高频微振/激光协同调控Fe基非晶合金涂层搭接区纳米相增塑机理研究

Fe-based amorphous coatings have the excellent properties of high strength, high hardness, high wear resistance, high fatigue strength. The coatings have a very broad application prospects. But crack initiation often appears in the surface of overlapping zone while fabricating large area amorphous coatings. In this study, high frequency micro vibration will be introduced into the process of fabricating amorphous coatings by laser. Nano particles will generate in the coating with the combined effect of heat and force. Nano particles will increase the amount of shear bands and change the extension ways of shear bands. This can improve the plasticity and toughness and reduces the crack sensitivity of amorphous coatings. In this project, firstly, the influence rules of high frequency micro vibration on microstructure in single amorphous coating were studied. Secondly, the influence rules of high frequency micro vibration on microstructure in overlapping zone of multiple amorphous coatings were studied, too. The precipitation mechanism of plastic phase in overlapping zone under high frequency micro vibration conditions will be analyzed. At the same time, the interaction mechanism of plastic phase and amorphous phase will be described according to the characterization of microstructure of the coatings. Finally, a plasticized model of nano plastic phases in overlapping zone will be established base on mesomechanics of composite material and the plastification mechanism of plastic nanocrystalline phase will be explained in detail. Therefore, this project has an important significance for the design, synthesis and metallurgical behavior of large area amorphous coatings by laser processing in the future。

Fe基非晶涂层具有高强度、高硬度、高耐磨性、高疲劳强度等优异的性能，具有极为广阔的应用前景，但研究发现大面积制备此类涂层时在搭接区塑性差，易萌生裂纹。本课题拟利用高频微振同步处理激光非晶化涂层，热-力协调控制涂层搭接区凝固过程，引入纳米相增加非晶剪切带数量及改变剪切带扩展路径，提高搭接区塑性储备和涂层的抗裂性。本项目首先研究高频微振对单道涂层组织形成的影响规律；其次研究高频微振对多道非晶涂层搭接区组织的影响机制：调节高频微振参数，解析高频微振对搭接区纳米相析出作用；同时，根据对涂层微观结构的表征阐述纳米相与非晶基体的相互作用机理；最后，基于复合材料细观力学阐明纳米相增殖、复杂化剪切带增塑搭接区机理并建立模型。本项目研究对后续大面积激光非晶涂层的设计、合成及其冶金行为的研究有着重要意义。

近年来，随着块体非晶合金（BMGs，Bulk Metallic Glasses）理论及应用研究获得长足的进步，非晶合金涂层更是显示出了巨大的应用潜力。本项目结合微振和激光熔覆技术在钢基体表面制备了铁基非晶纳米晶复合涂层，基于热-力协调控制涂层在大面积制备时的凝固过程，利用塑性纳米相增加涂层塑性，提高涂层抗裂性，解析了微振对涂层组织的形成机理，阐明了微振对搭接接头增塑的作用过程。实验结果表明：涂层主要晶相组成为非晶相、M23C6 (M=Fe,Cr,Mo)、γ-(Fe,Cr,Mo)及bcc-Fe三种随着激光熔覆扫描速度的增强使得结晶相含量明显下降，峰宽增加。在扫描速度为3000mm/min时涂层按照微观形貌的不同涂层从底部到顶部可以分为三层：第一层为柱状晶体，第二层为单元结构被结晶相填充，第三层为单元结构由晶相和非晶相组成。通过TEM对涂层中第三层的单元结构进行分析发现，非晶相与M23C6共存于无定型状态的灰色区域，不同形状的白色结晶相结晶相为γ-(Fe,Cr,Mo)。当激光扫描速度较慢时bcc-Fe相以等轴晶的形式分布于涂层中。显微硬度测试结果表明涂层在扫描速度为3000mm/min时显微硬度值为1447.9HV，平均显微硬度为1353HV。纳米压痕实验结果表明涂层中的不同显微形貌物相的硬度的差异，且正是这些差异为涂层提供了一定的塑性，使得涂层在纳米压痕实验过程中没有产生裂纹。为减少涂层中由于溶质分布不均而产生较大的残余应力导致涂层出现微小裂纹，采用在激光熔覆过程中加入微振的方法使得熔体受振动的影响产生更强的搅动效果，减少快速凝固给涂层带来的缺陷。实验结果表明振动的加入减少了涂层中白色颗粒相的体积，且无规则形状的灰色区域面积明显增大，也即是增加了非晶含量。振动的加入有效地减少了涂层裂纹产生的倾向，对涂层纳米厌压痕试验后的区域进行分析发现，即使在受外力加载的条件下涂层仍表现出了塑韧性并且纳米压痕附近区域未出现裂纹。本项目研究对后续大面积激光非晶涂层的设计、合成及其冶金行为的研究有着重要意义。