Laser additive manufacturing applied to nuclear components repair and Co-based materials replacement in friction areas

Abstract

International audienceLaser additive manufacturing is a recent technology that turns a CAD modelled object into a physical one, layer by layer, by addition of projected melted metallic powders. The process is compatible with a vast array of metals and complex geometries and provides a good metallurgical quality. The potential of this process for nuclear industry materials has been assessed on two applications, nuclear components repair and friction resistant coatings using Ni-based alloys instead of Co-based alloys. For generation II&III reactors, repairing presents an advantage over part replacement in terms of cost and delay. Indeed, a number of nuclear components with complex geometries are unique and the difficulty to reproduce them in a timely manner with standard shaping methods results in a more global unavailability. We report about repair of defects on Stellite®6 parts using laser cladding technology.In fast neutron reactors, parts subjected to wear conditions are usually made of cobalt-based alloys. Cobalt may however be released and activated into 60Co, thus contaminating the primary circuit. Hence the motivation to use cobalt-free alloys. Also, the laser cladding process can increase the performances of nickel-based hardfacing materials compared to the standard PTAW coating process.In both cases we have observed occurrences of crack formation. A correlation between process parameters, structural properties of the projected materials and crack formation was found. We describe how the process parameters control the inherent extensive thermal cycling and consequently the properties of the final material, and we propose a methodology to avoid crack formation. The great flexibility of the laser projection process opens the door to deposition with composition gradients that allows avoiding cracks by accommodating the inducing strain inside the material