Effect Of Coherent Nanoprecipitates On The Tensile Behavior Of A FCC-Structured High-Entropy Alloy

As a new design concept of metal materials,high-entropy alloy has attracted wide attention of researchers since its inception.Due to their multiple major components,high-entropy alloys usually exhibit a simple disordered solid solution microstructure due to the amplification effect of mixing entropy,and also may have special properties such as lattice distortion and sluggish diffusion.In addition,high-entropy alloys have a great possibility space on composition,microstructure,and properties.In recent years,researchers have found that FCC 3d transition metal high-entropy alloys exhibit excellent toughness and plasticity over a wide range of temperatures and thus have great potential for structural applications.However,their strength does not yet have advantage as compared to traditional metal materials.As a result,exploration and optimization of the strengthening methods for them is needed.In this paper,a new kind of high-entropy alloy Al_0.2CrFeCoNi₂Cu_0.2was designed and prepared.Different alloy samples with single-phase FCC structure and FCC matrix+dispersed nano-scale L1₂-（Ni,Cu）₃Al precipitates were obtained by mechanical heat treatment,and their tensile properties at room temperature and cryogenic temperature as well as the corresponding plastic deformation mechanism were characterized and analyzed.This paper found that the dispersed nano-coherent precipitation phase can produce excellent strengthening effect on the alloy.Through dislocation cutting mechanism,precipitation phase can promote massive dislocation plane-gliding as the main plastic deformation mechanism,causing the formation and dynamic refinement of dislocation slip band,finally leading to the substantial increase in alloy yield strength and work hardening ability at the same time.In addition,when the temperature dropped from room temperature to cryogenic temperature,we found that single-phase FCC solid solution alloy samples formed a large number of nano-deformation twins during the stretching process due to the decrease of the stacking fault energy,resulting in great improvement in the alloy work hardening and fracture resistance ability.However,the deformation mechanism of alloy samples with FCC matrix+dispersed coherent precipitated phase structure is still dominated by dislocation plane-gliding,which is mainly due to the enrichment of Al element from the matrix into the precipitated phase,which causing increase in the stacking fault and inhibiting the occurrence of deformation twins.