Deformation processes of additively manufactured interstitial-strengthened high entropy alloy: In-situ high-energy synchrotron X-ray diffraction and microstructural appraisal

Additively manufactured components often exhibit pronounced anisotropy due to the heterogeneous microstructure generated by the complex and repetitive thermal cycling history. Grain orientation is one of the determinant microstructural features that influences the activation of different deformation mechanisms. In this work, laser powder-bed fusion (LPBF) was applied to fabricate Fe49.5Mn30Co10Cr10C0.5 interstitial-strengthened high entropy alloy (iHEA). Fabrication was performed at angles of 0° and 90° relative to the main laser scanning direction, and the plastic deformation behavior of these two oriented specimens was studied. The initial microstructure of the LPBF-built iHEA was composed of a complex heterogeneous columnar grains containing high-density dislocation network and a large number of stacking faults, as well as nano-precipitates and elemental segregation of Mn at subgrain boundaries. During uniaxial tension in-situ high-energy synchrotron X-ray diffraction (HE-SXRD) was performed to track the deformation processes and mechanisms of this metastable iHEA. The influence of different deformation mechanisms on the mechanical responses of the current LPBF-built iHEA was scrutinized combining in-situ HE-SXRD with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) analyses, which not only gives insights into the macrostructural evolution but also provides comprehensive characterization on microstructural responses and the orientation-dependent effects imposed by the fabrication constraints originally imposed. The implemented multiscale characterization revealed the presence of a strain-induced fcc to hcp phase transformation, which is influenced by the growth texture close to <110> along the building direction. Moreover, EBSD and TEM analysis of the fracture regions uncovered the formation of nanosized deformation twins, confirming the simultaneous activation of phase transformation- and twinning-induced plasticity (TRIP and TWIP) effects. The results obtained in this work gain new insights into orientation-dependent deformation behavior of additively manufactured iHEA, which facilitates the microstructural design when exploiting the TRIP/TWIP effects.