GB2038358A - Amorphous Fe-B-Si Alloys - Google Patents

Abstract

Iron-boron-silicon ternary amorphous alloys having high saturation magnetization, high crystallization temperature and low coercivity are obtained by selecting a narrow range of iron, boron and silicon. Figure 4 shows a composite of saturation magnetization contour lines of various iron, boron and silicon alloys at room temperature (30 DEG C) having a magnetization of at least about 174 emu/g at about 30 DEG C, an intrinsic coercivity after annealing of less than 0.03 oersteds and a crystallization temperature of at least about 320 DEG C. The iron-boron-silicon amorphous metal alloys of the present invention fall within the shaded regions A, B, C, D, E, F, A, indicated with the preferred alloys lying within the region a, b, c, d, a. <IMAGE>

Description

SPECIFICATION Iron-Boron Silicon Ternary Amorphous Alloys The present invention relates generally to the metal alloy art and is more particularly concerned with novel amorphous metal alloys having a unique combination of magnetic and physical properties, and is further concerned with ribbons and other useful articles made therefrom.

While it has been recognized by those skilled in the art that amorphous metals with high saturation magnetization might be used to advantage in electrical apparatus such as distribution and power transformers, such alloys are lacking in necessary ductility and stability for this purpose. Thus, the iron-rich alloy Fe80B20 has a 47rims of approximately 16,000 Gauss but begins to crystallize within two hours at about 3250C and is quite difficult to produce on ductile ribbon form for electrical machinery apparatus.

Other amorphous alloys known heretofore have somewhat greater stability and adequate ductility for this purpose, but their saturation magnetization is too low.

Our UK Patent Application No. 7908931 (Publication No. 2023173A) describes and claims an iron-boron-silicon amorphous metal alloy containing from 80 to 84 atom percent iron, from 12 to 1 5 percent boron and from 1 to 8 atom percent silicon.

This invention is based upon the discovery that a very narrow range of iron, boron and silicon amorphous alloys have both the desired magnetization and other properties for superior performance in electrical apparatus such as motors and transformers. Consequently it is now possible by means of this invention to provide an amorphous metal in the form of a ribbon sufficiently ductile to be readily used in electrical apparatus construction which has good magnetic properties and elevated temperature stability.

Accordingly, the present invention provides an iron-boron-silicon amorphous metal alloy simultaneously having values of saturation magnetization at about 300C of at least about 1 74 emu/g, intrinsic coercivity of less than about 0.03 oersteds and crystallization temperature of at least about 3200 C, said alloy consisting essentially of iron, boron and silicon and having a composition in the region A, B, C, D, E, F, A of Figure 4.

The present invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a ternary diagram plotting saturation magnetization for a variety of iron, boron and silicon alloys at room temperature (300C); Figure 2 is a ternary diagram plotting coercivity for a variety of iron, boron and silicon alloys; Figure 3 is a ternary diagram plotting the crystallization temperature for said alloys; and Figure 4 is a composite of the saturation magnetization contour lines of Figure 1 and the coercivity contour lines of Figure 2 with the 3200C contour line from Figure 3 superimposed thereon.Shaded region A, B, C, D, E, F, A designates those iron-boron-silicon ternary amorphous metal alloy compositions simultaneously exhibiting the properties of saturation magnetization of at least about 1 74 emu/g at about 300C, intrinsic coercivity after annealing of less than about 0.03 oersteds and crystallization temperature of at least about 3200C.

Referring now to the drawings and particularly Figure 1, it can be seen that a superior group of alloys is formed from all alloys of iron, boron and silicon within the broken lines, i.e. of from 80 atom percent iron, 1 9 atom percent boron and 1 atom percent silicon to 81 3/4 atom iron, 16 1/4 atom percent boron and 6 atom percent silicon to 82 1/4 atom percent iron, 11 3/4 atom percent boron and 6 atom percent silicon. However, this designation includes only part of the spectrum of iron-boron-silicon amorphous metal alloys exhibiting the unique confluence of properties comprising this invention. This complete spectrum is described hereinafter in connection with Figure 4.

In Figure 1 saturation magnetizations are plotted from a variety of amorphous alloys.

Mgnetizations at room temperature and below were determined on small weighed specimens in a vibrating sample magnetometer to a maximum field of 20 KOe. Results were extrapolated to H = co using a 1/H2 function. Values above room temperature were obtained from the relative magnetization curves normalized to the value of magnetization at room temperature. From an examination of the diagram it can be seen that the alloys of the invention have a desirable saturation magnetization of 1 78 emu/g at room temperature (3O0C).

In Figure 2 the intrinsic coercivity is plotted forA a number of iron-boron-silicon alloys which was determined on 1 Ocm long ribbons set into a 20 cm long solenoid which was then annealed for 120 min. at a few degrees centigrade below the crystallization temperatures shown in Figure 3. A smail sense coil was connected to an integrating flux meter and the magnetization vs field was then displayed on an X-Y recorder as the field was slowly varied. From an examination of the diagram it can be seen that the lowest coercivity of 0.02 Oe is found with the alloys having the desirable high saturation magnetization of 1 78 emu/g reported in Figure 1.

In Figure 3 crystallization temperatures are reported as determined by noting the temperature at which the coercivity starts to increase after 2 hour exposures at increasing temperature. From an examination of the diagrams it can be seen that the alloys found to have high saturation magnetization and low coercivity are also found to have acceptably high crystallization temperatures. Crystallization temperatures up to 3400C are obtained for the 6 percent silicon alloys compared to 310-31 50C for the Fe82B,8 alloy. This is desirable as it permits the alloy to be annealed to relieve the stresses and reduce the initial high coercive field without permitting the amorphous alloy to crystallize and lose its desirable magnetic qualities.Thus with the alloys of the invention it is possible to anneal above about 34O0C without crystallization occurring.

Figure 4 presents a composite of the gradient lines of Figures 1 and 2 with the 32O0C contour line of Figure 3 added thereto. It is this unification of data, which focuses on the discovery whereby for the first time those amorphous alloys of the iron-boron-silicon system have been identified in which there is a confluence of the properties of high room temperature and low coercivity. As can be seen from Figure 1, there is a sharp increase in the steepness of the gradient of the saturation magnetization contour lines from the value of 1 74 emu/g to higher values.It was never previously recognized that amorphous alloys in this system could be found with the unusual combination of properties of saturation magnetization at room temperature (i.e. about 300 C) of at least about 1 74 emu/g, intrinsic coercivity of less than about 0.03 oersteds and crystallization temperature of at least about 3200C. Alloys exhibiting this unusual collection of properties are found in the shaded area bounded by the gradient lines of coercivity, saturation temperature and crystallization temperature whose intersctions are labelled A, B, C, D, E, F.Even more effective alloy compositions are located in the area designated a, b, c, d defined by the compositions 81 atom percent iron, 1 6 atom percent boron and 3 atom percent silicon (point a); 81 3/4 atom percent iron, 1 5 1/4 atom percent boron and 3 atom percent silicon (point d); 81 1/2 atom percent iron, 13 1/2 atom percent boron and 5 atom percent silicon (point b), and 82 atom percent iron, 13 atom percent boron and 5 atom percent silicon. Fe813Bt5 ,Si3 and Fe81,7B133Si5 as well as the optimum composition, which has an iron content of 81 1/2 atom percent, a boron content of 14 1/4 atom percent and a silicon content of 4 atom percent are part of area a, b, c, d.

In practising this invention, novel alloys defined above and claimed herein are prepared suitably by mixing together the alloy constituents in the required proportions in the form of powders and then melting the mixture to provide molten alloy for casting to ribbon of the desired dimensions.

The casting operation is preferably carried out through the use of the method disclosed and claimed in our copending U.K. Patent Application No. 7908931 (Publication No. 2023173A). The apparatus described in that application as implementing the therein-claimed method may likewise be used to provide long lengths of ribbon of this invention of uniform width and thickness and smooth edges and surfaces. Cooling is carried out in the casting operation at a rate sufficient to produce amorphous material.

While variations in melting point temperatures between alloys of this invention may impose requirements which vary with respect to alloy melting and casting operations, the preparations and processing of these alloys can be carried out with uniformly satisfactory results by following the above proceedure and using the described equipment. In other words, the results of this invention are reproducible in a substantially routine manner so long as the compositional limitations stated above and in the appended claims are strictly observed in the preparation of the alloys.

Ribbons of amorphous alloys claimed herein and having the properties detailed in Figures 1, 2 and 3 are made by directing a stream of the alloy onto the surface of a rapidly revolving chill roll or drum as described in Example 1 of our copending UK Patent Application No. 7908931 (published No. 2023173A). A typical ribbon has a thickness of 0.0025 cm and is 0.13 cm wide. The amorphous nature of the resulting ribbon is confirmed by X-ray diffraction, differential scanning calorimetry, and by magnetic and physical property measurements. When segments are annealed in purified nitrogen for two hours at temperatures ranging from 1 000C to 400"C the crystallization temperature is taken as that temperature, for the 2 hour anneal, at which the coercive force abruptly increases.

To prepare a transformer or motor stator, strips of the aforsaid alloy about 1/2" wide and 2 mils thick can be coated with a binder such as polyamide-imide and the strips placed 6 layers deep in a non-magnetic die cavity of stainless steel lined with Teflon-coated aluminium with alternating layers at 900. The strips are held in place by means of permanant magnets placed under the die and the composite pressed at 2000 psi and 3300C for 2 minutes after allowing the die to preheat to 33O0C for a few minutes without pressure to equilibrate and drive out excessive air and water from the die and ribbon.

The composite is then annealed at 3250C for 2 hours and found to have a low coercive force and a high saturation magnetization.

Other composites are formed with or without a binder with similar results. Other suitable binders include the epoxies, polyamide-imides, cyanoacrylates, and phenolics. The binder should have a coefficient of thermal expansion compatible with the metal ribbon, be electrically insulating, cure rapidly and be able to meet the thermal requirements of the intended application and annealing if required. In some applications there are further requirements such as being compatible with commercial refrigerants when used for air conditioning compressor motors. The above method for preparing a stator is described and claimed in US Patent Application Serial No.

961,261.

To prepare a wound-type transformer the amorphous metal foil, with widths, for example, up to 6 inches wide, may be wound on a mandrel with a circular or rectangular cross-section. The number of turns wound onto the mandrel, and the width of the tape, will depend on the transformer rating.

It will be understood by those skilled in the art that slight but obvious modifications can be made which will fall within the scope of the invention such as, for example, an article of manufacture claimed herein may comtain a minor amount of crystalline material which will not seriously impair its desirable properties. Accordingly, depending upon the particular article of manufacture and its intended use the article may contain up to 10% of crystalline material.

Claims (9)

Claims

1. An iron-boron-silicon amorphous metal alloy simultaneously having values of saturation magnetization at about 300C of at least about 1 74 emu/g, intrinsic coercivity of less than about 0.03 oersteds and crystallization temperature of at least about 3200C, said alloy consisting essentially of iron, boron and silicon and having a composition in the region A, B, C, D, E, F, A of Figure 4.

2. An alloy as claimed in claim 1 further defined as being of a composition in the area of the iron-boron-silicon ternary diagram defined by the compositions 81 atom percent iron, 16 atom percent boron and 3 atom percent silicon, 81 3/4 atom percent iron, 1 5 1/4 atom percent boron and 3 atom percent boron and 3 atom percent silicon, 81 1/2 atom percent iron, 13 1/2 atom percent boron and 5 atom percent silicon, and 82 atom percent iron, 13 atom percent boron and 5 atom percent silicon.

3. An alloy as claimed in claim 1 of the formula Fe81 3Bas 157Si3.

4. An alloy as claimed in claim 1 of the formulaFe81,5B14,5Si4.

5. An alloy as claimed in claim 1 of the formula Fe815B14s5si5

6. An alloy as claimed in claim 1 substantialiy as hereibefore described.

7. A ribbon of amorphous metal alloy as claimed in any one of the preceding claims

8. A transformer using the alloy of any one of the preceding claims.

9. A motor component using the alloy as claimed in any one of the preceding claims.