短时真空热处理对第二代镍基单晶高温合金表面组织的影响

Effect of Short-Time Vacuum Heat Treatment on Surface Microstructure of Second-Generation Ni-based Single-Crystal Superalloy

摘要:

研究了一种第二代镍基单晶高温合金经过真空固溶热处理后表面化学成分和显微组织的变化，重点研究了加氩气分压和不加氩气分压两种条件对铸件表层的影响。结果表明，在高温真空热处理过程中，加氩气分压进行固溶热处理时，试棒表面出现贫Cr层，表面层形成了明显的3层分布，接近基体的过渡层主要为γ′相+拓扑密堆相（TCP），次表层为γ′相+TCP+β相，表层为γ′相+β相。此时，金属Al和Ni元素在表面沉积。不加氩气分压处理时，试棒表面同样出现贫Cr层，形成了过渡层主要为γ′相+TCP相，表层为γ′相+TCP+β相的2层结构。真空热处理过程中，铸件表面元素的挥发、沉积、氧化、扩散等反应将同时发生。受温度、真空度和分压压力的影响，铸件表面将出现沉积层、贫化层和过渡层。同时对过程中各类反应的热力学和动力学原理进行了详细分析。

Abstract:

The surface composition and microstructure evolution of a second-generation Ni-based single crystal superalloy were investigated during vacuum solution heat treatment. The effects of adding argon partial pressure and not adding argon partial pressure on the surface layer of casting were studied. Results show that during the high-temperature vacuum heat treatment of the test bars, when argon partial pressure is applied during solution heat treatment, a Cr-depleted layer forms on the surface, exhibiting three-layer structure: transition layer (adjacent to the substrate) composed of γ′ phase and topologically close-packed (TCP) phase; sub-surface layer composed of γ′ phase, TCP phase, and β phase; surface layer composed of γ′ phase and β phases. In this case, Al and Ni are deposited on the surface. Conversely, when heat treatment is conducted without argon partial pressure, a Cr-depleted layer still forms, but with a two-layer structure: transition layer composed of γ′ phase and TCP phase and surface layer composed of γ′ phase, TCP phase, and β phase. During vacuum heat treatment, reactions such as volatilization, deposition, oxidation, and diffusion of surface elements occur simultaneously. Depending on the temperature, vacuum level, and argon partial pressure, condensation layer, depletion layer, and interdiffusion layer may be formed on the surface. This study analyzed these phenomena in detail based on the thermodynamics and kinetics of relevant reactions.