Strain-sensitive topological evolution of twin interfaces

Twin Boundaries (TBs) are fundamental interfaces in materials science which, despite over a century of research, continue to surprise us. A longstanding anomaly the field is experimental observation Type II TB NiTi with two distinct indicial identities: (0.720511¯)≈(344¯) and (899¯). The nanostructure this interface still unclear, varying propositions put forth past 4 decades. We consider multi-scale energetics, employing Molecular Statics simulations anisotropic elasticity formalisms, establish Terrace-Disconnection (TD) topology as energy-minimal nanostructure. theoretical framework developed based on continuum strain-energy arguments determine influence microstructural strain local twin volume fraction topology. It shown that it energetically favorable for evolve across continuous spectrum identities under coupled both parameters. Consequently, observations were thus far considered contrasting proposed states within spectrum, transposing evidence evolving capability TB. This topological evolution fundamentally arises from strain-mediated change dislocation-spacing (equivalently, dislocation-density). further propose prevalence behavior I Compound TBs (in NiTi) exhibiting seamless transition between coherent semi-coherent states, significantly changing dislocation-densities (upto 8-fold) irrational Miller-index non-zero strain. An “Evolving Interface” theory an extension Topological Modeling framework, allowing determination equilibrium topologies at unsymmetric fractions.