激光表面重熔（LSM）K439B高温合金氧化过程中元素扩散与亚表层孔隙形成耦合机制

表面细晶、芯部粗晶的高温合金材料因具有良好的抗疲劳性能而被应用于高性能航空发动机结构件的制造。K439B高温合金长期服役温度可高于800℃，适用于制造下一代战斗机和燃气轮机的热端部件。发动机燃烧室机匣和涡轮后机匣等热端部件在服役中承受高温和高载荷，但缺乏涂层和气冷保护。随发动机工作温度的升高, 合金的高温氧化严重影响了其服役寿命。本项目采用激光表面重熔（Laser Surface Melting, LSM）技术，制备表面细晶、芯部粗晶的K439B高温合金。增加合金表层晶界数量，在高温氧化过程中促进Cr原子外扩散形成致密的Cr2O3膜以减缓Ni、Co等原子外扩散和O原子内扩散，有效提高K439B高温合金抗氧化性并减少亚表层中孔隙数量。项目研究将揭示K439B高温合金晶粒尺寸、元素扩散、抗氧化性和亚表层孔隙四者之间的耦合规律。揭示表面改性高温合金的高温氧化机理，为合金的工程应用提供理论指导。

The superalloys with fine grains in surface region and coarse grains in core area are applied in high performance engines due to their high fatigue resistance. K439B superalloy was designed to applied in the next generation fighter and gas turbine due to its long service life above 800℃. The high-temperature parts without thermal barrier coating, such as combustor casing and engine casing, are exposed at high temperature and suffer high stress under service condition. Thus, the severe oxidation behavior will shorten their service lives with the increased temperature. Laser Surface Remelting (LSM) technique is applied to remelt the surface of K439B superalloy in this project and hope to produce a surface modified material with fine grains in surface and coarse grains in core. The aim of this work is to generate a dense and protective oxide film on the surface of K439B superalloy quickly with the fast outward diffusion of Cr atoms through grain boundaries, and suppress the outward diffusion of Ni/Co atoms and the inward diffusion of O atoms. The generation of holes led by the outward diffusion of metallic atoms in subsurface could be suppressed as well. This project will focus on the effect of grain size on the diffusion behavior of atoms, the oxidation resistance, and the generation behavior of the pores. This work could promote the oxidation theory of surface modified superalloy and provide guidance for the application of this alloy.