Evaluation of phase stability and diffusion kinetics in novel BCC-structured high entropy alloys

Figures & data

Figure 1. Temperature vs. phase fraction results calculated by the Thermo-Calc for equimolar alloys: (a) AlCrFeMnV; (b) CoCrFeMnV; (c) AlCrMnTiV; (d) AlFeMnNbV; (e) AlFeMnNbTi; (f) AlFeMnTiV; (g) AlMnNbTiV; (h) AlCrFeMoW; (i) AlCrNbVW; (j) AlCrFeMoV.

Figure 2. Isopleths of the Al-Cr-Fe-Mn-V phase diagram for: (a) Al; (b) Fe; (c) V; (d) Mn; (e) Cr. In all cases, all other elements are assumed to be in an equimolar ratio.

Table 1. Nominal and EDS measured compositions for the alloys used in the experiments. The melting (T_m, solidus) and Tamman (T_T) temperatures were calculated with use of Thermo-Calc software.

	Nominal composition [at.%]					Measured composition [at.%]					Temp [°C]
	Al	Cr	Fe	Mn	V	Al	Cr	Fe	Mn*	V	Tm	TT
A	20	20	20	20	20	20.7	20.5	20.3	18.4	20.1	1628	994
B	12	28	28	12	20	12.8	30.5	28.2	7.3	21.2	1668	1021
C	28	12	20	12	28	28.8	12.4	20.4	9.9	28.4	1632	997
D	20	12	28	12	28	20.6	12.9	27.7	11.0	27.9	1668	1021

*The differences between nominal and experimental content of Mn originate from the its relatively low T_m, leading to evaporation.

Figure 3. The exemplary diffusion profiles determined for the Al-Cr-Fe-Mn-V diffusion couples, both experimental and theoretical values are presented: (a) couple A-C, T = 1100°C, t = 24 h; (b) couple A-D, T = 1075°C, t = 24 h; (c) couple B-C, T = 1050°C, t = 46 h; (d) couple B-D, T = 1025°C, t = 72 h.

Table 2. The determined values of tracer diffusion coefficients $D_i^{\ast }$ for each experimental temperature. The values of $D_{i,0}^{\ast }$ and E_a are also provided.

		Tracer diffusion coefficients $D_i^{\ast }$ [m/s^2]
T [°C]	Time [h]	Al	Cr	Fe	Mn	V
1025	72	3.99·10^−15	1.51·10^−15	2.15·10^−15	2.22·10^−15	5.91·10^−15
1050	48	7.15·10^−15	3.59·10^−15	2.53·10^−15	5.00·10^−15	9.96·10^−15
1075	24	1.17·10^−14	5.02·10^−15	4.61·10^−15	8.01·10^−15	1.90·10^−14
1100	24	2.24·10^−14	7.76·10^−15	7.84·10^−15	1.25·10^−14	2.61·10^−14
$D_{i,0}^{\ast }$	[m/s^2]	${1.3}_{-0.3}^{+5.0}\cdot {10}^{-1}$	${9.3}_{-8.3}^{+78}\cdot {10}^{-3}$	${6.1}_{-6.0}^{+345}\cdot {10}^{-3}$	${8.6}_{-8.2}^{+159}\cdot {10}^{-2}$	${8.4}_{-8.2}^{+407}\cdot {10}^{-1}$
Ea	[kJ/mol]	336.0 ± 15.1	311.9 ± 24.9	264.5 ± 45.0	336.7 ± 32.9	302.9 ± 43.3

Figure 4. Arrhenius plot for the Al-Cr-Fe-Mn-V system: (a) tracer diffusion coefficients; (b) intrinsic diffusion coefficients. The open points correspond to the values determined for each considered temperature, while the lines represent the linear fits.

Figure 5. The values of tracer diffusion coefficients of different elements, in different BCC-structured metals and alloys [34,49–53]: (a) Al; (b) Cr; (c) Fe; (d) Mn; (e) V. All plots are presented in the temperature scale normalized with respect to the melting point value T_m of respective materials. The Tamman temperature, corresponding to the 2/3 of the absolute T_m value of is denoted by the vertical gray line. The open circles for the Al-Cr-Fe-Mn-V system correspond to the experimental points determined in this study, while the violet line shows the respective linear fit. Data for Co-Cr-Fe-Mn-Ni, FCC-structured system is also shown for reference [28,34,49–53].

Mehrer H, editor. Diffusion in solid metals and alloys. Berlin: Landolt–Börnstein; 1990.

 Google Scholar

Dabrowa J, Zajusz M, Kucza W, et al. Demystifying the sluggish diffusion effect in high entropy alloys. J Alloy Compd. 2019;783:193–207.

 Web of Science ®Google Scholar