Abstract
Twinning is a phenomenon that occurs, e.g., during deformation, martensitic transformation and film growth. The present study shows that the crystallography of twinning can be described by two twinning modes along the complete Bain transformation path and beyond connecting body-centered and face-centered cubic structures. To probe this concept, we used strained epitaxial films of the Fe-Pd magnetic shape memory system. As the substrate acts as an absolute reference frame, we could show by pole figure measurements that all observed twinning can be a body-centered and face-centered cubic twinning mode. This continuously transforms towards identity when approaching the complementary structure.
Highlights
In the field of physical metallurgy, materials, such as shape memory alloys, high-strength materials, high-temperature alloys and multiferroics, exhibit different kinds of twinning phenomena, which have a strong influence on the functional properties
Fe-Pd exhibits a martensitic transformation that follows the concept of the Bain path for deformation of a unit cell from face-centered cubic to body-centered cubic [10,11]
Deformation twins are created by external straining, and transformation twins occur during spontaneous straining of the crystal lattice during a martensitic transformation
Summary
In the field of physical metallurgy, materials, such as shape memory alloys, high-strength materials, high-temperature alloys and multiferroics, exhibit different kinds of twinning phenomena, which have a strong influence on the functional properties. Regarding a face-centered atom of the austenitic fcc unit cell (dark grey shaded atoms) as the corner of the bct unit cell (bright grey shaded atoms), this bct unit cell is tetragonal instead of cubic and aligned along the h110i directions of the fcc unit cell This highlights the key feature of the Bain path—a simplified description of the transformation using a single parameter: the tetragonal distortion reflected by the c/a|fct -ratio. The advantage for those compound twins is that the crystal orientation can be obtained either by a mirror operation or by a 180◦ rotation According to this general description and the notation given, the elementary twin reaction can be extended to be valid along the Bain path, which continuously connects the fcc to the bcc lattice by a tetragonal distortion [12,16]. We experimentally provide the adaptive nanotwinning in highly strained Fe-Pd films (Section 5.4)
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