Simulated Research On Mechanical Behavior Of CoCrCuFeNi High Entropy Alloy

Unlike traditional metals and alloys,which contain one or two principal elements,high entropy alloys(HEAs)generally contain five or more principal elements.As a new kind of material,HEAs have shown excellent mechanical and chemical properties,and have good application prospects in aerospace,shipbuilding and other fields.CoCrCuFeNi,with a simple face-centered cubic(FCC)structure,is the earliest discovered quinary highentropy alloy and also one of the most studied high-entropy alloy systems.Recently,the CoCrCuFeNi HEA system has received more and more attention because it undergoes the interesting liquid-phase separation(LPS)phenomenon.It has been reported that the microstructure inhomogeneity caused by liquid phase separation significantly affects the mechanical properties of CoCrCuFeNi HEA.In addition,temperature and twin boundaries also have effects on the mechanical properties of CoCrCuFeNi HEA.By discussing the relationship between the structure and properties of materials and their potential deformation mechanisms,the materials can be designed purposefully and their application prospect can be expanded.Based on the relevant experimental results,molecular dynamics(MD)simulation method was adopted in this paper to investigate the effects of temperature,phase separation and twin boundaries on the mechanical properties of equi-atomic ratio CoCrCuFeNi HEA were investigated at the micro scale.The main research contents and results of this paper are as follows:(1)The effect of temperature on the mechanical properties and related deformation behavior of the CoCrCuFeNi HEA was studied.The simulation results show that the CoCrCuFeNi HEA has obvious elastic softening at elastic deformation stage,which is originated from the decrease of the interatomic force gradient.The elastic modulus and yield strength of the alloy increase with temperature decreasing.With the temperature increasing,the atomic thermal motion becomes more intensive and thus the bonding energy between atoms becomes lower.Hence,the lattice of the alloy is more easily to deform and the bonds between atoms are easily to break.In addition,the lower the temperature is,the lower the stacking fault energy is,and the earlier the deformation twin occurs in the sample,indicating that the twinning deformation ability of the alloy is enhanced.(2)The effect of phase separation on the mechanical properties and related deformation behavior of the CoCrCuFeNi HEA was studied.The results show that Cu-rich grain boundaries can seriously reduce the plasticity of the alloy and lead to intergranular fracture of the sample.At the same time,the strength of the alloy was slightly reduced by Cu-rich grain boundaries.Cu-rich grains can seriously reduce the strength of the CoCrCuFeNi HEA.The larger the volume fraction of Cu-rich grains is,the more obvious the decrease of strength.The reason is that the resolved shear stress required to start slip systems in Cu-rich grains is much smaller than that required in Cu-depleted grains,resulting in plastic deformation tends to occur in Cu-rich grains.Furthermore,an uneven stress distribution was detected,where the stress on Cu-depleted grains was much higher than that on Cu-rich grains.(3)The effect of twin boundaries on the mechanical properties and related deformation behavior of the CoCrCuFeNi HEA was studied.Samples with twin boundaries in each grain were constructed.The number of twin boundaries in each grain can be changed by controlling the twin-boundary spacing.The simulation results show that the strength of the sample first increases with decreasing twin-boundary spacing,reaching a maximum at the spacing of 1.88 nm,and then drops progressively with further decreasing.The strength of the alloy increases with the decrease of the twin-boundary spacing because the twin boundaries can serve as barriers to partial dislocations gliding on slip planes.But as the twin-boundary spacing decreases further,the strength decreases.The reason for this softening is that there exists a transition in deformation mechanism and the twin-boundary spacing has reached a critical value.At this point,the strengthening due to dislocation pile-up and cutting through twin planes switches to a dislocation-nucleation controlled softening mechanism with partial dislocation nucleation at grain boundary-twin boundary intersections and motion of partial dislocations parallel to the twin boundaries.