P. Zhang¹*, Y. Yuan¹*, J. Li², P. Liu¹, Z. H. Gao³, X.F. Gong³, Y.F. Gu¹*

¹ Xi’an Thermal Power Research Institute Co., Ltd., ² Xi’an Jiaotong University, ³ Dongfang Turbine Co., Ltd.

*pengzhangnas@163.com; yuanyong@tpri.com.cn; guyuefeng@tpri.com.cn

As the basic mechanical properties, the tensile/compressive properties and corresponding deformation mechanisms of SC nickel-based superalloys have been widely investigated in the past. These studies disclosed that that dislocation climb dominated the plastic deformation at the beginning of plastic deformation, and then shearing of γ′ precipitates by pairs of a/2<101> dislocations might operate actively in the later stage of plastic deformation at high temperatures (above 950 °C, depending on the alloy composition)[1-4]. Whereas, recently, we found that apart from the above two deformation modes, shearing of γ′ precipitates by a<001> dislocations and stacking fault shearing as well as especially microtwinning occurred in the [001]-oriented SC nickel-based superalloy CMSX-4 during compressive deformation at 1000 °C [5]. It is widely reported that the operative deformation mechanisms are intimately associated with the chemical compositions of the alloys [1-4]. Then, a question arises as to whether the operation of the three deformation modes is an isolated finding in CMSX-4 or is prevalent in SC nickel-based superalloys during compressive deformation at high temperatures.

Figure 1. (a)-(h) TEM images showing the microstructures in the alloy CM247LC and other three [001]-oriented SC nickel-based superalloys René N5, DESC-1 and PWA1483 and before((a)-(d)) and after((e)-(h)) compressive deformation at 1000 °C and a strain rate of 2.5×10-4 s-1: (a) and (e), CM247LC; (b) and (f), René N5; (c) and (g), DESC-1; (d) and (h) PWA1483; the arrowheads indicate the spots of microtwins; (i) engineering stress-strain curves of the four alloys at 1000 °C.

Thus, in this study, deformation mechanisms in three [001]-oriented SC nickel-based superalloys PWA1483, René N5, DESC-1(a new designed alloy) and the directionally solidified nickel-based superalloy CM247LC have been studied in compression at 1000 °C and a strain rate of 2.5×10-4 s-1. We found that the yield strength of the four alloys, together with that of CMSX-4, are in order: PWA1483<CM247LC<DFSC-1<CMSX-4<René N5. After around 2.0% plastic strain, the deformation microstructures in the four alloys are investigated using transmission electron microscopy. It is interesting to find that stacking fault shearing and microtwinning control the plastic deformation of PWA1483 and DFSC-1, whereas plastic deformation of René N5 and CM247LC is accomplished mainly by dislocation climb together with shearing of γ′ precipitates by pairs of a/2<101> dislocations with the equal and dissimilar Burger vectors, though the above two processes also take place frequently in René N5. Thus, our study provides new insights into understanding the deformation mechanisms in nickel-based superalloys. Finally, based on the experimental observations, the relationship between the strength and operative deformation mechanism is discussed.

References

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[2] M. Feller-Kniepmeier, T. Link, I. Poschmann, et al: Acta Mater., 1996, vol. 44, pp. 2397-2407.

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[5] P. Zhang, Y. Yuan, J. Li, et al: Metall. Mater. Trans. A, 2022, vol. 53, pp. 388-397.