Preparation,Structure And Magnetic Properties Of Bulk Anisotropic Nanohybrid Permanent Magnets

Permanent magnets（PMs）are significant for the developing of the society.A variety of single-phase permanent magnets has been developed in the past one hundred years for various applications.Each type of the single-phase magnets has its advantages and drawbacks in their properties.For instance,Sm-Co based magnets have high thermal stability while their magnetization and energy product values are low when compared to the Nd-Fe-B based magnets that have high magnetization but quite low thermal stability.The moderate Curie temperature of the Nd-Fe-B magnets（⁵80 K）makes them less desirable for power-related applications at elevated temperatures.In order to apply in high-temperature technologies and satisfy the application of emerging technologies,the alternative PMs with the merits including less rare-earth elements,large（BH）_maxax and good thermal stability should be developed.Nanohybrid PMs,which combine advantages and avoid shortcomings of different types of PMs,can possess a high energy product,a low cost and a good thermal stability.However,these reported nanohybrid magnets usually include a lot of rare earth elements,have coarse grain size or difficult to obtain the desired hard-phase texture.Based on the research background,this thesis aims to synthesize several kinds of anisotropic bulk nanohybrid magnets(Nd₂Fe₁₄B/α-Fe,[SmCo₇/α-Fe（Co）]@[Nd₂Fe₁₄B/α-Fe]and SmCo₇/α-Fe（Co）@Nd₂Fe₁₄B)by high-pressure thermal compression deformation combined with the high-energy ball milling and melt spinning techniques.The structures and magnetic properties have been studied in detail for these deformed nanohybrid magnets.Anisotropic bulk Nd₂Fe₁₄B/α-Fe nanohybrid magnets have been prepared by high-pressure thermal compression deformation of the blends of Nd-lean Nd₉Fe_85.5Cu_1.5B₄amorphous and Nd-rich Nd_13.6Fe_73.6Ga_0.6Co_6.6B_5.6.6 nanocrystalline alloys.The nanohybrid magnets have a high fraction（²4 wt%）ofα-Fe phase and exhibit a（00l）texture for Nd₂Fe₁₄B nanocrystals in both Nd-lean and Nd-rich regions.The Nd-lean region containsα-Fe and Nd₂Fe₁₄B nanograins with equivalent sizes of¹9 nm and²7 nm and the Nd-rich region comprises lath Nd₂Fe₁₄B nanograins with 20-35 nm in thickness and 50-142nm in length.This nanohybid magnet exhibits a maximum energy product of 23 MGOe and a good thermal stability,β_{（RT-250℃）}=-0.3%℃^-1.Anisotropic bulk multiphase[SmCo₇/α-Fe（Co）]@[Nd₂Fe₁₄B/α-Fe]nanohybrid magnets have been synthesized by high-pressure thermal compression deformation of the mixtures of as-spun Nd₉Fe_85.5Cu_1.5B₄ amorphous and as-milled SmCo-based amorphous-nanocrytalline alloys.The synthesized magnets are composed of alternating SmCo₇/α-Fe（Co）and Nd₂Fe₁₄B/α-Fe nanocomposite regions laying perpendicular to the pressure direction.A（00l）crystallographic texture are simultaneously observed for the SmCo₇ and Nd₂Fe₁₄B nanocrystals in the SmCo₇/α-Fe（Co）regions and Nd₂Fe₁₄B/α-Fe regions,respectively.The SmCo₇/α-Fe（Co）regions have approximately equiaxed SmCo₇ andα-Fe（Co）nanograins with a size of¹2 nm and Nd₂Fe₁₄B/α-Fe regions comprise lath-shaped and approximately equiaxed nanograins with an equivalent grain size of¹9 nm for theα-Fe phase and²9 nm for the Nd₂Fe₁₄B phase.The synthesized magnet with a high-contentα-Fe（Co）andα-Fe phases,up to 30 wt%,exhibits a maximum energy product of 25 MGOe and a low coercivity temperature coefficient ofβ_{（RT-250℃）}=-0.27%℃^-1.The energy product of the obtained magnet increases at first and then decreases with the increase of the Nd₉Fe _85.5Cu_1.5B₄ amorphous alloy content,peak at 30wt%of Nd₉Fe_85.5Cu_1.5B₄ loading.The energy product of the magnet increases with deformation amount in the range ofe=68%to 80%.Anisotropic bulk multiphase layered SmCo₇/α-Fe（Co）@Nd₂Fe₁₄B nanohybrid magnets have been synthesized by high-pressure thermal compression deformation of the blendsofas-milledSmCo-basedamorphous-nanocrytallineandNd-rich Nd_13.6Fe_73.6Ga_0.6Co_6.6B_5.6.6 nanocrystalline alloys.The synthesized magnets with 25.6 wt%soft phase are composed of SmCo₇/α-Fe（Co）nanocomposite layers and Nd₂Fe₁₄B nanocrystalline layers laying perpendicular to the pressure direction.A（00l）crystallographic texture are simultaneously observed for the SmCo₇ nanocrystals and Nd₂Fe₁₄B nanocrystals in the SmCo₇/α-Fe（Co）nanocomposite layers and the Nd₂Fe₁₄B nanocrystalline layers,respectively.The SmCo₇/α-Fe（Co）layers have approximately equiaxed SmCo₇ andα-Fe（Co）nanograins with a size of¹1 nm and the Nd₂Fe₁₄B layers have lath Nd₂Fe₁₄B nanograins with²3 nm in thickness and⁷5 nm in length.This nanohybid magnet exhibits a maximum energy product of 31 MGOe and a good thermal stability,β_{（RT-250℃）}=-0.28%℃^-1.The energy product of the obtained nanohybrid magnet increases with deformation amount in the range ofe=50%to 82%.