METHOD FOR THE PRODUCTION OF AMORPHIC METALS BY ELECTROMAGNETIC SUBCOOLING OF A METAL / ALLOY

Abstract

Method for producing an at least partially amorphous metal, the method comprising the following steps: Heating a metal to a molten state; and Cooling the molten metal below its melting point, whereby the molten metal is subjected to an electric current during cooling, which is at least one of the following: electromagnetically induced in the molten metal by applying a magnetic AC field to the molten metal; and directly applied to the molten metal by at least one electrode that contacts the molten metal after the metal has reached its molten state; where cooling the molten metal includes reducing the temperature of the molten metal to ambient temperature.

Description

AREA OF INVENTION

[0001] This invention relates to the production of glassy or amorphous metals and, in particular, to obtaining a crystallization-free supercooled melt by applying sufficient amounts of electric current during the cooling process to prevent crystallization and the formation of a stable supercooled melt, which is used as a precursor for the production of glassy or amorphous metals when cooled to ambient temperature. BACKGROUND OF THE INVENTION

[0002] The ability to produce amorphous metals, also called metallic glass, from the liquid phase in significant quantities has long been attempted. Practical production limitations imposed by the need for a combination of rapid cooling, pristine process environments and alloy compositions have restricted the applicability of known production methods.

[0003] Perhaps the most highly praised quality of metallic glasses is their combination of mechanical strength, elasticity, hardness, and rigidity. Crystalline metals / alloys, beyond a very small scale, exhibit lattice defects that disrupt the long-range order of the atomic structure. These defects are generally the initiation points of mechanical defects.

[0004] Lacking crystals and such crystal defects, amorphous metals are often more efficient than their crystalline counterparts in terms of strength and elasticity. In addition to their mechanical strength, the absence of grain boundaries and lattice defects, amorphous alloys are corrosion- and wear-resistant, making them well-suited as components in harsh chemical and mechanical environments. Furthermore, because amorphous alloys can be kept in a state of flux at relatively low temperatures without crystallizing, they can be bent into complex shapes using processes similar to thermoplastic forming.

[0005] Metallic glass is expected to have an electrical conductivity two orders of magnitude lower than that of the metal / alloy in its crystalline structure. Consequently, efforts are being made to achieve not only the mechanical strength of metallic glass but also improved electrical conductivity. Furthermore, it has been observed that metallic glass made from ferromagnetic materials can exhibit soft magnetization, meaning almost no hysteresis in the BH diagram, as the magnetic field is pulsed above and below zero. This property translates into very low losses when used as magnetic cores in transformers or other magnetic components.

[0006] Supercooling, also known as undercooling, is the process by which the temperature of a liquid is lowered below its melting point without crystallizing. Thermodynamically, the preferred state for most materials is a crystalline solid state if the temperature is below the melting point of the specific material. The crystallization process is always initiated by one or more nucleation events in the liquid. The nucleation process is categorized as either heterogeneous or homogeneous, with heterogeneous nucleation being supported or catalyzed by a foreign element, for example, by entrained impurities or the container wall, and homogeneous nucleation being induced by the base metal itself. For each category, nucleation is a random process, and the driving force increases with undercooling. Once a nucleus of sufficient size has formed, crystal growth follows.However, if a liquid can be sufficiently supercooled, the crystallization kinetics become excessively slow, and the liquid freezes in an amorphous solid state without a crystalline structure. The temperature range in which this occurs is called the glass transition region and varies from material to material.

[0007] In general, to achieve a glass transition for metallic liquids, the liquid must be cooled sufficiently rapidly from its melting point to the glass transition to prevent nucleation and crystal formation. The required cooling rate depends on the material, and most prior art efforts focus on finding suitable glass formers, i.e., alloy compositions that have an inherently slow crystallization kinetic and / or a glass transition temperature close to that of the liquid in the system.

[0008] There are several empirical rules for producing a good glass former. Among these rules is the idea that good glass formers often contain at least three different elements, and that these should differ by at least 12% in atomic radius. The stoichiometry of such glass former compositions is often also close to the low eutectics. Such compositions often have lower mobility when supercooled and therefore require a somewhat more moderate critical cooling rate. Cooling a melt to a rate higher than this critical rate prevents crystallization, and the melt solidifies into glass. In fact, limited to processes known from the prior art, many metallic glasses can only be produced with a thickness of a few millimeters.Furthermore, to achieve significant subcooling, it is generally considered necessary to work in pristine process environments to remove foreign substances and external nucleating agents from the melt. If such nucleating agents are present in the melt, it often undergoes heterogeneous nucleation.

[0009] From US patent 2004 / 0016477A1, a method for producing a magnetic alloy is known in which a raw material of the magnetic alloy is melted and then supercooled taking into account a peritectic point of the alloy.

[0010] From US patent 2007 / 0107467A1, a method for producing an object from metallic glass is known in which a molten metal is solidified while an electromagnetic vibration force is applied to the molten metal.

[0011] US 2014 / 0090797A1 describes a process for melting a raw material of metallic glass, in which the raw material is melted in a crucible and the melt is used in an injection molding process.

[0012] From US 2012 / 0 006 085 A1 a method is known in which an amorphous metal is deformed by applying electric and magnetic fields perpendicular to each other.

[0013] CN 1 01 100 705 A discloses a method for casting metal in which the metal is melted and cast. Subsequently, electrodes are inserted into the cast metal and the type of crystal structure of the hardened material is influenced by applying a pulsed electric current with a current in the range of 1,000 to 4,000 A and a frequency of 100 to 1,000 Hz.

[0014] US Patent 2006 / 0 137 778 A1 discloses a method for producing metallic composite material in which a molten alloy composition is cooled at a cooling rate of less than 1,000 °C / s, wherein the melt is heated with an electric current of at least 300 A / cm² 2 is subjected to pressure for at least one hour to produce crystallites with a size of 50 µm, thus forming an amorphous microcrystalline or amorphous nanocrystalline material. BRIEF SUMMARY OF THE INVENTION

[0015] The object of the invention is solved by a method according to one of claims 1 and 15.

[0016] It was found that a considerable degree of subcooling of metals, pure metals, and several alloys can be achieved without requiring either dramatic cooling rates or pristine process conditions. The result is that glassy metals can be produced without quenching or stringent processing requirements. In particular, it was found that when a melt is exposed to an electric current, either magnetically induced or directly applied, crystallization can be suppressed during cooling, and a considerable degree of subcooling can be achieved without crystallization. As a result of the process according to the invention, amorphous metals can be obtained without quenching when the temperature of the subcooled melt is brought to ambient temperature.

[0017] This process can either completely eliminate the need to quench a melt to achieve the amorphous state for mass production, or it can be used in conjunction with existing process methods, reducing the need for rapid quenching.

[0018] Furthermore, the system does not rely on pristine process environments or the use of specialized alloy compositions to achieve and maintain a subcooled state. Moreover, by increasing the current during cooling, a lower degree of subcooling can be achieved.

[0019] It was also found that maintaining a reducing environment around the molten metal improves the process. Such an environment can include, for example, atmospheric hydrogen or additives such as small amounts of carbon added to the melt. The choice of reducing agent for a specific metal depends on the thermodynamic equilibrium between the metal oxide and the specific reducing agent at operating temperatures, up to 200° Celsius above the melting point.

[0020] As described below, a method for undercooling a melt without rapid quenching involves heating the metal to a molten state and then allowing the molten metal to cool below its melting point while the melt is subjected to electromagnetic energy or electric current of sufficient strength to suppress crystallization during cooling. The electromagnetic field strength and the resulting current density, or direct current application, are assumed to be important parameters in suppressing nucleation and preventing crystal growth during cooling below the metal's melting point, at which crystallization typically occurs.

[0021] In one embodiment, a metal, such as nickel, cobalt, copper, or iron, is placed in a crucible surrounded by a coil driven at a frequency and with a current set to induce eddy currents in the metal of sufficient strength to melt it. In a preferred embodiment, it was found that a nickel-niobium alloy and a nickel-boron alloy give off an amorphous phase at room temperature.

[0022] It is preferred that the metal be exposed to a reducing agent, such as hydrogen or carbon, in sufficient quantities to remove the oxides present in the metal. The current in the coil is then reduced, resulting in cooling of the molten metal. The energy from the coil at this reduced current keeps the metal atoms just sufficiently in the molten state to prevent the supercooled melt from transitioning to a crystalline state or exhibiting recalescence at temperatures below its melting point.

[0023] In an alternative embodiment, the magnetic or inductive coupling with the metal and the power source is replaced by conductive coupling elements. That is, electricity is sent directly through the metal. The power source drives a current of sufficient magnitude to melt the metal. Once the metal is melted, the current is reduced to a level sufficient to prevent the metal atoms in the supercooled melt from re-crystalline or recalescent.

[0024] Furthermore, it has been found that for certain metal systems, the degree or extent of subcooling can be increased if the applied current can be increased during cooling. The increased amount of ohmic heating resulting from increasing the applied current is counteracted by also increasing the rate of heat dissipation from the system. This can be achieved by contacting a conductive heat sink with the main container of the molten metal. The ability to dissipate heat from the melt using thermal conductivity requires an identical amount of heat being added to the melt when a subcooled static state is reached.

[0025] The theory exists that crystallization is inhibited due to the discrepancy in electrical conductivity between the nucleating solid state and the background liquid. The solid state typically has a higher electrical conductivity, and the nucleating phases will locally experience a higher current density compared to the liquid mass, as predicted by standard electrodynamics. This higher current density generates additional heat where crystal growth would otherwise occur. This additional heat limits growth rates and melts the crystallization nuclei, thus preventing crystallization.

[0026] Unlike the core of a pure metal phase, metal oxides can have a lower electrical conductivity than the liquid mass. The presence of such oxides can have the opposite effect. That is, current densities across the oxides become locally lower than in the surrounding melt, which consequently reduces ohmic heating locally. This, in turn, can result in crystallization.

[0027] The problem can be solved or mitigated by removing the oxides present in the melt using a reducing agent, such as hydrogen, which will reduce the oxides to pure metals and a gas component, steam or CO2 / CO in these cases, the latter of which will leave the system.

[0028] The metal subcooling processes described above do not require extreme cooling rates, pristine environments, or complex alloy structures. This removes many of the practical limitations of metal subcooling for the production of metallic glasses.

[0029] More precisely, the three problems solved by the subject matter of the invention are the following: 1) the ability to control the subcooling of metals without resorting to complex alloy compositions, 2) the ability to subcool metals in a “dirty” reactor, i.e., a reactor that provides numerous nucleation sites, 3) the ability to significantly subcool metals without requiring rapid quenching.

[0030] If sufficient electrical current is applied during cooling, this method can be used to produce amorphous metals without quenching. Even if an amorphous state cannot be achieved using this method alone for a particular metal or alloy composition, due to the level of continuous supercooling available, which is significantly below its melting temperature, additional quenching using prior art methods can result in a reduced quenching rate because the starting point is significantly below the melting temperature. This allows for a greater thickness of the glass material produced.

[0031] Another advantage of this method is that, if crystallization is allowed to occur, either at normal solidification temperature or in a supercooled state when the melt is exposed to an electric current, the crystal structure can be manipulated. As a result, crystal size and orientation can be tailored to the applied field during the crystallization isotropy of any given material. Therefore, this approach offers a novel method for tailoring the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] These and other functions of the invention will be understood in conjunction with the detailed description and the drawings, of which: Fig. 1. A schematic representation of a system is used to achieve subcooling without the use of rapid quenching; Fig. 2 a current-versus-time diagram of the current applied to the coil of Fig. 1 applied current is; Fig. 3 is a temperature-versus-time diagram that shows an example of temperature conditions during subcooling in the apparatus. Fig. 1 represents; Fig. 4 is a schematic representation, similar to the Fig. 1, where, however, a heat sink is placed in thermal contact with the main vessel to increase heat dissipation from the metal during the process, which requires a higher coil current to achieve the same temperature as without the presence of the heat sink, which in turn leads to increased crystallization suppression; Fig. 5 is a schematic representation of an alternative embodiment in which the metal rod to be melted and supercooled is carried in a non-conductive mold; Fig. 6. A current-versus-time diagram of the current in the metal rod. Fig. 5 applied energy is; Fig. 7 is a temperature-versus-time diagram of the metal rod after melting, which shows the transition to a supercooled state without crystallization; Fig. 8 an alternative embodiment which is the use of a metal plate to which current is applied in order to melt the metal with a non-conductive mold which is equipped with a coolant; Fig. 9 is a schematic representation of the use of a single coil for induction melting and subsequent treatment of a metal, which shows the magnetic flux lines and a height-to-depth ratio h / d = 1; Fig. 10 is a schematic representation of the use of a split coil for melting and processing the sample, wherein Fig. 9 represents the magnetic field lines and a height-to-depth ratio of h / d greater than 5; Fig. 11 a schematic representation of the use of the coils on each side of the sample to be melted, in which two different current strengths are applied to the coils with a phase relationship between the first and second coils to generate the specified magnetic current; Fig. 12 is a front view of the experimental setup with an induction coil used in the process of subcooling metals; Fig. 13 a close-up view of the front of the secondary container assembly Fig. 1 is; Fig. 14 a close-up view of the front of the secondary container assembly Fig. 4 is; Fig. 15 a side view of the secondary container assembly Fig. 13 is; Fig. 16 A schematic representation of the water columns used to regulate back pressure on the primary and secondary tank equipment from Fig. 13 is used; Fig. 17 is a schematic representation of the experimental apparatus using a direct current for melting and supercooling a metal; Fig. 18 a series of temperature-versus-time and coil current-versus-time diagrams for an experiment in which nickel is repeatedly supercooled and a small amount of carbon is in thermal contact with a water-cooled aluminium heat sink according to Fig. 4, where only the coil is shown during cooling; Fig. 19A is a diagram that records the time the metal is in a subcooled state versus the coil current during the cooling step for each of the cooling steps shown in Fig. 17 are shown; Fig. 19B is a diagram showing the maximum degree of subcooling during each cooling step. Fig. 17 versus the coil current during the cooling step for each of the cooling steps that are in Fig. 17 are depicted, recorded; Fig. 20 a series of temperature-versus-time and coil current-versus-time graphs for an experiment which uses the induction coil to repeatedly subcool 4.39 g of pure nickel without the use of a heat sink; Fig. 21 a time-temperature transformation diagram in the upper half of the in Fig. 20 cycles shown and in the lower half of a time-temperature transformation diagram of a similar experiment to the one in Fig. Figure 20 is shown, but a heat sink was used and the sample size was 0.45 g of pure nickel; Fig. 22 a series of temperature-versus-time and coil current-versus-time diagrams for an experiment that repeatedly subcools iron and carbon without the use of a heat sink, showing only the coil during cooling; Fig. 23A is a diagram that represents a record of the time the metal spends in a state of undercooling versus coil current during the cooling step for each of the cooling steps that are in Fig. 22 are shown; Fig. 23B is a diagram which shows a maximum degree of subcooling during each cooling step in Fig. 22 represents versus coil current during the cooling step for each of the cooling steps that are in Fig. 22 are shown; Fig. 24 is a series of temperature-versus-time and applied current-versus-time diagrams for a nickel sample produced in a DC reactor. Fig. 17 is treated; Fig. 25A and Fig. 25B X-ray diffraction patterns of the same sample are shown. Fig. 24A represents the patterns that were made from a scan of the surface of the metal and Fig. 24B shows a pattern from a scan made of a powder that was filed from the same sample; Fig. 26 is a series of diagrams which represent the final cooling steps of a sample where crystallization is triggered by completely switching off the coil current; Fig. 27 is a photo of the sample, which after solidification in Fig. 26 was taken; Fig. 28 a photograph of the sample taken using a field to limit crystallization; Fig. 29 is an XRD X-ray diffraction pattern of a NiNb sample, which represents the formation of an amorphous material; and, Fig. 30 is an XRD x-ray diffraction plan of a NiB sample, which represents the formation of an amorphous material. DETAILED DESCRIPTION

[0033] The most important scientific finding revealed herein is that when a melt is exposed to either an electromagnetic field or direct current, the natural nucleation process and crystal growth are suppressed. This allows the melt to be significantly supercooled, i.e., without crystallization for considerable periods, thus providing a stable supercooled melt. Furthermore, the stronger the applied field, the greater the degree or depth of supercooling, enabling a temperature below the equilibrium melting temperature to be achieved. It is noted in the literature that the viscosity of the melt increases upon supercooling. If the melt is sufficiently supercooled, the viscosity reaches such a level that crystallization is kinetically inhibited, and the melt solidifies in an amorphous or glassy structure.The temperature at which crystallization is possible is called the glass transition temperature. The glass transition temperature varies for different materials. The invention disclosed herein can therefore be used to completely supercool a metal / alloy melt below the glass transition temperature, thereby producing a glass material without the use of any prior art processes. Alternatively, it can be used in conjunction with prior art processes to significantly reduce the amount of heat that needs to be removed by rapid quenching to produce a glass material.

[0034] The subcooling method disclosed herein has proven robust enough to function in environments rich with nucleation sites, where otherwise heterogeneous nucleation would lead to crystallization. Furthermore, the method has been proven effective for more than one metal system, demonstrating its versatility.

[0035] In general, the change in heat content over time of the treated metal sample can be denoted by U. Assuming that the applied electromagnetic (EM) field is the only heat source in the metal, the heat source per unit time can be denoted by S, where S is a function that increases with the strength of the applied field. For a given setup, the heat losses of the metal sample include conduction losses, convective losses, and radiation losses, which together are denoted by Q. The thermal balance can be expressed as... ΔU=−Q+S.

[0036] If the metal is in a steady state at a temperature T, there is no change in the heat content of the metal, i.e., ΔU = 0, and the losses are compensated by the source, i.e., Q = S. Increasing the heat extracted per unit time, that is, increasing Q, requires a stronger field, that is, a larger S, to achieve a steady state at the same temperature T.

[0037] The experimental evidence presented herein shows that the field strength determined by the coil current, in embodiments described in Fig. 1, Fig. 4, Fig. 9, Fig. 10 are shown, and by applied current in embodiments which are in Fig. 5 and Fig. 8 can be shown, in addition to the injection of heat into the metal sample, crystallization is suppressed.

[0038] With reference to Fig. 1. To supercool a metal in one embodiment, a metal 10 is first placed in a primary containment vessel, such as a glass-like quartz crucible, and is inductively heated by passing a current through a working coil 2, which circulates around the metal 10 to be melted, although the metal can possibly be melted by other means without departing from the scope of the invention. In one embodiment, the current to the coil is generated by a 250-300 kHz generator and is controlled by a current control module 8, such that the current to the coil 2 has sufficient strength to heat the metal 10 to its molten state, at which point the current to the coil 2 is reduced to create conditions for a cooling process.

[0039] Operating at lower frequencies would increase the skin depth, i.e., the penetration of the field into the metal, and is therefore expected to increase crystallization suppression.

[0040] To remove oxygen from the system, a bath of either helium, argon, nitrogen, neon, or other inert gases is introduced into the primary containment vessel 1. It has been documented in the literature that metal oxides present in the melt can impede its ability to supercool. Therefore, a reducing agent can be introduced into the primary containment vessel 1 in quantities sufficient to remove any previously present oxides from the metal and to prevent the formation of new oxides. Examples of such a reducing agent include, but are not limited to, graphite powder or a small addition of hydrogen to the purification gas.

[0041] In another embodiment, a secondary safety container, such as an external chamber 3, can comprise the container 1 and can be used to hold an optimal temperature control medium 5, such as water, steam or oils, to regulate the temperature outside the container 1.

[0042] In one embodiment, a temperature sensor including an optical fiber 6 runs from an optical pyrometer 7 to the melt, since it is desirable to measure the temperature of the melt as it transitions from a molten state to a glassy or solid state.

[0043] As in Fig. As shown in 2, the current to the working coil begins in Fig. 1 is high enough to bring the metal 10 into a molten state and allows the reducing agent to remove any oxides present. This current is then reduced to allow cooling. In the case of nickel, the output current to the working coil 2 is from Fig. In one embodiment, the current is 175 A and is then gradually reduced. Note that the frequency of the RF energy in the coil is between 250 and 300 kHz, regardless of the current. With this step-down current function, the current does not drop to zero, but rather to a level where the metal is supercooled without crystallization.

[0044] During experimentation, it was found that reducing the energy in the coil from 175 A to 107 A resulted in subcooling to a thermally steady state. In one experiment, a thermally steady state was achieved at 290 K below the melting point of nickel for a period of 400 seconds.

[0045] It turned out that this undercooling is significantly below the melting or fusion temperature of metal, with crystallization typically occurring when the temperature of the melt drops by as little as 2° Celsius. It was found that imparting energy to the melt, as described herein, suppresses crystallization.

[0046] Therefore, a finding of this invention is that the supercooling of a metal can be induced without the use of rapid quenching. In one embodiment, this is achieved by introducing electromagnetic energy into the melt during the cooling process, which brings the molten metal to supercooled temperatures below its melting point. A specific finding of this invention is that the supercooled temperature can be maintained without recalescence for significant periods of time in an environment where heterogeneous nucleation is expected to rapidly crystallize the metal.

[0047] As in Fig. 3 presented and more thoroughly through experimental data presented in Fig. The temperature, which corresponds to the current levels of the 20, is documented and shown. Fig. 2 corresponds to the melting temperature of pure nickel at 280 K below the melting temperature without crystallization, as proven by recalescence.

[0048] Typically, the melt would begin to crystallize when it falls below its melting point, by as little as 2° Celsius. It was found that by maintaining coil 2, as described above, during radiation cooling of the melt, a supercooled state for the nickel was maintained for more than 2000 seconds in one embodiment. Therefore, a thermally stable supercooled state for the cooling melt was achieved at supercooling levels of ΔT > 280 K for an extended period.

[0049] As in Fig. Figure 4 describes a system for further increasing the degree of subcooling, using the equipment and procedures that are described with Fig. 1 are associated. This is achieved by providing an additional cooling modality and by increasing the energy applied to the melt by an amount equal to the energy derived from the cooling modality. By being able to add more energy to the melt as it cools, crystallization is further suppressed. This allows for an increase in the depth of undercooling ΔT, the temperature difference between the normal melting point of the metal and the temperature associated with a supercooled steady state. The crystallization suppression effect is more thoroughly documented with experimental data presented in Fig. 21 are shown, in which apparatuses similar to those described in Fig. As shown in Figure 4, a heat sink is provided in the form of an aluminum surface in thermal contact with the bottom of the primary container used to hold the molten metal. This heat sink, or additional cooling modality, is called a "cold foot" and is placed in thermal contact with the primary receiving container 1 of the metal 10. A current totaling 400 A is required to bring the nickel to the molten state. It has been found that a current of approximately 250 A allows the system to maintain a thermally steady state at a subcooling temperature of over 295 K below normal solidification temperature for an extended period. Note that the heat sink 7 contains a chamber 9 into which a coolant 11 is entered through line 13, exits the line as shown in Figure 15, and is discharged from chamber 9 as shown in Figure 17.

[0050] In one embodiment of the invention, approximately 1.7 g of pure nickel was used as metal 10. The experiments were carried out in a quartz crucible in an argon-hydrogen mixture atmosphere at ambient temperature. Conventional theory suggests that undercooling a sample of this size to a ΔT level above 300 K should not be possible in practice unless all heterogeneous nucleation sites are removed or rapid quenching is used. However, it was found that moderate cooling rates of less than 20 K / s achieved the specified levels of undercooling, and no special actions were required to remove the nucleation agents, other than the reduction environment. Furthermore, the melt was maintained in a steady state at this level of undercooling for extended periods.

[0051] The process of subcooling metals requires neither: 1) extreme cooling rates, nor 2) the need for pristine environments, nor 3) the need for complex alloy structures, nor 4) the need for ultra-small or ultra-thin samples, thereby removing many or most of the practical limitations for producing metallic glass.

[0052] Significant levels or depths of subcooling of several metals, such as pure nickel, pure cobalt, pure copper, as well as nickel and carbon or iron and carbon, have been achieved. The actual procedure is very straightforward. Simply exposing the melt to applied energy at energy levels below those corresponding to the melting temperatures of the metal acts as a suppressor of molten metal crystallization. Other energy sources can be used instead of the excitation coil. It is clear that the strength of the applied field relative to the heat dissipation rate is an important determinant of the levels of subcooling that can be achieved. This can be seen by comparing Fig. 17, Fig. 18A and Fig. 18B. These figures correspond to the arrangement in Fig. 4, where a heat sink requires a stronger field and actually allows the liquid to reach lower temperatures without crystallization.

[0053] With reference to Fig. Section 5 shows a further alternative embodiment.

[0054] Instead of using inductive heating to melt the pure metal, a pure metal rod 20 is inserted into a non-conductive mold 22. The metal rod in the non-conductive mold 22 is melted in a reduction environment by using alternating or direct current from a source 26, so that the metal rod 20 is melted in the non-conductive mold 22. The current applied to the rod 20 is in Fig. 6 is represented as a step function such that, when the current is reduced, the molten metal cools in the presence of the energy supplied by the power source 26. The temperature profile is shown in Fig. Figure 7 shows that after melting and reducing the current to bring the metal to the fusion temperature, a supercooled state is achieved due to the application of the current. The melt is supercooled by regulating the current through rod 20, similar to how the current through coil 2 was regulated relative to Fig. 1 and Fig. 4.

[0055] In relation to Fig. Instead of using a rod, a metal plate 28 is contained in the straight, non-conductive mold 32. The metal plate is contacted at one end by current from a power generator 34 and operates in the same way as in conjunction with Fig. 5, Fig. 6 and Fig. 7 described.

[0056] In relation to Fig. 17, a diagram of the experimental apparatus relating to the embodiment in Fig. 5 refers to a process in which the metal sample 1 is placed in a primary receiving vessel made of glassy quartz. The metal is contacted by two graphite electrodes 2, which conduct an electric current through the metal. The choice of electrode material depends on its thermal stability at operating temperature, i.e., between 50 and 200°C above the melting point of the primary metal, its dissolution in the melt, and its thermal and electrical conductivity. The primary receiving vessel is housed within a secondary receiving vessel 3, which is sealed at one end of each electrode. The electrodes are connected to leads 4, which are connected to a DC power supply. The secondary receiving vessel is purified through inlets / outlets 5 with either an inert gas or an inert gas with added hydrogen. The electrodes not only conduct an electric current but also conduct heat away from the molten metal.This requires cooling at the supply lines, which is possible by blowing compressed air through the nozzles 6.

[0057] Regarding the embodiment, which is in Fig. 1 is shown, and with regard to now Fig. 9. A so-called coil can be used, in which the height of the coil h is approximately equal to the diameter d of the coil.

[0058] Alternatively and in relation to Fig. 10, in a version with a long coil, the h / d ratio is greater than 5.

[0059] In a further embodiment and with regard to Fig. In 11, two coils are used, with a sample placed between them. The applied currents are applied as shown, with a possible phase shift between the currents in the two coil groups ranging from zero to π / 2. Experimental setup

[0060] Referring to Fig. Figures 12-17, which are shown, are a description of the experimental setup used in the subject matter of the invention.

[0061] Referring to Fig. 12, the primary safety vessel 1, comprising a tube made of non-susceptor material, has a working coil 2 located at its distal end. Coil 2 is coupled to an induction current source 20 as shown. The primary safety vessel is located in a housing 42, which constitutes a secondary safety vessel 3. The tube comprising the primary safety vessel 1 communicates with a concentric gas supply channel 22 through which an optical pyrometer fiberglass probe 6 passes. Channel 22 includes a gas inlet port 24 to which a gas inlet line 26 is connected, carrying an air purification medium such as helium, argon, nitrogen, or neon.Channel 22 contains concentric internal conduits such that the gas inlet port 24 is connected to the innermost internal channel, with a gas outlet port 28 connected to a gas outlet line 30 that communicates with the outermost internal channel, so that cleaning gas is directed downwards into the primary containment vessel 1 and removed from the primary containment vessel via the gas outlet line 30. Note that the fiber optic probe 6 includes a viewing window 29.

[0062] In relation to Fig. 13 will show that the secondary safety container 3 contains a cabinet 42 which includes the primary safety container 1 and the coil 3 with an optional control medium which was introduced into the cabinet at the opening 30, which allows water, steam, alcohol or oil to circulate through the cabinet around the primary safety container 1 and is expelled through outlet opening 32.

[0063] Referring to Fig. In section 14, the primary safety vessel 1 with working coil 2 is provided with an aluminum heat sink 34 at the base 36 of the primary safety vessel tube. An inlet cooling medium 11 is introduced into the aluminum heat sink 32 and exits it through a hose of the outlet cooling medium 36, which is coupled to the outlet port 38 that communicates with the interior of the heat sink 34. The cooling medium thus provides a heat dissipation medium to cool the heat sink.

[0064] Referring to Fig. Figure 15, in which similar elements have similar reference symbols, shows the secondary receiving inlet line 40 with a connection to opening 30 in the secondary safety container 3. Cabinet 42 is shown here with a cover 44, which is secured to the cabinet of the primary safety container 42. Also shown is the induction working head 20, which is coupled to the working coil by an electrical cable duct 46 and a connection device 48 in cabinet 42. Note that the lens 50 is located on top of the viewing window 52, ​​which is coupled to the optical pyrometer by means of the fiber optic cable 6.

[0065] Referring to Fig. Figure 16 shows a pair of pressure regulators 56 and 58 to regulate the pressure in the primary and secondary safety containers and are each coupled to the primary receiving inlet line 26 and the secondary receiving inlet line 40 to regulate the pressure of the gases introduced into the primary and secondary safety containers.

[0066] Referring to Fig. 17. The direct current embodiment of the invention comprises a primary safety container 1 in which a metal rod 20 is located within an open tube. This tube, which encloses an open safety container 1, is contacted at both ends by electrodes 60. These electrodes are electrically connected to the electrical terminals 62 and DC connection cables 64 for supplying current to the metal rod 20. Connection 66 is used to connect a gas inlet 70, which carries a reducing gas in a safety container 72, shown in the dotted outline, which surrounds the primary safety container 1. Connection 68 connects a gas outlet 76 for removing the reducing gas from the safety container. Due to the open end of the tube 1, the gas in the safety container 72 circulates within this tube.

[0067] It is assumed that ports 66 and 68 and electrical terminals 62 will be extremely hot and in one embodiment are cooled by compressed air cooling nozzles 80 and 82.

[0068] More precisely, and with regard to the operation of the various elements, what is described are the function and properties of the specified parts of the system.

[0069] Primary Reception 1. Safety Container 1 consists of a tube made of a non-susceptor material with a closed end. Quartz glass, with its excellent thermal shock resistance and high operating temperature, was the material of choice; however, zirconium and aluminum oxide have also been used successfully. An additional (open) tube made of a non-susceptor material (e.g., aluminum oxide or quartz), placed inside the quartz tube, acts as a gas outlet to achieve gas circulation closer to the metal surface. The susceptor metal sample, along with any possible additives, is placed at the bottom of the quartz tube, which is collinear with the central axis of the coil. The sample is also positioned inside the receiving device at the center of the working coil.Several different dimensions at the closed end of the tube have been used to date, including, but not limited to: 1) outer diameter 19 mm, inner diameter 13 mm, 2) outer diameter 18 mm, inner diameter 15 mm and 3) outer diameter 12 mm, inner diameter 9 mm.

[0070] Working coil 2. The working coil 2 shown is made of copper, which allows internal water circulation for cooling purposes. The coil is coated with a dielectric material to prevent short circuits. The coil consists of four turns and has an inner diameter of 22 mm and a length of approximately 20 mm. For most of the samples treated, the coil was operated at 160–180 A during the heating steps (approximately 60 seconds) and approximately 110–140 A during the cooling step when no heat sink was present. With a heat sink present, the current levels on the coil during the heating step are approximately 350–450 A and during the cooling step 180–250 A.

[0071] Secondary recording 3. The working coil and primary recording equipment are housed in the second recording cabinet, which is made of non-susceptor material capable of maintaining low to medium pressure in terms of meters of water column.

[0072] Primary Receiving Gas Circulation 4. Gas circulation for the primary containment vessel is provided by an inlet flow controlled by a mass flow controller connected to the PLC (Programmable Logic Controller) / desktop computer. This circulation allows for convective cooling of the sample's top surface. Various inert cooling media have been used (e.g., He, N₂, Ar) as well as non-inert gases, such as CO and a mixture of Ar / H₂ (4% H₂) at different flow rates. Most experiments are conducted using an Ar or Ar / H₂ mixture at an average flow rate of 0.25 L / min. The back pressure on the primary gas stream is maintained slightly higher, at approximately 2.5 cm water column (one inch), compared to that in the secondary receiving apparatus, to detect cracks and potential leaks in the primary receiving apparatus.

[0073] Secondary Receiving Gas Circulation 5. The gas circulation for the secondary containment vessel includes the circulation of a cooling medium within the secondary receiving device, which provides a means of regulating the temperature outside the primary containment vessel and thus also dissipating heat from it. These experiments, which used the secondary receiving device, were run with a 1–4 L / min flow rate of N₂. The back pressure on the secondary gas flow is maintained slightly lower, at approximately 2.5 cm water column (one inch), compared to that in the primary flow, in order to detect cracks and possible leaks in the primary receiving device.

[0074] Optics for the IR pyrometer 6. The infrared radiation from the susceptor sample is collected via a sapphire or quartz optical fiber and transmitted to a sensor via a quartz fiber optic cable. The optical fiber is directed downwards through an open inner tube within the primary containment vessel. Since quartz has high transmittance in the sensor's operative infrared spectrum, a lens can also be aligned from outside the primary containment vessel. External alignment reduces disturbances caused by turbulence in the melt.

[0075] Optical Pyrometer 7. A Williamson™ dual-wavelength IR pyrometer with a nominal operating range of 480–1750°C can be used to monitor the temperature of the melt. Note that the crystallization of the supercooled melt can be observed visually by the sample, which will exhibit rapid recalescence, and as a spike in the temperature readings.

[0076] Power Source 8. In one embodiment, the power sources are from Ambrell™ and are capable of delivering up to 10 kW (max. 600 A) to the working coil. The frequency is internally modulated for circuit adjustment depending on the load, generally between 250 and 300 kHz.

[0077] Heat sink 9. Placing a water-cooled aluminum heat sink in thermal contact with the primary containment vessel increases the conductive heat loss from the metal. Therefore, to achieve the same sample temperature as in a setup without a heat sink, a stronger field or a higher coil current is required.

[0078] 10. Circulating Water. The aluminum heat sink is cooled by circulating water in thermal contact with the aluminum oxide. The incoming water temperature is regulated at approximately 22 degrees Celsius using a constant temperature device from PolyScience, and the flow rates used were approximately 1.5–3.8 liters (0.4–1 gallon) per minute. method

[0079] The hypothermia experiments conducted to date mainly use the one in Fig. 1 and Fig. The apparatus described in section 4 includes a container 1 in which a sample is placed and inductively heated by an induction heating coil 2. The current to the induction heating coil is then reduced to allow cooling. Note that in this embodiment, the influence exerted by the coil prevents crystallization or recalescence. This was all carried out in an oxygen-free environment due to an oxygen-purifying inert or reducing gas stream 4, which filled the container 1 above the metal 10. A temperature control stream occupies the space between the container 1 and the surrounding enclosure 3 to safely manage the heat outside the container 1, although such a temperature control medium is considered optional.

[0080] After the metal has been brought to its molten state by induction heating in conjunction with the application of RF current from current control module 8 at 250–300 kHz and 175 A, or 400 A if the heat sink is used, the current is reduced. The current applied to the induction coil is low enough to allow the metal to cool below its melting point, yet sufficient to inhibit crystallization. Consequently, the current can maintain the melt in a supercooled state for an extended period. For a 4.39 g nickel sample with a purity of 4N5, a current of 108 A resulted in a continuous state of supercooling of more than ΔT = 290 K during cooling.

[0081] More precisely, a 10 kW power source is used to generate a radio-frequency alternating current in an induction coil with an inner diameter of 22 mm and a height of 20 mm, featuring four turns. The frequency depends on the charge and is fixed to approximately 250–300 kHz to compensate for the power source's internal circuitry. The power source is remotely controlled by a PLC / desktop computer. The supercooled metals are placed at the bottom of a sealed glass quartz tube, which is then mounted on the center of the coil along with the susceptor material, the metal sample. This arrangement allows for visual inspection of the sample during the process.

[0082] The metal temperature was measured using a dual-wavelength pyrometer connected to the sensor via a quartz fiber optic cable. The temperature measurements were transferred to a computer via PLC, enabling real-time monitoring of temperature trends.

[0083] Definitive confirmation of a glassy state cannot be given in real time. However, temperature measurements supported by visual inspection of the metal during cooling can provide clear indications of whether crystallization has occurred or not.

[0084] Crystallization of the sample is detected either by recalescence, a visually recognizable event involving bright illumination, as well as a recognizable peak in temperature measurements, or by observing a thermal standstill of the cooling temperature curve at the equilibrium melting point.

[0085] Induction heating is controlled by current applied to the coil. The high sensitivity to the metal's position in the alternating field necessitates careful current calibration at the start of each cycle. The quartz tube is purified with an inert or reducing gas, such as argon or an argon-hydrogen mixture, before initial heating, and a low gas flow is maintained throughout the experiment. After the metal is initially melted, the system is allowed to remain in the reduction environment before the energy applied to the coil is reduced to levels corresponding to temperatures below the melting point. Once a cycle is complete, the samples are cooled to approximately room temperature before being removed from the reactor. Weight measurements of the sample before and after the experiments, along with XRF analysis, allow for the identification of any impurities present. Experimental results

[0086] Typically, the heating and cooling during the phase transition exhibits a significant latent heat of phase transition in both the heating and cooling stages of the cycle. This is evidenced by an approximately isothermal or thermal standstill in the temperature trend at the equilibrium melting / solidification temperature. If an electromagnetic field is applied during cooling, the phase transition can be suppressed, as demonstrated by a lack of thermal standstill when passing through the melting point and recalescence below the equilibrium melting temperature, leading to undercooling as shown in [reference]. Fig. 17, Fig. 20 and Fig. 22 leads.

[0087] In Fig. 18 and Fig. 20. The temperature / current measurements establish a subcooled state for an extended period. As in Fig. Figure 20 shows that the measurements were recorded from an experiment carried out with nickel, 4N5 (99.995%) purity, as shown in Figure 20. Fig. Figure 18 shows measurements recorded from an experiment in which carbon was added at a rate of 0.5 wt.%. The in Fig. The experimental setup used in 18 included a water-cooled aluminum heat sink in thermal contact with the base of the primary receiving device, as shown in Fig. Figure 4 shows the dotted vertical lines in the temperature graph indicating times when the current to the coil decreases. Similarly, dashed lines indicate the increase in the current to the coil. The current graph in Fig. Figure 18 only shows the current during cooling to provide higher resolution. The current during heating was held at 360–365 A and regulated only to maintain a consistent temperature of the superheated melt from cycle to cycle. As shown in Fig. As can be seen in Figure 18, increasing the coil current during cooling allows the melt to reach lower levels of subcooling before recalescence, and ultimately the current is high enough to completely prevent recalescence. Further increases in current beyond this minimum critical current raise the minimum temperature reached during the cooling step, as more energy is transferred to the melt. Fig. Article 19B illustrates this conflict of objectives.

[0088] Fig. 19A indicates the period the molten metal remains in a supercooled state during each cooling step. Note that a higher current allows for a longer period of supercooling. Note that the maximum time in each supercooling step has been limited to 90 seconds, which is why the trend in Fig. 19A is stagnating.

[0089] A system comprising pure nickel, which behaves qualitatively differently than nickel with added carbon. To demonstrate the significant effect of the crystallization suppression provided by the induced electric currents, comparisons were made with nucleation rates at various temperatures for pure nickel, as found according to the prior art. For pure nickel and returning to Fig. 20. At temperatures approximately 300 K below the melting point of nickel, homogeneous nucleation is expected. In reactor environments of embodiments 1 and 4, heterogeneous nucleation is expected at temperatures far below this level, and the fact that the specified level of subcooling was achieved without any measures other than a reduction environment is considered remarkable. Nevertheless, it is conventionally assumed that a single nucleation event is sufficient to trigger the crystallization of an entire sample; that is, the probability of crystallization scales with the volume / mass of the sample.

[0090] Referring to Fig. Figure 21 shows the period marked with a dashed line before homogeneous nucleation is expected for a sample of a certain mass at any given temperature, as suggested by published prior art data. As indicated by the solid line, the observed nucleation rates are significantly lower for a 0.45 g nickel sample. Interestingly, the deviation from expected rates is greater for a smaller sample. This observation is attributed to the penetration depth of the electromagnetic field and the corresponding spatial distribution of the induced electric currents. Using the same field frequency for different sample sizes, the proportion of the sample exposed to the electric currents is greater for a smaller sample.Since the induced electric currents are assumed to be the main factor in the suppression of crystallization, this explains why the deviation from expected behavior is greater for smaller samples.

[0091] Data from other experiments conducted on a system including iron and carbon can be incorporated into Fig. 22, Fig. 23A and Fig. 23B can be read. The same effect of a minimum critical current to achieve a maximum stable level of subcooling as in Fig. 18, Fig. 19A and Fig. The 19B process for nickel plus carbon is also noticeable here. Therefore, the process is not specific to nickel, but is also applicable to other systems.

[0092] Data from an experiment with nickel using direct current can be found in Fig. Figure 24 can be read. Two cooling cycles are shown in the temperature-versus-time and current-versus-time graphs. This behavior differs significantly from the data collected using the induction coil. For example, there is a notable thermal standstill in both cooling curves, indicating partial normal solidification. However, it is important to note that after this thermal standstill, if the current through the sample is completely switched off or reduced, a notable spike occurs in the temperature measurements, providing evidence for the solidification of a supercooled melt. This provides conceptual proof that at least a portion of the sample was held in a subliquid state by the applied currents.

[0093] The main scientific and expected difference between the DC and induction setups is that the current density in the latter should be uniform throughout the metal, since there are no frequency or penetration depth problems with direct current. This is an advantage of the DC setup, as the current itself reaches the center of the sample. The disadvantage is that the electrodes in contact with the melt introduce potent nucleation sites, which a glassy quartz tube does not, at least not to the same extent. One interpretation of the temperature diagrams is that some of the metal actually solidifies, as is usually indicated by the thermal standstill. However, the observed recalescence in the diagrams suggests that some of the liquid may still remain supercooled.

[0094] From an engineer's perspective, there is also a problem with heat transfer that must be considered. Regardless of the electrode material chosen—graphite in this case—it will not only be a good electrical conductor but also a good thermal conductor. Therefore, with the relatively small dimensions tested to date, significant thermal gradients occur.

[0095] Furthermore, experimental evidence suggests that the sample's ability to supercool is sensitive to both the integrity of the quartz crucible and the amount of oxides present in the sample. If the quartz tube fractures and releases quartz grains into the melt, supercooling is difficult to achieve. The role of oxides in catalyzing nucleation is well known in the art. A common mitigation practice for this problem is to employ some type of getter system, a component that removes trace impurities, such as oxygen from a gas stream, to ensure a very low partial pressure of oxygen in the reactor. Alloy blocks are also typically pickled with acids to remove surface oxides present within the alloy blocks. Instead, a reducing agent in the form of carbon, e.g.,Graphite is introduced into the reactor, or hydrogen is added to the purification gas. The experimental procedure begins with a soaking time of up to 30 minutes at a temperature above the metal's melting point to ensure homogeneous distribution of any added carbon and the reduction of most of the oxides present.

[0096] Finally, if a metal is allowed to crystallize when exposed to an electromagnetic field, the crystal structure can be manipulated, for example, the crystal size or crystal orientation. Fig. 25A An XRD pattern from a scan taken on the surface of a treated metal sample reveals directional solidification, as evidenced by the absence of (1,1,1) and (2,2,2) diffraction peaks of nickel. As in Fig. As shown in Figure 25B, these peaks often appear when scanning a powder ground from the same sample. Therefore, the field aligns the crystal structure during solidification. Such manipulation can lead to improved properties, such as electrical and thermal conductivity.

[0097] As in Fig. As seen in Figure 26, a sample was allowed to solidify under significant supercooling without an applied current. In this case, the current to the coil sample was switched off, resulting in immediate solidification, as evidenced by the recalescence of the sample, as can be seen through the tip. As described above, the application of an electromagnetic current significantly removes or delays the onset of recalescence.

[0098] Referring to the photos from Fig. 27 and Fig. Figure 28 shows the upper parts of the samples in which a field was not applied and in which a field was applied as shown. The main distinguishing feature is that by completely interrupting the field, the pinching effect on the metal, exerted by Lorentz forces on the induced current, is eliminated. As a consequence of this, and as shown in Fig. As shown in Figure 27, the sample begins to collapse under gravity and crystallization occurs before the surface has given way and the jagged appearance on the top of the sample is visible. Fig. 27 compared to the smooth surface in Fig. 28 is represented.

[0099] Referring to Fig. 29, and the graphical XRD representation of a NiNb sample is shown, indicating a remarkable amorphous phase in the material, as suggested by the amorphous bulging at low 2θ angles. This amorphous phase was achieved using the apparatus from Fig. 4, in which the molten sample was cooled to ambient temperature in its supercooled state. The result is that at least part of the sample has amorphous phase properties.

[0100] Referring to Fig. Figure 30 also presents a graphical XRD representation of a NiP sample, indicating a remarkable amorphous phase in the material, as suggested by the amorphous bulging at low 2theta angles. This amorphous phase was achieved using the apparatus from Fig.4, in which the molten sample was cooled to ambient temperature in its supercooled state. The result is that at least part of the sample exhibits amorphous phase properties.

[0101] In short, the result is the same for both samples, as a remarkable amorphous phase exists to allow the molten metal to cool while simultaneously providing sufficient energy to prevent crystallization during undercooling, with the undercooled material being cooled to ambient temperatures to achieve an amorphous metal at room temperature.

[0102] In summary, the results demonstrate the ability to cool a melt in a controlled manner to significant levels of undercooling without crystallization, as evidenced by the absence of both thermal stagnation and recalescence. Furthermore, XRD analysis of various samples reveals the presence of an amorphous phase at room temperature. If a sufficiently strong electromagnetic field can be applied during the cooling of a suitable material to bring it to its glass transition temperature, then four of the main problems in the production of glassy metals are solved: 1) the ability to produce amorphous metals in a "dirty" reactor containing numerous nucleation sites, 2) the ability to produce amorphous metals without requiring rapid quenching, and 3) the ability to increase the size of the produced glassy metal since quenching is not necessary.In addition to these three problems 4), it is likely that this method will allow a much greater variety of compositions of the glassy metals to be produced, including pure metals such as those used in the previous experiments.

[0103] Even if the strongest available fields are insufficient to achieve the glass transition temperature for any given metal system using this method alone, combining this method with known methods will lower the limit of the amount of heat that must be removed by quenching. Therefore, the three problems mentioned above will at least be mitigated by combining this method with prior art processes for the production of glassy metals.

[0104] Repeated experiments have demonstrated the ability to subcool a system comprising nickel, nickel plus small amounts of carbon, iron plus carbon, pure cobalt, and pure copper, respectively, by controlling the amount of energy injected into the melt. This opens the door to the production of glassy metals from far more starting metals and metal alloys than currently thought possible. The presented data were derived using the metal in contact with quartz crucibles, meaning that the environment offers a multitude of potential nucleation sites. Previous efforts to produce amorphous metals often require much more complex reactors that attempt to limit or eliminate these heterogeneous nucleation sites.Finally, the possibility of maintaining a metal in a thermally stable state at significantly subcooled temperatures further points to the possibility of controlling the processing of glassy metals.

[0105] The use of electromagnetic fields during cooling appears to be the main factor in suppressing normal solidification and recalescence. The current hypothesis is that the anisotropy of a supercooled melt with small solid clusters preferentially absorbs the energy from the applied EM field at the solid / liquid surface, melting the formed clusters.

[0106] Although current efforts use an induction coil to expose the molten metal to an electromagnetic field, applying a current directly to the material has produced qualitatively the same effect of suppressing crystallization. Such direct coupling would significantly increase the ability to form glassy metals into any desired shape, e.g., rolled sheets, rods, beams, and other geometric forms.

[0107] Although the present invention has been described in connection with the preferred embodiments shown in the various figures, it should be understood that other similar embodiments may be used, or modifications or additions may be made to the described embodiment to perform the same function of the present invention without departing from it. Therefore, the present invention should not be limited to a single embodiment, but should correspond in its scope and protection to the list of claims set forth in the appended patent claims.

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