Effect of thermomechanical treatment on the microstructure and mechanical properties of a novel heavily alloyed nickel base superalloy

V.M. Imayev, S.K. Mukhtarov, A.V. Logunov, A.A. Ganeev ORCID logo , R.V. Shakhov, R.M. Imayev show affiliations and emails
Received 03 April 2019; Accepted 07 May 2019;
This paper is written in Russian
Citation: V.M. Imayev, S.K. Mukhtarov, A.V. Logunov, A.A. Ganeev, R.V. Shakhov, R.M. Imayev. Effect of thermomechanical treatment on the microstructure and mechanical properties of a novel heavily alloyed nickel base superalloy. Lett. Mater., 2019, 9(2) 249-254
BibTex   https://doi.org/10.22226/2410-3535-2019-2-249-254

Abstract

EBSD orientation map and corresponding misorientation-angle distribution for grain boundaries obtained for the superalloy after thermomechanical treatment and ageing (HABs – high-angle grain boundaries). Such microstructure was attained in the most part of the workpiece.The work has been devoted to study of microstructure and mechanical properties of a novel heavily alloyed heat resistant nickel base superalloy in the cast and heat treated condition and the thermomechanically treated (TMT) condition. The cast condition after heat treatment including homogenization annealing, solid solution treatment and ageing was characterized by a coarse γ grain size and uniformly distributed dispersed γ' precipitates with a size of dγ' = 0.1– 0.25 μm. It was established that TMT under optimal conditions led to development of recrystallization processes, which provided formation of refined recrystallized microstructure with a γ grain size of dγ = 2 – 60 μm. The obtained microstructure condition contained mostly dispersed γ' precipitates with a size of dγ' = 0.1– 0.3 μm. The volume fraction of relatively coarse γ' particles, which were not dissolved during TMT, was about 10 %. The TMT condition was aged in the same manner as the cast condition. Tensile tests and long-term strength tests were performed for the both superalloy conditions. The strength properties in the TMT condition were found by 30 – 50 % higher than those obtained in the cast and heat treated condition. At the same time, the ductility in the TMT condition was found also significantly higher than in the cast and heat treated condition. The following tensile properties were obtained for instance at room temperature: σUTS / σ0.2 =1802 / 1355 MPa and δ =16 % for the TMT and aged condition, and σUTS / σ0.2 =1255 / 1132 MPa and δ = 8.5 % for the cast and heat treated condition. The long-term strength at 650°C in the TMT and aged condition was found also to be significantly higher than that in the cast and heat treated condition. Excellent mechanical properties of the superalloy after TMT are explained in terms of the increased amount of the γ' phase, the effective solid solution strengthening due to heavy alloying with refractory metals and the refined microstructure obtained after TMT.

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Funding

1. Russian Science Foundation - Grant No. № 18-19-00594