原位颗粒增强钛基复合材料的制备与性能研究

发布时间：2018-05-16 03:29

本文选题：粉末冶金 + 高能球磨　；参考：《吉林大学》2017年博士论文

【摘要】：钛基复合材料由于具有高比强度、比模量,且具有比钛合金更优异的高温抗蠕变性能、抗氧化性能及高的热稳定性和热疲劳强度等,成为航空航天领域最具发展潜力的结构材料之一。通过原位合成法制备钛基复合材料,具有增强体与基体界面清洁、结合性好,且热力学稳定性高等突出优点,近年来已成为研究的热点。复合材料中增强体的尺寸和形貌特征,及其在基体中的分布特点等对复合材料的性能有很大的影响,因此研究原位颗粒增强相的形成机理及其对复合材料性能的影响机制,对高性能原位颗粒增强钛基复合材料的开发和应用具有重要意义。本研究以具有优良的热加工性、抗氧化性和高耐磨性的钛基复合材料为目标,采用粉末冶金原位合成法制备钛基复合材料,以Ti-7Al合金(α-钛合金)为钛基复合材料的基体,通过粉末高能球磨与反应热压烧结工艺相结合的方法,制备Ti-7Al-B(TiB/Ti)及Ti-7Al-B-C(TiB+TiC/Ti)颗粒增强钛基复合材料。在原位颗粒增强相的形成、高温压缩流变机制、高温氧化及摩擦磨损理论基础上,设计开发低成本、高性能钛基复合材料,为其工业应用奠定理论和工艺基础。本文的研究主要包括以下几个方面:(1)研究了粉末高能球磨及反应热压烧结工艺,成功制备了晶粒细小的原位自生颗粒增强钛基复合材料。采用粉末原位反应法,利用高能球磨加热压烧结工艺成功制备了近全致密的TiB/Ti及(TiB+TiC)/Ti颗粒增强钛基复合材料,获得晶粒细小的基体组织及颗粒增强相。其微观组织分析表明,颗粒增强相与基体界面清洁、结合性好,在基体中弥散分布。高能球磨使Ti、Al、B(C)粉末细化,并实现了组元间的固溶及部分机械合金化,因而获得的烧结组织晶粒细小,TiB/Ti复合材料中TiB增强相的直径尺寸均在1μm以下。(TiB+TiC)/Ti复合材料烧结前粉末在高能球磨作用下形成了无定形结构,烧结过程中原子的有序化过程阻碍了增强相的长大,形成了平均直径小于100nm的纳米级TiB晶须和平均直径约2μm的等轴状TiC颗粒。同时,TiB和TiC增强相对晶界运动有阻碍作用,抑制了基体晶粒的长大,细化了基体组织。(2)研究了复合材料高温变形流变行为及组织演变规律。通过对TiB/Ti及(TiB+TiC)/Ti颗粒增强钛基复合材料的高温变形流变行为的研究,揭示了流变应力随变形温度和应变速率的变化规律:峰值流变应力随变形温度的升高而降低,随应变速率的升高而升高;且温度越低的条件下,应变速率变化对流变应力峰值的影响越大;而应变速率越低,峰值应力随温度下降幅度越小。TiB/Ti及(TiB+TiC)/Ti复合材料的热高温变形过程是热激活过程,其高温热变形激活能分别为166.02和208.23kJ.mol-1,两复合材料的软化机制均为以动态回复为主,动态再结晶为辅。建立了TiB/Ti及(TiB+TiC)/Ti复合材料的高温变形本构方程和流变应力方程。高温热压缩过程中,复合材料中原位生成的细小弥散的TiB和TiC增强体,对位错有强烈的阻碍作用,使位错在边界累积形成位错亚晶;增强体在基体内转动时引起两侧晶格产生位相差,也会形成亚晶。这些亚晶都可以作为动态再结晶的核心,为动态再结晶提供有利条件。复合材料的微观组织在高温下保持稳定,经高温变形后基体晶粒及TiB和TiC增强相都没有明显长大。这使材料可以在热加工后仍能保持加工前良好的力学性能,同时也为这种材料在高温下服役提供了可能性。(3)研究了复合材料的摩擦磨损性能及其摩擦磨损机理。摩擦磨损研究表明,在外加载荷20-50N,滑动速度0.3-1.2m/s条件下,Ti-7Al合金、TiB/Ti及(TiB+TiC)/Ti复合材料的磨损失重均随载荷和滑动速度的增加而增加。TiB和TiC增强相的加入有效提高了材料的磨损性能,TiB/Ti和(TiB+TiC)/Ti复合材料的磨损失重较Ti-7Al合金显著降低,在实验条件范围内分别约为Ti-7Al合金的57%和27%。以上实验条件范围内,Ti-7Al合金的主要磨损机制为氧化剥层磨损和磨粒磨损,TiB/Ti复合材料的磨损机制为较轻的氧化剥层磨损和磨粒磨损,(TiB+TiC)/Ti复合材料的磨损机制为微切削磨损和疲劳剥层磨损。(4)研究了复合材料的高温抗氧化性能,并阐明了其氧化机制及氧化膜生长机理。对TiB/Ti和(TiB+TiC)/Ti复合材料及其基体合金在700℃、800℃和900℃进行60h恒温断续氧化实验,发现三种材料的氧化产物都只有TiO_2和Al2O3,均形成了连续且厚度均匀的氧化膜。氧化膜为复杂的多层复合结构,按元素分布情况,氧化膜由外到内可分为TiO_2层、高Al2O3层、TiO_2层、TiO_2+Al2O3混合层等。形成这种复杂结构的原因是,在高温氧化过程中,Al的氧化物Al2O3在反应热力学方面的优势和Ti的氧化物TiO_2在生长动力学方面的优势,竞争起主导作用的结果。TiB/Ti和(TiB+TiC)/Ti复合材料及其基体合金的氧化动力学曲线均为类似抛物线形状,即氧化初期,增重速度较快,随氧化时间增加,氧化增重减缓。两种复合材料的氧化增重均低于基体合金,(TiB+TiC)/Ti复合材料的抗氧化性能最佳,在700℃、800℃和900℃氧化60h后的氧化增重比基体合金分别降低了约15%、21.5%和24.5%。分析原因为,复合材料细小的晶粒和弥散分布的增强相,为Al离子的扩散提供了大量短程快速通道(晶界和相界面),使氧化初期更大范围内的Al离子能够参与到反应中来,形成致密性更高的Al2O3层,从而抑制了后续TiO_2生成过程中Ti和O的扩散,降低了氧化速度。
[Abstract]:Titanium matrix composites have become one of the most promising structural materials in the field of Aeronautics and Astronautics because of their high specific strength, specific modulus, high temperature resistance to high temperature, high thermal stability and thermal fatigue strength, which are better than titanium alloys. It has been a hot spot in recent years. The size and morphology of the reinforced body in the composite and its distribution in the matrix have a great influence on the properties of the composites. Therefore, the formation mechanism of the in-situ particle reinforced phase and its composite materials are studied. The effect mechanism of material properties is of great significance for the development and application of high performance in situ particle reinforced titanium matrix composites. This study aims at titanium matrix composites with excellent thermal processing, oxidation resistance and high wear resistance. The titanium matrix composites are prepared by in situ powder metallurgy (P / M) synthesis method, with Ti-7Al alloy (alpha titanium alloy) as the target. Ti-7Al-B (TiB/Ti) and Ti-7Al-B-C (TiB+TiC/Ti) particle reinforced titanium matrix composites are prepared by high energy ball milling and reactive hot pressing sintering of titanium matrix composites. On the basis of the formation of in situ particle reinforced phase, high temperature compression rheology mechanism, high temperature oxidation and friction and wear theory, the low cost is designed and developed. The high performance titanium matrix composites have laid the theoretical and technological basis for their industrial applications. The research in this paper mainly includes the following aspects: (1) the high energy ball milling and the reaction hot press sintering process have been studied. The in-situ particle reinforced titanium matrix composites with fine grain are prepared successfully. The powder in situ reaction method is used to make use of high energy ball milling. The nearly fully compact TiB/Ti and (TiB+TiC) /Ti particle reinforced titanium matrix composites were prepared by the heating and pressure sintering process. The fine grain structure and particle reinforced phase were obtained. The microstructure analysis showed that the particle reinforced phase and the matrix interface were clean, good binding and dispersed in the matrix. High energy ball milling made Ti, Al, B (C) powder refined, and The solid solution and partial mechanical alloying between the components are realized, and the sintered microstructure is fine. The diameter of the reinforced phase of the TiB in TiB/Ti composite is below 1 m. (TiB+TiC) the amorphous structure of the powder is formed before the high energy ball milling. The ordering process of the atoms hinders the enhancement during the sintering process. With the growth of the phase, the nanoscale TiB whiskers with an average diameter of less than 100nm and the average diameter of the TiC particles with an average diameter of about 2 m are formed. At the same time, TiB and TiC enhance the relative grain boundary movement, which inhibits the growth of the matrix grain and refine the matrix. (2) the rheological behavior and microstructure evolution of the composite materials at high temperature are studied. Through T The rheological behavior of iB/Ti and (TiB+TiC) /Ti particles reinforced titanium matrix composites at high temperature was studied. The variation of the rheological stress with the deformation temperature and strain rate was revealed. The peak rheological stress decreased with the increase of the deformation temperature and increased with the increase of the strain rate; and the change of strain rate to the rheological stress under the condition of the lower temperature The greater the effect of peak force, the lower the strain rate, the smaller the decrease of the peak stress with the temperature, the heat and high temperature deformation process of.TiB/Ti and (TiB+TiC) /Ti composites is a heat activation process, the activation energy of the thermal deformation at high temperature is 166.02 and 208.23kJ.mol-1 respectively. The softening mechanism of the two composite material is mainly dynamic recovery, and the dynamic recrystallization is a dynamic recrystallization. The constitutive equation and the rheological stress equation of the high temperature deformation of TiB/Ti and (TiB+TiC) /Ti composites are established. In the process of high temperature thermal compression, the small dispersed TiB and TiC reinforcement in the composite in situ have a strong hindrance to the dislocation, and the dislocation is accumulated as a dislocation subcrystal in the boundary, and the reinforcement is caused by the rotation of the matrix. These subcrystals can serve as the core of the dynamic recrystallization and provide a favorable condition for dynamic recrystallization. The microstructure of the composite remains stable at high temperature, and the grains of the matrix and the TiB and TiC phases are not obviously grown after high temperature deformation. This makes the material still able to remain after hot processing. It is possible to maintain good mechanical properties before processing, and also provide the possibility for this material to serve at high temperature. (3) the friction and wear properties of the composites and their friction and wear mechanisms are studied. The friction and wear study shows that the Ti-7Al alloy, TiB/Ti and (TiB+TiC) /Ti composites are loaded under the loading of 20-50N and sliding speed 0.3-1.2m/s. The wear loss is increased with the increase of load and sliding speed, and the addition of.TiB and TiC enhanced phase effectively improves the wear resistance of the material. The wear loss of TiB/Ti and (TiB+TiC) /Ti composites is significantly lower than that of Ti-7Al alloy. In the experimental conditions, the Ti-7Al alloy is about 57% and 27%. above the experimental conditions, respectively. The main wear mechanism is oxidation peeling wear and abrasive wear. The wear mechanism of TiB/Ti composites is light oxidation peeling wear and abrasive wear. The wear mechanism of (TiB+TiC) /Ti composites is micro cutting wear and fatigue peeling wear. (4) the oxidation resistance of composite materials at high temperature is studied, and the oxidation mechanism and oxygen are clarified. TiB/Ti and (TiB+TiC) /Ti composites and their matrix alloys were subjected to 60H constant temperature intermittent oxidation at 700, 800 and 900 C. It was found that the oxidation products of the three materials were all TiO_2 and Al2O3, which formed a continuous and uniform thickness of the oxide film. The oxide film was a complex multilayer composite structure. From outside to inside, the membrane can be divided into TiO_2 layer, high Al2O3 layer, TiO_2 layer and TiO_2+Al2O3 mixed layer. The reason for this complex structure is that in the process of high temperature oxidation, the advantages of Al oxide Al2O3 in reaction thermodynamics and the growth kinetics of Ti oxide TiO_2 in the growth kinetics are the leading result of.TiB/Ti and (TiB+TiC). The oxidation kinetic curves of /Ti composite and its matrix alloy are similar to the shape of parabola. That is, the weight increase speed is faster in the early stage of oxidation and the oxidation weight increases with the oxidation time. The oxidation weight gain of the two composites is lower than that of the matrix alloy, and the oxidation resistance of (TiB+TiC) /Ti composite material is the best, at 700, 800 and 900. The oxidative weight gain after H is reduced by about 15%, 21.5% and 24.5%., respectively. The reason for the analysis is that the fine grain of the composite and the enhanced phase of dispersion distribution provide a large number of short range fast channels (grain boundary and phase interface) for the diffusion of Al ions, so that the Al ions in the larger scope of the initial oxidation can be involved in the reaction and form the densification. The higher Al2O3 layer inhibited the diffusion of Ti and O in the subsequent TiO_2 generation process and reduced the oxidation rate.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB333

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