The effect of substrate surface oxides on the bonding of NiCr alloy particles HVAF thermally sprayed onto aluminum substrates

The effect of substrate surface oxides on splat-substrate bonding was investigated by thermally spraying NiCr particles onto aluminum substrates with surface oxide layers grown hydrothermally and electrochemically. Cross sections of bonded solid and molten splats revealed substantial deformation of both the substrate and the surface oxide. In spite of the substantial substrate deformation, there was no significant loss of the surface oxide material and there was no observed diffusion of the substrate oxide into the NiCr particle or vice versa. For solid splats, the substrate oxide was still present over the entire splat-substrate interface, however for molten splats, the oxide had been penetrated in several locations allowing close proximity of the splat metal to the substrate metal. These results strengthen the theory that oxide layers impede bonding and that successful bonding occurs only when the surface oxide is substantially deformed or disrupted to produce mechanically interlocking features at the interface. © 2010 ASM International.