Study On The Microstructure And Magnetic Properties Of L1₂ And B2 Type High Entropy Intermetallic Compounds

Similar to high-entropy alloys,high-entropy intermetallic compounds are a new type of material,which not only has the characteristics of multi-principal elements in high-entropy alloys,but also has the orderliness of traditional intermetallic compounds.This paper takes high-entropy intermetallic compounds as the research object,calculates the characterization parameters of existing and new high-entropy intermetallic compounds,and studies the relationship between the characterization parameters and the high-entropy intermetallic compounds and their structures.Preliminarily summarized the law of the influence of added elements on the formation and crystal structure of high-entropy intermetallic compounds.According to this law,three kinds of high-entropy intermetallic compounds with different structures were selected,and their microstructure and magnetic properties were studied.In this paper,the characterization parameters such as mixing enthalpy,mixing entropy,and valence electron concentration of 23 kinds of high-entropy intermetallic compounds with different added elements are calculated,and it is concluded that there is a certain relationship between the characterization parameters.The mixing entropy has a negative correlation with the valence electron concentration;the mixing enthalpy has a positive correlation with the valence electron concentration;the free energy of the system also has a positive correlation with the valence electron concentration.Si element also has a certain effect on the characterization parameters of high-entropy intermetallic compounds.In high-entropy intermetallic compounds containing Si,the mixing enthalpy is basically negatively correlated with the atomic radius difference,and the free energy is also negatively correlated with the atomic radius difference.It is found that the element types and valence electron concentration of the alloy can not only distinguish the types of high-entropy intermetallic compounds,but also have a certain influence on the phase structure of the compounds.The second type of sublattice multi-principal high-entropy intermetallic compound has a higher valence electron concentration,and the valence electron concentration of the Ni-based HEI2 type high-entropy intermetallic compound is higher than 8,which is easier to form the FCC/L1₂structure phase;The valence electron concentration(VEC)of the Co-based HEI2 high-entropy intermetallic compound is between 6.87 and 8,which makes it easier to form the FCC/L1₂+BCC/B2 structure;the valence electron concentration(VEC)of the HEI3high-entropy intermetallic compound is between 6.87 and 8,it is easier to form FCC/L1₂+BCC/B2 structure.After obtaining the parameter calculation results and the preliminary element addition law,three high-entropy intermetallic compounds were selected for microstructure research.The study found that Fe Co Ni Al high-entropy intermetallic compounds belong to B2 type high-entropy intermetallic compounds,while Ni Al Si Mn Ti high-entropy intermetallic compounds and Co Al Si Ti high-entropy intermetallic compounds belong to L12-type high-entropy intermetallic compounds.The Fe Co Ni Al high-entropy intermetallic compound is composed of B2+BCC structure phase and FCC structure phase.After annealing,the FCC structure phase becomes finer and more uniformly distributed in the BCC structure phase;The Co Al Si Ti high-entropy intermetallic compound is composed of two FCC structural phases,an ordered L12 structural phase and a BCC structural phase.After annealing,the BCC structural phase melts back,and the FCC structural phase and the ordered L12structural phase become more uniform.to separate out;Ni Al Si Mn Ti high-entropy intermetallic compound is composed of ordered L12 structure phase and FCC structure phase.After annealing,the FCC structure phase grows up,but the specific phase structure does not change significantly.Finally,the magnetic properties of three magnetic high-entropy intermetallic compounds are studied.Studies have found that the element types and microstructure have an effect on the surface magnetic domain structure of magnetic high-entropy intermetallic compounds.Annealing also has a certain effect on the magnetic domain structure.After annealing,the surface magnetic domain structures of the three magnetic high-entropy intermetallic compounds have been significantly refined.Analysis of the thermomagnetic curves of the above three magnetic high-entropy intermetallic compounds shows that the Fe Co Ni Al magnetic high-entropy intermetallic compound undergoes two magnetic phase transitions during the heating process,and a spin glass transition occurs in the low temperature region.The Co Al Si Ti magnetic high-entropy intermetallic compound also undergoes a magnetic phase transition at 255K,that is a transition from a ferromagnetic state to a paramagnetic state.At the same time,it is found that a blocking peak of paramagnetic to ferromagnetic transition appears at 225K.The thermomagnetic curve of Ni Al Si Mn Ti magnetic high-entropy intermetallic compound shows obvious thermomagnetic curve law of soft magnetic material,and its Curie temperature is about 257K.