【作者】 申玉芳；

【导师】 邹正光；

【作者基本信息】 广西大学 ， 化学工艺， 2012， 博士

【摘要】 Cermets的综合性能主要取决于金属和陶瓷两相的界面结合性能。由于金属与陶瓷在物理及化学性质上的截然不同,使得二者的界面结合性能受多方面因素的制约,主要有界面润湿性、界面结合强度、界面缺陷、界面应力等。其中,润湿性是最关键的影响因素之一。因此,对金属／陶瓷结合界面的研究一直以来都是金属陶瓷领域里热点科学问题之一。有关金属陶瓷界面的研究分为实验研究和理论研究两个方面。但是,两方面的研究对金属陶瓷界面润湿性和结合性等界面行为的微观作用机制的把握都仍有不足。而界面结合性对第三相在界面上的富集和界面缺陷等界面行为非常敏感。因此,第三相添加剂和界面缺陷等界面行为对金属陶瓷界面性能的微观影响机制是金属陶瓷界面领域里需待探索的重要课题。本研究从单相金属和陶瓷的晶体结构参数入手,把计算材料学用于含第三相和界面缺陷的金属／陶瓷界面的研究,借助计算机模拟研究金属陶瓷界面结合的微观机制以及影响界面性能的本质。主要对本征TiC/Fe的界面、缺陷界面、掺杂界面、TiC(Al2O3)/Ti-Al(Fe-Al)金属／陶瓷体系的界面结构、电子构型和界面结合性作了深入研究,揭示了金属陶瓷界面结合和润湿的微观机制,主要内容包括以下四个方面：首先,对本征TiC/Fe的理想金属陶瓷界面的电子结构和成键进行了研究。发现纯体相TiC中主要存在两种强成键类型,TiC之间形成的pda共价键和Tid-Tid形成的ddδ金属键。纯体相Fe晶体中主要存在成键类型为Fed-Fed形成的dd金属键。两相中各晶相表面的表面能大小排序如下：TiC(100)<TiC(210)<TiC(111-c)<TiC(110)<TiC(111-Ti)<TiC(211)Fe(100)<Fe(110)<Fe(310)<Fe(311)<Fe(111)对理想TiC/Fe界面结合的研究发现,本征TiC(100)/Fe(100)界面上以Fe-C联结时界面粘附功最大：2400mJ/m2。另外,界面陶瓷相的层数会影响TiC/Fe界面的结合性,随着TiC层数由1至3层变化,界面粘附功逐步减小,分别为3.325J/m2,2.106J/m2,1.770J/m2,界面润湿性变差。其次,考察了界面周围点空位缺陷类型和空位分布对界面性能的影响,进而重点考察了C空位含量对体相和界面电子结构、界面成键和界面结合性的影响规律。对点空位缺陷类型和位置的研究表明,C空位和Ti空位两种点空位缺陷的空位形成能相比,前者为后者的1/10。C空位、Ti空位和Fe空位三种空位的空位形成能均与其在晶体中的位置有关,由表面层向晶体体相内部,空位形成能逐渐增大,C空位、Ti空位的存在均有利于界面润湿性和结合性地的改善。对TiCx(x=0.75-1.0)中有序C空位对TiC体相电子结构和成键类型的影响规律以及TiC/Fe界面的结合性和润湿性研究发现,有序C空位的存在使得TiC中化学键产生变化,形成新的Vcp-Tid pdK键；与不含有序C空位的理想界面相比,TiCx/Fe界面上Ti-C共价键性、有序C空位周围的Ti-Ti金属键性有所加强,而体相内部的离子键性有所增加。这些电子结构的变化有利于TiC/Fe两相润湿性的改善,增强界面的结合性。TiC0.75/Fe比TiC/Fe界面的润湿性更好,主要原因在于含C空位的界面在费米能级以下的成键态增加,费米能级以上的反键态有所减少,另外,界面体系的beta-PDOS中发现存在三个空位峰(-0.567eV,-3.985eV,-4.745eV),前者为d轨道特征,后两者为p-d成键轨道特性。再次,研究了过渡金属元素添加剂Me=Mo、W、V、Nb、Co、Ni、Cd、Ag对TiC/Fe界面结合性能的影响,发现添加Mo、W、V、Ni、Co元素取代复合材料中的金属元素均能有效改善TiC/Fe复相陶瓷界面的润湿性,Cd、Ag则不利于界面性能的改善。这些添加剂既能进入金属相也能进入陶瓷相形成固溶体,由于其形成固溶体的难易程度不同。Mo、W、Co王要以碳化物形式固溶进TiC相晶格,少量以合金的形式固溶进Fe相,但是,对改善界面润湿性起关键作用的是后者；Ni、V,虽然其主要以固溶进入Fe相晶格形成MeFe合金的形式存在于金属陶瓷复合材料中,但是,对改善界面润湿性起关键作用的是以碳化物形式固溶进TiC相的少部分过渡金属元素。过渡金属元素改善金属陶瓷界面润湿性的本质在于,界面上C原子的p轨道与Me原子的d轨道态电子发生了重叠杂化,形成了强的C-Me极性共价键,同时,强化了界面C-Fe和C-Ti的共价键性,另外,Me-Fe和Me-Ti形成了d-d金属键。最后,对原位SHS法合成的Ti-Al/Al2O3陶瓷的XRD物相和结构进行了实验研究,确定了其主晶相为Al2O3,y-TiAl和a2-Ti3Al三种物相,且Ti-Al合金位为(γ+α2)两相层状结构。并利用第一性原理对TiAl-Ti3Al-Al2O3界面的电子结构和成键类型分析表明,界面上的O原子与Ti和A1结合成键,以O-Al, O-Ti离子键的形式形成界面键合,与纯A1203陶瓷体相内的O-Al相比,复合陶瓷界面上形成的O-Al共价键性有所增加,界面结合增强。计算了TiC/Ti-Al(Fe-Al)界面电子结构和界面性能,结果发现,TiC/FeAl和TiC/Ti3Al界面均有强极性共价键形成,TiC/FeAl界面主要为C-Fe键；TiC/Ti3Al界面主要为C-Ti和C-Al两种键。界面上金属间化合物与陶瓷间形成的共价键性比TiC晶体内部的共价键性略有增强。而且,界面金属性增强也是界面结合性增强的主要原因之一。更多还原

【Abstract】 The comprehensive properties of cermets critically depend on the interficial binding properties of metals and ceramics within one device. Due to a large dissimilarity in physical and chemical properties of both phases, the interficial binding properties are influenced by such factors as wetting of metals to ceramics and interfacial stesses, especially the former. Therefore, the study on interfacial of metal/ceramics have been one of the hot topics in cermets field.Generally speaking, there are two aspects of studies on interfaces of cermets, i.e. experimental and theoretical. However, both of them give less microscopic view to wetting and bonding behavior of metal/ceramic interfaces. Especially enrichment of the third phase and defects at metal/ceramic interfaces would have great infulence on the interfacial behaviors and properties of materials. It is therefore very important to explore the microscopic mechanisms of the impact of additives and defects on interfacial properties of cermets.First principles studies of bulk metal Fe and ceramic TiC, pure TiC/Fe interfaces,TiC/Fe interfaces with additives and point defects, TiC(Al2O3)/Ti-Al(Fe-Al) interfaces were made. The interfacial atom structures, electronic structures and interfacial bonding/binding were thoroughly analysized. The thesis are mainly devided into four parts: Firstly, electronic structure and bonding of intrinsic structre of bulk TiC, Fe and their interfaces were studied. Results showed that two main bonding types were formed in bulk TiC, i.e. pdσ covalent bond between Cp-Tid and dda metallic bond between Tid-Tid, while, there are mainly dd metallic bond between Fed-Fed in bulk Fe. The surface energies of both phases show as follows:TiC(100)<TiC(210)<TiC(111-c)<TiC(110)<TiC(111-Ti)<TiC(211)Fe(100)<Fe(110)<Fe(310)<Fe(311)<Fe(111)Studies of adhesion at TiC(100)/Fe(100) interfaces showed that if Fe-C bond formed at the interface, adhesion would reach at a miximum value:2400mJ/m. Moreever, the interfacial bonding properties of TiC/Fe can also be influenced by the number of TiC layers. The interfacial adhesion varied from3.325J/m2,2.106J/m2to1.770J/m2with the number of TiC layers changing from1,2to3. Wetting and binding properties at TiC/Fe interfaces decreased with the increase of the layers of ceramic phase.Secondly, the effect of point defects types and distribution of electroc and bonding properties at interfaces were also studied, especially C vacancies(Vc). Results showed that the formation energy of Vc was1/10smaller than that of VTj. Vacancy formation energy in surfaces was smaller than that of inside bulk. Vc and VTi point defects are both favoriable to wetting and binding properties of TiC/Fe interface. Study on electronic structures and bonding in TiCx(x=0.75-1.0), wetting and adhesion at TiC/Fe interfaces showed that ordered Vc could change the bonding types in TiCx phases, forming new types of bond, i.e. VCp-Tid pdπ which was not found in Vc free TiC. Ti-C covalent bonds and Ti-Ti metallic bonds around Vc became stronger at TiCx/Fe interface compared to VC free TiC/Fe interface, while there showed a increase in ionic bonding in the internal of TiCx phases. Wetting properties at TiCx/Fe interface were improved after the changes in electronic structures and bond types caused by VC. TiC0.75/Fe interfaces showed better wetting and adhesion than that of TiC/Fe. This is mainly due to the fact that the bonding states under fermi level are increased, while the antibonding states up the fermi level are decreased. Morever, three vacancy peaks were found in beta-PDOS of TiC0.75/Fe interface. They are at-0.567eV,-3.985eV and-4.745eV, the former being of d character, and the latter two p-d.Thirdly, the effect of transition metal additives (Me=Mo, W, V, Nb, Co, Ni, Cd, Ag) on interfacial properties of TiC/Fe were analysized. It was found that Mo, W, V, Ni, Co can improve the wetting properties of TiC/Fe interfaces, while Nb, Cd, Ag can’t. The additives may either incorporate into the crystal structures to the metallic phase or the ceramic phase, while the degree of difficulty is different. Mo,W,Co were incorporated mainly into structure of TiC with less amount into Fe phase. However, Ni, V were incorporated mainly into structure of Fe, only lesser amount of them incorporated into TiC. However, it was the lesser part incorporations not the main part that plays a key role in improving the wettability of TiC/Fe interfaces. The key mechanisms in improving the wettablility and adhesion of TiC/Fe interfaces is that:p orbital of C interfacial atom hybridizated with d orbital of Me, forming strong C-Me polar covalent bond, with C-Fe and C-Ti covalent bond strengthened at the same time. Morever, d-d metallic bond were also formed between Me and Fe, Ti.Lastly, interfacial properties of TiC(Al2O3)/Ti-Al(Fe-Al) cermets were studies. Ti-Al/Al2O3cermets were prepared by in-situ SHS method. XRD and SEM eximinations were made to give a detailed information of phases and microscopic structures, which was confirmed to be TiAl-Ti3Al-Al2O3. First principles studies were made to the new structures and it was found that O-Al and O-Ti bonds were formed between Ti3Al-Al2O3interface. O-Al interfacial bond showed more covalent characters than that in bulk A12O3. Studies on TiC/Ti-Al(Fe-Al) interfaces showed that covalent bonding were formed on both TiC/FeAl and TiC/Ti3Al intefaces. They are C-Fe bonds at TiC/FeAl, C-Ti andC-Al bonds at TiC/Ti3Al. It was also found that interfacial bonding between intermetallic phases and TiC ceramics were more covalent characteric than that of bulk TiC. Morever, interfacial bonding in cermets showed more metallic characters than that in bulk ceramics, giving rise to the wettability and adhesion properties of TiC/Ti-Al(Fe-Al) interfaces.更多还原