The rise of innovative additive manufacturing (AM) methods calls for a reassessment of the significance of the directional grain growth (DGG) phenomenon beneath the melting pool and due to the localized, intrinsic applied heat. Here establishing a computational framework for systematically examining such DGG can greatly assist, since experimental measurements remain quite challenging.

We advanced a combined mean-field modelling and phase-field simulation framework [1, 2] to account for additional driving force during the evolution of a polycrystalline body. The simulations were realized by OpenPhase software package [3]. The obtained results reveal that a steady-state power-law grain growth kinetic can be established during DGG, giving a growth exponent that is generally larger than 0.5 (normal grain growth). This is found to be dictated by the interference between curvature-driven dynamics at grain boundary junctions and directional driving force.

Most interestingly, we found that the slowest growth kinetics is achieved for the intermediate driving forces, whereas the growth exponent approaches asymptotically a constant value when increasing the intensity of the driving force [4]. Figure 1 depicts the growth exponent as a function of driving force and two cross-section views of evolving microstructures under different driving forces.

The simulation findings were analysed in the context of a new mean-field model. We show that an extra model parameter can capture the influence of external driving forces on the grain growth and thus can be used for preassessment of the DGG during AM process [4].

References

[1] R. Darvishi Kamachali, I. Steinbach Acta Materialia., 2012, 60, 2719.

[2] R. Darvishi Kamachali et al. Acta Materialia., 2015, 90, 252.

[3] M. Tegeler at al. Comput. Phys. Comm., 2017, 215, 173.

[4] V.M. Kindrachuk, R. Darvishi Kamachali Materialia, 2024, 33, 101989.