EP0007062B1

EP0007062B1 - Preparation of phosphorus-containing metallic glass-forming alloy melts

Info

Publication number: EP0007062B1
Application number: EP19790102260
Authority: EP
Inventors: Wiktor J. Ambasz; Robert C. Linares
Original assignee: Allied Corp
Current assignee: Allied Corp
Priority date: 1978-07-17
Filing date: 1979-07-04
Publication date: 1981-10-21
Also published as: EP0007062A1; DE2961066D1; CA1120728A

Description

BACKGROUND OF THE INVENTION

Recent advances in the metallurgical arts include development of alloys which, when rapidly quenched from the melt at rates in excess of about 10" to 1061 C per second, form glassy (amorphous) solids. Such glass-forming alloys commonly are based on transition metals, usually iron, nickel and/or cobalt, in conjunction with one or more metalloids of phosphorus, boron and carbon. Glass-forming alloys are, for example, described in U.S. Pat. 3,856,513 issued December 24, 1974 to Chen et al.
Preparation of phosphide based melts of glass-forming alloys under ambient atmosphere leads to oxide inclusions in the glassy metal product. The conventional method of excluding the ambient atmosphere by vacuum melting leads to possible losses of phosphorus values from the melt due to evaporation. Iron phosphide is a basic ingredient in many glass-forming metallic alloy compositions, and in the high purity form required for such purpose, it is quite costly. Inexpensive forms of iron phosphide available are impure and contain phosphorus in form which can evaporate upon heating, and which tends to form volatile phosphorus pentoxide, and which poses a safety hazard and results in changes of the alloy composition. Glassy solid structures are obtained from such alloys by processes such as the melt spin process wherein a fine jet of the molten alloy is impinged upon a rapidly moving chill surface for solidification. Orifice diameters in this process are exceedingly small, and orifice pluggage on account of solid impurities contained in the melt can represent serious problems. Iron, cobalt or nickel based phosphorus-containing glass-forming alloys which additionally contain boron as a metalloid are particularly prone to contamination with solid particles. In such alloy, these particles were found to be predominantly small particles of Ti0₂ and/or TiB03, both of which have high melt points, and both of which are relatively insoluble in the melt. It was found that titanium is an impurity commonly contained in ferrophosphorus; which is used as a source of phosphorus in making these alloys, although titanium may also be present as contaminant in other raw materials employed in making these alloys.
Boron containing fluxes have been suggested in steel manufacture, see DE(C) 649,284, and it has been suggested that one could reduce contamination of a metal melt with particulate metal oxides by mixing the melt with boric acid (DE(C) 678,763). Also it has been suggested that a molten metal bath could be covered with a layer of boron trioxide (DE(C) 639,131). There is a need, however, for a refining flux for the alloys such as described in U.S. Patent 3,856,513 which would reduce oxidation of and loss of phosphorus values from such alloys, especially phosphorus-containing iron, nickel and/or cobalt-based alloys. Use of an alloy comprising boron trioxide and iron, nickel and/or cobalt has been found to achieve superior results.
According to the invention therefore there is provided a process of melting metal alloys in which the exposed surface of said metal alloy is covered with a layer of a molten flux composition containing boron trioxide characterised in that the alloy is a phosphorus-containing glass forming transition alloy of formula M_aP_bY_c wherein,

M is a metal selected from the group consisting of iron, cobalt, nickel, and mixtures thereof in any proportion;
P represents phosphorus;
Y is a metalloid selected from the group consisting of boron, carbon, and mixtures thereof in any proportion;
a, b and c are in atomic percent;
a is 70 to 90,
b is 1 to 20,
the sum of b + c is 10 to 30,
the sum of a + b + c being 100,

Thus the present invention provides refining flux for reducing oxidation of and loss of phosphorus values from phosphorus-containing alloys, especially phosphorus-containing iron, nickel and/or cobalt-based alloys.
Thus phosphorus-containing metallic glass-forming alloy melts are covered with a layer of molten boron trioxide flux. Such layer protects the melt from oxidation, dissolves oxide particulates and impurities from the molten metal alloy and prevents the evaporation of phosphorus values. The flux floating on the alloy melt will not interfere with subsequent casting or spinning operations, and the alloy melt can be replenished directly through the flux layer. Alloys prepared according to the process of the present invention leave minimum residues in the jetting crucible in subsequent melt spin operations.
Phosphorus-containing iron, nickel and/or cobalt-based alloys are melted under a boron trioxide flux additionally comprising oxides or iron, nickel and/or cobalt. The flux layer protects the molten alloy from oxidation, reduces or eliminates contamination of the melt with particulate matter, especially metal oxides, and prevents loss of phosphorus values by vaporization.

DETAILED DESCRIPTION OF THE INVENTION

Metallic glass-forming alloys which benefit from protection by boron trioxide flux contain phosphorus as a metalloid component, alone or together with other metalloids, such as boron, carbon and silicon. The phosphorus component of such alloys is usually contributed by ingredients having the formulas FeP_x, NiP_x, CoP_., MnP_x, wherein x is between 0.3 and 1.1 and preferably between 0.5 and 1. Preferred alloy compositions include alloys utilizing as source of phosphorus FeP wherein x is between 0.5 and 1. Preferred alloy compositions include transition metal alloys containing between 3 and 25 weight percent phosphorus. These alloys have a phosphorus partial pressure of less than 2.67 Pa (20 um Hg), and melting points of between 900°C and 1200°C.
Phosphorus-containing alloys based on one or more of iron, nickel and/or cobalt which benefit from melting under the refining boron trioxide flux which additionally contains oxides of iron, nickel and/or cobalt have the general formula M_aP_bY_c wherein M is a_metal selected from one or more of the group consisting of iron, cobalt and nickel; P represents phosphorus; Y represents a metalloid selected from one of both of the group consisting of boron and carbon; and a, b and c are in atomic percent, wherein a is 70 to 90, b is 1-20, the sum of b + c is 10 to 30, the sum of a + b + c being 100. The phosphorus content of the alloy will ordinarily be derived from ferrophosphorus, which may be of any suitable phosphorus content, such as commercially available grades containing 18 and 25 percent by weight phosphorus.
The boron trioxide may be of any degree of commercial purity but is preferably of about 95 weight percent purity, more preferably better than about 98 weight percent purity, the balance being represented by incidental impurities or intentional additives which are substantially inert, that is to say, that they do not materially interfere with the intended function of the boron trioxide flux.
Suitable boron trioxide fluxes have a melting point between about 400°C and 600°C, preferably between about 400° and 500°C, and have a vapor pressure of below about 2.67 Pa (20 µm Hg).
In the fluxes of the present invention which additionally contain an oxide of iron, cobalt and/or nickel, the oxide is suitably chosen to correspond to the major metal component of the alloy. For example, if iron is the only or major metal component of the alloy, the oxide component in the flux desirably, but not necessarily, is an oxide of iron. Nickel- containing melts desirably are refined under a flux-containing nickel oxide. The flux desirably contains from 20 to 80 percent by weight boron trioxide.
In the melting operation the metal oxide (e.g. iron, cobalt or nickel oxide) coacts with the boron trioxide to obtain the desired result. It is believed that oxygen from the metal oxide combines with titanium metal contained in the melt as an impurity, perhaps forming TiO₂, which is then bound in the molten flux. The boron trioxide seems to act as a coagulant for the titanium dioxide as well as for other particulate matter which may be contained in the melt. Moreover, the boron trioxide, because of its acidic character, seemingly tends to prevent oxidation of phosphorus, if present, to the five valent oxide state, as might occur due to presence of small amounts of oxygen in the melt. In the five valent state, phosphorus is volatile under refining conditions encountered in making the alloys here under consideration.
Of the oxides of iron, namely FeO, Fe₂0₃ and Fe₃0₄, all are suitable, FeO being preferred. Likewise, any of the oxides of cobalt, CoO, Co₂O₃, as well as Co₃O₄, may be employed. However, for reasons of high cost, use of oxides of cobalt is not ordinarily preferred. Nickel oxide, for reasons of availability as well as effectiveness, is the preferred metal oxide. Metal oxides of commercial degree of purity are suitable for use.
In the metal oxide containing fluxes, the boron trioxide is desirably employed in amount of 20 to 80 percent by weight, preferably 30 to 70 percent by weight, most preferably 40 to 60 percent by weight of the flux, the balance being represented by the metal oxide. Of course, if desired, other components which do not materially interfere with the protective and refining functions of the flux may be included in the flux composition for any desired purpose, e.g. melting point reduction, although addition of other components is not ordinarily preferred.
The flux compositions are employed in amount sufficient to provide a flux layer of between about 1 and 50 millimeter thickness, preferably between about 2 and 10 millimeter thickness on top of the molten metal alloy. It is an advantage of these flux compositions that their solubility in the alloys is generally low, so that gross contamination of the alloy with the flux is avoided. Furthermore, minor contamination of the alloy with boron values from the flux is generally not deleterious, that is to say that such contamination would not adversely affect the glass-forming capabilities of the alloy, nor its properties in the solid state.
The temperature of the alloy melt can be between about 1000°C and 1500°C, and preferably between about 1100°C and 1400°C. The temperature of the boron trioxide flux can be between about 900°C and 1400°C.
To prevent oxidation and loss of phosphorus value from the alloy, the boron trioxide flux should be present at temperatures leading normally to oxidation and/or evaporation of phosphorus values, and in particular the boron trioxide should be present when the alloy is in the molten state. The boron trioxide, to obtain the full benefit of its function, is desirably added to the cold charge. If it is added after the alloy is melted, considerable amounts of phosphorus can be lost.
To fulfill its refining function, the flux should remain in contact with the surface of the melt at melting temperature for a time period for at least about one minute, desirably of at least about 5 minutes. Contact times of, say, between about 5 minutes and 5 hours, desirably of between about 30 minutes and about 3 hours are eiminently suitable. If desired, the melt may be agitated. Suitable melting furnaces include those lined with high temperature ceramic materials. Preferred furnace linings are made from magnesia, zirconia and alumina. If desired, suitable inert atmospheres may be provided above the flux, including such as those provided by helium or argon. Alternatively, the melting operation may be conducted under vacuum. However, provision of inert atmospheres is not essential. If an inert atmosphere is supplied, argon is preferred.

Example

This example illustrates production of an alloy containing Fe: 45.9 ± 1 percent by weight; Ni: 44.6 _± 1 percent by weight; P: 7.85 _± 0.32 percent by weight; B: 1.45 ± 0.11 percent by weight. The raw materials charged are iron, electrolytic fragments, 99.9 percent pure; nickel pellets, 99.9 percent pure; ferrophosphorus, low silicon grade (less than about 0.5 percent silicon); nickel-boron, low aluminum grade (as available, for example, from Shieldalloy Company). Prior to and during the charging operation the furnace is purged with argon gas. The required amounts of iron, nickel and ferrophosphorus are charged to the furnace, and the charge is gradually heated until melting. At that point, an oxidizing acid flux consisting of about 50 weight percent nickel oxide and about 50 weight percent B₂O₃ is added to the molten charge in an amount of about 3.63 kg (8 lbs.) per 1134 kg (2,500 lb.) metal charge to produce about a 0.32 cm (1/8 inch) thick layer of flux. The melt is refined under this flux at a temperature of about 1,180° to 1,200°C for 20 to 30 minutes, taking care to avoid temperatures in excess of 1200°C during the refining operation. Thereafter, the flux is skimmed and the nickel boron is added to the melt. The heat is finished under an argon blanket. Total refining and holding time at the 1,180° to 1,200°C is about 45 to 60 minutes. The refined alloy is then cast at about 1,000°C.
Using identical raw materials, alloy of the above composition prepared using the Ni0/B₂0₃ flux as above described had a titanium content of only 0.04 percent by weight, whereas an alloy obtained under otherwise identical conditions from the same raw materials, but without use of the flux, had a titanium content about 0.16 percent by weight. Furthermore, alloy prepared under conditions of the present, invention had significantly lower contamination with other oxidizable elements which tend to form insoluble solid oxides. As a consequence, metal refined in accordance with the present invention, as above described, caused substantiallly less restriction of a casting nozzle in a subsequent spin casting operation.

Claims

1. A process of melting metal alloys in which the exposed surface of said metal alloy is covered with a layer of molten flux composition containing boron trioxide characterised in that the alloy is a phosphorus-containing glass forming transition alloy of formula MaPbYc wherein,

M is metal selected from the group consisting of iron, cobalt, nickel, and mixtures thereof in any proportion;

P represents phosphorus;

Y is a metalloid selected from the group consisting of boron, carbon, and mixtures thereof in any proportion;

a, b and c are in atomic percent; and

a is 70 to 90,

b is 1 to 20,

the sum of b + c is 10 to 30,

the sum of a + b + c being 100,

and wherein the flux comprises oxides of iron, nickel and/or cobalt together with boron trioxide.

2. A process according to claim 1 wherein said alloy has a phosphorus content of between 3 weight percent and 25 weight percent.

3. A process according to either of claims 1 and 2 wherein said flux in contact with the melt is at a temperature within. the range of 900°C to 1400°C.

4. A process according to any one of claims 1 to 3 wherein the flux composition is employed in amount sufficient to provide a flux layer of between 2 and 50 mm thickness.

5. A process according to any one of claims 1 to 4 wherein the flux comprises between about 20 and 80 percent by weight of B_z0₃, and between about 80 and 20 percent by weight of one or more oxides of iron, cobalt and nickel.

6. A process according to any one of claims 1 to 5 wherein the alloy component M is an alloy of iron and nickel.

7. A process according to any one of claims 1 to 6 wherein the alloy contains both phosphorus and boron.

8. A process according to any one of claims 1 to 7 wherein the flux comprises between about 20 and 80 weight percent of B₂0₃, and correspondingly between about 80 and 20 weight percent of NiO.

9. A process according to any one of claims 1 to 8 wherein the alloy comprises about 46 ± 1 percent by weight of Fe; about 45 ± 1 percent by weight of Ni; about 8 ± 0.5 percent by weight of P; about 1 ± percent by weight of B, wherein the phosphorus is derived from ferrophosphorus, wherein the flux comprises about equal amounts of NiO and B₂0₃, and the molten alloy is held in contact with the flux for a period of between about 5 minutes and 5 hours.