Formation,crystallization Behavior And Properties Of FeCoNi-based High Entropy Amorphous Alloys

In recent years,high entropy（HE）alloys have been widely investigated due to the high strength,high hardness,high fracture toughness at low temperature,and excellent softening resistance at high temperature.Hence,the HE alloys exhibit a great potential in engineering applications.Profiting from the design thought of HE alloys with multi-primary components,the glassy alloys with HE characteristics have attracted increasing attentions in structural and functional metal material fields.In the present work,Fe,Co and Ni with equiatomic as primary components of the HE alloys,and the early transition metals（Cr,Mo,Nb）and metalloid elements（B,C）served as additional components to design HE amorphous alloys.HE amorphous ribbons,bulk metallic glasses and HE glassy composite materials have been successfully prepared by the melting spun technique and copper module casting method,respectively.Moreover,all HE alloys have been systematically characterized to investigate the amorphous/glass formation ability,thermodynamic properties,crystallization and mechanical properties.(Fe_0.25Co_0.25Ni_0.25Cr_0.125Mo_0.125)_100–xB_x（x=11～31 at.%）HE amorphous ribbons are successfully obtained by replacing Cr with Mo in（Fe,Co,Ni,Cr）-B HE system.HE amorphous alloys show more coordinated atomic configurations due to the Mo replacement,which could improve glass-forming ability（GFA）,thermal stability and mechanical properties.Based on this system,HE bulk metallic glass with critical size of 2.5 mm is obtained by doping C.The crystallization behavior of（Fe,Co,Ni,Cr,Mo）-B HE amorphous ribbons with the low B content is investigated,and the influence of crystallization on microstructure evolution and mechanical performance is summarized.The[am’’+bcc+fcc]nanocomposite with high thermal stability and hardness is fabricated.The elemental partition during crystallization induced by heating is considered as key factor in formation of[am’’+bcc+fcc]nanocomposite.(Fe_0.25Co_0.25Ni_0.25Cr_0.125Mo_0.0625Nb_0.0625)_100–xB_x（x=8～14 at.%）HE amorphous ribbons are successfully prepared by melting spun technique.The microstructures,thermal stability and mechanical properties of HE amorphous ribbons in as-spun and annealed states are characterized.The glass transition phenomenon is found in TM-HE alloy with the as-reported lowest B content.Nb addition improves the glass transition of the HE amorphous alloy.Moreover,HE bulk metallic glass composite alloys with high yield strength and plasticity are prepared by copper mold casting method.Based on the design thought of high-order multiplication of Fe-based alloy components,(Fe_0.334Co_0.333Ni_0.333)_84–xCr₈Mo₄Nb₄B_x（x=2～24 at.%）HE alloys are successfully prepared.The glass forming ability,microstructure,thermal stability,crystallization behavior,and mechanical properties are investigated systematically.The high-order multiplication of Fe-based alloy components can reduce the lowest B content for amorphous phase formation.