As a member of second generation advanced high-strength steels (AHSS), high-manganese steels (HMnS) have been reported as suitable alloys for lattice structures with high energy-absorption capacity produced by laser powder bed fusion (LPBF). Different deformation mechanisms, e.g., transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), can be activated in HMnS by an alloy design approach through tailoring the alloy’s stacking fault energy (SFE). For instance, with increasing Al concentration (from 0 up to 5 wt.%) in X30Mn22 HMnS, the SFE of the alloy was increased and therefore the prevalent deformation mechanism changed from TRIP to TWIP, and then to dislocation slip accompanied by reduced mechanical twinning. In addition to bulk materials, the same trend was also observed in f2ccz lattice structures of X30Mn22, X30MnAl22-1, and X30MnAl22-5 alloys under compression. It was revealed that HMnS lattice structures have higher weight-specific energy-absorption capacity in comparison to well-established AM materials such as Ti6Al4V and AISI 316L. Nevertheless, strain localisation at z-strut (vertical strut) nodes of the f2ccz structures resulted in formation of brittle ε-martensite phase in X30Mn22 and X30MnAl22-1 at the early deformation stages and consequently led to failure of these structures. Digital image correlation (DIC) analysis performed on X30Mn22 lattice under compression showed that the disintegration of the struts, which ultimately caused the collective failure of the lattice, started from the high-strain regions where brittle martensite phase was formed.

In order to avoid strain localisation and the early TRIP effect without compromising on energy-absorption capacity, a new geometry that is based on the modification of f2ccz structure was proposed. In line with the scope of this contribution, the vertical z-struts of the f2cczz structure were replaced by curvy ones in the new structure in order to ensure a better load distribution along orthogonal directions to the applied load and thereby preventing strain localisation at the nodes where the vertical struts intersect the cross-struts. Compression data of the proposed structures of X30Mn22 with different relative densities indicates that they are more stable in the plateau region compared to f2ccz structures and the energy-absorption capacity could be further increased.