Rapid Solidification Simulation And Microstructure Analysis Of Ni-Co Magnetic Materials

Nickel-cobalt alloys have been studied as important engineering materials for decades due to their unique properties such as high strength,good wear resistance,thermal conductivity,and electrocatalytic activity.In addition,the use of nickel-cobalt alloys has been extended to electroforming techniques for producing three-dimensional,complex-shaped finished components.At present,only a few researchers have used theoretical calculation methods to simulate and calculate the properties and preparation process of Ni-Co alloys.The microstructure determines the macroscopic properties,so the research on the microstructure of Ni-Co alloy is particularly important.In this paper,the molecular dynamics simulation method is used to simulate the formation and evolution of the microstructure of Ni-Co alloys during rapid solidification under different components and pressures.The simulated data were analyzed in detail using microstructure characterization methods such as average atomic energy,two-body distribution function,common neighbor clusters,standard cluster analysis method,and micro-visualization.When using Ni_?100-x?Co_x?x=10,20,30,40,50,60,70,80,90?as different components to rapidly solidify Ni-Co nanocrystalline materials,Micro-analysis methods such as average atomic energy,two-body distribution function,and standard cluster analysis method,found that when the composition of the system is Ni_?100-x?Co_x?x=40,50,60,70,80,90?,Ni-Co alloy system formed the crystal structure mainly composed of clusters fcc,hcp and bcc,while in Ni_?100-x?Co_x?x=10,20?,amorphous formed in Ni-Co alloy system structure.In the solidification process of Ni-Co alloy,the critical component for forming crystals and amorphous is Ni₇₅Co₂₅.The lower Co content is more conducive to the formation of crystal structure,and the crystallization is most obvious when the composition is Ni₅₀Co₅₀.When the composition is Ni₄₈Co₅₂,it undergoes a secondary phase transition during solidification,and many fcc clusters are formed in the final solidified state.The abrupt change in the number of fcc clusters will cause the distribution of the structure in the system,which is also a reflection of the secondary phase change that occurs when the liquid Ni-Co alloy solidifies with the Ni₄₈Co₅₂component.In the liquid Ni-Co alloy,two kinds of crystal clusters,fcc,hcp,and bcc,coexist at the beginning.However,during the solidification process of the Ni₄₈Co₅₂system,the metastable hcp and The bcc structure is mostly transformed into a more stable fcc structure,which also results in more consistent and tight local bonding of the solidified end state.The microstructure evolution characteristics of liquid Ni-Co alloys during rapid solidification under different pressures?P0=0GPa,P5=5GPa,P10=10GPa,P20=20GPa,P30=30GPa,and P40=40GPa?were analyzed and obtained:During the solidification of Ni-Co alloy at a cooling rate of 10¹²K/s,when the pressure is lower than 10GPa,the increase in pressure has a certain promotion effect on the formation of the crystal structure of the system.There is a certain inhibitory effect on the formation of.In the process of Ni-Co alloy solidifying at a cold rate of 10¹²K/s,as the pressure increases,the top nine types of bond types are consistent in total number percentage.In the smaller pressure systems of P0,P5,and P10,the change of S421 is the main,and in the P20,P30,and P40 systems,the change of S421 is the main change,but the numbers of S422,S444,and S666 start to rise.In Ni-Co alloys in the P0,P5,P10,P20,and P30 systems,the fcc clusters increase with decreasing temperature,and the number of fcc clusters in the solidified state increases first and then decreases with increasing pressure.When the pressure was P20,P30,and P40,the number of hcp and bcc clusters in the system began to increase significantly and increased with the increase of pressure.