Although grain boundary engineering (GBE) has been widely used to enhance the properties of polycrystalline materials, it is challenging to optimize the grain boundary segregation character distributions (GBSCDs) for specific properties due to the complicated segregation behaviors associated with grain boundary energies or their excess volumes (i.e. FeMnNiCoCr, W-Ti, or W–Ta [1,2]). Because the macroscopic properties in the polycrystalline are generally correlated with the grain boundary energies, the foundations of GBE are mainly established on the relationships between the grain boundary energy distributions (GBEDs) and the grain boundary character distributions (GBCDs) as well as how to tailor the GBCDs particularly via thermomechanical processing. We recently developed the grain boundary energy functions for Fe and W [3,4] based on the topologies and scaffolding subsets of grain boundary energies, previously obtained from atomistic simulations [5,6]. Considering that the segregation behaviors at the grain boundaries are related to the GBEDs [1], it might be possible to model the segregation behaviors at W (or Fe) grain boundaries specified by the five macroscopic degrees of freedom (three for misorientation and two for plane inclination). Because the anisotropies of GBCDs in polycrystalline metals are strongly correlated with the grain boundary energy anisotropy determined from the differences between the maximum energy and the energy of coherent twin, the decreasing in the maximum boundary energy through solute segregations would lead to a lower energy anisotropy, resulting in the more uniform GBCDs. Consequently, the magnificence of grain boundary segregation engineering (GBSE) is not governed by the low-energy boundaries as in the case of a traditional GBE, but in fact primarily contributed from the high-energy boundaries having plenty of room (excess volume), in which we can manipulate the nanoscale segregations for specific properties.

References

[1] L. Li, R. D. Kamachali, Z. Li, and Z. Zhang, “Grain boundary energy effect on grain boundary segregation in an equiatomic high-entropy alloy”, Physical Review Materials, 4, 053603, 2020 

[2] A. Tamer AlMotasem, T. Huminiuc, and T. Polcar, “Factors controlling segregation tendency of solute Ti, Ag and Ta into different symmetrical tilt grain boundaries of tungsten: First-principles and experimental study”, Acta Materialia, 211,116868, 2021.

[3] O. Chirayutthanasak, R. Sarochawikasit, A. Wisitsorasak, N. Rujisamphan, T. Frolov, T. Oppelstrup, S. Dangtip, G. S. Rohrer, and S. Ratanaphan, “Anisotropic grain boundary area and energy distributions in tungsten”, Scripta Materialia, 209, 114384, 2022.

[4] R. Sarochawikasit, C. Wang, P. Kumam, H. Beladi, T. Okita, G. S. Rohrer, and S. Ratanaphan, “Grain boundary energy function for α iron”, Materialia, 19, 101186, 2021.

[5] S. Ratanaphan, D. L. Olmsted, V. V. Bulatov, E. A. Holm, A. D. Rollett, and G. S. Rohrer, “Grain boundary energies in body-centered cubic metals”, Acta Materialia, 88, pp. 346-354, 2015.

[6] S. Ratanaphan, T. Boonkird, R. Sarochawikasit, H. Beladi, K. Barmak, and G. S. Rohrer, “Atomistic simulations of grain boundary energies in tungsten”, Materials Letters, 186, pp. 116-118, 2017.