原位合成Cu/TiC材料的热力学计算

比较了Cu-Ti-C三元系中各种可能反应的标准吉布斯自由能,同时利用循环试算法计算了Cu-Ti-C反应体系的绝热温度和Cu的熔化率.结果表明:TiC为热力学最稳定产物,制备Cu/TiC在热力学上是可行的;随着Cu含量的增加,反应变得困难,自蔓延燃烧合成法不宜制备低TiC含量的材料;提高预热温度,反应变得容易;反应体系的绝热温度和Cu的熔化率都与预热温度有关.     

Ti-C-Al-Ni系热爆反应产物形貌及热力学分析

研究Ti-C-Al-Ni系热爆合成NiAI/TiC的形貌，并进行了热力学分析。结果表明：Ti、C含量对产物形貌有显著影响。当体系中Ti、C含量较少（≤15%）时，TiC和NiAl均为圆球状。随着Ti、C含量的增加，NiAl发生熔化；当Ti、C含量达50%左右，TiC颗粒镶嵌在熔融的NiAl基体上，形成较致密的金属间化合物基复合材料；Ti、C含量进一步增加，TiC颗粒变得粗大且不规则，少量NiAl覆盖于其上。产物形貌实际上是由燃烧反应的绝热温度Tad和瞬时液相量所决定的。随着TiC含量的增加，反应体系的Tad提高，NiAl液相量增加，当Ti、C含量达50%时，合成产物中液相量达到最大。     

Al-Ti-CaC2体系自蔓延反应及其热力学分析

对Al-Ti-CaC<,2>体系自蔓延反应过程中有关反应的Gibbs自由能ΔG及最高热力学温度进行了一系列计算,并对Al(50%,质量分数,下同)、Ti(30%)、CaC<,2>(20%)混合粉末进行了压制,并将压制试样在氩气保护下进行了加热烧结试验.结果表明,Tic、CaAl<,2>、TiAl<,2>、Al<,4>G<,3>具有较好的热力学稳定性,在1 200 K以上时,由TiAl<,3>、Al<,4>C<,3>反应,合成TiC;Al-Ti-CaC<,2>体系的最高热力学温度随预热温度提高而增加;在体系中Al含量为50%、预热温度为1 000 K条件下,计算的最高热力学温度大于2 400 K,自蔓延反应易于发生;试验时压制试样加热到963 K时发生剧烈反应.X射线衍射分析表明反应产物中含有TiC、CaAl<,2>、TiAl<,3>,TiAl<,3>为不完全反应产物.试验与热力学分析结果基本符合.     

工艺参数对SHS法制备TiC-Ni(Mo)金属陶瓷复合材料的影响

为了研究预压坯相对密度、预热温度、反应物配比、孔隙率等工艺参数对TiC-Ni(Mo)铝基金属陶瓷复合材料高温合成过程的影响作用,采用自蔓延燃烧合成(SHS)技术在7A52铝合金表面制备了TiC-Ni(Mo)金属陶瓷复合涂层,利用扫描电镜(SEM)、X射线衍射分析(XRD)对涂层的物相结构进行了分析。结果表明:体系的燃烧速度随预压坯相对密度的提高呈先增后减的趋势,预压坯的最佳相对密度约为55%;体系的燃烧温度随预热温度增长而增长,最佳预热温度区间在400~450K;体系的绝热温度随体系中Ni-Mo含量的提高而降低,最合适的配比方案为TiC-20Ni(Mo)。     

不同温度下Ti40合金的疲劳裂纹扩展行为

研究了Ti40合金在室温、300、500和600℃下的疲劳裂纹扩展行为,计算了Ti40合金在300、500、600℃下当△K为20 MPa m1/2时与裂纹扩展密切相关的表观激活能.结果表明:随温度升高,Ti40合金疲劳裂纹扩展速率增加;不同温度下的疲劳裂纹扩展曲线在△K为45.50MPam1/2处相交于一点.表观激活能值随温度升高先增加后减小,在500℃时达到最大,由此可见,500℃是Ti40合金热力学等性质发生变化的转折点.     

碳含量对Ti-Al-C系燃烧合成Ti3AlC2粉体的影响

实验表明在Ti—Al—C体系中，C含量对燃烧合成Ti3A1C2影响很大：C含量(原子分数)较低时(22．64％-28．07％)，燃烧产物主要物相为Ti2A1C；C含量较高时(29．31％-32．79％)，燃烧产物主要物相为Ti3A1C2．Ti3A1C2的燃烧合成反应温度高于Ti2A1C的燃烧温度，Ti3A1C2的生成量随燃烧反应温度升高近似呈对称分布．从反应物原料摩尔配比和热力学原理角度，探讨了不同C含量对燃烧产物组成的影响机理．     

Ni含量和热处理对Ti-Ni形状记忆合金相变和形变行为的影响

用示差扫描量热仪和拉伸试验对比研究了不同温度退火态Ti50.5，Ni49.5、Ti49.8Ni50.2和Ti49.4Ni50.6合金的相变特性和形变行为。中温退火态Ti50.5Ni49.5和Ti49.8Ni50.2合金冷却／加热时的相变类型为A→R→M／M→A（A—母相，R—R相，M—马氏体），Ti49.4Ni50.6合金的相变类型为A→R→M／M→R→A。随Ni含量增加，Ti—Ni合金的相变温度降低，相变热滞增加。随退火温度Tn升高，这3种合金的马氏体相变温度升高，热滞减小；Ti50.5Ni49.5合金的R相相变温度TR恒定不变；Ti49.8Ni50.2和Ti49.4Ni50.6合金的TR先升高后降低。室温下，Ti50.5Ni49.5合金呈现形状记忆效应，Ti49.4Ni50.6合金呈现超弹性，Ti49.8Ni50.2合金呈现形状记忆效应＋超弹性。近等原子比和富镍Ti—Ni合金的形状记忆特性优于贫镍合金。随Ta升高，三合金拉伸曲线的平台应力减小；Ti49.4Ni50.6超弹性合金的滞弹性面积增大，阻尼性增强，能量储存密度和储存效率减小。Ta=673～773K时，Ti—Ni合金的形状记忆特性良好，Ta超过823K后，该特性变差。     

Fe-Ti-C-Al体系中二元相的原位生成热力学计算

用溶液热力学方法研究了在1 400～1 600℃温度范围内,Ti、C、Al等元素对Fe-Ti-C-Al体系的影响。计算结果表明,在1 600℃时,TiC能在Fe溶液中直接反应生成,并且Al能促进各反应生成吉布斯自由能变的降低。在1 400～1 600℃温度范围内,Ti含量的增加能促进Ti Al3和Fe2Ti的降低,Fe3C的升高;C含量的增加能够促进Fe3C、TiC和Ti Al3的降低;此外,过量的C能促进Fe2Ti的升高。     

W含量及预热温度对Ti—W—C体系燃烧合成产物的影响研究

研究了W含量及预热温度对Ti-W-C体系燃烧合成产物相组成及粉末形貌的影响。研究结果表明，体系W含量减少，或燃烧之前进行预热，通过提高体系的燃烧温度，其燃烧反应机制由扩散－固溶机制转变为熔化－溶解－析出机制；结果，燃烧反应随之完全,有利于合成单相（Ti,W)C粉末，且产物粉末粒度增加，同时合成单相所需的预热温度随W含量增加而提高。     

自蔓延高温反应过程中热化学的编程计算

研究了自蔓延高温反应过程中热化学的计算问题。在建立有关热力学数据阼的基础上用FOXBASE语言编程计算了自蔓延高温反应过程中的绝热温度以及加入稀释剂后自蔓延高温反应发生所必需的最低预热温度。计算了一些常见的自蔓延高温反应的绝热温度,并将所计算的值和资料所报道的绝热温度进行了比较分析,同时示例计算绘制厂预热温度和稀释剂含量对反应绝热温度影响的曲线。利用计算结果和差热分析示例绘制丁热爆-自蔓延-普通反应合成的模式状态图。     

CALCULATION OF ADIABATIC TEMPERATURE THROUGH COMPUTER PROGRAM IN PROCESS OF COMBUSTION SYNTHESIS

The adiabatic temperature in the process of self-propagating high temperature synthesis iscalculated through FOXBASE language program on the base of establishing thermodynamic datapool concerned.The adiabatic temperature of some common self-propagating high temperaturesynthesis has been calculated,and the computed results are compared with the adiabatic tempera-ture reported.At the same time,the curve about the influence of preheating temperature andadding diluent on T_(ad)is drawn as an example.     

Combustion synthesis of fine TiFe series alloy powder by magnesothermic reduction of ilmenite

Fine TiFe series alloy powder was fabricated by magnesothermic reduction of ilmenite as main raw material. Adiabatic temperature of the FeTiO3-Mg system was studied through thermodynamic analysis. Meanwhile, the characteristics of TiFe series alloy were described by XRD, SEM and grading analysis. It is shown that combustion synthesis of the FeTiO3-Mg system can carry out due to its strong exothermic reaction through adiabatic temperature calculate. Ultrafine TiFe series alloy powder after leached for 5 h has reasonable phases and morphology with the particle distribution of 0.2 to 1 μm. It indicates that in-situ magnesothermic reduction of natural ilmenite is a feasible way to fabricate ultrafine powder with a relatively lower cost.     

低温镁热还原TiO2制备金属钛粉的热力学研究

本文针对TiO₂镁热还原产品氧含量高的问题进行了热力学研究,计算了反应体系的吉布斯自由能和绝热温度,绘制了反应优势区图,结果表明当反应温度高于1681 K时TiO无法被镁还原。针对这一问题,提出添加稀释剂的思路以实现对还原过程温度的抑制,计算了不同NaCl、MgCl₂添加量和初始温度对反应绝热温度的影响,指出了钛氧化物充分还原的热力学条件。最后分别以NaCl和NaCl-MgCl₂共熔盐作为稀释剂进行了实验研究,实现了钛氧化物的充分还原。     

Influence of nanocrystalline Ni–Ti reaction agent on self-propagating high-temperature synthesized porous NiTi

Nanocrystalline Ni–Ti was used in self-propagating high-temperature synthesis (SHS) to fabricate porous NiTi. The SHS of porous NiTi using elemental powders was also prepared for comparison. Results showed that the main phase was NiTi with unreacted Ni when using elemental powders, which is detrimental to medical use. A large amount of Ti₂Ni secondary phase was also detected. By employing mechanically alloyed nanocrystalline Ni–Ti as a reaction agent, the secondary intermetallic phase (i.e. Ti₂Ni) was significantly reduced and the unreacted Ni was eliminated. The addition of 25 wt% nanocrystalline Ni–Ti reaction agent produced porous NiTi with an average porosity of 52–55 vol% and a general pore size of 100–600 μm under preheating temperatures of 200 and 300 °C. This general pore size in the range of 100–600 μm is beneficial to biomedical application for osseointegration. By further increase of the reaction agent to 50 wt% in the reactant, a porous NiTi part was produced at ambient temperature (i.e. no preheating was necessary) and a dense part was formed at preheated temperature of 200 °C due to the large amount of energies in the nanocrystalline reaction agent. This revealed that the use of nanocrystalline reaction agent effectively lowered the activation barriers for combustion synthesis reaction.     

原位合成TiB和TiC增强钛基复合材料热力学

根据热力学理论编程计算了钛与Ｂ４Ｃ反应的反应生成焓ΔＨ与Ｇｉｂｂｓ自由能ΔＧ以及反应式（ｘ＋５）Ｔｉ＋Ｂ４Ｃ＝ｘＴｉ＋４ＴｉＢ＋ＴｉＣ的绝热温度。计算结果表明：钛与Ｂ４Ｃ反应释放出大量热,反应能自发维持,而过量钛与Ｂ４Ｃ反应更易生成ＴｉＢ和ＴｉＣ增强体。由于钛作为稀释剂吸收热量,随着过剩钛含量的增加,反应的绝热温度逐渐下降,过剩钛完全熔解的初始温度逐渐升高。     

Laser cladding of iron- base alloy on al-si alloy and its relation to cracking at the interface

The present study established the basic operating range and diagram for cladding, by means of a laser, a cast Al-Si alloy substrate with an iron-base material. Considering that the main difficulty was interface cracking during this processing, the factors affecting the interface cracking ratio (ICR) were investigated from two aspects: the laser processing parameters (e.g., laser power, traverse speed, powder-feed rate, preheating temperature of the substrate, tempering temperature) and the material factor, including the composition of clad. The substrate temperature and the tempering temperature were found to be important for controlling ICR, and the content of Al and Ni in the clads also had significant influence on ICR. The intermetallic compounds formed in the interface region were analyzed to understand the effect of Ni content on ICR. Clads of thickness from 1.2 to 1.5 mm that were crack free and had good fusion were achieved by controlling the substrate temperature or adjusting the Al content in the clads.     

高温气相反应合成金红石型纳米TiO2颗粒的研究

在高温气相反应器中,利用掺 ＡｌＣｌ３的 ＴｉＣｌ４氧化反应制备金红石型纳米 ＴｉＯ２颗粒研究了氧气预热温度、反应器尾部氮气流量、反应温度、停留时间等对 ＴｉＯ２颗粒大小的影响结果表明：提高氧气预热温度和加大反应器尾部氮气流量对控制产物粒径有利, ＴｉＯ２粒径随反应温度升高和停留时间延长而增大当反应温度为１３７３Ｋ, ＡＩＣｌ３与ＴｉＣｌ４摩尔比为 ０．２５、停留时间为１．７３ｓ时,纯金红石相纳米ＴｉＯ２颗粒的粒径分布为 ３０－５０ｎｍ．     

Thermodynamic analysis of Ti powder synthesized by SHS thermitreaction

According to the thermodynamics theories, the reactive Gibbs free energies, the reactive adiabatic temperature, the melting rate of Ti and the gasification mass of Mg in the Mg-TiO2 and AI-TiO2 systems were theoretically calculated and analyzed respectively. The results show that the reactions of Mg-TiO2 and AI-TiO2 are very easy to take place and the reaction of producing various suboxides of Ti may occur in Mg-TiO2 and AI-TiO2 reaction system; the adiabatic temperature of Mg-TiO2 becomes lower with increasing mass fraction of Mg. The adiabatic temperature is below 1 800 K when the mass fraction of excessive Mg exceeds 25%; The adiabatic temperature of AI-TiO2 also becomes lower with increasing mass fraction of AI, but it becomes higher with the preheat temperature increment. The adiabatic temperature plateau is the result of Ti melting endotherm; owing to the gasification of a great deal of Mg in Mg-TiO2 reaction process, Mg should be properly excessive in order to get Ti.     

Reduction of Nickel Oxide with Ethanol

This work aims to investigate the reduction behavior of NiO powder by ethanol vapor at 600–1100 K for the reaction times up to 60 min. The products were characterized by mass measurement, x-ray diffraction, and scanning electron microscopy techniques. The reaction of NiO with ethanol essentially consisted of oxide reduction followed by C deposition. At 600 K, significant oxide reduction was attained. Full oxide reduction was observed at 650–1100 K within 10–15 min. At this temperature range, the reduction reaction was controlled by external mass transfer of gaseous species. At the lower temperature range 600–650 K, the reduction rate was sensitive to the temperature change and influenced by the total gas flow rate to a lesser degree. The temperature dependence of C uptake was explained by Boudouard reaction. The results of this study demonstrate that NiO can be completely reduced to Ni by ethanol as predicted by the thermodynamic analysis.