CeO_(2)含量对激光熔覆Ni45A+TiC复合涂层组织和性能的影响

Effect of CeO_(2) Content on Microstructure and Properties of Ni45A+TiC Composite Coatings by Laser Cladding

目的提高模切刀具刃口层硬度和耐磨性,使刃口层内部组织无缺陷。方法以Ni45A-TiC-CeO_(2)为熔覆材料,采用激光熔覆技术在AISI 1045钢表面制备不同含量稀土氧化物复合涂层。通过测试,分别研究不同含量CeO_(2)(质量分数0%~5%)对熔覆层物相组成、显微组织、显微硬度和耐磨性能的影响规律。结果添加CeO_(2)后,熔覆层的物相主要包括TiC、Ni_(3)Fe、Cr_(7)C_(3)、Cr_(23)C_(6)等,少量CeO_(2)的加入未改变熔覆层内主要相的生成,在CeO_(2)的质量分数为5%的条件下,在熔覆层中观测到Ce_(2)O_(3)相。当CeO_(2)的质量分数为2%时,Ni45A-TiC-CeO_(2)复合涂层表面无渣、无裂纹、润湿角较小、宏观形貌最好,从表面到与基体结合处涂层的显微组织无枝晶,组织得到明显细化,TiC形貌细化,且分布较均匀;平均显微硬度最高,为1388.6HV,是未添加CeO_(2)刃口层的1.151倍;平均摩擦因数和平均磨损体积最小,平均磨损体积为0.259×10^(-3)mm^(3),相较于未添加CeO_(2)的熔覆层,降低了47.358%,涂层的耐磨性能最好。结论添加适量CeO_(2)有助于改善涂层的宏观形貌,细化微观组织,提高涂层的显微硬度和耐磨性能。

The tool edge layer needs to have high hardness and wear resistance while the internal organization of the edge is required to be free of defects such as pores and cracks.However,due to the rapid heating and cooling rates in the laser cladding process,there are large thermal and phase change stresses in the cladding layer,and there are differences in physical and chemical properties between the enhanced phase and the base material,which can lead to defects such as coarse grains,pores and cracks in the cladding layer,thus the application of laser cladding technology in tool edge manufacturing is severely limited.Ni45A-TiC-CeO_(2)was used as the cladding material to study the effect mechanism of rare earth element CeO_(2)on the properties of laser-cladding coatings.The rare-earth-oxide composite coatings with different contents were prepared on the surface of AISI 1045 steel by laser cladding.The tests were used to study the effect of different CeO_(2)contents(0%-5%)on the phase composition,microstructure,microhardness,and wear resistance of coatings.The phases of coatings added with CeO_(2)mainly included TiC,Ni_(3)Fe,Cr_(7)C_(3),and Cr23C6.The addition of small CeO_(2)contents did not change the main phase composition in coatings.When the CeO_(2)content was 5%,the phase of Ce2O_(3)was observed.The microstructure of the molten layer with different CeO_(2)contents was observed by scanning electron microscopy,which showed that there were significant differences in the microstructure of the molten layer with different CeO_(2)contents.When the CeO_(2)content was 2%,the surface of Ni45A-TiC-CeO_(2)composite coatings had no slags and no cracks,with smaller wetting angles and better macroscopic features.The structure was refined with no dendrite in the coating microstructure from the surface to the joint with substrates.The morphology of TiC was refined and the distribution was relatively uniform.When the CeO_(2)content further increased,the aggregated rare-earth compounds were found in the melt layer tissue,which affected the uniformity of the microstructure of the melt layer and gas discharge,and also promoted the generation of pores and cracks.The hardness of the edge layer showed a"parabolic"trend with the addition of CeO_(2).With the increase of CeO_(2)content,the hardness of the coating tended to increase firstly and then decrease.The average microhardness was maximum(1388.6HV),which was 1.151 times that of the edge layer without CeO_(2).The average friction factor and average wear volume were the minimum,the average wear volume was 0.259×10−3 mm3.The wear volume was decreased 47.358%and the wear resistance of coatings was optimal compared with that of coatings without CeO_(2).The addition of appropriate amount of CeO_(2)helps to improve the macroscopic morphology of the coating,enhance the diffusion and wettability of substrates and coatings,refine the microstructure and TiC morphology,and improve the microhardness and wear resistance of the coating,and obtain an edge layer with good microstructure and properties and no defects.The results can provide a theoretical basis for the laser additive manufacturing of tool edges.