Hot deformation induced microstructure evolution of a novel as-extruded Ni-based P/M superalloy

ABSTRACT

Hot extrusion (HEX) and isothermal forging (ITF) are two critical processing methods in manufacturing of Ni-based powder metallurgy (P/M) superalloys. Hot compressions with different parameters were performed on a novel Ni-based P/M superalloy in as-extruded condition to simulate ITF and the related microstructure evolution. The results revealed that the as-extruded alloy was fully recrystallised with no preferred orientation, while hot deformation at relatively high strain rate could induce the formation of <101> texture. Low-angle grain boundaries were formed due to the rearrangement of deformation-induced dislocations. The existence of high-angle grain boundaries led to dislocation pile-ups and resultant local stress concentration. The grains were remarkably refined after hot deformation due to dynamic recrystallisation and corresponding reduction of average grain size varied from 20 to 67%. The average particle size of γ′ phases enlarged after hot deformation through an Ostwald ripening process and varied from ∼142.5 to ∼235.0 nm in different conditions while their initial sizes were ∼137.2 nm. The effect of strain rate on the particle size of γ′ phases was much greater than the deformation temperature that exhibited a stronger influence on their area fraction.

KEYWORDS:

• EBSD
• microstructure
• hot deformation
• grain size
• superalloy

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors acknowledge the financial supports by National Science and Technology Major Project [Grant number 2017-VI-0009-0080] and Key Area Research and Development Program of Guangdong Province [Grant number 2019B010935001].