Investigation of sluggish diffusion in FCC Al_0.25CoCrFeNi high-entropy alloy

Abstract

To validate the 'sluggish diffusion' in high-entropy alloys, interdiffusion coefficients of individual elements and tracer diffusion coefficient of Ni were experimentally determined in FCC Al 0.25 CoCrFeNi alloy. The tracer diffusion coefficient was determined without the application of radio-tracers using a novel analytical method proposed by Belova et al. based on linear response theory coupled with Boltzmann-Matano approach and Gaussian distribution function. Sluggish diffusion kinetics was not observed in alloys with higher configuration entropy in comparison to alloys with lower configuration entropy. Correspondingly, potential energy fluctuations in alloys with higher configuration entropy may not always result in anomalously slow diffusion kinetics. IMPACT STATEMENTDiffusion is determined not to be necessarily sluggish in Al 0.25 CoCrFeNi high-entropy alloy by experimental measurement of chemical and tracer diffusion coefficients.

Measurement of Interdiffusion and Tracer Diffusion Coefficients in FCC Co-Cr-Fe-Ni Multi-Principal Element Alloy

“…Based on the sluggish diffusion postulate, diffusion should be slow in alloys with higher configurational entropy of mixing. If so, average effective interdiffusion coefficients Ni in Co-Cr-Fe-Ni, Al-Co-Cr-Fe-Ni [3,19] , and Al-Co-Cr-Fe-Ni- Mn [4] alloys. The…”

“…Co and Deff Fe is the highest in quinary Al-Co-Cr-Fe-Ni alloy and contradicts the sluggish diffusion hypothesis based on Deff i determination. Figure 7 compares the temperature-dependent tracer diffusion coefficient of Ni, D Ã Ni in various quaternary and quinary FCC HEAs, i.e., CoCrFeNi [18] , CoCrFeNiMn 0.5 [11] , CoCrFeNiMn [18] , and Al 0.25-CoCrFeNi [19] . The D Ã Ni is the lowest in quaternary CoCr-FeNi alloy and the highest in quinary Al 0.25 CoCrFeNi alloy.…”

“…However, more recent work by Vaidya et al [16][17][18] measured the tracer diffusivity of each constituent element via radiotracer experiments and reported that diffusion may not be sluggish in CoCrFeNi and CoCrFeNiMn alloys when examined with absolute temperature, however, may be sluggish at temperature normalized with respect to the melting point. In addition, several other investigations on experimental determination of tracer diffusion coefficients [19][20][21][22][23][24] suggested that diffusion is not sluggish at absolute temperature but may be at inverse homologous temperature. Limited studies had measured interdiffusion coefficients in HEAs.…”

“…However, the uncertainty in crossover composition of diffusion path can increase with an increase in number of components in the alloy or the composition range of an element in the terminal alloys of diffusion couple. [27] Significant magnitude of off-diagonal interdiffusion coefficients suggested that there is a strong diffusional interaction among constituent elements, which was neglected by Tsai et al [11] Recently, Mehta and Sohn, [3,4,19] suggested that the sluggish diffusion effect may not be generalized for all HEAs based on average effective interdiffusion coefficients measurement in Al-Co-Cr-Fe-Ni and Al-Co-Cr-Fe-Ni-Mn alloys. Other investigations [29][30][31] also suggested that the sluggish diffusion effect cannot be generalized for all HEAs.…”

Microstructure and Magnetic Field-Induced Strain of a Ni-Mn-Ga-Co-Gd High-Entropy Alloy

“…Numerous studies have reported that the main phase of a high-entropy alloy is of type B2, to which the structure of the Ni2MnGa-based FSMAs matrix belongs [15][16][17][18][19]. These high-entropy alloys exhibit excellent mechanical and physical properties, which is due to the combination of a high degree of alloying elements in the solution and a sluggish diffusion effect [20]. Lattice distortion in a high-entropy alloy generally leads to increased diffusion activation energies in the lattice, which, in turn, reduces the effective diffusion rate of the atoms.…”