Laser cladding of nickel base hardfacing material: Material analyses and manufacturing process evaluation on a scale one demonstrator

In fast neutron reactors, contact areas of moving parts usually require cobalt-free hardfacing coatings, as cobalt is highly activated under neutron flux. This is particularly critical for the insert holes of the diagrid for the positioning of the hexagonal fuel tubes that have to be internally coated. In this article, we propose to present the development of the cobalt-free hardfacing material up to the manufacturing of the inner clads with a specific deep laser cladding nozzle. In previous presentations, laser cladding has been identified as a deposition process that could increase the performances of the hardfacing materials compared to the standard process (Plasma Transferred Arc Welding). In parallel, the potential interest of some nickel base materials such as Colmonoy® 52 or Tribaloy® T700 has been demonstrated. Unfortunately, the deposition of these fragile alloys requires a preheating of the substrate over 450 °C. More recently, Nucalloy® 453, a new hardfacing nickel base alloy has been evaluated and demonstrated simpler deposition conditions that requires lower preheating temperature (<300 °C). The article presents the evaluation of Nucalloy® 453 with material analysis and wear tests. The microstructural characterization is compared to Colmonoy® 52, which is a similar NiFeCrSiBC alloy. Finally, the laser cladding of a scale one demonstrator is presented: two inner zones of a 1 m cylinder of 100 mm diameter are laser cladded, thanks to a deep cladding nozzle. The advantage of the laser cladding process is compared to Plasma Arc Transferred Welding.