Preparation Of High Performance NdFeB/SmCo Composite Permanent Magnets For Oil And Gas Exploration Motors

High-temperature magnetic pump is one of the key processes in oil and gas production.It is widely used in petroleum,petrochemical and chemical industries as a high-temperature medium for transportation of petroleum and printing materials.Therefore,there are strict and special requirements for the high magnetic performance and high temperature stability of the inner and outer rotor permanent magnets of the magnetic pump.NdFeB permanent magnet material is a new permanent magnet material with high magnetic properties and economic availability.However,the low temperature stability and pooer corrosion resistance of NdFeB limit its application in high temperature and corrosive environment.Compared with NdFeB,SmCo permanent magnets have high temperature stability and corrosion resistance,while its expensive and the magnetic properties are lower.Therefore,it is very important for research and application to prepare the composite magnets with well comprehensive performance by combining two kinds of magnets.In this article,the microstructure,magnetic properties and temperature stability of SmCo/NdFeB composite magnets are studied by XRD,MPMS3,SEM,TEM and other testing techniques.Anisotropic Sm₂Co₁₇/NdFeB dense composite bonded magnets were prepared by orientation molding technique.The variation of magnet composition,phase structure and magnetic properties were studied.The formation of the two-phase planetary structure was found in that the composite bonded magnet,and the best magnetic properties were obtained when the NdFeB content was 70 wt.%:M_r=99.53 emu/g,H_c=13.75 kOe,?BH?_max=14.15 MGOe.To obtain high performance SmCo nanocrystalline magnetic powder,the SmCo amorphous powder was first prepared by high energy ball-milling techniques.And then,the effect of annealing temperature on the phase structure,micro-morphology and magnetic properties was investigated.After annealing at 750°C,the nanocrystalline SmCo₇ phase was obtained,and its?BH?_max reached to 12.32 MGOe,the grain size was 11.3 nm.Moreover,Co addition effectively improved the stability of the SmCo₇ phase.In order to obtain a dense composite magnet,the isotropic nanocrystalline SmCo₇/NdFeB dense composite magnet was prepared by spark plasma sintering?SPS?.The variation of magnet composition,phase structure and magnetic properties were studied in detail.The composite magnet exhibited good single-phase demagnetization behavior.When the NdFeB content was10 wt.%,the composite magnet had a maximum coercivity H_c=15.4 kOe and remanence ratio of M_r/M_s=0.7,which had strong exchange coupling.After annealing,the magnetic properties were improved,and?BH?_max was increased by a maximum of 23.6%.The anisotropic nanocrystalline SmCo₇/NdFeB dense composite magnet was further prepared by thermal deformation technique.The results show that different deformation techniques have an important influence on the magnetic properties and phase structure of the composite magnet.After thermal deformation,the single-phase SmCo₇ and NdFeB magnets obtained good c-axis texture and high magnetic properties.Due to the diffusion and segregation between elements,the magnetic properties of the composite magnet were decreased,but the temperature stability improved.