Study On The Effect Of Zr On The Mechanical And Magnetic Properties In 2:17-type SmCo Magnets

Due to the high Curie temperature,good temperature stability and corrosion resistance,the 2:17-type SmCo rare-earth permanent magnetic material has been attracted in high temperature fields,such as the microwave communication,aviation,military military.In recent years,with the development and application of science and technology,the higher requirements in high temperature magnetic and temperature stabilities have been put forward to meet the need of application of strict environment conditions.Based on the close relationship between microstructure and mechanical/magnetic properties in SmCo magnet,the Sm(CobalFe0.09Cu0.09Zrx)7.68(x=0.020,0.025,0.030,0.035)magnets are prepared by the sintered powder metallurgy process in this paper,and the effect of Zr element on SmCo magnetic cellular structure and lamellar structure.Meanwhile,the phase structure characteristics and high temperature mechanical properties,thermoelectric properties are investigated.The main research contents and results are listed as follows:The influence of Zr content on the microstructure and magnetic properties is studied.According to the microstructure change,the results show that the increasing Zr content lead to increase lamellar phase density,which are from x=0.020 for 0.04 nm-1 to x=0.030 for 0.06 nm-1;and refine cellular structures,which are from x=0.020 for 83.88 nm to x=0.030 for 58.16 nm.When Zr content is up to 0.030,more Zr6(Co,Fe)23 phase form and precipitate out gradually.The analysis on magnetic properties show that the demagnetization curve of square degree and coercive force enhancement are improved at room temperature to 773 k.When x=0.030,the peak magnetic properties of Br=9.48 kGs,Hcj=30.17 kOe,(BH)m=21.79 the MGs are achieved;When the temperature is above 773 k,the coercivity increases monotonously with the increase of Zr content,which suggests that the role of Zr play a role on stable phase structure at high temperature.At the same time,the formation mechanism of the coercivity is from pinning mechanism to nucleation mechanism gradually.The effect mechanism of microstructure on mechanical anisotropy and fracture behavior is analyzed.The results found that mechanical anisotropy is associated with lamellar structure,and cellular structure and precipitate out of the second phase have an isotropic influence on the mechanical strength.The rivers and steps patterns of fracture morphology are observed by SEM,which show the characteristics of cleavage brittle fracture.Furthermore,the indentation method is used to analyze crack propagation morphology.It found that the crack terminate or bypass the oxide to propagate,so show strong mechanical strength,and microcracks is easy to form in the Zr6(Co,Fe)23 and holes.The results of bending strength analysis show that the mechanical strength of magnets present anisotropic,mechanical anisotropy tends to be isotropic with the increasing Zr content,and inverse anisotropy appears at x=0.0285.Meanwhile,the increasing Zr content result in bending strength with ?C axis direction increase gradually,which show that lamellars are helpful to improve the mechanical strength of magnets.Analysis on thermal expansion,thermal conductivity and the resistivity,the role of Zr content on the thermoelectric properties in Sm2Co17 magnet was studied.Results showed thatthe thermal expansion of magnets are anisotropic at the different Zr content;with the increase of the Zr content,the difference of thermal expansion anisotropy(35)L increase gradually.For the same Zr content,temperature rise and thermal conductivity increases;with the different content of Zr,when x<0.030,thermal conductivity present anisotropy;When x>0.030 or higher,it tends to isotropic.As for the //C axis and ?C axis,resistivity shows anisotropy and increases with the increase of Zr content.The lattice structure distortion caused by Zr atoms with large radius replace Co atoms(c decrease and a increase in 2:17 phase;a reduced,c increasing in 1:5 phase),which make the distance between the atoms and the amplitude change,and lead to Sm2Co17 magnet thermoelectric properties changes with the different Zr content.