Effect of Ta on Tensile Behavior and Deformation Mechanism of a Nickel-Based Single Crystal Superalloy

doi:10.1007/s40195-024-01753-6

Abstract

Abstract:

The effects of Ta on the tensile behavior and deformation mechanisms of a Ni-based single crystal superalloy were investigated in this study from room temperature to elevated temperature. The findings demonstrated that the higher content of Ta could improve the tensile properties of the alloy at different temperatures. Due to the different deformation mechanisms at various temperatures, the influence of Ta on tensile deformation varied. At room temperature, the higher content of Ta enhanced the solid solution strengthening, which would enhance the tensile strength of 6.5Ta alloy. After standard heat treatment of 6.5Ta alloy, precipitation of the secondary γʹ phase would hinder the movement of dislocations. When the temperature was elevated to 760 °C, the higher content of Ta not only promoted the interaction of stacking faults to form Lomer-Cottrell (L-C) locks that impeded dislocation motion, but also reduced the occurrence of dislocation pile-up groups, thus enhancing the yield strength. At 1120 °C, due to the narrower γ channels and higher APB energy in γʹ phase of the alloy with higher Ta addition, the processes of bypassing and shearing of dislocations were hindered, respectively. Meanwhile, the denser and more regular dislocation networks were formed in 6.5Ta alloy; and thus, the tensile strength of 6.5Ta alloy was enhanced. This study systematically investigated the effect of Ta on the tensile behavior at three different temperatures, which provided an important theoretical basis for the design of nickel-based single crystal superalloys in the future.

Key words: Ta, Single crystal superalloy, Tensile behavior, Stacking fault, Deformation mechanism

Mingtao Ge, Xinguang Wang, Yongmei Li, Zihao Tan, Xipeng Tao, Yanhong Yang, Liang Wang, Chunhua Zhang, Song Zhang, Yizhou Zhou, Xiaofeng Sun. Effect of Ta on Tensile Behavior and Deformation Mechanism of a Nickel-Based Single Crystal Superalloy[J]. Acta Metallurgica Sinica (English Letters), 2024, 37(11): 1921-1934.

Figures/Tables 15

Fig. 1 Content of Ta element in different generations of nickel-based SX superalloys

Table 1 Nominal compositions of the two experimental SX superalloys (wt%)

Alloy	Cr	Co + W + Mo	Re	Al	Ta	Ni
5.5Ta	4.6	18.0	3	5.9	5.5	Bal.
6.5Ta	4.6	18.0	3	5.9	6.5	Bal.

Table 2 Standard heat treatment procedures of the two experimental SX superalloys

Alloy	Standard heat treatment procedures
5.5Ta	1308 °C/1 h + 1313 °C/3 h + 1323 °C/4 h, air cooling (AC) → 1100 °C/6 h, AC → 870 °C/24 h, AC
6.5Ta	1313 °C/1 h + 1318 °C/3 h + 1328 °C/4 h, air cooling (AC) → 1100 °C/6 h, AC → 870 °C/24 h, AC

Fig. 2 Microstructures of γ and γ′ phase in a-c 5.5Ta alloy and d-f 6.5Ta alloy after standard heat treatment: a, d SEM images of the experimental alloys, b, e size distribution of γ′ phase and c, f Feret ratio (λ) of γ′ phase

Fig. 3 Tensile engineering stress-strain curves of a 5.5Ta alloy and b 6.5Ta alloy at different temperatures

Fig. 4 Tensile properties of two experimental alloys: a yield strength, b elongation

Fig. 5 Fracture surfaces of a-c 5.5Ta alloy and d-f 6.5Ta alloy at different temperatures: a, d RT, b, e 760 °C, c, f 1120 °C. Inset-fracture features at higher magnification

Fig. 6 TEM micrographs of the deformation microstructure of two experimental a 5.5Ta alloy, b 6.5Ta alloy after tensile fracture at RT. c Schematic illustration of the possible formation of stacking faults and dislocations pairs in γʹ phase

Fig. 7 TEM micrographs of the deformation microstructure of two experimental a 5.5Ta alloy, b 6.5Ta alloy after tensile fracture at 760 °C

Fig. 8 TEM micrographs of the deformation microstructure, dislocation networks and the spacing of dislocation networks in two alloys: a-c 5.5Ta alloy and d-f 6.5Ta alloy

Fig. 9 Width of the stacking faults in two alloys at RT: a 5.5Ta alloy and b 6.5Ta alloy

Fig. 10 Elemental partitioning coefficients between the γ and γʹ phase. $K^{\prime } = C_{i}^{\gamma } /C_{i}^{{\gamma^{\prime } }}$ was defined as the ratio of the elements in the γ phase to the γʹ phase. The elements preferentially segregated to the γ′ phase, with $K_{i}^{{\gamma /\gamma^{\prime } }}$ < 1. Conversely, the elements segregated to the γ phase, with $K_{i}^{{\gamma /\gamma^{\prime } }}$ > 1

Fig. 11 Secondary γʹ phase in the deformation microstructure of 6.5Ta alloy: a TEM-EDS mapping results of secondary γʹ phase, b the effect of secondary γʹ phase on tensile properties of alloys at RT

Fig. 12 Specific morphologies and formation mechanisms of a, b Type A and c, d Type B L-C locks in the deformed microstructure after tensile at 760 °C

Fig. 13 Width of γ channel in two different experimental alloys after tensile test at 1120 °C: a, b 5.5Ta alloy; c, d 6.5Ta alloy

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