Studys Of The Effect Of HDDR And HD On The Structure And Magnetic Properties Of Sm₃(Fe,M)₂₉N_x/α-Fe(M=Co, Ti)

Sm3(Fe,Co,Ti)29Nx with a structure of monoclinic Nd3(Fe,Ti)29 and Excellent intrinsic magnetic properties is a kind of iron-base rare earth intermetallic compound. The processing of such compound is very complex and as a metastable phase during the preparation some stabilizing element is needed. In this work the magnetic powder of Sm3(Fe,Co,Ti)29Nx and Sm3(Fe,Co,Ti)29Nx/α were prepared with more than one elements added as alloying agents and pulverized by HD (Hydrogenation Decrepitation) or HDDR (Hydrogenation -Disproportionation - Desorption - Recombination) treatment. X-ray diffraction, scanning electronic microscope, transmission electron microscope and vibrating-sample magnetometer were used to analysis the processing parameters, microstructure and magnetic properties. In this work the HD and HDDR treatment were systematically studies and the effect of such treatment on other processes and magnetic properties were analyzed.The master alloys were prepared according to four stoichiometric compositions of Sm3.75Fe21.5Co6Ti1.5, Sm3Fe21.5Co6Ti1.5, Sm3.75Fe18.5Co9Ti1.5 and Sm3Fe18.5Co9Ti1.5 The master alloy formed in the 3:29 phase with an addition of some 2:17 phase.All the four kinds of alloys retained the composition of the master alloy after HD treatment. HD treatment had an excellent pulverizing effect and the process is easy to carry out. The optimal temperature for HD was determined to be 350℃. It is found that during HD treatment the mount of a-Fe should be strictly controlled for the increase of a-Fe will lead to the decrease of Ms and Hc.The Hydrogenation-Disproportionation process will have completed after 1 hour hydrogen treatment at 800℃ with the products of a-(Fe,Co,Ti) and the hydride of Sm. Thedecrease of the pressure of hydrogen can stimulate the reaction during Desorption -Recombination. Alloys after HDDR treatment showed better magnetic properties because the exchange coupling effect between the soft and hard magnetic phase was induced by HDDR.The effect of different pulverizing processes on nitrogenation were analysed and the optimal time for nitrogenation was given. The compounds after nitrogenation had a high Curie tempterature due to the addition of Co. The non-uniform of the size of the magnetic powder particles and the a-Fe contained in the uncoupling 3:29 phase were the main cause that leads to low magnetic properties.