In situ characterization by synchrotron x-ray radiography of the growth dynamics of equiaxed grains in Al-10wt.%Cu alloys

Abstract : The development of dendritic equiaxed grains in thin samples is monitored by in situ and real-time x-ray radiography on Al-10wt.%Cu alloys solidified by isothermal cooling down at the European Synchrotron Radiation Facility (ESRF). In situ radiography allows direct insight into dynamical phenomena that cannot be reconstructed after growth from metallography on metallic materials. This presentation is focused on the analysis of equiaxed grain growth from the very early stages to a state where dendritic grains are no longer visibly changing, close to coherency. Characteristic parameters of primary interest for materials processing and theoretical modeling and numerical simulation are discussed. The transition of equiaxed grain envelope growth driven by primary dendrites arms to growth driven by secondary arms is analyzed. The quantitative evolution of the projected internal solid fraction and total solid fraction is compared with major analytical models. Advantages and limitations of x-ray monitoring on thin 3D-samples will be discussed.