Phase Equilibria in the Al–Co–Cr–Fe–Ni High Entropy Alloy System: Thermodynamic Description and Experimental Study

Abstract

In this paper we present and discuss phase equilibria in the quaternary Al-Cr-Fe-Ni and the quinary Al-Co-Cr-Fe-Ni alloy systems based on experimental data from DTA/DSC, SEM/EDS, and SEM/EBSD on as-cast and isothermally annealed samples. These data as well as literature data were used for developing a new Al-Co-Cr-Fe-Ni thermodynamic description by the CALPHAD approach. Considerable efforts in this direction have been made already and commercial databases for high entropy alloys are available, e.g., TCHEA4 and PanHEA. We focus on comparing our new thermodynamic database with computations using TCHEA4 for two section planes, i.e., quaternary Al x CrFe 2 Ni 2 and quinary Al x CoCrFeNi, where x is the stochiometric coefficient. According to our new thermodynamic description a single-phase field BCC-B2 is stable over a wider temperature range in both section planes, giving rise to dual-phase microstructures along solid state phase transformation pathways. In the section plane Al x CoCrFeNi the two-phase field BCC-B2 + σ predicted by the new database is stable between 600 and 800 • C, while in TCHEA4 this phase field extends to nearly 1000 • C. Furthermore, our new database showed that the solidification interval with primary BCC-B2 phase in quinary as well as quaternary section planes is narrow, being in a good agreement with presented micro-segregation measurements. Additionally, computed phase fields and phase-field boundaries in the quinary section plane correspond well to the experimental results reported in the literature.

Design and Production of a New FeCoNiCrAlCu High-Entropy Alloy: Influence of Powder Production Method on Sintering

“…The calculations in Figure 13 also present the formation of a minor FCC-L12 phase, in accordance with a possible dissolution of an ordered FCC-L12 found on DTA curves and referenced by [ 31 ].…”

“…The thermal analysis of the as-homogenised samples shown in Figure 4 presents the heating events around 600 • C with a little endothermic peak for both BE-1200TT and BE-1300TT that could represent the dissolution of an ordered FCC-L12 phase as previous authors have found [31]. Around 1100 • C for BE-1300TT, a change in the slope suggests a phase transformation.…”

“…The curve for the gas atomised powder in Figure 5 exhibits some irregularities in the temperature range around 1250 °C before reaching a two-stage melting reaction around 1340 °C, which suggests the appearance of various phases. In the DTA heating curves for the At-samples, both curves present two endothermic peaks, the first one again at 601 °C that could correspond also to the dissolution of an ordered FCC-L12 [ 31 ] and the second one that corresponds to the melting. Moreover, around 1100 °C there is a change of slope in the curve for At-1300 samples suggesting a phase transformation.…”

Effect of heat treatments on microstructure and mechanical properties of Al0.5CoCrFeNi complex concentrated alloy

“…4) calculated by Zhang et al [20] and experimental results reported by Butler and Weaver [28], the ageing at temperatures below 840 • C should lead to the formation of σ phase. The thermodynamic calculations of Stryzhyboroda et al [22] indicate the stability of σ phase up to a temperature of 960 • C. However, the ageing time of 25 h at both ageing temperatures of 800 and 900 • C is too short for the formation of a sufficient amount of σ phase, which can be identified by the XRD or EDS analysis in the present work.…”

“…Despite the previous works on CCAs, only limited information has been reported on heat treatments, precipitation hardening and mechanical properties of Al 0.5 CoCrFeNi alloy. Besides, contradictory informations on phase transformation temperatures and phase equilibria have been reported by several authors [19][20][21][22][23] for this system.…”