【作者】 戎磊；

【导师】 李铸国；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2011， 硕士

【摘要】 运用激光熔覆技术制备的WC颗粒增强Ni基合金涂层以优良的耐磨性能在当前得到了广泛应用。然而Ni基合金与WC硬质相之间存在较大的性能差异,WC容易沉积于结合界面,出现应力集中并产生裂纹等问题。制备WC含量从表面至界面呈梯度分布的Ni/WC复合涂层,则可以较大地缓解热应力,有效解决涂层裂纹问题,并获得优异的力学性能。本文主要研究利用多层叠加激光熔覆制备WC颗粒增强Ni基合金梯度涂层。通过优化激光熔覆工艺得到良好的涂层成形效果,并利用预热措施有效解决裂纹问题,同时观察分析涂层的微观组织,测试其力学性能,最终得到性能优异的WC颗粒增强Ni基合金梯度涂层。研究结果表明,单道熔覆过程中,随WC含量增加,熔覆层的稀释率逐渐增大,熔覆层上部γ-Ni枝晶先粗化后变细,熔覆层下部的γ-Ni枝晶组织由于稀释率增加而持续增多。不同WC含量的单道熔覆层中,WC溶解形成的碳化物析出后分别以树枝状、块状与粒状等形态存在。单道熔覆层平均硬度随WC含量的增加而增加,当WC质量分数增加到30%时,熔覆层平均硬度可达到基体的4.3倍。对基板采取350℃预热可取得比较理想的熔覆效果,与未预热时相比,350℃预热条件下Deloro60搭接熔覆涂层裂纹完全消除,且熔覆层硬度下降的程度很有限,可作为制备梯度涂层一个良好的基础。在此基础上制备的WC颗粒增强Ni基合金梯度涂层的微观组织主要由γ-Ni枝晶,γ-Ni、Ni₃B、Ni₃Si等组成的多元共晶及弥散分布的M₆C、M₂₃C₆、M₇C₃、Cr_B等强化相构成。Ni/WC梯度涂层中从下往上随WC含量增加而形成的强化相数量逐渐增多,种类也呈现出有层次的分布,γ-Ni枝晶则逐渐减少。Ni/WC梯度涂层的显微硬度从界面到表面连续增大,表面最高硬度可达到1400 HV,约为基体硬度的8倍。各梯度亚层的显微硬度均高于相应成分的单道熔覆涂层,整个梯度涂层平均显微硬度达960 HV,约为基体硬度的5.6倍。摩擦磨损试验结果显示,Ni/WC梯度涂层表面的耐磨性可达到CCS-B基材的3.8倍,显示了优异的耐磨性能。更多还原

【Abstract】 Laser cladded Ni-based alloy coating reinforced by WC particles has broad application due to its excellent wear-resistant property. But because of many differences of the property between Ni-based alloy and WC particle, WC particles incline to deposit on the interface, which is apt to bring on stress concentration and form crack. If the Ni-based alloy gradient coating reinforced by WC particles in which the content of WC distributes gradiently from surface to interface is produced, it will relax the thermal stress greatly so that to eliminate the crack of coating and gain excellent mechanical property.This article is about producing Ni-based alloy gradient coatings reinforced by WC particles through multilayer laser cladding. The main content is to optimize laser cladding technics to gain the good formation of coating, eliminate the crack of coating through preheating, analyze the microstructure of coating, test the mechanical property of coating and finally produce Ni-based alloy gradient coating reinforced by WC particles with excellent property.The result of the research goes as follows. In the process of single track laser cladding Ni-based WC composite coatings, with the increasing content of WC particles, the dilution rate of cladding layer increases,γ- Ni dendrites in the top of cladding layers first coarsen then refine, and dendrites in the bottom of cladding layers coarsen steadily. In the single track laser cladding layers with different WC content, WC particles dissolve and react with surrounding elements to form different carbides, which exist in the shape of branch, block and grain. The average hardness of cladding layers increases with the adding of WC. When the weight percent of WC increases to 30%, the hardness of cladding layers is four point three times of the substrate. It can get good cladding effect through preheating the substrate under 350℃. Compared with no preheating, the crack of Deloro60 overlap cladding layer can be eliminated completely and the reduction of cladding layer hardness is little under 350℃preheating, so it is a good base of gradient coating. The phase of gradient coating produced based on Deloro60 overlap coating mainly containsγ-Ni branch, eutectic includedγ-Ni、Ni₃B、Ni₃Si and dispersed hard phase included M₆C、M₂₃C)6、M₇C₃、CrB and so on. With the increasing of WC content in the gradient coating, there are more hard phases whose kinds are also different because of the dissolution of WC, and the quantity ofγ-Ni dendrites decrease. The microhardness of Ni/WC gradient coating increases continuously from interface to the surface, and the highest hardness of surface can reach 1400 HV, which is about eight times of the substrate. The microhardness of every inferior layer are higher than the single track cladding layer with the same component. The average microhardness of gradient coating is about 960 HV, which is about five point six times of the substrate. The wear testing shows that the wear- resistant property of Ni/WC gradient coating is about three point eight times of the CCS-B substrate, which shows excellent wear- resistant property of Ni/WC gradient coating.更多还原