铸铁制动盘仿生表面的激光熔覆制备研究

发布时间：2019-04-10 06:52

【摘要】：我国轨道交通正在向高速、快捷化方向发展,随之对列车制动盘性能提出了更高的要求,而制动盘材料是影响其制动性能的一个重要因素。传统的灰铸铁材料制动盘在制动过程中,会产生严重的摩擦磨损和热疲劳破坏,影响制动盘的制动性能和使用寿命。灰铸铁材料已经很难满足现代轨道列车的发展需求,因此,从抗热疲劳性能和耐磨性能两个方面对其进行改性研究具有重要意义。本文依托激光熔覆技术,采用预置合金粉末的方法,在灰铸铁基体表面上进行激光熔覆制备研究。长期生存在海滩的贝类生物,它们经过大自然亿万年的进化,使其对所处的环境具有极强的适应能力。从仿生学角度对其体表进行观察,研究其具有优异耐磨性能和抗疲劳性能体表的形态、结构和材料,为灰铸铁制动盘材料的表面改性研究提供了思路。本文基于仿生学理论,以贝类生物的条纹形态为仿生试样的设计模型,结合制动盘的特殊形状,进行仿生表面设计,利用正交设计方法优化激光工艺参数,并研究激光参数对熔覆层宽度和高度的影响,利用激光熔覆技术制备出形态、结构和材料耦合的仿生试样。利用显微硬度计、扫描电子显微镜SEM以及XRD等仪器对单元体的成分、硬度分布、组织形貌和物相进行分析。同时,做仿生试样和未处理灰铸铁试样的热疲劳性能和摩擦磨损性能对比试验,分析研究仿生试样和未处理试样的硬度、组织形貌、磨损量和磨损形貌,论文得出以下主要结论:(1)脉宽是激光加工参数中对熔覆层宽度和高度影响最大的因素,正交设计得出的优化参数组合为电流180A、脉宽10ms、频率10Hz、离焦量8mm。(2)激光熔覆制备的单元体有致密组织结构,与基体形成冶金结合,熔覆质量满足预定要求。经测试表明,单元体的硬度是灰铸铁基体的2倍。(3)热疲劳试验结果表明,热疲劳使试样的硬度降低,与未处理灰铸铁试样相比,仿生试样硬度下降的幅度较小。(4)热疲劳试验结果表明,热疲劳使材料的组织粗化,产生裂纹,与未处理灰铸铁试样相比,仿生试样的裂纹数量增长速度慢,并且其表面最大裂纹长度较小,说明仿生激光熔覆制备提高了材料的抗热疲劳性能。(5)摩擦磨损试验结果表明,未处理试样的磨损量是仿生试样的1.4倍,同时,仿生试样的磨损形貌明显优于未处理试样,这说明仿生激光熔覆制备大大提高了材料的耐磨性能。(6)论文的研究成果为后续仿生激光熔覆灰铸铁制动盘的制备及实际应用提供了一定的参考。
[Abstract]:China's rail transit is developing towards the direction of high speed and quickness, and the brake disc material is an important factor that affects the braking performance of the train, which has a higher requirement for the performance of the train brake disc. In the process of braking, the traditional gray cast iron brake disc will cause serious friction, wear and thermal fatigue damage, which will affect the braking performance and service life of the brake disc. Gray cast iron has been difficult to meet the development needs of modern rail trains. Therefore, it is of great significance to study the modification of gray cast iron from two aspects: thermal fatigue resistance and wear resistance. In this paper, the laser cladding on the surface of gray cast iron was carried out by using the method of pre-placed alloy powder based on laser cladding technology. Long-lived shellfish living on the beach, after hundreds of millions of years of evolution of nature, they have a strong adaptability to the environment. From the view of bionics, the morphology, structure and materials of the body surface with excellent wear resistance and fatigue resistance were studied, which provided a thought for the surface modification of gray cast iron brake disc material. In this paper, the bionic surface design is carried out based on bionic theory, the fringe shape of shellfish is taken as the design model of biomimetic specimen, and the laser parameters are optimized by orthogonal design method, and the special shape of brake disk is combined with the bionic surface design. The influence of laser parameters on the width and height of cladding layer was studied. The bionic samples of morphology, structure and material coupling were prepared by laser cladding technique. The composition, hardness distribution, microstructure and phase of the unit were analyzed by microhardness tester, scanning electron microscope (SEM) and scanning electron microscope (XRD). At the same time, the thermal fatigue properties and friction and wear properties of biomimetic samples and untreated gray cast iron samples were compared, and the hardness, microstructure, wear amount and wear morphology of biomimetic samples and untreated samples were analyzed and studied. The main conclusions are as follows: (1) the pulse width is the most important factor in laser processing parameters. The optimized parameters are current 180A, pulse width 10ms, frequency 10Hz, and the optimum parameters obtained by orthogonal design are current 180A, pulse width 10ms, frequency 10Hz, and the optimum parameters are current 180A, pulse width 10ms, frequency 10Hz. The defocusing amount of 8 mm. (2) the unit prepared by laser cladding has dense microstructure and metallurgical bonding with the matrix. The cladding quality meets the predetermined requirements. The test results show that the hardness of the unit is twice as high as that of the gray cast iron matrix. (3) the results of thermal fatigue test show that the hardness of the sample is reduced by thermal fatigue, compared with the untreated gray cast iron sample. The hardness of biomimetic specimens decreases slightly. (4) the results of thermal fatigue test show that thermal fatigue results in the coarsening of the microstructure and the formation of cracks. Compared with the untreated gray cast iron samples, the number of cracks in the biomimetic specimens increases slowly. Moreover, the maximum crack length on the surface is small, which indicates that the thermal fatigue resistance of the materials is improved by bionic laser cladding. (5) the friction and wear test results show that the wear amount of untreated samples is 1.4 times that of biomimetic samples, and at the same time, the thermal fatigue resistance of the materials is improved by bionic laser cladding. The wear morphology of biomimetic specimen is obviously better than that of untreated sample. This shows that the preparation of biomimetic laser cladding greatly improves the wear resistance of the material. (6) the research results of this paper provide a certain reference for the preparation and practical application of the subsequent bionic laser cladding gray cast iron brake disc.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4

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