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Critical Review of High Entropy Alloys and Related Concepts (Postprint).

AD1035288

Publication Date	2016
Personal Author	Miracle, D. B.; Senkov, O. N.
Page Count	66
Abstract	High entropy alloys (HEAs) are barely 12 years old. The field has stimulated new ideas and has inspired the exploration of the vast composition space offered by multi-principal element alloys (MPEAs). Here we present a critical review of this field, with the intent of summarizing key findings, uncovering major trends and providing guidance for future efforts. Major themes in this assessment include definition of terms; thermodynamic analysis of complex, concentrated alloys (CCAs); taxonomy of current alloy families; microstructures; mechanical properties; potential applications; and future efforts. Based on detailed analyses, the following major results emerge. Although classical thermodynamic concepts are unchanged, trends in MPEAs can be different than in simpler alloys. Common thermodynamic perceptions can be misleading and new trends are described. From a strong focus on 3d transition metal alloys, there are now seven distinct CCA families. A new theme of designing alloy families by selecting elements to achieve a specific, intended purpose is starting to emerge. A comprehensive microstructural assessment is performed using three datasets: experimental data drawn from 408 different alloys and two computational datasets generated using the CALculated PHAse Diagram (CALPHAD) method. Each dataset emphasizes different elements and shows different microstructural trends. Trends in these three datasets are all predicted by a structure in - structure out (SISO) analysis developed here that uses the weighted fractions of the constituent element crystal structures in each dataset. A total of 13 distinct multi-principal element single-phase fields are found in this microstructural assessment. Relationships between composition, microstructure and properties are established for 3d transition metal MPEAs, including the roles of Al, Cr and Cu. Critical evaluation shows that commercial austenitic stainless steels and nickel alloys with 3 or more principal elements are MPEAs.
Keywords	Alloys Microstructure Mechanical properties Thermodynamics Transitional metals Refractory metals Refractory metal alloys Entropy Materials science Crystal structure Phase transformations Solid solutions Enthalpy Intermetallic compounds Crystal lattices Thermal properties Electrical properties Magnetic properties Hardening Hea(high entropy alloys) Mpea(multi-principal element alloys) Cca(complex concentrated alloys) Multicomponent Transition metal alloys Calphad(calculated phase diagram) Functional properties Lattice distortion
Source Agency	Non Paid ADAS
NTIS Subject Category	71N - Nonferrous Metals & Alloys
Corporate Authors	Air Force Research Lab., Wright-Patterson AFB, OH. Materials and Manufacturing Directorate.
Supplemental Notes	Acta Materialia , 122, 01 Jan 0001, 01 Jan 0001,
Document Type	Technical Report
Title Note	Journal Article
NTIS Issue Number	201725
Contract Number	FA8650-10-D-5226-0005

Critical Review of High Entropy Alloys and Related Concepts (Postprint).

Critical Review of High Entropy Alloys and Related Concepts (Postprint).
AD1035288

Publication Date	2016
Personal Author	Miracle, D. B.; Senkov, O. N.
Page Count	66
Abstract	High entropy alloys (HEAs) are barely 12 years old. The field has stimulated new ideas and has inspired the exploration of the vast composition space offered by multi-principal element alloys (MPEAs). Here we present a critical review of this field, with the intent of summarizing key findings, uncovering major trends and providing guidance for future efforts. Major themes in this assessment include definition of terms; thermodynamic analysis of complex, concentrated alloys (CCAs); taxonomy of current alloy families; microstructures; mechanical properties; potential applications; and future efforts. Based on detailed analyses, the following major results emerge. Although classical thermodynamic concepts are unchanged, trends in MPEAs can be different than in simpler alloys. Common thermodynamic perceptions can be misleading and new trends are described. From a strong focus on 3d transition metal alloys, there are now seven distinct CCA families. A new theme of designing alloy families by selecting elements to achieve a specific, intended purpose is starting to emerge. A comprehensive microstructural assessment is performed using three datasets: experimental data drawn from 408 different alloys and two computational datasets generated using the CALculated PHAse Diagram (CALPHAD) method. Each dataset emphasizes different elements and shows different microstructural trends. Trends in these three datasets are all predicted by a structure in - structure out (SISO) analysis developed here that uses the weighted fractions of the constituent element crystal structures in each dataset. A total of 13 distinct multi-principal element single-phase fields are found in this microstructural assessment. Relationships between composition, microstructure and properties are established for 3d transition metal MPEAs, including the roles of Al, Cr and Cu. Critical evaluation shows that commercial austenitic stainless steels and nickel alloys with 3 or more principal elements are MPEAs.
Keywords	Alloys Microstructure Mechanical properties Thermodynamics Transitional metals Refractory metals Refractory metal alloys Entropy Materials science Crystal structure Phase transformations Solid solutions Enthalpy Intermetallic compounds Crystal lattices Thermal properties Electrical properties Magnetic properties Hardening Hea(high entropy alloys) Mpea(multi-principal element alloys) Cca(complex concentrated alloys) Multicomponent Transition metal alloys Calphad(calculated phase diagram) Functional properties Lattice distortion
Source Agency	Non Paid ADAS
NTIS Subject Category	71N - Nonferrous Metals & Alloys
Corporate Authors	Air Force Research Lab., Wright-Patterson AFB, OH. Materials and Manufacturing Directorate.
Supplemental Notes	Acta Materialia , 122, 01 Jan 0001, 01 Jan 0001,
Document Type	Technical Report
Title Note	Journal Article
NTIS Issue Number	201725
Contract Number	FA8650-10-D-5226-0005