Magnetics Hysteresis Properties and Microstructure of High-Energy (Nd,Dy)–Fe–B Magnets with Low Oxygen Content

Magnetic properties and microstructure of high-energy (Nd,Dy)–Fe–B magnets with Dy of no more than 1 wt % prepared via a low-oxygen routine are studied. Oxygen content in magnets does not exceed 0.20 wt %. 0.5 wt %–Dy addition reliably stabilizes the coercivity MHc higher than 13 kOe; in this case, the maximum energy density product (BH)max of magnets is 48.5–49.5 MG Oe. High magnetic hysteresis properties are gained via optimization of chemical and phase compositions of magnets, as well as their microstructure. The grain size of the main Nd2Fe14B phase is approximately 3.5 μm; and according to X-ray analysis, the weight fraction of additional Nd-rich phases (NdOx and Nd2O3) does not exceed 2.5%. Scanning electron microscopy study has demonstrated that in triple junctions of Nd2Fe14B grains there are two types of inclusions (В and С) of the NdOx phase, which significantly differ by their chemical composition. С-phase inclusions with low oxygen content (х ≈ 0.03) are enriched in Fe (40–50 wt %); whereas, В-phase with high oxygen content (х ≈ 0.70) contains 3–5 times less Fe. The angular dependences of coercivity of (Nd,Dy)–Fe–B magnets are presented.

Hysteresis Properties of Corroded High Strength Steel

In order to study the effects of corrosion damage on the hysteresis properties of high strength steel (HSS), dry-wet cycle corrosion tests were conducted on Q690D steel to obtain 6 batches of corroded specimens, and cyclic loading tests were performed on them to analyse the degradation law of hysteresis curve, skeleton curve and hysteretic energy, and then establish the hysteresis constitutive model of corroded HSS steel. Results indicated that although the hysteresis curves of corroded specimens are still smooth and full, corrosion damage would result in the continuous decrease of peak stress, and lead to the linear reduction of hysteresis energy. Besides, the cyclic hardening coefficient K’ and cyclic hardening index n’ of HSS would also decrease linearly with corrosion degree. Based on these experimental results, a new hysteresis constitutive model for corroded HSS steel was proposed, and its validity was verified.

Влияние атомов замещения и внедрения на магнитные свойства соединения Sm-=SUB=-2-=/SUB=-Fe-=SUB=-17-=/SUB=-

(Sm1-xRx)2Fe17 (R = Ho, Er) alloys with х = 0.1, 0.2 and 0.4 were prepared by induction melting under inert gas atmosphere. The structure and magnetic hysteresis properties of both the initial compositions and hydrides based on them are investigated. It was found that (Sm1-xRx)2Fe17Нy hydrides like the parent compounds have a rhombohedral Th2Zn17-type of crystal structure (sp.gr. R m). Hydrogenation results in a significant increase in the Curie temperature and saturation magnetization at room temperature. Compositions with potentially high magnetic characteristics have been determined.