Microstructural Templates Consisting of Isostructural Ordered Precipitate / Disordered Matrix Combinations: Microstructural Evolution and Properties: Session II
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 2:30 PM
March 1, 2022
Room: 254A
Location: Anaheim Convention Center
Session Chair: Sriswaroop Dasari, University of North Texas; Eric Lass, The University of Tennessee, Knoxville
2:30 PM Introductory Comments
2:35 PM Invited
Deformable Intermetallic Nanorods Leads to an Excellent Strength-ductility Combination in a High Entropy Alloy: Bharat Gwalani1; Sriswaroop Dasari2; Vishal Soni2; Shivakant Shukla1; Abhinav Jagetia2; Priyanshi Agrawal2; Rajiv Mishra2; Rajarshi Banerjee2; 1Pacific Northwest National Laboratory; 2University of North Texas
Thermodynamic modeling has been employed to design this HEA with large L12 volume fraction. Thermo-mechanical processing by isothermal annealing of the conventionally processed bulk cold-rolled alloy directly at precipitation temperatures, has been applied to produce a high density of uniformly distributed L12 nanorods within refined FCC grains, resulting from concomitant recrystallization and discontinuous precipitation processes. The nanorod morphology of the discontinuous L12 product has been established from three-dimensional atom probe tomography. The refined grains result in a complete coverage of the microstructure with discontinuously precipitated intermetallic nanorods. This nanorod strengthened HEA exhibits an exceptionally high room temperature yield strength of ~1630 MPa, good tensile ductility of ~15%, and an ultimate tensile strength of ~1720 MPa. These results open a new strategy for design of fine-grained microstructures strengthened via ordered intermetallic phases, exploiting the beneficial effects of discontinuous precipitation, for achieving very high room temperature tensile strengths while maintaining good ductility.
3:05 PM Invited
Free Energy Landscape, Transformation Pathway and Alloy Parameters Leading to Various Isostructural Ordered Precipitate Microstructures: Kamalnath Kadirvel1; Shalini Roy Koneru1; Rajarshi Banerjee2; Hamish Fraser1; Yunzhi Wang1; 1The Ohio State University; 2University of North Texas
Order-disorder transformations may occur by nucleation and growth of the ordered phase from an disordered matrix (typical first-order transition); congruent ordering followed by either decomposition or spinodal decomposition of the ordered phase, and disordering again of one of the two ordered phases in the latter; spinodal decomposition in the disordered phase followed by congruent ordering of one of the disordered phases, etc. In this presentation, we explore microstructural evolution along these transformation pathways by phase field simulations using corresponding free energy landscapes and study the effects of asymmetry of a miscibility gap, alloy composition, lattice mismatch and elastic modulus mismatch among the ordered and disordered phases, and heat treatment on the final two-phase or multi-phase microstructures. Order-disorder reactions of both the first and second kinds will be considered. The simulation results offer insights on possible transformations pathways leading to the microstructures observed in multi-principle element alloys explored recently by experiments.
3:35 PM Invited
High Temperature Deformation Pathways in Ordered L12- and Immm-based Compounds: Thomas Mann1; Dongsheng Wen1; Sae Matsunaga1; Marisol Koslowski1; Michael Fahrmann2; Michael Titus1; 1Purdue University; 2Haynes International
Ordered intermetallic compounds exhibit complex deformation pathways that depend on their thermo-physical properties. In this presentation, we will first elucidate the role of symmetry and planar defect energies on the theoretical shear strength of γ’’’-Immm Ni2(Cr,Mo,W) precipitates in HAYNES® 244®. We have found that both low- and high-energy deformation pathways exist in the γ’’’ phase utilizing first-principles calculations, a continuum Peierls-Nabarro model, and phase field dislocation dynamics. Preliminary experimental evidence of deformation at elevated temperature suggests that microtwinning is enabled by the energetic disparity in these pathways. Next, we will report on recent efforts to predict and quantify solute segregation in γ’-strengthened NiCo-based alloys using a combination of first-principles calculations and high-resolution transmission electron microscopy. We have observed that segregated stacking fault energies in NiCo-based alloys can be significantly reduced when Co partitions to the stacking faults. The effects on mechanical properties resulting from solute segregation will be further discussed.
4:05 PM Break
4:25 PM Invited
Core/Triple Shell Precipitates in Al-Er-Sc-Zr-(V,Nb,Ta) Alloys: Keith Knipling1; 1Naval Research Laboratory
Al-Sc alloys are strengthened by nanoscale Al3Sc precipitates. By alloying with faster-diffusing Er and slower-diffusing Zr additions, complex core/double-shell precipitates are formed, with precipitates consisting of an Er-enriched core surrounded by a Sc- and Zr-enriched shells. The Er-enriched core enhances strength while the Zr-enriched outer shell improve thermal stability. The present study seeks ultimate strength and coarsening resistance by alloying Al-Er-Sc-Zr alloys with Group 5 additions (M = V, Nb, Ta), which are expected to be slower diffusers than Zr. By sequential nucleation of the constituent solutes we have engineered Al3(Er,Sc,Zr,M) precipitates with core/triple shell compositions. Relationships between the observed mechanical properties and the precipitate sizes and compositions are established using atom-probe tomography throughout the microstructural evolution of the alloys.
4:55 PM Concluding Comments