a b s t r a c tRecent studies indicated that high-entropy alloys (HEAs) possess unusual structural and thermal features, which could greatly affect dislocation motion and contribute to the mechanical performance, however, a HEA matrix alone is insufficiently strong for engineering applications and other strengthening mechanisms are urgently needed to be incorporated. In this work, we demonstrate the possibility to precipitate nanosized coherent reinforcing phase, i.e., L1 2 -Ni 3 (Ti,Al), in a fcc-FeCoNiCr HEA matrix using minor additions of Ti and Al. Through thermomechanical processing and microstructure controlling, extraordinary balanced tensile properties at room temperature were achieved, which is due to a well combination of various hardening mechanisms, particularly precipitation hardening. The applicability and validity of the conventional strengthening theories are also discussed. The current work is a successful demonstration of using integrated strengthening approaches to manipulate the properties of fcc-HEA systems, and the resulting findings are important not only for understanding the strengthening mechanisms of metallic materials in general, but also for the future development of high-performance HEAs for industrial applications.

We demonstrate, using first-principles calculations, that the electronic structure of FeSe1−xTex (x=0.5) is topologically non-trivial, characterized by an odd Z2 invariant and Dirac cone type surface states, in sharp contrast to the end member FeSe (x=0). This topological state is induced by the enhanced three-dimensionality and spin-orbit coupling due to Te substitution (compared to FeSe), characterized by a band inversion at the Z point of the Brillouin zone, which is confirmed by our ARPES measurements. The results suggest that the surface of FeSe0.5Te0.5 may support a non-trivial superconducting channel in proximity to the bulk.PACS numbers: 74.70.Xa, Among the Fe-based superconductors, the FeSe 1−x Te x family of compounds [1-4] is of particular interest. First, it has the simplest PbO structure (space group P 4/nmm) with Se (or Te) atoms forming distorted tetrahedra around Fe (see Fig. 1(a)) similar to the structure of FeAs planes in the families of FeAs-based high T c superconductors [5]. Second, the internal parameters can be systematically tuned by the substitution of Se by Te [6][7][8], which provides us a platform for in-depth study of possible superconducting mechanisms and topological characters. Thirdly, superconductivity has been observed for a wide range of composition x [2-4], and the transition temperature T c can be further enhanced by pressure [9][10][11]. More recently, superconductivity with T c higher than 77 K was suggested for single unit cell FeSe films [12] epitaxially grown on SrTiO 3 substrates.Despite these interesting properties though, the particularities of the system have still not been fully explored. Earlier studies, both theoretical and experimental, suggest the similarity of the electronic structures of the Fe chalcogenides (FeSe, FeTe) [13][14][15] and the FeAsbased [16][17][18] superconductors. Indeed, the low-energy physics around the Fermi level is dominated by the Fe-3d states, and the morphology of the Fermi surfaces is similar. On the other hand, a surprisingly stable (no splitting under external magnetic field) zero-energy bound state (ZBS) at randomly distributed interstitial excess Fe sites was observed in very recent scanning tunneling microscopy (STM) measurements on the surface of superconducting Fe(Te,Se) [19], suggesting possible topological feature of its electronic structure. Obviously, the * * these authors contributed equally to this work. 5p orbitals of Te are more extended and have stronger spin-orbit coupling (SOC) than the 4p orbitals of Se. The consequences of Te substitution, particularly for the bulk topological character of FeSe 1−x Te x , have been largely ignored in the literature and will be the main purpose of the present paper. Based on first-principles calculations combined with angle resolved photoemission spectroscopy (ARPES) measurements, here we report that the electronic structure of FeSe 0.5 Te 0.5 is topologically non-trivial, in sharp contrast to its end member FeSe. The topological properties of FeSe 0.5 Te 0.5 can be characterized ...

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