Microstructure Control by Utilizing the Instability of Nano-Structure

点击翻译按钮获取中文摘要

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.