Effect of μ-precipitates on the microstructure and mechanical properties of non-equiatomic CoCrFeNiMo medium-entropy alloys

Abstract Non-equiatomic Co17.5Cr12.5Fe55Ni10Mo5 (Mo5) and Co18Cr12.5Fe55Ni7Mo7.5 (Mo7.5) medium-entropy alloys were synthesized by vacuum induction melting, cold rolling, and subsequent annealing treatment at various temperatures (900–1200 °C) and they were investigated to exploit the precipitation strengthening in addition to solid solution strengthening of alloys. The effect of annealing temperature and Mo content on the microstructure and mechanical properties are systematically analyzed. From the microstructural analysis, a Mo-rich μ phase is observed in the face-centered cubic (fcc) matrix. Increasing the Mo content and low annealing temperature enhance the formation of μ phase, which is consistent with the thermodynamic calculation results. The formation of μ phase effectively enhances the strength of the Mo7.5 alloy by precipitation strengthening, and suppression of grain growth and recrystallization by Zener pinning effect. These lead to superior combination of tensile strength as high as 1100 MPa and large ductility. Our results provide insights not only into μ-phase strengthening of fcc-structured alloys, but also into the future development of high-performance MEAs.

[1]  Ke An,et al.  Phase‐Transformation Ductilization of Brittle High‐Entropy Alloys via Metastability Engineering , 2017, Advanced materials.

[2]  Bin Liu,et al.  Ductile CoCrFeNiMox high entropy alloys strengthened by hard intermetallic phases , 2016 .

[3]  D. Miracle,et al.  A critical review of high entropy alloys and related concepts , 2016 .

[4]  J. Seol,et al.  Boron doped ultrastrong and ductile high-entropy alloys , 2018, Acta Materialia.

[5]  Yong Zhang,et al.  Microstructure and compressive properties of multicomponent Alx(TiVCrMnFeCoNiCu)100−x high-entropy alloys , 2007 .

[6]  Dierk Raabe,et al.  A novel, single phase, non-equiatomic FeMnNiCoCr high-entropy alloy with exceptional phase stability and tensile ductility , 2014 .

[7]  Jan-Olof Andersson,et al.  The Thermo-Calc databank system☆ , 1985 .

[8]  Sangho Kim,et al.  Brittle intermetallic compound makes ultrastrong low-density steel with large ductility , 2015, Nature.

[9]  C. Tasan,et al.  Composition Dependence of Phase Stability, Deformation Mechanisms, and Mechanical Properties of the CoCrFeMnNi High-Entropy Alloy System , 2014 .

[10]  F. J. Humphreys,et al.  Recrystallization and Related Annealing Phenomena , 1995 .

[11]  D. Field,et al.  The role of annealing twins during recrystallization of Cu , 2007 .

[12]  Je-hyun Lee,et al.  Mechanical behavior and solid solution strengthening model for face-centered cubic single crystalline and polycrystalline high-entropy alloys , 2018, Intermetallics.

[13]  Bernd Gludovatz,et al.  Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures , 2016, Nature Communications.

[14]  Jien-Wei Yeh,et al.  Criterion for Sigma Phase Formation in Cr- and V-Containing High-Entropy Alloys , 2013 .

[15]  Wei Zhang,et al.  High-Entropy Alloys with a Hexagonal Close-Packed Structure Designed by Equi-Atomic Alloy Strategy and Binary Phase Diagrams , 2014 .

[16]  H. Kim,et al.  Cryogenic strength improvement by utilizing room-temperature deformation twinning in a partially recrystallized VCrMnFeCoNi high-entropy alloy , 2017, Nature Communications.

[17]  Hyuk-Joong Lee,et al.  Thermodynamic calculation on the stability of (Fe,Mn)3AlC carbide in high aluminum steels , 2010 .

[18]  Lu Zhang,et al.  Design of non-equiatomic medium-entropy alloys , 2018, Scientific Reports.

[19]  T. Shun,et al.  Nanostructured High‐Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes , 2004 .

[20]  D. Ponge,et al.  Improvement of the work hardening rate of ultrafine grained steels through second phase particles , 2005 .

[21]  Sunghak Lee,et al.  Trade-off between tensile property and formability by partial recrystallization of CrMnFeCoNi high-entropy alloy , 2017 .

[22]  Y. Estrin,et al.  Constitutive modeling of deformation behavior of high-entropy alloys with face-centered cubic crystal structure , 2017 .

[23]  Dierk Raabe,et al.  Mechanical and microstructural single-crystal Bauschinger effects: Observation of reversible plasticity in copper during bending , 2010 .

[24]  Kaisheng Ming,et al.  Precipitation strengthening of ductile Cr15Fe20Co35Ni20Mo10 alloys , 2017 .

[25]  T. Nieh,et al.  Effects of Al addition on structural evolution and tensile properties of the FeCoNiCrMn high-entropy alloy system , 2014 .

[26]  R. Reed,et al.  The precipitation of topologically close-packed phases in rhenium-containing superalloys , 2001 .

[27]  C. Tasan,et al.  Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off , 2016, Nature.

[28]  Xuefei Zhang,et al.  Effect of molybdenum on phases, microstructure and mechanical properties of Al0.5CoCrFeMoxNi high entropy alloys , 2018 .

[29]  T. Shun,et al.  Microstructure and mechanical properties of multiprincipal component CoCrFeNiMox alloys , 2012 .

[30]  Feng He,et al.  Strengthening the CoCrFeNiNb0.25 high entropy alloy by FCC precipitate , 2016 .

[31]  B. Blanpain,et al.  Pinning effect of second-phase particles on grain growth in polycrystalline films studied by 3-D phase field simulations , 2007 .

[32]  X. C. Li,et al.  Microstructure and Properties of FeAlCrNiMox High-Entropy Alloys , 2016, Journal of Materials Engineering and Performance.

[33]  J. Robson,et al.  Particle effects on recrystallization in magnesium?manganese alloys: Particle pinning , 2011 .

[34]  Reinhard Pippan,et al.  Mechanical properties, microstructure and thermal stability of a nanocrystalline CoCrFeMnNi high-entropy alloy after severe plastic deformation , 2015 .

[35]  Huizeng Li,et al.  Microstructures and compressive properties of multicomponent AlCoCrCuFeNiMox alloys , 2010 .

[36]  D. Miracle,et al.  Mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys , 2011 .

[37]  J. Yeh,et al.  Effects of Al addition on the microstructure and mechanical property of AlxCoCrFeNi high-entropy alloys , 2012 .

[38]  J. Yeh,et al.  Sluggish diffusion in Co-Cr-Fe-Mn-Ni high-entropy alloys , 2013 .

[39]  C. Liu,et al.  Precipitation hardening in CoCrFeNi-based high entropy alloys , 2017 .

[40]  H. Bei,et al.  Relative effects of enthalpy and entropy on the phase stability of equiatomic high-entropy alloys , 2013 .