Thermal-shock behaviour of plasma-sprayed Al sub(2)O sub(3)-13wt.%TiO sub(2) coatings on Al-Si alloy influenced by laser remelting

A graded coating consisting of an Ni-clad Al bond layer, a 50wt.% Ni-clad Al+50wt.%(Al sub(2)O sub(3)-13wt.%TiO sub(2)) intermediate layer and an Al sub(2)O sub(3)-13wt.%TiO sub(2) over-layer (or ceramic layer), was produced on an Al-Si alloy substrate by plasma spraying and then was remelted by laser-beam irradiating. The thermal-shock resistance of the plasma-sprayed coating and the laser-remelted coating was investigated in this study. The plasma-sprayed coatings show a lot of spallation at the different depths of coatings and a few macrocracks in the ceramic layer during thermal cycling, but the laser-remelted coatings show a great amount of network microcracks in the ceramic layer and only a little spallation at the interface between the intermediate layer and the bond layer. Thus the laser remelting treatment improved the spalling resistance of plasma-sprayed coating to thermal shock, but cracking resistance to thermal shock remains a problem to be solved by further investigation.