激光熔覆Cu_p增强Fe基复合涂层微结构转变机制的研究

发布时间：2018-01-08 23:20

本文关键词：激光熔覆Cu_p增强Fe基复合涂层微结构转变机制的研究　出处：《南昌航空大学》2015年硕士论文　论文类型：学位论文

【摘要】：激光熔覆技术具有熔覆层与基体结合强度高,熔覆过程中热影响区及热变形小,组织致密,容易实现机械自动化等一系列优点,被广泛应用在航空、航天、模具、汽车工业、化工等领域。激光熔覆材料包括Ni基、Co基、Fe基合金粉末及金属-陶瓷复合粉末。其中,铁基合金粉末因价格低廉,与钢铁基材的成分相近,润湿性好,结合强度高等特性,具有最广阔的应用前景。但是,铁合金熔覆层的硬度、耐磨性能等有待进一步提高,涂层中容易产生裂纹也是亟待解决的问题之一。因此,本文采用激光熔覆技术,利用铜铁合金液相分离特性,采用原位生成增强相富Cu颗粒(Cup)的方法在A3钢板表面制备具有高硬度的Cup增强Fe基复合涂层,研究了激光工艺参数及化学成分对涂层宏观尺寸、显微结构与涂层性能等的影响,得到的主要结果如下:控制其余工艺参数不变,当增加激光扫描速度时,Cup增强Fe基单道涂层的高度和宽度减小,稀释率变化不大;当增加激光功率时,涂层宽度变化不大,涂层高度增大。在A3钢板表面激光熔覆Cup增强Fe基多道涂层的最优工艺参数为:P=2 kW,Vp=10 g/min,Db=5.0 mm,Vs=8 mm/s,搭接率40%。激光熔覆Cup增强Fe基单道复合涂层由α-Fe和ε-Cu组成。涂层出现分层,由底部的富铁层和顶端的富铜层组成。由于铜铁的液相分离,涂层底部结构为富铜颗粒弥散分布在富铁基体中;涂层顶部的结构为富铁颗粒弥散分布在富铜基体中。同时,颗粒物中还发生二次液相分离现象。另外,涂层内富铁层的凝固具有方向性,从基材向上的显微结构依次为平面晶→胞状晶→树枝晶→等轴晶。随激光扫描速度的增加,富铁基体的晶粒变细小,富铜颗粒也变得细小且弥散。但是,当激光扫描速度增加到12mm/s时,富铜颗粒的尺寸变化得大小不一。激光熔覆层的抗电化学腐蚀性能与铜含量、激光扫描速度及熔覆层表面质量有关,铜含量的增加能提高激光熔覆Cup增强Fe基复合涂层的抗电化学腐蚀性能。激光熔覆层的显微硬度会随着激光扫描速度的增加而增大,其中存在第二相颗粒强化、弥散强化、固溶强化和细晶强化等多种强化机制。当激光扫描速度为12mm/s时,制备的Cu20Fe80和Cu35Fe65多道涂层中观察到裂纹和气孔。获得大小均匀的富铜或富铁颗粒,提高这些颗粒的弥散程度,降低熔覆层与基材间的温度梯度等方法均能有效改善熔覆层的开裂敏感性。
[Abstract]:The laser cladding technology of cladding layer and the substrate bonding strength is high, the cladding process of heat affected zone and thermal deformation small, compact structure, easy to implement a series of mechanical automation, is widely used in aviation, aerospace, mold, automotive industry, chemical industry and other fields. Laser cladding materials including Ni, Co base, Fe base alloy powder and metal ceramic composite powder. The Fe based alloy powder for low prices, and steel material with similar composition, wettability and bonding strength and other characteristics, is the most promising. However, the cladding layer of iron alloy hardness and wear resistance of the coating need to be further improved. Which is easy to produce cracks and problems to be solved. Therefore, this paper using laser cladding technique, using the characteristic of liquid phase separation of Cu Fe alloys, in-situ reinforced phase Cu rich particles (Cup) method with high hardness was made on the surface of A3 steel plate The Cup reinforced Fe based composite coatings, the effects of laser processing parameters and chemical composition of macroscopic size on coating microstructure and influence the coating performance, the main results obtained are as follows: the control of the other parameters constant, the increase of laser scanning speed, Cup enhanced Fe based single coating height and width decreases, the dilution rate little change; when the laser power increases, the coating width changed little, the coating height increases enhanced. The optimum process parameters of Fe based multi-layer coating on the surface of A3 steel laser cladding Cup: P=2 kW, Vp=10 g/min, Db=5.0 mm, Vs=8 mm/s, Fe based composite coating reinforced by single channel -Fe and -Cu alpha epsilon lap the rate of 40%. laser cladding Cup coating. Delamination, composed of copper rich layer of iron rich layer at the bottom and top of the copper and iron. Due to the liquid phase separation, coating bottom structure of Cu rich particles dispersed in the iron rich matrix structure for top coating; Iron rich particles dispersed in the copper rich matrix. At the same time, the separation of two fluid particles in the phenomenon also occurred. In addition, the solidification of the Fe rich layer in the coating from the substrate with a directional microstructure to turn to plane crystal cellular crystal, dendrite to equiaxed grains with increasing laser. The scanning speed of grain, iron rich matrix becomes fine, copper rich particles became fine and dispersion. However, when the laser scanning speed increased to 12mm/s, copper rich particle size changes with different sizes. The laser cladding layer and the corrosion resistance of the copper content, the laser scanning speed and cladding layer the surface quality, the increase of copper content can improve the laser cladding Cup enhanced the electrochemical corrosion resistance of Fe composite coating. The microhardness of the laser cladding layer increases with the increase of laser scanning speed, which are strengthening, second phase particle dispersion strengthening, solid solution strengthening And the fine grain strengthening and other strengthening mechanism. When the laser scanning speed of 12mm/s, observed cracks and porosity of prepared Cu20Fe80 and Cu35Fe65 multi coating. Obtain uniform rich copper or iron rich particles, increase the dispersion degree of these particles, the lower cladding layer and the substrate between the temperature gradient method can effectively improve the cracking of cladding layer.

【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

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