Microstructural Templates Consisting of Isostructural Ordered Precipitate / Disordered Matrix Combinations: Microstructural Evolution and Properties: On-Demand Oral Presentations
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

Monday 8:00 AM
March 14, 2022
Room: Materials Design
Location: On-Demand Room


Microstructural Engineering in NiCoCr Medium Entropy Alloys: Nithin Baler1; Abdulla Samin M V1; Surendra Kumar Makineni2; 1Indian Institute of Science Bangalore; 2Indian Institute of Science Bangalore
    Equiatomic NiCoCr medium entropy alloys hold promise for structural applications due to their excellent combination of fracture toughness, strength/ductility, and hardening rates at room and cryogenic temperatures. However, a key challenge is to increase their stability at high temperatures. This talk will showcase the synergy of grain size distribution and dual-phase ordered precipitates to achieve an optimum combination of ultra-high-strength and ductility at room and high temperatures. A microstructural tuning map will be presented as a function of strength/ductility from which one can select the process condition to get the desired composite microstructure.

Precipitate Strengthening and Stabilization Mechanisms in Cast and Additively Manufactured Al-Cu-Mn-Zr Alloys: Jonathan Poplawsky1; Richard Michi1; Sumit Bahl1; Brian Milligan2; Patrick Shower3; Lawrence Allard1; Matthew Chisholm1; Dongwon Shin2; Kevin Sisco4; Alex Plotkowski1; Ryan Dehoff1; Allen Haynes1; Amit Shyam1; 1Oak Ridge National Laboratory; 2Colorado School of Mines; 3GE Global Research; 4University of Tennessee, Knoxville
    A microstructure rich in θ’ precipitates (Al2Cu) is critical for AlCu alloys’ strength, but these alloys soften after exposures to temperatures >250oC. Mn and Zr microsolute additions stabilize the θ’ microstructure after 350oC, >200 hrs exposures. Advanced microscopy and computational techniques revealed that interfacial Mn segregation creates solute drag and decreases the interfacial energy, which allows for the slower diffusing Zr/Ti to form an L12 structure at the θ’ interfaces, further stabilizing the microstructure. Recently, an additively manufactured (AM) Al-Cu-Mn-Zr (ACMZ) alloy was developed that is stronger than the cast-ACMZ counterpart after 200 hr exposures to 300, 350, and 400 °C, which is partly due to the unique microstructure and solute supersaturation achieved by rapid solidification. The differences in the microstructure and mechanical properties of the cast and AM-ACMZ alloys will be discussed. The microscopy was conducted at ORNL’s CNMS, which is a U.S. DOE Office of Science user facility.

On the Detailed Morphological and Chemical Evolution of Phases during Laser Powder Bed Fusion and Common Post-processing Heat Treatments of IN718: Sophie Primig1; Vitor Rielli1; Alessandro Piglione2; Minh-Son Pham2; 1University of New South Wales; 2Imperial College London
     Recently, IN718 has shown great viability for laser powder bed fusion (LPBF) additive manufacturing of aerospace parts. However, the detailed microstructure-property relationships during thermal profiles typical to LPBF are not yet well understood. Using atom probe microscopy, we report on the detailed morphological and chemical evolution of phases in IN718 after LPBF with chessboard versus meander scanning strategies, and common ageing treatments. Due to differences in scanning vector length, coarser dendritic structures, Laves particles and Al clusters are found in the chessboard strategy. Coarser matrix grains and a higher dislocation density are detected in the meander strategy. The formation of σ phase at grain boundaries, a nucleation site for MC carbides, must be considered for selection of post-processing treatments. Retained Laves phase after direct ageing causes lower fractions of nanoscale γ" precipitates. A quadruple fraction of stable, larger γ" precipitates is found after homogenization and ageing, causing partial matrix recrystallization.

The Origin and Stability of Nanostructural Hierarchy in Nickel-base Superalloys: Subhashish Meher1; Larry Aagesen1; Tresa Pollock2; L. J. Carroll1; 1Idaho National Laboratory; 2University of California, Santa Barbara
    A combined experimental and phase-field modeling approach has been used to explore a hierarchical structure at nanoscale for enhanced coarsening resistance of ordered γ′ precipitates in an experimental, multicomponent, high-refractory nickel-base superalloy. The hierarchical microstructure formed in this alloy is composed of a γ matrix with γ′ precipitates that contain embedded, spherical γ precipitates, which do not directionally coarsen during high-temperature annealing but do delay coarsening of the larger γ′ precipitates. Chemical mapping via atom probe tomography suggests that the supersaturation of Co, Ru, and Re in the γ′ phase is the driving force for the formation of this hierarchical microstructure. Representative phase-field modeling highlights the importance of larger γ′ precipitates to promote stability of the embedded γ phase and to delay coarsening of the encompassing γ′ precipitates. These results suggest that the hierarchical material design has the potential to influence the high-temperature stability of precipitate strengthened metallic materials.

Design of Precipitation Strengthened Metastable High Entropy Alloys: K. G. Pradeep1; 1Indian Institute of Technology Madras
    FeMnCoCr based high entropy alloys (HEA) are the only identified, yet prominent, metastable, multi-component systems that can exhibit the unique behavior of transformation induced plasticity (TRIP). The emergence of HCP phase during deformation from the metastable parent FCC solid solution phase provides the much required phase-interface strengthening without compromising the ductility. However, to further improve the mechanical properties of these metastable alloys especially the yield strength, the TRIP effect alone appears to be not sufficient. Hence, this presentation will focus on the design aspects of concomitant precipitation strengthened FeMnCoCr based metastable HEAs. The crucial challenge of inducing precipitates that are chemically homogenous in the metastable, FCC structured, low-stacking fault energy solid solution matrix without disturbing its unique behavior of TRIP will be discussed.

Seeing the Shearing of Short-range Order with Dislocations in the High-entropy Alloy: Jae Bok Seol1; Jongun Moon2; Hyo Ju Bae1; Jae Wung Bae3; Hyokyung Sung1; Jung Gi Kim1; Hyoung Seop Kim2; 1Gyeongsang National University; 2POSTECH; 3Max-Planck-Institut für Eisenforschung GmbH
    Recent studies have dedicated to short-range order (SRO) visualization and its impact on complex concentrated solutions, through the combined electron-beam diffraction and atomic imaging of transmission electron microscopy. However, a key challenge has still remained as to how varying the uniaxial strain rates has a profound effect on the SRO degree, mechanical and thermal properties of high-entropy alloys (HEAs), particularly under near-constant stacking-fault energy conditions. Herein we found that, employing higher tensile strain rate under quasi-static conditions at 77 K, results in higher degree of SRO in an interstitially hardened Fe40Mn40Cr10Co10 (at%) alloy. This corresponds to the increased density of SRO domains, i.e., higher degree of SRO implies the higher amounts of SRO rather than SRO sizes. Additionally, we showed the shearing of such domains with successive dislocations inside the early formed planar slip band during the tensile tests.