB2颗粒团的晕圈基本为圆形,围绕TiC颗粒团的晕圈基本为花瓣状。在Fe元素存在的条件下,由于晕圈之间的融合以及晶粒核心颗粒不同造成的晕圈形状差异对晶粒的生长方式有重要影响。在晕圈形状相同的条件下,Fe含量对晶粒生长行为影响显著,随着Fe含量增加,晶粒的树枝化程度变大。     

SiCf/Ti-6Al-4V复合材料的界面研究

采用扫描电镜、透射电镜和X射线衍射仪研究了用中国制备SiC纤维增强的Ti-6Al-4V复合材料的界面反应,发现在SiC纤维的C涂层和Ti-6Al-4V基体之间形成的界面反应产物为细晶粒和粗晶粒的TiC,而无C涂层的SiCf/Ti-6Al-4V的界面反应产物,从SiC纤维到Ti-6Al-4V基体,依次为细晶粒的TiC+Ti5Si3、粗晶粒的TiC和Ti3SiC2.还测量了界面反应区厚度并讨论了界面反应机理.     

原位[TiB2(p)+TiCp]/Fe复合材料的制备和微结构

热力学分析表明，Fe-Ti-B-C熔体具有反应生成TiB2和TiC的可能性，TiB2和TiC热力学稳定性相当。试验结果表明，利用Fe-Ti-B-C熔体反应可以制备TiB2和TiC颗粒增强铁基复合材料，TiB2颗粒和TiC颗粒均匀分布于α-Fe晶粒中，TiB2颗粒比TiC颗粒具有更大的平均尺寸。     

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。