【作者】 李闪；

【导师】 陈国清； 周文龙；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2012， 硕士

【摘要】 镍基合金熔点低,流动性好,具有良好的耐磨、耐腐蚀、耐热和抗氧化等综合性能,并且成本较钴基低廉。为了提高核泵不锈钢的耐磨性能,采用等离子弧堆焊的方法,在不锈钢表面堆焊一层具有优良性能的镍基合金,既能发挥该合金的优良性能,又节约贵重金属。利用金相显微镜、电子探针、XRD衍射仪、荧光光谱分析仪、扫描电镜以及显微硬度计,对镍基合金涂层的显微组织及硬度进行分析。使用MMS-2A型微机控制磨损磨损试验机,对堆焊层的摩擦磨损性能进行了研究,同时利用扫描电镜,对磨损形貌进行观察,研究其磨损机理。同时研究了堆焊电流对镍基合金堆焊层组织、硬度及耐磨性能的影响,还研究了不同镍基合金粉末等离子堆焊层的显微组织、硬度和耐磨性。结果表明镍基合金堆焊层显微组织随着距熔合线距离而变化,堆焊层由y-Ni基体和多种形态的析出相组成,析出相有CrB、M23(C,B)6、Cr7C3、Cr583、Ni3Si。显微硬度随着距熔合线的距离而变化,中间层硬度较低。研究了多种磨损工艺参数对摩擦磨损性能的影响：随着载荷的增加,磨损量逐渐增加,摩擦系数下降；随着转速的增加,磨损量先降低后增加,而摩擦系数降低；随着磨损时间的增加,磨损量逐渐增加,而磨损率降低,平均摩擦系数降低；同时还研究了粗糙度对堆焊层摩擦磨损性能的影响,粗糙度降低时,磨损量先降低后升高。磨损机制是以粘着磨损、磨粒磨损、氧化磨损还有疲劳现象的综合磨损机制。堆焊电流对镍基合金涂层的组织性能影响都很大,电流太低,成型性不好；电流太高,出现烧蚀现象,性能急剧下降。140A电流下的堆焊层,组织杂乱,190A电流下堆焊层组织较粗大,160A电流下,成型性好,组织小均匀,堆焊层性能最优,硬度最高,并且耐磨性最好。镍基合金粉末成分含量的不同,得到的堆焊层组织和性能差别很大。Ni40A合金堆焊层以树枝晶和晶间析出相组成；Ni50A合金堆焊层树枝晶较少,析出相形态多样；Ni60A合金堆焊层在γ-Ni基体上均匀地分布着大量的硼化物和碳化物强化相。Ni60A合金堆焊层显微硬度最高、耐磨性最好；Ni40A合金堆焊层硬度最低、耐磨性最差。更多还原

【Abstract】 The Ni-based alloy have many advantages, such as a lower melting point, good liquidity, abrasive resistance, corrosion resistance, oxidative resistance. Meanwhile, the cost is lower than that of Co-based alloy. In order to improve the abrasive resistance of stainless steel used in nuclear pump, the Ni-based alloy is deposited on the surface of stainless steel by plasma tranferred arc welding. It not only make the best of excellent performance of Ni-based alloy, but also save the precious metals.The coating of the Ni-based alloy was charaterized by metalloscope, electron probe, X-ray diffractometer, fluorescence spectrum analyzer, scanning electron microscope, and microhardness tester. The friction and wear properties were investigated on the MMS-2A friction-wear testing machine. The scanning electron microscope was used for wear surface morphology, which was intended for analysing the wear mechanism. Besides, the influence of welding current and different alloy powder for the microstrcture, microhardness, and wear resistance were researched.The results indicate that the microstructure morphology of the Ni-based alloy coating varied with the distance from the fusion line. The coating consisted of y-Ni matrix and the other precipitates, such as CrB, M23(C,B)6,Cr7C3, Cr5B3, and Ni3Si. The microhardness varied with the distance from the fusion line and the hardness of the middle layer was lower than the other area. The effect of wear technological parameter on friction and wear properties were investigated. With the increase of the load, the wear weight and the friction coefficient decreased. With the increase of the revolving speed, the friction coefficient decreased and the wear weight decreased firstly and increased subsequently. With the increase of the time, the wear weight increased, but the wear rate and the average frction coefficient reduced. When the roughness was reduced, the wear weight decreased firstly and increased subsequently. The wear mechanism included to adhesive wear, abrasive wear, oxidation wear, and fatigue.The influence of welding current on microstructure and properties was significantly. When the current was lower, the forming performance was poor. When the current was high, the coating ablator appeared and the properties dropped rapidly. The microstructure was mess under the current of140A and that was coarse under190A. When the welding current was160A, the coating had good forming performance, fine microstructure, the highest hardness, and the excellent wear resistance. The microstructure and properties of coating were influenced by the element content of Ni-based alloy powder. The microstructure of Ni40A alloy coating, which consisted of dendrite and intercrystalline precipitates, had the lowest hardness and the worst wear resistance. The dendrite was fewer and morphology was diverse of Ni50A alloy coating. A amount of borides and carbides distributed on y-Ni matrix of Ni60A alloy coating, which had the highest hardness and excellent wear resistance.更多还原