热等静压作用下镍基高温合金蠕变空洞愈合机理及动力学研究

Hot isostatic pressing (HIP) rejuvenation technology can be utilized to heal the service-exposed creep damages of the critical hot section components in turbine engines, in order to extend the service life. The optimal HIP parameters are generally determined from a large amount of experimental data and engineering experience, but the investigation on the healing mechanism and kinetics of creep cavities under HIP can provide better guidance for optimizing HIP parameters. In this project, a nickel-based superalloy K465 widely used in engines is selected, and the experimental studies of the influences of HIP temperature, hydrostatic pressure and soaking time on the healing behavior of creep cavities are initially conducted. The formation of the concentrically-oriented γ' rafting structure is further investigated through the microstructural analysis and the stress-strain field in the vicinity of the creep cavity, in order to reveal the physical mechanism of cavity healing for nickel-based superalloys under HIP. The healing kinetics model for creep cavities under the coupling effect of stress and diffusion is then established based on the thermodynamics theory. The parametric analysis for the effects of HIP temperature and hydrostatic pressure on the healing kinetics is accomplished, constructing the HIP healing map. Finite element method is adopted to model the evolution of creep cavities under HIP, considering the cavity morphology and the size distribution. The studies can provide a theoretical basis for the optimization of HIP parameters and hence the development of the life-extending technology for the hot-section components in engines.

热等静压恢复技术能够愈合发动机关键热端部件在服役过程中产生的蠕变损伤，延长其使用寿命。最佳的热等静压工艺参数通常是根据大量的试验数据和工程经验获得，而蠕变空洞在热等静压作用下的愈合机理及动力学研究可以更好地指导工艺参数的优化。本项目以发动机用镍基高温合金K465为研究对象，从热等静压温度、压力和保持时间对蠕变空洞愈合行为的影响规律的试验研究入手，采用微观组织分析手段和蠕变空洞附近的应力应变场分析对愈合时出现的同心γ'筏化结构作深入研究，揭示蠕变空洞在热等静压作用下愈合的物理机制。基于材料热力学理论建立在应力和扩散耦合作用下蠕变空洞的愈合动力学模型，完成热等静压温度和等静压力对空洞愈合动力学影响的参数分析，构建热等静压愈合图。考虑空洞形貌及尺寸分布特点，采用有限元方法模拟蠕变空洞在热等静压作用下的演变过程，为热等静压工艺参数的优化提供理论基础，进而为发动机热端部件延寿技术的发展提供科学依据。

热等静压恢复技术被用于修复发动机关键热端部件在服役过程中产生的蠕变损伤，以延长热端部件的使用寿命。但是，最佳的热等静压工艺参数通常是根据大量的试验数据和工程经验获得的，通过研究蠕变空洞在热等静压作用下的愈合机理及动力学行为可指导HIP工艺参数的优化。本项目主要研究了热等静压(HIP)温度、等静压力和保持时间对蠕变空洞愈合行为的影响规律，在 HIP 温度不足以完全溶解一次γ′相但却可以有效引起显微空洞愈合的情况下蠕变空洞附近会出现γ′相同心筏排结构和一次γ′相贫化区。采用有限元方法分析了蠕变空洞附近应力场的各向异性分布特性，研究了热等静压参数和空洞几何特征对蠕变空洞愈合行为的影响。根据扩散理论和蠕变空洞应力场分布解释了同心γ′筏化结构的形成机制，等静压力作用下产生的不均匀各向异性应力场作为驱动力引起γ′相形成元素由贫化区向筏排区定向扩散是γ′相筏排结构形成的主要原因。考虑应力与扩散的耦合效应和气体内压的影响，基于蠕变空洞愈合机理采用热力学理论建立了空洞在热等静压作用下的演变动力学模型，通过特征参量分析指出了不同HIP条件下的空洞愈合主导机制，完成了HIP 温度和等静压力对空洞愈合动力学影响的参数分析，构建了热等静压愈合图。项目研究成果可为热等静压工艺参数的优化提供理论基础，从而为发动机热端部件延寿技术的发展提供科学依据。