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The phase metastability and precipitation are now considered to be an important strategy in designing Fe-rich high entropy alloys (HEAs). In this study, the influence of silicon addition on the initial and strain-induced microstructure evolution and related mechanical property of Fe52-xMn27Cr15Co6Six ( x = 0, 0.3, 0.5, 1.0, 1.5, at.%) HEAs was systematically investigated by utilizing the in-depth microstructural characterization coupled with X-ray diffractometer (XRD), secondary electron microscopy (SEM), and transmission electron microscopy (TEM). The addition of Si to Fe52-xMn27Cr15Co6Six HEAs facilitates the triplex structure consisting of fcc-y matrix, thermally-induced s-martensite and sigma phase ( a). The lattice distortion energy by Si atoms is suggested to promote the formation of a phase consisting of Cr, Si and Co and consequently influence the metastability of the matrix. In 0.3 at.% Si HEA, the strain-induced body-centered tetragonal (bct)-type a'-martensite were observed at the intersection of bi-directional strain-induced s-martensite laths, enhancing the ultimate tensile strength to similar to 851 MPa from similar to 618.3 MPa with ductility increment (similar to 73.1% from similar to 71%). In 0.3 at.% Si and 0.5 at.% Si alloys, the granular-type a phase was observed both at grain boundaries and in grain interior, and the size of granular-type a phase at grain boundary and intra-granular a phase were found to be similar. The deformation mode altered from the transformation-induced plasticity (TRIP) to twinning-induced plasticity (TWIP) with an increase of Si content to 1.5 at.%, due to the enhanced fcc-y stability induced by the compositional modulation driven by increased a phase formation. The propagation of microcracks inside brittle a phase could be suppressed by homogeneous slip through strain-induced martensite transformation (SIMT) in HEAs with low Si addition of 0.3at.% -0.5 at.%. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
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GISCIENCE & REMOTE SENSING, v.62, no.1, 2025-12