High strength and ductility achieved in friction stir processed Ni-Co based superalloy with fine grains and nanotwins. (20th April 2022)

• Record Type: Journal Article
• Authors: Wang, Miao; Huang, Xingwei; Xue, Peng; Wu, Shangquan; Cui, Chuanyong; Zhang, Qingchuan
• Is Part Of: Journal of materials science & technology. Volume 106(2022)
• Page Start: 162
• Page End: 172
• Publication Date: 2022-04-20
• Subjects: Superalloy -- Friction stir processing -- Grain refinement -- Nanotwins; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2021.06.082
• Languages: English
• ISSNs: 1005-0302

Abstract

Highlights: A high-strength and high-melting-point Ni-Co based superalloy (GH4068) was for the first time subjected to FSP. The yield strength of FSP samples increased to about 1.3 GPa (70% higher than the base material) with a negligible loss of ductility at RT. An excellent strength-ductility synergy was obtained at 400 °C, i.e., the yield strength and elongation of the FSP sample both were increased by more than 50% compared with the BM. The stresses contributed from the multimechanistic model was quantified to analyze the raised strength in the FSP sample. The combined effect of fine grains and nanotwins resulted in an excellent strength–ductility synergy. The microstructure of fine grains without primary γ′ was obtained. Abstract: The trade-off between strength and ductility has been an enormous difficulty in the field of materials for an extended time due to their inverse correlation. In this work, friction stir processing (FSP) was for the first time performed to high-strength and high-melting-point Ni-Co based superalloy (GH4068), and enhanced strength and ductility were achieved in FSP samples. At room temperature, the FSP sample demonstrated significantly higher yield strength and ultimate tensile strength (1290 and 1670 MPa) than that of the base material (BM, 758 and 904 MPa) and advanced wrought GH4068 alloy (982 and 1291 MPa), concurrent with high tensile ductility (∼24%). Compared with the BM, 70% higher yield strength of the FSP sample results from the remarkable contribution of grain-boundary and nanotwin strengthening, which has been confirmed by the multimechanistic model studied in this work. More importantly, with increasing temperature, an excellent strength-ductility synergy was obtained at 400 °C, i.e., the yield strength of the FSP sample was increased by more than 50% compared with the BM (from 789 to 1219 MPa); more interestingly, the elongation was also significantly increased from 17.9% in the BM to 28.5% in the FSP sample. Meanwhile, the Portevin-Le Chatelier effect was observed in the engineering stress-strain curve. The occurrence of this effect may be attributed to the interaction between solutes and defects like twins and mobile dislocations. Moreover, the grain refinement mechanism of FSP samples was proved to be discontinuous dynamic recrystallization. Graphical abstract: Image, graphical abstract