Combined Atom Probe Tomography and TEM Investigations of CoCrFeNi, CoCrFeNi-Pd_x(x=0.5, 1.0, 1.5) and CoCrFeNi-Sn

Abstract

The structure of a family of high entropy alloys based on the composition CoCrFeNi, to which Pd and Sn have been added, is presented. The results stem from combined investigations by atom probe tomography as well as by scanning and transmission electron microscopy on samples produced by arc melting. Although CoCrFeNi is of fcc structure, the sample is not homogeneous on atomic scale. The addition of Pd as a fth element retains the fcc lattice with the indication of the coexistence of at least two additional phases. The addition of Sn changes the general structure considerably.

Crystalline Structures of Some High Entropy Alloys Obtained by Neutron and X-Ray Diffraction

“…The grain sizes were derived from the widths of the dierent as-tted main hkl peaks measured at the dierent positions and taking into account the experimental resolution. The obtained values varied from about 500 to larger than 5000 Å demonstrating a large grain size and shape variation in accordance with the microscopy studies [10]. Furthermore, the lattice constants calculated from each separate peak, assuming a fcc lattice, vary, as can be seen in Fig.…”

“…An extrapolation to x = 1.0 yields a lattice constant of about 3.615 Å in good agreement with the present work. SEM studies of the alloys for x = 0.5 [18] and x = 1.0 [10] have shown that the microstructures of the ingots were dendritic with Sn-and Ni-rich interdendritic regions.…”

Microstructure evolution and thermal stability of equiatomic CoCrFeNi films on (0001) α-Al2O3

“…This paper focuses on the equiatomic CoCrFeNi alloy. Above 873 K, it has a face-centered cubic (fcc) structure as shown both experimentally [6,[17][18][19][20][21] and by numerical and first principle calculations of phase diagrams [21][22][23][24][25]. The fcc CoCrFeNi remains stable after annealing treatments up to 1373 K, as shown in [18] (1 h at 1273 K) and in [20] (1 h at 1373 K).…”

The Effect of Electronic Structure on the Phases Present in High Entropy Alloys

“…More recent studies of some alloys have found that many are not simply single phase, or stable against transformation. For example, it has been found that on heat treatment, additional complex phases form in CCFN-Mn 1.0 8, and that other alloys, are not homogenous on the atomic scale and perfect solid solutions are not obtained910. However, the simple phase HEAs appear to retain their structures from the as-cast condition as a majority phase when annealed below a defined temperature, unless a) heat treated for extensive durations (500 h) leading to the appearance of grain-boundary precipitates811, or b) the composition is subjected to severe plastic deformation12.…”