Interstitial high-entropy alloys: Interstitial atoms enable joint twinning and transformation induced plasticity in strong and ductile high-entropy alloys

High-entropy alloys (HEAs) consisting of multiple principle elements provide an avenue for realizing exceptional mechanical, physical and chemical properties.

Fig. 1: (a) XRD and EBSD patterns reveal that the structure consists of f.c.c. and h.c.p. phases (DP structure). (b) EDS maps and BSE images from the region marked in (a) show the uniform distributions of all elements at the grain-scale. (c) ECCI analysis shows stacking faults and h.c.p. phase within the f.c.c. matrix. Three-dimensional APT tip reconstructions taken from the region marked in (a) are given in Supplementary Fig. S1.

© Max-Planck-Institut für Eisenforschung GmbH

Fig. 1: (a) XRD and EBSD patterns reveal that the structure consists of f.c.c. and h.c.p. phases (DP structure). (b) EDS maps and BSE images from the region marked in (a) show the uniform distributions of all elements at the grain-scale. (c) ECCI analysis shows stacking faults and h.c.p. phase within the f.c.c. matrix. Three-dimensional APT tip reconstructions taken from the region marked in (a) are given in Supplementary Fig. S1.

© Max-Planck-Institut für Eisenforschung GmbH

In this project we pursue a novel strategy for designing a new class of HEAs incorporating the additional interstitial element carbon. This results in joint activation of twinning- and transformation-induced plasticity (TWIP and TRIP) by tuning the matrix phase’s instability in a metastable TRIP-assisted dual-phase HEA. Besides TWIP and TRIP, such alloys benefit from massive substitutional and interstitial solid solution strengthening as well as from the composite effect associated with its dual-phase structure. Nanosize particle formation and grain size reduction are also utilized. The new interstitial TWIP-TRIP-HEA thus unifies all metallic strengthening mechanisms in one material, leading to twice the tensile strength compared to a single-phase HEA with similar composition, yet, at identical ductility.

Supplementary

Fig. S1: Typical APT analysis on the coarse-grained interstitial TWIP-TRIP-HEA

© Max-Planck-Institut für Eisenforschung GmbH

Fig. S1: Typical APT analysis on the coarse-grained interstitial TWIP-TRIP-HEA

© Max-Planck-Institut für Eisenforschung GmbH

The alloy was homogenized at 1200 ^oC for 2 h and followed by water-quenching. The region where the APT tips were taken from is marked in the EBSD pattern in Fig. 1a. (a) Three-dimensional APT tip reconstructions of atom positions in a typical tip. (b) Statistical binomial frequency distribution analysis results showing that the binomial curves obtained from experiments match the curves corresponding to a total random distribution. Several parameters were used to assess the quality of the fit, as listed in the inserted table. n_d and μ are the number of degrees of freedom for a given ion and normalized homogenization parameter, respectively. The values of μ for all elements are close to 0, confirming the random distribution of elements in the coarse-grained interstitial TWIP-TRIP-HEA.