| In recent years,as a new type of smart material,magnetic shape memory alloy has excellent physical properties and great theoretical research value.It has attracted much attention due to its great potential in the magnetic driven applications.Ni-Mn-In ferromagnetic shape memory alloys have attracted much attention because of their novel properties.In order to improve the inherent high brittleness and increase the martensitic transformation temperature,the effects of Cu doping on the crystal structure and basic physical properties of Ni-Mn-In magnetic shape memory alloy have been investigated by the combination of theoretical calculations and experiments.The main conclusions are listed as follows:(1)The proper structural models of parent austenite,6M and NM martensitic phases were established for Ni24Mn17-xIn7Cux(x=1,2,3,4 and 5)alloys by the first-principles calculations,and the atomic preferential occupancy of doped Cu is determined.The results show that the doped fourth component Cu prefers to occupy the sites of excess Mn atoms.(2)The ground state energies and the formation energies of FA,6M and NM phases in Ni24Mn17-xIn7Cux(x=1,2,3,4 and 5)alloys have been investigated,thereby,their phase stability and martensitic transformation sequences have been determined.The results show that the formation energy of FA,6M and NM phases increased with the increase of Cu content The martensitic transformation sequences of Ni24Mn17-xIn7Cux(x=1-5)alloys are:FA?FIM 6M?FIM NM when x=1;FA?FM 6M?FIM NM with 2?x?3;FA?FM 6M?FM NM until x?4.There is a magnetostructural coupling characteristics during 1?x?3 from the formation energy point of view.(3)The magnetic properties of Ni24Mn17-xIn7Cux(x=1,2,3,4 and 5)alloys were also investigated.The variation of the total magnetic moment for FA,6M and NM phases,with different alloy compositions,were further explained from the view of the atomic magnetic moment under the ferromagnetic and ferrimagnetic states,and the mechanism of the magnetic change was discussed from the perspective of the density of electronic states(DOS).(4)This work verifies the results of the first-principles calculations by experimental method.The microstructure of Ni24Mn17-xIn7Cux(x=0.5,1.0,1.5,2.0,2.5 and 3.0)alloys was investigated.At room temperature,when x=0.5-1.5,martensitic structure appears;When x?2,the second phase precipitates begin to appear at the grain boundaries and in the grains.The content of precipitates increases with the increase of Cu content,and the alloy exhibits austenite and second-phase structure at room temperature.(5)Ni24Mn17-xIn7Cux(x=2.0,2.5 and 3.0)alloys,the content of Ni and Cu in the second phase is higher,and the content of In is lower than the average alloying composition,indicating that the second phase is Ni-rich,Cu-rich and In-poor precipitate.The precipitation of second phase will change the effective composition of the matrix,so that the Ni content in the matrix is low,and the In content is relatively high,which leads to the decrease in the corresponding e/a of the effective matrix component,so that the martensitic transformation temperature will be lowered.(6)In the Ni24Mn17-xIn7Cux(x=0.5,1.0,1.5,2.0,2.5 and 3.0)alloys,the phase transition temperature of the x<2 sample increases gradually with the increase of Cu content,because the valence electron concentration e/a increases with the substitution of Cu for Mn.Then the phase transition temperature drops.This is mainly due to the precipitation of the second phase in the matrix from x=2,and the precipitation of the second phase causes the change of the composition of the matrix.(7)With the increase of Cu content,the vickers hardness of Ni24Mn17-xIn7Cux(x=0.5,1.0,1.5,2.0,2.5 and 3.0)alloys increases gradually.It shows that doping Cu can effectively improve the mechanical properties of Ni-Mn-In alloy.However,a large amount of doped Cu will precipitate the second phase,which has a negative effect on the magnetic shape memory effect of the alloy,so the Cu content should be controlled within a reasonable range. |
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