ADVANCED MATERIALS & PROCESSES | OCTOBER 2024 47 14 SMJ HIGHLIGHTS Shape Memory and Superelasticity: Advances in Science and Technology (SMJ) is the official journal of the International Organization on Shape Memory and Superelastic Technologies (SMST), an affiliate society of ASM International. The journal publishes original peer-reviewed papers that focus on shape memory materials research with contributions from materials science, experimental and theoretical mechanics, physics with cognizance of the chemistry, underlying phases, and crystallography. It also provides a forum for researchers, scientists, and engineers of varied disciplines to access information about shape memory materials. The first two articles were taken from our March 2024 issue. The third is taken from the June 2024 special issue, which has a focus on Elastocalorics. They were selected by Shape Memory Editor-in-Chief Huseyin Sehitoglu. SMJ is available through springerlink.com. For more information, visit asminternational.org/smst. March 2024 EFFECTS OF POINT DEFECTS ON THE MONOCLINIC ANGLE OF THE B19" PHASE IN NiTi-BASED SHAPE MEMORY ALLOYS Yingchao Li, Sam Bakhtiari, Hong Yang, Martin Saunders, Daqiang Jiang, and Yinong Liu This study investigated the effects of a variety of point defects on the monoclinic angle of the B19″ martensite in NiTi, including Ni and Ti vacancies, Ni–Ti anti-sites in the lattice, third element substitution, and Ni and Ti enrichments in the B2 stoichiometry. Their effects were studied by density functional theory calculations on the monoclinic B19″ phase as a proxy for the experimentally observed B19' phase. It was found that vacancies and Ni–Ti anti-sites reduce the monoclinic angle of B19″, whereas third element substitution of Ni and Ti may affect the monoclinic angle in both directions depending on the third element and the host element it replaces. Enriching Ni or Ti content to deviate from the B2 stoichiometry decreases the monoclinic angle. A change in the monoclinic angle of the B19″ phase implies variation in the characteristic strains associated with the transformation. Thus, these findings may provide a new angle on possible interpretations of the variations of recoverable transformation strains experimentally observed of NiTi shape memory alloys (Fig. 1). Fig. 1 — Effect of anti-site defect on the monoclinic angle of the B19″ structure. (a) Schematic of a 3 × 3 × 3 supercell of the B19″ lattice in relaxed state. (b) Schematic of the random swapping of one Ni atom and one Ti atom to create a pair of anti-site defect. (c) Effect of the anti-site concentration on the monoclinic angle of the B19″ structure. (a) (b) (c)
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