No abstract

High‐entropy alloys (HEAs) with their almost limitless number of possible compositions have raised widespread attention in material science. Next to wear and corrosion resistive coatings, their application as tunable electrocatalysts has recently moved into the focus. On the other hand, fundamental properties of HEA surfaces like atomic and electronic structure, surface segregation and diffusion as well as adsorption on HEA surfaces are barely explored. The lack of research is caused by the limited availability of single‐crystalline samples. In the present work, the epitaxial growth of face centered cubic (fcc) CoCrFeNi films on MgO(100) is reported. Their characterization by X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDX), and transmission electron microscopy (TEM) demonstrates that the layers with a homogeneous and close to equimolar elemental composition are oriented in [100] direction and aligned with the substrate to which they form an abrupt interface. X‐ray photoelectron spectroscopy (XPS), low‐energy electron diffraction (LEED), and angle‐resolved photoelectron spectroscopy are employed to study chemical composition and atomic and electronic structure of CoCrFeNi(100). It is demonstrated that epitaxially grown HEA films have the potential to fill the sample gap, allowing for fundamental studies of properties of and processes on well‐defined HEA surfaces over the full compositional space.

Non-contact evaluation of transformation temperatures via bend and free recovery tests requires precise optical evaluation of shape changes of NiTi components. A variety of experimental setups is documented in the literature, but the influence of the evaluation method on the transformation temperatures is rarely assessed in detail. In the present work, the reverse transformation of bent wires is evaluated comparing the tracking of the lowest wire point and the tracking of the curvature. For calculating curvatures, different approaches of fitting the wire outline were applied. Fourth degree polynomials and ellipse segment fits were found to cause high noise toward the end of the reverse transformation, second degree polynomials and circle segment fits led to increased sensitivity in that region. Accordingly, the evaluation of curvature allowed to resolve a two-stage reverse transformation, which was otherwise obscured. The reasons for this effect are discussed comparing curvatures as determined by the different evaluation methods.