In situ study of phase transformations during laser-beam welding of a TiAl alloy for grain refinement and mechanical property optimization

•At high heating rate, the material disintegrates directly into the liquid phase.•High heating rate generates superheated γ, serving as nucleation sites for β grains.•Lamellae colonies are refined and mechanical properties are improved by fast heating.•Low heating rate leads to phase transformation and no visible superheated γ.

In 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.