Study On Preparation,Structure And Properties Of Nd-Fe-B-Hf And Co-Hf Permanent Magnetic Alloys

Since its discovery,Hf element has been widely used in various fields such as atomic reactors,rocket propulsion,resistive materials,heat-resistant materials,etc.In recent years,researchers have found that the Hf element has shown greater application prospects in permanent magnetic materials.In order to further explore the application of Hf element,this article mainly divided into two parts to study the application of Hf element in permanent magnetic materials,the first part is the study on preparation,structure and properties of Nd-Fe-B-Hf permanent magnet alloys,and the second part is the study on preparation,structure and properties of Co-Hf permanent magnet alloys.Firstly,Nd₂₇Fe_72-xB₁Hf_x(x=0,3),Nd₂₉Fe_70-xB₁Hf_x(x=0,3),Nd₃₁Fe_68-xB₁Hf_x(x=0,3)alloy ribbons were prepared by the melt fast quenching method,and the effects of Hf element addition on the phase composition,microstructure,magnetic properties,exchange coupling,coercivity mechanism,high temperature magnetic properties and thermal stability of Nd-Fe-B permanent magnetic alloys with different Nd contents were systematically investigated in this paper.According to the study of the magnetic properties at room temperature,the addition of Hf elements in Nd-Fe-B alloys with Nd content of 27 wt%leads to an increase in the coercivity and a decrease in the remanence and maximum magnetic energy product,while in Nd-Fe-B alloys with Nd content of 29 wt%and 31 wt%,the addition of Hf elements leads to a decrease in the coercivity and an increase in the remanence and maximum magnetic energy product.According to the study of high temperature magnetic properties and thermal stability,the coercivity of Nd-Fe-B alloys with different Nd contents was improved to different degrees with the addition of Hf elements,and it is noteworthy that the coercivity,remanence and maximum magnetic energy product were also improved in Nd-Fe-B alloys with Nd contents of 29 wt%and 31 wt%.With the addition of Hf elements,the remanence temperature stability and coercivity temperature stability deteriorate in Nd-Fe-B alloys with Nd content of 27 wt%,while in Nd-Fe-B alloys with Nd content of 29 wt%and 31 wt%,the remanence temperature stability deteriorates and the coercivity temperature stability improves.Secondly,Co_87.5Hf_12.5 alloy ribbons with different wheel speeds,Co_100-xHf_x(x=12.5,14.5,16.5,18.5,20.5)alloy ribbons with different Hf content and Co_83.5-xHf_16.5B_x(x=0,1,3,5)alloy ribbons with different B content were prepared by melt quenching method and explorative research was conducted on them.According to the study of Co_87.5Hf_12.5 alloys at different wheel speeds,the magnetic properties of Co_87.5Hf_12.5 alloys can be effectively improved by adjusting the wheel speed.The coercoerity,remanence and maximum magnetic energy product reach the maximum values at the wheel speed of 35 m/s,which were 160k A/m,0.69 T and 37 k J/m³,respectively.Co_87.5Hf_12.5 alloys have good high temperature magnetic properties and thermal stability,and still exhibits good thermal stability at 773 K,its remanence temperature coefficient and coercivity temperature coefficient are-0.11%/K and-0.19%/K,respectively.According to the research of Co_100-xHf_x alloys,it shows that the Co_100-xHf_x alloys with high content of Hf will lead to the cubic structure Co₂Hf phase generated.When x=16.5,the coercivity reached a maximum of 253 k A/m,the remanence and maximum magnetic energy product were 0.44 T,28 k J/m³,respectively.When x=12.5,the remanence and maximum magnetic energy product reaches the maximum were 0.69 T,37k J/m³,respectively,the coercivity was 160 k A/m.At 773 K,the remanence temperature coefficient and coercivity temperature coefficient of Co_83.5H_16.5alloys were-0.12%/K and-0.17%/K,respectively.According to the study of Co_83.5-xHf_16.5B_x alloys,it can be seen that the B atoms with a smaller atomic radius enter the lattice and replace atoms with a larger atomic radius with the addition of B atoms,the addition of B atoms has a significant effect on the improvement of the magnetic properties at room temperature.When x=3,the coercivity reaches the maximum value of 312 k A/m,and when x=1,the remanence and magnetic energy product reach the maximum values,which were 0.48 T and 32 k J/m³,respectively.The Co_81.5Hf_16.5B₃ alloys also have good high-temperature magnetic properties and thermal stability.After three high-temperature cycles,the temperature coefficient of remanence and the temperature coefficient of coercivity were-0.18%/K and-0.21%/K at 773 K,respectively.