Capillary stability limits for liquid metal in melt spinning

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.

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In situ TEM observations of melting in nanosized eutectic Pb-Cd inclusions embedded in Al

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167391 ◽

1996 ◽

Vol 54 ◽

pp. 986-987

Author(s):

S. Hagège ◽

U. Dahmen ◽

E. Johnson ◽

A. Johansen ◽

V.S. Tuboltsev

Keyword(s):

Electron Microscope ◽

Melt Spinning ◽

Ternary Alloys ◽

Solid Matrix ◽

Eutectic System ◽

In Situ Tem ◽

In Situ Observation ◽

Orientation Relationships ◽

Transmission Electron

Small particles of a low-melting phase embedded in a solid matrix with a higher melting point offer the possibility of studying the mechanisms of melting and solidification directly by in-situ observation in a transmission electron microscope. Previous studies of Pb, Cd and other low-melting inclusions embedded in an Al matrix have shown well-defined orientation relationships, strongly faceted shapes, and an unusual size-dependent superheating before melting.[e.g. 1,2].In the present study we have examined the shapes and thermal behavior of eutectic Pb-Cd inclusions in Al. Pb and Cd form a simple eutectic system with each other, but both elements are insoluble in solid Al. Ternary alloys of Al (Pb,Cd) were prepared from high purity elements by melt spinning or by sequential ion implantation of the two alloying additions to achieve a total alloying addition of up to lat%. TEM observations were made using a heating stage in a 200kV electron microscope equipped with a video system for recording dynamic behavior.

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Electron spectroscopic imaging (ESI) on multiphase polymer materials

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153713 ◽

1989 ◽

Vol 47 ◽

pp. 348-349

Author(s):

H.-J. Cantow ◽

M. Kunz ◽

M. Möller

Keyword(s):

Energy Loss ◽

Melt Spinning ◽

Chromatic Aberration ◽

Element Distribution ◽

Polymer Materials ◽

Specific Energy Loss ◽

Transmission Electron ◽

Multicomponent Polymer ◽

Diffraction Patterns ◽

Image Planes

In transmission electron microscopy the natural contrast of polymers is very low. Thus the contrast has to be enhanced by staining with heavy metals. The resolution is limited by the size of the staining particles and by the fact that electrons with different energy are focused in different image planes due to the chromatic aberration of the magnetic lenses. The integration of an electron energy loss spectrometer into the optical coloumn of a transmission electron microscope offers the possibility to use monoenergetic electrons and to select electrons with a certain energy for imaging. Thus contrast and resolution are enhanced. By imaging only electrons with an element specific energy loss the element distribution in the sample can be obtained. In addition, elastic bright field images and diffraction patterns yield excellent resolution. Some applications of the method on multicomponent polymer materials are discussed.Bulk polymer samples were prepared by ultramicrotoming at room temperature or well below the glass transition temperature. Very thin films for the direct observation of the structure in semicrystalline polymers were obtained by melt-spinning. Specimens were examined with a ZEISS CEM 902 operated at 80 kV.

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