Viswanathan Panchanathan

The microstructure of hot formed neodymium-iron-boron magnets with energy product 48 MG Oe

Melt‐spun Nd–Fe–B ribbons containing small amounts of Co, Ga, and C were die upset to 60% and 70% reduction in height in an argon atmosphere between 750 and 800 °C. The magnet, which was die upset 70%, has a remanence of 14.2 kG, Hci of 14.8 kOe, and (BH)max of 48 MG Oe. The interior of the magnet consists of well‐aligned Nd2Fe14B grains separated by a Nd‐rich intergranular phase. Intermixed with such aligned grains, we observed zones of unaligned fine‐grained material without any intergranular phase. Since the intergranular phase is a key factor for deformation and alignment and it is uniformly distributed in the hot pressed precursor, it will be possible to enhance the alignment further by controlling the redistribution of the intergranular phase during die upsetting.

Effect of additive elements on magnetic properties and irreversible loss of hot‐worked Nd‐Fe‐Co‐B magnets

There has been limited work on the effects of alloying elements on the properties of hot‐worked anisotropic magnets. The coercivity mechanisms for sintered and rapidly solidified Nd‐Fe‐B magnets are different, and additives can have different effects on magnetic properties. The present study was conducted to clarify the effects of various alloying elements on the properties of hot‐worked magnets. Ribbons of composition (Nd13.6−xRx)(Fe77.6−yTyCo2.8)B6.0 (R=Ce and Dy; T=Al, V, Cu, Ga, Zr, Nb, Mo, and Sn; x=0, 1, and 2; y=0, 0.5, and 1.0) were prepared by melt spinning. Anisotropic magnets were made at 1073 K with 55.6% reduction in height by die upsetting. Room‐temperature magnetic properties and irreversible losses after exposure at 323–473 K were determined. The results showed that small amounts of Al, V, Cu, and Ga enhanced the remanence of the magnets, while Dy, Al, Ga, Zr, Nb, and Mo improved the coercivity. Dy, Ga, and Mo additions were effective in increasing the heat resistance temperature (HRT), de...

Microstructure of high‐remanence Nd‐Fe‐B alloys with low‐rare‐earth content

The microstructure and magnetic properties of bonded and fully dense magnets produced from melt‐spun ribbons of the composition RE4.5TM76Ga1B18.5 have been investigated, where RE refers to a mixture of Nd and Dy, and TM refers to a mixture of Fe and Co. Results show that annealing overquenched ribbons with about 3 wt. % Dy and 3 wt. % Co at 700 °C can produce materials with Hci≂4 kOe, Br≂11.5 kG, and (BH)max≂14.5 MGOe, the latter being comparable to those of commercial ribbons containing three times as much Nd. The microstructure of annealed ribbons consists of about 30% Nd2Fe14B grains, 65% Fe3B grains, and 5% α‐Fe grains. The grains of all the phases are nearly spherical. The grain diameters are in the 30–50 nm range. Hot‐pressed magnets made from overquenched ribbons are fully isotropic, with magnetic and microstructural characteristics similar to those of the annealed ribbons. The high remanence and low coercivity correlate well with the microstructure consisting of a uniform mixture of the hard Nd2Fe...

Studies on low rare earth Nd-Fe-B compositions

Investigations have been carried out to evaluate the optimum Nd-Fe-B composition to have H/sub ci/ of at least 4 kOe. The optimum composition for the best magnetic properties is as follows: TRE 18 wt.%, B 1 wt.% and balance Fe. The magnetic properties are B/sub r/, 10.1 kG, H/sub ci/ 4.3 kOe and BH/sub max/ 12.5 MGOe. All the additives (Ga, Nb, Mo, V, Cr) with or without cobalt addition did not improve the magnetic properties. The bonded magnets made using this material had B/sub r/ value slightly higher than the standard MQP-B powder. The low coercivity of these materials limit their operating temperature to 80/spl deg/C. This material having Nd/sub 2/Fe/sub 14/B//spl prop/-Fe shows improved saturation behavior compared to those having Nd/sub 2/Fe/sub 14/B/Fe/sub 3/B and Nd/sub 2/Fe/sub 14/B structures. It would then be a good candidate for applications where magnetization is difficult.

Hot workability of melt‐spun Nd‐Fe‐Co‐B magnets

Anisotropic Nd‐Fe‐B magnets are produced from melt‐spun ribbons by hot working technique. The processing is facilitated by improved workability. In order to obtain a sound magnet, it is important to suppress the crack initiation and growth. An investigation was carried out to study the deformation mechanism of the alloy system and to improve workability by changes in alloy composition. Alloy ribbons with composition (Nd13.6−xRx) (Fe77.6−y Ty Co2.8)B6.0 [R=Ce, Dy; T=Al, Si, V, Cu, Ga, Zr, Nb, Mo, Sn; x= 0, 1, 2; y=0, 0.5, 1.0] were prepared by melt spinning and then hot pressed into fully dense compacts. These compacts were upset in a hot working simulator. Hot workability was evaluated by measuring the crack opening displacement on the surface at the half height of the upset specimen. The relationship between strain rate and flow stress was found to be expressed by the equation: e = Aσn exp( − Q/RT). Values of n and Q were obtained for quarternary composition (Nd‐Fe‐Co‐B). The effects of strain and strai...

Radially oriented high energy product Nd-Fe-B ring magnets

This paper deals with the extruded radially oriented magnets made from rapidly solidified Nd-Fe-B material. The effect of chemical composition on the magnetic properties and hot workability was studied for various compositions in Nd-Fe-Co-Ga-B system. The composition ranges of Nd and B which shows maximum energy product and hot workability were determined.

Low rare-earth Nd–Fe–B bonded magnets with improved irreversible flux loss

The effects of Nb addition on magnetic properties and irreversible flux loss were studied on bonded magnets with compositions of Nd8Fe86−xB6Nbx, where x=0–3. An irreversible flux loss was measured at Pc=2 after exposure at 393 K for 3.6 ks in air. It was found that the Nb addition of 2 at. % or more decreased the irreversible flux loss. The value was less than 5%, similar to that obtained with MQP-B magnets. Br decreased with the increase in Nb content. The effect of Nd content on the magnetic properties and irreversible flux loss was also studied on the bonded magnets with compositions of NdxFe92−xB6Nb2, where x=6–8. The bonded magnet with the optimum composition of Nd6.5Fe85.5B6Nb2 had  Br similar to that of MQP-Q magnets that did not contain Nb, and the value of irreversible flux loss was comparable to that of MQP-B magnets. A multipole magnetizability test on the bonded magnets with the above optimum composition was carried out, and the total flux of the bonded magnets was about 10% higher than that o...

Effect of additives on hot deformation behavior of melt-spun Nd-Fe-Co-B magnets

The effect of various additives on hot workability was investigated for alloy systems of (Nd13.6−xRx)(Fe77.6−yTyCo2.8)B6.0: R=Ce, Dy; x=0, 1, 2; T=Al, Si, V, Cu, Ga, Zr, Nb, Mo, Sn; y=0, 0.5, 1.0. A semiquantitative comparison of the effect of various additives was made by measuring the crack opening displacement (CODmax) in test specimens deformed in an open (unconstrained) configuration. Among the additives, cerium and silicon improved the hot workability while niobium and tin severely deteriorated the workability. The remanence anisotropy ratio was inversely related to CODmax. Detailed microstructural investigations were carried out with alloys which had only cerium or tin to study the reason for their hot workability behavior in comparison to the base alloy. The improved hot workability of cerium added alloy is related to the lower melting temperature of the intergranular phase and faster grain growth compared to the base alloy. Tin addition prevented grain growth with no endothermic peak in a differe...

Effect of Co content on magnetic properties of hot-worked Nd-Dy-Ce-Fe-Co-B magnets

The effect of cobalt addition on magnetic properties of hot-worked Nd-Dy-Ce-Fe-Co-B magnets was studied. Ribbons with composition (Nd/sub 11.6/Dy/sub 1/Ce/sub 1/) (Fe/sub 80.4-x/Co/sub x/)B/sub 6/, where x=0, 2.8, 5.5, 8.4, and 11.2, were prepared by melt spinning. Anisotropic magnets were made by die upsetting at 1073 K with 55.6% reduction in height. The temperature coefficient of Br, alpha , was improved with increase in cobalt content. Addition of 2.8 at.% cobalt considerably improved the temperature coefficient of Hci, beta , compared to the base alloy; however, further additions of cobalt did not improve beta . Also, irreversible flux losses showed similar behavior as beta . Microstructural investigations showed the existence of a cobalt-rich phase in the 11.2 at.% cobalt specimen. Lower values of beta with cobalt-containing specimens may be ascribed to a combination of the changes in the anisotropy field of 2-14-1 phase and their microstructure. >

Effect of grain size on magnetic properties of melt spun Md-Fe-B magnets

Introduction The bonded Nd-Fe-B market has been experienced the fastest growth of any permanent magnet industry. The rapidly solidified Nd-Fe-B forms the basis for the entire bonded magnet industry. Other techniques such as atomization are being investigated; however all the production powders are manufactured by melt spinning. The melt spun powders due to the nature of quenching process are generally isotropic in nature. The technical development activities in isotropic powders have been concerned with improvements in remanence, lowering the total losses , squareness of demagnetization curve etc. High temperature bonded magnets with low losses were developed using niobium addition as an additive to Nd-Fe-B systems. This publication deals with the improvement in remanence and squareness of the demaenetization curve of isolrocdc wwders. 1 . Expe&nentals Detailed investigations were carried out to studv the effect of wheel meed on the properties and gr& size of the material in Nd,2Fe8,,5B, system. Thk alloy was melt spun in an inert atmosphere over wheel speeds of 10 to 30 d s in laboratory melt spinner. The properties of the ribbon and the annealed powder were measured using VSM. X-ray diffraction studies were carried out for melt spun ribbons and annealed powders prepared at various speeds to determine the phase distribution and grain size of Nd,Fe,,B phase. Results -e 1 shows the grain sue of Nd,Fe,,B phase observed in as-spun ribbon as a function of wheel speed. It was found that the grain size of Nd,Fe,,B pha:se was coarser in the bee surface compared to wheel surface at any wheel speed. Figure 2 shows the variation in (BH)max of annealed powder as a function of wheel speed. Figs. 1 and 2 clearly show that the variation in grain size between wheel and free surface leads to lower magnetic properties, and it is possible to reduce this variation to a minimum with increase in the energy product by proper processing conditions. Figure 3 shows the variation in energy product with mean grain size of the annealed powder. This figure indicates that energy produd 15 MGOe or greater k