【作者】 韩娜；

【导师】 朱建锋；

【作者基本信息】 陕西科技大学 ， 材料工程， 2012， 硕士

【摘要】 三元层状化合物Ti₂AlC因其具有多种优良的性能而受到了越来越多的关注。它结合了陶瓷与金属共同的优点：良好的导电、导热性能，低的密度，良好的可加工性能，高的抗热震性能和抗高温氧化性能等。然而，由于其相对低的硬度和强度，在很大程度上限制了其广泛应用。这一缺陷主要是因为其结构中Al原子层与Ti6C八面体层所形成的化学键键强较弱所致。复合化和固溶强化是目前改善Ti₂AlC材料综合性能的两种有效措施。目前，制备Ti₂AlC基固溶体或者复合材料的方法多为直接混合法，所合成的产物存在晶粒粗大、分散性差等缺点而导致该材料的性能难以进一步提高。本研究在Ti-Al-C体系中分别引入金属氧化物V₂O₅与Nb₂O₅，利用Al与V₂O₅和Nb₂O₅之间的铝热反应原位生成第二相Al₂O₃，同时还原出的金属单质V或者Nb替代Ti₂AlC中的Ti，从而形成（Ti,V）2AlC/Al₂O₃和（Ti,Nb）2AlC/Al₂O₃复合材料。为了对比试验，本文利用Ti粉，Al粉以及碳黑为原料，采用热压烧结工艺制备了单相Ti₂AlC材料。借助X射线衍射（XRD）、扫描电镜（SEM）以及能谱分析（EDS）等系统研究了不同体系合成（Ti,M）2AlC/Al₂O₃（M=V或者Nb）复合材料的原位反应过程和显微结构；结合力学性能研究了V₂O₅与Nb₂O₅的加入量对产物结构与性能的影响，并探讨了该复合材料的断裂方式与增强、增韧机理。主要结论如下：合成单相Ti₂AlC材料的结果表明：当Ti:Al:C的摩尔比为2:1.1:0.7时，在1350℃温度下合成了纯度较高的Ti₂AlC化合物，其相对密度达到99%，晶粒大小约为1μm。材料的维氏硬度（Hv）、弯曲强度（σb）与断裂韧性（KIC）分别为6.79GPa，271MPa和4.08MPa·m1/2。Ti-Al-C-V₂O₅合成（Ti,V）2AlC/Al₂O₃复合材料的研究表明：当热压温度为700℃时，Ti和Al首先发生反应形成一系列Ti-Al金属间化合物（Ti3Al、TiAl、TiAl3）；当温度上升到900℃时，发生了Al与V₂O₅之间的铝热还原反应，生成了Al₂O₃相，并有TiC相形成；当温度为1100℃时，形成了（Ti,V）2AlC基体相；当温度上升到1350℃时，杂质相消失，形成了高纯度的（Ti,V）2AlC/Al₂O₃复合材料。由于原位反应过程中的放热反应，使该复合材料的合成温度较传统合成方法降低了200-300℃。随着产物中Al₂O₃含量的提高，基体晶粒尺寸逐渐变小，分布更加均匀，但当Al₂O₃含量超过10wt%时，第二相颗粒团聚比较严重。该复合材料的硬度和抗压强度随Al₂O₃含量的提高而增大，但其弯曲强度和断裂韧性出现峰值变化，当产物中Al2O3含量为10wt%时达到最大值434.36MPa和5.68MPa m1/2，与单相Ti2AlC相比分别提高了132%和166%。该材料力学性能的改善源自于固溶强化和第二相复合的综合效果。利用同样的制备工艺，以Nb₂O₅、Ti、Al和碳粉为原料成功制备了（Ti,Nb）₂AlC/Al₂O₃复合材料。其反应过程与微观结构与（Ti，M）₂AlC/Al₂O₃复合材料类似，当产物Al₂O₃质量百分比为5wt%（原料中Nb₂O₅为7.69wt%）时，其弯曲强度与断裂韧性相对单相Ti₂AlC来说，分别提高了57%与9%。但与（Ti，M）₂AlC/Al₂O₃复合材料相比较，其性能还有一定的差距，原因有待进一步研究。更多还原

【Abstract】 The ternary layered compound Ti₂AlC possesses remarkable properties thatcombines many of the merits of both metals and ceramics, and has attractedincreasing attention due to its good electrical and thermal conductivity, lowdensity, ready machinability, excellent thermal shock resistance and hightemperature oxidation resistance. To date, unfortunately, its wide application isstill limited by its relatively low hardness and low strength, which originatedfrom the comparatively weak bonding between the Al layers and edge-sharedTi6C octahedral in the structure. At present, both composite strengthening andsolid-solution are effective approachs for improving fracture toughness andflexural strength of Ti₂AlC.Until now, the most common way to fabricate the Ti₂AlC based compositesis to mix the raw materials, and then hot pressing. However，the synthesizedproducts have defects, such as coarse grains and poor dispersion, which limitfurther increasing the properties. In this work, in-situ hot-pressing method withexothermic reaction of Al-V₂O₅or Al-Nb₂O₅in Ti-Al-C system, has been used tofabricate （Ti,V）₂AlC/Al₂O₃and （Ti,Nb）₂AlC/Al₂O₃composites, in which theAl₂O₃enforcing phase was in-situ formed by thermite reaction of Al-V₂O₅orAl-Nb₂O₅, at the same time, the in-situ formed M （V or Nb） atom substituted Tito form （Ti,M）₂AlC matrix phase. For comparison, fully dense Ti₂AlCmonolithic phase was also synthesized by hot pressing method using Ti, Al andC as starting materials. The reaction mechanisms and microstructures of the（Ti,M）₂AlC/Al₂O₃（M=V or Nb） composites were investigated in details by X-raydiffraction （XRD）, scanning electron microscopy （SEM） and energy dispersiveanalysis （EDS）. The effects of V₂O₅and Nb₂O₅addition on the microstructuresand properties were also studied. Furthermore, the fracture models, strengtheningand toughening mechanisms were analyzed. The main results are shown as follows:The results of the synthesis for Ti₂AlC compound show that the fully denseTi2AlC ceramic was synthesized at1350℃using the molar ratio of Ti:Al:C as2:1.1:0.7. The as fabricated Ti2AlC possesses a relative density of99%and agrain size of about1μm. The Vickers hardness （Hv）, flexural strength （σb） andfracture toughness （KIC） are6.79GPa,271MPa and4.08MPa·m1/2, respectively.The synthesis process of （Ti,V）₂AlC/Al₂O₃composite with the rawmaterials of Ti-Al-C-V2O5is as follows: When the hot pressing temperature was700℃, series of Ti-Al intermetallics （Ti3Al、TiAl、TiAl3） were formed byreaction of Ti and Al. When the temperature increased to900℃, Al₂O₃and Vwere formed by the thermite reaction between Al and V2O5, at the same time,TiC was also formed.（Ti,V）2AlC phase was formed as the temperature increasedto1100℃. Finally, when the temperature was increased to1350℃, high purity（Ti,V）2AlC/Al₂O₃composite was successfully synthesized, which was decreasedby200-300℃compared with the traditional synthesis methods. The grain sizeof the matrix was deceased by increasing the Al₂O₃content, and the more Al₂O₃distribution, the more uniform in the matrix. The Vickers hardness （Hv） andcompressive strength increased with the increasing of Al₂O₃content. But asAl₂O₃content was further increased over10wt%, the Al₂O₃particles becameagglomerate seriously. The flexural strength （σb） and fracture toughness （KIC）were obtained the maximum values of434.36MPa and5.68MPa m1/2at10wt%Al₂O₃content, which were increased by132%and166%, respectively,compared with those of the monolithic Ti2AlC. This improvement results from acomprehensive effect of solid solution and the second phase strengthening.The （Ti,Nb）₂AlC/Al₂O₃composites were also successfully synthesized fromelemental powder mixtures of Nb2O5, Ti, Al and carbon by using the samesynthesis technique. The reaction path and microstructure were similar to thoseof the （Ti,V）2AlC/Al₂O₃composite. Compared with the monolithic Ti₂AlC, theflexural strength and fracture toughness were enhanced by57%and9%,respectively, when the Al₂O₃was5wt%（7.69wt%Nb2O5）. However, incomparison with the （Ti,V）2AlC/Al₂O₃composites, the mechanical properties of（Ti,Nb）2AlC/Al₂O₃composites are still lower, and the reason would be furtherinvestigated in detail.更多还原