Advances in Multi-Principal Element Alloys II: Structures and Mechanical Properties I
Sponsored by: TMS Structural Materials Division, TMS Functional Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Alloy Phases Committee
Program Organizers: Peter Liaw, University of Tennessee; Michael Gao, National Energy Technology Laboratory; E-Wen Huang, National Yang Ming Chiao Tung University; Jennifer Carter, Case Western Reserve University; Srivatsan Tirumalai; Xie Xie, Ford Motor Company; James Brechtl, Oak Ridge National Laboratory; Gongyao Wang, Globus Medical

Wednesday 8:30 AM
March 22, 2023
Room: Aqua D
Location: Hilton

Session Chair: Michael Gao, National Energy Technology Laboratory; Koichi Tsuchiya, NIMS

8:30 AM  Invited
Tunability of Deformation Mechanisms through Integration of Compositional and Microstructural Domains: Rajiv Mishra1; 1University of North Texas
    This overview presentation focuses on opportunities for tunable performance by manipulating deformation mechanisms in high entropy alloys (HEAs) or concentrated alloys. In a recent review, we highlighted an approach that integrates compositional and microstructural domains. This approach will be presented with an emphasis on metastability engineering. The enhanced metastability triggers a combination of shear induced phase transformation and twinning, thereby expanding beyond the slip based mechanisms. The emerging metastable HEAs give greater flexibility for tailoring transformation-induced plasticity (TRIP) and twinning induced plasticity (TWIP). For TRIP HEAs, the ductility can be extended to as high as 50% while maintaining a strength exceeding 1 GPa. Concurrent phase transformation at the crack tip has been shown to push the fatigue endurance limit. Hierarchical activation of micromechanisms in these highly metastable HEAs provide excellent opportunities for enhanced structural performance.

8:50 AM  Invited
Creep of High Entropy Alloys and Superalloys at NETL: Kyle Rozman1; Michael Gao2; Martin Detrois2; Paul Jablonski2; Ömer Doğan2; 1Site Support Contractor; 2National Energy Technology Laboratory
    The National Energy Technology Laboratory (NETL) is uniquely poised to develop and test metallic alloys. Facilities range from a supercomputer to aid in computational design and machine learning of alloy properties to manufacturing capabilities to realize the designed alloy to test facilities to measure the mechanical performance of the alloy. Creep testing has found sulfur proved important in improving the creep lifetime of CoCrFeNi and CoCrFeNiMn alloys. Additionally, NETL’s computationally designed CoCrFeNiMo alloy appears to have creep performance near commercial superalloy Haynes 230. This talk will focus on the achievements to date regarding NETL’s high temperature creep program regarding high entropy alloys.

9:10 AM  Invited
Mechanical Determination of Peak Short-range Ordering in CrCoNi via Nanoindentation: Mingwei Zhang1; Qin Yu1; Carolina Frey2; Flynn Walsh3; Madelyn Payne3; Punit Kumar1; Dongye Liu3; Easo George4; Tresa Pollock2; Mark Asta1; Robert Ritchie1; Andrew Minor1; 1Lawrence Berkeley National Laboratory; 2University of California, Santa Barbara; 3University of California, Berkeley; 4University of Tennessee, Knoxville
    Despite the recent success of directly imaging short-range ordering (SRO) in multi-principal element alloys (MPEAs) via energy-filtered TEM (EFTEM), the effect of SRO on their mechanical properties has not been explored in detail. In the present study, we report on the results from nanoindentation experiments on splat quenched, water quenched, and 600 – 1000 ºC aged CrCoNi samples that were intended to generate different extents of SRO. Complementary uniaxial tensile experiments on bulk polycrystalline samples were also performed to generate a comparison between the effect of SRO on bulk mechanical properties and nanomechanical properties. Although no notable difference was observed in macroscopic properties, the nanoindentation results exhibit a clear increase in pop-in loads after aging, where peak strength that corresponds to maximum SRO was observed at the aging temperature of 900 ºC. This trend is also qualitatively verified by direct EFTEM characterization of SRO.

9:30 AM  Invited
Elastic and Plastic Behavior of Binary and Ternary Refractory Multi-principal-element Alloys: Rui Feng1; George Kim2; Dunji Yu1; Yan Chen1; Wei Chen2; Peter Liaw3; Ke An1; 1Oak Ridge National Laboratory; 2Illinois Institute of Technology; 3The University of Tennessee, Knoxville
    Refractory high-entropy alloys (HEAs) or multi-principal-element alloys (MPEAs) have drawn much attention due to their great potential for extreme environment applications. In this study, we study the elastic and plastic behavior of the equiatomic binary and ternary refractory, NbV, NbTiV, and MoNbV MPEAs, which are the essential subsystems of several model refractory HEAs. The elastic behavior of these alloys is investigated by in-situ neutron diffraction and first-principles calculations, revealing the role of constituent elements in affecting elastic properties. The plastic deformation behavior of the alloys is understood by the observation of dislocation slips and the analysis of neutron diffraction profiles. The present work provides valuable insights into the design of ductile and strong refractory high-entropy alloys by rational alloy-design strategy.

9:50 AM  Invited
Deformation by Dislocations, Twinning, and Phase Transformations in Compositionally Complex FCC Solid Solutions: Michael Mills1; Jiashi Miao1; Connor Slone2; Veronika Mazanova1; Milan Heczko1; Maryam Ghazisaeidi1; 1Ohio State University; 2Exponent Inc.
    The equiatomic CrCoNi alloy is an fcc solid solution that exhibits intriguing behaviors including very large strain hardening and cyclic hardening rates, large fracture toughness, and strong dependence of the yield strength at low temperature. Detailed characterization using a variety of electron microscopy methods has revealed that these behaviors are closely linked to the interplay between dislocation-mediated plasticity, microtwinning, and an fcc-to-hcp transformation. The development of these mechanisms as a function of deformation for both ambient and cryogenic temperatures is discussed. The effect of Al and Ti, and the presence of nanoscale L12 ordering domains, on the deformation mechanisms will also be presented. Fundamental insights into these experimental results are also provided by density functional theory, atomistic, and continuum-level calculations.

10:10 AM Break

10:30 AM  Invited
High Strain Rate Deformation Behavior of Multi-Principal Element Alloys: Shristy Jha1; Saideep Muskeri1; Phillip Jannotti2; Jeffrey Lloyd2; Rajiv Mishra1; Sundeep Mukherjee1; 1University of North Texas; 2DEVCOM Army Research Laboratory
    The mechanical response of several model MPEAs was evaluated at quasistatic, dynamic, and ballistic strain rates. The microstructure after quasistatic deformation was dominated by highly deformed grains. High density of deformation bands was observed at dynamic strain rates but there was no indication of cracks or twinning. Ballistic response was evaluated for several single- and multi-phase MPEAs. The deformed microstructure after ballistic impact was dominated by adiabatic shear bands, microbands, and dynamic recrystallization. Rigorous characterization in the form of mechanical testing, scanning electron microscopy, and spatially resolved nano-indentation for ballistically impacted plates was used to connect microstructural details to aspects of ballistic behavior governing performance. Based on the results, it was shown that although the addition of a harder secondary phase improves strength, cracks that initiate and propagate within the harder phase and ultimately across the target plate drastically reduce the ballistic performance of the two-phase MPEAs.

10:50 AM  Invited
Effect of High-pressure and Shear Strainig on FCC-HCP Transformation in Cr20Mn20Fe20Co40-xNix High Entropy Alloys: Koichi Tsuchiya1; Jangho Yi1; Sangmin Lee1; Masashi Miyakawa1; 1National Institute for Materials Science
    CrMnFeCoNi alloys are the best-known FCC-based high-entropy alloys and are known to exhibit high strength and ductility at cryogenic temperatures. Zhang et al. reported that this alloy transforms to HCP under hydrostatic pressure of 25 GPa at room temperature (F. Zhang et al., Nature Comm.,8(2017)15687). In this presentation, we will report FCC-HCP transformation in Cr20Mn20Fe20Co40-xNix alloys induced by hydro-static pressure up to 9.4 GPa using a belt-type high-pressure generator, and compare with the results of shear straining under pressure by high-pressure torsion. It was revealed that the increasing pressure stabilize the HCP phase, which agrees with the predication by thermodynamic calculation

11:10 AM  Invited
Low-temperature Deforamtion in High-entropy Alloys: M. Naeem1; Haiyan He1; Stefanus Harjo2; Takuro Kawasak2; Xun-Li Wang1; 1City University of Hong Kong; 2Japan Atomic Energy Agency
    It is amazing that multi-component high entropy alloys (HEAs) can form a single-phase solid-solution with a simple FCC (face-centered-cubic) structure. Due to the favorable crystal structure and the metastable FCC phase, several additional deformation mechanisms become available in FCC HEAs. In situ loading study with neutron diffraction has proven to be a powerful approach to characterize the activation of different deformation modes and their interactions at low temperatures. Measurements at 15 K in CrCoNi-based HEAs have revealed a myriad of deformation mechanisms, including stacking fault, twinning, phase transformation, and serration, in addition to dislocation slip. The in situ neutron diffraction data are used to estimate the contributions of different deformation modes to the strain hardening. It is shown that the cooperation of these different deformation mechanisms led to the extremely large ductility at low temperatures.

11:30 AM  
High-throughput Characterization and Nanoindentation of TiZrHfNbTa High-entropy Alloy Library with Gradient Composition: Changjun Cheng1; Renfei Feng2; Michel Haché1; Yu Zou1; 1University of Toronto; 2Canadian Light Source
    High-entropy alloys (HEAs) are novel multiple component materials, exhibiting promising mechanical properties at a wide temperature regime. For such materials, slight composition variance is usually accompanied by structure transition, which will subsequently affect the properties significantly. However, traditional methods can only fabricate materials with a single or just a few compositions. In this work, by using the magnetron co-sputtering technique, we fabricate nanoscale TiZrHfNbTa HEA thin films with gradient compositions on Silicon wafers; based on synchrotron X-ray diffraction and fluorescence mapping, we can observe an obvious phase transition from BCC to amorphous structures along with the composition change. The enthalpy and configurational entropy affect the critical cool rate, leading to the sudden change of structures. The large-scale nanoindentation mapping identifies the corresponding nanohardness and elastic modulus in different regions. Both solid solution strengthening and Hall-Patch effect influence the mechanical properties of our high-throughput HEA library with gradient composition.

11:50 AM  
Refractory Alloys with Ru-based B2 Precipitation-strengthened Microstructures: Sebastian Kube1; Carolina Frey1; Kaitlyn Mullin1; Chiyo McMullin1; Ravit Silverstein1; Tresa Pollock1; 1University of California Santa Barbara
    To strengthen Refractory Multi Principal Element Alloys at 1200°C and beyond, one strategy aims to design stable microstructures of B2 precipitates embedded within a BCC matrix, which emulates the γ-γ’ structure found in Superalloys. Here, we focus on Ru-based B2 intermetallics as one promising group of precipitates with a high thermal stability. We comprehensively explore the resulting space of alloy systems. We arc-melt a wide range of compositions and determine phase stability and mechanical performance under various thermal processing conditions.