In situ and real-time analysis of TGZM phenomena by synchrotron X-ray radiography

The development of brilliant third-generation synchrotron X-ray sources, together with advances in X-ray optics and detectors, has provided timely efficient tools for in-depth understanding of physical phenomena in a broad spectrum of situations. Synchrotron X-ray radiography enables in situ and real-time observation of microstructure evolution, i.e. a direct access to dynamical phenomena which could not be anticipated from post-mortem analysis. Dedicated experiments are carried out at the European Synchrotron Radiation Facility (ESRF) in Grenoble (France) in Al-based alloys to study the dynamics of temperature gradient zone melting (TGZM) phenomenon. TGZM occurs when a liquid–solid zone is submitted to a temperature gradient and leads to the migration of liquid droplets or channels through the solid, up the temperature gradient. The thorough characterisation of both the initial solid during the thermal stabilisation phase prior to solidification (static TGZM) in Al–3.5 wt% Ni alloy and the dendritic microstructure in the later stage of solidification in Al–7.0 wt% Si alloy is performed. Based on experimental observations, quantitative data (in particular liquid-migration velocity) are measured and a very good agreement is found with theoretical analysis.