Superalloys 2024: General Session 8: Disk Alloy Manufacture
Program Organizers: Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346

Wednesday 11:20 AM
September 11, 2024
Room: Exhibit Hall
Location: Seven Springs Mountain Resort

Session Chair: Satoshi Utada, National Institute for Materials Science; Sammy Tin, University of Arizona

11:20 AM
Methods for Characterising Oxide Inclusions & Porosity in Powder Ni Alloys for Disc Rotor Applications: Mark Hardy¹; ¹Rolls-Royce Plc
    Oxide inclusions and porosity are present in nickel alloys that are made using powder metallurgy. Both features can nucleate fatigue cracks. Surface oxide inclusions can significantly reduce fatigue lives. This is evident if lives are compared to those for crystallographic cracks that develop from slip bands, which are characterized by facets on fracture surfaces. Pores mainly occur from trapped gas in powder particles, whereas inclusions typically arise from melting the alloy and from powder manufacture. Since most inclusions are too small to be detected from ultrasonic inspection, probabilistic lifing assessment is required to ensure the risk of failure from “melt anomalies” in disk rotors is acceptably low. Such calculations apply a mathematical description of inclusion size and frequency. This paper examines methods for characterizing size and frequency of oxide inclusions and porosity from powder and billet material, which includes material that contains oxide inclusions or “seeds” that were added intentionally to understand fatigue behavior. Large bar tensile (LBT) testing of billet material was found to be the most capable method for characterizing inclusion size. However, rate of occurrence information cannot be measured directly; it must be implied by fitting inclusion size data to probability functions. Given uncertainties with this approach, a method has been devised to measure rate of occurrence directly. Inspections of polished surfaces of billet material have been shown to be viable for production use. Porosity of a coarse powder fraction has been characterized by mounting powder in resin so that automated image capture and analyses could be undertaken on polished surfaces. Finally, the sizes of the very low frequency of larger inclusions, which are detected by ultrasonic inspection of billet, have been characterized from electron microscopy on polished surfaces.

11:45 AM
Effect of Strain Rate on Dynamic Recrystallization of a Typical γ-γ’ Nickel-Based Superalloy with Initial Bimodal Precipitation: Federico Orlacchio¹; Daniel Pino Munoz²; Madeleine Bignon²; Chi-Toan Nguyen¹; Ilusca Soares Janeiro²; Marc Bernacki²; Nathalie Bozzolo²; ¹SAFRAN; ²MINES ParisTech PSL -Research University, CEMEF - Centre de Mise en Forme des Matériaux, CNRS UMR 7635
    The effect of strain rate on microstructure evolution of a γ-γ' nickel-based superalloy during hot deformation has been examined in this study. The experiments were conducted below the γ'-phase solvus temperature, at 1050 °C with various strain rates (10^-1, 10^-2 and 10^-3 S^-1) up to different macroscopic strain level (0.2, 0.8 and 1.3). An inverse effect of strain rate on dynamic recrystallization has been observed with an increase in the recrystallized fraction as strain rate increases, for a fixed macroscopic strain level. Scanning electron microscope and electron backscattered diffraction analysis were employed to investigate the deformed microstructures in terms of γ phase evolution and γ' precipitation state. A constant average size value of recrystallized grains at 1 μm is obtained for all tested conditions, suggesting that nucleation of new dynamically recrystallized grains is favored at the expense of the growth of recrystallized grains during hot deformation, which is inhibited. Furthermore, the complete absence of fine γ' precipitation within dynamically recrystallized grains, reveals a strong interaction between the progress of recrystallization front and the presence of fine γ' precipitates.

12:10 PM
Precipitation of γ′ in Two γ-γ′ Ni-based Superalloys During the Solvus Transition Stage of Ingot to Billet Conversion; Effects on γ Grain Structure and Implications for Open Die Forging: Angus Coyne-Grell¹; Marcos Pérez¹; Ioannis Violatos¹; Jérôme Blaizot²; Christian Dumont²; Sebastien Nouveau²; ¹University of Strathclyde; ²Aubert et Duval
    UdimetŽ720Li and AD730ŽUDIMET is a registered trademark of Special Metals Corporation. AD730 is a registered trademark of Aubert & Duval are γ-γ' Ni-based superalloys manufactured through casting and wrought processing, i.e. using ingot-to-billet conversion. These alloys are intended for use in safety critical aeroengine components, and there are strict requirements on the microstructural characteristics they must achieve at the end of the conversion process. Conventional ingot-to-billet conversion is an expensive and complex process, requiring multiple open-die forging operations and reheating steps to achieve a homogeneous microstructure. A main goal of this conversion process is to refine the as-cast grain structure, which comprises grains centimetres in size, down to a grain size of approximately 20 ěm. The present work studies the microstructural evolution of Udimet 720Li and AD730 billet material at the “solvus transition” stage of the conversion process, i.e. the controlled cooling through the solvus temperature. The formation of γ' prime precipitates during controlled cooling from supersolvus temperatures, and their interaction with the grain structure is the focus of this work. It is shown that the size and morphology of the grains in both alloys are significantly affected by discontinuous precipitation during cooling through the solvus temperature, and a method to exploit this during industrial ingot-to-billet conversion is suggested.

12:35 PM
Full-field Microstructure Modeling During Forging a Polycrystalline γ-γ’ Nickel-based Superalloy: Chi-Toan Nguyen¹; Daniel Galy¹; Jean-Michel Franchet¹; Jérôme Blaizot²; Christian Dumont²; Lucie Le Saché¹; Julien de Jaeger¹; Baptiste Flipon³; Nathalie Bozzolo³; Marc Bernacki³; ¹Safran; ²Aubert & Duval; ³CEMEF
    The present paper demonstrates great capability of the full-field finite element DIGIMUŽ software included recrystallization models to simulate the microstructure evolution during forging an industrial part in René 65, a γ-γ' nickel-based superalloy. The macroscopic forging conditions simulated by the finite element FORGEŽ software were used as the thermo-mechanical inputs of the microstructure simulations in the DIGIMUŽ software. The recrystallization models in the DIGIMUŽ software were calibrated from torsion tests on laboratory-scale samples at sub-solvus and super-solvus temperatures from 1000 °C to 1150 °C and at strain rates ranging from 10^-2 to 0.75 s^-1. The calibrated model is able to predict, correctly, the mean and distribution of grain sizes in different deformation conditions of laboratory-scale samples and, more importantly, for eight different positions of interest in an industrial part forged by multiple operations at sub-solvus temperatures and followed by a solution heat treatment. The differences between the predicted and experimental average grain sizes are in the range of 0.5 to 1.0 ASTM (which is around 1.5 to 3.0ľm difference when comparing to the experimental grain size of 10 ASTM ~ 11ľm). The model will help with understanding and optimizing of forging processes to achieve desirable microstructures and, in turn, the mechanical properties of aircraft engine forged components.