In situ heating SEM observation of the bainitic transformation process in Cu–17Al–11Mn (at.%) alloys

To understand the bainitic transformation behavior in Cu–17Al–11Mn (at.%) alloys, dynamic in situ observation during heating was carried out in a scanning electron microscope (SEM). In this study, after optimizing the sample preparation method and observation conditions, we successfully observed the transformation process with sufficient resolution and contrast. From the observation results, bainite is first formed preferentially at the grain boundaries of the parent phase. Bainite is also formed inside the grains to relax the elastic strain generated by the initial bainite. Regarding the growth mode, in the early stage of the transformation, bainite grows along the longitudinal direction, and in the late stage, it grows along the lateral direction. The growth rate of the bainite was also evaluated by continuous observation of the same plate. Dynamic in situ observation of a martensitic transformation in the same alloy was also performed to compare the growth mode with that of bainite, and it was found that the behavior is considerably different between bainitic and the martensitic transformations.