Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

High-Temperature Deformation of Inconel 718PlusTM

[+] Author and Article Information
Utkudeniz Ozturk

Polytechnic University of Catalonia,
Av. Diagonal, 647,
Barcelona 08028, Spain
e-mail: utkudeniz.ozturk@upc.edu

Jose Maria Cabrera, Jessica Calvo

Centre Tecnologic Manresa (CTM),
Plaza de la Ciencia, 2, Manresa,
Barcelona 08242, Spain;
Polytechnic University of Catalonia,
Av. Diagonal, 647,
Barcelona 08028, Spain

1Corresponding author.

Contributed by the Manufacturing Materials and Metallurgy Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 20, 2016; final manuscript received July 27, 2016; published online October 11, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(3), 032101 (Oct 11, 2016) (7 pages) Paper No: GTP-16-1243; doi: 10.1115/1.4034539 History: Received June 20, 2016; Revised July 27, 2016

Since its introduction in 2003, alloy 718PlusTM spurred a lot of interest owing to its increased maximum service temperature over conventional Inconel 718 (704 °C versus 650 °C), good formability, and weldability together with its moderate cost. Understanding the high-temperature deformation characteristics and microstructural evolution is still of interest to many. It is known that the service performance and hot-flow behavior of this alloy are a strong function of the microstructure, particularly the grain size. To develop precise microstructure evolution models and foresee the final microstructure, it is important to understand how and under which forming conditions softening and precipitation processes occur concurrently. In this work, the softening behavior, its mechanisms, and the precipitation characteristics of 718PlusTM were investigated in two parallel studies. While cylindrical compression tests were employed to observe the hot-flow behavior, the precipitation behavior and other microstructural phenomena such as particle coarsening were tracked via hardness measurements. A precipitation–temperature–time (PTT) diagram was reported, and modeling of the flow curves via hyperbolic sine model was discussed in the light of the PTT behavior. Both “apparent” approach and “physically based” approach are implemented and two different sets of parameters were reported for the latter. Finally, recovery and recrystallization kinetics are described via Estrin–Mecking and Bergstrom, and Avrami kinetics, respectively.

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Fig. 1

Experimentally determined TTT diagram of alloy 718PlusTM [6]

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Fig. 2

Raw data, smoothing, and polynomial fitting

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Fig. 3

Temperature variation during 1000 °C tests for different strains

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Fig. 4

PTT diagram of 718PlusTM. Red line denotes 245 HV limit.

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Fig. 5

Selected flow curves

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Fig. 6

Experimentally determined TTT diagram of 718PlusTM showing only δ precipitation [11]

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Fig. 7

(a)–(g) Plots that are used to retrieve material constants of apparent approach, (h) plot to determine α′ and B in physically based approach, and (i) comparison of resulting peak stresses with the experimental values

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Fig. 8

Softening and hardening parameters versus Zener–Hollomon parameter

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Fig. 9

Curves used to determine the DRX kinetics. Top to bottom: 950 °C, 1000 °C, and 1050 °C.

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Fig. 10

Dependence of K on Zener–Hollomon parameter




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