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) + AlZr(2) + AlZr(3) -> Al(4)Zr(5) + Al(3)Zr(2) -> Al(3)Zr(2) + AlZr(2) -> Al(2)Zr -> Al(2)Zr + Al(3)Zr. This resulted in an epitaxial columnar crystal growth at the re-melt substrate boundary, a band of backward growth Al(3)Zr(2) dendrites towards the lower half of the coating, and a two-phase eutectic dendritic growth of Al(2)Zr + Al(3)Zr 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). (C) 2011 Elsevier B.V. All rights reserved.