Interdiffusion in the FCC-structured Al-Co-Cr-Fe-Ni high entropy alloys: Experimental studies and numerical simulations

High-Entropy Alloys: A Current Evaluation of Founding Ideas and Core Effects and Exploring “Nonlinear Alloys”

“…29 Increasing the number of components seems to give more negative activation enthalpies as long as the comparison is made using T m /T. 24,30 At the same time, reported D 0 values differ by 4 orders of magnitude 26,30 and must be considered. These differences may originate from a trapping effect that can alter the correlation factor between atomic jumps 25 or from differences in diffusion entropy 30 that come from the strain produced at the diffusional saddle point and from local vibrational changes associated with the introduction of a vacancy.…”

“…Dąbrowa et al overcome this assumption by using the Darken-Manning analysis coupled with Levenberg-Marquardt or genetic algorithm optimization methods. 26 In addition to reanalyzing the data from Tsai et al, new diffusion data were generated in AlCo-Cr-Fe-Ni alloys. The new analysis of the original data from Tsai et …”

“…As a result, diffusion of a given species can be accelerated or retarded in the presence of a third element, and effects such as ''uphill'' diffusion (atomic flux ''up'' the concentration gradient) are observed. 26 A mechanistic view of diffusion in HEAs is still evolving. Chemical and thermodynamic considerations can retard (for negative deviations from ideal solutions) or accelerate (for positive deviations from ideal solutions) interdiffusion.…”

Influence of Annealing on the Microstructures and Oxidation Behaviors of Al8(CoCrFeNi)92, Al15(CoCrFeNi)85, and Al30(CoCrFeNi)70 High-Entropy Alloys

“…HEAs also exhibit the inherent potential to be alloyed with high concentrations of Al and/or Cr to promote enhanced oxidation resistances without necessarily forming various intermetallic phases that can be deleterious to strength [5][6][7]. In addition, HEAs have been reported to exhibit sluggish diffusion kinetics [8][9][10] and high thermal stabilities [11][12][13], making them ideal candidates for use in high temperature applications. However, a fundamental understanding of the active oxidation mechanisms are required in order to effectively implement HEAs in these environments.…”

“…This particular alloy system is ideal for a fundamental oxidation study since it contains both Al and Cr, which are known to produce protective Cr 2 O 3 and/or Al 2 O 3 scales [30]. Additionally, the AlCoCrFeNi system is one of the most thoroughly investigated to date [1,4,10,14,[31][32][33][34][35][36][37][38][39][40][41][42][43]. This paper will systematically report the influence of annealing on the microstructures and active oxidation mechanisms.…”