Design Strategy for Synergistic Strengthening of W and Al in High-W Superalloys

doi:10.1007/s40195-025-01845-x

Abstract

Abstract:

To investigate the influence of W and Al on the microstructure and mechanical properties of a high-W superalloy, the Thermo-Calc calculation was utilized to simulate the microstructure with various W and Al contents. The results indicated that the concentration of W and Al exceeded 15.7 wt% and 5.9 wt%, respectively, the abnormal tungsten-rich α-W phase would precipitate. Compared with the results of orthogonal experiment, the precipitation of α-W phase is consistent with thermodynamic calculation results. The presence of Al not only influenced the precipitation of α-W phase but also impacted the eutectic content and the γʹ-size, both of which showed an increase with higher Al concentrations. Excessive W and Al contents promoted the precipitation of α-W phase, escalating the site of crack nucleation, and ultimately decreasing the plasticity. In the process of creep deformation (975 °C / 235 MPa), the rafted γ' phases were more continuous with increasing W contents, which increased the difficulty of dislocation climbing. As Al content increased, the density of interfacial dislocation network increased. The dislocations were entangled with each other, and the hindrance of dislocation movement was enhanced, which improved the stress rupture life. However, the precipitation of the hard and brittle α-W phase was attributed to the excessive W and Al, which increased the tendency of crack formation and significantly diminished the stress rupture life. The alloy exhibited the highest stress rupture life of 110.46 h when the W and Al contents were 15.7 wt% and 5.9 wt%, respectively.

Key words: High-W superalloys, Thermo-Calc, Orthogonal experiments, Microstructure, Mechanical properties

Xiang Fei, Naicheng Sheng, Zhaokuang Chu, Han Wang, Shijie Sun, Yuping Zhu, Shigang Fan, Jinjiang Yu, Guichen Hou, Jinguo Li, Yizhou Zhou, Xiaofeng Sun. Design Strategy for Synergistic Strengthening of W and Al in High-W Superalloys[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(6): 1057-1068.

Figures/Tables 14

Table 1 Primary chemical composition (wt%)

Alloy	Al	W	Co	Cr	Nb + Ti + Hf	C	Ni
1	5.9	15.3	7.8	5.1	3.7	0.1	Bal.
2	5.9	15.7	7.8	5.1	3.7	0.1	Bal.
3	5.9	16.1	7.8	5.1	3.7	0.1	Bal.
4	5.6	15.7	7.8	5.1	3.7	0.1	Bal.
5	6.2	15.7	7.8	5.1	3.7	0.1	Bal.

Fig. 1 Results of Thermodynamic calculation: a phase composition, b the statistics of the results of different W and Al

Fig. 2 Microstructures with different W and Al contents: a, f 15.3 wt% W, 5.9 wt% Al, b, g 15.7 wt% W, 5.9 wt% Al, c, h 16.1 wt% W, 5.9 wt% Al, d, i 15.7 wt% W, 5.6 wt% Al, e, j 15.7 wt% W, 6.2 wt% Al

Fig. 3 Eutectic area fraction and the γ′-size: a various W content, b various Al content

Fig. 4 The γ' phase morphologiees with various W and Al contents: a, f 15.3 wt% W, 5.9 wt% Al, b, g 15.7 wt% W, 5.9 wt% Al, c, h 16.1 wt% W, 5.9 wt% Al, d, i 15.7 wt% W, 5.6 wt% Al, e, j 15.7 wt% W, 6.2 wt% Al

Fig. 5 Segregation coefficient K of each element: a various W content, b various Al content

Table 2 Elemental contents of γ and γ′ phase with various W and Al contents (wt%)

Alloy	Phase	Cr	Co	Ni	W	Nb	Ti	Al
1	γ	5.502	8.668	57.082	19.536	0.96442	0.47696	4.518
1	γ′	4.234	8.28	66.286	14.48	0.9719	0.63394	5.974
2	γ	5.41	8.284	57.618	19.308	1.17252	0.55224	5.036
2	γ′	4.488	8.252	66.776	14.178	1.15288	0.70118	5.482
3	γ	5.876	9.192	58.132	19.478	0.84212	0.4409	4.484
3	γ′	4.348	8.57	65.018	15.51	0.98792	0.62198	5.978
4	γ	6.14	8.578	57.722	18.59	1.25692	0.5791	4.306
4	γ′	4.592	8.092	66.512	13.384	1.382	0.78684	5.52
5	γ	6.554	9.054	55.19	20.86	1.07384	0.52858	4.746
5	γʹ	4.708	8.506	64.356	15.372	1.17898	0.6793	6.632

Fig. 6 Tensile properties at room temperature: a various W content, b various Al content

Fig. 7 Overall and local morphologies of tensile fracture at room temperature of alloys with different W and Al contents: a, f 15.3 wt% W, 5.9 wt% Al, b, g 15.7 wt% W, 5.9 wt% Al, c, h 16.1 wt% W, 5.9 wt% Al, d, i 15.7 wt% W, 5.6 wt% Al, e, j 15.7 wt% W, 6.2 wt% Al

Fig. 8 Microstructure on longitudinal-section and stress distribution (KAM diagram) with various W and Al contents: a, f 15.3 wt% W, 5.9 wt% Al, b, g 15.7 wt% W, 5.9 wt% Al, c, h 16.1 wt% W, 5.9 wt% Al, d, i 15.7 wt% W, 5.6 wt% Al, e, j 15.7 wt% W, 6.2 wt% Al

Fig. 9 Stress rupture life: a various W contents, b various Al contents

Fig. 10 Longitudinal-section microstructures with different W and Al contents: a, f 15.3 wt% W, 5.9 wt% Al, b, g 15.7 wt% W, 5.9 wt% Al, c, h 16.1 wt% W, 5.9 wt% Al, d, i 15.7 wt% W, 5.6 wt% Al, e, j 15.7 wt% W, 6.2 wt% Al

Fig. 11 Dislocation and carbide morphologies of alloys with different W and Al contents after creep deformation: a 15.3 wt% W, 5.9 wt% Al, b 15.7 wt% W, 5.9 wt% Al, c 16.1 wt% W, 5.9 wt% Al, d, d1-3 diffraction spots and element distribution of M23C6 carbide at 16.1 wt% W, 5.9 wt% Al, e 15.7 wt% W, 5.6 wt% Al, f 15.7 wt% W, 6.2 wt% Al, g morphology and diffraction spots of M6C carbide at 15.7 wt% W, 6.2 wt% Al, h, h1-3 element distribution of MC and M6C carbide at 15.7 wt% W, 6.2 wt% Al

Fig. 12 Schematic illustration of the formation process of cracks: a when W, Al content is lower; b when W, Al content is higher

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