Diagnostic of laser remelting of HVOF sprayed Stellite coatings using an infrared camera

Thermally sprayed coatings can be remelted to improve their microstructure and functional properties. Among other remelting technologies, laser remelting has the advantage of precise control of the remelting process by suitably chosen parameters. It enables the remelting of the whole thickness of the coating and creation of a metallurgical bonding with the substrate or remelting of the coating only to a certain depth and maintaining the advantage of thermally sprayed coatings' lamellar microstructure. In this study, HVOF sprayed Stellite coatings on a steel substrate were remelted by a high power diode laser. The experiment was designed to evaluate the role of the process speed on the depth of remelting, comparing cases of a different coatings and sample thicknesses using Near-infrared (NIR) camera. The temperature field in the melting area was evaluated and related to the achieved depth of remelting. The study shows that the IR measurement can be used for prediction of the achieved depth of remelting during a laser remelting, regardless of the coating/substrate thickness ratio.