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11 times smaller than that of AMALLOY3D (18 ± 5 μm). Such considerable grain refinement resulted from the interaction between the BN nanoparticles, which are thought to react with the Al liquid during PBF-LB, forming by-products which favour heterogeneous grain formation during cooling [6].
Finally, tensile testing was conducted to investigate the tensile performances of both materials. AMALLOY3D-HT showed a significant improvement of about 40% with respect to AMALLOY3D, along with an increase in ultimate tensile stress and just a minor reduction of elongation at failure. Such enhancements of the tensile behaviour were attributed to the drastic change of grain size and consequent increment of strength via the Hall-Petch mechanism [7].
Conclusions
Figure 3: Contour plots of relative density achieved in the investigated processing windows for (a) AMALLOY3D and (b) AMALLOY3D-HT. Optical Micrographs of the samples produced with optimal processing conditions of (c) AMALLOY3D and (d) AMALLOY3D-HT.
This work describes new aluminium metal matrix composites produced via small additions of BN to an alloy specifically designed for AM applications (AMALLOY3D). The resulting AMALLOY3D-HT material showed an improved flowability without compromising the PBF-LB processing window. Moreover, such overall improvement of the processability was paired with grain isotropy and consequent 40% increase of tensile strength, making AMALLOY3D-HT a very attractive material for the aerospace and automotive industries.
References
[1] E. O. Olakanmi, et al. Prog Mater Sci, vol. 74, pp. 401–477, 2015.
[2] M. Yamaguchi et al. Acta Mater, vol. 61, no. 20, pp. 7604–7615, 2013.
[3] O. N. Çelik et al. Particulate Science and Technology, vol. 31, no. 5, pp. 501–506, Sep. 2013, doi: 10.1080/02726351.2013.779336.
[4] A. A. Martin et al. Nat Commun, vol. 10, no. 1, Dec. 2019, doi: 10.1038/s41467-019-10009-2.
Figure 4: Inverse pole figure (IPF) maps and pole figures of (a) AMALLOY3D and (b) AMALLOY3D- HT. The colour legend of the IPF maps was selected so that the (001) family of directions is parallel to the BD.
does not cause shifts in the processing window. Figure 3(c-d) depict optical micrographs of AMALLOY3D and AMALLOY3D-HT, respectively, processed with their optimal process parameters. It is noteworthy that both alloys reached values of relative density greater than 99.9% and were used for microstructural characterisation and tensile testing.
Electron Backscatter Diffraction (EBSD) analysis was carried out to investigate the potential changes in the crystallographic arrangement of grains between the two materials (Figure 4). AMALLOY3D was characterised by columnar grains elongated towards the building direction and the presence of a (001) fibre texture also parallel to the BD (Figure 4(a)). This peculiar crystallographic arrangement is a direct
consequence of the heat dissipation of the PBF-LB process and is typical for Al-based alloys [5]. Conversely, AMALLOY3D-HT showed an extremely refined grain structure and the complete absence of crystallographic texture, making this material extremely isotropic (Figure 4(b)). The grain size of both materials was measured using the equivalent circle diameter assumption. AMALLOY3D-HT was characterised by a grain size of 1.6 ± 0.4 μm, more than
[5] N. T. Aboulkhair, et al. Prog Mater Sci, vol. 106, p. 100578, Dec. 2019, doi: 10.1016/J. PMATSCI.2019.100578.
[6] G. Del Guercio et al. Additive Manufacturing Letters, vol. 11, p. 100237, 2024, doi: https://
doi.org/10.1016/j.addlet.2024.100237.
[7] N. Hansen, Scr Mater, vol. 51, no. 8, pp. 801–806, 2004, doi:
https://doi.org/10.1016/j. scriptamat.2004.06.002.
* Federico Bosio, Chinmay Phutela, Stuart Robertson, Nesma T. Aboulkhair
Contact: Giuseppe Del Guercio
Giuseppe.Delguercio@
tii.ae www.tii.ae
Giuseppe Del Guercio is a researcher in the Additive Manufacturing Group of the Technology Innovation Institute, in Abu Dhabi.
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