High Entropy Alloys IX: Alloy Development and Properties: Structures and Mechanical Properties I
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Peter Liaw, University of Tennessee; Michael Gao, National Energy Technology Laboratory; E-Wen Huang, National Chiao Tung University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical
Tuesday 8:30 AM
March 16, 2021
Room: RM 10
Location: TMS2021 Virtual
Session Chair: Lei Lu, Institute of Metal Research, Chinese Academy of Sciences; Hyoung Kim, Pohang University of Science and Technology
8:30 AM Keynote
Current Perspectives in High Entropy Alloys: Diran Apelian1; Benjamin MacDonald1; Cheng Zhang1; Enrique Lavernia1; 1University of California, Irvine
Since their discovery in 2004, high entropy alloys (HEAs) have generated significant interest from the materials science community due to unique phase formation as well as reports of exceptional mechanical performance in select compositions. While the field of HEAs now understands that entropy alone does not dictate the phase formation in complex compositions, it continues to expand, discovering promising HEAs for various applications by approaching alloy design from a different direction than conventional alloy design. Two key and specific directions of research include the critical evaluation of the impact of atomic scale compositional fluctuations on alloy properties, and integrated computational materials engineering approach to developing refractory based HEAs with optimal mechanical behavior at elevated temperatures. Through this presentation the state of the art will be established in both of these areas of research and the efforts ongoing at the University of California Irvine will be presented and discussed.
9:00 AM Invited
FCC-HCP Transformation in Cr-Mn-Fe-Co-Ni High Entropy Alloys:- Mechanical Property and Nanograin Formation: Koichi Tsuchiya1; Jangho Yi1; Baozhen Jiang1; Je In Lee2; 1National Institute for Materials Science; 2Pusan National University
A series of high-entropy alloys with different FCC/HCP phase stability was designed. Ingots of Cr20Mn20Fe20Co40-xNix (x=0~20) were prepared by HF melting and rolled into the bar. They are heat treated at 1473 K for 48 hrs followed by water quench. Samples with 0~5mol%Ni are composed of HCP and FCC phases after the heat treatment, while others are in the FCC single phase state. For the 15~20Ni alloys, HPT led to a drastic increase in micro-Vickers Hardness (Hv). This can be attributed to the rapid progress of grain refinement. BSD-SEM observations revealed that pronounced formation of lamellar structures of about 100 nm width separated by nanotwins. They accelerate an increase in dislocation density and led to the formation of equiaxed nanograins (~50 nm) by continuous dynamic recrystallization. Meanwhile, hardness increase was less significant for the lower Ni content alloys with higher HCP stability.
9:25 AM
Low Cycle Fatigue Behavior and Cyclic Plastic Response of Equiatomic CrCoNi Medium-entropy Alloy: Milan Heczko1; Veronika Mazanova1; Connor Slone1; Ivo Kubena2; Jiri Tobias2; Tomas Kruml2; Easo George3; Maryam Ghazisaeidi1; Jaroslav Polak2; Michael Mills1; 1The Ohio State University; 2Institute of Physics of Materials CAS; 3Oak Ridge National Laboratory
Equiatomic CrCoNi alloy was subjected to strain-controlled low cycle fatigue tests at room temperature in a wide interval of strain amplitudes. Fatigue hardening/softening curves, cyclic stress-strain curves and fatigue life curves were evaluated. The evolution of the internal critical stresses and the effective saturated stress during cyclic loading was analyzed using a generalized statistical theory of the hysteresis loop model. The deformation substructure was studied by atomic resolution electron microscopy and correlated with the cyclic response. Correlation of mechanical test data, modeling and characterization reveals details of the deformation mechanisms such as highly planar slip, deformation twinning and FCC-HCP transformation, which govern cyclic strength, cyclic plastic response and the fatigue life. Performance of the CrCoNi alloy, which is characterized by good cyclic strength combined with superior resistance to cyclic plastic deformation, is compared and discussed in relation to other structural alloys used in real service conditions.
9:45 AM Invited
Deformation Twinning in FCC High- and Medium-entropy Alloys: Haruyuki Inui1; Koudai Niitsu1; Kyosuke Kishida1; 1Kyoto University
High-entropy alloys (HEAs) comprise a novel class of scientifically and technologically interesting materials. Among these, equatomic CrMnFeCoNi and its derivative quaternary and ternary alloys with the FCC structure are noteworthy because their strengths are by far higher than those of conventional FCC alloys and their tensile ductility increases with decreasing temperature while maintaining outstanding fracture toughness. Most of these high- and medium-entropy alloys are known to possess a stacking-fault energy and hence to twin at low temperatures, contributing outstanding fracture toughness. We investigate the deformation twinning behavior of single crystals of these high- and medium-entropy alloys as a function of temperature and crystal orientation, to see how these parameters as well as stacking-fault energy affect the twinning behavior such as the twinning (initiation) stresses and strains to be accumulated prior to twining.
10:10 AM Invited
High-strain-rate 2000% Superplasticity in A
nanostructured High-entropy Alloy: Hyoung Seop Kim1; Nhung Thi-Cam Nguyen1; Peyman Asghari-Rad1; Praveen Sathiyamoorthi1; Alireza Zargaran1; Chong Soo Lee1; 1Pohang University of Science and Technology
Superplasticity describes a material’s ability to sustain large plastic deformation in the form of a tensile elongation to over 400% of its original length, but is generally observed only at a low strain rate (~10^−4 s^−1), which results in long processing times that are economically undesirable for mass production. Superplasticity at high strain rates in excess of 10^−2 s^−1, required for viable industry-scale application, has usually only been achieved in low-strength aluminum and magnesium alloys. Here, we present a superplastic elongation to 2000% of the original length at a high strain rate of 5×10^−2 s^−1 in an Al9(CoCrFeMnNi)91 (at%) high entropy alloy nanostructured using high-pressure torsion. The high-pressure torsion induced grain refinement in the multi-phase alloy combined with limited grain growth during hot plastic deformation enables high strain rate superplasticity through grain boundary sliding accommodated by dislocation activity.
10:35 AM
Intermediate Temperature Precipitation in the HfNbTaTiZr Multi-principal Element Alloy: Megan Emigh1; Noah Phillips2; Leah Mills2; Sean Murray2; Tresa Pollock1; 1University of California, Santa Barbara; 2ATI Specialty Alloys and Components
HfNbTaTiZr is a refractory multi-principal element alloy that exhibits high strength combined with good ductility at room temperature. In this investigation, the microstructure and mechanical properties under tensile load are investigated at select temperatures. At 800°C, the HfNbTaTiZr alloy exhibited significantly decreased ductility relative to room temperature behavior. The low 800˚C ductility was associated with intergranular fracture and grain boundary precipitation. At a testing temperature of 1200°C, HfNbTaTiZr exhibited high ductility enhanced by dynamic recrystallization. The reduction in cross sectional area at room temperature, 800˚C, and 1200˚C were 48%, 5%, and 62% respectively. Complementary thermodynamic calculations predict two BCC phases and an HCP phase to be stable between 703-804°C. These experimental and computational results underscore a need to understand the high temperature phase equilibria of refractory MPEs so that their microstructure and mechanical properties can be better controlled across the temperature ranges of interest.