In situ monitoring of direct laser metal deposition of a nickel-based superalloy using infrared thermography

Metal additive manufacturing is growing its impact on high-tech industrial sectors so far. The capability to recover and repair worn components, with costs that are gradually more affordable, is giving a boost to the development of these technologies. The direct laser metal deposition (DLMD) technology is taking a leading role in this domain. Manufacturing components, with high mechanical properties, require a careful process design and a continuous control. The monitoring of the thermal field thus assumes a crucial role in processes in which high-power sources are involved. Thermal treatments influence the microstructure, morphology and the grain size of the depositions indeed, which determine high-performance standards. In this work, an ytterbium fibre laser source was used to build single-track depositions of a nickel-based superalloy powder on a substrate of the same material. Temperature field monitoring was performed using a high-frequency (100 Hz) IR thermal camera, allowing an accurate monitoring of peeks temperature, thermal cycles and thermal gradients. Thermal data and process parameters were compared with metallographic analysis to capture the relation between the geometrical and microstructural characteristics of clads. The study focuses on the influence of the powder feed rate and energy density on thermal parameters. An innovative approach to the solidification map method, commonly implemented with numerical simulations of welding and additive manufacturing, has been successfully applied to experimental data giving results consistent with the literature.