Twinning in a high stacking fault energy FeCoNi alloy

Avala Lavakumar , Shuhei Yoshida , Jesada Punyafu , Shiro Ihara , Yan Chong , Hikaru Saito , Nobuhiro Tsuji , Mitsuhiro Murayama

Twinning in a high stacking fault energy FeCoNi alloy

Scripta Materialia 230 (2023) 115392


Material development has been an important aspect of human civilization as a whole. If we look into the history of human civilization, the growth era has been described by the materials discovery such as Stone, Bronze, and Iron ages. Examples from the modern era include steels that consist primarily of Iron, to which elements such as carbon and chromium are added for strength and corrosion resistance. Such a strategy is well-known as “alloying”. With few exceptions, the basic alloying strategy of adding relatively small amounts of secondary elements to a primary element has remained over millennia. However, such a primary-element approach drastically limits the total number of possible element combinations and, therefore, alloys, most of which have been identified and exploited. Researchers developed the new strategy by mixing multiple principal elements in relatively high (often equiatomic) concentrations. These alloys are commonly referred as equiatomic (or) high/medium entropy (or) complex concentrated alloys.


In this research, one such equiatomic alloy FeCoNi has been considered, showing high stacking fault energy (SFE) around 70 mJ/m2. In general, the deformation behavior of high SFE materials is governed by dislocations. As a result, bulk alloys with high SFE have, till today, not unleashed the excellent strain hardening (combination of strength and ductility) reserves provided by mechanical twins and stacking faults. Here, we showed that grain refinement could enhance the mechanical properties of High SFE FeCoNi. Further, this alloy showed excellent strain hardening capability at cryogenic temperature (-196oC). It is one of few metallic alloys demonstrating how to conquer the strength-ductility paradox, the general trade-off trend of strength and ductility. We also experimentally confirmed that the deformation by twinning occurred at low temperatures despite of its high stacking fault energy (SFE). This research study would provide new insights into current and future equiatomic (or) medium/high entropy alloys showing high SFE. Our results are transformative to the mechanical behavior of other metallic alloys beyond differences in their intrinsic materials parameters.