Ferrous glassy alloy with a large supercooled temperature interval

Abstract: The present invention provides a ferrous metal glassy alloy having temperature interval ΔTx of supercooled liquid as expressed by the following formula: ΔTx = Tx - Tg (where, Tx is an onset temperature of crystallization, and Tg is a glass transition temperature) of at least 40 K, which realizes magnetic properties as a bulky alloy.

Description: FIELD OF THE INVENTION The present invention relates to a ferrous metal glassy alloy. More particularly, the present invention relates to a novel metal glassy alloy, available as a bulky alloy having a far larger thickness than a conventional amorphous alloy thin ribbon, excellent in magnetic properties. PRIOR ART AND PROBLEMS Some of the conventional multi-element alloys are known to have a wide temperature region in which they are in a state of a supercooled liquid before crystallization and constitute metal glassy alloys. It is also known that these metal glassy alloys form bulky alloys having a far larger thickness than the conventionally known amorphous alloy thin ribbon. The metal glassy alloys known as above include Ln-Al-TM, Mg-Ln-TM, Zr-Al-TM, Hf-Al-TM, and Ti-Zr-Be-TM (where, Ln is alanthanide metal and TM indicates a transition metal). However, none of these conventionally known metal glassy alloys are magnetic at room temperature, and this has led to a significant restriction in industrial uses. These alloys, while showing the supercooled liquid state, are not practical because of the small temperature interval ΔTx of the supercooled liquid region, i.e., the difference (Tx - Tg) between the onset temperature of crystallization (Tx) and the glass transition temperature (Tg), practically resulting in a poor metal glass-forming ability. EP-A-0 018 507 discloses glassy alloys consisting essentially of about 6 to 18 atom % boron, about 2 to 14 atom % beryllium and about 72 to 85 atom % iron plus incidental impurities, providing a combination of improved thermal stability, minimal reduction in saturation magnetisation and a maximum reduction in saturation magnetostriction. EP-A-0 004 546 discloses glassy alloys consisting essentially of about 10 to 18 atom % boron, about 2 to 10 atom % beryllium and about 72 to 80 atom % iron plus incidental impurities, providing a combination of improved thermal stability while retaining the saturation magnetisation of the base iron-boron alloy. Following this observation, the presence of an alloy which has a wide temperature region of supercooled liquid and is capable of forming a metal glass through cooling would overcome the thickness restriction imposed on a conventional amorphous alloy thin ribbon and should be metallurgically attractive. In practice, however, the conventional metal glassy alloys which are not magnetic at room temperature have the aforesaid inevitable limitations. SUMMARY OF THE INVENTION The present invention was developed in view of the above-mentioned circumstances, and has an object of providing a novel metal glassy alloy which overcomes the limitations of the conventional technology, permits manufacture as a bulky metal, and further allows application as a magnetic material. The present invention provides a magnetic ferrous metal glassy alloy which comprises, in atom percent: aluminium from 1 to 10% gallium from 0.5 to 4% phosphorus from 9 to 15% carbon from 5 to 7% boron from 2 to 10% and optionally silicon from 0.5 to 4% germanium from 0.5 to 4% Nb, Mo, Hf, Ta, W, Cr up to 7% nickel up to 10% cobalt up to 30% iron and incidental impurities forming the balance; the alloy having a temperature interval ΔTx of a supercooled liquid as expressed by the following formula: ΔTx = Tx - Tg (wherein Tx is an onset temperature of crystallisation, and Tg is a glass transition temperature) of at least 40K. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a photograph of an electron diffraction pattern in place of a drawing of Example 1; Fig. 2 shows an X-ray diffraction pattern of Example 1; Fig. 3 shows a DSC curve of Example 1; Fig. 4 shows a B-H curve of Example 1; Fig. 5 shows an X-ray diffraction of Example 2; Fig. 6 shows a DSC curve of Example 2; and Fig. 7 shows a B-H hysteresis curve of Example 2. DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention as given in claim 1 provides a novel magnetic metal glassy alloy at room temperature, which permits formation of a new bulky alloy. Among ferrous alloys, Fe-P-C, Fe-P-B and Fe-Ni-Si-B ones are observed to exhibit glass transition. These alloys have however a very small temperature interval ΔTx of up to 25 K of the supercooled liquid, and cannot practically form metal glassy alloys. The metal glassy alloy of the present invention has in contrast a temperature interval ΔTx of the supercooled liquid of at least 40 K or even 60 K, which represents a remarkable temperature range which has not been anticipated at all to date for a ferrous alloy from conventional findings. Furthermore, the alloy of the present invention is excellent also in magnetic properties which are actually novel and is far superior in practical applicability to the conventional amorphous alloys applicable only as thin ribbons. The alloy of the present invention is characterized by a chemical composition, as described above and as claimed. Applicable semi-metal elements include, for example, phosphorus, carbon, boron, silicon and germanium. The ferrous metal glassy alloy of the present invention comprises, in the following amounts, in atomic percentage: aluminum from 1 to 10%, gallium from 0.5 to 4%, phosphorus from 9 to 15%, carbon from 5 to 7%, boron from 2 to 10%, and iron balance and may contain incidental impurities. Also it may contain from 0.5 to 2% silicon or 0.5 to 4% germanium. Another embodiment covers an alloy composition containing, in addition to any niobium, molybdenum, chromium, hafnium, tantalum and tungsten in an amount of up to 7%, up to 10% nickel and up to 30% cobalt. In any of the embodiments of the present invention, the ferrous metal glassy alloy has a temperature interval ΔTx of supercooled liquid of at least 40 K, or even 60 K. In the present invention as described above, the metal glassy alloy can be manufactured through melting and casting, or quenching by means of a single roll or dual rolls, or further the in-rotating-liquid spinning process or the solution extraction process, or high-pressure gas atomization, into bulk, ribbon, wire or powdered shape. In this manufacture, there is available an alloy having a thickness and a diameter more than ten times as large as those for the conventional amorphous alloy. These alloys show magnetism at room temperature and a better magnetism as a result of an annealing treatment. They are therefore useful for various applications as a material having excellent soft ferromagnetic properties. As to manufacture, it should be added that an optimum cooling rate, depending upon the chemical composition of the alloy, means for manufacture, and size and shape of the product, may usually be set within a range of from 1 to 10 2 K/s as a standard. In practice, the cooling rate may be determined by confirming whether or not such crystal phases as Fe 3 B, Fe 2 B, or Fe 3 P precipitate in the glassy phase. Now, the metal glassy alloy of the present invention is described further in detail by means of working examples. Example 1 Iron, aluminum and gallium metals, an Fe-C alloy, an Fe-P alloy and boron as raw materials were induction-melted in an argon atmosphere, and cast into an alloy ingot of Fe 72 Al 5 Ga 2 P 11 C 6 B 4 in atomic ratio. A ribbon having a cross-sectional area of 0.02 × 1.5 mm 2 was prepared in an argon atmosphere from the thus prepared ingot by the single roller melt-spinning process. It was confirmed through X-ray diffraction and TEM that the resultant ribbon had a metal glassy nature. Glass transition and crystallization were evaluated by means of a differential scanning calorimeter (DSC). Figs. 1 and 2 illustrate an electron diffraction pattern and an X-ray diffraction pattern, both demonstrating that the above alloy is of the glassy phase. Fig. 3 illustrates a DSC curve, suggesting that the alloy has a temperature interval of a supercooled liquid, which represents the temperature difference (Tx - Tg) between the glass transition (Tg) temperature and the onset temperature of crystallization (Tx) of 61 K. As a result of measurement at a scanning rate of 0.33 K/s by means of a differential thermal analyzer (DTA), the above alloy has a melting point (Tm) of 1,271 K, giving a ratio Tg/Tm of 0.58. Evaluation of the magnetic properties of the alloy revealed that the as-quenched alloy and the alloy after an annealing treatment at 723 K for 600 s exhibited hysteresis B-H curves with 1.59 kA/m at room temperature as shown in Fig. 4. Bs, He, λ s and µe were as shown in Table 1. This result suggests that the above-mentioned metal glassy alloy has excellent soft ferromagnetic properties. Example 2 An alloy having an atomic composition of Fe 73 Al 5 Ga 2 P 11 C 5 B 4 was melted in the same manner as in Example 1, and a bar-shaped alloy sample having a circular cross-section was prepared through injection molding in a copper die. The sample had a length of about 50 mm and a diameter of from 0.5 to 2.0 mm. Forming was carried out under a pressure of 0.05 MPa. Observation of the outer surface permitted confirmation that the alloy has a smooth surface and a satisfactory metallic gloss, with a good formability. Then, after etching the alloy with a solution comprising 0.5% hydrofluoric acid and 99.5% distilled water at 293 K for 10 s, the cross-section was observed by means of an optical microscope. This microscopic observation revealed that a crystal phase was non-existent and the alloy comprised a glassy phase. The results of an X-ray diffraction analysis of samples having a diameter of 0.5 mm and 1.0 mm are shown in Fig. 5: broad peaks are observed only at and around a 2 of 43.6° and a peak corresponding to a crystal phase is not found at all. This suggests the fact that, even with a diameter of 1.0 mm, the resultant alloy comprises a glassy phase. Fig. 6 illustrates DSC curves for alloy samples having diameters of 0.5 mm and 1.0 mm and a ribbon sample as in Example 1. In all cases, the curves demonstrate a glass transition temperature (Tg) of 732 K, an onset temperature of crystallization (Tx) of 785 K and a temperature interval of supercooled liquid (ΔTx) of 53 K. Fig. 7 shows a hysteresis B-H curve. Magnetic properties were confirmed to be equivalent with those in Example 1. It is needless to mention that the present invention is not limited at all by the above-mentioned examples, and that various embodiments are possible as to its chemical composition, manufacturing process, annealing treatment, shape and the like. According to the present invention, as described above in detail, there is provided a ferrous metal glassy alloy which overcomes the restrictions such as those of thickness in conventional amorphous alloy thin ribbon, can be supplied as a bulky alloy, and is expected to be applicable as a material having magnetic properties.

Claims: A magnetic ferrous metal glassy alloy which comprises, in atom percent: aluminium from 1 to 10% gallium from 0.5 to 4% phosphorus from 9 to 15% carbon from 5 to 7% boron from 2 to 10% and optionally silicon from 0.5 to 4% germanium from 0.5 to 4% Nb, Mo, Hf, Ta, W, Cr up to 7% nickel up to 10% cobalt up to 30% iron and incidental impurities forming the balance; the alloy having a temperature interval ΔTx of a supercooled liquid as expressed by the following formula: ΔTx = Tx - Tg (wherein Tx is an onset temperature of crystallisation, and Tg is a glass transition temperature) of at least 40K. A ferrous metal glassy alloy which comprises an alloy as claimed in claim 1 which has been annealed.

Inventors: INOUE AKIHISA, INOUE, AKIHISA
Applicants: JAPAN RES DEV CORP, RESEARCH DEVELOPMENT CORPORATION OF JAPAN
Application year: 1996
Main classification: C22C45
IPC codes: C22C38, C22C45, H01F1