Interstitial Atoms enable Design of TWIP and TRIP High Entropy Alloys
Concept and alloy design
We start from the high-entropy alloy design philosophy and transfer it from simple solid-solution bcc/fcc systems to intermetallic-based materials with a B2 matrix. The chosen composition lies in a multicomponent system in which a B2-type ordered phase coexists with a bcc solid solution, allowing us to exploit both configurational entropy and phase partitioning to stabilize a dual-phase microstructure. The design target is a microstructure in which a continuous B2 matrix provides high strength, while ductile bcc regions act as compliant domains that accommodate plasticity and crack-tip blunting.
To this end, we select alloying elements that favor B2 ordering (e.g., strong A–B type ordering pairs) and others that preferentially partition to the bcc phase, thereby tuning lattice parameters, elastic mismatch, and antiphase boundary (APB) energies. We use thermodynamic considerations and phase stability trends to place the composition in a regime where both phases form under conventional casting and subsequent thermal treatments, rather than requiring rapid solidification or far-from-equilibrium processing.
HEAs were originally proposed to contain multiple principal elements in near-equimolar ratios to stabilize single-phase solid solutions through maximizing configurational entropy. Recently, motivated by the fact that maximized configurational entropy is not the sole factor determining phase stability of HEAs, a novel metastable transformation-induced plasticity dual-phase (TRIP-DP) HEA with exceptional strength and ductility has been developed. Based on this approach, we propose a new class of HEAs which is interstitially alloyed and unifies all known metallic strengthening mechanisms in one material.
We use carbon as interstitial element in line with two main trends which can be deduced from previous studies on advanced steels:
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