The microstructural evolution and hardness of the equiatomic CoCrCuFeNi high-entropy alloy in the semi-solid state

Abstract The semi-solid slurries of the CoCrCuFeNi high entropy alloy (HEA) were fabricated through the recrystallization and partial melting (RAP) process by cold-rolling and partial remelting. Based on Kim's theory, the solidus-liquidus temperature range and the fraction of the liquid phase as a function of temperature were examined from the Differential Scanning Calorimetry (DSC) curve. The effect of isothermal temperature and soaking time on the microstructural evolution of the CoCrCuFeNi HEA in a semi-solid state were analyzed. The results showed that the globular structure was obtained without the new phase formed for the semi-solid slurries, containing two face-centered-cubic (FCC) solid-solution phases. The average grain size of the globular grain and the globular degree increased with increasing the isothermal temperature and soaking time. The study of the coarsening kinetics indicated that the coarsening process could be described by the modified liquid film migration model. The sluggish diffusion effect of the current HEA leaded to the low coarsening rate, compared with other conventional alloys. However, the existence of the liquid phase in the semi-solid state resulted in a higher grain growth rate for the CoCrCuFeNi HEA with a lower activation energy of 206.9 kJ/mol, compared with the diffusion couple and the grain growth process for the other HEAs at low temperatures. To evaluate the mechanical properties, Vickers hardness was measured to represent the strength of the CoCrCuFeNi HEA. The CoCrCuFeNi semi-solid slurries showed a Hall-Petch type relationship of the average grain size dependence on Vickers hardness.

[1]  Akira Takeuchi,et al.  Classification of Bulk Metallic Glasses by Atomic Size Difference, Heat of Mixing and Period of Constituent Elements and Its Application to Characterization of the Main Alloying Element , 2005 .

[2]  Patrick S. Grant,et al.  Isothermal grain coarsening of spray formed alloys in the semi-solid state , 2002 .

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

[4]  T. Langdon,et al.  Microstructure and properties of a CoCrFeNiMn high-entropy alloy processed by equal-channel angular pressing , 2017 .

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

[6]  Carl Wagner,et al.  Theorie der Alterung von Niederschlägen durch Umlösen (Ostwald‐Reifung) , 1961, Zeitschrift für Elektrochemie, Berichte der Bunsengesellschaft für physikalische Chemie.

[7]  K. Dahmen,et al.  Microstructures and properties of high-entropy alloys , 2014 .

[8]  Xiaojia Nie,et al.  Comparison of microstructural evolution of 7075 aluminum alloy fabricated by SIMA and RAP , 2016 .

[9]  H. Atkinson,et al.  Microstructural Coarsening of Semi-Solid Aluminium Alloys , 2008 .

[10]  Merton C. Flemings,et al.  Behavior of metal alloys in the semisolid state , 1991 .

[11]  Qiang Chen,et al.  Microstructural evolution of previously deformed AZ91D magnesium alloy during partial remelting , 2009 .

[12]  Ł. Rogal.  Semi-solid processing of the CoCrCuFeNi high entropy alloy , 2017 .

[13]  I. Lifshitz,et al.  The kinetics of precipitation from supersaturated solid solutions , 1961 .

[14]  N. Tsuji,et al.  Effect of low temperature on tensile properties of AlCoCrFeNi2.1 eutectic high entropy alloy , 2017 .

[15]  J. Yeh,et al.  Microstructure and mechanical property of as-cast, -homogenized, and -deformed AlxCoCrFeNi (0 ≤ x ≤ 2) high-entropy alloys , 2009 .

[16]  George M. Pharr,et al.  Recovery, recrystallization, grain growth and phase stability of a family of FCC-structured multi-component equiatomic solid solution alloys , 2014 .

[17]  Ying Ma,et al.  Effects of processing parameters on microstructure and ultimate tensile strength of thixoformed AM60B magnesium alloy , 2012 .

[18]  C. Liu,et al.  Effects of Nb additions on the microstructure and mechanical property of CoCrFeNi high-entropy alloys , 2015 .

[19]  J. Yeh,et al.  Phases, microstructure and mechanical properties of AlxCoCrFeNi high-entropy alloys at elevated temperatures , 2014 .

[20]  Ravi Sankar Kottada,et al.  Thermal stability and grain boundary strengthening in ultrafine-grained CoCrFeNi high entropy alloy composite , 2017 .

[21]  P. Liaw,et al.  Microstructure and mechanical behaviors of GdxCoCrCuFeNi high-entropy alloys , 2017 .

[22]  B. Cantor,et al.  Nucleation of solidification in liquid droplets , 1991 .

[23]  T. G. Nieh,et al.  Grain growth and the Hall–Petch relationship in a high-entropy FeCrNiCoMn alloy , 2013 .

[24]  R. Ritchie,et al.  A fracture-resistant high-entropy alloy for cryogenic applications , 2014, Science.

[25]  B. Zhang,et al.  Microstructural origins of high strength and high ductility in an AlCoCrFeNi2.1 eutectic high-entropy alloy , 2017 .

[26]  Baolong Zheng,et al.  Microstructure and strengthening mechanisms in an FCC structured single-phase nanocrystalline Co25Ni25Fe25Al7.5Cu17.5 high-entropy alloy , 2016 .

[27]  Sheng Guo,et al.  Ultrafine-Grained AlCoCrFeNi2.1 Eutectic High-Entropy Alloy , 2016 .

[28]  E. D. Freitas,et al.  Rheology and microstructural development of a Al–4wt%Cu alloy in the semi-solid state , 1999 .

[29]  M. Ketabchi,et al.  Microstructure Evolution of Semi-Solid 7075 Aluminum Alloy During Reheating Process , 2011 .

[30]  H. Atkinson,et al.  Recrystallisation in the Semi-Solid State in 7075 Aluminium Alloy , 2008 .

[31]  K. An,et al.  A precipitation-hardened high-entropy alloy with outstanding tensile properties , 2016 .

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

[33]  S. Annavarapu,et al.  Inhibited coarsening of solid-liquid microstructures in spray casting at high volume fractions of solid , 1995 .

[34]  Liu Wei,et al.  Microstructure Evolution of Semisolid Mg-2Zn-0.5Y Alloy during Isothermal Heat Treatment , 2016 .

[35]  Sung Soo Kim,et al.  Coarsening behaviour of Mo grains dispersed in liquid matrix , 1983 .

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

[37]  M. Aghaie-Khafri,et al.  The Study of an Al-Fe-Si Alloy After Equal-Channel Angular Pressing (ECAP) and Subsequent Semisolid Heating , 2012 .

[38]  J. Gan,et al.  Thermal Stability and Performance of NbSiTaTiZr High-Entropy Alloy Barrier for Copper Metallization , 2011 .

[39]  J. Yeh,et al.  On the superior hot hardness and softening resistance of AlCoCrxFeMo0.5Ni high-entropy alloys , 2011 .

[40]  F. Khomamizadeh,et al.  Effect of predeformation and heat treatment conditions in the SIMA process on microstructural and mechanical properties of A319 aluminum alloy , 2009 .

[41]  Helen V. Atkinson,et al.  Modelling the semisolid processing of metallic alloys , 2005 .