Coating toughness estimation through a laser shock testing in ni-cr-b-si-c coatings

Ni-Cr-B-Si-C coatings deposited by PTA or laser cladding are used to provide wear and corrosion resistance to a coated substrate. Colmonoy 5-52® and Nucalloy 453® were studied because they are cobalt-free alloys and potential substitutes to cobalt-based hardfacing alloys. Indeed, cobalt-based Stellite 6, one the most used hardfacing alloys, can be activated under neutron flux causing issues for deconstruction of nuclear facilities. Stellite 6® is well-known to present a good compromise between hardness and toughness which also explain its ability to be easily deposited by all welding processes without cracking. The aim of this study is to evaluate the coating toughness for a panel of microstructures using a laser thermal shock test to induce damage into the microstructure, in the close vicinity of the irradiated area. The laser-induced damage, such as crack length or damaged volume, provides a visual criterion to classify coatings resistance against Stellite 6. The crack-path analysis also provides some informations on phases controlling toughness. As a consequence, relations between metallurgy/solidification and toughness behaviour were established. These relations help to tune the process parameters to enhance both hardness and toughness.