H13钢表面激光熔覆Co基合金覆层组织与性能分析
发布时间：2018-12-13 11:22
【摘要】：激光熔覆技术是集激光加热熔化、熔池中物质交互作用及快速凝固成形等多学科交叉的一门新技术,主要应用于表面改性与堆焊再制造。该课题在原有实验的基础上,利用脉冲式激光在不同激光功率下制备新型的Co基合金覆层。主要研究内容包括激光功率对Co基合金覆层的组织形貌、物相和稀释率的影响,对Co基材料的非晶形成能力进行分析,借助模拟软件对覆层的温度场进行计算,结合热力学与动力学对其微观组织形成机制进行总结分析,最后研究了激光功率对Co基合金覆层的物理性能的影响。对覆层的上中下三部分的微观组织特征进行分析,发现覆层的中上部以非晶相为主,非晶相中存在有带状分布的等轴晶,覆层熔合线区域以枝晶为主,生长方向垂直于熔合线指向覆层,激光功率为467W时,枝晶的高度最小为10μm。覆层内的Fe元素在结晶相区域发生聚集现象,通过XRD计算得出非晶相的含量,激光功率为467W时覆层的非晶相含量最大。随着激光功率的增大,覆层的稀释率增大。通过Inoue三原则和Yan参数法分别对新型合金覆层微观组织形成机制进行理论分析,验证该材料在激光熔覆的制备工艺下具有非晶形成能力。通过甩带技术将覆层制备为纯非晶,计算其临界冷却速率、约化温度和ΔT_x,说明该覆层具有强的非晶形成能力和高的热稳定性。借助Marc模拟软件对不同功率下的合金覆层的温度场进行模拟计算,得出覆层的冷却速率均大于临界冷却速率。结合热力学与动力学理论对覆层进行分析,研究发现结晶相与非晶相混合的覆层的形成主要是极高的冷速、熔体的流动、溶质的扩散、Fe元素的聚集导致的异质形核共同作用的结果。研究了不同激光功率对Co基合金覆层硬度的影响,当激光功率为467W时,覆层的硬度达到了1192.5HV0.2,覆层中上部区域的硬度发生上下波动的现象,是因为非晶相与结晶相硬度相差较大,随着距覆层表面的距离变大,覆层的硬度整体呈现下降趋势。对不同功率下的覆层和基体的耐蚀性和耐磨性进行分析。在3.5wt.%Na Cl溶液和1mol/l HCl溶液中,激光功率为467W的覆层腐蚀电位最高,激光功率为583W的覆层腐蚀电流最小,在HCl溶液中467W的覆层优先出现钝化现象,在阻抗实验中,激光功率为467W的覆层的阻抗半径最大,说明其在这两种腐蚀环境下的耐蚀性最强。温度为20oC时,覆层的磨擦系数基本在0.15附近,激光功率为467W覆层的磨损量最小,磨痕深度最小,说明其耐磨性最大。覆层的磨损形式以磨粒磨损为主,同时伴有少量的黏着磨损,基体的磨损为大量的黏着磨损和磨粒磨损。
[Abstract]:Laser cladding technology is a new technology which combines laser heating and melting, material interaction in molten pool and rapid solidification forming. It is mainly used in surface modification and surfacing remanufacture. Based on the previous experiments, a new Co based alloy coating was prepared by pulse laser at different laser power. The main research contents include the influence of laser power on the microstructure, phase and dilution rate of Co based alloy coating. The amorphous forming ability of Co based material is analyzed, and the temperature field of the coating is calculated by means of simulation software. The mechanism of microstructure formation was summarized and analyzed by thermodynamics and kinetics. Finally, the effect of laser power on the physical properties of Co based alloy coating was studied. The microstructure of the upper, middle and lower parts of the coating is analyzed. It is found that the middle and upper part of the coating is dominated by amorphous phase, and there are banded equiaxed crystals in the amorphous phase, and dendrite dominates in the fusion line region of the coating. The growth direction is perpendicular to the fusion line, and the height of the dendrite is 10 渭 m when the laser power is 467 W. The content of amorphous phase was calculated by XRD. The content of amorphous phase was the largest when the laser power was 467 W. With the increase of laser power, the dilution rate of the coating increases. The formation mechanism of microstructure of the new alloy cladding was theoretically analyzed by Inoue three principles and Yan parameter method respectively. It was verified that the material had the ability of amorphous formation under the laser cladding process. The coating was prepared into pure amorphous by belt throwing technique, and the critical cooling rate, reduction temperature and 螖 T _ x were calculated, which indicated that the coating had strong amorphous forming ability and high thermal stability. The temperature field of the alloy coating under different power is simulated by Marc software. The results show that the cooling rate of the coating is higher than that of the critical cooling rate. Based on the thermodynamics and kinetics theory, it is found that the formation of the coating mixed with crystalline phase and amorphous phase is mainly due to the extremely high cooling rate, melt flow, solute diffusion, etc. The aggregation of Fe elements results in the coaction of heterogeneous nuclei. The effect of different laser power on the hardness of Co based alloy coating is studied. When the laser power is 467 W, the hardness of the coating reaches 1192.5 HV0.2, and the hardness of the upper and middle parts of the coating fluctuates up and down. Because the hardness of amorphous phase and crystalline phase is different, the hardness of the coating decreases with the increase of the distance from the surface of the coating. The corrosion resistance and wear resistance of coating and matrix under different power were analyzed. In 3.5wt.%Na Cl solution and 1mol/l HCl solution, the coating with 467W laser power has the highest corrosion potential, the coating with 583W laser power has the lowest corrosion current, and the coating with 467W in HCl solution preferentially passivates, and in the impedance experiment, the corrosion potential of the coating is the highest when the laser power is 467W. The maximum impedance radius of the coating is obtained when the laser power is 467 W, which indicates that the coating has the strongest corrosion resistance in these two corrosion environments. When the temperature is 20oC, the friction coefficient of the coating is about 0. 15, and the laser power of 467 W is the smallest, and the wear depth is the smallest, which indicates that the wear resistance of the coating is the greatest. The wear form of the coating is mainly abrasive wear, accompanied by a small amount of adhesive wear, the matrix wear is a large number of adhesive wear and abrasive wear.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.44
[Abstract]:Laser cladding technology is a new technology which combines laser heating and melting, material interaction in molten pool and rapid solidification forming. It is mainly used in surface modification and surfacing remanufacture. Based on the previous experiments, a new Co based alloy coating was prepared by pulse laser at different laser power. The main research contents include the influence of laser power on the microstructure, phase and dilution rate of Co based alloy coating. The amorphous forming ability of Co based material is analyzed, and the temperature field of the coating is calculated by means of simulation software. The mechanism of microstructure formation was summarized and analyzed by thermodynamics and kinetics. Finally, the effect of laser power on the physical properties of Co based alloy coating was studied. The microstructure of the upper, middle and lower parts of the coating is analyzed. It is found that the middle and upper part of the coating is dominated by amorphous phase, and there are banded equiaxed crystals in the amorphous phase, and dendrite dominates in the fusion line region of the coating. The growth direction is perpendicular to the fusion line, and the height of the dendrite is 10 渭 m when the laser power is 467 W. The content of amorphous phase was calculated by XRD. The content of amorphous phase was the largest when the laser power was 467 W. With the increase of laser power, the dilution rate of the coating increases. The formation mechanism of microstructure of the new alloy cladding was theoretically analyzed by Inoue three principles and Yan parameter method respectively. It was verified that the material had the ability of amorphous formation under the laser cladding process. The coating was prepared into pure amorphous by belt throwing technique, and the critical cooling rate, reduction temperature and 螖 T _ x were calculated, which indicated that the coating had strong amorphous forming ability and high thermal stability. The temperature field of the alloy coating under different power is simulated by Marc software. The results show that the cooling rate of the coating is higher than that of the critical cooling rate. Based on the thermodynamics and kinetics theory, it is found that the formation of the coating mixed with crystalline phase and amorphous phase is mainly due to the extremely high cooling rate, melt flow, solute diffusion, etc. The aggregation of Fe elements results in the coaction of heterogeneous nuclei. The effect of different laser power on the hardness of Co based alloy coating is studied. When the laser power is 467 W, the hardness of the coating reaches 1192.5 HV0.2, and the hardness of the upper and middle parts of the coating fluctuates up and down. Because the hardness of amorphous phase and crystalline phase is different, the hardness of the coating decreases with the increase of the distance from the surface of the coating. The corrosion resistance and wear resistance of coating and matrix under different power were analyzed. In 3.5wt.%Na Cl solution and 1mol/l HCl solution, the coating with 467W laser power has the highest corrosion potential, the coating with 583W laser power has the lowest corrosion current, and the coating with 467W in HCl solution preferentially passivates, and in the impedance experiment, the corrosion potential of the coating is the highest when the laser power is 467W. The maximum impedance radius of the coating is obtained when the laser power is 467 W, which indicates that the coating has the strongest corrosion resistance in these two corrosion environments. When the temperature is 20oC, the friction coefficient of the coating is about 0. 15, and the laser power of 467 W is the smallest, and the wear depth is the smallest, which indicates that the wear resistance of the coating is the greatest. The wear form of the coating is mainly abrasive wear, accompanied by a small amount of adhesive wear, the matrix wear is a large number of adhesive wear and abrasive wear.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.44
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