825合金热加工过程相变化规律研究

研究了825合金经不同温度(600—1 050℃)热处理时相析出规律。结果表明,在此温度区间,晶界上析出M23C6,750—800℃为析出峰,M23C6相开始析出温度在940℃以下。Ti C相最高形成温度在940—980℃之间,形成位置在晶界上。热加工过程中形成的Ti C相经动态再结晶后存在于原始晶界上。热加工过程中形成的Ti C完全溶解温度在1 070—1 100℃之间。基体形貌为孪晶奥氏体。     

A位掺杂Bi4Ti3O12陶瓷的铁电性能研究

用传统固相烧结工艺,制备了纯相的Bi4Ti3O12 (BTO)陶瓷,A位掺杂的Bi3.25La0.75Ti3O12(BLT),Bi3.15Nd0.85Ti3O12(BNdT)铁电陶瓷.X射线衍射结果表明,所有样品均为单一的层状钙钛矿结构,La、Nd掺杂未改变BTO的晶体结构.铁电测试结果表明,BTO、BLT和BNdT陶瓷的剩余极化2Pr值分别为12.4、23.8和39.4μC/cm2.A位掺杂后,BLT、BNdT的2Pr值比未掺杂的BTO分别提高了1.92和3.18倍.漏电流测试表明,BLT、BNdT陶瓷的漏电流密度比BTO明显降低.A位掺杂显著提高了BTO陶瓷的铁电性能.     

7050铝合金在不同温度变形的动态析出行为

研究了7050铝合金在不同温度变形的动态析出行为,结果表明:7050铝合金在不同温度的变形过程中MgZn2相动态析出不影响流变应力的波动,变形加速了动态析出过程;随着变形温度的升高,部分析出相MgZn₂颗粒由球状变成板条状,尺寸增大数量减少,在450℃变形过程中粗大的板条状MgZn₂相易破碎;同时,位错密度减低,位错胞团变成离散位错墙。析出相钉扎位错和阻碍晶界迁移,主要以亚稳态η′和平衡态η形式存在,在变形过程中不会产生微裂纹。     

TC11钛合金线性摩擦焊界面微观组织演变

为了探明TC11钛合金线性摩擦焊过程中界面金属微观组织演变规律,采用光学显微镜和扫描电镜来研究飞边与接头的微观组织。结果表明,线性摩擦焊界面演变过程可依次分为摩擦磨损、黏着剪切、界面金属形成金属键连接并发生大变形、动态再结晶四个阶段。当摩擦时间足够长时,整个摩擦界面温度趋于均匀,在界面上将形成一层厚度均匀的塑性金属层,α相完全转变为β相,并且初生β相晶粒将发生动态再结晶过程。随着摩擦时间的延长,界面温度升高,初生β相动态再结晶晶粒尺寸增大。     

颗粒动态散射光分形特征的提取及温度影响

颗粒的动态散射光信号具有分形特征,通过对其分析可获取颗粒粒径的信息.本文研究了颗粒动态散射光的波动及其分形特征的提取,并通过对颗粒平移扩散系数的分析,研究了温度对动态散射光分形维数的影响.采用粒径为60nm、90nm、200m、300nm、450m的标准聚苯乙烯颗粒进行了实测,分别求取了不同温度下颗粒动态散射光信号的分形维数.实验结果表明,当颗粒粒径相同时,温度越高,分形维数越大;当温度相同时,粒径越小,分形维数越大.     

TC21钛合金热变形过程中片层α相动态球化行为研究

目的 定量分析不同热变形参数下片层α相的演化行为,探究不同热变形参数对TC21钛合金中片层α相动态球化行为的影响规律,并探讨片层α相在动态球化过程中的组织演变机理。方法 基于Thermecmastor-z热模拟试验机对TC21钛合金开展不同变形参数的热压缩试验,结合SEM-EBSD材料表征技术进行显微组织的表征。结果 随着温度从890℃升高至950℃,片层α相的平均厚度从0.65μm先增大至0.72μm后减小至0.16μm;在高温、低应变速率的条件下,片层α相球化百分数约为59%,而在低温、高应变速率条件下,片层α相球化百分数降至约26%;随着应变速率由0.001 s^-1升至1 s^-1,片层α相球化百分数的增量由10%减少至不足2%。结论 温度的高低主导了片层α相尺寸的变化趋势;变形温度的升高及应变速率的降低加速了片层α相的球化进程,而应变速率为主要影响因素;在α+β两相区变形过程中,LAGBs常形成于片层α相内部位错塞积程度较高的区域,并以此作为发生动态球化的界面。随着动态球化百分数的增大,α相中LAGBs的体积分数减小,而HAGBs的体积...     

Ti-10V-2Fe-3Al合金热变形的研究

利用Gleeble3500热模拟试验机对Ti-10V-2Fe-3Al合金两种状态在不同变形温度及不同变形速率条件下的热变形行为进行了研究。结果表明，不同初始状态对合金的应力应变行为影响较大，经过固溶处理后在低于相变点变形时合金的流变应力比较高，但在高于相变点变形时流变应力没有明显差异；合金的应力指数与合金的状态和应变速率有关，大概以0．1s^-1为界分为低应变速率和高应变速率两部分；合金的表观激活能与材料的状态、变形温度及变形速率有关。当两种状态下的合金在温度为650～800℃、应变速率为0．001～0．1s^-1范围内变形时，β相内只发生动态回复，而α相除了发生动态回复外还可能发生动态再结晶；合金在相变点以上变形时只存在着单一的动态回复机制。     

Sr0.4Ba0.6Nb2O6物相形成过程的XRD分析

采用X射线衍射技术（Guinier-Hagg相机）分析了Sr0.4Ba0.6Nb2O6（SBN40）原始混合粉料经不同温度煅烧后的相组成，并利用PIRUM程序对不同反应温度下形成铌酸锶钡相的晶胞尺寸进行了计算。结果表明：在Sr0.4Ba0.6Nb2O6的形成过程中将出现中间相Na5Nb4O15、Sr5Nb4O15、SrNb2O6与BaNb2O6，而SrNb2O6与BaNb2O6最终反应生成铌酸锶钡。反应生成的铌酸锶钡的晶胞参数随反应温度的升高而变小。依据这些实验结果，文中提出了Sr0.4Ba0.6Nb2O6相的形成机制。     

Sr0.4Ba0.6Nb2O6物相形成过程的XRD分析

采用X射线衍射技术(Guinier-Hagg相机)分析了Sr0.4Ba0.6Nb2O6(SBN40)原始混合粉料经不同温度煅烧后的相组成,并利用PIRUM程序对不同反应温度下形成铌酸锶钡相的晶胞尺寸进行了计算.结果表明:在Sr0.4Ba0.6Nb2O6的形成过程中将出现中间相Na5Nb4O15、Sr5Nb4O15、SrNb2O6与BaNb2O6,而SrNb2O6与BaNb2O6最终反应生成铌酸锶钡.反应生成的铌酸锶钡的晶胞参数随反应温度的升高而变小.依据这些实验结果,文中提出了Sr0.4Ba0 6Nb2O6相的形成机制.     

温敏凝胶流变性能动力学研究

应用动态流变实验测定了温敏共聚物的流体特性,分析其在溶胶-凝胶转变过程共聚物溶液随温度变化形成凝胶机理。以室内合成的四元共聚物溶液为基础,采用动态流变实验测定了该共聚物溶液在不同温度、浓度下的剪切模量和损耗模量的变化,确定了凝胶特性,并与试管倒置法比较了凝胶温度。实验结果表明,临界温度为143℃,在一定浓度下(高于接触浓度C*),低于此温度共聚物溶液具有一般粘性流体特性;高于此温度可形成凝胶网络结构;溶液在测试温度(65～240℃)内,其损耗角从56.27°逐渐变为31.04°,溶液体系从粘性流体逐渐到粘弹性流体过渡;说明该溶液在一定浓度下具有温敏特性。     

On the Order–Disorder Surface Phase Transition and Critical Temperature of Pure Metals Originating from BCC, FCC, and HCP Crystal Structures

The excess surface Gibbs energy and surface tension of pure liquid metals (originating from bcc, fcc, and hcp solid metals) of ordered and disordered surface structures are compared in this paper. It is shown that at a special temperature T ^* an order–disorder surface phase transition is expected in all liquid metals from a low-temperature ordered surface state to a high-temperature disordered surface state. This surface phase transition is similar to the first-order bulk solid–liquid phase transition (melting). The values of T ^* appear in the temperature interval between the melting point and the critical point of metals. Critical temperatures of metals are estimated from the equation for high-temperature disordered surfaces.     

Electrical conductivity of the ferroelectric sodium vanadate,potassium vanadate,lithium vanadate and their solid solutions

The d.c. electrical conductivity of sodium vanadate, potassium vanadate, lithium vanadate and their solid solutions sodium-potassium vanadate, sodium-lithium vanadate were measured by a two-probe method in the temperature range covering their transition points. These materials show sharp change in conductivity at their phase transition temperatures. In sodium, potassium and lithium vanadates an exponential increase in d.c. conductivity is observed in ferroelectric region while discontinuities are observed above the transition temperatures. The activation energy in paraelectric state of the solid solutions is found to be higher than in ferroelectric state. In solid solutions the activation energy depends upon sodium vanadate concentration.     

Low-temperature interface reaction in aluminium-silicon carbide particulate composites produced by mechanical alloying

An experimental investigation has been carried out on the reaction that takes place between 3 and 20 μm SiC particles and the aluminium alloy 1050 matrix of composite materials prepared by a mechanical alloying process. The work is different from that undertaken by other researchers in that the SiC-Al interface reaction has been studied in the temperature range 853–933 K, i.e., with the matrix initially in the solid state. Differential thermal analysis, X-ray diffraction and scanning electron microscopy all show that the SiC-Al reaction initiates in the solid state at temperatures as low as 883 K. The reaction produces Al4C3 and Si, the latter entering into solid solution in the aluminium matrix. At temperatures exceeding 903 K, the reaction produces a liquid phase and at this stage the speed of the interface reaction increases significantly. The results are discussed in terms of Al-Si-C metastable equilibrium and the kinetics of the reaction. This revised version was published online in November 2006 with corrections to the Cover Date.     

高能球磨时间和退火温度对制备TiNi合金粉的影响

为获得高能球磨时间和退火温度对TiNi机械合金粉特性的影响机制,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、差示扫描量热法(DSC)等分析方法对TiNi合金粉进行了研究。结果表明,机械合金的相成分随着在氩气保护气氛中的球磨时间和退火温度的不同而发生变化。球磨22h的产物是非晶态TiNi合金、Ti的固溶体、Ni的固溶体,球磨27h的产物是非晶态TiNi合金粉和Ni固溶体相,球磨30h发生了明显的固相反应,生成了TiNi、Ni3Ti、Ti3Ni4等物相;在650℃/5h和1000℃/5h下的退火产物都是Ni3Ti、Ti2Ni、TiNi2、TiNi和TiC,但在上述2个退火温度下TiNi并不是主要物相,其中在650℃退火时TiNi的含量明显更低。     

Microstructure, electrical and magnetic properties of polycrystalline La0.85K0.15MnO3 manganites prepared by different synthesis routes

Influence of different synthesis techniques (solid state reaction, sol–gel and co-precipitation) on the structure, microstructure, magnetic and electrical properties of polycrystalline La_0.85K_0.15MnO₃ (LKMO) sintered at 900 °C is investigated. All the as-synthesized compounds were confirmed as single phase and hexagonal structure at room temperature. The nano-crystallite size and average grain size were increased from the sample synthesized through solid state, sol–gel and co-precipitation techniques. The electrical and magneto-transport properties of polycrystalline LKMO was relied on the synthesis method. Significant decreases in metal–insulator transition temperature (T_p) with the increment of resistivity were observed for co-precipitation synthesized sample when comparing with solid state and sol–gel synthesized samples. Magnetization was decreased while ferro-paramagnetic transition temperature (T _c) was shifted toward lower temperature from solid state synthesized sample to co-precipitation synthesized sample. Furthermore, co-precipitation synthesized sample achieved the highest negative magnetoresistance at room temperature.     

Temperature-dependent Raman spectroscopic study of the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl

The spectral behaviors of 4-n-pentyl-4'-cyanobiphenyl (5 CB) have been studied by means of temperature-dependent Raman spectros-copy in the range between --70 and 70 degrees C. The nu(C identical with N) bands in the Raman spectra were found splitting below the transition temperature from the solid to the nematic liquid crystalline phase at approximately 24 degrees C, suggesting the existence of solid crystalline polymorphism. The interfacial structures of 5 CB on metal plate surfaces have been reexamined by surface-enhanced Raman scattering (SERS) at different temperatures. On Ag and Au, the asymmetric shapes of the nu(C identical with N) bands suggest that there should exist different binding schemes for 5 CB on metal surfaces. These asymmetric bands in the nu(C identical with N) stretching region were found to vary in changing temperature.     

Electrical conductivity of ferroelectric sodium vanadate,rubidium vanadate,cesium vanadate and their solid solutions

The d.c. electrical conductivity of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions sodium-rubidium vanadate and sodium-cesium vanadate were studied by a two-probe method in the temperature range covering their transition points. The electrical conductivity shows sharp change at the phase transition temperature of these materials. In NaVO₃, RbVO₃ and CsVO₃, increase in d.c. conductivity is observed in the ferroelectric region while nonlinearities are observed above transition temperatures. In solid solutions, the activation energy in the paraelectric state is higher than that in the ferroelectric state and depends upon sodium concentration.     

The electrical and interface properties of metal-ferroelectric (lanthanum substituted bismuth titanate: BLT)-insulator-semiconductor (MFIS) structures with various insulators

We have investigated metal-ferroelectric-insulator semiconductor (MFIS) structures with lanthanum substituted bismuth titanate (BLT) as a ferroelectric layer and lanthanum oxide (LO) or zirconium silicate (ZSO) as an insulating buffer layer between BLT and Si substrate. The morphology of BLT films deposited on LO or ZSO oxide was not changed due to the good thermal stability of LO and ZSO films. But an interface reaction between BLT and buffer layer started at high annealing temperature (750 °C), which was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The maximum memory window was 3.59 V at a sweep voltage of 7 V with the LO film annealed at 650 °C and a thickness of 5 nm. With BLT/LO annealed at 750 °C, the window was decreased due to the reaction between the BLT film and LO. The memory window was about 1 V lower with a ZSO film because ZSO film has a lower dielectric constant than LO film. The MFIS structure annealed at 750 °C had a lower leakage current density because the electrical properties of the buffer layer (La oxide or Zr silicate) were improved by the thermal process.     

New promising Co-free thermoelectric ceramic based on Ba–Fe–oxide

Thermoelectric ceramics are based in a limited number of transition metal oxides (Co, Mn, Ni,…) which produce materials with high thermoelectric performances. Based on previously existing thermoelectric phases, the phase diagram equilibrium can help to design new thermoelectric ceramics based on other transition metals (for example, Fe). In this work, BaFeO_x ceramics have been prepared by the classical solid state method using different sintering temperatures. The produced materials have shown promising thermoelectric properties when treatment temperatures are in the perovskite zone domain of the phase equilibrium diagram. In spite of the good values for the Seebeck coefficients, power factor is low due to the high resistivities measured in all cases.     

Ca掺杂EuMnO3体系的磁性和磁卡效应研究

采用传统的高温固相反应法制备了钙钛矿氧化物Eu1-xCaxMnO3(x=0,0.1,0.2,0.3,0.4,0.5)多晶体系样品。通过样品的XRD谱线、磁化强度随温度、外加磁场的变化曲线(M-T、M-H)等数据研究了Ca不同掺杂量对钙钛矿氧化物EuMnO3系列多晶样品的居里温度、磁熵变、磁相变等的影响。结果表明,Eu1-xCaxMnO3(x=0,0.1,0.2,0.3,0.4,0.5)系列陶瓷样品呈现良好的单相性,空间点群为Pnma。低浓度掺杂的样品存在一个TC,高浓度掺杂的样品出现两个磁转变点,且由于双交换相互作用,随着Ca的掺杂,TC逐渐增大,当掺杂量达到0.4时,低温下的TC却明显减小。根据-ΔSM和RCP值可知,Eu0.7Ca0.3MnO3是该组样品中比较适合做磁制冷的材料。通过对Loop曲线的分析可知该组样品经历了由一级相变向二级相变转变的过程。