Role of impinging powder particles on melt pool hydrodynamics, thermal behaviour and microstructure in laser-assisted DED process: A particle-scale DEM – CFD – CA approach

• Published in: International journal of heat and mass transfer 2020-09, Vol.158, p.119989, Article 119989
• Main Authors: Aggarwal, Akash, Chouhan, Arvind, Patel, Sushil, Yadav, D.K., Kumar, Arvind, Vinod, A.R., Prashanth, K.G., Gurao, N.P.
• Format: Article
• Language: English
• Subjects: Cellular automata; Computational fluid dynamics; Computer simulation; Deposition; Discrete element method; Epitaxial growth; Evolution; Fluid flow; Fluid mechanics; Free surfaces; Grain growth; Grain structure; Hydrodynamics; Laser beam heating; Laser-assisted directed energy deposition; Lasers; Marangoni convection; Mathematical models; Microstructure; Molten pool hydrodynamics; Nickel base alloys; Particle trajectories; Particles impingement; Solidification; Substrates; Superalloys; Supercooling; Temperature distribution; Thermal simulation; Thermodynamic properties
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2020.119989

•A novel multi-physics computational framework for L-DED process is proposed.•Particle-scale thermofluidic model is integrated with Cellular Automata approach.•Realistic Inconel-625 particle stream predicted by DEM modelling is utilized.•Results reveal highly oscillatory and chaotic melt flow due to impinging particles.•Predicted melt pool, temperature, and grain structure compare well with experiments. High speed imaging of molten pool free-surface hydrodynamics in laser-assisted directed energy deposition process clearly revealed a highly oscillatory and dynamic melt flow due to impinging powder particles. Surprisingly, most of the reported computational work exclude the injection of powder particles and rather adopt a homogeneous mass and energy addition approach, and therefore provides less accurate predictions. In this work, we develop a coupled multi-physics particle-scale approach utilizing the discrete element method for particle trajectory prediction, the computational fluid dynamics for free-surface thermo-fluidic modelling and the cellular automata method for grain growth evolution. In the model, the governing physical phenomena, such as laser-powder interaction, in-flight particle heating, phase change (melting, vaporization and solidification), free-surface evolution, molten pool hydrodynamics and impinging particles-melt interaction have been considered. Experiments for the deposition of Inconel-625 on an Inconel-625 substrate are carried out, and the model predictions are validated with the experimental measurements. For the first time, the predicted thermo-fluidic simulation results reveal highly oscillatory, chaotic and random melt flow attributed to the impinging powder particles. During the deposition, it is found that the role of the Marangoni convection is less significant as compared to the momentum imparted by the impinging powder particles in the melt pool. Using the simulated thermal undercooling data, cellular automata-based grain growth simulation predicts elongated columnar dendrites in the melt pool that grows epitaxially from the melt pool interface and stretches towards the centre. Using the Kurz-Fisher model, the effect of local thermodynamic solidification conditions on the size of dendritic microstructure is also described. The predicted melt pool geometry, temperature field and grain structure compare well with the experimental measurements.