Presentation Information
[P1-36]Effect of gallium alloying on hysteresis properties of the Re-(Fe,Co)-Ga-B permanent magnets
*Andrey Vladimirovich Protasov1, Aleksandra Romanovna Soltus1, Denis Aleksandrovich Kolodkin1, Ludmila Alekseevna Stashkova1 (1. M.N. Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences (Russia))
Keywords:
NdFeB,Permanent magnets,Gallium alloying
High-energy permanent magnets based on the Nd-Fe-B system are widely used in various fields of science and technology. The main disadvantage of these magnets is known to be low temperature stability of magnetic properties because of the low Curie temperature of Nd2Fe14B phase (TC ~ 310 °C), which limits their application in devices operating at elevated temperatures.
The following approaches are used to increase the coercive force HC to 20 kOe and improve the temperature stability of the hysteresis characteristics of Nd-Fe-B magnets:
1) Partial substitution of cobalt for iron leads to a significant increase in the Curie temperature TC of Nd2(Fe,Co)14B phase and a decrease in the absolute value of a;
2) Partial substitution of dysprosium for neodymium in the composition of the initial alloy allows one to increase the anisotropy field and the coercive force;
3) The HC value of magnets can reach 20 kOe by alloying Re2(Fe,Co)14B based alloys with a small amount of gallium. This approach allows reducing the content of heavy rare earth elements in the alloy, which leads to decrease in the cost of the original alloy.
Thus, the aim of this work is to obtain high coercivity permanent magnets based on the Re-(Fe,Co)-Ga-B system with HC values > 20 kOe and (BH)max > 30 MGsOe at room temperature and the temperature coefficient a of no more than |-0.06| %/°C in the temperature range from 23 to 100 °C and to study the influence of two-stage low-temperature heat treatment modes on the hysteresis properties and microstructure of magnets.
The optimization of the alloy composition and the use of a two-stage heat treatment scheme for the Re-(Fe,Co)-Ga-B magnet produced by low-oxygen technology make it possible to reach the levels of hysteresis characteristics: Br = 11.7 kG, MHC = 20.8 kOe, BHC = 11.2 kOe, (BH)max = 32.9 MGe at room temperature and to decrease the temperature coefficient of induction a = |-0.053| %/°C in the temperature range of 23-100 °C. The formation of the non-magnetic Laves phase Re(Fe,Co,Cu,Ga)2 in the grain boundary region helps to increase the HC value of the magnet to 20.8 kOe. It is found that one of the main reasons for the increase of HC is the improvement of the isolation of the grains of the main magnetic phase Re2(Fe,Co)14B provided by a decrease in the magnetization of the grain-boundary Re(Fe,Co,Cu,Ga)2 phase that is accounted for by the presence of gallium atoms in it.
Funding: This study was supported by the Russian Science Foundation, project no. 24-12-20025, and the Goverment of the Sverdlovsk Region and the framework of the State Assignment of the Ministry of Education and Science and Higher Education of the Russian Federation (topic "Magnet" no. 122021000034-9)
The following approaches are used to increase the coercive force HC to 20 kOe and improve the temperature stability of the hysteresis characteristics of Nd-Fe-B magnets:
1) Partial substitution of cobalt for iron leads to a significant increase in the Curie temperature TC of Nd2(Fe,Co)14B phase and a decrease in the absolute value of a;
2) Partial substitution of dysprosium for neodymium in the composition of the initial alloy allows one to increase the anisotropy field and the coercive force;
3) The HC value of magnets can reach 20 kOe by alloying Re2(Fe,Co)14B based alloys with a small amount of gallium. This approach allows reducing the content of heavy rare earth elements in the alloy, which leads to decrease in the cost of the original alloy.
Thus, the aim of this work is to obtain high coercivity permanent magnets based on the Re-(Fe,Co)-Ga-B system with HC values > 20 kOe and (BH)max > 30 MGsOe at room temperature and the temperature coefficient a of no more than |-0.06| %/°C in the temperature range from 23 to 100 °C and to study the influence of two-stage low-temperature heat treatment modes on the hysteresis properties and microstructure of magnets.
The optimization of the alloy composition and the use of a two-stage heat treatment scheme for the Re-(Fe,Co)-Ga-B magnet produced by low-oxygen technology make it possible to reach the levels of hysteresis characteristics: Br = 11.7 kG, MHC = 20.8 kOe, BHC = 11.2 kOe, (BH)max = 32.9 MGe at room temperature and to decrease the temperature coefficient of induction a = |-0.053| %/°C in the temperature range of 23-100 °C. The formation of the non-magnetic Laves phase Re(Fe,Co,Cu,Ga)2 in the grain boundary region helps to increase the HC value of the magnet to 20.8 kOe. It is found that one of the main reasons for the increase of HC is the improvement of the isolation of the grains of the main magnetic phase Re2(Fe,Co)14B provided by a decrease in the magnetization of the grain-boundary Re(Fe,Co,Cu,Ga)2 phase that is accounted for by the presence of gallium atoms in it.
Funding: This study was supported by the Russian Science Foundation, project no. 24-12-20025, and the Goverment of the Sverdlovsk Region and the framework of the State Assignment of the Ministry of Education and Science and Higher Education of the Russian Federation (topic "Magnet" no. 122021000034-9)