Fe-C-Ti-Mn合金系中TiC原位生成反应的热力学分析

根据溶液热力学理论对Fe C Ti Mn体系中TiC增强体的原位合成进行了热力学分析。计算表明,体系中TiC优先于Fe3C和Fe2Ti形成,且在热力学上比Fe3C和Fe2Ti稳定。多数情况下,TiC基体合金在液态未凝固时即可形成,而Fe3C和Fe2Ti则是在合金凝固和冷却过程中才有可能析出。随C含量增加,形成TiC和Fe3C的可能性增大;随Ti含量增加,形成Fe2Ti的可能性增大,而形成Fe3C的可能性减小;高Ti高C时,有利于形成TiC,高Ti低C时有利于形成Fe2Ti;高C低Ti时有利于形成Fe3C;添加适量的Mn既可有效抑制Fe3C的形成,又明显降低TiC的合成温度,使大多数TiC的合成反应发生在合金熔体充满铸型后的冷却、凝固过程中,可能解决TiC过早析出、熔体粘度增大、充型困难等问题。     

机械诱发自蔓延反应合成Ti3AlC2的机理研究

以3Ti／Al／2C粉体为原料,采用机械合金化的方法以合成Ti3AlC2材料。研究结果表明,在机械合金化过程中诱发自蔓延反应,反应会产生大量坚硬的小块体颗粒,大小约为0．2-11mm。粉体的组成相为TiC、Ti3AlC2、Ti2AlC,而块体仅含有TiC和Ti3AlC2。获得的粉体和块体产物中Ti3AlC2含量分别约为63wt％和84．8wt％。提出了一个机械诱发自蔓延反应合成Ti3AlC2的反应机制,即Ti3AlC2是从固相TiC与Ti-Al液相中形核并长大。     

冷焊焊缝中的碳化物研究

利用SEM，TEM，EPMA等方法研究了不同合金系统的冷焊焊缝中碳化物的分布、形态，分析了碳化物在冷焊条件下的形成过程．结果表明，Nb、Ti碳化物倾向大，可以在液态金属中形成碳化物，但单独加入且含量较高时，碳化物尺寸过大，分布不均匀，对基体固溶强化较弱；单独加入V时形成了网状碳化物；适量Nb，Ti，V同时加入，获得了均匀分布的颗粒碳化物及强韧的基体，碳化物以液态金属中氧化物为形核核心，在冷却过程中外延长大为多层结构的复合碳化物．     

原位合成TiC/Fe基复合材料的组织结构和磨损性能

利用粉末冶金技术,在真空状态下使Fe-Ti-C体系进行碳化反应原位合成TiC/Fe基复合材料,用扫描电镜(SEM)、X射线衍射(XRD)分析复合材料的组织结构和相组成,用热分析法和高温X射线衍射研究Fe-Ti-C体系原位合成的反应机理,用MM-200磨损试验机对复合材料进行耐磨性实验.研究结果表明,反应合成的复合材料主要相组成为TiC、α-Fe和Fe3C,所合成的硬质相TiC颗粒细小,在铁基体中均匀分布.三元体系Fe-Ti-C的反应机理为,首先在765.6 ℃发生Fe的同素异构转变,即α-Feγ-Fe;其次在1078.4 ℃,Ti与Fe共熔而形成低共熔体Fe2Ti;最后在1138.2 ℃,C与Fe2Ti反应生成TiC.在重载干滑动磨损条件下此复合材料显示了很好的耐磨性能.     

过冷合金熔体非平衡凝固中形核方式的竞争

本文立足于经典形核理论和非热形核理论，分析了过冷熔体非平衡凝固中连续形核同位置饱和的竞争．决定过冷熔体形核方式的关键因素是初始熔体的过冷度与异质核心的尺寸．随着净化的进行，熔体过冷度提高，N1，r^＊以及△G^＊逐渐降低，它们之间的相互竞争使形核方式从位置饱和向连续形核转变，并解释了过冷Ni-Sn与Ni-Si共晶合金中观察到的组织变化．表明低过冷下Ni-Sn合金形核方式为位置饱和；Ni-Si共晶合金中，△T〈180K时形核方式为位置饱和，180K以后，形核方式从位置饱和转变为连续形核．     

高炉炉缸形成Ti(C,N)粘结层的实验室模拟

在实验室条件下,模拟高炉冶炼钒钛磁铁矿时炉缸处Ti(C,N)粘结层生成过程.通过热力学分析,反应在试验条件下可以进行.TiC、TiN生成的起始温度分别为1467K和1408K.采用金相显微镜、SEM和XRD等对试验坩埚中渣-石墨边界层进行分析.结果得到,反应随恒温时间的延长Ti(C,N)粘结层增厚并趋于复杂化,形成由渣、铁、Ti(C,N)以及碳颗粒组成的混合层.其中,Ti(C,N)以点散状分布.     

冷焊焊缝中的碳化物研究

利用SEM ,TEM ,EPMA等方法研究了不同合金系统的冷焊焊缝中碳化物的分布、形态 ,分析了碳化物在冷焊条件下的形成过程 .结果表明 ,Nb、Ti碳化物倾向大 ,可以在液态金属中形成碳化物 ,但单独加入且含量较高时 ,碳化物尺寸过大 ,分布不均匀 ,对基体固溶强化较弱 ;单独加入V时形成了网状碳化物 ;适量Nb ,Ti ,V同时加入 ,获得了均匀分布的颗粒碳化物及强韧的基体 ,碳化物以液态金属中氧化物为形核核心 ,在冷却过程中外延长大为多层结构的复合碳化物     

钨极氩弧熔敷技术制备含TiC颗粒增强涂层的研究

在碳钢基体表面预涂一定混合比例的钛铁和石墨，用钨极氩弧热源熔敷，使Ti元素和C元素在高温下原位反应，获得TiC颗粒增强的综合性能优异的铁基复合材料涂层；试验测试和分析表明，熔敷层中原位生成了TiC增强颗粒；熔敷层微观组织主要有珠光体、铁素体、马氏体、少量残余奥氏体、TiC颗粒等组成；涂层表面硬度达到了HRC55以上；越靠近熔覆层表面，硬度越高，具备良好的耐磨性能。     

原位TiCP/Fe复合材料的制备工艺优化

采用反应铸造法在工业化生产上制备了原位TiCp/Fe复合材料，在保证Ti与C反应质量比为4：1的基础上，通过正交试验设计及金相组织观察和性能测试，研究了不同成分配比和工艺参数对材料组织与性能的影响，优化了该材料的制备工艺，结果表明：C和Ti质量分数增加，TiC颗粒体积分数增加，可提高材料的性能；Si质量分数过高，可降低冲击韧性；反应温度在1600－1700℃范围内，对材料性能影响波动不大；随着保温时间延长，TiC反应合成充分、尺寸会变大。     

Ni-Ni3Sn系近共晶合金深过冷形核规律

采用大体积液态金属的微观净化技术，在Ni-Ni3Sn合金系中使Ni-(2.5-17.5)at%Sn和Ni-(17.8-25.0)at%Sn两组合金分别获得了最大达351K和303．5K的“极限”形核过冷度，并使其极限过冷度保持30个循环过热周期不衰减。实验发现，Ni-Ni3Sn系近共晶合金深过冷凝固时，Ni3Sn总是领取先于α（Ni）相形核。根据实验数据和表面异质形成核速率模型，求得Ni3Sn和α（Ni）相异质形核时的异质形核因子f(θ）分别为0．8103和0．12406；求得过冷熔体中Ni3Si和α（Ni）相等形核速率时的温度－成分曲线完全处于共晶点左边，表明在近共晶成分过冷熔体中，金属间化合物Ni3Sn易于α（Ni）形核。     

Al-Ti-C grain refiner made by ultrasonic levitation

An electrostrictive uniaxial ultrasonic levitation reaction system was designed to perform TiC synthesis reaction by suspending graphite powder in Al-3Ti melt and an Al-3Ti-0.15C grain refiner alloy was obtained. The results show that sound pressure node in which graphite suspends is formed in the melt between radiation block and reflecting board by ultrasonic and TiAl3 particles congregate around C powder. Meanwhile, due to ultrasonic cavitation, dissolved TiAl3 provides better surface condition for the synthesis reaction of TiC. The reaction route is that C and dissolved Ti react to form TiC. Ultrasonic cavitation has a thermal activation effect on TiC particles and Al-3Ti-0.15C refiner has excellent microstructural refining effect on α-Al.     

Synthesis of Ti3SiC2/TiB2 Composite by In-situ Hot Pressing (HP) Method

Ti3SiC2/TiB2 composite was successfully obtained by hot pressing Ti/TiC/Si/B4C power mixtures.Volume fraction of TiB2 in Ti3SiC2/TiB2 composite can not exceed 10%.Incorporation of excessive TiB2 will affect the reactions process.TiC and Ti5Si3 were two important intermediate phases during the whole reactions.The microstructure characteristics of the Ti3SiC2/TiB2 composites were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The experimental results show that the grains of Ti3SiC2/TiB2 composite are structured in a layered form,and the formation of TiB2 particles as reinforcements with elongated or equiaxed shape distributes in Ti3SiC2 matrix.     

(Ti,Fe)-Al-C体系钢铁基复合材料的热力学计算与分析

利用溶液热力学理论,研究了(Ti,Fe)AlC体系钢铁基复合材料可能的反应产物的吉布斯自由能变化。热力学实验模型是在FeC熔液中加入钛铁合金(Ti,Fe)和纯铝块,继续加热到1600℃,熔液经过充分混合、反应后随炉冷却到常温。计算结果表明,TiC先于Fe2Ti、Fe3C等相生成,但始终没有Al4C3和TiAl3相产生;体系中TiC的热力学稳定性最高;在凝固过程中,TiC相优先析出,随后可能有Fe2Ti、Fe3C等相析出;铝含量的增加能够促进TiC、Fe2Ti、Fe3C等相的生成。     

Kinetics of Combustion Synthesis in Ti-C-3Ni-Al System

The Kinetics and mechanisms of the combustion reaction in theTi-C-3Ni-Al system were studied. Samples were prepared by igniting compacts of elemental Ti, C, Ni and Al powders with a heating tungsten coil under an inert argon atmosphere. The activation energies of Ti+C+50wt%(3Ni+Al)→TiC+50%Ni3Al and Ti+C+80wt%(3Ni+Al) →TiC+80%Ni3Al exothermic reactions were determined by measuring the combustion wave velocity and the combustion temperature, which are 129kJ.mol-1 and 79kJ*mol-1, respectively. The mechanism of formation of products for Ti-C-3Ni-Al system was found:metal phases (Ti-3Ni-Al) are melted in combustion process,and carbon dissolves into the liquid metal and TiC is subsequently precipitated out of solution, and Ni3Al is crystallized during the cooling process. The mechanism is fairly similar with that of Ti+C→TiC and Ti+C+Ni→TiC+Ni. There are two reactions (Ti+C→TiC, 3Ni+Al→Ni3Al) in the Ti+C+3Ni+Al system, and the wave velocity is mainly controlled by the velocity of Ti + C→TiC, but the velosity of 3Ni+Al→Ni3Al may play a significant role when Ni3Al contents are higher than 70wt%.     

Grain Refining Performance of SHS Al—50TiC Master Alloys for Commercially pure Aluminum

An Al-50wt^TiC composite was directly synthesized by self-propagating high-temperature synthesis(SHS) technology,and then was used as a grain refining master alloy for commercially pure aluminun.The microstructure and grain refining performance of the synthesized master alloy were emphatically investigated.The SHS master alloy only ocntained submicron TiC particles except for Al matrix.Moreover,TiC particles were relatively free of agglomeration.Grain refining tests show that adding only 0.1wt^ of the master alloys to the aluminum melt could transform the sturcture of the solidified samples from coarse columnar grains to fine almost 1.5h at 1003K.Therefore,it is concluded that the SHS master alloy is an effective grain refiner for aluminum and its alloys,and that it is highly resistant to the grain refining fading encountered with most grain refiners.     

钛在铁水中的行为

由热力学计算结果分析了高炉冶炼含ＴｉＯ２铁矿时钛的物理化学行为,指出：有固体碳存在果,渣界面不能有纯ＴｉＮ生成,应该析出Ｔｉ（Ｃ３Ｎ）固溶体,     

铸造铝合金熔体处理工艺性分析

铝合金熔体处理的主要任务是提高合金液的纯净度,而提高纯净度的手段是精炼(净化).铝液的精炼处理是铝合金熔炼过程中的关键工序之一,精炼能除氢和除渣,净化铝液,达到消除铸件针孔的目的,并直接影响铝铸件的力学及使用性能.本文对多功能精炼剂处理ZL101合金熔体的工艺进行了分析,结果表明:铝合金液在未加精炼剂时,凝固试样的表面粗糙,其中气孔多而且尺寸较大;在经精炼剂除气后,凝固试样表面光滑,气孔少而且尺寸较小.因此可知,精炼剂的加入量,加入温度,保温时间对精炼处理至关重要.     

TiC/Ti-Al基复合材料的燃烧合成

为了改善Ti-Al金属间化合物的脆性,利用SHS/PHIP工艺制备了TiC/Ti-Al基复合材料.理论分析表明,绝热温度随C质量分数的增加而呈升高趋势,当体系中碳的质量分数≥2%时,该体系能完成自蔓延过程.采用电子扫描显微镜,X射线衍射仪对合成产物进行了分析.结果表明,合成产物中除存在基体相Ti3Al和TiAl和增强相TiC外,还存在许多三元相Ti3AlC和Ti2AlC相;随着Al质量分数的增加,增强相的形貌由颗粒状逐渐变成棒状或片状;复合材料的硬度和压缩强度随C质量分数的增加逐渐增加,但密度及相对密度随C质量分数的增加呈先增加后降低的趋势.当C的质量分数达到4%时,其实际密度和相对密度均达到最大.     

Dissolution-precipitation mechanism of self-propagating high-temperature synthesis of TiC-Cu cermets

The mechanism of self-propagating high-temperature synthesis (SHS) of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope (SEM) with energy dispersive X-ray (EDX) spectrometry, and the combustion temperature was measured. The results showed that the com- bustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solu- tion. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.