液压油缸激光表面强化研究

发布时间：2018-03-05 20:39

  本文选题：激光表面强化　切入点：微观组织　出处：《华中科技大学》2012年硕士论文　论文类型：学位论文

【摘要】：液压油缸由于其工作环境的多为高温、潮湿，因此其表面经常会出现腐蚀，磨损等失效形式，而在修复过程中，如果采用整体更换则会使成本过高，因此人们多采用表面强化技术对其进行局部的修复以达到继续使用的目的。而激光表面强化以其具有的诸多优势，在修复表面方面具有极大的前景。 本次课题采用光纤和CO2两种激光器，以45钢作为基材，进行激光表面强化实验。研究激光表面强化合适的工艺参数和影响因素。对激光合金化试样进行了XRD、SEM、硬度，耐蚀性和耐磨损性能检测，并对激光处理的强化机制进行了探讨 在显微组织方面，经SEM分析表明，激光淬火后表层组织区域可以分为熔化区和热影响区两部分，且均由马氏体组织组成，但是熔化区的组织较粗大；激光合金化后表层组织区域由合金化区，过渡区和热影响区三部分组成，合金化层由于温度梯度和凝固速度之比的不同，由平面晶、胞状晶、树枝晶以及等轴晶组成。过渡区则是由细小针状马氏体组成，热影响区主要由残余奥氏体、马氏体、珠光体和铁素体组成。实验所选用的激光种类和激光合金化中激光的参数都会对表层的结构和其显微组织造成影响。激光功率的加大和扫描速度的提高都能达到细化晶粒的效果。而激光熔覆之后截面可分为熔覆层，合金化层和热影响区三个部分，，从熔覆层到热影响区，组织逐渐由等轴晶，到树枝晶，到胞状晶，平面晶，最后到热影响区的马氏体组织，并且在添加WC的情况下，WC会呈雪花状或片状分布在熔覆层内。 对表层的截面进行了硬度检测，结果表明合金化层和熔覆层的显微硬度相比基体都有了明显的提高，分别可以达到500HV和900HV。在不影响激光处理的效果范围内增大激光功率或者提高激光扫描速度可以获得较高的表层硬度。晶粒细化，合金元素的弥散强化和析出相的固溶强化。 对激光处理后的材料表层进行了耐磨性能和耐蚀性能的测试，发现经过激光合金化和激光熔覆之后的涂层在耐磨和耐蚀性能上均有较大的提升，耐磨性能相比基体提升了5倍以上，激光工艺参数对材料的耐蚀性和耐磨性均有较大影响 在基体表面熔覆Fe基合金粉末和WC粉末混合的涂层之后发现耐蚀性有了稍微的下降，推测可能是由于WC粉末加入的比例对其耐蚀性有一定的影响。
[Abstract]:Because the working environment of the hydraulic cylinder is mostly high temperature and humidity, the surface of the cylinder is often damaged by corrosion and wear. In the repair process, if the whole replacement is adopted, the cost will be too high. Therefore, surface strengthening technology is often used to repair the surface in order to achieve the purpose of continued use, while laser surface strengthening has great prospects in repairing the surface because of its many advantages. In this paper, the laser surface hardening experiments were carried out with 45 steel as the substrate by using two kinds of laser fiber and CO2 lasers. The suitable technological parameters and influencing factors of laser surface strengthening were studied. The hardness of laser alloyed samples was studied. The corrosion resistance and wear resistance are tested, and the strengthening mechanism of laser treatment is discussed. In the aspect of microstructure, SEM analysis shows that the surface microstructure area after laser quenching can be divided into melting zone and heat affected zone, and both of them are composed of martensite structure, but the microstructure of melting zone is relatively large. After laser alloying, the surface layer is composed of alloying zone, transition zone and heat affected zone. The alloying layer is made up of plane crystal and cellular crystal due to the difference of temperature gradient and solidification rate. The transition zone is composed of fine acicular martensite, and the heat affected zone is mainly composed of residual austenite, martensite, The composition of pearlite and ferrite. The type of laser selected in the experiment and the laser parameters in laser alloying will affect the structure and microstructure of the surface layer. The increase of laser power and the increase of scanning speed can be achieved. The effect of grain refinement. After laser cladding, the cross section can be divided into cladding layer, The microstructure of alloying layer and heat affected zone from cladding to heat affected zone is gradually from equiaxed crystal to dendrite to cellular crystal, plane crystal, and finally to martensite structure of heat affected zone. When WC is added, the WC will be snowflake or flake in the cladding layer. The hardness of the surface section is tested. The results show that the microhardness of the alloying layer and the cladding layer are obviously improved compared with the matrix. The surface hardness, grain refinement, diffusion strengthening of alloy elements and solution strengthening of precipitated phase can be obtained by increasing laser power or laser scanning speed in the range of no effect of laser treatment, 500 HV and 900HV, respectively. The wear resistance and corrosion resistance of the laser treated coating are tested. It is found that the coating after laser alloying and laser cladding has a great improvement in wear resistance and corrosion resistance. The wear resistance of the material is more than 5 times higher than that of the matrix. The laser process parameters have great influence on the corrosion resistance and wear resistance of the material. It was found that the corrosion resistance decreased slightly after the coating of Fe-base alloy powder and WC powder mixed on the substrate surface, which may be due to the influence of the proportion of WC powder on the corrosion resistance.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TH137.51;TG174.4


本文编号：1571792