Advances in Multi-Principal Element Alloys II: Poster Session II
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, FCA US LLC; James Brechtl, Oak Ridge National Laboratory; Gongyao Wang, Globus Medical
Tuesday 5:30 PM
March 21, 2023
Room: Exhibit Hall G
Location: SDCC
J-47: Machine Learning On-the-fly KMC Study of Vacancy Diffusion of Concentrated Ni-Fe Model Alloys: Wenjiang Huang1; Xianming Bai1; 1Virginia Polytechnic Institute
Defect diffusion in concentrated alloys plays a key role on governing their unique properties. The defect diffusion depends on its local atomic environment and varies from site to site in such alloys due to the chemical disorder. On-the-fly determination of the defect migration barrier using the standard nudged elastic band (NEB) method is computationally expensive and often impractical. In this work, we coupled machine learning and kinetic Monte Carlo (KMC) to study vacancy diffusion in concentrated Ni-Fe model alloys. Based on about 23,000 pre-calculated NEB barriers, an artificial neural network (ANN) based model is developed to predict the vacancy migration barriers for arbitrary local atomic environments. The ANN model is then coupled with the on-the-fly KMC to study the vacancy diffusion in the full composition range at both high and low temperatures. The sluggish diffusion mechanism in this specific alloy system is discussed based on our ANN-KMC results.
Mechanical Properties and Deformation Mechanisms in TiMoNbZr Medium Entropy Alloys: A Molecular Dynamics Study: Avinash Chavan1; Mangal Roy1; 1IIT Kharagpur
The concept of refractory multicomponent system provides an interesting approach in designing novel metallic biomaterial. Multicomponent system consisting of biocompatible elements targeting biomedical applications. In the present work an atomic model of equiatomic TiMoNbZr medium entropy alloy was built using a melting and quick quenching method and mechanical behaviour of the equiatomic alloy under uniaxial compression and tensile loading are further studied using atomistic simulation. The plastic deformation of TiMoNbZr is affected by the motion of dislocation loops. The prismatic dislocation loops inside TiMoNbZr are formed by the dislocations with the Burgers vectors of a/2 [1 1 1]. In addition, elastic constants were calculated at 0 K for bcc TiMoNbZr alloy and validated with DFT results. Results illustrate a superior metallic biomaterial that possess a desirable combination of high strength and low modulus for the application of biomaterials.
J-48: Mechanical Properties and Dislocation Activities of B2 High-Entropy Intermetallic Compounds: Ya-Jing Lee1; Ting-Ying Shih1; Cheng-Yuan Tsai1; Shou-Yi Chang1; 1National Tsing Hua University
Light-weight intermetallic compounds of great interest have been developed for decades for potential applications to aerospace industry. Although they have the advantage of high yield strength, however, the problem of low ductility remains. In this study, NiTi- and TiAl-based, ordered B2-phase high-entropy intermetallic compounds were hence developed. Their macro-to-nanoscale mechanical behaviors were investigated by using the compression tests of bulks, micropillars and nanopillars. The influence of multicomponent-altered structure ordering on dislocation activities was studied by molecular dynamics simulations. Experimental results indicated the uniform deformation, good plasticity and high work hardening of the high-entropy intermetallic compounds owing to the multiple slips of short dislocations than the long slips of complete dislocations. Cyclic compression at elevated temperatures caused the recovery of the small defects. Molecular dynamics simulations also suggested the plastic deformation mediated by the small-range activities of many short dislocations and the small-step motion of many neighboring atoms.
J-49: Mechanical Properties and Plastic Instabilities of FeAlCr-based Complex Concentrated Alloys: Tomas Tayari1; Michal Knapek1; Peter Minárik1; Josef Stráský1; Josef Pešička1; 1Charles University
The systematic study of equiatomic FeAlCrMo and FeAlCrV medium-entropy alloys in compression revealed their mechanical properties which are supreme to conventional alloys. On the other hand, these alloys exhibit unusual serrated flow observed around 400 °C and a strain rate of 10-4 s-1. This contribution presents a study of deformation behavior of an equiatomic FeAlCrNi – a novel medium-entropy alloy – in comparison with the alloys mentioned above. FeAlCrNi is a notable alloy exhibiting a specific microstructure composed of the BCC and B2 phases. Owing to the high content of passivating elements, Al and Cr, and the absence of Mo or V, it also possesses excellent resistance to high temperature oxidation at 800 °C essentially by forming a protective Al2O3 scale.
J-50: Mechanical Properties of Medium Entropy Alloys: Sheron Tavares1; Jesse Callanan2; David Jones2; Daniel Martinez2; Bingfeng Wang3; Saryu Fensin2; Marc Meyers1; 1University of California San Diego; 2Los Alamos National Laboratory; 3Central South University
Five equiatomic medium Entropy Alloys were prepared by vacuum Induction melting, homogenized, and recrystallized after plastic deformation. Their compositions, based on the Cantor HEA alloys: chromium, manganese, iron, cobalt, and nickel, and with the removal of one element, form five alloys.The quasi-static and dynamic mechanical properties were established and the propensity for shear localization was evaluated through hat-shaped specimens. The evolution of the structure upon mechanical deformation is compared to the mechanical properties. These MEAs have properties that match those of HEAs.
J-51: Metastability Engineering of Partially Recrystallized C-doped Non-equiatomic CoCrFeNiMo Medium-entropy Alloy: Hyeonseok Kwon1; Alireza Zargaran1; Peyman Asghari-Rad2; Eun Seong Kim1; Gang Hee Gu1; Jungwan Lee1; Jongun Moon1; Jae Wung Bae3; Hyoung Seop Kim1; 1POSTECH; 2Pennsylvania State University; 3Pukyong National University
Ferrous medium-entropy alloys (FeMEAs) are coming into attention these days for their excellent cost-effectiveness and mechanical properties owing to FCC-to-BCC deformation-induced martensitic transformation (DIMT). However, the FeMEAs usually possess low yield strength compared with high tensile strength and ductility. In this study, partially recrystallized microstructure consisting of coarse non-recrystallized grains with profuse mechanical twins and ultrafine recrystallized grains is presented as a solution to the problem. Nanosized M23C6-type and M6C-type carbides were also precipitated. Dislocation strengthening, precipitation strengthening, grain boundary strengthening, and twin boundary strengthening significantly improved strength of the partially recrystallized FeMEA. In addition, transformation-induced plasticity effect from the FCC-to-BCC DIMT activated by BCC nucleation at defects within the non-recrystallized grains effectively enhanced the work hardenability, leading to excellent strength and ductility. This study provides an insight to optimize the microstructure and corresponding mechanical properties of metastable metallic materials.
Microalloying Technology: A Promising Strategy for Designing Nanostructured High-entropy Alloy Films: Wenyi Huo1; Łukasz Kurpaska1; Hyoung Seop Kim2; Stefanos Papanikolaou1; 1National Centre for Nuclear Research; 2Pohang University of Science and Technology
In the manufacturing engineering for nanofabricated devices, polycrystalline metal thin films are indispensable as electrical resistors and structural elements. However, it is still a daunting task to design such metal films with structural and functional properties (e.g., hardness and resistivity) combined. High-entropy alloy film is considered as a promising candidate material suitable to go further in the simultaneous enhancement of both mechanical and electrical properties of thin film resistor. In this work, the remarkable microalloying (<2.0 at.%) enhancement in several sputtered CoCrFeNi high-entropy alloy films was investigated from a multitechnique approach. High resolution transmission electron microscope characterization shows in particular that there are unusual multifold nanotwins, and nanoscale polytypes. The knowledge of the relationship between structure and properties of such new materials was explored.
J-52: Microstructural and Mechanical Analysis of Cobalt-Free High Entropy Alloys: Morgan Ashbaugh1; Jerome Downey1; Jannette Chorney1; 1Montana Technological University
In recent years, high entropy alloys (HEA) have become a topic of great interest due to their enhanced mechanical properties. Though multiple HEA compositions have been created and analyzed to determine possible applications, the enormous number of possible combinations and variations of HEA compositions means that a relatively small amount of HEAs have been examined. In this study, select HEAs were designed and analyzed to determine their structure and properties for potential application as substitutes for cobalt in cemented carbides. Samples of the HEAs were examined using optical microscopy, electron backscatter diffraction, hardness testing, and toughness testing
J-53: Microstructure and Hardness of (CoCrCuTi) 100-x Fex with Duplex Hexagonal-Cubic Multi Principal Element Alloys: Brittney Terry1; Reza Abbaschian1; 1University of California, Riverside
In this presentation, we report on the influence of Fe additions on the microstructure and properties of (CoCrCuTi) 100-x Fex Multiprincipal Element Alloys containing 5, 10, 15, and 20% Fe. The alloys were prepared by arc melting and electromagnetic levitation processing. The CoCrCuTi alloy with additions of less than approximately 20% Fe shows a primary dendritic hexagonal Laves C14 phase with an FCC Cu- rich interdendritic matrix, similar to those observed with additions of Mn. Small Ti- rich dendrites are also observed throughout the material. When Fe addition is increased beyond 20%, liquid phase separation of an FCC Cu- rich phase is observed. The HCP dendritic phase was found to have high hardness, approaching ~1000 HV, yet they have low toughness. Cooling rate and melt stirring effects on the dendritic microstructure and toughness are also presented.
Microstructure and Mechanical Properties of In-situ TiC Reinforced Nb-Ta-V-Ti High Entropy Alloys: Jeong Pyo Lee1; Jeong Eun Kim1; Gian Song1; Jin Kyu Lee1; 1Kongju National University
High entropy alloys (HEAs) are defined as a class of multicomponent alloys consisting of five or more principal elements with equal or near equal compositions. HEAs prepared by mechanical alloying and subsequent consolidation process are a promising method to obtain homogeneous microstructures and enhanced mechanical properties. Recently the study of TiC particle reinforced HEA matrix composites has attracted scientists’ interest due to properties such as high-temperature strength and promising resistance to wear oxidation.In this study, the effect of TiC particle formation on the microstructure and mechanical properties of Nb-Ta-V-Ti HEAs was investigated. The HEA matrix composites were synthesized by high-energy ball milling followed by spark plasma sintering. Structural characterization was performed using X-ray diffractometry (XRD), scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The compressive strength of HEAs was measured at room and elevated temperature with a strain rate of 1x10-3s-1.
Microstructure and Mechanical Property of Gas Tungsten Arc and Friction Stir Welds of L12 Precipitate FCC High-entropy Alloy: Po-Ying Hsieh1; Chih-Hsien Liao1; Hung-Chih Liu1; Po-Ting Lin1; Pai-Keng Shen1; Shao-Wei Hunag1; Yutaka S. Sato2; Che-Wei Tsai1; 1National Tsing Hua University; 2Tohoku University
The welding technology is significant in the application of HEAs in the industry. In this study, we discussed the mechanical properties and microstructure of Al0.2Co1.5CrFeNi1.5Ti0.3 after welding by gas tungsten arc (GTA) welding and friction stir welding (FSW), respectively. First, GTA welding of precipitated HEAs resulted in formation of the dendrites in fusion zone, and the hardness and the tensile strength of the GTA weld decreased to 68% and 51% of those of the base metal, respectively. However, FSW exhibited the excellent mechanical properties, which were still over 94% of hardness value and tensile strength of the base metal. The microstructure was characterized by discontinuous dynamic recrystallization and the grain refinement effect in the stir zone. After tensile test with digital image correlation, the GTA weld had the low strength with nonuniform deformation in the fusion zone, while FS weld showed the high strength with uniform deformation.
J-54: Microstructure, Mechanical Properties, and Long-term Stability of FeMnNiAlCr High Entropy Alloys for Concentrated Solar Power Systems: Edwin Jiang1; Xiaoxue Gao1; Andrew Pike1; Ian Baker1; Jifeng Liu1; Geoffroy Hautier1; 1Dartmouth College
Concentrated solar power (CSP) offers advantages in cost-effective energy storage on harvesting solar energy and the capability to provide electricity when the sun is absent. However, currently-employed tubing materials cannot work at temperatures exceeding 873 K due to mechanical, corrosion, and oxidation limitations, which restrict the conversion efficiency. High entropy alloys (HEAs) are being considered to solve the challenge due to their novel mechanical properties at high temperatures. In this study, we present microstructural characterization, tensile strength, and creep properties of FeMnNiAlCr high entropy alloys, with different Mn content (x = 32.9 – 42 at. %) at temperatures of 873-1023 K. The effect of recrystallization on the microstructures and mechanical properties were also studied. Both as-cast and recrystallized alloys exhibit high strength, good creep resistance, and long-term stability at high temperature. In-situ deformation experiments were conducted in the transmission electron microscope to examine the deformation mechanisms.
J-55: Minor Addition of Boron on Macro- and Micro-Mechanical Properties of Refractory High-Entropy Alloys: Ping-Hsu Ko1; Ya-Jing Lee1; Shou-Yi Chang1; 1National Tsing Hua University
Refractory high-entropy alloys with good mechanical properties and high thermal stability have been intensively developed for applications at elevated temperatures. However, many of them suffer from the problem of intergranular fracture-caused low ductility. Their macro-mechanical properties and microscale plastic deformation as well as the strengthening of grain boundary are worth investigations for improving fracture toughness. In this study, 0.1 at.% boron was added in HfMoxNbTaTiZrVy alloys, and the nanoindetations of differently-oriented grains, micropillar compression tests and macro-compression tests were conducted. Nanoindenting hardness indicated that these alloys exhibited lessened plastic anisotropy. The compression of micropillars showed uniform plastic deformation with multiple small slip traces and a high work hardening rate, instead of large load drops. In the macro-compression tests, the alloys had high yield strengths of 1500 MPa but low ductility. With the minor addition of boron, the ductility was improved, and the intergranular fracture was inhibited.
J-56: Nanoindentation Creep of Electrodeposited Nanocrystalline NiFeCo Medium Entropy Alloy: Lizhong Lang1; Michel Haché1; Yu Zou1; 1University of Toronto
Traditional methods to fabricate nanocrystalline multi-principal high entropy alloys (nc-MPEAs), such as high pressure torsion, require significant energy input, which hinder the scalable production and drive up the cost of nc-MPEAs. Electrodeposition, as another way to produce nanocrystalline metals, however, haven’t received much attention in application on MPEAs until recently. Recently, electrodeposited medium entropy alloy NiFeCo has been successfully prepared in high hardness and thermal stability. As deposited by a new technique, however, the mechanical properties of electrodeposited NiFeCo under extreme conditions remain unexplored, including creep, fatigue, or high strain rate deformation. In this work, the authors probed the indentation creep behavior of electrodeposited high entropy alloys with newly developed constant contact pressure method. The creep resistance was predicted in terms of activation volume and creep life. The creep mechanisms were also discussed, as well as the influence of elemental composition and heat treatment.
J-57: Neutron Diffraction and Total Scattering Investigation of an Unusual Long-range Order-Disorder Transition Competing with Short-range Ordering in 10-component Oxides: Dawei Zhang1; Yan Chen2; Heidy Vega1; Tianshi Feng1; Dunji Yu2; Michelle Everett2; Joerg Neuefeind2; An Ke2; Renkun Chen1; Jian Luo1; 1University of California San Diego; 2Oak Ridge National Laboratory
Neutron diffraction and total scattering are combined to investigate a series of single-phase 10-component compositionally complex fluorite-based oxides (10CCFBOs) A long-range order-disorder transition (ODT) occurs at x = 0.81 ± 0.01, from the ordered pyrochlore to disordered defect fluorite. In contrast to ternary oxides, this ODT occurs abruptly without an observable two-phase region; moreover, the phase stability in 10CCFBOs deviates from the well-established criteria for simpler oxides. Rietveld refinements of neutron diffraction patterns reveals the detailed atomistic mechanism of the ODT. We further discover short-range weberite-type order in Nb-rich compositions based on diffuse scattering and small-box modelling. Interestingly, the weberite-type short-range order emerges before the ODT, coexisting and interacting with long-range pyrochlore order, and persist into the long-range disordered defect fluorite structure after the ODT. Notably, a drop in the thermal conductivity is coincident with emergence of the short-range order, instead of the long-range ODT.
J-58: Non-Equatomic Composition Effect on the Thermodynamic Properties of MoNbTaW: Sarah O'Brien1; Matthew Beck1; 1University of Kentucky
One of the key characteristics of single-phase Multi-Principal Element Alloys (MPEAs) is the increased entropy, specifically the configurational entropy. An ongoing discussion is the role of vibrational entropy (Svib) and phonon density of states (pDOS) in stabilizing single-phase MPEAs. It has been seen that the vibrational properties of MPEAs, specifically the refractory MPEA MoNbTaW, are affected by small variations in the local configuration and composition due to differences in lattice strain and interatomic interactions. It has also been shown that non-equatomic compositions can increase the stability in certain systems. We have used density functional perturbation theory to explore the connection between the shifted compositions of MoNbTaW and of both pDOS and Svib. The concentrations of specific elements and local configuration of atoms is also explored. The results highlight the impact of specific elements and local arrangement on the stability of this refractory MPEA.
J-59: On the Molten State Processing of Refractory Complex Concentrated Alloys: Calvin Belcher1; Sakshi Bajpai1; Benjamin MacDonald1; Enrique Lavernia1; Diran Apelian1; 1University of California Irvine
The study of RCCAs has been motivated by their potential for applications which require high temperature strength and stability. Molten state processing of RCCAs through arc melting has been the main processing pathway to produce industrially representative microstructures. However, despite some progress, challenges remain, particularly in controlling impurity elements in RCCAs. Moreover, and perhaps more critically, the influence of impurity elements on the physical behavior of RCCAs is not well understood. In this work, the chemistry of the chamber environment during arc melting was studied using a mass spectrometer. Process methodologies were studied to control impurity gas elements such as oxygen and nitrogen in arc melted RCCAs. Furthermore, by arc melting NbMoTaW and TiNbZr RCCAs in various environments, relationships between RCCA constituents and impurity element absorption were explored. Through mechanical testing, X-Ray diffraction, and electron microscopy, the behavior of impurity elements in various RCCA compositions will be reviewed and discussed.
J-60: On the Pursuit of Stress-induced Transformation Effect in the High-entropy Ti-Zr-Nb-Mo-Al System: Mariano Casas-Luna1; Dalibor Preisler1; Jiří Kozlík1; Miloš Janeček1; Josef Stráský1; 1Charles University
The empirical relationship between the bond order (Bo) and the d-orbital energy level (Md) is widely used in the design of titanium alloys with enhanced mechanical properties. This approach was introduced later in the development of titanium-rich multi-principal element alloys (MPEAs) that could exhibit superior strengthening properties by stress-induced transformation effects, such as transformation-induced plasticity (TRIP), and twinning-induced plasticity (TWIP). These deformation effects can provide at once strength and ductility in MPEAs, highlighting the importance of finding and adjusting the numerous compositions of such alloys.In this study, the Bo-Md approach was applied to produce several MPEAs of the Ti-Zr-Nb-Mo-Al system. The chemical compositions were selected aiming to obtain a stress-induced transformation effect in the high-entropy system, varying from 20 to 35 at.% of Ti. Results show the dependence of the final phase composition with the Zr/Al content, impacting the microhardness and compressive deformation mechanism of the produced MPEAs.
J-61: Order-Disorder Effects in Mixed BCC/FCC FeNiMoW MPEA: Sarah O'Brien1; Matthew Beck1; 1University of Kentucky
MPEAs of mixed BCC and FCC elements yield complex multi-phase microstructures, often including solid solution phases that are themselves MPEAs. Equiatomic multi-phase FeNiMoW alloys have been demonstrated to exhibit desirable high-strain rate mechanical properties attributed to adiabatic shear banding (ASB). Evidence suggests that ASB in equiatomic FeNiMoW alloys occurs in grains containing lamellae-like alternating regions of an FCC solid solution phase (approximate composition Fe40Ni40Mo15W5) and a Mo rich/W poor rhombehedral phase. Here we demonstrate the application of DFT-based atomistic calculations to reveal the heat capacity, elastic, magnetic, and order-disorder properties (including transition temperatures) of solid solution and “semi-ordered” MPEAs using Fe40Ni40Mo15W5 as an application-relevant model system. Results suggest the importance of order-disorder transitions associated with BCC elements in the FCC lattice in determining thermodynamic stability and mechanical properties of this MPEA.
J-62: Phase-field Crystal Modeling of Deformation Mechanics in BCC Refractory Metal-based MPEAs: Kate Elder1; Joel Berry1; Amit Samanta1; Aurelien Perron1; Scott McCall1; Joseph McKeown1; 1Lawrence Livermore National Laboratory
Refractory metal-based multi-principal element alloys (MPEAs) with a body centered cubic (BCC) structure can maintain excellent mechanical properties at high temperatures. However, the dominant plasticity mechanisms (e.g. edge versus screw dislocation processes) are debated. Difficulty in addressing this issue with atomistic simulations stems partly from the fact that high-temperature plasticity involves rapid dislocation glide, slow dislocation climb, and slow diffusional composition rearrangements. Relative to traditional alloys, these processes are further complicated by the atypical composition environments in MPEAs. To explore the microstructural origin of refractory MPEA mechanical performance, phase-field crystal (PFC) modeling, a phenomenologically time-averaged atomistic method, is used. This technique describes glide, climb, and compositional diffusion kinetics while spanning atomistic to microstructural length scales. A new PFC model for direct simulation of high-temperature dislocation kinetics in MPEAs will be presented along with results and insights from simulated deformation experiments. Prepared by LLNL under Contract DE-AC52-07NA27344.
J-63: Phase Stability in Ti-Zr-Nb Refractory Medium Entropy Alloys from Atomistic Simulations: Sally Issa1; Céline Varvenne1; Guy Tréglia1; Hakim Amara2; 1Aix Marseille Université, CNRS, CINAM; 2LEM ONERA
Refractory high entropy alloys having a bcc structure are of great interest because of their excellent mechanical properties retained up to elevated temperatures. But their stability needs to be better understood, and ab initio calculations can provide valuable and accurate insights. Selecting the Ti-Zr-Nb system as a model alloy for group IV and V RHEAs, we map phase stability from dilute to high concentration, equiatomic alloys. We consider both ordered and disordered alloys, the latter being generated as special quasi random structures. In particular, the bcc stability zone is identified as rather extended in alloy composition: this is interpreted in terms of electronic effects and local lattice distortions. In mechanically unstable zones, we show that substitutional defects, like vacancies, always act as phase destabilizers towards more compact and possibly more complex crystallographic structures. We discuss important implications for phase transformation mechanisms and for experimentally observed alloy microstructures.
Cancelled
Phase Stability of Hf-Mo-Nb-Ta-Ti Refractory Multi-Principal Element Alloys: Anthony Botros1; Carolina Frey1; Noah Phillips2; Tresa Pollock1; 1UCSB; 2ATI
Refractory Multi-principal Element Alloys (drawn from combinations of Cr, Hf, Mo, Nb, Ta, Ti, V, W, and Zr) present an opportunity for structural alloys with operation temperatures above 1200°C. However, deleterious phases that form at intermediate temperatures present a challenge. A series of arc-melted Hf-Mo-Nb-Ta-Ti alloys are analyzed in both their as-cast and annealed conditions to determine the effect of composition on phase formation. Effect of oxygen on phase stability and lattice parameters are also examined. A comparison to CALPHAD predictions and literature alloys is presented.
J-64: Plastic Behavior of Phase-separated FCC Complex Concentrated Alloys: Shawn Chen1; Ibrahim Altarabshe1; 1Louisiana Tech University
Complex Concentrated Alloys (CCAs)with multiple elements mixed in high mole fractions have received exceedingly broad attention in the field of materials design due to their large compositional space and potentially superior mechanical properties, the latter being largely determined by the dislocation behaviors and its interaction with microstructures in the CCAs. Based on the compositions in experimentally obtained phase-separated CCAs, this work first uses atomistic simulations to measure the energy barrier of single edge and screw dislocations across the phase-interfaces in three different phase-separated FCC CCAs. Larger scale atomistic simulations and concurrently coupled atomistic simulations are then conducted to study the dislocation evolution as well as the resulting plastic mechanical responses.This work will shed light on the fundamental mechanistic understanding of the effect of dislocation phase-interface interaction on their mechanical properties.
J-65: Plastic Deformation of BCC Medium-entropy Alloys in the Ti-Zr-Nb Systems: Shohei Onda1; Shu Han1; Zhenghao Chen1; Kyosuke Kishida1; Haruyuki Inui1; 1Kyoto University
Ti-Zr-Nb-Hf-Ta BCC high-entropy alloy (HEA) and its derivative medium-entropy alloys (MEAs) have received considerable attentions as new structural materials because of good retention of high strength up to very high temperatures as well as excellent ductility even at liquid nitrogen temperature. Recently, strength of Ti-Zr-Nb-Hf-Ta based HEA/MEAs has been reported to depend strongly on the combination of elements and their chemical compositions. However, the underlying mechanism that controls the element/composition dependent strength has not been fully clarified yet. In the present study, plastic deformation behavior of polycrystals of BCC MEAs in the Ti-Zr-Nb ternary system was systematically investigated by uniaxial mechanical tests (tension and compression) at room temperature as a function of chemical composition. Deformation microstructures were investigated by optical microscopy and transmission electron microscopy in order to identify the loading-axis dependence of the slip planes and dislocation structures, respectively.
J-66: Plastic Deformation of Single Crystals of Ternary Equiatomic Alloys with the FCC Structure: Seiko Tei1; Shougo Kuroiwa1; Le Li1; Zhenghao Chen1; Kyosuke Kishida1; Haruyuki Inui1; 1Kyoto University
After the discovery of the Cr-Mn-Fe-Co-Ni equiatomic FCC solid-solution alloy with high strength and ductility, its derivative ternary and quaternary alloys have been the subject of extensive research. Early studies using polycrystals of various equiatomic FCC solid-solution alloys based on the Cr-Mn-Fe-Co-Ni alloy have suggested that the combination of elements is one of the most important factors that control the mechanical properties of these materials because both the highest strength and highest ductility are obtained for the Cr-Co-Ni ternary alloy. However, the detailed mechanism controlling the mechanical properties of these new FCC solid-solution alloys has not been fully clarified yet, partly because of the lack of fundamental experimental data obtained using single crystals. In the present study, we systematically investigated fundamental mechanical properties of a series of ternary equiatomic FCC solid-solution alloys based on the Cr-Mn-Fe-Co-Ni alloy by tension and compression tests of single crystals at low temperatures.
J-67: Preferential Composition during Nucleation and Growth in Multi-Principal Elements Alloys: Saswat Mishra1; Alejandro Strachan1; 1Purdue University
Multi-principal elements alloys (MPEAs) have excellent high-temperature mechanical and irradiation-resistant properties. These properties are a result of high entropy in these systems. During operation, the alloy can undergo rapid local melting and recrystallization. Knowledge of the conditions around the nucleation of these alloys is critical from both applied and basic science points of view. Unfortunately, the experimental determination of nucleation is challenging owing to the small length and time scales. Thus, we use molecular dynamics simulations to calculate the composition of the nucleus as it grows in a CoCrCuFeNi equiatomic MPEA. We use polyhedral template matching to look at the crystal structure, followed by a cluster analysis that follows the composition of the nucleus as it grows. We observe that nucleation prefers specific compositions.
J-68: Processing-Structure Relationship in Additive Friction Stir Deposited AlxCoCrFeNi Complex Concentrated Alloys: Michael Amling1; Malcolm Williams2; Paul Allison2; Mark Weaver1; 1University of Alabama; 2Baylor University
This study investigates the process-structure relationship for bulk Al0.04CoCrFeNi and Al0.2CoCrFeNi complex concentrated alloys (CCAs) produced via additive friction stir deposition (AFSD). Bulk deposits were produced using the AFSD machine from cast HEA feedstock. The presence of equilibrium and nonequilibrium phases after deposition were determined via x-ray diffraction. Energy dispersive x-ray spectroscopy and electron backscatter diffraction were utilized to quantify elemental segregation, grain size and grain/phase morphology after deposition. The feedstock grain size was significantly reduced during processing due to dynamic recrystallization. The Al0.2CoCrFeNi CCA exhibited a substructure different than cast due to the AFSD process. This substructure was analyzed using both transmission electron microscopy and atom probe topography to determine the elemental segregation seen between the phases and to view precipitate evolution during processing. The microstructures are discussed relative to cast materials with the same or similar compositions.
J-69: Recrystallization Behavior of NbTiZr-Containing Refractory Multi-Principal Element Alloys: Adira Balzac1; Benjamin Ellyson1; Kester Clarke1; Amy Clarke1; 1Colorado School of Mines
Refractory multi-principal element alloys (RMPEAs) are promising candidates for ultra-high temperature applications. The recrystallization behavior of these alloys is not yet well explored, and some have exhibited dynamic recrystallization atypical of BCC alloys, developing a necklace microstructure characteristic of low stacking fault energy FCC alloys. Understanding static and dynamic recrystallization behavior is crucial to developing thermomechanical processing pathways that lead to homogenous and reproducible mechanical properties. This study explores the recrystallization behavior of several NbTiZr-containing RMPEAs during and after hot- and cold-working. Deformation at various strain rates and temperatures with and without annealing heat treatments serves to develop an understanding of the extent of the recrystallized microstructure on these parameters. The knowledge gained from this study will allow us to develop models to predict recrystallization behavior, as well as the effects of recrystallization on microstructure, mechanical properties, and performance of RMPEAs.
J-71: Relaxation and Diffusion Processes at High Temperature in Fe-Mn-Cr-Ni-Co High Entropy Alloy Studied by Mechanical Spectroscopy: Jose San Juan1; Lucía Del-Río1; Guillaume Laplanche2; María Nó1; 1Universidad del Pais Vasco; 2Ruhr Universität Bochum
High entropy alloys (HEA) exhibit in general a sluggish diffusion making them more stable at high temperature being this aspect relevant for its creep behavior. However, the compositional complexity of the HEA makes the study of the atomic diffusion processes more difficult than in conventional alloys.In the present work the study of the relaxation processes associated with the atomic diffusion mechanisms in a Fe-Mn-Cr-Ni-Co HEA. This is approached through mechanical spectroscopy and measuring the internal friction spectra and dynamic modulus variation in the temperature range between 300ºC and 1000ºC. Two relaxation processes have been identified in the internal friction spectra, as well as the diffusional mechanism associated with the precipitation of some stable phases. The analysis of the internal friction spectra allows obtaining the activation energy of the active relaxation processes, establishing a relationship with the diffusive atomic species.
J-72: Shape Memory Effect in CrMnFeCoNi Multi-principal Element Alloys: Je In Lee1; Jinsurang Lim1; Wook Ha Ryu2; Hyun Seok Oh3; Eun Soo Park2; Koichi Tsuchiya4; 1Pusan National University; 2Seoul National University; 3Massachusetts Institute of Technology; 4National Institute for Materials Science
High-entropy alloys, which have multi-principal elements with near equiatomic composition, have drawn significant attraction for developing novel structural and functional materials with exceptional properties. In the present study, we show the influence of alloy composition on the phase transformation and shape memory behavior in CrMnFeCoNi high-entropy alloy system. With CALPHAD approach, we calculate the difference in Gibbs free energy between austenite fcc and martensite hcp phases, and find a substantial increase in thermodynamic equilibrium temperature between both phases. The transformation temperatures in the non-equiatomic CrMnFeCoNi alloys can be increased with increasing the Co/Ni and/or Cr/Mn ratio, which is comparable to that of B2-based shape memory multicomponent alloys with noble metals or refractory metals. It is expected that these results could open a new field of HEA applications as high-temperature SMAs.
J-73: Solid Particle Erosion Resistance of Eutectic High-entropy Alloys Using an Improved Air-jet Sandblaster Method: Wandong Wang1; Yu Zou1; 1University of Toronto
Solid particle erosion describes a wear phenomenon, where a high-pressure gas stream carrying solid particles with kinetic energy impacts the component surface. Eutectic high-entropy alloys (EHEAs) show an excellent strength-ductility combination and good work hardening behavior, which are feasible for erosion application. In this study, an improved air-jet sandblaster was used to test the erosion performance of EHEAs. Instead of building a hole on the sample surface, several shallow channels were formed to ensure the consistency of the abrasive flow rate and to collect a bigger dataset for analysis. A non-contact optical profilometer was used to calculate the erosion rate. The effect of particle speed and impact angles (20, 30, 45, 60, and 90 degrees) on EHEAs were investigated. The results show that compared a 316 stainless steel, EHEA has low erosion rates, and it shows an obvious superiority in a high-speed particle condition.
J-74: Study of the Grain Growth Kinetics and Hall-Petch Relationship in Fe-rich Multi-principal Element Alloys: David Silva1; Gustavo Bertoli1; Michael Kaufman2; Amy Clarke2; Francisco Coury1; Claudemiro Bolfarini1; 1Federal University of São Carlos; 2Colorado School of Mines
Recently, multi-principal element alloys (MPEAs) derived from Cantor's alloy (CoCrFeNiMn) with varying Fe content have been investigated theoretically and experimentally. In relation to other strengthening mechanisms, grain refinement tends to be the most effective to increase strength with smaller plasticity losses. In this work, the recrystallization behavior, grain growth kinetics, and corresponding hardness variation of three FCC MPEAs are studied. The annealed and deformed samples were characterized to observe the active deformation mechanism on each composition. Experimental results indicate that the grain size and hardness of these MPEAs follow the Hall-Petch equation. The activated deformation mechanism is heavily dependent on the composition. The grain growth exponent n, kinetic constant k, and activation energy for grain growth QG of the Fe-rich MPEAs were calculated. These values will be discussed and compared to other MPEAs systems in the literature.
Synchrotron X-ray Diffraction and Tomography Simultaneous Studies of Multiple Phase Transformation Dynamics in Al-based Multiple Component Alloys: Kang Xiang1; Shi Huang1; Hongyuan Song1; Jiawei Mi1; 1University of Hull
we used synchrotron X-ray diffraction and tomography simultaneously to study in real-time the multiphase dynamic evolution of Al-Fe-Mn-Si multicomponent alloys during the solidification process. The onset of phases nucleation was identified in-situ by diffraction. Then the subsequent growth of the phases in 3D space can be tracked by tomography in real-time. As the solidification proceeds, the 3D morphology and the spatial relationship of those phases were continuously monitored and recorded. In this way, the whole nucleation and phase growth dynamic process of the multiphases in 3D space can be systematically studied. The research provides comprehensive structure evolution information for us to fully understand the formation of the complex structures in such alloy system which is essential for the alloy design and optimization.
J-75: Synthesis and Characterization of Novel Multi-element Magnesium-based Medium Entropy Alloys: Srivatsan Tirumalai1; Khin Tun1; Manoj Gupta1; 1The University of Akron
In this technical presentation the results of a study on development of low-density multicomponent alloys, based on the Mg-Al system, will be highlighted and discussed. Alloy design was based on use of multi-element alloying approach with the prime intent of increasing the mixing entropy so as to be categorized as medium entropy alloys (MEAs). For the new alloys developed, the concentration of each alloying element remained at ≥ 5 atomic percent with magnesium [60 to 70 atomic percent] being the dominant base material. The calculated mixing entropy of the newly developed alloys was ≥ 1R [R = gas constant, 8.314 J/K mol], thereby qualifying each of the alloys to be a medium entropy alloy. The developed magnesium-based medium entropy alloys, Mg60Al20Cu10Zn5Mn5 and Mg70Al10Cu10Zn5Mn5, were synthesized using the technique of disintegrated melt deposition [DMD]. Subsequent to synthesis, characterization studies were done to understand microstructural development and influence on mechanical properties.
Cancelled
J-76: The AlMo0.5NbTa0.5TiZr Refractory High Entropy Superalloy: Experimental Findings and Comparison with Calculations Using the CALPHAD Method: Patricia Suarez Ocano1; Leonardo Agudo Jácome1; Suzana G. Fries2; Inmaculada Lopez-Galilea2; Reza Darvishi Kamachali1; 1Bundesanstalt für Materialforschung und -prüfung (BAM); 2Ruhr-Universität Bochum (Bochum, Nordrhein-Westfalen)
In the as-cast state, the AlMo0.5NbTa0.5TiZr refractory high entropy superalloy shows a mixture of A2 and B2 phases, both in the dendritic and interdendritic regions. A mostly amorphous phase, rich in Al and Zr, is found within the interdendritic region. The as-cast state is compared with the state annealed at 1400 °C for 24 h, which in turn are compared with equilibrium and Scheil calculations using two different databases (CALPHAD method). A previously hypothesized spinodal decomposition during cooling as the mechanism responsible for the patterned A2/B2 microstructure is confirmed via the CALPHAD calculations. Furthermore, differential thermal analysis reveals a good agreement between measured phase transformation temperatures and calculated values. Finally, these findings allow better understanding of the solidification path and equilibrium stability of this alloy, giving a base for improvements in the field of new refractory superalloy design.
The Precipitated Strengthening of Eta Phase on the Non-equimolar CoCrNiTi Medium-entropy Alloys: Pai-Keng Shen1; Hung-Chih Liu1; Shao-Lun Lu2; Hung-Wei Yen2; Jien-Wei Yeh2; Che-Wei Tsai1; 1National Tsing Hua University; 2National Taiwan University
In high-entropy alloys (HEAs) and traditional alloys, η-Ni3Ti precipitation is usually avoided due to its brittleness. However, studies have demonstrated that using thermal mechanical process to control precipitates in nano-size is an effective approach to overcome strength-ductility dilemma. Herein, we focus on a non-equimolar CoCrNiTi medium-entropy alloy (MEA) which consists of face-centered cubic (FCC) matrix and Ni3Ti η phase precipitation. The microstructures of η precipitation are observed to achieve uniform and nano-scale morphology. Hardness and tensile test are also conducted to testify the mechanical properties. In addition, a novel processing is utilized and compared with conventional cold-rolling and aging procedure. The results indicate that our technique brings about more uniformly distributed precipitations and higher hardness than traditional ones. Moreover, the alloys are 200 to 300 MPa higher in yield strength (YS) and ultimate tensile strength (UTS) without losing ductility. The causes of the superior properties are also discussed.
J-107: Thermal Super-jogs Control High-temperature Strength in Nb-Mo-Ta-W Alloys: Sicong He1; Xinran Zhou1; Jaime Marian1; 1University of California, Los Angeles
Refractory multi-element alloys (RMEA) with bcc structure have been extensively studied over the last decade due to their potential for high-temperature applications. In this work, we propose a new strengthening mechanism based on thermal super-jogs in edge dislocation. The basis for the formation of super-jogs is in the vacancy formation energy distributions of RMEA. Vacancies at edge dislocation cores relax into super-jogs, hardening the alloy due to jog-pinning. At the same time, these super-jogs can displace diffusively along the glide direction, relieving some of the extra stress. We implement these mechanisms into a specially-designed hybrid kinetic Monte Carlo/Discrete Dislocation Dynamics approach (kMC/DD). The kMC module sets the timescale dictated by thermally-activated events, while the DD module relaxes the dislocation line configuration in between events. We find that the balance between super-jog pinning and super-jog diffusion confers an extra strength to edge dislocations that is in remarkable agreement with experimental measurements.
J-77: Transmission Electron Microscopy of Temperature Dependent Deformation Mechanisms in Multi-principal Element Alloys: Madelyn Payne1; Mingwei Zhang2; Punit Kumar2; Mark Asta2; Robert Ritchie2; Andrew Minor2; 1University of California, Berkeley; 2Lawrence Berkeley National Laboratory
Multi-principal element alloys (MPEAs) have attracted attention from the metallurgy community due to their exceptional properties, often at both high and low temperatures. Transmission electron microscopy (TEM) provides a means to investigate various deformation mechanisms producing remarkable mechanical properties in both face-centered cubic (fcc) and body-centered cubic (bcc) MPEA systems. High-resolution TEM and four-dimensional scanning electron microscopy (4D-STEM) analysis reveal an extended sequence of deformation mechanisms that produce exceptional fracture toughness. Spatially-resolved structural information from 4D-STEM datasets uncover how stacking faults, hcp laths, and nanotwins operate synergistically to prolong strain-hardening. Here we report both ex situ and in situ TEM observations of deformation mechanisms in both fcc MPEAs and bcc refractory MPEAs across a wide range of temperatures.
Ultra-low Thermal Conductive Metallic Material: High Entropy Alloy Foam: Kook Noh Yoon1; Khurram Yaqoob2; Je In Lee3; Jin Yeon Kim1; Eun Soo Park1; 1Seoul National University; 2National University of Sciences and Technology; 3Pusan National University
Generally, it is well-known that the thermal conductivity of the metallic material decreases as the number of alloying elements increases. In this point of view, high entropy alloy (HEA), which is constituted of several principal elements, will exhibit abnormally low thermal conductivity for metal due to the high lattice distortion. Meanwhile, a porous body can also offer a great hindering effect on heat flow through materials. Thus, porous HEA can offer lower thermal conductivity than any other metallic material owing to the combination effect of composition and structure. In the present study, therefore, we fabricated HEA foam by dealloying a phase separating HEA, FeCoCrNi-Cu. In particular, we will systematically assess the property correlation between thermal conductivity and strength depending on the porosity. Indeed, we develop novel HEA foam with ultra-low thermal conductivity and high strength, which might be successfully applied as a heat shield material.