Phase Transformation Kinetics of a FCC Al0.25CoCrFeNi High-Entropy Alloy during Isochronal Heating

Abstract

The phase transformation kinetics of a face-centered-cubic (FCC) Al0.25CoCrFeNi high-entropy alloy during isochronal heating is investigated by thermal dilation experiment. The phase transformed volume fraction is determined from the thermal expansion curve, and results show that the phase transition is controlled by diffusion controlled nucleation-growth mechanism. The kinetic parameters, activation energy and kinetic exponent are determined based on Kissinger–Akahira–Sunose (KAS) and Johnson–Mehl–Avrami (JMA) method, respectively. The activation energy and kinetic exponent determined are almost constant, indicating a stable and slow speed of phase transition in the FCC Al0.25CoCrFeNi high-entropy alloy. During the main transformation process, the kinetic exponent shows that the phase transition is diffusion controlled process without nucleation during the transformation.

The Effects of Annealing at Different Temperatures on Microstructure and Mechanical Properties of Cold-Rolled Al0.3CoCrFeNi High-Entropy Alloy

“…However, the amount of (Cr-Fe-Co)-rich σ precipitate is far lower than that of the (Al-Ni)-rich B2 precipitate, as shown in Figures 5 and 6. This can be attributed to the fact that the mixing enthalpy of Ni and Al is much negatively lower than the other atom pairs of the five principal elements [16]. Thus, the B2 phase is the main precipitate for this temperature range.…”

“…Work hardening and refining hardening can be employed to increase the yield strength of HEA alloys [10,11]. Moreover, alloying is also an effective method to increase the yield stress by solid solution hardening or precipitation hardening [12][13][14][15][16]. The FCC Al 0.3 CoCrFeNi is the most widely studied precipitation hardening HEA alloy [16][17][18][19][20].…”

“…Moreover, alloying is also an effective method to increase the yield stress by solid solution hardening or precipitation hardening [12][13][14][15][16]. The FCC Al 0.3 CoCrFeNi is the most widely studied precipitation hardening HEA alloy [16][17][18][19][20]. It has been reported that two stable phases (L1 2 and B2 phases) with order structure can be favorably precipitated within the FCC matrix [18,21,22].…”

Thermal–Mechanical Processing and Strengthen in AlxCoCrFeNi High-Entropy Alloys

“…It is a way of establishing the reasonable heat treatment parameters to enhance performance. Wang et al have inspected the phase transformation kinetics of the fcc Al 0.25 CoCrFeNi (Wang et al, 2018b) and fcc + bcc Al 0.5 CoCrFeNi (Wang et al, 2017a) HEAs during an experiment on isochronal heating by thermal dilation. The estimated activation energy and kinetic exponent were almost stable, indicating a slow and steady phase transition in an Al 0.25 CoCrFeNi HEA ( Figure 2A).…”

“…In Ⅲ 2 FIGURE 2 | (A) The local Avrami exponent (blue circle) as a function of phase transformed fraction of Al 0.25 CoCrFeNi HEA (4 K/min). The green zone represents the range of n from 1 to 1.5 (Wang et al, 2018b). (B) Variation in n with the increasing volume fraction of Al 0.5 CoCrFeNi HEA (3 K/min).…”