小角中子散射原位研究镍基高温合金第二相析出演化行为

In Situ Small-Angle Neutron Scattering Study of Precipitation and Evolution Behavior of Secondary Phases in Ni-Based Superalloys

γ′和γ′′相是镍基高温合金中的重要强化相,为了阐明其在热处理中的析出演化机制,本工作以广泛使用的GH4169合金为对象,采用小角中子散射原位研究了固溶时效热处理中第二相的析出演化行为,并借助TEM对非原位样品进行验证分析。结果表明:合金中第二相主要在时效过程中析出,包括球状γ′相和γ′与γ′′复合相(以γ′′/γ′/γ′′三明治结构为主)。其中,球状γ′相数量随时效进行不断增多;复合相在一级时效中大量形成,但在二级时效中数量变化不大。此外,2类析出相尺寸均在一级时效时逐渐增大,在二级时效时几乎不变。在整个时效过程中,球状γ′相与基体相界面逐渐尖锐,而复合相越来越扁,其界面成分波动始终显著。由此可知,第二相的析出演化行为受控于界面元素扩散机制。

Theγ′andγ′′phases are crucial strengthening components in Ni-based superalloys.Understanding their precipitation and evolution mechanism during heat treatment is essential for tailoring the mechanical properties of the superalloys.Herein,GH4169 superalloy was used to investigate the precipitation and evolution behaviors of secondary phases during in situ standard heat treatment by time-of-flight small-angle neutron scattering.Further,transmission electron microscopy was employed to observe the secondary phases generated in samples after ex situ heat treatment.Results showed that the secondary phases,including the sphericalγ′phase and coprecipitates(mainly theγ′′/γ′/γ′′sandwich structure),mostly occurred during the aging treatment.After the formation of coprecipitates during the first aging treatment(AT1),their quantity apparently remained stable during the second aging treatment(AT2).Furthermore,the average size of theγ′phase and coprecipitates gradually increased during the AT1 stage while remaining almost constant during the AT2 stage.Throughout the aging process,the interface between sphericalγ′phase andγmatrix exhibited a decreased composition fluctuation,while the interface fluctuation of coprecipitates was always significant.Thus,it can be inferred that the precipitation and evolution behaviors of secondary phases are controlled by the element diffusion at the interface.