Fabrication Of Nanocomposite Magnetic Materials By Mechanical Alloying And Magnetic Properties Analysis

Nanocomposite Magnetic Materials are composed of hard magnetic phase and soft magnetic phase which exchange-coupled at nanoscale. These materials are considered to be the next generational rare earth permanent magnetic material with higher magnetic properties and wide application.This dissertation investigated fabrication of SmCo5/α-Fe and Nd-Fe-B/α-Fe nanocomposite magnetic materials by mechanical alloying (MA), relationship between magnetic properties and additional elements Co, Ti, Dy, Tb. Besides, a new kind of hard magnetic phase/hard magnetic phase of SmCo5/Nd2Fe14B nanoscale magnetic material with (BH)max enhanced and high temperature magnetic properties was investigated.For the study on the fabrication of Sm-Co/α-Fe by MA, techniques of XRD, TEM, SEM were applied to research the microstructure of SmCo5and α-Fe during the high energy ball milling, it was found that the grain size of SmCo5and α-Fe decrease with the milling time due to the dislocation multiplied, grain size of SmCo5decrease to5nm after1hour milling and appear to amorphous, soft hard phase α-Fe grain size reduce to5nm after2hour milling and keep BCC structure with the milling time. Hysteresis loop showed the coercivity decrease with the milling time due to hard phase of SmCo5structure decomposed. But the magnetization increase with the milling time, because of the FeCo formed where the Fe diffuse into SmCo5.Nd-Fe-B/α-Fe based nanocomposite magnetic materials with Co addition have been prepared by ball-milling and warm compaction. It was found that Co added into the magnetical hard phase improves magnetic properties significantly, especially Mr/MS ratio and coercivity, in comparison to the composite counterparts without Co addition or with Co additions only in the soft phase or in both phases. The effect on the magnetic properties of the selective Co addition is attributed to enhanced inter-diffusion cross the hard/soft interface that improves the interface conditions for effective inter-phase exchange coupling. By optimizing Co content in the Nd15Fe79-xCoxB6hard phase, an energy product about167.1kJ/m3can be obtained in the isotropic Nd2(FeCo)i4B/a-(FeCo) nanocomposite magnets compared to119.4kJ/m3of Nd2Fe14B/α-Fe nanocomposite magnets prepared under the same conditions with the same grain size and microstructure, owing to the strengthened inter-granular exchange interactions. Nanocomposite Sm-Co/Nd-Fe-B hybrid magnetic materials have been successfully prepared by high-energy ball milling. After appropriate annealing, homogenous microstructure with SmCo5, Nd2Fe14B and a-Fe phases were developed. A maximum energy product of111.4kJ/m3was obtained in the nanocomposite magnets, which is20%higher than that of SmCo5single-phase magnets. The thermal stability was highly enhanced compared to pure Nd2Fe14B shown in the M-T measurement. It was also observed that SmCo2phase forms at a relatively low temperature if a large amount of NdaFe14B is used during preparation, which deteriorates the magnetic properties significantly.