球墨铸铁表面激光熔覆钴基合金组织及性能研究

发布时间：2018-05-18 06:43

本文选题：球墨铸铁 + 激光熔覆　；参考：《沈阳航空航天大学》2017年硕士论文

【摘要】：球墨铸铁具有较高强度、一定韧性和塑性,同时还具有耐磨、减震、易切削、对缺口不敏感等特性,可代替碳钢和合金钢制造一些受力复杂,强度、韧性和耐磨性要求高的零件,如曳引轮、曲轴、缸套、轧辊等,因此在工业中得到了广泛应用,但球墨铸铁在苛刻的使用环境中,经常因表面经受磨损而导致失效。目前此类零件修复方法主要有热喷涂、堆焊等,但性能和使用效果有待进一步提高。为了显著提高球墨铸铁表面硬度和耐磨性能,本文采用激光熔覆方法,在球墨铸铁QT600-3表面制备了Co基合金、5%TiC/Co基合金、10%TiC/Co基合金、30%TiC/Co基合金熔覆层并探索了在球墨铸铁表面激光熔覆TiC/Co基合金熔覆层最佳熔覆工艺。通过GX71型Olympus金相显微镜、Zeiss-Sigma扫描电镜、X′Pert MPD Pro型X射线衍射仪、JEOL2100F型透射电镜、HVS1000数显显微硬度计、MM200型磨损试验机等分析手段,系统分析熔覆层的微观组织及缺陷、物相组成及硬度和耐磨性等性能,研究熔覆层合金材料成分及激光熔覆工艺参数对熔覆层的影响规律,揭示了熔覆层的耐磨机理,并对Co基、TiC/Co基熔覆合金的激光熔覆工艺参数进行优化,获得的研究结果如下:(1)球墨铸铁QT600-3表面激光熔覆层表面成形良好,无裂纹、气孔等缺陷;熔覆层分为熔化区、结合区和热影响区,熔覆层与基体冶金结合良好;熔化区由表层的树枝晶和内部的胞状晶组成,在热影响区发生了组织转变,形成了马氏体并且球状石墨部分溶解,直径变小。(2)TiC颗粒在熔覆层中呈熔化和未完全熔化状态,含量由基体到熔覆层表层逐渐增加。(3)Co基合金熔覆层主要由γ-Co、CoCx和Cr_7C_3相组成,TiC/Co基合金熔覆层主要由γ-Co、TiC、CoCx和少量的Cr_7C_3相组成。(4)Co基合金或者TiC/Co基合金熔覆层硬度随着离球墨铸铁基体表面距离增加,在热影响区和结合区硬度快速提高,而在熔覆层硬度增加缓慢,直到熔覆层表层硬度又有快速提高。(5)相比球墨铸铁表面激光熔覆钴基合金熔覆层的硬度,TiC/Co基合金熔覆层硬度显著提高,且随着TiC含量的增加而增加。Co基合金熔覆层的最高硬度达到1077HV0.2,提高到球墨铸铁基体的4倍以上。当TiC含量达到30%时,熔覆层的硬度达到1278.8HV0.2,提高到球墨铸铁基体的5倍以上。(6)30%TiC/Co基合金熔覆层的磨损表面没有明显的犁沟和凸起的颗粒,熔覆层磨损机制主要以磨粒磨损为主,平均摩擦系数为0.2315,耐磨性较球墨铸铁基体提高了210倍;Co基合金熔覆层磨损表面具有明显的犁沟和局部撕脱现象,磨损机制主要为磨粒磨损和粘着磨损,平均摩擦系数为0.4914,耐磨性较球墨铸铁基体提高了74倍。(7)在本研究范围内,球墨铸铁表面激光熔覆Co基合金熔覆层最佳工艺参数为:激光功率P=3kW、熔覆速度V=350mm/min,光斑直径为2mm,搭接率1.5;球墨铸铁表面激光熔覆TiC/Co基合金熔覆层最佳工艺参数:激光功率P=3.4KW,熔覆速度V=400mm/min,光斑直径为2mm,搭接率为1.5。
[Abstract]:Ductile iron has high strength, ductility and ductility, at the same time, it also has the characteristics of wear resistance, shock absorption, easy cutting and insensitivity to notches. It can replace carbon steel and alloy steel to make some complicated force and strength. Parts with high toughness and wear resistance, such as traction wheel, crankshaft, cylinder liner and roller, are widely used in industry. At present, the main repair methods of this kind of parts are thermal spraying and surfacing welding, but the performance and application effect need to be further improved. In order to improve the surface hardness and wear resistance of nodular cast iron, the laser cladding method is used in this paper. Co-base alloy 5TiC- / Co-based alloy and TiC- / Co-based alloy cladding layer were prepared on the surface of nodular cast iron QT600-3. The optimum cladding process of TiC/Co based alloy cladding on the surface of ductile iron by laser cladding was investigated. By means of GX71 Olympus metallographic microscope and Zeiss-Sigma scanning electron microscope and X-ray diffractometer JEOL2100F transmission electron microscope and HVS1000 microhardness tester MM200, the microstructure and defects of the cladding layer were systematically analyzed. The phase composition, hardness and wear resistance of the cladding layer were studied. The influence of the composition of the alloy material and the laser cladding process parameters on the cladding layer was studied, and the wear resistance mechanism of the cladding layer was revealed. The laser cladding process parameters of Co-based TiC- / Co-based cladding alloy are optimized. The results obtained are as follows: 1) the surface of the laser cladding coating of nodular cast iron QT600-3 is well formed, free of cracks, porosity and other defects, the cladding layer is divided into melting zone, In the bonding zone and heat affected zone, the cladding layer binds well to the matrix metallurgy, and the melting zone consists of dendrites in the surface layer and cellular crystals in the inner layer. The microstructure changes in the heat affected zone, martensite is formed and the nodular graphite is partially dissolved. The diameter of TiC particles in the cladding layer becomes smaller, and the tic particles are melted and not completely melted in the cladding. The content from the substrate to the surface of the cladding layer increased gradually. The coating mainly consisted of 纬 -CoCX CoCx and Cr_7C_3 phase, mainly composed of 纬 -CoC / Co base alloy cladding layer and a little Cr_7C_3 phase. The hardness of the cladding layer of Co base alloy or TiC/Co base alloy was with the separation of nodular ink. The surface distance of cast iron matrix is increased, The hardness increases rapidly in the heat-affected zone and the bonding zone, while the hardness increases slowly in the cladding layer. The hardness of the laser cladding cobalt-based alloy cladding layer was significantly higher than that of the nodular cast iron surface laser cladding coating, and the hardness of the TiC- / Co-based alloy cladding layer was significantly increased, until the surface hardness of the cladding layer increased rapidly. With the increase of TiC content, the maximum hardness of the cladding layer is 1077HV0.2, which is more than 4 times of that of ductile iron matrix. When the content of TiC reaches 30, the hardness of the cladding layer reaches 1278.8 HV0.2, which is more than 5 times of that of nodular cast iron. There is no obvious ploughing groove and raised particles on the wear surface of the cladding layer. The wear mechanism of the cladding layer is mainly abrasive wear. The average friction coefficient is 0.2315. The wear resistance is 210 times higher than that of the nodular cast iron matrix. The wear surface of the cladding layer has obvious ploughing and local avulsion, and the wear mechanism is mainly abrasive wear and adhesion wear. The average friction coefficient is 0.4914, and the wear resistance is 74 times higher than that of the ductile iron matrix. The optimum technological parameters of laser cladding Co-based alloy coating on the surface of nodular graphite cast iron are as follows: laser power Pu 3kW, cladding speed VN 350mm / min, spot diameter 2mm, lap ratio 1.5.The optimum technological parameters of laser cladding TiC/Co base alloy cladding on nodular cast iron surface are as follows: The optical power is 3.4kW, the cladding speed is 400 mm / min, the spot diameter is 2 mm, the lap ratio is 1.5 mm.
【学位授予单位】：沈阳航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4

【相似文献】