【作者】 余冬梅；

【导师】 张建斌；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2014， 硕士

【摘要】 基于高能量密度激光束的3D打印即增材制造(material additive manufacturing)变革了产品的制造方式,成为国内外的研究热点。3D打印对塑料等高分子材料的打印趋于成熟,而对金属材料及陶瓷材料的打印因涉及热应力开裂等问题而进展缓慢。本文选用Stellite6/TiCN混合粉末为原材料,通过优化激光工艺参数、改善成分配比制备Stellite6/TiCN复合涂层,采用激光熔覆技术研究复合涂层的组织及性能,为3D打印的原材料选择提供科学依据和技术支持。Stellite6良好的自我脱氧和造渣的性能,有助于获得氧化物含量低、气孔率少的熔覆层；其优异的浸润性对合金的流动性及表面张力产生有利影响。TiCN兼有TiC和TiN两种材料的优点,如高熔点、高硬度、耐磨性、热稳定性,以及良好的润湿性、导电导热性、化学稳定性和生物相容性。利用光学显微镜、扫描电子显微镜、X射线衍射仪、电子探针、显微硬度计、磨损试验和盐雾腐蚀箱等方法表征或检测所制备的激光熔覆层的组织、相组成、硬度、耐磨性及耐蚀性。通过多组工艺参数对比Stellite6/TiCN复合涂层,并结合熔覆层的组织和性能测试,本实验优化后的激光工艺参数为：最佳激光输出功率P=4kW,激光束光斑直径D=2mm,激光束扫描速度V=7mm/s,搭接率1mm,Ar气保护。熔覆层由熔覆区、热影响区和基体区组成。从熔池与基体界面到熔覆层表面存在不同的凝固形态,依次为平面晶(在界面处)、胞状晶和树枝晶。熔覆层合金粉末成分配(?)kStellite6+(0-50%wt.)TiCN呈现梯度递变。实验结果表明,若不添加TiCN熔覆粉末,分布均匀的纯Stellite6熔覆层组织比较粗大；若添加了TiCN粉末后,熔覆层组织显然细化,表明TiCN粉末的添加有助于熔覆层组织细化晶粒。此外,由于激光束热源快热快冷的特点,熔覆层的凝固速度和熔池中TiCN的浓度对TiCN再次析出的生长形貌具有一定的影响。当TiCN含量较少(0-20%wt.)时,TiCN完全固溶于共晶组织中,并未析出TiCN,显微组织由初析树枝晶(γ-Co相)和枝间共晶((Cr,Mo)23C6、(Cr,Fe)7C3)组成；随TiCN含量的增加(大于30%wt.),熔覆层以TiCN的熔合-析出机制为主,且组织中析出了TiCN。激光熔覆Stellite6/TiCN合金粉末中TiCN的含量对复合涂层的平均显微硬度有显著的影响。当TiCN的含量达到30%wt.时,复合涂层的平均硬度最大为1027HVo.2,相比于基体平均硬度(183.3HVo.2)提高了约560%。室温下的磨粒磨损实验表明,激光熔覆层有效地改善了基体表面的耐磨性能,硬质相TiCN颗粒及其高温分解产物起到了有效承载作用,很好地降低了其表面磨损量。Stellite6/TiCN复合涂层与基体40CrNiMo置于盐雾腐蚀箱内连续喷雾(5%的氯化钠水溶液)8h,以模拟海水环境的加速腐蚀方法来测定其耐腐蚀性能。腐蚀速率：30％wt.(TiCN)<20％wt.(TiCN)<50％wt.(TiCN)<10％wt.(TiCN)<40％wt.(TiCN)<O％wt.(TiCN)<40CrNiMo,涂层的耐蚀性显然优于基体材料,得益于具有良好耐蚀性的TiCN析出。更多还原

【Abstract】 Based on the high energy density of the laser beam,3D printing (namely material additive manufacturing) is innovation of the way that the product are manufactured, which has become a central issue at home and abroad. For polymer materials like plastics,3D printing tends to mature, while it makes a slow progress for metals and ceramic materials due to cracking caused by thermal stress. Stellite6/TiCN mixed powder selected as raw material, is fabricated composite coating by laser cladding technology through the optimization of laser processing parameters and improving the composition ratio of Stellite6/TiCN to investigate microstructure and performance of composite coatings, so that it could offer scientific basis and technical support for selection of raw materials for3D printing.Good self-deoxy performance and slagging of Stellite6help to get the cladding layers of low oxide and less porosity; its excellent wettability is favorable to the liquidity and surface tension of alloys. TiCN combines the advantages of TiC and TiN, such as high melting point, high hardness, good resistance to wear, thermal stability, good wettability, thermal and electrical conduction, chemical stability and biocompatibility.The microstructure, phase composition, hardness, resistance to wear and corrosion are detected or characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, electron probe microanalysis, microhardness tester, wear test and salt spray corrosion box.In contrast to multiple processing parameters of composite coating of Stellite6/TiCN, combining with microstructure and performance of the cladding layer, the laser processing parameters in this experiment are optimized as follows:the optimal laser output power P=4kW, spot diameter D=2mm, scanning speed V=7mm/s, overlap rate is1mm, in Ar gas shield. Cladding layer consist of cladding region, heat-affected zone and the base zone. Different solidification morphology appears in the cladding layer from the interface between the pool and substrate to the surface of substrate, which are plane crystal (at the interface), cellular dendrite and dendrites.The composition ratios of alloy powder (Stellite6+(0-50%wt.)TiCN) in cladding layers appear to be gradient. Experimental results show that the content of TiCN has a significant effect on the microstructure of coating. The microstructure of coating distributes evenly and is coarse without adding TiCN powder; while the microstructure obviously turn fine with adding, which suggest that TiCN powder is helpful to grain refinement of cladding layers. In addition, the solidification rate of cladding layer and the concentration of TiCN in molten pool have some influence on the morphology of TiCN secondary phase due to the laser beam with rapid heating and cooling. When the content of TiCN is less (0-20%w1.), TiCN completely dissolves in the eutectic microstructure without the precipitated TiCN secondary phase, and the microstructure consists of primary dendrite (y-Co phase) and the interdendritic eutectic ((Cr, Mo)23C6,(Cr, Fe)7C3) composition; with the increase in the content(more than30%wt.) of TiCN, the fusion-precipitation mechanism of TiCN in cladding layer dominates, and the precipitated TiCN appears in microstructure.The content of TiCN in Stellite6/TiCN composite cladding layers has a significant effect on the average microhardness. When the content of TiCN reaches30%wt., the average microhardness of composite layers reaches a maximum of1027HVo.2, and increases by about560%in comparison with that of the substrate (183.3HV0.2).Abrasive wear test at room temperature indicates that the cladding layers have improved resistance to wear of the substrate, and the hard phase TiCN particles and their decomposed product at elevated temperature largely bear the loads in cladding layers and significantly reduce the surface wear.The specimens with Stellite6/TiCN cladding layers and the substrate40CrNiMo are placed in the salt spray corrosion box for8h continuous spray (5%sodium chloride solution) to measure its resistance to corrosion by simulating the accelerated corrosion of marine environment. Corrosion rate:30%wt.(TiCN)<20%wt.(TiCN)<50%wt.(TiCN)<10%wt.(TiCN)<40%wt.(TiCN)<0%wt.(TiCN)<40CrNiMo. The cladding layers are clearly superior in resistance to corrosion in comparison with the substrate, benefiting from the precipitated TiCN with good resistance to corrosion.更多还原