Deformation and Damage Mechanisms of High Temperature Alloys: Microstructural Evolution during Material Processing
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee
Program Organizers: Mark Hardy, Rolls-Royce Plc; Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346; Jeremy Rame, Naarea; Akane Suzuki, GE Aerospace Research; Jean-Charles Stinville, University of California, Santa Barbara; Paraskevas Kontis, Norwegian University of Science and Technology; Andrew Wessman, University of Arizona

Monday 8:30 AM
February 28, 2022
Room: 304B
Location: Anaheim Convention Center

Session Chair: Mark Hardy, Rolls-Royce plc; Akane Suzuki, GE Research

8:30 AM  Invited
Influence of Gamma’ Precipitates on Recrystallization and Grain Growth Phenomena in Ni Based Superalloys : Smith-Zener Pinning and So Much More: Nathalie Bozzolo1; 1MINES-ParisTech
    Due to the rapid evolution of the γ’ phase during forging operations and the strong coupling with recrystallization phenomena, grain size control of wrought γ-γ’ nickel-based superalloys is by far more complex than it is for other alloys such as Inconel 718. A number of specific phenomena observed in different γ-γ’ alloys will be presented, including heteroepitaxial recrystallization and the dissolution and re-precipitation mechanisms that accompany the migration of a recrystallization front and possibly lead to the formation of twin related precipitates. The mechanisms to be modelled to build up a predictive simulation tool for γ-γ’ alloys of course also include the classical Smith Zener pinning phenomenon. The later indeed controls the grain size evolution during solution treatment with no stored energy at play, but the latter is, by far, not the only one that has to be considered to cover a complete forging route.

9:00 AM  
Forging and Heat Treatment Conditions that Produce Visible Grains in a Nickel Alloy: Mark Hardy1; Ross Buckingham1; Kevin Severs2; Christos Argyrakis1; Sammy Tin3; 1Rolls-Royce Plc; 2ATI Forged Products Cudahy; 3University of Arizona
    Experiments were undertaken to understand forging and heat treatment conditions that give rise to large, visible grains in a nickel alloy after super-solvus heat treatment. Such grains are undesirable as they can reduce material properties. The information from experiments is required to design a forging practice to manufacture closed die forgings. The alloy is a development composition, which contains about 51 % gamma prime and has been produced by powder metallurgy. Compression tests were conducted to specified upsets on right circular cylinder and double cone test pieces. Segments of these were heat treated and examined to characterise grain size. The results of these experiments are understood having reviewed billet microstructure, the results of process simulations, and the results of electron backscattered diffraction on forged material.

9:20 AM  Invited
Precipitate Free Zone Formation in an Alumina-forming Austenitic Stainless Steel and the Effect on Mechanical Properties: Andrew Peterson1; Ian Baker1; 1Dartmouth College
    Alumina-forming austenitic stainless steels (AFAs) are a class of iron-based alloys being studied for use in high temperature applications, many of which are strengthened by nano-sized L12-structured precipitates. However, a L12 precipitate free zone (PFZ) can form along grain boundaries (GBs) at long creep times, which will likely have a negative effect on the creep strength. In this study, the formation mechanism and growth of L12 PFZs during creep in the AFA Fe-20Cr-30Ni-2Nb-5Al were studied using electron microscopy and energy dispersive x-ray spectroscopy. The PFZ formation and growth is due to the dissolution of L12 precipitates because of depletion of nickel and aluminum near larger Laves phase and B2-structured precipitates covering the GBs. Micro-cracks observed in the PFZ at long creep times suggest that fracture initiates in the PFZ, ultimately compromising the creep strength of the alloy. This research was supported by National Science Foundation Grant DMR 1708091.

9:50 AM Break

10:10 AM  
Precipitate Free Zones (PFZ) Formation at Grain Boundaries in γ/γ Ni-based Superalloys: Guillaume Burlot1; Jonathan Cormier1; Anne Joulain1; Dominique Eyidi1; Patrick Villechaise1; 1Institut Pprime
    Formation and growth of secondary γ' precipitate free zones (PFZ) in the vicinity of grain boundaries in five superalloys has been investigated for different heat treatment times and temperatures. It has been shown that PFZ mainly form during close-to- γ'-solvus heat treatments and are associated to the precipitation of intergranular γ' precipitates.Since these precipitates have similar chemical composition to intragranular secondary γ', depletions on precipitate-former elements could lead to the dissolution of secondary γ' near the grain boundaries and finally to the formation of PFZ. PFZs width evolutions have been described using a parabolic evolution and their kinetics obey an Arrhenius-type law indicating a diffusion-controlled process.The influences of the grain size, the presence of intergranular particles and the composition of the alloys were also investigated, as well as the influence of PFZ on tensile properties.

10:30 AM  
Preferential Precipitation of γ' on Annealing Twin Boundaries in Superalloys: Semanti Mukhopadhyay1; Hariharan Sriram1; Shakthipriya Basker Kannan1; Charles Xu1; Ashton Egan1; Fei Xue2; Longsheng Feng1; Richard DiDomizio3; Andrew Detor3; Katelun Wertz4; Milan Heczko1; Robert Hayes5; Gopal B. Viswanathan1; Christopher Zenk6; Emmanuelle Marquis2; Maryam Ghazisaeidi1; Stephen Niezgoda1; Yunzhi Wang1; Michael Mills1; 1The Ohio State University; 2University of Michigan; 3GE Global Research Center; 4Air Force Research Laboratory; 5Metals Technology Inc.; 6Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
    In several Ni-based superalloys, annealing twin boundaries (ATBs) are susceptible sites for strain localization and subsequent failure. Although attempts have been made to explore this strain localization, the overall mechanistic understanding is still lacking. Moreover, in some Ni and Co-based superalloys investigated in the present study, such strain localization events appear to be further complicated by the presence of γ′ and γ′′ precipitates on all the ATBs. Microstructural characterization has revealed preferential γ′ and γ′′ precipitation on the ATBs. These ATB precipitates exhibit morphology, size, and composition very similar to the precipitates evolving elsewhere in the system. Aberration-corrected STEM-based microstructural study of the ATB precipitates indicates three-layer segregation at the twin boundary within γ′ precipitates. Long-term phase stability of the precipitates and their effect on the mechanical behavior have been evaluated in an IN718-based system using a combination of advanced characterization techniques complemented by phase-field and crystal plasticity modeling.