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摘 要 很多工程材料在服役过程中，容易在材料表面出现磨损、疲劳等破坏，一定程度上限制了材料的使用条件和范围，缩短了材料的使用寿命。在钢表面激光熔覆镍基合金可以大幅度改善材料的表面性能，提高材料的表面硬度、耐磨性、耐蚀性等，但是由于Fe和Ni 在物理化学性能上存在较大差异，熔覆层易出现气孔裂纹等缺陷。而稀土具有细化晶粒，净化组织，改善熔覆层力学性能的特点，所以将镍基合金粉末与稀土氧化物混合作为熔覆材料，一定程度上可以减少熔覆层缺陷，提高熔覆层性能。 本文以45#钢为基体，Ni60、Ni60+ CeO2、Ni60+ Y2O3粉末为熔覆材料，利用激光熔覆多道搭接工艺制备了含不同百分含量稀土氧化物的熔覆层。通过对熔覆层进行着色探伤、显微组织观察、显微硬度测定的试验，分析不同含量的稀土氧化物对熔覆层表面裂纹数量、显微组织、硬度的影响规律，并对搭接区域的显微组织和硬度进行观察和测定，分析搭接区域显微组织的特点和硬度变化趋势。结果表明：当添加 0.4%的 CeO2时可以有效抑制熔覆层表面的裂纹，细化晶粒，最大程度的提高熔覆层的显微硬度；在Ni60中加入 Y2O3并没有减少熔覆层表面的裂纹，但当加入 0.4%的 Y2O3后熔覆层的显微硬度有很大程度的提高，且显微组织变得细小而均匀；在搭接区域两侧显微组织出现明显变化，且搭接区域显微硬度低于熔覆层其他部位；整个熔覆层的晶体形态符合组织定向凝固的生长特点。 58964
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毕业论文关键词：激光熔覆；镍基合金；稀土；显微组织；显微硬度
Abstract It’s easy to appear surface wear and fatigue damage on many engineering materials in the service process, which limits the application condition and scope of materials, reduces the service life of the material. Laser cladding is one of a surface modification technology which achieve rapidly heating and melting of the alloy powder or ceramic powder and the substrate surface under the action of laser beam. And with self cooling, It can formation the coating which has a certain excellent performance of anti abrasion, corrosion resistance and thermal oxidation. What’s more, because of the operation environment is much better and easier to realize automatic operation, it has broad application prospect. The laser cladding of multitrack process meet the people requirements on the preparation of large area and high performance coatings, has become a frontier problem in the field of laser cladding technology. This paper to take the steel 45# as matrix, Ni60, Ni60 + CeO2, Ni60 + Y2O3 powder as cladding materials, preparation containing different percentages of rare earth oxide cladding layer by laser cladding of multitrack process. Through the penetrant inspection of cladding layer, experimental of microstructure observation and microhardness determination to analysis the effect of different content of rare earth oxides on the number of cracks on the surface of coating, microstructure and hardness .In addition, to analysis overlap region of the microstructure characteristics and the hardness variation trend, observed the microstructure and measured the hardness of overlap region. The results show that when added with 0.4% CeO2 can effectively inhibit the coatings showed cracks, grain refinement, maximum improve the microhardness; Y2O3 did not decrease the coating surface crack, but when adding 0.4% Y2O3 coating microhardness and microstructure becomes finer and uniform; in the overlap region, the microstructure has significant changes and microhardness of lap region below other parts of the coating; crystal morphology of the cladding layer with the growth characteristics of directional solidification.
Key words: laser cladding; Ni based alloy; rare earth elements; microstructure; microhardness