Abstract
Using an efficient hybrid Cellular Automata/Phase Field (CA-PF) dendrite growth model in combination with a solid-state phase transformation model, microstructure evolution and solid-state phase transformation were predicted during laser direct deposition (LDD) of H13 tool steel powder within a large domain across multiple deposition tracks and layers. Temperature and surface geometry data were provided by a comprehensive physics-based laser deposition model. The computational efficiency of the CA-PF model allows for simulating domains large enough to capture dendrite growth across an entire molten pool and into multiple neighboring LDD tracks and layers. The microstructure of the target track is strongly affected by heat from neighboring tracks including re-melting, re-solidification and solid-state phase transformation including austenitization, martensite formation and martensite tempering. Dendrite size and growth direction across the entire fusion zone, as well as predicted hardness values, are found to be in good agreement with experimental results.
Highlights
Laser direct deposition (LDD) of metals is a multi-track, multi-layer additive manufacturing (AM) process where fine metal powders are blown into the same focal point as the laser, either coaxially [1] or off-axis [2]
This work combines the simulation capabilities of the Cellular Automata/Phase Field (CA-Phase Field (PF)) model, as presented by Tan et al [50], with the solid phase transformation model presented by Bailey et al [9] for the purpose of predicting melting, solidification, dendrite growth and solid phase transformation during multi-track and multi-layer laser direct deposition (LDD) of H13 tool steel
To predict solidification microstructure and dendrite growth with the Cellular Automata (CA)-PF model during additive manufacturing of H13 tool steel, this complex tool steel alloy is first approximated as a ternary alloy
Summary
Laser direct deposition (LDD) of metals is a multi-track, multi-layer additive manufacturing (AM) process where fine metal powders are blown into the same focal point as the laser, either coaxially [1] or off-axis [2]. The CA-PF model and the solid phase transformation model discussed in this paper get their needed temperature and surface geometry field data from a validated, comprehensive multi-physics thermal model [1, 52] that was developed in-house This model considers multi-phase heat transfer from conduction, convection and radiation, as well as free-surface tracking of the molten pool surface via the level-set method [53]. The details of this thermal model are skipped for brevity, as it is well described in Ref. data to calculate the solute diffusion within the CA domain and determine the initial shape of the solid/liquid interface. For each interface cell within the CA domain, the CA model sends and receives data to and from the PF model which calculates the growth kinetics along the solid/liquid interface
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