摘要45号钢是最常用的优质碳素结构钢，在机械制造业使用广泛。但在实际使用中其耐磨蚀、耐腐蚀性能较差，因此为改善 45 号钢表面的力学性能，提高其 耐磨及耐腐蚀性能，常需在其表面激光熔覆高性能涂层。80612

本文以 45 号钢表面不同工艺参数熔覆的 Ni45 涂层为研究对象，利用金相显 微镜与扫描电子显微镜分析熔覆层微观组织构成；利用 X 射线衍射仪对涂层的 物相组成进行分析；利用显微硬度计测试涂层截面的显微硬度；利用 CS 电化学 工作站测量熔覆层分别在 NaCl 腐蚀液与 NaCl+H2SO4 腐蚀液中的极化曲线，得 出熔覆工艺参数对熔覆层的组织与耐腐蚀性能的影响。

研究结果表明，熔覆层与基体实现了良好的冶金结合，没有气孔等缺陷。熔 覆区域由表及里可分为熔覆区、合金化区、热影响区三个部分。熔覆区主要是树 枝晶与等轴晶；合金化区主要是平面晶与柱状晶；热影响区主要是淬火马氏体组 织。 物相分析结果表 明 ， 熔覆层主要由 γ-(Ni， Fe)、 FeNi3 、 M23(C,B)6 及 Cr2Fe6。7Mo0。11Ni1。3Si0。3 四相组成。显微硬度测试结果显示，熔覆层显微硬度为 450-

550HV，比基体高约 2。5 倍。同时扫描速度与功率越低，熔覆层的显微硬度越高。 腐蚀性能分析表明激光功率越大、扫描速度越快，熔覆层的耐腐蚀性能越好。

毕业论文关键词:  涂层；组织结构；工艺参数；显微硬度；电化学

Abstract 45# steel is the most commonly used quality carbon structural steel, and also widely used in the mechanical manufacturing industry。 However, in practice, the steel has poor erosion-corrosion-resistance and corrosion resistance,so in order to improve the mechanical properties of the 45# steel surface and improve the erosion-corrosion- resistance and corrosion resistance, and it often needs to use high performance coating on the surface with the laser cladding。

The paper adopts 6 kinds of process parameters, takes the Ni45 coating on the surface as the research object, using the metallographic microscope and scanning electron microscope to analyse the composition of the microstructure of the cladding layer。 The paper also uses the X-ray diffraction to analyse the coating phase composition, by microhardness to analyse coating hardness distribution, uses CS electrochemical workstation to measure polarization curve of ladding layer respectively in NaCl and NaCl+H2SO4 solution, and gets a conclusion that the effect of cladding parameters on the microstructures and corrosion resistance。

The results show that the cladding layer and the substrate can achieve a good metallurgical bonding, without porosity and so on。 The cladding region can be pided into three parts: cladding, alloying and heat-affected area。 The cladding area mainly has dendritic crystal and equiaxial crystal。 The alloying area mainly has plane crystal and columnar crystal。 The heat affected area is mainly the quenched martensite structure。 The results of phase analysis show that the cladding layer is mainly composed of γ- (Ni,Fe), FeNi3, M23(C,B)6 and Cr2Fe6。7Mo0。11Ni1。3Si0。3。 Microhardness test results show that the cladding hardness is 450-550HV, about 2。5 times higher than the substrate。 The lower the scanning speed and power is, the higher the microhardness of the cladding layer is。 Corrosion performance analysis shows that the larger the laser power is, the faster the scanning speed is ,and the better corrosion resistance of the cladding layer has。

Keywords: coating; organizational structure; process parameters; microhardness;

electrochemist

目 录

第一章  绪论 1

1。1 45 号钢零件的失效形式