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

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).