Microstructure, mechanical properties and corrosion resistance of laser direct energy deposited AlMo_0.25FeCoCrNi_2.1 high-entropy alloy: adjusted by annealing heat treatment

Figures & data

Figure 1. (a) The SEM map, (b) particle size distribution and (c) associated EDS mapping results of the mixed AlMo_0.25FeCoCrNi_2.1 powders. The inserted image in (a) is the high-magnification SEM map of pure Mo particles.

Figure 2. (a) Schematic diagram of the multilayer LDED process with a zigzag scanning strategy, (b) the geometrical descriptions of the LDEDed thin-wall build and tensile samples.

Figure 3. (a) XRD patterns of AlMo_0.25FeCoCrNi_2.1 HEA with various annealing times, (b) the local amplified of the 2θ ranging from 38° to 50°.

Figure 4. (a) Three-dimensional and (b) X-Z section OM observations of the microstructure in as-deposited AlMo_0.25FeCoCrNi_2.1 alloy. (c) High-magnification SEM image and (d) associated EDS results of the microstructure selected in the middle region of banded layers shown in (b).

Figure 5. (a) The IPF map, (b) GND density map and (c) average grain size of the as-deposited AlMo_0.25FeCoCrNi_2.1 microstructure. (d) The high-magnification IPF map, (e) phase map and (f) IPFs of amplified region from (a).

Figure 6. SEM maps and associated EDS mapping results of representative regions (a) P1, (b) P2, (c) P3, (d) P4 and (e) P5 in as-deposited microstructure shown in Figure 4.

Figure 7. (a) TEM map, (b) associated EDS mapping results and (c) SAED patterns of flower-like structure of microstructure in region P3 shown in Figure 6(c).

Table 1. EDS point results of structures in region P3 (at. %).

Spectrum	Structure	Al	Cr	Fe	Co	Ni	Mo
1	Incipient BCC	24.1	6.2	9.5	13.6	46.1	0.5
2	Incipient FCC	5.5	19.3	18.7	18.0	33.3	5.2
3	Granular σ	6.0	30.5	17.2	17.0	18.1	11.2
4	short rod-like σ	6.1	28.3	17.5	17.5	19.6	11.1
5	Short rod-like σ	3.3	31.3	17.6	17.3	18.6	11.9
6	Short rod-like FCC	4.8	20.8	20.6	19.5	29.76	4.5

Figure 8. (a) TEM maps, (b) EDS mapping results and (c) SAED patterns of nanoscale lamellar structure in region P4 shown in Figure 6(d).

Figure 9. Schematic illustration of the dynamic melting-solidification process of during the LDED of AlMo_0.25FeCoCrNi_2.1 HEA.

Table 2. Atomic size, melting points, density and mixing enthalpy of elements in mixed AlMo_0.25FeCoCrNi_2.1 HEA.

Parameters	Al	Cr	Fe	Co	Ni	Mo
Atomic size (Å)	1.43	1.25	1.24	1.25	1.25	2.01
Melting point (°C)	660	1907	1539	1495	1453	2620
Density (g/cm3)	2.70	7.19	7.86	8.90	8.90	10.20
ΔHmix (KJ/mol)
Al		−10	−11	−19	−22	−5
Cr			−1	−4	−7	0
Fe				−1	−2	−2
Co					0	−5
Ni						−7

Figure 10. The SEM maps and associated EDS results of annealed microstructure in the representative regions (a)-(c) P2, (d)-(f) P3 and (g)-(i) P4.

Figure 11. (a) TEM map, (b) high-magnification TEM map, (c) associated EDS test results and (d) associated SAED patterns and HRTEM images of coarse FCC phases in region P2 of AHT-26 sample.

Figure 12. (a) TEM map, (b) high-magnification TEM map, (c) associted EDS test results and (d) associated SAED patterns and HRTEM images of fine FCC/BCC eutectic structures in region P2 of AHT-26 sample.

Figure 13. (a) TEM map, (b) local amplified TEM map, (c) EDS mapping results and (d) SAED patterns of flower-like structures and precipitations in region P3 of AHT-26 sample.

Figure 14. The hardness variations of as-deposited and annealed AlMo_0.25FeCoCrNi_2.1 samples.

Figure 15. The tensile stress-strain curves of as-deposited and annealed AlMo_0.25FeCoCrNi_2.1 samples.

Table 3. Tensile properties of AlMo_0.25FeCoCrNi_2.1 HEA at room temperature.

Samples	UTS (MPa)	E (%)
AHT-0	993.0	3.7
AHT-2	1034.6	1.6
AHT-10	915.8	7.3
AHT-26	963.9	4.6

Figure 16. The tensile fracture morphologies of (a)-(b) AHT-0, (c)-(d) AHT-2, (e)-(f) AHT-10 and (g)-(h) AHT-26 samples. (i) and (j) are the high-magnification SEM map and associated EDS mapping results of bare Mo particles in (a). (k) and (l) are the high-magnification SEM maps of selected regions in (g) and (h), respectively.

Figure 17. (a) Kinetic potential polarisation curves, (b) Bode plots, (c) Nyquist plots and (d) Equivalent circuit of as-deposited and annealed AlMo_0.25FeCoCrNi_2.1 samples.

Table 4. Electrochemical corrosion parameters of as-deposited and annealed AlMo_0.25FeCoCrNi_2.1 samples.

Samples	Ecorr (mVSCE)	Icorr (μA/cm^2)
AHT-0	−248.87	0.65
AHT-2	−268.68	0.20
AHT-10	−254.89	0.23
AHT-26	−223.80	1.20

Table 5. Equivalent circuit parameters of impedance spectra of as-deposited and annealed AlMo_0.25FeCoCrNi_2.1 samples.

Samples	Rs (Ω·cm^2)	Rt (Ω·cm^2)	Rf (Ω·cm^2)	CPEf		CPEdl
				Y0 (μF/cm^2)	nf	Y0d (μF/cm^2)	ndl
AHT-0	9.800	4.350E4	2.506E2	1.880E-5	0.8471	2.413E-6	0.998
AHT-2	8.973	1.411E4	1.175E5	1.563E-5	0.8701	7.196E-4	0.998
AHT-10	10.07	1.019E4	1.008E5	1.264E-5	0.8869	7.323E-4	0.998
AHT-26	9.985	5.029E4	4.383E-2	1.116E-5	0.8584	3.259E-5	0.800

Figure 18. Corrosion surface morphologies and associated EDS mapping results of high-magnification regions of (a) AHT-0, (b) AHT-2, (c) AHT-10 and (d) AHT-26 samples after kinetic potential polarisation test.

Figure 19. Schematic illustration of the destroy mechanism of passive film completeness on the FCC phase by precipitated needle-like B2 phases during the annealing heat treatment.

Data availability statement

The authors declare that all data supporting the findings of this study are available within the paper.