Eutectic growth in laser cladding of zr-coating on AZ91D magnesium substrate

Zr-bearing coatings were fabricated on an AZ91D magnesium substrate by means of a two-step method. First, pure zirconium powder was plasma sprayed on the substrate and, subsequently, laser cladding was performed on top of the spray deposited layer. The process led to the formation of a zirconium coating containing zirconia. The coating comprises three layers; on top of the substrate is the plasma sprayed layer, followed by the laser re-melt layer and finally an outermost laser-clad layer. The microstructure and phase of the coating were studied. The results show that rapid solidification occurred in the laser-clad layer and resulted in a directional eutectic cellular and eutectic dendrite growth of (Zr) + ZrO2. The maximum velocity for co-operative lamellar growth of the (Zr) + ZrO2eutectic and its corresponding lamellae spacing were calculated based on the TMK model.