Effect of hot working on the microstructure and tensile properties of a novel PM Re-bearing nickel base superalloy

Abstract

The work is devoted to study of an experimental PM nickel-based superalloy Ni-16(Al, Ti, Nb, Ta)-30(Cr, Co, Mo, Hf, W, Re) (wt.%). The initial as-HIP' ed material was prepared as cylinders with a size of ∅100 × 200 mm. The hot workability of the superalloy was evaluated by compression tests of small samples under isothermal conditions. The tests were performed at temperatures of 1150 -1240°C with a strain rate of έ =10 −4 -10 −1 s −1 . Some samples were subjected to preliminary homogenization annealing. Examination of the deformed samples by SEM made it possible to define the hot working conditions providing development of recrystallization processes and formation of a uniform fine-grained structure. It was established that preliminary homogenization of as-HIP' ed material followed by fractional forging with intermediate recrystallization annealings in the temperature range of (T s − 40) -(T s −15), where T s is the γ' solvus temperature, provided a uniform development of recrystallization. The obtained forgings were subjected to ageing or solid solution treatment and ageing. In the fine-grained condition obtained by hot working and heat treatment, the material exhibited tensile properties comparable to the best properties achievable in disc nickel-based superalloys.

The Effect of Forging and Heat Treatment Variables on Microstructure and Mechanical Properties of a Re-Bearing Powder-Metallurgy Nickel Base Superalloy

“…Carbide particles with a size of 1-8 µm were observed. The volume fractions of the γ phase and carbide particles were defined as about 75% and not more than 1%, respectively [8]. Unfavorable TCP phases were not detected.…”

“…As a result, sound forgings with a size of about Ø80 mm × 10 mm were obtained. Note that the forging procedure was earlier developed on the basis of compression tests of superalloy samples at subsolvus temperatures [8].…”

“…The alloy composition measured by energy dispersive X-Ray (EDS) analysis was very close to the nominal composition. The γ solvus temperature (T s ) defined via quenching experiments from temperatures 1200 • C to 1250 • C was defined as T s ≈ 1240 ± 5 • C [8].…”

“…In particular, ever-increasing demands are being placed on nickel base superalloys, which are widely used for the manufacturing of rotary engine parts such as high-pressure discs in GTE [2,3]. For this purpose, experimental heavily alloyed disc superalloys doped with Re have been recently designed [4][5][6][7][8]. Rhenium is known to be a quite unique alloying element regarding nickel base superalloys.…”

“…It is known that it is typically found in the matrix γ phase, providing significant solid solution hardening and slowing down diffusion processes in the γ phase and at interphase boundaries, contributing to an increase in the strength and creep resistance of superalloy [9][10][11]. Rhenium is now added both to powder-metallurgy (PM) [6][7][8] and ingot-metallurgy (IM) [4,5] superalloys. In our previous works, the effect of forging and heat treatment variables on microstructure evolution and mechanical properties has been studied for an IM Re-bearing nickel base superalloy SDZhS-15 [4,5].…”