AbstractIn situ time-resolved X-ray diffraction by synchrotron radiation was used to monitor the phase transformations and grain-refining processes during laser-beam welding of a γ-TiAl-based alloy. The heating rate plays an important role of grain refinement. A high heating rate suppresses solid–solid phase transformations. The superheated γ grains serve as heterogeneous nuclei for β grains on subsequent solidification and refine the lamellar colonies. At low heating rate, diffusion-based transformations are observed on heating and coarse lamellae are formed after welding. The refined lamellar colonies improve the mechanical properties.