Microstructural Templates Consisting of Isostructural Ordered Precipitate / Disordered Matrix Combinations: Microstructural Evolution and Properties: Session I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Rajarshi Banerjee, University of North Texas; Eric Lass, University of Tennessee-Knoxville; Bharat Gwalani, North Carolina State Universtiy; Jonah Klemm-Toole, Colorado School of Mines; Jessica Krogstad, University of Illinois at Urbana-Champaign; Ashley Paz Y Puente, University of Cincinnati; Keith Knipling, Naval Research Laboratory; Matthew Steiner, University of Cincinnati

Tuesday 8:00 AM
March 1, 2022
Room: 254A
Location: Anaheim Convention Center

Session Chair: Rajarshi Banerjee, University of North Texas, Denton; Bharat Gwalani, Pacific Northwest National Lab


8:00 AM Introductory Comments

8:05 AM  Invited
Novel Nickel-based Alloys for High Temperature Structural Applications: Boateng Twum Donkor1; Sonali Ravikumar1; Anurag Sharma1; Jie Song1; Vijay Vasudevan2; 1University of Cincinnati; 2University of North Texas
    Molten chloride and fluoride salt fast reactors (MSR) are under active development because they offer several operational and safety advantages over other types of reactors. Modern designs require structural materials with superior corrosion, creep, thermomechanical fatigue, irradiation damage and Helium bubble and tellurium-induced grain boundary embrittlement resistance to high temperatures of 750-950°C. Nickel-base alloys generally perform better than all other alloys studied to date, though none yet have the set of properties to meet these demanding conditions. We will report on the development of the next generation of nickel-base alloys based on the Ni-Mo-W-Cr-X system that combine solid solution strengthening with ordered and other precipitates for superior high temperature properties. An ICME approach is combined with a detailed experimental processing, testing, characterization and modeling program. Results of the alloy design strategy, phase equilibria and transformations and evolution of microstructure and high temperature mechanical properties will be presented. The irradiation and corrosion behavior in molten chloride salt of selected alloys will also be presented. Future directions will be discussed.

8:35 AM  Invited
Tuning the Degree of Chemical Ordering in the Solid Solution of a Complex Concentrated Alloy and Its Impact on Mechanical Properties: Sriswaroop Dasari1; Abhinav Jagetia1; Abhishek Sharma1; M.S.K.K.Y. Nartu1; Vishal Soni1; Bharat Gwalani1; Stephane Gorsse1; Rajarshi Banerjee1; 1University of North Texas
    Using binary enthalpies of mixing in Co-Cr-Fe-Ni base alloy system, a complex concentrated alloy (CCA), the equiatomic CoFeNi has been identified, which should form a random solid solution. Subsequent experimental validation established that this alloy is indeed a near random FCC solid solution. The same thermodynamic basis has been employed to systematically engineer the degree of chemical ordering within the random CoFeNi alloy, from short-range ordering, to long-range ordered domains, by adding controlled amounts of Al and Ti, since these elements have a strong ordering tendency with Co, Fe, and Ni. This change in the degree of chemical ordering has a strong influence on the tensile yield strength of the alloy, ranging from ~181 MPa in case of CoFeNi to ~793 MPa in case of the Al0.3Ti0.2Co0.7FeNi1.7 CCA. These experimentally measured yield strengths of the candidate CCAs are in close agreement with predicted values afforded by simple strengthening models.

9:05 AM  Invited
The Role of Precipitate Size Distribution and Morphology on Ni Superalloy Deformation Micromechanisms: James Coakley1; Muhammad Awais2; Jonathan Cormier2; Ke An3; Neil D'Souza4; Howard Stone5; 1University of Miami; 2École nationale supérieure de mécanique et d'aérotechnique; 3Oak Ridge National Laboratory; 4Rolls-Royce plc.; 5University of Cambridge
    The initial microstructures of Ni superalloys differ depending on engine component and service conditions. The microstructures then evolve during engine operation with a concomitant evolution of material properties and deformation micromechanisms. In the current work, single crystal Ni superalloy CMSX-4 has been processed to represent four critical microstructures that arise in superalloys: (i) a unimodal gamma-prime size distribution used in blade applications; (ii) a bimodal gamma-prime size distribution used in disc applications; (iii) a rafted gamma-prime size distribution that arises during blade operating conditions; (iv) a bimodal gamma-prime size distribution with rafted gamma-prime and cooling gamma-prime. In-situ neutron diffractometry is utilized during low temperature tensile deformation in order to compare the strengthening and deformation micromechanisms across these very different microstructures, and will be presented.

9:35 AM Break

9:55 AM  
Investigation of Nucleation Mechanisms Associated with the Formation of Coprecipitates in Ni-based Superalloys: Hariharan Sriram1; Semanti Mukhopadhyay1; Michael Mills1; Yunzhi Wang1; 1Ohio State University
    Experimental studies have shown a wide variety of γ'/γ” coprecipitates in IN718-based alloys. Although the coprecipitate's growth and coarsening mechanisms have been investigated, the heterogeneous nucleation mechanisms of γ” on existing γ' that lead to different types of coprecipitates are yet to be understood. We analyze the individual and combined effects of concentration field and coherency elastic stress field associated with existing γ' at different sizes on nucleation of γ". The chemical driving force for nucleation is calculated using the CALPHAD databases, while the contributions from elastic interaction and anisotropic interfacial energies between different interfaces are quantified by comparing results from phase-field simulation and experimental characterization. Subsequently, an explicit nucleation algorithm is used in phase-field simulations to study nucleation and early stage of growth. Furthermore, insights gained from the analysis will be used as inputs in fast-acting precipitation models to design heat treatments for the coprecipitate alloys.