Amorphous ribbon

Nd-Fe-B and Pr-Fe-B nanocomposites are rare-earth deficient with respect to the R2Fei4B stoichiometry. The soft phase which is formed is Fe3B or a-Fe. The control of the soft grain size is crucial to preserve a significant coercivity. This can be obtained by crystallisation of amorphous ribbons. The annealing temperature must be high enough to allow crystallization of the... 

Two major alloy systems in the family of soft magnetic nanostructures are Fe-Si-B-Nb-Cu [1, 4-6] and Fe-M-B-(Cu) (M= Zr, Hf or Nb) [3, 7-9], commercially known as FINEMET (or VITROPERM) and NANOPERM, respectively. They are produced by primary crystallization of amorphous ribbons. Hence, the nanostructural formation upon crystallization as well as the mechanism of magnetic softening has been actively studied for these two... 

The magnetically soft nanostructure in F1NEMET or NANOPERM is a direct result of primary crystallization of amorphous ribbons. Here, we discuss this type of crystallization process with emphasis on the nano-structural formation upon crystallization. 

In the present work the NO + NH3 reaction over Pt foil, decomposition of NO on Cu-ZSM-5 zeolite, and the total combustion of m-xylene over Pd2NisoNb4g amorphous ribbon (I), Pd/stainless steel flakes (II) and Pd/clinoptilolite (III) will be discussed based upon our earlier results. 

The demands of practical applications led to attempts to overcome the high electric resistance of thin ribbons by a new technical solution of laser-induced surface vitrification (105, 106). First an amorphous alloy ribbon was adhered uniformly to a nickel plate by heat treatment. Subsequently, this surface alloy layer was transformed to the amorphous structure by laser surface melting and self-quenching (107). A sample consisting of Pd56Rh23P oSi9 adhered to bulk crystalline nickel exhibited anodic characteristics very similar to those of the melt-spun amorphous ribbon (102). Clearly, similar improvements forced by practical demands will be a part of the future use of amorphous alloys. 

Ferrites have become a reference material developments associated with other new magnetic materials, such as the extra-hard rare-earth inter-metallics (Buschow, 1990), or the extra-soft amorphous ribbons (Boll Hilzinger, 1983) are often assessed by comparison with ferrites. 

Methods based on quenching from the melt, such as piston and anvil, double piston, torsion catapult and roller casting (Luborsky, 1980) permit larger quantities of amorphous materials to be obtained. The last of these, also known as melt spinning, is probably the method most used to obtain amorphous ribbons of thickness 10-60 pm, width up to 17 cm and virtually infinite length. In this method, the molten alloy is propelled through a small hole or a slot onto a massive, cold metallic disc rotating... 

A potential drawback for applications of amorphous ribbons is that, being metastable phases, crystallisation can occur as the working temperature increases, with disastrous effects for the magnetic properties. For these reasons, crystallisation phenomena have been widely studied. The crystallisation temperature, 7, can be readily determined by differential scanning calorimetry (DSC), where it appears as a strong, exothermic... 

From the point of view of applications, there are three groups of amorphous ribbons Fe-based alloys, which are inexpensive with high... 

Valenzuela, R. Irvine, J. T. S. (1992). Effects of thermal annealing on the magnetization dynamics of vitrovac amorphous ribbons. Journal of Applied Physics, 72, 1486-9. 

A technique commonly used to prepare amorphous alloys is melt spinning, developed originally by Bedell (1975). This method produces thin amorphous ribbons with a thickness of 10-40 jam. A melt-spinning apparatus is shown schematically in fig. la. The melt is contained in a quartz or alumina vessel (A) which... 

Other factors that govern the quenching efficacy are the Jet diameter and the speed at which the wheel rotates. These two factors together are mainly responsible for the final dimensions of the amorphous ribbons. Fine orifice diameters and high wheel rotation speeds lead to relatively thin ribbons. The width of the ribbons generally increases with increasing wheel rotation speed as a result of a more effective spreading of the melt. In this respect an important influence is also exerted by the Jet velocity, which is determined by the ejection pressure of the inert gas. 

The melt-spinning method permits the eontinuous production of amorphous ribbons on a manufacturing scale at veloeities between 10-50 m/s. As such the method has received much attention in cases where the dimensions of the ribbons have to meet specific requirements. Details of the process have been studied by means of high-speed motion pictures (Walter, 1978 Hillmann and Hilzinger, 1978),... 

Relatively large amounts of amorphous ribbons are furthermore involved in the manufacturing of flexible woven magnetic shields (Mendelsohn et al., 1976 Sellers, 1977 Shiau et al., 1978 Borek, 1982). The dimensions of the woven materials can be made up to 100 cm wide and as long as needed. The strength and flexibility of the narrow ribbons lend themselves also to the manufacttxre of braided and spirally wrapped shields (Smith, 1982). 

M. Maret, P. Chieux, P. Hister, M. Atzmon, W. L. Johnson W. L. In Short range order in Niss Yqj and CU33 Yqt amorphous ribbons, Proceedings of the fifth Conference on Rapid Quenching and Solidification of Metals (RQ5) Wurzburg, 1984. 

Ama] Mdssbauer, magnetic order determination Fe75Pi5Cio amorphous ribbon prepared by eentrifhgal solidifieation... 

Small amounts of C added (also B, Si and Al) in order to get liilly amorphous ribbon. 

Anagnostou andNiarchos (1990) reported on structure and magnetic properties of melt-spun SmFeio.gTii 2Bj alloys with x = 0.2 and 0.4. The added boron acts as a glass former and leads to amorphous ribbons, but after annealing a partial crystallization to the ThMni2 phase is observed. A best coercivity of about 0.6 T was obtained in ribbons annealed at 850 C for 5 min. 

Fig. 41. Scanning electron micrograph showing the tensile fracture appearance of Alg YgNij amorphous ribbon.

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