Microstructural evolution and tensile property of 1Cr15Ni36W3Ti superalloy during thermal exposure

doi:10.1016/j.jmst.2020.09.035

Abstract

Abstract:

1Cr15Ni36W3Ti was thermally exposed at 580 ℃ and 680 ℃, respectively, up to 3000 h. The γ’ phase and intergranular TiC carbides continuously coarsened during exposure. None of η, laves or σ phase was discovered in the exposed samples, indicating good microstructure stability under the present exposure conditions. The ripening process of the γ’ phase could be well modelled utilizing the LSW theory. The evolutions of the yield and tensile strengths were monotonous during exposure at 580 ℃. However, a transition point in strengths was detected in the tensile samples exposed at 680 ℃ for 300 h. Accordingly, the critical γ’ diameter was measured to be 13-14 nm. The γ’/dislocations interaction mechanism transformed from shearing to looping with the γ’ diameter exceeding the critical point. The combination of the weakly coupled dislocations model and the Orowan looping model yielded a critical diameter of 13.1 nm which coincided well with the measured one, indicating the applicability of these two strengthening models for 1Cr15Ni36W3Ti. The present exposure conditions did not exert a profound effect on the fracture mode. All the tensile samples underwent a typically ductile fracture with a dimple pattern dominating the fracture surface. The dispersed deformation induced by the prevalence of dislocation looping in the over-aged tensile samples retarded the propagation of intergranular cracks. The declined precipitation hardening increment and the enhanced deformation homogeneity partially recovered the tensile ductility in the over-aged samples exposed at 680 ℃.

Key words: Superalloy, γ' Phase, Thermal exposure, Microstructure, Tensile property, Fracture

Haoze Li, Ming Gao, Min Li, Yingche Ma, Kui Liu. Microstructural evolution and tensile property of 1Cr15Ni36W3Ti superalloy during thermal exposure[J]. J. Mater. Sci. Technol., 2021, 73: 193-204.

Figures/Tables 15

Fig. 1. Equilibrium phase constitution of the experimental alloy calculated as a function of temperature utilizing the Thermo-Calc software.

Fig. 2. EPMA elemental mappings of the interdendritic phase in the casting material.

Fig. 3. OM images of the hot rolling (a) and solution treated (b) microstructures.

Fig. 4. BF images showing the (a) intragranular and (b) intergranular microstructures of the experimental alloy after the two-stage aging treatment; (c) SADP detected under [011] zone axis of the secondary TiC carbide.

Fig. 5. TEM images showing the (right) intragranular and (middle) intergranular microstructures of the experimental alloy after thermal exposure at 580 ℃ for (a), (b) 100 h, (d), (e) 600 h and (g), (h) 3000 h, respectively; (c), (f) and (i) are the SADPs captured under the low-indexed zone axis of the secondary TiC carbides.

Fig. 6. TEM images showing the (right) intragranular and (middle) intergranular microstructures of the experimental alloy after thermal exposure at 680 ℃ for (a), (b) 100 h, (d), (e) 600 h and (g), (h) 3000 h, respectively; (c), (f) and (i) are the SADPs captured under the low-indexed zone axis of the secondary TiC carbides.

Fig. 7. Plots of the (a) average diameter and (b) area fraction of the γ’ phase vs. thermal exposure time at 580 ℃ and 680 ℃.

Fig. 8. LSW analysis of the γ’ coarsening processes during exposure at 580 ℃ and 680 ℃.

Fig. 9. Evolution of the room-temperature tensile properties during thermal exposure at 580 ℃ and 680 ℃.

Table 1 Input parameters used to calculate the CRSS increments based on various precipitation hardening models.

f (%)	ε (%)	b (Å)	G (GPa)	γ_APB (J/m²)	A	W
13.5	0.563	2.53	76.58	0.55	0.72	1

Fig. 10. Calculations of CRSS increments vs. γ’ diameter based on various precipitation hardening mechanisms.

Fig. 11. TEM images showing the intragranular microstructures of the partially deformed tensile specimens under different conditions: (a) heat-treated states; (b) 580 ℃/100 h; (c) 580 ℃/3000 h; (d) 680 ℃/100 h; (e) 680 ℃/300 h; (f) 680 ℃/3000 h.

Fig. 12. SEM images showing the (Top) fracture surfaces and the (bottom) correspondingly longitudinal microstructures of the tensile specimens under different conditions: (a), (c) heat treated state; (b), (d) 580 ℃/3000 h.

Fig. 13. SEM images showing the (Top) fracture surfaces and the (bottom) correspondingly longitudinal microstructures of the tensile specimens after thermal exposure at 680 ℃ for (a), (d) 100 h, (b), (e) 300 h and (c), (f) 3000 h.

Fig. 14. TEM images showing the intergranular microstructures of the partially deformed tensile specimens under different thermal exposure conditions: (a) 580 ℃/100 h; (b) 580 ℃/3000 h; (c) 680 ℃/300 h; (d) 680 ℃/3000 h.

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