Study On Diffusion Behavior Of Al,Cr And Ni In AlCoCrFeNi High Entropy Alloys

High-entropy alloy is a new type of alloy which has been developed in recent years.Studies have shown that the diffusion rate of atoms in high-entropy alloys is much lower than that of conventional alloys.This sluggish diffusion effect of the high-entropy alloy makes the high-entropy alloy have good thermal stability,high oxidation resistance,and contributes to the formation of nanocrystals in the high-entropy alloy matrix.The atomic diffusion behavior in high-entropy alloys is also important for understanding the processes of solidification,phase transformation,recovery and recrystallization of high-entropy alloys.At present,the research on the diffusion behavior of high-entropy alloys is still very limited,and that still lacks a understanding of its diffusion mechanism.In this paper,AlCoCrFeNi high entropy alloys were used to study the diffusion behavior of Al,Cr and Ni.According to the pseudo-binary diffusion couple method,the effects of diffusion temperature,time and magnetic field on the diffusion behavior of Cr and Ni are systematically studied.The diffusion couple of high entropy alloy and pure Al is used to investigate the diffusion behavior of Al.The diffusion coefficient was calculated from the kinetic point by detecting the change of interface composition and the thickness of the diffusion layer by electron probe microanalysis(EPMA),and the diffusion constant and diffusion activation energy were obtained from the thermodynamic point of view.The main conclusions were as follows:(1)With the temperature increaseing,the thickness of the diffusion layer increases significantly.The diffusion distance is parabolic with the diffusion time.The diffusion interface of the pseudo binary Ni and Cr diffusion couple does not produce a new phase.The diffusion of Al-HEA produced new phases at the interface at 823,793 and 773 K,but no new phase was produced at 723 K and 673 K.(2)The diffusion coefficients of Cr and Ni were calculated according to the Boltzmann-Matano method.Under the same heat treatment conditions,the diffusion coefficient changes slightly with the concentration.In the pseudo binary diffusion couple,the diffusion coefficient of Ni is smaller than the diffusion coefficient of Cr.The diffusion constant of Cr is 2.5×10-5 m2/s,the diffusion activation energy is 259.7 kJ/mol;the diffusion constant of Ni is 1.6×104 m2/s,and the diffusion activation energy is 285.1 kJ/mol.High entropy alloys diffuse more slowly than traditional FCC metals.(3)The effect of high magnetic field on the diffusion of high-entropy alloys is different at different temperatures.When the temperature is 1293 K,the 6 T high magnetic field can inhibit the diffusion of Cr and Ni elements.When the temperature is 1273 K,the high magnetic fields of 6 and 12 T can promote the diffusion of Cr.As for Ni,the "positive"magnetic field directions of 6 and 12 T(the concentration gradient direction is the same as the magnetic field direction)can promote the diffusion of Ni,and the "negative" magnetic field directions of 6 and 12 T(the concentration gradient is opposite to the magnetic field direction)can inhibit the diffusion of Ni.When the temperature is 1223 K,high magnetic field of 6 T promotes the diffusion of Ni and Cr.