High-rate superplasticity in an equiatomic medium-entropy VCoNi alloy enabled through dynamic recrystallization of a duplex microstructure of ordered phases

Shear band-driven precipitate dispersion for ultrastrong ductile medium-entropy alloys

“…The mechanical properties of the present alloys seem to follow a linear trend of the strength–ductility combination of the CoNiV alloys. It should be noted that it is challenging to further enhance the mechanical properties of CoNiV alloys, as the limited process windows in conventional processing restrict the refinement of grains to sizes smaller than ~2 μm 16 . Another strengthening mechanism should be embodied and the present approach enables further improvement in mechanical properties.…”

“…This property is ascribed from only solid-solution and grain-boundary strengthening at an average ~2 μm grain size in FCC-structured matrix. However, it is challenging to further enhance the mechanical properties of CoNiV alloys as an additional refinement of grains is restricted in conventional processing due to the limited process windows 16 . In this respect, precipitation strengthening can be an attractive candidate for further improving the mechanical properties.…”

A dual-phase alloy with ultrahigh strength-ductility synergy over a wide temperature range

“…This tensile response at 1073 K is typical of ultrafine-grained materials that reach their ultimate tensile strengths at very low strains but can sustain very high elongations until failure without strain hardening ( 19 ). Crystalline materials usually deform at high temperature via dynamic recrystallization (DRX), which involves grain boundary sliding to accommodate stresses (i.e., superplasticity) ( 20 , 21 ). Figure 2C illustrates a superior tensile strength and ductility combination of our newly developed alloy at room temperature compared to several established alloys such as transformation-induced plasticity (TRIP) steels, dual-phase steels, and even martensitic steels ( 14 , 22 , 23 ).…”

Ultra-strong and strain-hardenable ultrafine-grained medium-entropy alloy via enhanced grain-boundary strengthening

“…The novel mechanical properties of the VCoNi alloy were derived from the concept of the enhanced solid-solution strengthening induced by the large difference in atomic radius in the V-Co-Ni system as compared with those in conventional alloys. Moreover, beyond the substantial merits for good mechanical properties, the VCoNi MEA exhibits multi-functional performances, such as high resistance to hydrogen embrittlement due to low hydrogen diffusivity [16], good corrosion resistance due to the absence of a local potential gradient [16], and high strain-rate superplasticity, achieved via active dynamic recrystallization at high temperatures [17].…”

“…In other words, as grainboundary (GB) strengthening could be much more effective for VCoNi alloy than other FCC-structured alloys, it is perceived that further improvement of mechanical properties can be realized by nano-structuring. However, the verification of the proposed suggestions is very challenging because the single FCC phase could be obtained at high temperatures (over 850°C) in an equiatomic VCoNi system [17], which impedes the grain refinement by annealing at relatively low temperature conducted in conventional processing routes [18,19]. In this respect, a severe plastic deformation (SPD) along with post-annealing heat treatment can produce ultrafine-grained (UFG) materials by offering a considerably high driving force of recrystallization for grain refinement [18,19], while delicate processing controls are required to form fully recrystallized alloys maintaining UFG structures.…”