Microstructure Modification and Ductility Improvement for TaMoNbZrTiAl Refractory High Entropy Alloys via Increasing Ti Content

doi:10.1007/s40195-024-01707-y

Abstract

Abstract:

Here, the composition of TaMoNbZrTiAl refractory high entropy alloy (RHEA) is optimized by increasing Ti content to improve its mechanical property especially the ductility, through comparing two RHEAs with different Ti content. The RHEAs contain two body-centered-cubic (BCC) phases. The BCC phase in the dendritic region is rich in Ta, Mo and Nb, and the BCC phase in the interdendritic region is enriched in Zr, Ti and Al. The as-cast RHEA with a higher Ti content remains dendritic microstructures, and Ti is mainly enriched in the interdendritic region. After annealing treatment at 1300 °C for 48 h, the dendritic microstructures change into equiaxed-grain morphology, accompanied by needle-like micron precipitates at grain boundaries in the RHEA with higher Ti content. For the as-cast RHEAs, the fracture strain increases by ~ 6.6% and the uniform plastic strain increases by ~ 5.9% at the compression test due to the increase of Ti content. Our work offers a reference for the composition design of RHEAs and makes a preliminary exploration of the optimization of the microstructures and mechanical properties.

Key words: Refractory high entropy alloys, Solidification, Grain morphology, Microstructure, Mechanical property

Yujing Zhou, Siyi Peng, Yueling Guo, Xiaoxiang Wu, Changmeng Liu, Zhiming Li. Microstructure Modification and Ductility Improvement for TaMoNbZrTiAl Refractory High Entropy Alloys via Increasing Ti Content[J]. Acta Metallurgica Sinica (English Letters), 2024, 37(7): 1186-1200.

Figures/Tables 17

Table 1 Nominal and measured compositions of RHEA-Ti and RHEA-1.5Ti alloys by wet-chemical analysis (wt%)

Alloys		Ta	Mo	Nb	Zr	Ti	Al
RHEA-Ti	Nominal	35.36	18.76	18.16	17.83	9.36	0.53
	Wet-chemical	Bal.	18.1	17.8	18.6	9.8	0.6
RHEA-1.5Ti	Nominal	33.79	17.92	17.35	17.04	13.41	0.50
	Wet-chemical	Bal.	17.5	17.4	15.5	13.3	0.5

Fig. 1 a Phase evolution and b partition of elements during equilibrium solidification for the RHEA-Ti alloys predicted by Thermo-Calc simulations; c XRD spectra of the as-cast and annealed RHEA-Ti alloys

Fig. 2 a Phase evolution and b partition of elements during equilibrium solidification for the RHEA-1.5Ti alloys predicted by Thermo-Calc simulations; c XRD spectra of the as-cast and annealed RHEA-1.5Ti alloys

Fig. 3 EPMA-WDS mapping of a selected region for the as-cast RHEA-Ti alloy including Ta, Mo, Nb, Zr, Ti and Al. The points of P1-P3 are the representaive positions where quantitative measurements are performed

Table 2 EPMA-WDS measured compositions of the representative locations in the RHEA-Ti and RHEA-1.5Ti alloys (at.%). The positions of P1, P2 and P3 are labeled in Fig. 3. The positions of P4, P5 and P6 are labeled in Fig. 4

Alloys	Position	Ta	Mo	Nb	Zr	Ti	Al
RHEA-Ti	P1	29.3	21.3	21.1	9.8	17.6	0.9
	P2	11.4	13.5	14.5	33.1	23.6	3.9
	P3	9.0	11.6	12.9	39.5	21.9	5.1
RHEA-1.5Ti	P4	28.1	20.2	19.3	8.1	23.5	0.8
	P5	20.1	18.6	18.9	13.0	28.1	1.3
	P6	6.8	10.7	11.4	34.4	32.1	4.6

Fig. 4 EPMA-WDS mapping of selected regions for the as-cast RHEA-1.5Ti alloy including Ta, Mo, Nb, Zr, Ti and Al. The points of P4-P6 are the representative positions where quantitative measurements are performed

Fig. 5 a Selected positions for nanoindentation testing on the as-cast RHEA-Ti alloy; b reduced modulus and c hardness mapping of the tested region; d reduced modulus, e hardness values of all testing points

Fig. 6 Microstructures of the RHEA-Ti alloys via BSE imaging: a, c as-cast; b, d annealed; c and d zoom-in images of a, b, respectively

Fig. 7 a, b STEM-HAADF imaging of the edge of the dendrite trunk for the annealed RHEA-Ti alloy; c selected area electron diffraction (SAED) patterns taken from the dendrite trunk; d EDS mapping of a including Ta, Mo, Nb, Zr, Ti and Al, respectively. The deeper the color, the lower content of the elements

Fig. 8 a STEM-HAADF imaging of the interdendritic microstructure of the annealed RHEA-Ti alloy; b selected area electron diffraction (SAED) patterns taken from a; c EDS mapping of a including Ta, Mo, Nb, Zr, Ti and Al, respectively. The deeper the color, the lower content of the elements

Fig. 9 Microstructures of the RHEA-1.5Ti alloys via BSE imaging: a, c as-cast; b, d annealed, c and d zoom-in images of a and b, respectively

Fig. 10 a STEM-HAADF imaging of the edge of the grain boundary microstructures of the annealed RHEA-1.5Ti alloy; b and c zoom-in images of a; d EDS mapping of a including Ta, Mo, Nb, Zr, Ti and Al, respectively. The deeper the color, the lower content of the elements

Fig. 11 EBSD mapping for the annealed RHEA-1.5Ti alloy

Fig. 12 Compressive stress-strain curves of a as-cast, b annealed RHEAs at room temperature. Both as-cast and annealed alloy specimens are tested for each type of alloy

Fig. 13 Fracture surfaces of the a, b as-cast and c, d annealed RHEA-Ti alloys. b and d zoom-in images of a, c, respectively

Fig. 14 Fracture surfaces of the a, b as-cast and c, d annealed RHEA-1.5Ti alloys. b and d zoom-in images of a, c, respectively

Fig. 15 Schematic illustration of the microstructural evolution for TaMoNbZrTiAl RHEAs

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