Correlation between lattice distortion and friction stress in Ni-based equiatomic alloys

Abstract

Many recent efforts have been made to apply traditional theories for solid solution strengthening to explain the strength increase in concentrated equiatomic alloys (or high-entropy alloys), but always faced the challenge of differentiating solvent from solute atoms. In this report, we conducted a systematical analysis of Ni-based equiatomic alloys with a face-centered cubic structure and found that the lattice distortion in this alloy system could be simply described by the parameter of atomic size mismatch. It was found that lattice friction stresses of these alloys were well correlated with the lattice distortion. Dislocation core width in this Ni-based alloy system was also estimated and compared with that in the pure nickel. The intrinsically high strength in high-entropy alloys was probably resulted from a high lattice friction stress.

Ultrastrong Medium‐Entropy Single‐Phase Alloys Designed via Severe Lattice Distortion

“…This reduced width thus leads to the high friction stress, in agreement with the previous report. [28] Specifically, the width of a dislocation in the current VCoNi alloy presents the lowest value of 1.19 among all reported alloys. The degree of the dislocation width reduction could be a significant factor for generating the high friction stress because it represents a measure of the reduced distance over which the lattice is distorted due to the presence of a dislocation.…”

“…We compared the width of a dislocation normalized by the Burgers vector (w/b) for various Ni-containing equiatomic alloys ( Figure S2 and Table S3, Supporting information). [21,28,29] The σ 0 and w/b closely follow an inverse exponential relationship. The remarkable shrinkage of the dislocation width is observed in multiprincipal element alloys compared to pure Ni or binary Ni alloy, rendering the dislocation movement more difficult.…”

“…This approach is in line with corresponding previous studies on solid solution distortion effects in HEAs and MEAs compared to conventional alloys using friction stress measurements. [20,[22][23][24][25][26][27][28] In addition, ab initio calculations have been recognized as a reliable method to investigate atomic scale solid solution structures and the associated local distortions. [39,40] First, the role of the atomic scale solid solution dependent lattice distortions on the mechanical properties was studied by performing tensile tests after varying the annealing conditions and under consideration of the alloy's average grain sizes (Table S1, Supporting information).…”

“…This means that the level of lattice distortion currently exploited in most substitutional solid solution alloys does not contribute significantly to the yield strength. [20,[22][23][24][25][26][27][28] Here, based on a combined theoretical and experimental approach, we show that the degree of lattice distortion is indeed a key parameter in controlling strengthening mechanisms for the design of hitherto unexplored ultrastrong medium-entropy single-phase alloys. For this purpose, we exploit vanadium (V) as a very efficient element in a Severe lattice distortion is a core effect in the design of multiprincipal element alloys with the aim to enhance yield strength, a key indicator in structural engineering.…”

Superior strength-ductility combination of a Co-rich CoCrNiAlTi high-entropy alloy at room and cryogenic temperatures

“…Obviously, in the present study, the multicomponent CoCrNi-AlTi alloy exhibits superior combination of yield stress and tensile elongation at both 293 K and 77 K. According to the microstructural features of the alloy, the additional yield stress should be the result of the following factors: solid solution strengthening, refined-grain strengthening, precipitation strengthening and second-phase strengthening. Firstly, owing to the addition of 3 at% Al, 3 at% Ti elements, the solid-solution hardening can be estimated to be around 175 MPa [13,14]. Secondly, by accounting for the refined-grain strengthening effect, the yield stress of the alloy with mean grain size of 10 μm can be estimated by σ YS =σ 0 +kd −1/2 [15,16], in which σ 0 is the lattice friction (218 MPa for the CoCrNi alloy [17]); and K is the Hall-Petch constant (568 MPa/μm −1/2 for CoCrNi -AlTi alloy [18]) and d is the mean grain size.…”