Microstructure of heat-resistant nikel alloy after high-temperature heat treatment

DOI: 10.62564/M4-OV1448

Galina Maksimova, Oksana Vlasova, Mary Golovkova

Frantsevich Institute for Problems of Materials Science National Academy of Science of Ukraine


The aim of this work is to study the microstructure of heat-intensive aviation alloy Ni-Co-Al-Cr (GTE) before and after high temperature heat treatment (HTHT) in vacuum at temperature 1280 оС. The alloy GTE is a three-phase system consisting of a γ-solid solution based on nickel with an FCC crystal lattice, dispersion precipitates of the strengthening γ'-phase based on the intermetallic compound Ni3Al (not less than 60-62 vol.%) and monocarbides type MC based on alloying elements (Ta, Nb, W)C. During operation, the structure of the alloy is degraded with the formation of pores, cracks, a change in the crystallographic features of the gratings of the γ- and γ'- phases and their dimensional mismatch with the initial parameters. It was found that the alloy GTE has a dendritic-cellular microstructure with axes of dendrites of the first and second order between which there is an eutectic with precipitates of carbides of the composition (Ta, Nb, W)C, round and significantly elongated, and in the form of individual particles ranging in size from 1 to 25 μm and multiple pores 1-10 μm in size. After the HTHT, the γ'-phase cuboids typical of heat-resistant alloys GTE are formed, the ideality of the shape of which depends on the temperature and exposure at a given temperature. The hardening γ'-phase in the alloy after the HTHT has a different size and shape in the axes of the dendrite and in the interdendritic space. In the interdendritic space the particle size of the γ′-phase is approximately 1.5 to 2 times larger than the size of the γ′-phase in the dendrite body and is 0.2 - 0.8 μm. The thickness of the layer of γ-solid solution is 0.1-0.2 microns. Carbide precipitates of 1 μm and 5 μm in size are observed. In the area of carbide precipitates, the degeneracy of the structure and coagulation of particles of the γ′- phase are fixed. Thus, it was shown in the work that only by high-temperature heat treatment it is impossible to restore the microstructure of the heat-resistant nickel alloy GTE after operation.

Keywords
the heat-resistant nickel alloy, the microstructure, high-temperature heat treatment

Acknowledgments
Not provided

References
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