非晶涂层中的残余应力及其对涂层性能的影响

Bulk metallic glasses (BMGs) are a novel type of metastable alloys developed in recent years. However, the applications of BMGs as structural materials have been severally blocked by the intrinsic brittleness of this type of alloys. Amorphous coatings based on BMG systems prepared by thermal spraying are recognized to be a promising route to overcome this drawback, and may extend the applications in surface engineering. Like other thermal sprayed coatings, the residual stress existed in the amorphous coatings is one the most important factor causing the failure of the coatings. In the present project, Fe-based amorphous coating will be prepared by high velocity oxy fuel (HVOF) technique, and the residual stress and its effect on structure and properties of the amorphous coatings will be extensively studied with various techniques. The detailed research content include: 1) measurement and affecting factors of residual stress in amorphous coatings ; 2) The effect of residual stress on properties of amorphous coatings; 3) The failure mechanism of amorphous coatings under residual stress coupled with extenal loading; 4) The change in residual stress, structure and properties of amorphous coatings with subsequent annealing treatment. The present project can enhance the understanding of the mechanism of residual stress in amorphous coatings and the correlation between residual stress and properties of the coatings. On the other hand, this project is of an important significance for the improvement of properties of the coatings through the modification of residual stress, and for the application of Fe-based amorphous coatings in various industrial fields.

块体非晶合金是近年来发展起来的新型亚稳材料，但其本征室温脆性严重制约了它们的应用范围。非晶涂层可以克服块体非晶合金这一弊端，其优异的防腐耐磨性能在表面工程领域具有广阔的应用前景。但残余应力是引起非晶涂层服役失效的主要原因，而针对非晶涂层中的残余应力及其对涂层性能的影响的研究仍十分欠缺。 本项目将以Fe基非晶涂层为对象，系统研究超音速热喷涂（HVOF）工艺对残余应力，以及残余应力对涂层性能及失效行为的影响。主要内容包括：1）非晶涂层中残余应力的测量及其影响因素；2）残余应力对非晶涂层性能的影响；3）在残余应力与外加载荷共同作用下非晶涂层的失效机制；4）后处理对非晶涂层残余应力及涂层结构和性能的影响。通过以上研究，揭示非晶涂层中残余应力的形成机理，阐明残余应力对涂层性能的影响规律，这对实现通过残余应力的调控提高非晶涂层的服役性能，促进其在工业各领域的应用具有重要的科学意义和实际意义。

残余应力被认为是影响热喷涂涂层性能与失效的关键因素。本项目以Fe基非晶涂层为研究对象，系统研究了非晶涂层中残余应力的测量与影响因素、残余应力对非晶涂层力学性能的影响、不同载荷模式下非晶涂层的失效行为、非晶基复合涂层的结构与性能调控、以及热喷涂3D打印大尺寸Fe基非晶及复合材料，获得了以下有意义的结果：1）提出2种适合非晶涂层的残余应力测量方法，分别为曲率法与纳米压痕法。两种试验测量方法以及有限元模拟均表明在非晶涂层中产生了残余拉应力，主要由沉积粒子的热应力引起。发现粉末粒径与涂层厚度是影响残余应力的2大关键因素。残余拉应力越大，非晶涂层结合强度以及界面韧性越低。2）在冲击或疲劳载荷模式下，非晶涂层表现出脆性断裂特征。为此，提出4类复合结构调控方法，分别为i) 引入不同层数的晶态NiCrAl；ii）非晶粉末化学镀改性；iii）高分子增强相原位碳化以及iv）引入陶瓷颗粒增强相Al2O3, 显著改善了涂层/基体界面结合，提高了涂层冲击韧性与疲劳性能，并对其增韧机理进行了深入探讨。3）通过热喷涂高能3D打印成功制备出超大尺寸Fe基非晶合金与复合材料(超过现有最大尺寸Fe基非晶)，并发现这类非晶材料具有高强度（接近2000 MPa）以及较好的断裂韧性（21 MPa m1/2, 是同成分吸铸态非晶的4倍）。截止目前，相关研究成果已经在Acta Materialia、Electrochimica Acta等期刊上发表SCI收录论文16篇，参加国际学术会议6次，申请发明专利4项，其中已授权2项，培养博士与硕士生6人。本项目研究对非晶涂层体系设计、性能调控以及服役应用有重要的指导意义与实用价值。