Exceptional strength-ductility combinations in new stainless transformative high entropy alloys

Complex concentrated alloys (CCAs) extend the compositional paradigm shift of high entropy alloys (HEAs) to new microstructural opportunities. A new class of transformative CCAs are emerging that take advantage of phase metastability to create exceptional level of interfacial strengthening through deformation induced transformation and twinning. Stainless Fe-Mn-Co-Cr-Si alloys exhibit potential for this combination of phase transformation and twinning. These alloys give greater flexibility for tailoring transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), which have guided design of next-generation steel alloys over the last 20 years to a new level. For TRIP CCAs, the ductility can be extended to as high as 50% while maintaining a strength exceeding 1 GPa. The Fe-Mn-Co-Cr-Si alloys show extensive gamma (f.c.c.) to epsilon (h.c.p.) phase transformation followed by additional twinning in the epsilon phase. Design of non-equiatomic CCAs provides a vast, and vastly unexplored compositional space for developing new alloys with tunable properties. Key opportunities for enhanced fatigue limit in TRIP CCAs will be presented.