Article information

Article`s title

Nickel Alloys Structure and Properties Control by Deformation-Thermal Treatment in Solid State

Authors

V.A. Valitov 1

Volume

3 (2016)

Keywords

Deformation, microstructure, nanocrystalline, nickel alloys, phase, recrystallization, reeling, solid state welding, superplasticity.

Abstract

Systematic studies of a large number of nickel- and iron-nickel-based alloys have been done to find out optimum conditions for hot and severe plastic deformation, ensuring the transformation of the initial coarse-grain structure into the ultra- fine-grain structure with given parameters within micrometer, submicron and nanometer range. It has been shown that a controlled change in the parameters of the hardening phase, its relation to the matrix and modes of deformation-thermal treatment can control the processes of structure formation in precipitation-hardening nickel alloys due to a purposeful change in the existing mechanisms of deformation and recrystallization. The findings were used as a basis for developing a single methodological approach to obtaining bulk and sheet semi- finished products of nickel alloys with ultra-fine-grain and nanocrystalline duplex structures. The idea of the method was to carry out an intensive deformation-thermal treatment with stepwise temperature decrease from 0.9–0,8 Tpl to 0.6–0.5 Tpl. As a result of such treatment stepwise refining of the initial coarse-grained structure up to nanocrystalline structural state was achieved. It has been found that in precipitation-hardening alloys (γ′; γ′′+δ) with submicrocrystalline and nanocrystalline structures there occurs low-temperature superplasticity effect which manifests itself at temperatures 200–350 ºС lower than in materials with microduplex structure. Herein 1.5–2-fold decrease in the flow stress and 1–1.5-order increase in the deformation rate is achieved. The correlation between the phase composition and the type of hardening of heterophased nickel alloys with thermal stability of submicrocrystalline and nanocrystalline structures was revealed. The efficiency of the use of semi-finished products with a prepared ultra-fine-grain structure for producing precise complex geometry parts with homogeneous structure and high complex of mechanical properties obtained by the methods of volumetric and local forming and further standard thermal treatment was proved. There was proposed a method of molding under superplastic conditions which allows producing parts such as aircraft engine disks from the ultra-fine-grain workpieces with a structure regulated by varying the radius, which provides a high complex of properties, optimized to the actual conditions of their use. Using precipitation hardening nickel alloy such as Inconel 718 as an example, it was shown that the formation of submicrocrystalline structure in workpieces enables realization of the effect of low temperature superplasticity in promising technological processes of pressure welding and pneumoforming.

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DOI:

https://doi.org/10.17277/amt.2016.03.pp.021-031

🗏

021-031

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