Phase evolution and dendrite growth in laser cladding of aluminium on zirconium

▶ Laser cladding of Al on pure Zr. ▶ A series of phase evolutions occurred across the laser-clad coating. ▶ Epitaxial crystal growth, backward dendrite growth and two-phase eutectic dendritic growth. ▶ Phase and microstructure evolution is discussed. Aluminium was laser clad on a pure zirconium substrate using the blown powder method. The microstructure across the laser-clad coating was studied. Starting from the bottom to the top surface of the coating, a series of phase evolutions had occurred: (Zr)→(Zr)+AlZr2+AlZr3→Al4Zr5+Al3Zr2→Al3Zr2+AlZr2→Al2Zr→Al2Zr+Al3Zr. This resulted in an epitaxial columnar crystal growth at the re-melt substrate boundary, a band of backward growth Al3Zr2 dendrites towards the lower half of the coating, and a two-phase eutectic dendritic growth of Al2Zr+Al3Zr towards the top of the coating. The evolution of the various phases and microstructures is discussed in conjunction with the Al–Zr phase diagram, the criteria for planar interface instability, and the theory of eutectic growth under rapid solidification conditions (the TMK model).