A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 2 5 1 5 5 FEATURE Fig. 3 — Phase field simulations of the B2-B19′ transformation in (a-e) a B2(black)+amorphous(white) composite and (f-j) a single B2 crystal without an amorphous structure. The four martensite variants v1, v2, v3, and v4 (see color key) can form self-accommodating herringbone microstructures. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) Fig. 4 — Molecular dynamic simulations of the B2-B19′ transformation in equiatomic NiTi for (a) pristine (b) interstitials (10−4 at.%), (c) vacancies (10−4 at.%), and (d) vacancy clusters (10−3 at.%) at 0.08 strain and (e) vacancy clusters (10−3 at.%) at 0.1 strain. See key for color of lattice sites. (a) (b) (c) (d) (e) consistent with the significantly larger nanoindentation load for irradiated NiTi (Fig. 1). The MD simulations (Fig. 4) predict that point defects and defect clusters also hinder the B2-B19′ martensitic phase transformation. At a total strain of 0.08 (loading), the pristine B2 structure (Fig. 4a) forms an internally twinned B19′ martensite structure while the simulations with interstitials (Fig. 4b) and vacancies (Fig. 4c) form the twinned B19′
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