【作者】 吕思婕；

【导师】 王慧远；

【作者基本信息】 吉林大学 ， 材料加工工程， 2012， 硕士

【摘要】 高熔点的金属间化合物在航空、航天和军工等领域倍受青睐。在众多金属间化合物中，由于Ti₅Si₃具有高熔点、低密度和抗高温氧化以及良好的热力学稳定性等诸多优异性能，而被认为是新型高温结构候选材料之一。但是，由于Ti₅Si₃属于复杂六方D88结构，对称性差，导致其具有很大的室温脆性和较低的断裂韧性。因此，如何解决其脆性问题是Ti₅Si₃能否成功应用的最大挑战。目前，国际上已开展了针对Ti-Si体系掺杂第三组元来改善Ti₅Si₃综合性能的研究工作，以期解决其本质脆性问题。第一性原理计算研究表明，在Ti₅Si₃中掺杂金属元素Nb、V和Cr可以提高Ti₅Si₃的体模量或降低剪切模量，进而有效改善其韧性。实验研究表明在Ti-Si体系中掺杂Fe、Ni和Al等金属组元可以与Ti或Si形成二元或三元的共晶液相，改变反应路径；反应结束后金属组元还可以作为粘结剂分布在晶界处，有助于提高Ti₅Si₃的综合性能。在Ti-Si体系中掺杂金属组元Cu不仅可以降低反应的开始温度，使反应更容易进行，而且还可以细化晶粒，提高致密性，进而有利于改善材料的性能。简而言之，通过掺杂第三金属组元Cu来改善Ti₅Si₃的组织和性能具有重要意义。然而，目前对于Cu-Ti-Si体系燃烧合成（Combustion Synthesis，简称CS）反应路径及其反应产物的研究较少。因此，本文基于绝热燃烧温度计算，研究了Cu含量和反应物粒度对Cu-Ti-Si体系CS反应路径的影响规律以及动力学因素（Cu含量、配比和粒度）对该体系CS反应产物的相组成和组织形貌的影响。此外，还利用（Combustion Synthesis plus Quick Press，简称CS/QP）方法制备了具有较高致密性的原位Ti₅Si₃和TiB2增强Cu基复合材料，并初步探讨了复合材料的微观组织和力学性能。本文的主要研究结果如下：（1） Cu-Si和Cu-Ti-Si液相的形成降低了反应的开始温度；Cu-Ti-Si体系的反应路径为：首先Cu和Si通过固固扩散反应形成Cu3Si；随着温度的升高，Cu3Si和Si在共晶温度附近（⁸02oC）发生反应，形成Cu-Si液相；随后Ti扩散到二元液相中形成Cu-Ti-Si三元液相；随着Ti和Si的不断溶解，大量的Ti₅Si₃通过溶解-反应-析出机制从饱和液相中析出；反应路径归纳为：Cu_（s）+Ti_（s）+Si_（s）→Cu₃Si_（s）+Ti_（s）+Si_（s）→（Cu–Si）（l）+Ti_（s）→（Cu–Ti–Si）_（l）→Cu_（l）+Ti₅Si_3（s）。（2） Ti和Si粒度对反应路径有较大影响：Ti_[15]Si_[15]Cu_[45]（下标为反应物尺寸，μm）体系中，在⁷95oC时，细Ti粉较容易扩散到Cu-Si液相中形成Cu-Ti-Si三元液相，随后在液相的辅助下，β-Ti和Si在⁹17oC反应形成了大量的Ti₅Si₃；在Ti[150]Si[15]Cu[45]体系中，粗Ti较难扩散到Cu-Si液相中，阻碍了三元液相的形成，因此使反应推迟到⁹48oC；对于Ti_[15]Si_[150]Cu₍[45]0体系，粗Si粉阻碍了Cu-Si液相的形成；相反，Cu-Ti在⁹60oC更容易形成共晶液相。Si扩散到Cu-Ti液相中形成Cu-Ti-Si液相，最后Ti₅Si₃从三元饱和液相中析出。（3）当Cu含量从10增加至50wt.%，反应产物均为Ti₅Si₃和Cu，但Ti₅Si₃晶粒尺寸从¹5减小至²μm，且形貌从长条状转变为光滑的鹅卵石状；此外，反应产物体积有先膨胀后收缩的趋势，Cu含量为20wt.%时，膨胀率达到最大值14.7%。Cu能够置换Ti原子固溶到Ti₅Si₃中。Cu粉和Ti粉粒度对产物种类、尺寸和形貌影响不大，Ti₅Si₃颗粒均为鹅卵石状或多边形状；而Si粉粒度对Ti₅Si₃形貌影响较大，当Si粉粒度从15增加到150μm，Ti₅Si₃颗粒从表面光滑的多边形状转变为表面有空洞的莲藕状。（4）通过CS/QP法能够制备出较高致密性的高体积分数原位Ti₅Si₃、TiB2和Ti₅Si₃+TiB₂颗粒增强Cu基复合材料，孔隙率分别为1.1%、5.0%和1.7%；Ti₅Si₃/Cu、TiB2/Cu和（Ti₅Si₃+TiB₂）/Cu复合材料的最大强度σUCS（屈服强度，σ0.2）分别为1040（686）、1262（1009）和1234（876） MPa，最大断裂应变εf分别为13.6、5.9和5.5%。更多还原

【Abstract】 Recently, high-melting intermetallic compounds have attracted considerable attentionbecause of their potential applications in many fields including aviation, aerospace, military,and so on. Among various intermetallics, titanium silicide （Ti₅Si₃） has been regarded as oneof the most promising high temperature structure materials on account of its high meltingtemperature, low density and excellent thermal stability. However, due to its complexhexagonal structure （D88）, Ti₅Si₃shows very low fracture toughness, which severely limitsits application. Hence, the major challenge in applying Ti₅Si₃is to reduce its brittleness orimprove the fracture toughness.More recently, researchers have conducted a sequence of work including doping thethird element in Ti-Si system to improve the mechanical properties of Ti₅Si₃. First-principlescalculation indicates that some alloying elements, such as Nb, V or Cr can increase bulkmodulus or reduce shear modulus of Ti₅Si₃, which could improve the ductility of Ti₅Si₃effectively. Experimental results suggest that doped metal elements, such as Fe, Ni and Alcan form binary or ternary eutectic liquids with Ti or Si in the Ti-Si system, whichparticipates in the reaction process or even changes the reaction pathway. As a result, metalelements serve as bonding agents distributing in boundaries of Ti₅Si₃grains after the reaction,thereby contributing to improving the performance of Ti₅Si₃materials.Some studies suggest that Cu doping in Ti-Si system can not only decrease the reactiontemperature of combustion synthesis （CS）, promoting the rate of reaction, but also refineTi₅Si₃particulates, improving the density. In short, it is of considerable significance to studythe influence of Cu doping on the improvement of Ti₅Si₃properties. However, less researcheffort has been carried out on the CS reaction pathway and products of Cu-Ti-Si system.Consequently, in the present study, based on the calculation of the adiabatic combustiontemperature, influences of Cu addition as well as Ti and Si particle sizes on the CS reaction pathway of Cu-Ti-Si system are investigated. Besides, particular attention is also paid to theinfluence of dynamic factors, such as Cu content, ratio of reactants and particle sizes, on thephase compositions and microstructures of CS reaction products of Cu-Ti-Si systems. Inaddition, the study also fabricated in situ Ti₅Si₃and TiB2reinforced Cu matrix compositeswith high densification by combustion synthesis plus quick press （CS/QP） process andinvestigated the microstructures and mechanical properties of composites. Results of thepresent studies are as follows:（1） The formation of Cu-Si and Cu-Ti-Si liquids is significantly reducing the reactiononset temperatue; the reaction pathway of Cu-Ti-Si system during CS could be described as:the Cu3Si was formed initially via solid state diffusion reaction between Cu and Si particles;with the temperature increasing, Cu-Si eutectic liquid was formed at about802oC betweenCu3Si and Si; and then Ti diffused into the surrounding Cu-Si liquid and led to the formationof Cu-Ti-Si ternary liquid; meanwhile, once the liquid reached a saturation stage with [Ti]and [Si] in the course of continuous dissolution, plenty of Ti₅Si₃could be developed from theliquids by a solution–reaction–precipitation mechanism. The reaction pathway of Cu-Ti-Sisystem is: Cu_（s）+Ti_（s）+Si_（s）→Cu3Si_（s）+Ti_（s）+Si_（s）→（Cu–Si）（l）+Ti_（s）→（Cu–Ti–Si）（l）→Cu（l）+Ti₅Si_3（s）.（2） The Ti and Si particle sizes have a great influence on the reaction pathway inCu-Ti-Si system: for Ti_[15]Si_[15]Cu_[45]system, fine Ti particle easily dissolves into Cu-Sibinary liquid to form Cu-Ti-Si ternary liquid at⁷95oC, which further participates intothe reaction of β-Ti and Si to yield abundant Ti₅Si₃particulates at⁹17oC; ForTi[150]Si[15]Cu[45]system, however, it is relatively difficult for coarse Ti particles to reactwith the Cu-Si liquid to form the ternary liquid and, thereby delaying the formation ofTi₅Si₃to⁹48oC; for Ti_[15]Si_[150]Cu_[45]system, coarse Si particle results in the formationof insufficient Cu-Si liquid initially, while Cu-Ti liquid forms at⁹60oC instead, whichfurther reacts with coarse Si to form the Cu-Ti-Si liquid, and the Ti₅Si₃are precipitated outof the ternary liquid.（3） When Cu content increases over the range of10-50wt.%, products only consistof Ti₅Si₃and Cu phases. while the average size of Ti₅Si₃decreases significantly from¹5 to²μm and the morphology of Ti₅Si₃transforms from the long strip to thecobblestone–like shape with a relatively smooth surface. Besides, the volume of productsexpanded and followed by shrink with the increasing of Cu content and the expansion ratereached the highest value of14.7%when Cu content was20wt.%. The Cu atoms can takeplace of Ti sites in Ti₅Si₃lattices. The sizes of Cu and Ti powders had little influence onthe type, size and morphology of reaction products, and Ti₅Si₃exhibited cobblestone–likeshape or polygon shape. However, the size of Si powder had a great effect on themorphology of Ti₅Si₃. The polygon-like shape of Ti₅Si₃changed from smooth surface topolyporous surface with the size of Si increasing from15to150μm.（4） In situ high volume fraction Ti₅Si₃, TiB₂and Ti₅Si₃+TiB₂particulates reinforcedCu matrix composites with high densification could be successfully fabricated by CS/QPmethod. The porosities of the three composites were1.1,5.0and1.7%, respecitively.Average values of σUCS（σ0.2） and εffor Ti₅Si₃, TiB₂and Ti₅Si₃+TiB₂reinforced coppercomposites were1040（686）,1262（1009） and1234（876） MPa, as well as13.6,5.9and5.5%, respectively.更多还原