激光熔覆Ni/SiC复合涂层及其性能的研究
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摘要
本文用GFT-IVB型7kw横流式CO_2激光器在45钢基体表面上进行了Ni60粉末及含有不同百分比SiC的Ni60／SiC混合粉末的激光熔覆试验。通过对不同材料的熔覆层的宏观、微观质量的对比分析，得出了最佳的熔覆材料体系和熔覆工艺参数。利用OM、SEM、XRD等手段进行了熔覆层的相组成和显微组织结构分析的分析，并阐述了激光熔覆过程中SiC对熔覆层的强化机理。利用盘销式磨损试验机进行了45钢、Ni60及含有不同百分比SiC的Ni60／SiC复合涂层的试样的耐摩擦磨损试验，并在观察Ni60、Ni60+25％SiC摩擦磨损形貌的基础上进行了熔覆层材料耐摩擦磨损机制的讨论。利用自制的冲蚀磨损试验机，进行了熔覆试样的耐冲蚀磨损试验，对熔覆层材料耐冲蚀磨损机理进行了探讨。本文最后还利用极化曲线图对熔覆层材料的耐腐蚀性能进行了一些有益的探讨。
激光熔覆工艺参数对熔覆层的宏观形貌、微观组织及涂层性能有极大的影响，在激光熔覆工艺参数为P=3kw，V_s=3mm／s，D=5mm的条件下，所得到熔覆层表面光滑致密、组织细小均匀、稀释率小、硬度高且与基体实现了良好的冶金结合。
微观组织分析表明，熔覆试样由表及里分为三个不同的组织区域：熔覆层、熔覆层与基体之间的结合带、热影响区。熔覆层中不同部位的凝固特征参数不同，形成的组织亦不同，最底部为典型的平面晶外延生长组织，然后呈现胞状晶、胞／枝过渡、枝晶到细小等轴晶的分层凝固特征。
物相分析表明，熔覆层的物相主要是由γ-Ni、Ni_(2.9)Cr_(0.7)Fe_(0.36)、Fe_7C_3、Fe_(0.79)C_(0.12)Si_(0.09)组成的，而无单独的SiC硬质相存在。这是因为在最优的激光熔覆工艺条件下，熔池的温度远远高于SiC的分解温度，在熔覆的过程中一部分SiC被烧损掉了，另一部分SiC分解为C和Si，它们与熔覆层中的合金元素形成新的硬质相，这些硬质相与涂层中强烈的固溶强化和残余应力一起对熔覆层起增强作用。
摩擦磨损试验表明，Ni60激光熔覆层的耐摩擦磨损性能比45钢基体提高了
浙江工业人学硕士学位论文
约个6倍，加入了S汇的复合涂层的耐磨性能比单纯的Ni60自熔合金涂层的耐
磨性能又有显著的提高，在相同工艺条件下，加入25％SIC后耐摩擦磨损性能比
Ni60又提高了 30W50o。另外，不论Ni60还是Ni60／SIC复合涂层的耐冲蚀性
能都比原45钢基体有大幅的提高。
腐蚀试验表明，不论是Ni60涂层还是Ni60／S汇复合涂层的腐蚀电流密度都
远小于45钢，说明熔覆层在所用的腐蚀介质中的腐蚀速率远比45钢小，但加入
SIC后的复合涂层的耐蚀性能反而有所下降。
In this article, we have carried out laser cladding experiments of Ni60 powders and Ni60 with different weight percentage of SiC composite powders on the surface of 45 steel substrate through a GFT-IVB 7kw crosscurrent type of CO2 laser apparatus. A proper material system and laser cladding parameters were ascertained by the comparison of analyses basing on the microscopic and macroscopic qualities of different cladding layers. By the means of OM, SEM, XRD etc., different layers' phase constitution and microstructure were observed and analyzed, the mechanism of SiC enforcement was also expatiated. Through a kind of disc-pin tribological wear experiment machine, we carried out tribological wear experiments on the surface of 45 steel, Ni60 coatings and Ni60 with different weight percentage of SiC composite coatings, the tribological wear mechanism was also discussed basing on the tribological wear configuration of variant wear experiment samples. Through a self-made erosion experiment machine, we carried out e
rosion experiments of laser cladding samples, and the erosion mechanism were discussed too. In the end, we made some useful discussion of different cladding layers' corrosion behavior by the way of polarization curves.
Laser cladding parameters have great impact on the microstructure, macro-configuration and the capability of the cladding layers. Under the cladding parameters of P=3kw, Vs=3mm/s, D=5mm, we obtained cladding coatings with good surface quality, fine microstructure, low dilution, high micro-hardness and good metallurgical combination interface with 45steel substrate.
The microstructure analysis results showed that, from the surface of the cladding specimen to the substrate 45steel, there are three distinct areas: the cladding area, the bonding area and the heat-affected area in the substrate. With the different solidification character parameters, it takes on different microstructure in the cladding layers. The typical microstructure was the typical extension growth on the plane basis at the bottom of the layers, cellular crystals near the bonding area, .dendrite crystal in the middle of the cladding layers and fine equi-axed crystals on the top of the layers.
Laser cladding layers mainly consists of Y -Ni, Ni2.9Cr0.7Fe0.36, Fe7C3, Fe0.79C0.12Si0.09, but single SiC phase is not found. Under the optimized cladding parameters, the temperature in the molten pool is far higher than the SiC decomposing temperature, which results one part of SiC was bumed while the others were decomposed of C and Si. The new hard phase which composing of C, Si and self-confusion alloy element enhanced the cladding layers along with the vehemence solid solution
intensification and the remaining stress.
Tribological wear experiments result shows the wear capability of Ni60 is 4 to 6 times as high as that of the 45steel substrate. Once the Ni60 self-confusion alloy affiliated with SiC, the tribological wear capability enhanced. Under the same cladding parameters, the tribological wear capability of Ni60+25%SiC composite coatings are 30 to 50 percent higher than that of the Ni60 self-confusion alloy. In addition, the erosion capability of Ni60 coatings is far better than that of the 45steel substrate, not to mention that of the Ni60+25%SiC composite coatings.
Polarization cure shows both the Ni60 and Ni60/SiC composite coatings' corrosion current density is far less than that of the 45steel substrate, which manifests the corrosion velocity of 45steel far lower than that of the Ni60 and the Ni60/SiC coatings. However, we found that the corrosion resistance of Ni60/SiC composite coatings is worse than that of pure Ni60 self-confusion alloy.
激光熔覆工艺参数对熔覆层的宏观形貌、微观组织及涂层性能有极大的影响，在激光熔覆工艺参数为P=3kw，V_s=3mm／s，D=5mm的条件下，所得到熔覆层表面光滑致密、组织细小均匀、稀释率小、硬度高且与基体实现了良好的冶金结合。
微观组织分析表明，熔覆试样由表及里分为三个不同的组织区域：熔覆层、熔覆层与基体之间的结合带、热影响区。熔覆层中不同部位的凝固特征参数不同，形成的组织亦不同，最底部为典型的平面晶外延生长组织，然后呈现胞状晶、胞／枝过渡、枝晶到细小等轴晶的分层凝固特征。
物相分析表明，熔覆层的物相主要是由γ-Ni、Ni_(2.9)Cr_(0.7)Fe_(0.36)、Fe_7C_3、Fe_(0.79)C_(0.12)Si_(0.09)组成的，而无单独的SiC硬质相存在。这是因为在最优的激光熔覆工艺条件下，熔池的温度远远高于SiC的分解温度，在熔覆的过程中一部分SiC被烧损掉了，另一部分SiC分解为C和Si，它们与熔覆层中的合金元素形成新的硬质相，这些硬质相与涂层中强烈的固溶强化和残余应力一起对熔覆层起增强作用。
摩擦磨损试验表明，Ni60激光熔覆层的耐摩擦磨损性能比45钢基体提高了
浙江工业人学硕士学位论文
约个6倍，加入了S汇的复合涂层的耐磨性能比单纯的Ni60自熔合金涂层的耐
磨性能又有显著的提高，在相同工艺条件下，加入25％SIC后耐摩擦磨损性能比
Ni60又提高了 30W50o。另外，不论Ni60还是Ni60／SIC复合涂层的耐冲蚀性
能都比原45钢基体有大幅的提高。
腐蚀试验表明，不论是Ni60涂层还是Ni60／S汇复合涂层的腐蚀电流密度都
远小于45钢，说明熔覆层在所用的腐蚀介质中的腐蚀速率远比45钢小，但加入
SIC后的复合涂层的耐蚀性能反而有所下降。
In this article, we have carried out laser cladding experiments of Ni60 powders and Ni60 with different weight percentage of SiC composite powders on the surface of 45 steel substrate through a GFT-IVB 7kw crosscurrent type of CO2 laser apparatus. A proper material system and laser cladding parameters were ascertained by the comparison of analyses basing on the microscopic and macroscopic qualities of different cladding layers. By the means of OM, SEM, XRD etc., different layers' phase constitution and microstructure were observed and analyzed, the mechanism of SiC enforcement was also expatiated. Through a kind of disc-pin tribological wear experiment machine, we carried out tribological wear experiments on the surface of 45 steel, Ni60 coatings and Ni60 with different weight percentage of SiC composite coatings, the tribological wear mechanism was also discussed basing on the tribological wear configuration of variant wear experiment samples. Through a self-made erosion experiment machine, we carried out e
rosion experiments of laser cladding samples, and the erosion mechanism were discussed too. In the end, we made some useful discussion of different cladding layers' corrosion behavior by the way of polarization curves.
Laser cladding parameters have great impact on the microstructure, macro-configuration and the capability of the cladding layers. Under the cladding parameters of P=3kw, Vs=3mm/s, D=5mm, we obtained cladding coatings with good surface quality, fine microstructure, low dilution, high micro-hardness and good metallurgical combination interface with 45steel substrate.
The microstructure analysis results showed that, from the surface of the cladding specimen to the substrate 45steel, there are three distinct areas: the cladding area, the bonding area and the heat-affected area in the substrate. With the different solidification character parameters, it takes on different microstructure in the cladding layers. The typical microstructure was the typical extension growth on the plane basis at the bottom of the layers, cellular crystals near the bonding area, .dendrite crystal in the middle of the cladding layers and fine equi-axed crystals on the top of the layers.
Laser cladding layers mainly consists of Y -Ni, Ni2.9Cr0.7Fe0.36, Fe7C3, Fe0.79C0.12Si0.09, but single SiC phase is not found. Under the optimized cladding parameters, the temperature in the molten pool is far higher than the SiC decomposing temperature, which results one part of SiC was bumed while the others were decomposed of C and Si. The new hard phase which composing of C, Si and self-confusion alloy element enhanced the cladding layers along with the vehemence solid solution
intensification and the remaining stress.
Tribological wear experiments result shows the wear capability of Ni60 is 4 to 6 times as high as that of the 45steel substrate. Once the Ni60 self-confusion alloy affiliated with SiC, the tribological wear capability enhanced. Under the same cladding parameters, the tribological wear capability of Ni60+25%SiC composite coatings are 30 to 50 percent higher than that of the Ni60 self-confusion alloy. In addition, the erosion capability of Ni60 coatings is far better than that of the 45steel substrate, not to mention that of the Ni60+25%SiC composite coatings.
Polarization cure shows both the Ni60 and Ni60/SiC composite coatings' corrosion current density is far less than that of the 45steel substrate, which manifests the corrosion velocity of 45steel far lower than that of the Ni60 and the Ni60/SiC coatings. However, we found that the corrosion resistance of Ni60/SiC composite coatings is worse than that of pure Ni60 self-confusion alloy.
引文
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2 J.Powell Surface Engineering with Laser, Processing Conference, London, 1985, Metal Society.
3 阎毓禾，钟敏霖高功率激光加工极其应用，天津科学技术出版社，1994
4 李儒荀，激光合金化工艺的研究，表面技术 1996 25(6)，13
5 杨洗陈，阎旒禾，应用激光，1988，8(6)：245～249
6 Kathuria.Y.E, Some aspects of laser surface cladding in the turbine industry, Surface and Coatings Technology v 132 (2000): 262～269
7 Zhou, Erhua, Zeng, Xiaoyan, Wu, Xinwei, Zhu, Beidi. Study on laser cladding of Fe-WC ceramic-metal composite coating, Jiguang Jishu/Laser Technology v 21 n 1 (1997): 34～37.
8 Sun,R.L., Yang, D.Z.,Guo, L.X.,Dong.S.L., Effect of laser parameter on microstrcture and microhardness of NiCrBSi laser cladding layer, Guangxue Jishu/Optical Technique v 27 n 1 (2001): 34～36.
9 Wang. A.H., Yue. T.M., YAG laser cladding of an Al-Si alloy onto an Mg/SiC composite for the improvement of corrosion resistance, Composites Science and Technologyv 61 n 11 (2001): 1549～1554
10 任振安，郭作兴，吴山力，工艺参数对铜基激光熔覆层组织及耐磨性的影响．焊接学报，2000，23(1)：69～72
11 张庆茂，刘文今，钟敏霖．宽带激光熔覆铁基合金显微组织与工艺参数的关系．应用激光，2001，21(4)：220～224
12 Resch.M., Kaplan.A.F.H., Schuocker.D., Laser-assisted generating of three dimensional parts by the blown powder process. Proceedings of SPIE-The International Society for Optical Engineering v 4184 (2001): 555～558
13 张思五，郑克全，郑立．中国激光，1993，20(12)
14 Hidouci, A., Pelletier, J.M., Ducoin, F., Dezert, D., El Guerjouma, R. Microstructural and mechanical characteristics of laser coatings. Surface and Coatings Technology v 123 n 1 (2000): 17～23
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