Modelling of the melt pool geometry in the laser deposition of nickel alloys using the anisotropic enhanced thermal conductivity approach

Use of appropriate modes of heat transfer in finite element modelling simulations of laser deposition is important for enhancing the reliability of the predicted results. An important contributory mode is melt pool convection, which is the focus of this work. Using the anisotropic enhanced thermal conductivity approach, this study examines the strategies relating to the choice of appropriate values for the thermal conductivity enhancement factors in the orthogonal axial directions x, y, and z. In order to investigate different combinations of values for these factors in the laser deposition of one track of Inconel 718 powder on an EN-43A mild steel substrate, finite element models were prepared and results from these were compared with the corresponding experimental results. The results of the study suggested that no thermal conductivity enhancement should be enforced in the direction of the depth of the sample. Thermal enhancement factors in the two orthogonal directions are required, but the factor in the direction parallel to the direction of beam scanning should be of greater magnitude. Analysis of the thermal gradients from the model also showed that failure to incorporate any allowance for the melt pool convection effect with appropriate choice of thermal conductivity enhancement factors in the finite element modelling of the laser deposition can result in overprediction of thermal stress, which can lead to undue threats of various forms of distortion during the deposition process.