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Analysis of thickness variation and stress state in hydroforming of complex T-shaped tubular part of nickel-based superalloy

Cui Xiao-Lei, Yuan Shijian

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

458--471

EN

Stress states on a multi-branch tubular part are the most complicated change in all types of hydroforming process, which result in severe variation of thickness. In this paper, an experimental and numerical research was conducted on a multi-step hydroforming process including intermediate annealing treatment to obtain effect of stress state on the thickness variation of a superalloy GH4169 complex T-shaped tubular part with expanded diameter, which corresponds to a real product used in aerospace industry. The material flow behavior at typical points on hydroformed tube blank was first analyzed. Then, the thickness variation on the hydroformed GH4169 tube blanks was discussed in every step. It is shown that the materials have different flow directions to form the side branch, where the thickness is always thinned during the four-step hydroforming process. Large axial feeding induces a continuous thickening between transition areas and tube ends. The thickness invariant dividing line in the side branch zone moves toward the tube ends with forming going on. However, in the hemisphere zone, it moves slightly towards the center of the side branch. Moreover, the stress states at three typical positions, as well as their effect on the thickness variation, were analyzed based on a sequential correspondence law between stress and strain components. On this basis, the mechanism of thickening in the left transition area, thinning at the top of side branch and thickness variation at the hemispheric pole was revealed. These results are very important for obtaining the thickness distribution of a complex T-shaped tubular part in multi-step hydroforming, and revealing the thickness variation mechanism by using engineering plasticity theory.

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Phase Transformations in Nickel base Superalloy Inconel 718 during Cyclic Loading at High Temperature

Jambor M., Bokuvka O., Novy F., Trsko L., Belan J.

Production Engineering Archives

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2017

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Vol. 15

15--18

EN

Nickel base superalloys are hi-tech materials intended for high temperature applications. This property owns a complex microstructure formed by matrix of Ni and variety of precipitates. The type, form and the amount of these phases significantly affect the resulting properties of these alloys. At sufficiently long exposure to high temperatures, the transformation phase can occur, which can lead to degradation of properties of these alloys. A cyclic plastic deformation can accelerate these changes, and they could occur at significantly lower temperatures or in shorter time of exposure. The aim of this study is to describe phase transformation, which can occur by a cyclic plastic deformation at high temperatures in nickel base superalloy Inconel 718.

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Fractography analysis of Inconel 718 fatigued at 700°C

Jambor M., Belan J., Bokuvka O., Novy F.

Production Engineering Archives

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2016

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Vol. 13, No. 4

20--25

EN

This work deals with the fractography analysis of nickel-base superalloy Inconel 718 fatigued at 700°C in air atmosphere in the high cycle region. During cyclic loading of this alloy at high temperatures some different mechanisms compared to cyclic loading at ambient temperature take place. Cyclic plastic deformation at high temperatures causes some structural changes, which could have some influence.