Nucleation centers for martensite with habitus {110} in the shape memory alloys

• Published in: IOP conference series. Materials Science and Engineering 2022-01, Vol.1213 (1), p.12006
• Main Authors: Kashchenko, M P, Kashchenko, N M, Chashchina, V G
• Format: Article
• Language: English
• Subjects: Crystal defects; Dislocation loops; Habits; Heusler alloys; Longitudinal waves; Martensite; Martensitic transformations; Nucleation; Shape memory alloys; Symmetry; Temperature dependence; Twin boundaries; Wave propagation
• ISSN: 1757-8981; 1757-899X
• DOI: 10.1088/1757-899X/1213/1/012006

The dynamic theory of martensitic transformations (MT) considers the formation of habit planes of martensite crystals as a consequence of the propagation of a controlling wave process (CWP). The general ideology makes it possible, by comparing the observed habits with calculations of the elastic fields of defects (as a rule, dislocations), to identify nucleation centers. In a number of cases (In-Tl alloys, Ni 50 Mn 50 alloys, Heusler alloys …) under MT in the shape memory alloys, {110} habits are observed (in the basis of the initial cubic phase), which often have a fine twin structure with twin boundaries of the same type. This highly symmetric structure is described by the CWP containing longitudinal waves (both relatively long-wavelength ℓ and short-wavelength s ) propagating along the 4-order symmetry axes. In this paper, it is shown that such habits are associated with rectilinear segments of dislocation loops with directions Λ along and Burgers vectors along (or ) orthogonal to Λ , both for sliding and for prismatic loops. The tetragonality, the relative volume change during the MT, and the dependence of the start temperature M s on changes in the concentration of alloy components are also briefly discussed.