Materials Design Approaches and Experiences V: Superalloys
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee, TMS: Integrated Computational Materials Engineering Committee
Program Organizers: Akane Suzuki, GE Aerospace Research; Ji-Cheng Zhao, University of Maryland; Michael Fahrmann, Haynes International; Qiang Feng, University of Science and Technology Beijing; Michael Titus, Purdue University

Monday 2:30 PM
February 24, 2020
Room: 33A
Location: San Diego Convention Ctr

Session Chair: Yunzhi Wang, The Ohio State University; Michael Fahrmann, Haynes International


2:30 PM  Invited
Design of Cobalt Base Single Crystal Superalloys: Sean Murray1; Colin Stewart1; Robert Rhein1; Carlos Levi1; Anton Van der Ven1; Tresa Pollock1; 1University of California, Santa Barbara
    Alloy design studies of single crystal Co-base superalloys strengthened with L12 precipitates have resulted in a suite of alloys with excellent high temperature creep strength. However, the engineering application of these alloys will require a balanced suite of properties. The status of computational and experimental design tools that have guided development toward this balance will be discussed. Early in the design process, density functional theory provided critical guidance for narrowing the compositional space. While Calphad-type databases provide critical information needed to assess solidification and phase equilibria, their development has been comparatively slower. Given the sparse information available in this compositional domain, combinatorial experiments have been effective for identifying compositions that achieve a balance of properties, including oxidation. Gaps in the alloy design infrastructure will be discussed.

3:00 PM  
Improved 3rd Generation Single Crystal Superalloy CMSX-4® Plus (SLS) – a Study of Evolutionary Alloy Development: Jacqueline Wahl1; Ken Harris1; 1Cannon-Muskegon Corp
    Throughout the aerospace and industrial gas turbine industry, computer-aided design, process modelling and ICME are synonymous with leading edge technology development methods. However, there remains value and benefit from the alternate, more traditional evolutionary design methodology where new alloys are developed based upon prior experience with existing alloys and lessons learned. Cannon-Muskegon Corporation has used this evolutionary method to develop and introduce CMSX-4® Plus (SLS) alloy, an improved 3rd generation, single crystal alloy based upon over 30 years of SX alloy development and commercial experience. It is useful and enlightening to review this development history, as it directly reflects upon the resultant alloy and explains the remarkable speed with which CMSX-4 Plus (SLS) alloy was developed and brought to market: 14 months from concept to patent application and first production heat. OEM engine certification, including development of a compatible coating/bond coat, was obtained approximately 6.5 years from start of development.

3:20 PM  
Development of Ni-based Alloys For Transportation Applications: Govindarajan Muralidharan1; John Chiles1; Dean Pierce1; Lawrence Allard1; Donovan Leonard1; Jonathan Poplawsky1; 1Oak Ridge National Laboratory
    High performance Ni-based alloys are required for use in exhaust valve applications in the next generation, high efficiency automotive engines. These alloys are expected to be available at low cost while being able to perform at temperatures up to 950°C in an exhaust gas environment. This talk will present our experiences in the computational design of alloys that would have the potential to meet these challenges. The use of advanced characterization techniques including atom probe tomography in the validation of alloy design will be highlighted. *Research sponsored by the U.S.DOE, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, under contract DE-AC05-00OR22725 with UT-Battelle, LLC. Atom probe tomography was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User facility.

3:40 PM  
Designing for Local Phase Transformation Strengthening in Nickel Based Superalloys: Ashton Egan1; Lola Lilensten2; Paraskevas Kontis2; Sammy Tin3; Michael Mills1; 1Ohio State University; 2Max-Planck-Institut für Eisenforschung GmbH; 3Illinois Institute of Technology
    Physics-based models connecting composition, microstructure and properties are needed to enable rapid and cost-effective alloy development. Our work supports this process by probing effects of critical alloying additions found to promote Local Phase Transformation (LPT) strengthening, which occurs along planar defects and benefits creep resistance. Compositionally simplified alloys, based on studies investigating bulk phase formation, allow for exploration of composition regimes promoting LPT. Characterization of these alloys involved compression creep testing, which presented a unique challenge, as well as coupling atomic resolution Scanning Transmission Electron Microscopy and Atom Probe Tomography. More complex commercial and experimental alloys also exhibit LPT, and the role of this phenomenon in dictating the operative deformation mechanism at higher temperature will be discussed. Combining these characterization techniques allows for understanding of both local atomic structure and local three dimensional composition at defects, providing insight into these segregation events and directions for modeling of this phenomenon.

4:00 PM Break

4:20 PM  Invited
New Alloy Design Strategy via Non-conventional Phase Transformation Pathways: Longsheng Feng1; Tianlong Zhang2; Dong Wang3; Yipeng Gao4; Yufeng Zheng1; Michael Mills1; Hamish Fraser1; Yunzhi Wang1; 1The Ohio State University; 2City University of Hong Kong; 3Xi’an Jiao Tong University; 4Idaho National Laboratory
    Microstructural engineering has been the cornerstone of alloy development. Recently the development of highly heterogeneous / gradient microstructures and the discovery of dynamic phase transformations at extended defects have attracted a lot of attentions. The former has been shown to have a synergistic combination of (rather than trade-off between) strength and ductility, e.g., ultrafine-grain strength with coarse-grain ductility, while the latter has been shown to have a significant improvement of the high-temperature work-hardening behavior and creep performance in Ni-base superalloys, and ultralow modulus and non-hysteretic linear superelasticity in metastable beta Ti-alloys. In this presentation, we demonstrate the possibilities to create such hierarchical and gradient precipitate microstructures and dynamic and localized phase transformations at stacking faults and twin boundaries through non-conventional transformation pathway engineering by using a combined CALPHAD, phase transition graph (PTG) and phase field approaches. The work is supported by NSF under DMREF programs.

4:50 PM  
Equilibrium Segregation and Localized Phase Transition at Stacking Faults in Ni-based Superalloys: Longsheng Feng1; You Rao1; Ashton Egan1; Michael Mills1; Maryam Ghazisaeidi1; Yunzhi Wang1; 1The Ohio State University
    Suzuki segregation has long been identified and verified in the experiment. Recent experiment findings suggest solute segregation may play an important role in the deformation process during creep. Interfacial segregation isotherm is adopted to predict the equilibrium solute concentration at the stacking fault. First principle calculations are used for solute-SF interaction. A clear correspondence between segregation enthalpy and solute enrichment is shown. The simulation predictions agree well with experimental observations. Moreover, localized phase transformation (LPT) inspired by segregation transition is studied through phase field simulations. The simulation results show that LPT occurs locally at stacking faults and the precipitate phase produced is confined locally at the faults and cannot growth into the bulk. The impact of such localized precipitates on the deformation behavior of the alloy will also be discussed. This work is supported by NSF under DMREF program.

5:10 PM  
Precipitate-mediated Dislocation Transformer in Ni-base Superalloys: Longsheng Feng1; Michael Mills1; Yunzhi Wang1; 1The Ohio State University
    It is our conventional wisdom that dislocations would not change their Burgers vectors in a shearing event. But in the γ”-strengthened Ni-based superalloys, the low-symmetry intermetallic (γ”, DO22) precipitates embedded in the γ matrix (FCC) would serve as a transformer to constantly transform <110>/2 dislocations into <112>/6 Shockley partials that are not the two partials associated with the <110>/2 dislocations. This discovery is made by computer simulations using the microscopic phase field model with ab initio calculations of the generalized-stacking-fault-energy (GSFE) surfaces as inputs. The transformed dislocation contents would therefore significantly change the deformation pathway and hence impact the strengthening effects. The constant production of Shockley partials may be responsible for the prevailing microtwinning in Alloy 718 that is strengthened mainly by γ” precipitates. This work is supported by NSF under DMREF program.