【作者】 刘研；

【导师】 周宏；

【作者基本信息】 吉林大学 ， 材料加工工程， 2013， 博士

【摘要】 蠕墨铸铁由于其在热效应较强的干滑动摩擦磨损条件下表现出高摩擦系数、低磨损率及优良的热疲劳性能，且制造工艺简单、成本低廉，被世界各国普遍应用于制造列车制动盘。制动盘的失效是磨损与热疲劳共同作用的结果，在以往的实验室基础研究中，两者的研究相对独立，为了使实验室基础研究更加贴近实际应用，本文提出了热疲劳性与耐磨性一体化研究的思路，考察了材料不同热疲劳程度对其耐磨性的影响。随着列车速度的提高，对制动盘材料的性能提出了更高的要求。利用激光可实现局部加工的特点，按照根据仿生学原理以材料和形态为耦元建立起来的仿生模型，在钢铁材料表面制造出仿生单元体，并与基体耦合形成耐磨损、抗疲劳的仿生表面，是近年来提出的一种新的提高钢铁材料性能的方法，由于对生产环境和使用环境做出相应改变的要求较低，也是受到产品生产者和使用者欢迎的一种途径。然而激光仿生熔凝处理的单元体仅存在于材料表层较浅的区域，对于磨损极限一般要求为单侧7mm的列车制动盘而言，激光仿生熔凝处理对其使用寿命的提高幅度是有限的，当仿生单元体因磨损而耗尽时，制动盘的磨损将回到原始状态，对制动装置的整体稳定性也会产生影响。另外，制动盘的质量及安装位置决定了其在列车部件中属于比较难更换的部件，也对提高制动盘的使用寿命提出了要求。从仿生原理的角度分析，激光仿生熔凝处理的仿生表面是材料与形态耦合出的软、硬相相间排布的非光滑表面，通过提高硬质相材料耦元的性能，可以提高非光滑表面的整体性能。因此提出了提高冷却速率的水介质激光仿生处理工艺。研究表明：与空气介质仿生处理工艺相比，水介质仿生处理工艺可以细化蠕墨铸铁仿生单元体的显微组织，仿生单元体的显微硬度也得到显著提高。在热疲劳实验中，与空气介质试样相比，水介质试样具有较好的抵抗热裂纹萌生的能力，但抵御热裂纹扩展的能力较差。仿生单元体上的裂纹是影响其抵御热裂纹扩展能力的关键因素。在磨损实验中，相同磨损条件下，水介质仿生蠕墨铸铁的耐磨性优于空气介质仿生蠕墨铸铁。随着仿生蠕墨铸铁的热疲劳程度加深（热疲劳循环次数增加/热疲劳温度提高），其耐磨性下降，但仿生试样的耐磨性始终优于未处理的试样，而水介质试样的耐磨性始终优于空气介质试样。仿生蠕墨铸铁的热疲劳对其耐磨性产生影响的根本原因是仿生单元体的显微组织在热疲劳过程中发生碎化，甚至层状剥离，导致仿生单元体的显微硬度下降。为了改善水介质仿生单元体抵御热裂纹扩展的能力，选用消除应力热处理（预热处理、后热处理）、二次激光熔凝处理和电脉冲处理三类途径、四种方法对仿生单元体进行了辅助处理。实验结果表明，四种方法均可改善水介质仿生单元体的抗热疲劳性，改善效果由大到小的顺序是：电脉冲处理＞激光二次熔凝处理＞后热处理＞预热处理。本文创新地将材料的热疲劳性能和耐磨性能的研究有机地结合起来，试分析材料的热疲劳对磨损性能的影响及仿生单元体的表面质量与材料的整体性能的联系，为水介质仿生蠕墨铸铁的工程应用提供理论依据及实验基础。更多还原

【Abstract】 It is generally used in the manufacture of train brake by countries around theworld based on its excellent property under conditions of dry sliding friction withstrong thermal effects, such as high friction coefficient, low wear rate and excellentthermal fatigue performance, and so on. Moreover its manufacturing process issimple and the cost is low. The main failure forms of brake disc are wear andthermal fatigue. The laboratory research of material wear properties and its thermalfatigue properties is usually independent. In order to make basic research inlaboratory more close to the practical application, the integration research ofthermal fatigue resistance and wear resistance is proposed, the thermal fatigueresistance of bionic vermicular cast iron processed in water is studied after its wearresistance has been studied.With the improvement of train speed, the higher performance of the brake discmaterials is need. According to the bionic model which was built by materialscoupling with forms, using laser surface local processing technology, a new methodto improve the performance of steel materials have been proposed in recent years,which can process bionic units on the surface of materials and make the bionicunits combine with the matrix to form the structure which has similar to the biological surface and has wear resistance, fatigue resistance. The bionic units onlyexist in the shallow range of the surface; while for train brake disc, their wear limitis7mm on unilateral side. The effect of laser bionic processing on improving itsservice life is limited, so the wear of brake disc is expected to return to originalstate, when the bionic units are run out, the overall stability of the brake disc willbe affected. Moreover the brake disc is one kind of parts which are difficult toreplace, because of its quality and installation location. It also needs to improve theservice life of the brake disc. Analysis from the perspective of the bionic principle,the bionic surface processed by laser bionic processing is the non-smooth surfaceformed by materials coupling with forms which characteristic is hard phasecombines with soft phase. Its overall performance can be improved by enhancingthe performance of bionic units. Therefore the laser bionic processing in water wasused to further improve the performance of bionic units.The researches of thermal fatigue properties and wear resistance areorganically combined. The influence of thermal fatigue on wear performance isstudied. The connection between the quality of the bionic units and the overallperformance of bionic specimens also is discussed. All of above provide theoreticaland experimental basis for the engineering application of laser bionic processing inwater.The conclusions are that:1. Using shells and leaves as biological prototype which have the performanceof wear resistance and fatigue resistance, the bionic surface on vermicular cast ironwhich has striped bionic units were obtained by water process. The microstructureof bionic unit is refined and its micro-hardness is raised from670HV to920HV.2. The time of the first thermal crack appearing on the bionic vermicular castiron processed in water lag behind than that processed in air, the time is200times thermal fatigue cycle. Under the same thermal fatigue condition, the thermal cracknumber of bionic vermicular cast iron processed in water is always less than that ofbionic vermicular cast iron processed in air. Yet the longest length of cracks islonger than that of processed in air. The laser bionic treatment in water improvesthe resistance to thermal cracks initiation. But more cracks of bionic unitsprocessed in water increase the chances that the cracks on unit and matrix cracksare overlapped together. So the resistance to thermal crack propagation of thebionic vermicular cast iron reduces.3. Under the same wear conditions, the wear resistance of bionic vermicularcast iron processed in water is increased by43%.4. The wear tests of bionic vermicular cast iron undergone thermal fatiguetests show that with the increasing of thermal cycles or thermal temperatures thewear resistance decreased and the wear loss linear increased. The equation of linerregression of wear loss belong to un-treated vermicular cast iron is y=0.554x-11.48,R2=0.9833, the x is used to show thermal fatigue cycles and the y is used to showwear losses. The equation of liner regression of wear loss belong to bionicvermicular cast iron processed in air is y=0.0363x-6.9, R2=0.9791, and that belongto bionic vermicular cast iron processed in water is y=0.0307x-8.08, R2=0.9812.From the slope of the trend lines, the slope of specimen treated in water is the least,so under the same wear conditions, its growth of wear loss is the least, and its wearresistance is the best.5. In the thermal fatigue tests, the microstructure of the bionic units broke, andeven layered dissection, it caused the wear resistance of the bionic vermicular castiron dropped. Under the same conditions, the wear resistance of bionic vermicularcast iron processed in water is always better than that of processed in air, becausetheir microstructure changes relatively lag behind. 6. After auxiliary process, the number of bionic units’ cracks and the chance ofthe units’ cracks lap over the matrix’s cracks reduced. The order of effects from bigto small is: electric pulse treatment﹥water bionic treatment﹥twice laser treatment﹥after heat treatment﹥preheat treatment.7. Twice laser process and electric pulse treatment can make bionic unitsprocessed in water formed network cracks which have less cross cracks. Theresistance to thermal crack propagation of the bionic vermicular cast iron enhanced.After electric pulse treatment, the micro-hardness of bionic units is improved, itproduced positive effects on wear resistance of bionic vermicular cast ironundergone thermal fatigue tests.更多还原