【作者】 田晓峰；

【导师】 尹衍升；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2009， 博士

【摘要】 近年来,公路、铁路交通的发展加速了汽车、火车等运输机械高速重载化的进程,从而对制动装置中摩擦材料的性能提出了更高的要求。车辆行驶速度的提升要求摩擦材料能够在较宽的速度、温度范围内具有稳定的摩擦性能。本文针对已有体系中的材料在使用中的某些缺陷,查阅、分析了大量国内外相关文献,在选用Fe₃Al/Si₃N₄作为基体材料研制开发了Fe₃Al/Si₃N₄基复合摩擦材料基复合摩擦材料,本文根据国际上摩擦材料研究及应用情况,主要从新型陶瓷材料配方的开发、优化、摩擦材料综合性能评定、摩擦磨损机制、摩擦过程热—力耦合作用等方面进行了研究。并获得初步成功。论文涉及材料学、热力学、摩擦学等诸多方面,研究内容富有创新性。本文针对以下几个方面进行了研究:一、用球磨机械合金化工艺制备了Fe₃Al粉体材料,并对Fe₃A1的形成过程和机理进行了研究。也对粉体的制备工艺和随后的热处理过程的必要性,进行了研究,并借用XRD, TEM, SEM, DSC等现代化的测试手段,对Fe₃Al形成过程的组织结构演变及Fe₃Al粉体的形貌进行了表征和测试。研究表明通过球磨机械合金化工艺,能够使A1、Fe元素粉末在球磨过程中使Al原子逐渐溶于Fe中形成无序a-Fe （A1）过饱和固溶体,通过随后在750℃低温退火工艺,无序a相通过A1原子有许重排和筹界移动,转变为有序度较高的DO3结构。通过该工艺,用相对低廉的A1、Fe粉体获得了制备Fe₃Al。采用基于TFDC理论建立的“二原子模型”计算机械合金化过程中Fe相和Al相的应变,结果表明Fe相应变为0.1142,Al相应变为-0.1961,说明Fe相膨胀,Al相收缩,这与XRD测试结果一致。这也为“二原子模型”在机械合金化金属间化合物领域的应用提供了有利证据。二、在系统分析欲制备的Fe₃Al/Si₃N₄复合材料结构和性能的基础上,分析计算了组元间的相容性,根据物理和化学相容原理,初步设计了复合材料配方,对它们进行混料。随后对其烧结工艺进行了优化,对其烧结原理进行了探讨。对制备的材料的性能和结构进行了研究,分析了烧结材料的相组成和界面结合方式。分析表明复合材料烧结后界面结合良好,界面处无明显的反应产物存在。发现材料的致密化过程受到原始粉料组成、粒度以及烧结温度、压力、保温时间等多种因素的影响。最佳工艺参数为:烧结温度1320℃,压力10-20MPa,保压10-30min,保温30-60min,此时致密度为90%-95%。烧结过程中未发现晶粒异常长大。三、根据摩擦材料的设计原则,选择Fe₃Al/Si₃N₄复合材料作为摩擦材料的基体组元,润滑剂为鳞片石墨,摩擦剂Al2O3。根据热力学原理,考察了Fe₃Al/Si₃N₄基摩擦材料中各组元之间的化学相容性。XRD, SEM, EMPA, TEM以及EDS分析表明,Fe₃Al基复合摩擦材料中的物相主要包括Fe₃Al、石墨、Al2O3、Si₃N₄、MgO,少量AlN。石墨和Al2O3均匀分布于基体。对制备的Fe₃Al/Si₃N₄基复合摩擦材料进行了力学性能测试,着重测试其不同工况条件和不同组元含量下材料的摩擦性能和磨损机理。研究表明加入石墨降低材料的力学性能,主要是因为石墨与其它相的界面是材料破坏的发源地。摩擦过程中,适量的石墨加入也能形成润滑膜。加入少量石墨时复合材料以轻微粘着磨损形式为主,加入大量时,石墨界面缺陷累积,材料力学性能急剧下降。在摩擦过程中,剪切断裂的大量的石墨颗粒的参与,使摩擦复合材料的磨损形式变为带有剥层脱落的剧烈磨粒磨损形式。Fe₃Al/Si₃N₄复合摩擦材料在制动过程中其磨损机制可能有磨粒磨损、粘着磨损、氧化磨损以及疲劳磨损四种形式,以磨粒磨损、氧化磨损和疲劳磨损为主。表现为微切削、微犁沟、点蚀以及剥落。四、利用有限元方法对摩擦材料摩擦热—力耦合过程进行了模拟,并在定速式摩擦磨损试验机上测试摩擦材料摩擦过程中摩擦表面温度变化情况。通过模拟结果与定速摩擦温升试验对比,发现模拟结果与试验结果较好吻合,证明有限元方法在摩擦材料摩擦过程热—力耦合分析的可行性,为新型摩擦材料配方的开发、摩擦材料磨损机制的研究提供了理论与试验依据。结果表明:在摩擦材料工作过程中,刹车片前端温度明显高于后端,在表面存在温度梯度,且随着制动压力的提高,摩擦表面最高温度相应提高,表面温度梯度越大。随着制动摩擦时间的推移,摩擦材料表面沿着滑动方向所受的剪切力逐渐增大,制动压力越大,剪切力越大,且增长速度越快。定速摩擦温升试验中,摩擦衬片材料表面温度随着制动摩擦时间的推移逐渐升高,随着制动压力的提高,摩擦表面温度上升速度加快。对比有限元模拟结果发现,模拟表面温度高于定速摩擦升温试验结果,主要是由于有限元模拟过程中忽略了摩擦热以空气对流、辐射、磨损微粒温升等形式的耗散。有限元模拟结果与试验结果中温度随时间的变化趋势基本相同。要得到更加准确的模拟结果,要在模型中增加材料的磨损、化学变化等因素。总之,本文尝试性的设计了Fe₃Al/Si₃N₄基复合摩擦材料体系,并试验性证明了设计的可行性,对设计的材料进行了力学性能测试,着重测试了其摩擦磨损性能。测试中,不但考虑其它组元对其摩擦性能的影响,而且模拟测试了该材料在一些复杂工况条件下的摩擦性能。抗氧化性实验和耐腐蚀性试验证明该材料优于传统的铁基摩擦材料,制动试验证明,该材料制动平稳,无明显的“热衰退”现象,是一种有潜在开发价值的摩擦制动材料。更多还原

【Abstract】 In recent years, the development of highway and railway has accelerated the process of high speed and loading of transport machines, which deserves higher properties of the friction material in the brake system. Higher speed of vehicles needs stable properties of the friction material in a comparatively larger scale of speed and temperature. This thesis has for the first time in China put forward a theory that friction materials were made by developing a new matrix named Fe3A1/ Si₃N₄-base . This dissertation, based on the study and application of friction materials in the world, is a study on new friction materials from the aspects of development, optimization, assessment of integrated properties of friction materials, friction wear mechanism and coupling of thermal and strength, etc.The composite has been made successfully. The study covers areas such as material science, thermodynamics, tribology and some other disciplines and the research is creative as well as systematical.The main contents are as follows:Fe₃Al powder was prepared by milling mechanical alloying technology. Relevant studies were conducted on its formation process and mechanism, its technology process and the necessity to apply annealing treatment. The structural evolution of Fe-Al elemental during mechanical alloying process, and the shape of Fe₃Al particle have been investigated and tested by means of XRD, TEM, SEM and DSC. Depending on milling mechanical alloying technology, with the increase in milling time, Al atom can dissolve crystal lattice of Fe, and form disordered a-Fe solid solution. During annealing at 750℃,through Al atom order rearrangement and removing of APS domains, the lower B2 ordered and higher ordered structure were obtained. Making use of the technology, relatively inexpensive Fe and A1 powder were made into Fe₃Al -base to prepare Fe₃Al-base composite.Based on systematic analysis of the structure and performance of Fe₃Al/Si₃N₄ materials to prepare, Further analysis and calculation were done on the physical and chemical compatibility between them. A new composite material formula was then developed and these components were mixed. Subsequently sintering technology was optimized and sintering theory was explored. The structure and performance of friction materials prepared were studied, and bond and structure of interface were studied in detail. The composite sintered presented favorable interface in the course of components and no obvious reaction products emerged. It was found that the densification process was affected by the component of original powders, particle size and processing parameters such as sintering temperature, pressure and holding time.The optimal parameters are as follows:sintering temperature 1320℃,pressure 10-20MPa, holding time for pressure 10-30min, holding time for temperature 30-60min, with the density of 90%-95%.On the ground of design principle of friction materials, Fe₃Al/Si₃N₄ composite material was chosen as the matrix, with flake graphite as lubricants, as friction particles. The chemical compatibility between the components according to the basic principle of thermodynamics was examined. XRD、SEM、EMPA、TEM and EDS investigations indicated that the main phases in the Fe₃Al/Si₃N₄-based composite friction materials are Fe3A1,graphite, Si₃N₄,AlN,MgO,Graphite and Al2O3 , a small quantity of AlN as impurity. Graphite and Al2O3 were dispersed uniformly in the matrix. Because of its unfavorable interface bonding with other bond,Graphite decreased mechanics capacity. In the course of friction test, graphite can shift into lubricating layer with a low graphite content, composite exhibited slight adhesion abrasion;while with a high graphite content, because of much boundary limitation, mechanics capacity declined sharply. When graphite slice cracked because of cutting to form much graphite particle, wear performance is transformed to heavier particle abrasion with brittle split of materials. The wear forms of the Fe₃Al/Si₃N₄-based friction materials are mainly particle wear, oxidation wear and fatigue wear, exhibiting the micro cutting, micro furrows, dot corrosion and spalling away.The coupling of thermal and strength of ceramic friction materials is simulated with finite element method （FEM）. And the temperature change of the friction face is tested on friction tester with constant speed. The comparison between the simulation result and the friction experiment with constant speed shows the consistency between the two. This proves the feasibility of finite element method in the analysis of coupling of thermal and strength, which provides theoretical and experimental foundation for the development of new friction materials and the study of wear mechanism of friction materials. The results of friction tests with constant speed show that the temperature of brake lining material surface rises with the passage of time. The higher the pressure is, the faster the temperature rises. It can be found that the temperature of friction interface calculated by FEM is higher the temperature measured in friction test. Ignoring the heat dissipation by means of cross-ventilation, radiation and temperature rising of abrasive particles induces the difference between the results of simulation and test. In order to obtain more exact results by means of simulation, wear and chemical reaction of friction material should be taken into account.To sum up, the thesis developed Fe3A1/Si₃N₄-base friction materials, and testified the feasibility of the formula. The experiment tested its mechanics capacity and probed its wear mechanism. The experiment not only explored the effects of other components its friction capacity, but also tested and simulated its friction capacity in complicated working conditions. It is testified that its capability of anti-oxidation and anti-corroding excelled one of Fe-base friction material.Braking test found that the material exhibited excellent braking performance, and possessed great potential in its development as a new friction braking material.更多还原