Phase transformations in rapidly solidified Nd33Fe77 alloy

1992 ◽  
Vol 50 (1) ◽  
pp. 56-57
Author(s):  
A. Zaluska ◽  
L.X. Liao ◽  
X. Chen ◽  
Z. Altounian ◽  
J.O. Ström-Olsen
Keyword(s):  
Phase Transformations ◽  
High Performance ◽  
Melt Spinning ◽  
Permanent Magnets ◽  
New Materials ◽  
Amorphous Precursor ◽  
Eutectic Melting ◽  
Subsequent Transformation ◽  
Fe Alloys ◽  
Rapidly Solidified

Nd-Fe alloys are important for high performance permanent magnets (usually in combination with B, C or N) and a knowledge of the metastable and stable phases of the system is necessary for the development of these new materials. An effective way to investigate such phases is by crystallizing an amorphous precursor.Amorphous ribbons of the binary alloy Nd33Fe77 were produced by melt-spinning. The phase transformations induced by heat treatment of the as-quenched ribbons is complex involving first the production of metastable phases followed by subsequent transformation into stable phases and finally eutectic melting.

EM of rapidly solidified permanent magnets

1992 ◽  
Vol 50 (1) ◽  
pp. 198-199
Author(s):  
Raja K. Mishra
Keyword(s):  
Melt Spinning ◽  
Permanent Magnets ◽  
Dark Field Image ◽  
Dark Field ◽  
Maximum Energy ◽  
Quench Rate ◽  
Maximum Energy Product ◽  
Energy Product ◽  
Annular Dark Field ◽  
Rapidly Solidified

The discovery of a new class of permanent magnets based on Nd2Fe14B phase in the last decade has led to intense research and development efforts aimed at commercial exploitation of the new alloy. The material can be prepared either by rapid solidification or by powder metallurgy techniques and the resulting microstructures are very different. This paper details the microstructure of Nd-Fe-B magnets produced by melt-spinning.In melt spinning, quench rate can be varied easily by changing the rate of rotation of the quench wheel. There is an optimum quench rate when the material shows maximum magnetic hardening. For faster or slower quench rates, both coercivity and maximum energy product of the material fall off. These results can be directly related to the changes in the microstructure of the melt-spun ribbon as a function of quench rate. Figure 1 shows the microstructure of (a) an overquenched and (b) an optimally quenched ribbon. In Fig. 1(a), the material is nearly amorphous, with small nuclei of Nd2Fe14B grains visible and in Fig. 1(b) the microstructure consists of equiaxed Nd2Fe14B grains surrounded by a thin noncrystalline Nd-rich phase. Fig. 1(c) shows an annular dark field image of the intergranular phase. Nd enrichment in this phase is shown in the EDX spectra in Fig. 2.

Microstructure of Rapidly Solidified Cu-Fe Alloys

1983 ◽  
Vol 28 ◽  
Author(s):  
Uwe Köster ◽  
Christoph Caesar
Keyword(s):  
Cross Sections ◽  
Contact Surface ◽  
Iron Content ◽  
Melt Spinning ◽  
Volume Fraction ◽  
Thermal Contact ◽  
Lattice Parameter ◽  
Good Thermal Contact ◽  
Fe Alloys ◽  
Rapidly Solidified

ABSTRACTRapidly solidified ribbons of Cu-Fe alloys with iron contents up to 20 at.−% have been prepared by melt-spinning. Optical and electron microscopy as well as x-ray and electron diffraction techniques were used to characterize quantitatively the microstructure, i.e., grain size and shape, solubility of iron, lattice parameter, volume fraction and distribution of precipitated iron-particles, etc.Whereas the free surfaces of melt-spun Cu-Fe ribbons have been found to be very smooth, the contact surfaces usually consist of isolated areas of good thermal contact with small equiaxed grains separated by bands without contact during casting and therefore poor heat transfer. The cross sections of the ribbons generally exhibit a strong anisotropy in their microstructure: very fine crystals adjacent to the contact surface develop into narrow columnar grains, generally significantly elongated and extending across the whole section. The average columnar width of the grains has been found to decrease significantly with increasing iron content. Precipitation of iron not only depends on the iron content but also on the distance from the contact surface.

Precipitates in hot pressed Nd-Fe-B magnets

1989 ◽  
Vol 47 ◽  
pp. 572-573
Author(s):  
Tsung-Yao Chu
Keyword(s):  
Elevated Temperature ◽  
High Performance ◽  
Melt Spinning ◽  
Permanent Magnets ◽  
Ion Beam ◽  
Boundary Phase ◽  
Full Density ◽  
Mechanical Grinding ◽  
Thin Sections ◽  
Argon Ion

High-performance permanent magnets based on the Nd-Fe-B ternary system can be prepared by melt-spinning of the molten alloy and subsequent pressing to full density at elevated temperature. The starting composition is always slightly rich in Nd compared to stoichiometric Nd2Fe14B in order to ensure the formation of the Nd-rich grain boundary phase. The excess Nd additions also serve to keep elemental Fe particles from precipitating but, instead, lead to unexpected precipitation within the Nd2Fe14B grains. The current research seeks to fully characterize the structure of the precipitates.Electron transparent specimens for TEM examination were prepared by mechanical grinding of thin sections cut from the hot pressed Nd0.135Fe0.815B0.05 magnets, followed by argon ion beam milling at 6 kV. Most of the samples were studied in a JEOL 1200EX STEM equipped with EDS, operating at 120 kV. A few samples were examined at higher resolution in a JEOL 200 CX TEM operated at 200 kV, employing a side entry goniometer stage and a LaB6 cathode.

A Transmission Electron Microscopy study of the B2-DO3 ordering phase transformations in Fe-6.3wt% Si after rapid quenching and annealing

1988 ◽  
Vol 46 ◽  
pp. 772-773
Author(s):  
J. E. Wittig
Keyword(s):  
Phase Transformations ◽  
Melt Spinning ◽  
Magnetic Behavior ◽  
Microscopy Study ◽  
Rapid Quenching ◽  
Electron Microscopy Study ◽  
Silicon Alloys ◽  
Brittle Behavior ◽  
Transmission Electron ◽  
Rapidly Solidified

Iron-silicon alloys are extensively used in transformer cores owing to exceptional soft magnetic behavior that is optimized at about 6.5 wt% Si. Unfortunately this equilibrium microstructure is completely brittle at room temperature. The brittle behavior coincides with the onset of an ordering reaction of the disordered A2 into the B2 and DO3 superlattices at approximately 5 wt% Si. Rapid solidification methods have been shown to improve the ductility of Fe- 6.3 to 6.5 wt% Si. In this investigation, rapidly quenched and annealed samples of Fe-6.3wt% Si were examined in the transmission electron microscope (TEM) to study the ordering phase transformations of this alloy and its effect on the mechanical behavior.Samples of Fe-6.3wt% Si were rapidly solidified by melt spinning into ribbons (t=20-80 microns) as well as by splatting using an opposing piston double anvil method. Rapidly quenched samples were subsequently heat treated in evacuated quartz tubes at 500, 600, and 700 C for 24 h.

Analytical Electron Microscopy of cast (Nd1-xRx)13Fe80C7 [R=Tb,Dy] permanent magnet materials

1990 ◽  
Vol 48 (4) ◽  
pp. 784-785
Author(s):  
Josef Fidler ◽  
Claudia Groiss ◽  
J. Eisses ◽  
K.H.J. Buschow
Keyword(s):  
Coercive Field ◽  
High Performance ◽  
Permanent Magnets ◽  
Magnetocrystalline Anisotropy ◽  
Analytical Electron Microscopy ◽  
Preparation Technique ◽  
Sintering Process ◽  
New Materials ◽  
Analytical Electron ◽  
Processing Techniques

High performance permanent magnets are based on compounds of the type SmCo5, Sm2Co17 and Nd2Fe14B exhibiting high magnetization and high magnetocrystalline anisotropy. The primary preparation technique for such magnets is the powdermetallurgical sintering process. The search for new materials and processing techniques led to the ternary system R-Fe-C.Compounds of the type R2Fe14C are isotypic with the crystal structure of Nd2Fe14B. Cast magnets based on R2Fe14C exhibit already a high coercive field, but decompose at higher temperatures into compounds of the type R2F17Cx. The transformation temperature Tt depends on the rare earth element and is about 850°C for the Nd-system and is larger than 1100°C for the Tb- and the Dy-system.The specimens investigated were cast in an arc furnace and annealed for 31 days at 850°C. Various magnets with different composition (Nd/Dy- and Nd/Tb-ratios) and coercivities were studied. The coercive field increases with decreasing Nd-content (see Table 1).

High performance Sm2+δ Fe15Ga2C2 permanent magnets made by melt spinning and hot pressing

1998 ◽  
Vol 83 (10) ◽  
pp. 5549-5551 ◽  
Author(s):  
J. van Lier ◽  
M. Kubis ◽  
W. Grünberger ◽  
L. Schultz ◽  
H. Kronmüller
Keyword(s):  
Hot Pressing ◽  
High Performance ◽  
Melt Spinning ◽  
Permanent Magnets

Metastable Phases in Rapidly Solidified Aluminum-Rich Al-Fe Alloys

1982 ◽  
Vol 19 ◽  
Author(s):  
D. Shechtman ◽  
L.J. Swartzendruber
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Melt Spinning ◽  
Gamma Ray ◽  
Resonance Spectrum ◽  
Metastable Phase ◽  
Metastable Phases ◽  
Transmission Electron ◽  
Fe Alloys ◽  
Rapidly Solidified

ABSTRACTAluminum-rich Al-Fe binary alloys up to and including Al3Fe were prepared by melt spinning in order to study the metastable phase structure and its transformation following heat treatment. Transmission electron microscopy and nuclear gamma-ray resonance were utilized in the study. The rapidly solidified structure was found to contain up to three metastable phases. One of the phases, with a composition and a gamma-ray resonance spectrum appropriate for Al6Fe, has either a globular or a cellular morphology upon quenching.

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