Thin metal sheet can be protected from abrasive wear under high temperatures by metallic coatings. Despite its potential to generate protective coatings, laser cladding on very thin substrates with a thickness less than 1 mm is only rarely described in literature.
In this work 200 µm thin sheets of a nickel-based superalloy 718 were line coated by laser cladding with a powder of a cobalt based alloy. The process window is very small due to the small thickness of the sheet, therefore a precisely controlled Yb fiber laser was used. To minimize the input of energy in continuous wave mode, line coating was generated by setting single overlapping points. This method reduced melting of the substrate surface to a minimum but melt enough of the coating material powder. Argon was used as shielding and powder delivering gas and the powder mass flow was about 8 g/min. The most important variable parameters were power, pulse length and frequency, feeding rate and working distance.
To optimize the laser cladding process parameters, the generated specimens were analyzed regarding width of the coated line, weld penetration and microstructure of coating, substrate and interface. The microstructure was analyzed by light optical and scanning electron microscope. The distribution of elements was investigated by energy dispersive X-ray spectroscopy. Especially the weld penetration plays an important role, as it has to show a certain minimum depth for providing good adhesion of the coating without influencing too much the back side of the substrate.