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Materials Science in Additive Manufacturing Heterostructures of A131 steel by DED

A B

C D

Figure 8. Room-temperature mechanism performances of A131 steel. (A) Room-temperature uniaxial strain-stress tensile curves. (B) True strain-stress
tensile curves. (C) Tensile properties (n = 3). (D) Hardness (n = 10)
Abbreviations: AB: As-built; HR: Hot rolling; HT: Heat treatment; ND: Nominal direction; TD: Transverse direction

This observation was attributed to the elimination of fine by abundant dimples. These defects likely originated from
martensite and the misorientation of the grains (Figure 7), small closed pores and inclusions inside the melt pools,
leading to significant anisotropy in resistance deformation which enlarged under tensile stress. Figure 9C highlights
along the TD orientation. broken, spherical inclusions surrounded by dimples. EDS
Figure 8D displays the Vicker hardness of A131 steels analysis (Figure 9C, inset) verified that these inclusions
along ND and TD, with corresponding values summarized were rich in oxygen (> 50 at%), identifying them as oxide
in Table S4. All steels exhibited notable hardness anisotropy, inclusions. Figure 9D features the middle of the fracture
with strength and elongation anisotropy ratios estimated surface, also revealing visible holes (Figure 9E) and oxide
in Table S5. In both AB and HT A131 steels, hardness was inclusions (Figure 9F). These defects likely contributed to
higher in ND compared to TD, whereas HR A131 steel a significant decrease in elongation and a rapid decline in
displayed the opposite trend. Similar to the tensile results, work-hardening rates. However, the prevalence of dimples
AB A131 steel displayed the highest hardness, achieving indicates that plastic deformation remained predominant
a 75.5% increase over HR A131 steel in ND (139 HV). under tensile loading.
After HT, HT A131 steel exhibited a notable decrement in 4. Discussion
hardness in both directions, likely due to the formation of
equiaxed grains with reduced misorientation. While HT In this experiment, AB A131 steel exhibited a unique
A131 steel had a similar phase composition to HR A131, heterogeneous structure composed of alternating
it offered only a marginal hardness advantage, though coarse- and fine-grain regions, leading to significantly
both retained higher anisotropy ratios than A131 steel enhanced mechanical performance. To reveal the
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fabricated using other DED methods or wire-arc AM. 44 formation mechanism of the heterostructure, a single-pass
deposition was carried out with the same DED parameters.
Figure 9 presents the fracture morphologies of AB A131
steel along ND. Figure 9A displays the fracture surface at the The overall cross-sectional microstructure is displayed
edge close to the necking section, with numerous internal in Figure S3, with high-magnification images presented
defects (white arrows). A magnified view (Figure 9B) reveals in Figure 10. Figure 10A displays an OM image of the
submicron holes (~20 µm) (Figure 9B, inset) surrounded top region, revealing a notable orientation of the crystals

Volume 4 Issue 3 (2025) 9 doi: 10.36922/MSAM025220038