Microstructure Control by Utilizing the Instability of Nano-Structure

用透射电镜观察了几种镍基和铁基合金中两相组织的形成和稳定性。主要结果如下：1. Ni-Al-Ti三元合金中γ+γ'（A1+L12）两相组织的形成和演变过程中的相分离行为随合金成分、热处理条件等的不同而表现出不同的特点。(1)γ固溶体发生相分离，在γ基体中形成γ沉淀颗粒。(2)γ'固溶体（γ'金属间化合物）发生相分离，在γ'基体中形成γ沉淀颗粒。（3）γ固溶体分相导致的γ'相的分相，2.沉淀相发生分相而在每个γ'相中形成新的颗粒的现象不仅在Ni基合金的γ+γ'相组织中存在，而且在Fe基合金的A2-FD 03两相组织中也存在。3.在沉淀颗粒的相分离过程中，TEM层析成像技术可以成功地应用于观察Ni-Al-Ti合金中析出相的三维形貌（即，已经存在的沉淀物的相分离）对于获得耐热合金所需的稳定的两相微结构是重要的和有用的。

The formation and the stability of two-phase microstructures in some Ni-base and Fe-base alloys were investigated by means of transmission electron microscopy observations. Main results obtained are as follows.1.Phase-separation behaviours which can be seen in the course of formation and evolution of γ+γ' (A1+L12)two-phase microstructure in Ni-Al-Ti ternary alloys exhibit various aspects depending on the alloy compositions, heat-treatment conditions, etc, as follows.(1) Phase-separation of γ solid solution takes place to form γ precipitate particles in y matrix.(2) Phase-separation of γ' solid solution (γ' intermetallics)takes place to form γ precipitate particles in γ' matrix.(3)Phase-separation of γ' precipitates, which appear due to the phase-separation of γ solid solution, takes place to form γ particles in each γ' precipitate.2.The phenomenon that the phase-separation of precipitate particles takes place to form new particles in each precipitate can be seen not only in γ+γ' microstructure in Ni-base alloys but also in other two-phase microstructures such as A2-FD03 in Fe-base alloys.3.In the course of the phase-separation of precipitate particles, the size of each precipitate does not change practically.4.TEM tomography can successfully be applied to observe the three-dimensional morphology of precipitates in a Ni-Al-Ti alloy.5.Utilizing the phase-separation phenomenon of two-phase microstructure(i.e. the phase separation of already existing precipitates)is important and useful to obtain a stable two-phase microstructure desirable to heat resisting alloys.