镁锂合金表面CrN薄膜的制备与研究

【作者】 曹得莉；

【导师】 陈玉强；

【作者基本信息】 牡丹江师范学院 ， 凝聚态物理， 2011， 硕士

【摘要】 镁锂合金是目前为止最轻的金属结构材料,具有密度小,比刚度、比强度高,减震性好等优点,广泛应用于电子产品、汽车及航空航天等领域;但是镁锂合金的耐腐蚀性差,阻碍了它本身的广泛应用。目前许多研究者对镁锂合金的腐蚀做了相关的研究,主要采用的处理方法有:物理方法、化学转化、化学镀、阳极氧化等。磁控溅射技术具有沉积速率高、薄膜质量好、工艺简单、对环境友好等优点成为薄膜工业化应用的主要方法。本文采用磁控溅射法在镁锂合金表面制备了CrN薄膜,分析了氮气流量,基底温度,溅射功率等参数对薄膜结构和性能的影响,优化了薄膜制备工艺。利用优化后的工艺参数制备了CrN/ZrN多层膜,并与单层CrN和单层ZrN薄膜进行对比,利用X射线衍射仪(XRD)、S-4800冷场发射电子显微镜(SEM)、原子力显微镜(AFM)来表征薄膜的物相结构、以及表面形貌。利用电化学工作站和析氢实验来评价薄膜在腐蚀溶液中的抗腐蚀性能。讨论了合金以及薄膜的腐蚀机制。研究结果表明:(1)在制备CrN薄膜时,氮气流量、基底温度及溅射功率都存在一最佳参数,过高和过低的工艺参数均使薄膜质量变差,薄膜的防腐性能也因工艺参数对薄膜缺陷、孔隙密度和膜基附着力产生作用而受到影响,工艺参数分别为20sccm、100℃和200W时,薄膜防腐性能最佳。(2)镁锂合金表面溅射沉积的氮化铬和氮化锆薄膜都呈柱状结构,且都存在择优取向生长。(3)单层氮化铬薄膜对镁锂合金的保护效果要优于单层氮化锆薄膜,薄膜沉积过程中产生的微裂纹是膜基系统发生腐蚀的主要场所,而析氢反应加快了这些缺陷处膜层的破坏,最终导致整个膜基系统的失效。(4)在由多靶磁控溅射制备的氮化铬/氮化锆多层膜中,膜层在微观尺度上是致密的。多层膜中的氮化铬薄膜与单层氮化铬膜相比更倾向于(111)面择优生长。(5)腐蚀试验表明,多层膜的防护性能优于单层膜,多层膜中制备工艺引起的随机缺陷是导致其破坏的主要因素,膜层的缺陷是膜基系统腐蚀破坏的快速通道,整个系统的失效由腐蚀源的扩展速度决定,而认为膜基系统的腐蚀破坏是一种短路腐蚀破坏行为。更多还原

【Abstract】 Magnesium-lithium alloy is the lightest metal material, with excellent properties, such as low density, high specific stiffness and strength, with good shock absorption ability, etc. It is widely used in the automotive, aerospace and microelectronics and many other fields. However, its poor corrosion resistance has hindered the wider use of Magnesium-lithium alloy. At present many researchers make the survey about corrosion resistance on Mg-Li alloy, the surface treatments are: physical methods, chemical conversion coating, chemical plating ,anodic oxidation treatment, and so on. Magnetron sputtering is the main method for the industrial application of film owing to its high deposition rate, simple process, and good film quality and environmentally friendly.In this paper, we used magnetron sputtering to prepare CrN coatings on Mg-Li alloy. The influences of deposition parameters were analyzed, such as nitrogen flow; substrate temperature and sputtering power on the properties and structure of the coatings and the preparation technological parameters were optimized. Using the optimized technological parameters deposited CrN/ZrN multiple coatings and compared with both Single-layer CrN films and ZrN films. X-ray diffraction (XRD), Scanning electron microscope (SEM), and Atomic formic microscope (AFM) were used to characterize the phase structure and the surface morphology of the coatings. Electrochemical methods and Hydrogen evolution experiment were applied to study the corrosion behavior of these coatings. In addition, their corrosion mechanism was analyzed .The main results include:(1)During the preparation of the CrN coatings, there was only one optimal parameter for nitrogen flow, deposition temperature and power. Too higher or too lower these parameters would lead to worse coating properties. Coatings’anti-corrosion property was decided in the coatings defects, pore density and adhesion between coatings and matrix; in single parameter factor experiment, anti-corrosion property of the coatings was the best when nitrogen flow, deposition temperature and power was 20sccm,100℃and 200W.(2)Both CrN coating and ZrN coating prepared with sputtering technique had a developed columnar microstructure and existed preferred orientation.(3)CrN coating had a better protection for Mg-Li alloy than ZrN. The defects which formed in the deposition process were the main sites for corrosion. The evolution of hydrogen which took place at these defects accelerated the damage of the coating. Finally, it led to the failure of the coating/substrate system.(4)CrN/ZrN coatings were dense in a microcosmic scope. The (111) texture of CrN layer was strongly strengthened in CrN/ZrN coating compared with that in CrN coating.(5)Corrosion test indicated that multiple coatings had better protection effect than monolayer. The defect in PVD coating was a short cut for corrosion and the failure of the system was determined by the enlargement of corrosion sources. Therefore, the corrosion failure of the system was considered as a kind of short circuit corrosion behavior.更多还原