Method for producing amorphous compact

Abstract

 A method of producing an amorphous compact by use of' amorphous fine particles, comprising the steps of applying a ultra high pressure (p) to said fine particles, and at the same time heating said fine particles to a temperature of more than 90% of a crystallization temperature (Tx) of the amorphous particles defined under an atmospheric pressure but less than a crystallization temperature (Tx(p)) thereof defined under said ultra high pressure (p).

Description

BACKGROUND DF THE INVENTION

[0001] This invention relates to a method for producing an amorphous compact of lump or bulk shapes, the amorphous compact having advantages such as low coercive force, high maximum magnetic permeability, and high specific resistance. Thus, it is used quite advantageously as magnetic materials.

[0002] Amorphous materials of metals, alloys, semiconductors or dielectrics etc. have a randomly arranged atomic structure which is basically different from that of conventional crystalline materials with a long range order. Thus, in the amorphous materials, there occur characteristics not obtainable from crystalline materials, i.e., high hardness, high strength, high permeability, high resistance to corrosion and etc.' For this reason the utilization of these characteristics has been studied, as well as the application thereof in various fields.

[0003] In general, amorphous materials have been produced by a liquid-quenching method, in which a metal or its alloy in a fluid state is rapidly quenched into an amorphous state. Typical examples of the liquid-quenching method include:

(1) a single roll quenching method, a twin-roll quenching method and a centrifugal quenching method, all of which are used for producing thin strips;

(2) Taylor method and free jet melt spinning method, both used for producing filaments; and

(3) a spray method and a cavitation method, used for producing powder.

[0004] The amorphous substance produced by these conventional method is of a ribon of a small thickness of several decades or several hundred micron meters at most, or of powder of several decades or several hundreds at most in grain size, or of a filament, with the result that the use of the amorphous substance has been limited to a very restricted, small-sized application.

[0005] Thus, a method has been recently studied by which an amorphous material can be formed into a lump shape so as to make the material utilizable in various fields of application. However, since the amorphous material has disadvantageous characteristics such as high hardness and a tendency to be transformed into a crystalline structure upon heating, it has caused extreme difficulty to produce a amorphous compact of the lump shape.

[0006] As an example, in a Japanese Patent Laid-Open Publication No. 7433/1984, there has been proposed a method of forming a compact of amorphous material in which a tubular container is filled with amorphous powder, and then an explosive is exploded around the container thereby causing the pressure-bonding of the powder into an amorphous compact.

[0007] However, this method has a number of drawbacks. That is, since the powder of the amorphous material is high in hardness in comparison with a crystalline material, the uniform application of impact pressure of high energy is necessary to obtain a uniform integrated compact, while there are apt to cause many problems such as the crystallization of the amorphous material, the occurrence of crack and blowholes and etc., if the pressure applied to the amorphous,powder material is excessive. Further, when producing it in an industrially large scale by use of the method, the cost of the amorphous compact becomes high.

[0008] Another method of obtaining a amorphous compact of a lump shape has been disclosed in Japanese Patent Laid-Open Publication Nos. 28501/1984 and 28502/1984. This method includes the steps of placing thin strips of amorphous material in contact relationship with each other and then compressing the strips under a predetermined pressure (of at least 0.006 Gpa) at a temperature less than the crystallization temperature (Tx) (namely a temperature of about 70-90 % of Tx), this kind of compressing being called as "hot pressing". Also, U.S. patent No. 4,298,382 discloses a method of integrating the amorphous thin strips, wherein said strips are placed in contact relationship with each other, and then hot pressed under a given pressure and at temperatures in a range from about 25°C below the glass-transition temperature (Tg) to about 15°C above the transition temperature (Tg) of the amorphous strips. That is, in the U.S. Patent, diffusion bonding and hot press compaction by means of pressurization and heating have been considered effective for amorphous materials as it was with crystalline materials. However, there is a problem that, if an amorphous material is heated to a temperature not less than the crystallization temperature thereof (Tx) or at the vicinity of the crystallization temperature (more than 90% of Tx), a part of or all of the amorphous material crystallizes during the hot-press compaction thereof. Thus, in prior art, a heating of the amorphous material to a temperature less than the crystallization temperature thereof has been.effected to obtain a compact, with the result that a resultant conventional compact has caused a relatively poor density not more than 90% of the theoretical density thereof, that is, there exist holes not less than 10% in the resultant conventional compact. Thus, in the conventional amorphous compact there has existed such problems that the magnetic properties of the amorphous compact are inferior in comparison with a thin strip of amorphous substance, and that high permeability can not be brought about in the amorphous compact when compared with magnetic materials such as permalloy and etc.

[0009] In view of the above problems, the present inventors also attempted to obtain a compact of a lump shape from the amorphous material in a powder form while using the above-mentioned diffusion-bonding process by means of pressurization and heating. They found that a heating of the powder close to its crystallization temperature (Tx) caused the crystallization of a part of or all of the amorphous powder, that another heating sufficiently below its crystallization temperature (Tx) did not yield a compact with its constituent powder particles bonded strongly and integrally with each other with the result of causing a brittle and easily broken compact.

[0010] After the repetition of various theoretical examinations and actual experiments, the present inventors has discovered that a superior amorphous compact of a lump shape can be obtained by using a particular phenomenon in which the crystallization temperature (Tx) of amorphous materials increases under a ultra high pressure (om the order of several Gpa, i.e., several 10⁹ _Pa).

[0011] There are few reports concerning the above-mentioned phenomenon that the crystallization temperature (Tx) of an amorphous material increases to an extent of about 10°C per about 1 Gpa is reported in Japanese Metal Society Vol. 21, No. 9, 1982, by W. K. Wang, H. Iwasaki and K. Fukamichi, J. Materer. Sci., 15 (1980), P2701. However, it should be noted here that these reports only refer to thin strips of amorphous materials, no investigation having been made concerning an amorphous material in a powder form nor has been made any study regarding the bonding strength and the density of an amorphous compact when producing the amorphous compact of a lump shape by use of a amorphous powder material.

[0012] Thus, the present inventors conducted an experiment in which an amorphous powder was heated under an ultra high pressure (of several Gpa), to a temperature higher than the crystallization temperature (Tx) thereof defined at an atmospheric pressure, and found that a amorphous compact in a lump shape can be obtained which is closely and integrally formed (with a density of at least 90% of the theoretical density). The invention is achieved on the basis of this discovery.

SUMMARY OF THE INVENTION

[0013] An object of the invention is to provide a method for manufacturing an amorphous compact of a lump shape having both a very high density and amorphous properties after the production thereof.

[0014] The invention provides a method of manufacturing a lump-shaped compact from the powder of amorphous material by utilizing the discovery that the crystallization temperature (Tx) of amorphous material is increased as the pressure applied thereto increases. The feature of the invention resides in that the lump shaped amorphous compact is produced by the hot-pressing of the powder of amorphous material under an ultra high pressure (p) and at a temperature higher than 90% of the crystallization temperature (Tx) of the material defined at the atmospheric pressure but lower than the crystallization temperature (Tx(p)) of the material defined under said ultra high pressure (p).

[0015] The term of "powder of amorphous material" used herein means a powder made by pulverizing amorphous materials such as those of metal or its alloy, semiconductor, dielectrics and etc., into finely-dimensioned particles which may be those obtained by a spray method, a cavitation method or a method of spraying into a rotating liquid or those obtained by pulverizing amorphous thin strips manufactured by a roll quenching method etc. The method of this invention can be used regarding any of amorphous materials in order to produce a lump-shaped compact, however, an appropriate composition selected from Fe alloys and Co alloys is appropriate in a particular case where ferro-magnetism is desired for a compact.

[0016] The heating temperatures employed in the manufacturing method of this invention can vary between a value higher than 90% of the crystallization temperature of amorphous material (Tx) under an atmospheric pressure and another value lower than the crystallization temperature of amorphous material (Tx(p)) under the ultra high pressure (p). The temperature range is limited because of the facts that a heating temperature equal to or less than 90% of the crystallization temperature (Tx) defined under the atmospheric pressure cause a poor bonding property in a resultant compact, resulting in brittleness and fear of breakage. On the other hand, a temperature higher than the crystallization temperature (Tx(p)) defined under the ultra high pressure (p) causes crystallization of a resultant compact.

[0017] When a compact is desired to have a density of 95% or more in comparison with the theoretical density thereof, it is preferable that the pressure be at least 1 Gpa and that the temperature nearly equal to or more than the crystallization temperature (Tx) defined under an atmospheric pressure but less than the crystallization temperature (Tx(p)) defined under the ultra-high pressure (p) used.

[0018] Furthermore, a higher pressure (p) is preferable when a compact with a much higher density and a much better bonding is desired. This is because the higher the pressure (p), the higher the crystallization temperature (Tx(p)) under said pressure (p), resulting in the fact that the heating thereof to a higher temperature can be achieved without causing the crystallization of the compact.

[0019] However, from a practical viewpoint, a pressure lower than 10 Gpa is preferable, because the apparatus for generating a higher pressure will otherwise be excessively large in size. Furthermore, when the formed body having a density not less than 95% is to be produced in an industrial scale, a relatively low pressure is preferred which is in an order of several Gpa, i.e., ranging from 1 Gpa to 5 Gpa, and preferably not less than 1 Gpa but less than 3 Gpa.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 

Figs. la and lb show high-temperature and high-pressure generating apparatus schematically shown in plan view and in side view, respectively;

Fig. 2 is a diagramatical perspective view showing the elements of the pressure cell for measuring the crystallization temperature (Tx);

Fig. 3 is a graph plotting a relation between the pressure (p) and the crystallization temperature (Tx(p));

Fig. 4 is a diagramatical perspective view showing the components of the pressure-cell for compacting used in the embodiments;

Fig. 5 is a photomicrograph of a compact obtained from Embodiment No. 1 in Table 1;

Fig. 6 is a photomicrograph of a compact obtained from Comparative example No. 15 in Table 1;

Fig. 7 is a T-T-T diagram plotting the results in Table 1;

Fig. 8 is a similar T-T-T diagram plotting the results in Table 2; and

Fig. 9 is also a similar T-T-T diagram plotting the results in Table 3.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] Before describing examples of the manufacturing method according to the invention, the crystallization temperature (Tx(p)) under a ultra-high pressure (p) will be explained in connection with (a) crystallization temperature, (b) high-temperature and high-pressure generating apparatus, (c) a pressure-measuring cell, and (d) results of measurement.

(a) Crystallization temperature (Tx):

[0022] The crystallization temperature (Tx) of an amorphous material is in general defined as the temperature at which the crystallization thereof is commenced, which temperature is measured as a point at which there occurs a change in the temperature curve plotted by a relation between the heat capacity and temperature by use of a differential scanning calorimeter. However, the crystallization temperature Tx described herein is detected by utilizing a phenomenon in which a sudden drop of electric resistance occurs at a time when the crystallization of an amorphous material is commenced, that is, the Tx temperature shown in part (I) of this specification is defined as the point of temperature at which the electric resistance begins to drop in the electric resistance versus temperature plot curve.

(b) High-temperature and high-pressure generating apparatus:

[0023] A high-pressure generator unit comprisis a cube-shaped pressure device (DIA-15) having a pressure chamber (9) of 15 x 15 x 15 mm³ in size, the construction of the device being shown in Fig. 1. Each of the six anvils 1 has a square top face with a side of 15 mm. Each anvil, having a 60 mm height and a 60 mm bottom diameter, is made of tungsten carbide (Igetalloy D-l) and was retained by a steel block ring (SNCM-11) with a 102 mm external diameter. A pressure plate made of a high speed steel (SKH3) supports the ring. The upper and lower ones in the six anvils (1) were fixed respectively to the guide blocks (5) and (6) in Fig. 1. Each of the guide blocks is provided with, along its four sides, a respective slide plane having a 45° inclination angle. Other four side anvils (1) are fixed respectively to the four side anvil supports, each having a slide plane with an inclination angle of 45°. By the so-called "wedge" effect, all of the six anvils (1), i.e., the four side ones plus the two upper and lower ones, move together synchronously toward the center of the pressure chamber (9) while branching a uniaxial vertical load.

[0024] A molybdenum disulfide layer and a tetrafluoroethylene sheet are provided on both the side anvil supports (2) and the guide blocks (5, 6) so as to provide lubrication. The center of the vertical guide blocks (5, 6) is alligned by means of four pieces of guide pins (7) each having a diameter of 65 mm. This pressure device is driven by a pressure proof test device having a control to exert a constant load of maximum 12 MN.

[0025] Regarding the heating of the specimen, there was used resistance heating by means of a cylindrical carbon-heater which was of a constant-power control type of 3 KW in maximum output comprising hall devices and thyristors. The heater was installed into the pressure cell (10) which will be described later. The heating current was fed to the specimen from current terminal plates (3) in Fig. 1 through the vertical anvils (1). Cooling water was circulated within the water passages (4) in the guide blocks" (5, 6) to cool the bottoms of the upper and lower anvils (1) thereby preventing an undesirable rise in temperature while heating the anvils.

(c) A pressure-cell (10) for measurement:

[0026] An explanation will now be made, referring to Fig. 2, in regard to the pressure cell (10) which is installed into the pressure chamber (9) of the above-mentioned high-temperature and high-pressure generator, so as to heat and pressurize the specimen of amorphous material.

[0027] Each of two pressure-medium bodies 11 is of a cubic pyrophillite having sides each of which is 20 mm in length, the cube being prepared by the sintering thereof for one hour at 500°C. Within these pressure-medium bodies (11) are inserted a cylindrical carbon-heater (12) (8 mm in external dia., 7 mm in internal dia., and 10 mm in height), two copper rings (13) (an upper one and a lower one each having a 7 mm external dia., a 5 mm internal dia., and a 4.7 mm height) and two stainless steel plates 14 (8 mm in dia. and 0.3 mm in thickness). Within the carbon heater 12, there are inserted a piece of cylinder (15) made of boron nitride (BN) (7 mm in external dia., 5 mm in internal dia., and 10 mm in height) and three pieces of columnar bodies made of BN, i.e., an upper one (16), a middle one (17), and a lower one (18), each having an external dia. of 5 mm, the heights being 5.0, 2.5 and 2.5 mm respectively. A specimen (19) is inserted between the columnar BN pieces (16) and (17), and subjected to pressure. The carbon heater (12) and the BN pieces (16, 17, 18), used for the heating and pressurizing process, had been previously fired to in a vacuum furnace at 1000°C for 5 hours to remove impurities and gas existing therein. This is necessary to prevent the impurities and/or gases from leaching during the heating and pressurizing process, thereby preventing the degradation of electric insulation of the heater and the BN pieces.

[0028] The four lead wires (20) made of pure aluminum wires (available from Jone refining-produced by Nippon Shinku, the dia. being 0.35 mm) were arranged into a four terminal bridge so as to enable a measurement of the electric resistance of the specimen (19). These lead wires (20) were connected to the four side-anvils (1), shown in Fig. 1, for the purpose of leading voltage and current to the anvils. A thermocouple (21) of a PR type (pt-pt 13% Rh) was inserted between the BN pieces (17) and (18). The lead wires (20) and the thermocouple (21) were guided through small BN tubes (22) having been fired in the same manner as above to provide an insulation regarding the carbon heater. In the above-mentioned experiments the machining accuracy of the pressure cell was kept in a range of +0.02 mm to -0.02 mm in order to improve the reproducibility thereof. Also, a thin layer of iron oxide red (hematite) was applied over the surfaces of the pressure cell (10) so as to increase friction between the cell and the anvil (1) and to improve the efficiency and the reproducibility of pressurization.

(d) Results of measurement:

[0029] The pressure cell (10) described above was set within a pressure chamber (9) in the high-temperature and high-pressure generator and there was measured the relationship between the electric resistance and the temperature (the rate of temperature increase being 2°C/min) regarding an amorphous material. Thus, Fig. 3 shows, by circle marks, the crystallization temperature (Tx(p)) plotted against the pressure (p), as obtained from the above-mentioned relationship. Fig. 3 shows a case where a thin strip specimen (19) (20 pm in thickness, 5 mm in length, and 3 mm in width) of amorphous Fe₇₈B₁₂Si₁₀ alloy was used. Also shown in the figure are the ranges of measurement error caused by the thermocouple used under high pressures.

[0030] As understood from Fig. 3, the crystallization temperature (Tx) of amorphous material increases depending on the pressure (p) and the rate of increase, i.e., ΔTx/Δp is about 10°C/Gpa. This shows that while the Tx temperature under the atmospheric temperature is about 507°C in the figure, it is increased, for example, to about 530°C under a 2 Gpa pressure and about 560°C under a 5.4 Gpa pressure. This means, accordingly, that amorphous material under an ultra high pressure (p) can keep its amorphous property without crystallization, even at a temperature not less than the crystallization temperature (Tx) defined under the atmospheric pressure. By using this phenomenon, it is possible to achieve the bonding of the amorphous material under a high pressure (p), without causing crystallization, even if the material is heated at temperatures near the Tx temperature under the atmospheric pressure (above 90% of the Tx temperature) or at a temperature equal to or higher than the crystallization temperature Tx under the atmospheric pressure.

II. Manufacturing method of an amorphous compact

[0031] (a) Pressure-cell (30) for production:

A pressure-cell (30) used for the production of an amorphous compact is explained hereinbelow with reference to Fig. 4. The pressure-cell (30) is of a construction basically similar to that of the pressure-cell (10) shown in Fig. 2.

[0032] Within the pressure-medium bodies (11) (a cube with each side of 20 mm) there are inserted a carbon heater (12) (9 mm in external dia., 0.5 mm in wall thickness, and 10 mm in height), two copper rings (13) (an upper one and a lower one each having an external dia. of 9 mm, a wall thickness of 0.5 mm, and a height of 4.5 mm) and two copper plates (14) (an upper one and a lower one each having a dia. of 9 mm and a thickness of 0.5 mm) for feeding the heating currents thereto. Each of pyrophillite columns (11') of 7 mm in external dia. and 4.5 mm in height used as insulators is inserted in the copper ring (13). Within the carbon heater (12) is placed a cylinder of boron nitride (15) (8 mm in external dia., 1 mm in wall thickness, and 10 mm in height). This BN cylinder in turn receives within its interior three columnar pieces of BN (31, 32, 33) (each with a 6 mm external dia., and respective heights of 2.5 mm, 1.5 mm and 2.5 mm). In a space between the BN pieces (31) and (32) there was charged powders (34) (3.5 mm in thickness) whose compositions are shown in Tables 1, 2 and 3. Also, within a space between the BN pieces (32) and (33) was provided the same thermocouple (21) as that shown in Fig. 2. All of these components are the same as those of the pressure cell (10) regarding the kind of the material, the degree of the machining accuracy and the manner of the heat treatment.

[0033] The above-mentioned powder (34) can be prepared either by pulverizing amorphous thin strips formed according to the single roll quenching method, into flakes (7.18 in density, 10 - 50 µm in thickness, 50 - 200 pm in length and 10 - 50 µm in width) or by utilizing the method of spraying into a rotating liquid to form particles having diameters ranging between 5 - 200 µm.

(b) Manufacturing steps

[0034] The powders having the compositions and the shapes shown in Tables 1 to 3 were charged uniformally within the pressure cell (30). This uniformity was achieved by the utilization of suitable vibration from outside of the cell. Subsequently, the pressure cell (30) was inserted into the chamber (9) of the high-temperature and high-pressure generator described above, and the specimen was heated at a rate of 20°C/min to a temperature 100°C below a predetermined temperature while applying pressure thereto at a predetermined level. The specimen was then subjected to a rapid heating to a predetermined temperature within several seconds. A pressurizing period of time lapsed after the temperature of the specimen became the predetermined level is defined herein as "forming period". Following the formation, the specimen was rapidly quenched by shutting off the heating current (the average cooling rate being about 140°C/sec). After the rapid quenching step, the pressure was decreased, and a resultant compact was taken out of the chamber. The amorphousness of the compact was confirmed by subjecting it to an X-ray diffraction analysis, an electron beam diffraction analysis and an observation test by TEM with high resolution. In a case where the existense of amorphousness was observed in all of these test, the specimen was judged to be amorphous, and marked by a circle in the Tables. The density of the compact was measured by using the Archimedian method and compared with that of an amorphous thin strip having the same composition as the compact. The ratio of the former density to the latter one is shown in the Tables. The hardness values in the Tables are the Vicker's hardness values which were measured on several surface portions of the compact, and averaged into mean values. The bondability of the powder was evaluated by observing whether or not the resultant compact breaks on the surface thereof when its surface is polished for effecting the above measurements. Emery papers were used for polishing the surface of the compact.

(c) Amorphous compact:

[0035] An amorphous material is known to commence crystallization at a particular temperature upon heating, however, the crystallization process is extremely complicated and the temperature of crystallization (Tx) depends upon temperature and a holding period of time. Generally speaking, the crystallization temperature (Tx) of an amorphous material is defined by a temperature at which a MS-I layer begins to appear which layer is a metastable phase with fine crystal grains of about 0 30 to 50 A in size precipitated uniformly therein. It has been known that the crystallization temperature (Tx) varies in dependence on a holding period of time, that is, as the period of time is increased the Tx temperature decreases, thus there occurring a rightward decrease of the Tx temperature in a time-temperature- transformation diagram (hereinafter referred to as a T-T-T diagram).

[0036] On the other hand, as already described in the section I regarding crystallization temperature (Tx(p)) under an ultra high pressure (p), the fact that a crystallization temperature (Tx) increases in dependence on a rise of pressure (p) in the ultra high pressure range was confirmed. Also, amorphous compacts were produced in accordance with the method already described in the section II "Manufacturing method of an amorphous formed body", the properties of which products are shown in Tables 1 to 3. These results are plotted into Figs. 7 to 9. By judging whether or not amorphousness exists in the product, there was determined the crystallization temperature (Tx) under their respective pressures (p). As a result, it was found that an increment of 55 to 60°C regarding the crystallization temperature (Tx) occurred under an ultra high pressure range of about 5.4 to 6 Gpa, i.e., a (Tx) increment of about 10°C per one Gpa ultra high pressure. In other words, although the crystallization temperature (Tx) varied in dependence on the holding time, it was confirmed to rise at a rate of 10°C/Gpa in the case of a predetermined holding and forming period of time.

[0037] As shown in Table 1, all of the compacts Nos. 1 to 8 made according to the manufacturing method of this invention had densities larger than 90%, no lattice image being observed by a high resolution TEM, all being of good amorphous structure with only a halo pattern or halo ring peculiar to amorphous structure when tested by an X-ray diffraction.







or an electron beam diffraction. Also, the compacts had good bonded characteristic, the hardness being as high as 830 - 910 in Vicker's hardness number.

[0038] This composition in Table 1 had crystallization temperature (Tx) of about 510°C in a holding time of several minutes and under the atmospheric pressure, however, the resultant compacts (Embodiments No. 3 and No. 5 in which a higher temperature of 550°C, a pressure of 5.4 Gpa. and a holding time period of one minute were used) kept their amorphousness without being crystallized, which compacts were bonded into a density not less than 95%, and were of higher hardness values than those of crystalline structures. Further although the crystallization temperature (Tx) under the conditions of atmospheric pressure and a holding period of time of 10 minutes was 465°C, a compact (Embodiment No. 2) made under the conditions of 10 minutes in forming period of time, 500°C in temperature higher than 465°C, and 5.4 Gpa in pressure showed good amorphousness and a density not less than 93%. A compact (Embodiment No. 8) made under the conditions of 465°C in temperature which is approximately equal to the temperature (Tx), 1.0 Gpa in pressure and 10 minute in forming period of time also showed good amorphousness and a density not less than 93%. Further, although the crystallization temperature (Tx) of this composition under the conditions of atmospheric pressure and holding period of time of 120 minutes was 407°C, there were shown good amorphousness and density not less than 90% with respect to both the compacts (Embodiments Nos. 1 and 4) formed under the conditions of 450°C in temperature which is higher than the Tx, 5.4 Gpa in pressure, and 120 minutes in forming period of time, and other compact (Embodiment No. 7) formed under the conditions of 407°C in temperature which is approximately equal to the crystallization temperature (Tx), 1 Gpa in pressure and 120 minutes in forming period of time.

[0039] Thus, it was found that the crystallization temperature (Tx(p)) under a pressure (p) not less than 1 Gpa, increased at a rate of about 10'C/Gpa, and that the compacts retained their amorphousness without crystallization, even if the temperature was equal to or more than the crystallization temperature (Tx) defined under atmospheric pressure, in a case where the temperature at which the compact was formed was less than the crystallization temperature (Tx(p)) defined under the respective pressure (p). Also, in a case where the temperature was higher than 90% of the crystallization temperature (Tx) defined under the atmospheric pressure, a resultant compact had a density not less than 90% and a good integrity (, that is, good bondability).

[0040] It was also found that, in order to obtain compacts well bonded having a density not less than 95%, there were necessary a pressure of at least 1 Gpa, and a temperature approximately equal to the crystallization temperature (Tx) defined under the atmospheric pressure, or a temperature higher than the crystallization temperature (Tx) defined under the atmospheric pressure but lower than the crystallization temperature (Tx(p)) defined under the respective pressure (p).

[0041] Moreover, the period of time required for forming may be varied in dependence on various factors such as working time, working property and cost etc., however, the period of time of at least several tens seconds or one minute was required in taking into account the thermal expansion of the pressure cell in the high-pressure generator which expansion occurs while it is heated to a predetermined temperature. From the viewpoint of industrial productivity, however, the period of time less than 1000 minutes is preferable. A forming period of time within two hours is more advantageous regarding cost and productivity. Also, as understood from Figs. 7 to 9, the forming effected in a shorter period of time obviously requires a higher temperature in comparison with the forming in a longer period of time.

[0042] Referring to the comparative examples in which the combinations of temperature and pressure outside of the range defined in this invention were employed, there were caused practical problems such as the crystallization of the amorphous body or the brittleness of the compact.

[0043] That is, in comparative examples Nos. 9 to 13 formed under a conditions of temperature higher than the crystallization temperature (Tx(p)) defined respective pressure and period of time regarding each of the compositions of the examples 9 to 13, no amorphousness was obtained although density not less than 90% was obtained. Also, in other comparative examples 14 to 15 formed at a temperature less than 90% of the crystallization temperature defined at an atmospheric pressure or under a pressure less than 1 Gpa, powder material was not bonded at all or was bonded insufficiently with the result that a resultant compact was extremely fragile.

[0044] Fig. 5 shows a microphotograph of a good compact obtained in accordance with Embodiment No. 1. In contrast, Fig. 6 shows a microphotograph of the comparative compact having inferior bonded structures in accordance with comparative example No. 15.

[0045] Similarly, the results shown in Table 2 and Table 3 were obtained respectively for Co-B-Si alloy and Ni-B-Si alloy.

[0046] . Accordingly, although the specific experimental results have been discussed only in respect to the alloys of Fe-B-Si, Co-B-Si and Ni-B-Si, those skilled in the art may readily produce a dense amorphous compact having compositions other than the above described ones according to the manufacturing method of this invention if those skilled in the art effects experiment on the basis of the present invention.

[0047] According to the invention, it became possible to obtain an amorphous compact having a very high density and good bondability by using particular pressure, temperature and forming period of time, while utilizing such phenomenon that the crystallization temperature (Tx) of amorphous materials increases under an ultra high pressure (p). The resultant compact of amorphous materials is larger in volume, as compared to conventional amorphous thin strips or powders. Thus, various applications of the compact are expected. Particularly, since the compact of the invention is high very much in density, the compact may be used in many usages as magnetic materials.

Claims

1. A method of producing an amorphous compact by use of amorphous fine particles, comprising the steps of applying a ultra high pressure (p) to said fine particles, and at the same time heating said fine particles to a temperature of more than 90% of a crystallization temperature (Tx) of the amorphous particles defined under an atmospheric pressure but less than a crystallization temperature (Tx(p)) thereof defined under said ultra high pressure (p).

2. A method of producing an amorphous compact by use of fine particles of an amorphous substance, comprising the steps of applying a ultra high pressure (p) to said fine particles, and at the same time heating said fine particles to a temperature not less than a crystallization temperature (Tx) of the amorphous substance defined under an atmospheric pressure but less than another crystallization temperature (Tx(p)) of the amorphous substance defined under said ultra high pressure (p).

3. A method of producing an amorphous compact as claimed in Claim 2, wherein the ultra high pressure is not less than 1 Gpa and less than 10 Gpa.

4. A method of producing an amorphous compact as claimed in Claim 2, wherein the ultra high pressure is not less than 1 Gpa but less than 5 Gpa.

5. A method of producing an amorphous compact as claimed in Claim 2, wherein the value of the crystallization temperature (Tx(p)) at the ultra high pressure (p) is equal to the total of the value of the crystallization temperature (Tx) at the atmospheric pressure and an increment proportional to the difference between the value of the ultra high pressure (p) and the value of the atmospheric pressure.

6. A method of producing an amorphous compact as claimed in Claim 5, wherein the rate of the increment is 10°C per pressure of one Gpa.

7. A method of producing an amorphous compact as claimed in Claim 2, wherein the pressurized particles are heated at a rate of about 20°C per one minute up to a temperature 100°C below a predetermined final temperature, then said particles being rapidly heated to the final temperature.

8. A method of producing an amorphous compact as claimed is Claim 2, wherein quenching of a resultant compact is effected after the completion of the forming of the particles.

9. A method of producing an amorphous compact as claimed in Claim 2, wherein temperature, pressure and a forming period of time are applied to the particles so that the hardness of a resultant compact is not less than 830 in Vicker's hardness.

10. A method of producing an amorphous compact as claimed in Claim 2, wherein temperature, pressure and forming period of time are applied to the particles so that the density of the compact is not less than 90% of the theoretical density of the compact.

11. A method of producing an amorphous compact as claimed in Claim 2, wherein the compact is of an alloy selected from the group consisting of Fe-B-Si alloy, Co-B-Si alloy and Ni-B-Si alloy.

Drawing