JP2016028834A - Formation of metallic glass by rapid capacitor discharge forging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means for shaping an amorphous material using rapid capacitor discharge heating (RCDF).SOLUTION: The present invention provides a forging apparatus and method for uniformly heating, rheologically softening, and thermoplastically rapidly forming into a net shape a metallic glass using a rapid capacitor discharge forming (RCDF) tool. The RCDF method utilizes the discharge of electrical energy stored in a capacitor to uniformly and rapidly heat a sample or charge of a metallic glass alloy to a predetermined "process temperature" between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy in a time scale of several milliseconds or less. Once the sample is uniformly heated such that the entire sample block has a sufficiently low process viscosity, the sample may be shaped into high quality amorphous bulk articles via forging in a time frame of less than 1 second.SELECTED DRAWING: Figure 1

Description

  The present invention relates generally to a novel method of forming metallic glass, and more particularly to a method of forming metallic glass using rapid capacitor discharge heating.

  Amorphous materials are a new class of engineering materials that have a unique combination of high strength, elasticity, corrosion resistance and workability from the molten state. Amorphous materials differ from conventional crystal alloys in that these atomic structures do not have the long-range order pattern typical of atomic structures in conventional crystal alloys. Amorphous materials generally cool the molten alloy at a “sufficiently rapid” cooling rate from a temperature above the melting temperature (or thermodynamic melting temperature) of the crystalline phase to a temperature below the “glass transition temperature” of the amorphous phase. As a result, nucleation and growth of alloy crystals are avoided. That is, amorphous alloy processing methods have always been interested in quantifying a “sufficiently rapid cooling rate”, also called “critical cooling rate”, to ensure the formation of an amorphous phase.

The “critical cooling rate” for the initial amorphous material was very fast, approximately 10 ⁶ ° C./sec. For this reason, conventional casting processes are not suitable for such high cooling rates, and special casting processes such as melt spinning and plane flow casting have been developed. Due to the substantially rapid crystallization kinetics of these early alloys, an extremely short time (approximately 10 ^-3 seconds or less) to remove heat from the molten alloy to avoid crystallization. Therefore, early amorphous alloys were also limited in the size of at least one dimension. For example, very thin foils and ribbons (thickness approximately 25 microns) have been successfully produced using these conventional techniques. The critical cooling rate requirements for these amorphous alloys severely limited the size of parts made from amorphous alloys, limiting the use of early amorphous alloys as bulk bodies and products.

  For many years, it was determined that the “critical cooling rate” was strongly dependent on the chemical composition of the amorphous alloy. Therefore, much research has focused on the development of new alloy compositions with much lower critical cooling rates. Examples of these alloys are shown in US Pat. No. 5,288,344, US Pat. No. 5,368,659, US Pat. No. 5,618,359, and US Pat. No. 5,735,975. And each of these patents is incorporated herein by reference. These amorphous alloy systems, also called bulk metallic glass or BMG, are characterized by a low critical cooling rate of a few degrees C / second, which processes bulk amorphous phase objects that are much larger than previously achievable And make it possible to form.

  While low “critical cooling rate” BMGs have become available, it has become possible to apply conventional casting processes to form bulk products having an amorphous phase. Over the past few years, LiquidMetal Technologies, Inc. Several companies, including, are working to develop commercial production technologies for the production of net-shaped metal parts made by BMG. For example, manufacturing methods such as permanent mold metal die casting and injection casting into heated molds are currently used in standard consumer electronic devices (eg, mobile phones and handheld wireless devices), hinges, fasteners, medical equipment, and other It is used to manufacture commercial hardware and components such as electronic component cases for value-added products. However, even if bulk solidified amorphous alloys provide some remedy for the fundamental drawbacks of solidification casting, especially for die casting and permanent casting processes, as described above, there are still problems to be addressed. . First of all, there is a need to make these bulk bodies from a wider range of alloy compositions. For example, currently available BMGs with large critical casting dimensions that can produce large bulk amorphous bodies include Zr-based alloys plus Ti, Ni, Cu, Al and Be and Ni, Cu, and P Limited to several groups of alloy compositions based on a very narrow selection of metals, including Pd-based alloys, which are not necessarily optimal from an engineering or cost standpoint.

  In addition, current processing techniques require fairly expensive machinery to ensure that appropriate processing conditions are generated. For example, most molding processes involve high vacuum or controlled inert gas environments, induction melting of materials into crucibles, casting metal into shot sleeves, and more sophisticated mold assembly games via shot sleeves. Require pneumatic injection into the cavity and cavity. These modified die casting machines can cost hundreds of thousands of dollars per machine. In addition, since BMG heating has been achieved by these conventional slow heat treatments, prior art processing and formation of bulk solidified amorphous alloys always reduces the glass transition temperature from above the thermodynamic melting temperature. Emphasis was placed on cooling the molten alloy to below temperatures. This cooling is achieved using either a single-step monotonous cooling operation or a multi-step process. For example, molds (made of copper, steel, tungsten, molybdenum, their composites, or other highly conductive materials) at ambient temperature can be used to easily and efficiently handle heat removal from molten alloys Is done. Because “critical casting dimensions” correlate with critical cooling rates, these conventional processes are not suitable for forming larger bulk bodies and products of a wider range of bulk solidified amorphous alloys. In addition, in many cases, the molten alloy is injected into the die at high speeds and pressures to ensure that sufficient alloy material is introduced into the die prior to alloy solidification, especially in the manufacture of complex and high precision parts. There is a need. Since metal is fed to the die at high speed under high pressure, such as in high pressure die casting, the molten metal flow tends to be Rayleigh Taylor instability. This flow instability is characterized by a high Weber number and is associated with flow head decomposition causing the formation of protruding seams and cells, which manifest as superficial and structural micro-defects in the cast part. Also, when non-vitrified liquid is trapped within a solid shell of vitrified metal, it tends to form shrinkage cavities or pores along the centerline of the die casting mold.

Attempts to remedy the problems associated with rapidly cooling materials from temperatures above the equilibrium melting point to temperatures below the glass transition have largely affected the dynamic stability and viscous flow characteristics of supercooled liquids. Emphasis was placed on use. Several, including heating the glass raw material above the glass transition where the glass relaxes to a viscous supercooled liquid, pressurizing to form a supercooled liquid, and then cooling below the glass transition before crystallization A method has been proposed. These attractive methods are essentially similar to the methods used to process plastics. However, in contrast to plastics that remain stable to crystallization over the softening transition for a very long period of time, metal supercooled liquids crystallize fairly rapidly when relaxed at the glass transition. Therefore, when the metal glass is heated at a conventional heating rate (20 ° C./min), the temperature range stable against crystallization is considerably small (50 to 100 ° C. higher than the glass transition), The liquid viscosity within the range is quite high (10 ⁹ -10 ⁷ Pa s). As a result of these high viscosities, the pressures required to form these liquids into the desired shape are very high and can exceed the pressures achievable with conventional high strength tools (<1 GPa) in many metallic glass alloys There is sex. In recent years, metallic glass alloys have been developed that are stable to crystallization when heated at conventional heating rates to considerably higher temperatures (165 ° C. above the glass transition). Examples of these alloys are described in U.S. Patent Application No. 20080135138 and G.S. Duan et al. (Advanced Materials, 19 (2007) 4272) and A.M. Shown in a paper by Wiest (Acta Materialia, 56 (2008) 2525-2630), each of which is incorporated herein by reference. As a result of their high stability to crystallization, processing viscosities as low as 10 ⁵ Pa-s become available, which means that these alloys are in a supercooled liquid state than conventional metallic glasses. It suggests that it is more suitable for processing. However, these viscosities are substantially higher than the processing viscosities of plastics, typically in the range of 10 to 1000 Pa-s. In order to achieve such low viscosities, metallic glass alloys can be heated to the typical values used for thermoplastic processing when heated by conventional heat treatment or by extending the temperature range of stability. In any case where it is heated at an unprecedented high heating rate that will reduce the processing viscosity, it should exhibit even greater stability to crystallization.

  Several attempts have been made to provide a method to instantaneously heat the BMG to a temperature sufficient for molding, thereby avoiding many of the problems discussed above, while at the same time expanding the types of formable amorphous materials. Yes. For example, U.S. Pat. No. 4,115,682 and U.S. Pat. No. 5,005,456; R. Yavarii (Materials Research Society Symposium Proceedings, 644 (2001) L12-20-1, Materials Science & Engineering A, 375-377 (2004) 227-234, and Applied Physics 160 1602) Each of these disclosures is incorporated herein by reference, all of which utilize the inherent conductive properties of amorphous materials to instantaneously heat the material to the molding temperature using Joule heating. However, so far these techniques have only been applied to local heating of the BMG sample to allow only local formation such as joining of such elements (ie spot welding) or formation of surface properties. Emphasis has been placed. None of these prior art methods teach how to uniformly heat the entire BMG sample volume so that a wide range of formation can be performed. Instead, all these prior art methods predict temperature gradients during heating and consider how these gradients affect local formation. For example, Yavari et al. (Materials Research Society Symposium Proceedings, 644 (2001) L12-20-1) describes: “The external surface of a BGM sample that is in contact with the electrode or in contact with the surrounding (inert) gas in the forming chamber allows the heat generated by the current to be dissipated from the sample by conduction, convection or radiation. On the other hand, the outer surface of the sample heated by conduction, convection or radiation is slightly hotter than the inside, because the crystallization and / or oxidation of the metallic glass is first Since it begins on the outer surface and interface, it is an important advantage for the method of the present invention, and if these are slightly below the bulk temperature, such undesirable surface crystal formation can be more easily avoided. "

  Another drawback of BGM's limited stability to crystallization above the glass transition is to measure thermodynamic and transport properties such as heat capacity and viscosity over the temperature range of a metastable supercooled liquid. It is not possible. Typical measuring instruments such as differential scanning calorimeters, thermomechanical analyzers, and Couette viscometers rely on conventional heating equipment such as electric and induction heaters, and thus the sample heating rate that has been considered conventionally (Typically <100 ° C./min) can be achieved. As discussed above, the metal supercooled liquid can be stable to crystallization over a limited temperature range when heated at conventional heating rates, and thus has measurable thermodynamic properties and Transport properties are limited to within the available temperature range. As a result, unlike polymers and organic liquids that are extremely stable to crystallization and whose thermodynamic and transport properties can be measured over the entire metastable range, the properties of metal supercooled liquids are: It can only be measured within a narrow temperature range just above the glass transition and just below the melting point.

US Pat. No. 5,288,344 US Pat. No. 5,368,659 US Pat. No. 5,618,359 US Pat. No. 5,735,975 US Patent Application No. 200801135138 US Pat. No. 4,115,682 US Pat. No. 5,005,456

Advanced Materials, 19 (2007) 4272 Acta Materialia, 56 (2008) 2525-2630 Materials Research Society Symposium Proceedings, 644 (2001) L12-20-1 Materials Science & Engineering A, 375-377 (2004) 227-234 Applied Physics Letters, 81 (9) (2002) 1606-1608)

  Therefore, there is a need to find a new technique that instantaneously and uniformly heats the entire BMG sample volume and enables a wide range of forming of amorphous metal. In addition, from a scientific point of view, there is also a need to find new ways to measure these using the thermodynamic and transport properties of metal supercooled liquids.

  In view of the foregoing, in accordance with the present invention, a method and apparatus for forming an amorphous material using rapid capacitor discharge heating (RCDF) is provided.

  In one embodiment, the present invention relates to a method for rapidly heating and shaping amorphous material using a rapid capacitor discharge, wherein the electrical energy quanta is uniform throughout a substantially defect-free sample having a substantially uniform cross-section. The entire sample is rapidly and uniformly heated up to a processing temperature between the glass transition temperature of the amorphous phase and the equilibrium melting temperature of the alloy, and the discharge is interrupted via at least two forging plates. And the heated sample is molded into an amorphous product while the heated sample is still at a temperature between the glass transition temperature and the equilibrium melting point of the amorphous material. In one such embodiment, the sample is heated to the processing temperature, preferably at a rate of at least 500 K / sec. In another such embodiment, the molding step uses conventional forming techniques such as, for example, injection molding, dynamic forging, stamp forging and blow molding.

In another embodiment, an amorphous material having a relative change in resistivity per unit of temperature change (S) of about 1 × 10 ⁻⁴ ° C. ⁻¹ is selected. In one such embodiment, the amorphous material is an alloy based on an elemental metal selected from the group consisting of Zr, Pd, Pt, Au, Fe, Co, Ti, Al, Mg, Ni, and Cu.

  In yet another embodiment, electrical energy quanta are discharged into the sample through at least two electrodes connected to the ends of the sample so that electrical energy is uniformly introduced into the sample. In one such embodiment, the method uses an electrical energy quantum of at least 100 joules.

In yet another embodiment, the processing temperature is approximately between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy. In one such embodiment, the processing temperature is at least 200K above the glass transition temperature of the amorphous material. In one such embodiment, the processing temperature is such that the viscosity of the heated amorphous material is about 1 to 10 ⁴ Pas-sec.

  In yet another embodiment, the forming pressure used to mold the sample is controlled to deform the sample at a sufficiently slow rate to avoid high Weber number flow.

  In yet another embodiment, the deformation rate used to mold the sample is controlled to deform the sample at a sufficiently slow rate to avoid high Weber number flow.

  In yet another embodiment, the initial amorphous metal sample (raw material) can be any shape having a uniform cross section, such as, for example, a cylinder, a sheet, a square and a rectangular solid.

  In yet another embodiment, the contact surface of the amorphous metal sample is cut parallel and polished flat to ensure good contact with the electrode contact surface.

  In yet another embodiment, the forged plate is either non-conductive or conductive.

In yet another embodiment, the application of molding force is
t _Fi > τ _RC and t _F0 <τ _C
And starts at time t _Fi and ends at time t _F0 , where (τ _RC ) is the RC time constant of the discharge and (τ _C ) is the time for the metallic glass to crystallize at the processing temperature.

  In yet another embodiment, the present invention relates to a rapid capacitor discharge apparatus for molding an amorphous material. In one such embodiment, the sample of amorphous material has a substantially uniform cross section. In another such embodiment, the at least two electrodes connect the electrical energy source to the sample of amorphous material. In such an embodiment, the electrode is attached to the sample such that a substantially uniform connection is formed between the electrode and the sample. In yet another such embodiment, the electromagnetic skin depth of the dynamic electric field is large compared to the charge radius, width, thickness and length. In yet another such embodiment, a forging tool is provided, the forging tool being in signal communication with at least two forging plates arranged in a formable relationship with the sample described above, an electrical energy source and the forging tool. The electrical energy source is sufficient to uniformly heat the entire sample to a processing temperature between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy. The forging tool described above can apply sufficient deformation force to form the heated sample described above into a net shape product, and the timing circuit can Detect the discharge, activate the forging tool and apply the deformation force to the heated sample mentioned above via at least two forging plates Add.

  In yet another embodiment, the electrode material comprises low yield strength and high electrical conductivity and heat, such as, for example, copper, silver or nickel, or an alloy formed to contain at least 95% copper, silver or nickel. It is selected to be a conductive metal.

In yet another embodiment, the timing circuit is configured to apply force simultaneously with or after the discharge of electrical energy. In another such embodiment, the application of molding force is
t _Fi > τ _RC and t _F0 <τ _C
And starts at time t _Fi and ends at time t _F0 , where (τ _RC ) is the RC time constant of the discharge and (τ _C ) is the temperature at which the metallic glass crystallizes at the processing temperature.

  In yet another embodiment, the “sitting” pressure causes the electrode contact surface to plastically deform at the electrode / sample interface such that the contact surface conforms to the microscopic features of the sample contact surface. Between the electrode and the initial amorphous sample.

  In yet another embodiment, the low current “sitting” electrical pulse locally softens any non-contact areas of the amorphous sample at the electrode contact surface, thus making the contact surface a microscopic view of the electrode contact surface. Applied between the electrode and the initial amorphous sample to conform to the characteristic features.

  In yet another embodiment of the apparatus, the electrical energy source uniformly heats the entire sample to a processing temperature between the glass transition temperature of the amorphous phase and the equilibrium melting temperature of the alloy at a rate of at least 500 K / sec. It is possible to generate sufficient electric energy quanta. In such an embodiment of the apparatus, the electrical energy source is at a rate such that the sample is adiabatically heated to avoid heat transport and the generation of thermal gradients and thus facilitate uniform heating of the sample. Or in other words, discharged at a rate much higher than the thermal relaxation rate of the amorphous metal sample.

  In yet another embodiment of the apparatus, the forged plate is either conductive or non-conductive.

  In yet another embodiment of the device, a pneumatic or magnetic drive system is provided for applying a deformation force to the sample. In such a system, the deformation force or deformation rate can be controlled so that the heated amorphous material is deformed at a sufficiently slow rate to avoid high Weber number flow.

  In yet another embodiment of the apparatus, the forming tool further comprises a heating element for heating the tool to a temperature preferably around the glass transition temperature of the amorphous material. In such embodiments, the surface of the formed liquid is cooled more slowly, thus improving the surface finish of the formed product.

  The specification is more fully understood with reference to the following figures and data graphs, which are presented as exemplary embodiments of the invention and should not be construed as a full citation of the scope of the invention. Absent.

FIG. 3 shows a flow chart of an exemplary rapid capacitor discharge formation method according to the present invention. FIG. 4 shows a schematic diagram of an exemplary embodiment of a rapid capacitor discharge formation method according to the present invention. FIG. 6 shows a schematic diagram of another exemplary embodiment of a rapid capacitor discharge formation method according to the present invention. FIG. 6 shows a schematic diagram of yet another exemplary embodiment of a rapid capacitor discharge formation method according to the present invention. FIG. 6 shows a schematic diagram of yet another exemplary embodiment of a rapid capacitor discharge formation method according to the present invention. FIG. 6 shows a schematic diagram of yet another exemplary embodiment of a rapid capacitor discharge formation method according to the present invention. FIG. 4 shows a schematic diagram of an exemplary embodiment of a rapid capacitor discharge formation method in combination with a thermal imaging camera according to the present invention. FIG. 4 shows a photographic image of experimental results obtained using an exemplary rapid capacitor discharge formation method according to the present invention. FIG. 4 shows a photographic image of experimental results obtained using an exemplary rapid capacitor discharge formation method according to the present invention. FIG. 4 shows a photographic image of experimental results obtained using an exemplary rapid capacitor discharge formation method according to the present invention. FIG. 4 shows a photographic image of experimental results obtained using an exemplary rapid capacitor discharge formation method according to the present invention. FIG. 4 shows a photographic image of experimental results obtained using an exemplary rapid capacitor discharge formation method according to the present invention. FIG. 5 shows a data plot summarizing experimental results obtained using an exemplary rapid capacitor discharge formation method according to the present invention. FIG. 2 shows a schematic diagram of an exemplary rapid capacitor discharge device according to the present invention. FIG. 2 shows a schematic diagram of an exemplary rapid capacitor discharge device according to the present invention. FIG. 2 shows a schematic diagram of an exemplary rapid capacitor discharge device according to the present invention. FIG. 2 shows a schematic diagram of an exemplary rapid capacitor discharge device according to the present invention. FIG. 2 shows a schematic diagram of an exemplary rapid capacitor discharge device according to the present invention. FIG. 11b is a photographic image of a molded product made using the apparatus shown in FIGS. 11a to 11e. FIG. 11b is a photographic image of a molded product made using the apparatus shown in FIGS. 11a to 11e. Is a diagram illustrating a 5mm images of the rod of Zr ₃₅ Ti ₃₀ Cu _8.25 Be _26.75 amorphous used as the starting material for these experiments. FIG. 15b shows an image of a plate forged between two MACOR dies from the rod of FIG. 15a to a thickness of 0.45 mm. 1 is a schematic diagram of an RCDF forging device according to an embodiment of the present invention. FIG. FIG. 6 shows a schematic diagram of an RCDF forging device according to another embodiment of the present invention. Diameter is a diagram showing an image of a raw material rod of 5mm of Zr ₃₅ Ti ₃₀ Cu _8.25 Be _26.75 of metallic glass. It is a figure which shows the image of the rod after forging was performed. It is a figure which shows the image of the forge screw which removed the waste material. It is a figure which shows the image of the screw | thread from which flashing was removed by grinding. It is a figure which shows the 100 time expansion SEM image of the outline of a stainless steel forging die. It is a figure which shows the 100 time expansion SEM image of the outline of the 10-32 screw | thread of commercial stainless steel. Is a diagram showing a 100 times magnified SEM image of the contour of the metallic glass made with forging process _{(Zr 35 Ti 30 Cu 8.25 Be} 26.75) of the present invention.

  The present invention uses a Joule heating extrusion or mold tool to rapidly and uniformly heat a metallic glass (typically with a processing time of less than 1 second), rheologically soften, and thermoplastically The present invention relates to a method for forming a net shape product. More specifically, the method utilizes a discharge of electrical energy stored in a capacitor (typically 100 Joules to 100 K Joules), and the glass transition temperature of the amorphous material on a time scale of a few milliseconds or less. The sample or charge (required amount) of the metallic glass alloy is uniformly and rapidly heated to a predetermined “processing temperature” approximately between the alloy and the equilibrium melting point of the alloy, which in the following is referred to as rapid capacitor discharge formation (RCDF). ). The RCDF process of the present invention has a relatively low electrical resistivity because the metallic glass is a frozen liquid, so that the material is heated at a rate such that the sample is adiabatically heated by appropriately applying an electrical discharge. Proceed from the observation that high dissipation can be achieved and efficient and uniform heating can be achieved.

  By rapidly and uniformly heating the BMG, the RCDF method extends the stability of the supercooled liquid to crystallization to a temperature substantially above the glass transition temperature, which makes the entire sample volume optimal for formation To a state associated with a high processing viscosity. The RCDF process can also take advantage of the entire viscosity range provided by the metastable supercooled liquid, which range is no longer limited by the formation of a stable crystalline phase. In summary, this process improves the quality of formed parts, increases the yield of usable parts, reduces materials and processing costs, expands the range of usable BMG materials, improves energy efficiency, and Enables reduction of capital costs. In addition, as a result of the instantaneous uniform heating that can be achieved with the RCDF method, thermodynamic and transport properties over the entire range of liquid metastability become available for measurement. Thus, by incorporating additional standard equipment such as temperature and strain measurement equipment into the rapid capacitor discharge device, properties such as viscosity, heat capacity and enthalpy can be measured over the entire temperature range between the glass transition and melting point. it can.

A simple flow chart of the RCDF technique of the present invention is shown in FIG. As shown, the process begins with the discharge of electrical energy (typically 100 Joules to 100 K Joules) stored in a capacitor into a sample block or charge of a metallic glass alloy. According to the present invention, the application of electrical energy is used to reach a predetermined “working temperature” that exceeds the glass transition temperature of the alloy, more specifically, the glass transition temperature of the amorphous material and the equilibrium melting point (Tg of the alloy). The sample can be heated rapidly and uniformly on a time scale from a few microseconds to a few milliseconds or less, to a processing temperature of approximately between 200 and 300 K). It has sufficient processing viscosity (˜1 to 10 ⁴ Pas-s or less) possible to facilitate.

Once the sample is heated uniformly and the entire sample block has a sufficiently low processing viscosity, the sample is high quality by any number of techniques including, for example, injection molding, dynamic forging, stamp forging, blow molding, etc. Can be formed into amorphous bulk products. However, the ability to shape a metallic glass charge is entirely dependent on ensuring that heating of this charge is rapid and uniform throughout the sample block. If uniform heating is not achieved, the sample will instead undergo local heating, such as joining the elements together or spot welding together, or a specific area of the sample. Although it may be useful for some techniques, such as shaping, such local heating is neither used nor can it be used to perform bulk molding of the sample. Similarly, if the sample heating is not rapid enough (typically around 500 to 10 ⁵ K / s), the material formed will lose its amorphous properties, or the molding technique will have excellent processability. Will be limited to those amorphous materials having the following characteristics (ie, high stability of the supercooled liquid to crystallization), which again reduces the usefulness of the process.

The RCDF method of the present invention ensures rapid and uniform heating of the sample. However, to understand the criteria necessary to obtain rapid and uniform heating of metallic glass samples using RCDF, it is first necessary to understand how Joule heating of metallic materials occurs It is. The temperature dependence of the electrical resistivity of a metal can be quantified with respect to the relative change in resistivity per unit of temperature change coefficient S, where S is defined as:
S = (1 / ρ ₀ ) [dρ (T) / dT] _T0 (Formula 1)
Where S is the unit of (1 / ° C.), ρ ₀ is the resistivity (ohm cm) of the metal at room temperature T ₀ , and [dρ / dT] _T0 is the room temperature taken to be a straight line. It is the temperature derivative of resistivity (ohm cm / C). A typical amorphous material has a large ρ ₀ (80 μΩcm <ρ ₀ <300 μΩcm), but is very small (and often negative) with S (−1 × 10 ⁻⁴ <S <+ 1 × 10 ⁻⁴ ). ) Value.

For this small S value found in amorphous alloys, a sample of uniform cross-section subjected to a uniform current density is resistively heated spatially and uniformly, and the sample is rapidly from ambient temperature T ₀ to final temperature T _F. Heated, this is the formula:
E = 1 / 2CV ² (Formula 2)
And depending on the total energy of the capacitor as indicated by the total heat capacity C _S (in joules / C) of the sample charge. _TF will be given by:
T _F = T ₀ + E / C _S (Formula 3)
Next, the heating time is determined by the time constant τ _RC = RC of capacitive discharge. Here, R is the total resistance of the sample (plus output resistance of the capacity discharge circuit). Therefore, theoretically, the typical heating rate of metallic glass can be expressed by the following equation.
dT / dt = (T _F −T ₀ ) / τ _RC (Formula 4)

In contrast, common crystalline metals have much lower values of ρ ₀ (1-30 μΩ-cm) and much higher S (˜0.01-0.1). This leads to large differences in behavior. For example, for common crystalline metals such as copper alloys, aluminum, or steel alloys, ρ ₀ is much smaller (1-20 μΩcm), but S is much larger, typically S is 0.01 ~ 0.1. A smaller ρ ₀ value in crystalline metal leads to a smaller dissipation in the sample (compared to the electrode), degrading the efficiency of capacitor energy coupling to the sample. Furthermore, when the crystalline metal melts, ρ (T) generally increases more than twice, and transitions from a solid metal to a molten metal. A large S value accompanying an increase in resistivity at the time of melting of a general crystalline metal leads to extremely nonuniform resistance heating at a uniform current density. The crystal sample will typically melt locally near the high voltage electrode or other interface within the sample. Second, the capacitor discharge of energy through the crystal rod leads to spatial locality and local melting of heating wherever the initial resistance was maximum (typically at the interface). In practice, this is based on capacitive discharge welding of crystalline metal (spot welding, bump welding, “stud welding”, etc.), where the local molten pool is to be welded to the electrode / sample interface or weld. Generated near other internal interfaces in the part.

As discussed in “Background”, prior art systems also recognize the inherent conductivity of amorphous materials, but have not been recognized to date to ensure uniform heating of the entire sample, It is also necessary to avoid the dynamic occurrence of spatial non-uniformity in energy dissipation within the heated sample. The RCDF method of the present invention describes two criteria that need to be adapted to prevent the occurrence of such non-uniformities and ensure uniform heating of the charge.
• Current uniformity within the sample. · Sample stability against the occurrence of power loss non-uniformity during dynamic heating.

Although these criteria appear to be relatively simple, they are at the interface between the electrode used to introduce the charge, the material used for the sample, the material used for the sample, the shape of the sample, and the sample itself. It imposes some physical and technical constraints on it. For example, the following requirements exist for a cylindrical charge of length L and area A = πR ² (R = sample radius).

Current uniformity within the cylinder during capacitive discharge requires that the electromagnetic skin depth Λ of the dynamic electric field be large compared to the relevant dimensional characteristics (radius, length, width or thickness) of the sample. . In the cylindrical embodiment, the relevant characteristic dimensions are obviously the charge radius R and depth L. This condition is satisfied when Λ = [ρ ₀ τ / μ ₀ ] ^1/2 > R, L. Here, τ is the “RC” time constant of the capacitor and sample system, and μ ₀ = 4π × 10 ⁻⁷ (Henry / m) is the permittivity of free space. If R and L are ˜1 cm, this represents τ> 10-100 μsec. Using the typical dimensions of the subject and the resistivity value of the amorphous alloy, this requires a suitably sized capacitor, typically a capacitance of 10,000 μF or more.

The stability of the sample against the occurrence of inhomogeneities in power loss during dynamic heating should be understood by performing a stability analysis that includes ohmic “joule” heating with current and heat flow controlled by the Fourier equation Can do. In samples with resistivity that increases with temperature (ie, positive S), local temperature changes along the axis of the sample cylinder can increase local heating and further increase local resistance and heat dissipation. become. At a sufficiently high power input, this leads to “localization” of the heating along the cylinder. In crystalline materials this results in local melting. This behavior is useful in welding when it is desired to create local melting along the interface between the components, but is highly undesirable when it is desired to heat the amorphous material uniformly. The present invention provides an important criterion for ensuring uniform heating. Using S as defined above, the inventors reveal that the heating is uniform in the following cases.
S <(2π) ² DC _S / L ² I ² R ₀ = S _crit (Formula 5)
Where D is the thermal diffusivity (m ² / s) of the amorphous material, C _S is the total heat capacity of the sample, and R ₀ is the total resistance of the sample. Using the typical D and C _S values for metallic glass, assuming length (L˜1 cm), and input power I ² R _o ˜10 ⁶ watts normally required for the present invention, S _crit ˜10 ^-4 to 10 ^-5 can be obtained. This criterion for uniform heating needs to be met for many metallic glasses (see S values above). In particular, many metallic glasses have S <0. Such materials (ie having S <0) will always meet this requirement for heating uniformity. Exemplary materials that meet this criteria are US Pat. No. 5,288,344, US Pat. No. 5,368,659, US Pat. No. 5,618,359, and US Pat. No. 5,735,975. The disclosures of these patents are incorporated herein by reference.

Other than the basic physical criteria of the applied charge and the amorphous material used, there are also technical requirements to ensure that the charge is applied as evenly as possible to the sample. For example, it is important that the sample be formed with a substantially defect-free and uniform cross-section. If these conditions are not met, heat will not dissipate evenly across the sample and local heating will occur. Specifically, if there are discontinuities or defects in the sample block, the physical constants discussed above (ie, D and C _S ) will differ in these respects, resulting in different heating rates. In addition, because the thermal properties of the sample are also dependent on the size of the article (ie, L), there will be local hot spots along the sample block when the article cross-section is changed. Furthermore, if the sample contact surface is not sufficiently flat and parallel, interface contact resistance will be present at the electrode / sample interface. Thus, in one embodiment, the sample block is formed to be substantially free of defects and have a substantially uniform cross section. It should be understood that the cross section of the sample block should be uniform, but as long as this requirement is met, there are no inherent constraints imposed on the shape of the block. For example, the block can take any suitable geometrically uniform shape such as a sheet, block, cylinder, etc. In another embodiment, the sample contact surface is cut in parallel and polished flat to ensure good contact with the electrodes.

  In addition, it is important that no interfacial contact resistance occurs between the electrode and the sample. To accomplish this, the electrode / sample interface needs to be designed to ensure that the charge is applied evenly, i.e., at a uniform density, so that "hot spots" do not occur at the interface. For example, if different parts of the electrode provide different conductive contacts to the sample, the spatial locality and local melting of the heating will occur anywhere where the initial resistance is maximum. This will result in a discharge weld where a local melt pool is created near the electrode / sample interface or other internal interface within the sample. In light of this requirement of uniform current density, in one embodiment of the present invention, the electrodes are polished flat and parallel to ensure good contact with the sample. In another embodiment of the invention, the electrode is made of a soft metal and a uniform “sitting” pressure is applied at the interface that exceeds the electrode material yield strength, but not the electrode buckling strength, so that the electrode is The entire interface is positively pressurized and does not buckle, and any non-contact area at the interface is plastically deformed. In yet another embodiment of the present invention, a uniform low energy “sitting” that is barely sufficient to raise the temperature of any non-contact region of the amorphous sample at the contact surface of the electrode to slightly above the glass transition temperature of the amorphous material. "Pulses are applied, thus allowing the amorphous sample to adapt to the microscopic features of the electrode contact surface. In addition, in yet another embodiment, the electrodes are positioned so that the positive and negative electrodes provide a symmetrical current path across the sample. Some suitable metals for the electrode material are Cu, Ag, and Ni, and alloys made substantially from Cu, Ag, and Ni (ie, containing at least 95% of these materials). .

Finally, assuming that electrical energy is successfully and uniformly discharged into the sample, if heat transport toward the cold ambient and the electrodes is effectively avoided, i.e., adiabatic warming is achieved, Will be heated uniformly. In order to produce an adiabatic temperature rise condition, dT / dt needs to be high enough to ensure that a thermal gradient due to heat transport does not occur in the sample, or τ _RC needs to be small enough. In order to quantify this criterion, the magnitude of τ _RC should be much smaller than the thermal relaxation time τ _th of the amorphous metal sample, which τ _th is given by:
τ _th = c _S R ² / k _S (Formula 5)
Where k _S and c _S are the thermal conductivity and specific heat capacity of the amorphous metal, and R is a characteristic length measure of the amorphous metal sample (eg, the radius of the cylindrical sample). When k _S ~10W / (mK) and ^{_{c S ~5 × 10 6 J /}} (m 3 K) and R~1 × 10 ^-3 represents an approximation of the Zr-based glass, we tau _th ~0 .5s is obtained. Therefore, uniform heating should be ensured using a capacitor with τ _RC much smaller than 0.5 s.

Turning to the molding method itself, a schematic diagram of an exemplary molding tool according to the RCDF method of the present invention is shown in FIG. As shown, the basic manual RCDF shaping tool includes an electrical energy source (10) and two electrodes (12). The electrode applies uniform electrical energy to a uniform cross-section sample block (14) made of an amorphous material having a sufficiently low S _crit value and a sufficiently high ρ ₀ value to ensure uniform heating. Used to do. Using uniform electrical energy, the sample is uniformly heated to a predetermined “working temperature” above the glass transition temperature of the alloy on a time scale of a few milliseconds or less. The viscous liquid thus formed is simultaneously molded according to preferred molding methods including, for example, injection molding, dynamic forging, stamp forging, blow molding, etc. to form a product on a time scale of less than 1 second.

  Any suitable source of uniform energy sufficient to rapidly and uniformly heat the sample block to a predetermined processing temperature, such as a capacitor having a discharge time constant of 10 μs to 10 milliseconds It should be understood that an electrical energy source can be used. In addition, any suitable electrode for providing uniform contact across the sample block can be used to transmit electrical energy. As discussed, in one preferred embodiment, the electrode is formed of a soft metal such as, for example, Ni, Ag, Cu, or an alloy made using at least 95% Ni, Ag and Cu, and the electrode / sample. It is held against the sample block under sufficient pressure to plastically deform the electrode contact surface at the interface to conform to the microscopic features of the sample block contact surface.

  While the above discussion is generally focused on the RCDF method, the present invention also relates to an apparatus for molding sample blocks of amorphous material. In one preferred embodiment shown schematically in FIG. 2, the injection molding apparatus can be incorporated with the RCDF method. In such an embodiment, the heated viscous liquid of amorphous material is formed into a mold cavity (18) that is held at ambient temperature using a mechanically loaded plunger to form a metallic glass net-shape component. Is injected into. In the embodiment of the method shown in FIG. 2, the charge is placed in an electrically isolated “barrel” or “shot sleeve” and has a conductive material having both high electrical and thermal conductivity ( A cylindrical plunger made of copper (such as copper or silver) is preloaded to the injection pressure (typically 1-100 MPa). The plunger functions as one electrode of the system. The sample charge rests on an electrically grounded base electrode. The stored energy of the capacitor is uniformly discharged into a cylindrical metallic glass sample charge if the above-mentioned certain criteria are met. The loaded plunger then moves the heated viscous melt to the net shape mold cavity.

  Although an injection molding technique has been discussed above, any suitable molding technique may be used. Some alternative exemplary embodiments of other molding methods that can be used in accordance with RCDF technology are shown in FIGS. 3-5 and discussed below. For example, as shown in FIG. 3, in one embodiment, a dynamic forging method may be used. In such an embodiment, the sample contact portion (20) of the electrode (22) will itself form a die tool. In this embodiment, the low temperature sample block (24) is held under compressive stress between the electrodes, and when the electrical energy is discharged, the sample block becomes sufficiently viscous that the electrodes can be pressed together under the predetermined stress. This causes the amorphous material of the sample block to conform to the shape of the die (20).

  In another embodiment, schematically illustrated in FIG. 4, a stamping method has been proposed. In this embodiment, the electrode (30) clamps or otherwise holds the sample block (32) between them at either end. In the illustrated schematic, a thin sheet of amorphous material is used, but it should be understood that this technique can be modified to work with any suitable sample shape. When electrical energy is discharged through the sample block, a molding tool or stamp (34) including opposing molds or stamp faces (36) as shown is pre-determined against a portion of the sample held therebetween. Together, thereby stamping the sample block into the final desired shape.

In yet another exemplary embodiment schematically illustrated in FIG. 5, a blow molding technique can be used. Again, in this embodiment, the electrode (40) clamps or otherwise holds the sample block (42) between them at either end. In a preferred embodiment, the sample block comprises a thin sheet material, but any suitable shape can be used. Regardless of the initial shape, in the exemplary technique, the sample block is positioned in the frame (44) on the mold (45) to form a substantially hermetic seal;
As a result, the opposing side surfaces (46 and 48) of the block (ie, the side facing the mold and the side facing away from the mold) can be exposed to different pressures, ie, a positive or negative vacuum of gas. become. As electrical energy is discharged through the sample block, the sample becomes viscous and deforms under different pressure stresses and conforms to the contour of the mold, thereby forming the sample block into the desired final shape.

  In yet another exemplary embodiment shown schematically in FIG. 6, fiber drawing techniques can be used. Again, in this embodiment, in this embodiment, the electrode (49) is in good contact with the sample block (50) near either end of the sample and the tensile force is at either end of the sample. Will be applied. A flow of cold helium (51) is blown over the drawn wire or fiber, allowing cooling below the glass transition. In a preferred embodiment, the sample block comprises a cylindrical rod, but any suitable shape can be used. As electrical energy is discharged through the sample block, the sample becomes viscous and is uniformly stretched under tensile stress, thereby drawing the sample block into a wire or fiber of uniform cross section.

  In yet another embodiment, shown schematically in FIG. 7, the present invention relates to a rapid capacitor discharge apparatus for measuring the thermodynamic and transport properties of a supercooled liquid. In one such embodiment, the sample (52) is held under compressive stress between two paddle-shaped electrodes (53) and the thermal imaging camera (54) is focused on the sample. When electrical energy is discharged, the camera is activated and at the same time the sample block is charged. After the sample has become sufficiently viscous, the electrodes will be pressed together under a predetermined pressure to deform the sample. If the camera has the required resolution and speed, a series of thermal detections can capture the simultaneous heating and deformation process. With this data, time, heat, and deformation data can be converted to time, temperature, and strain data, input power and applied pressure can be converted to internal energy and load stress, This provides sample temperature, temperature dependent viscosity, heat capacity and enthalpy information.

  While the above discussion has focused on the basic features of some exemplary molding techniques, it should be understood that other molding techniques can be used with the RCDF method of the present invention, such as extrusion or die casting. . Furthermore, additional elements can be added to these techniques to improve the quality of the final product. For example, to improve the surface finish of a product formed according to any of the above molding methods, the mold or stamp is heated to around or just below the glass transition temperature of the amorphous material, thereby smoothing surface defects. be able to. In addition, in order to obtain a product with a better surface finish or net shape part, a high "Weber number" by controlling the compression force in the case of any of the above molding techniques and in the case of injection molding techniques. The instability of the melt front resulting from the flow of water can be avoided, i.e. atomization, spraying, streamlines, etc. can be prevented.

  The RCDF molding techniques and alternative embodiments discussed above are like casings for electronics, brackets, housings, fasteners, hinges, hardware, watch parts, medical parts, cameras and optical parts, jewelry, etc. It can be applied to the production of small, complex net-shaped high performance metal parts. The RCDF process can also be used to produce small sheets, tubes, panels, etc. that can be dynamically extruded through various types of extrusion dies used in conjunction with RCDF heating and injection systems.

  In summary, the RCDF technology of the present invention enables rapid and uniform heating of a wide range of amorphous materials and provides a relatively inexpensive and energy efficient method of forming amorphous alloys. The advantages of the RCDF system are described in more detail below.

- rapid and uniform processability of the thermoplastic molding and formation of the reinforcing BMG thermoplastics by heating, severely limited by the tendency of the BMG to crystallize when it is heated above the these glass transition temperature T _g Is done. Rate of crystal formation and growth of supercooled liquid over a T _g is rapidly increased with temperature, the viscosity of the liquid decreases. In ～20C / min the conventional heating rates, crystallization occurs when the BMG is heated to a temperature above a T _g only [Delta] T = 30 to 150 ° C.. This ΔT determines the highest temperature and the lowest viscosity at which the liquid can be processed thermoplastically. In practice, the viscosity is greater than 10 ⁴ Pa-s, more typically limited to 10 ⁵ to 10 ⁷ Pa-s, which severely limits net shape formation. With RCDF, the amorphous material sample can be uniformly heated at the heating rate in the range of 10 ⁴ to 10 ⁷ C / s and formed simultaneously (total processing time of several milliseconds is required). The sample then has a much larger ΔT resulting in a thermoplastic net with a much lower processing viscosity in the range of 1 to 10 ⁴ Pa-s (this is the range of viscosities used in plastic processing). It can be formed into a shape. This requires a much lower load load, shorter cycle times and results in a much better tool life.

-Enables processing of a much wider range of BMG materials with RCDF A significant increase in ΔT and a significant reduction in processing time to a few milliseconds allows processing a very wide variety of glass forming alloys. Specifically, RCDF can be used to process an alloy with a small ΔT, or an alloy with very rapid crystallization kinetics and consequently very little glass-forming ability. For example, cheaper or other more desirable alloys based on Zr, Pd, Pt, Au, Fe, Co, Ti, Mg, Ni, and Cu and other inexpensive metals are likely to have a small ΔT and a strong tendency to crystallize. It is a bad glass-shaped organism. These “marginal glass forming” alloys cannot be thermoplastically processed using any of the currently practiced methods, but can be readily used with the RCDF method of the present invention.

RCDF is a very material efficient conventional process currently used to form bulk amorphous products such as die casting requires the use of raw material volumes that far exceed the volume of the part being cast. This is due to the fact that the entire die discharge content in addition to the casting includes gates, runners, sprues (or biscuits), and flushes (all of which are necessary for the passage of molten metal towards the die cavity). . In contrast, the RCDF release content in most cases will contain only parts, and in the case of injection molding equipment, it will contain only shorter runners and much thinner biscuits compared to die casting. Thus, the RCDF method is particularly attractive in applications involving the processing of expensive amorphous materials such as the processing of amorphous metal jewelry.

RCDF is extremely energy efficient :
Competing manufacturing techniques such as die casting, permanent casting, investment casting and metal powder injection molding (PIM) are inherently very energy inefficient. In RCDF, the energy consumed is only slightly greater than that required to heat the sample to the desired processing temperature. High temperature crucibles, RF induction melting systems, etc. are not necessary. Furthermore, there is no need to pour molten alloy from one vessel to another, thereby reducing the required processing steps and the potential for material contamination and material loss.

RCDF provides technology that is relatively small, small and easily automated :
Compared to other manufacturing technologies, RCDF manufacturing equipment is small, small, clean, easy to automate with minimal moving parts, and is suitable for essentially all “electronic” processes .

-Does not require environmental atmosphere control :
The several millisecond time scale required to process a sample with RCDF minimizes the exposure of the heated sample to ambient air. Thus, the process can be performed in the ambient environment, as opposed to current processing methods where long atmospheric exposure results in severe oxidation of the molten metal and final parts.

Exemplary Embodiment
Additional embodiments in accordance with the present invention are intended to be within the scope of the above comprehensive disclosure and are not intended to be waived in any way by the above non-limiting examples. Those skilled in the art will recognize.

Example 1: Resistance Heating Study In BMG, a simple experimental spot welding machine is demonstrated to demonstrate the basic principle that capacitive discharge by ohmic heat dissipation in a cylindrical sample results in uniform and rapid sample heating. Used as a molding tool. The machine Unitek 1048B spot welder stores up to 100 joules of energy in a 10 μF capacitor. The stored energy can be controlled accurately. The RC time constant is approximately 100 μsec. To confine the sample cylinder, the two paddle electrodes were provided with a flat parallel surface. The spot welding machine has a spring-loaded upper electrode that allows an axial load to be applied to the upper electrode with a force up to 80 Newtons. As a result, it can apply a constant compressive stress in the range of up to -20 MPa to the sample cylinder.

Small right cylinders of several BMG materials with a diameter of 1-2 mm and a height of 2-3 mm were made. The sample mass ranged from ˜40 mg to about ˜170 mg and was selected to obtain a T _{F well} above the glass transition temperature of a particular BMG. The BMG materials are Zr—Ti based BMG (Vitreloy 1, Br of Zr—Ti—Ni—Cu—Be), Pd based BMG (Pd—Ni) having a glass transition (T _g ) at 340C, 300C, and ˜430C, respectively. -Cu-P alloy) and Fe-based BMG (Fe-Cr-Mo-PC). All of these metallic glasses have S to 1 × 10 ⁻⁴ << S _crit .

Figures 8a to 8d show a series of test results for a Pd alloy cylinder with a radius of 2mm and a height of 2mm (Figure 8a). The resistivity of the alloy is ρ ₀ = 190 μΩ-cm, and S is ⁻¹ × 10 ⁻⁴ (C ⁻¹ ). Energy E = 50 (FIG. 8b), 75 (FIG. 8c), and 100 (FIG. 8d) joules were stored in the capacitor bank and discharged into a sample held under a compressive stress of ˜20 MPa. The degree of plastic flow in BMG was quantified by measuring the initial and final height of the processed sample. It is particularly important to note that the sample is observed not to be bonded to the copper electrode during processing. This may be due to the high electrical and thermal conductivity of copper compared to BMG. In short, copper does not reach a temperature high enough to be wetted by “melt” BMG during the processing time scale (˜several milliseconds). Furthermore, it should be noted that there is little or no damage to the electrode surface. The final processed sample is freely removed from the copper electrode after processing and is shown in FIG. 9 with a length scale criterion.

The initial and final cylinder heights were used to determine the total compressive strain generated in the sample when deformed under load. The engineering “strain” is given by H ₀ / H, where H ₀ and H are the initial (final) height of the sample cylinder, respectively. The true distortion is given by ln (H ₀ / H). This result is plotted against the discharge energy in FIG. These results indicated that the true strain appears to be a nearly linear increase function of the energy discharged by the capacitor.

These test results show that the plastic deformation of the BMG sample blank is a well-defined function of the energy discharged by the capacitor. After many tests of this type, the plastic flow of the sample (for a given sample geometry) is a very well-defined function of energy input, as clearly shown in FIG. It can be judged that there is. In short, using RCDF technology, plastic processing can be accurately controlled by input energy. Furthermore, flow characteristics change qualitatively and quantitatively with increasing energy. Under a compressive load applied with ~ 80 Newtons, a clear development in flow behavior can be observed with increasing E. Specifically, in a Pd alloy, the flow of E = 50 Joules is limited to strains of ln (H ₀ / H _F ) ˜1. Although the flow is relatively stable, there is also evidence of some shear thinning (eg, non-Newtonian flow behavior). For E = 75 joules, a more expanded flow is obtained from ln (H ₀ / H _F ) ˜2.
In this region, the flow is “Newtonian” with a smooth and stable melt front moving through the “mold” and uniform. For E = 100 Joules, very large deformations are obtained with a final sample thickness of 0.12 cm and a true strain of ˜3. There is clear evidence of high “Weber number” flow rate collapse, streamlines, and liquid “spatter” characteristics. In short, a clear transition can be observed by the melt front from stable to unstable moving in the “mold”. Thus, using RCDF, the qualitative nature and range of plastic flow can be systematically and controllably changed by simple adjustment of applied load and energy discharged to the sample.

Example 2 Injection Molding Apparatus In another example, an RCDF injection molding apparatus as a practical prototype was configured. A schematic of the device is shown in Figures 11a to 11e. Experiments conducted on the molding apparatus have demonstrated that a few grams of mold charge can be used to inject net shape products in less than a second.
The illustrated system can store ˜6 K joules of electrical energy and can be used to produce a small net shape BMG component with a controlled machining pressure of up to ˜100 MPa.

  The entire machine consists of several independent systems including an electrical energy charge generation system, a controlled processing pressure system, and a mold assembly. The electrical energy charge generation system comprises a capacitor bank, a voltage control panel and a voltage controller, all of which have a set of electrical leads (62) and electrodes (64) so that a discharge can be applied to the sample blank via the electrodes. And interconnected to the mold assembly (60). The controlled processing pressure system (66) includes an air supply, a piston regulator, and an air piston, all of which have a control circuit so that a controlled processing pressure of up to 100 MPa can be applied to the sample during molding. Are interconnected through. Finally, the molding apparatus also includes a mold assembly (60), which is described in more detail below, in which the electrode plunger (68) is in a fully retracted position. It is shown in

The entire mold assembly is shown removed from the larger device in FIG.
As shown, the entire mold assembly includes upper and lower mold blocks (70a and 70b), upper and lower portions (72a and 72b) of the split mold, and leads for carrying current to the mold cartridge heater (76). It includes a line (74), an insulating spacer (78), and an electrode plunger assembly (68), shown in this figure in a “fully recessed” position.

  In operation, a sample block of amorphous material (80) is positioned within the insulating sleeve (78) above the split mold (82) from the gate, as shown in FIGS. 11c and 11d. This assembly is itself positioned in the upper block (72a) of the mold assembly (60). An electrode plunger (not shown) is then positioned in contact with the sample block (80) and a control pressure is applied through the air piston assembly.

When the sample block is in place and is in positive contact with the electrode, the sample block is heated by the RCDF method. The heated sample becomes viscous and is controllably pushed into the mold (72) via the gate (84) under the pressure of the plunger. In this exemplary embodiment, the split mold (60) takes the form of a ring (86), as shown in FIG. 10e. A sample ring made of an amorphous material of Pd ₄₃ Ni ₁₀ Cu ₂₇ P ₂₀ formed using the exemplary RCDF apparatus of the present invention is shown in FIGS. 12a and 12b.

  This experiment provides evidence that a composite net shape part can be formed using the RCDF technique of the present invention. The mold is formed in the shape of a ring in this embodiment, but this technology is applied to electronic equipment, brackets, housings, fasteners, hinges, hardware, wristwatch parts, medical parts, cameras and optical parts, jewelry, and others. Those skilled in the art will recognize that the present invention is equally applicable to a wide range of products, including small, complex, net-shaped high performance metal parts such as casings.

Example 3: Forging Method and Apparatus As described schematically with respect to FIG. 3, dynamic forging can be performed using the RCDF method of the present invention. Forging is a general method of heating and pressing a metal part into a desired shape. Forging of metallic glass is accomplished by first heating the metallic glass charge above the glass transition and applying force with a forging plate to push the softened metallic glass into a two-dimensional or three-dimensional object after the charge has softened. be able to. As shown in FIG. 3, the forging plate thus serves as both a plunger and a mold, and thus has a high degree of thermal conductivity, and necessarily high electrical conductivity. However, the presence of the engraved cavity in the forged plate surface prevents the efficient application of electrical energy to the metallic glass charge, and thus in most cases prevents the forged plate from functioning as an electrode. Thus, in one embodiment, a forging method is described in which the electrodes are physically separated from the forging plate. Specifically, in this embodiment, the method and apparatus allow electrical energy to be efficiently dissipated through a less electrically conductive metallic glass charge rather than flowing through a more electrically conductive plate. Secured.

(Non-conductive forging)
In simple geometric parts such as plates made of alloys that are robust glass formers such as Vitreloy-1, the forging die can be made from high temperature ceramics such as MACOR. Since the ceramics are insulated, they can be in contact with the sample while the current is discharged. Thus, pressure can be applied by the forging die while capacitive discharge heating is performed, eliminating the need for additional control circuitry. In addition, the low thermal diffusivity of ceramics allows the metallic glass to be maintained at high temperatures for longer time periods. This allows the material to be forged into fairly thin parts at lower pressures if the metallic glass is sufficiently robust and does not crystallize for a longer time. Thus, in one embodiment of the present invention, a nonconductive die is used to forge a metallic glass part.

  In one exemplary embodiment, the non-conductive forging tool was formed using a pneumatic piston drive with a 3-1 / 4 inch bore in conjunction with a 0.792F capacitor bank. The MACOR plate was attached to a pneumatic drive that used a guide rod to hold the MACOR plate in parallel.

In one embodiment, such a non-conductive forming device is used to forge a thin plate from a 5 mm diameter amorphous rod made of the Vitreloy-1 variant (Zr ₃₅ Ti ₃₀ Cu _8.25 Be _26.75 ), and two MACOR The plate was attached to a forging setup. The rod was clamped between two copper electrodes at its two ends. Prior to capacitive discharge, 20 psi pressure was applied by a MACOR plate to the rod section between the electrodes. The capacitor bank discharges 93 volts and delivers an energy density of 2100 J / cc to rapidly heat the sample to between Tg and Tm. The rod was formed to soften instantaneously between the MACOR plates by the applied pressure and then cooled by conduction to the plates. The resulting plate shown in FIG. 13 is completely amorphous and has a thickness of 0.45 mm.

(Conductive forging)
Metal dies are due to their high thermal conductivity and the relative ease with which they can be machined into complex geometries for marginal glass forming alloys or to make parts with complex geometries. Need to be used. However, due to their low electrical resistivity, they are preferably not in contact with the metal glass during capacitive discharge, and current will flow primarily through the die, which will prevent metal glass from being formed, Causes non-uniform heating of the metallic glass at the die interface that will promote partial welding and damage to the die. Therefore, in order to successfully forge with a metal die using RDHF, it is necessary to effectively uncouple the heating phase from the forming phase.

This is because, in this embodiment, the conductive forged plate is electrically insulated from the capacitive discharge circuit during the discharge process, and after the discharge is completed, the conductive plate rapidly applies a force so that the softened metallic glass is substantially netted. This is accomplished by allowing it to be deformed into a shape. Specifically, according to one embodiment of the present invention, the application of force is
t _Fi > τ _RC and t _FO <τ _C
Should start at time t _Fi and end at time t _FO, where (τ _RC ) is the RC time constant of the discharge circuit and (τ _C ) crystallizes the metallic glass at the operating temperature. It's time. Typical τ _RC values range from 0.1 ms to 10 ms, depending on the capacitor and resistance of the discharge circuit, and typical τ _C values depend on the stability of the metallic glass forming liquid to crystallization, The range is from 10 ms to 1000 ms.

  An exemplary setup of the present invention is presented in FIG. In this setup, the forged plate (100) cannot contact the metallic glass charge (102) during the discharge process, and the current path from the highly conductive electrode (103) to the metallic glass charge is in place. (104) and is insulated via an insulator (105) or the like. After the discharge process is complete, the forged plate is then activated by an electric / pneumatic mechanism or other suitable high speed drive mechanism (not shown) to rapidly apply force to form the softened metallic glass.

An exemplary setup for a high speed drive mechanism based on electro / pneumatic actuation is shown in FIG. In this exemplary device, the sensor / timer circuit (106) detects the onset and decay of capacitive discharge by measuring the voltage and current in a portion of the discharge circuit (108). The timer is started upon detection of discharge by the sensor of the sensor / timer circuit. After a delay time of τ _RC as described in the above inequality, the air valve (110) applies pressure to the softened metallic glass (112) through the forged plate (113) via the air piston (114). Operates on. Again, as discussed above with respect to the forging inequality, the entire process should be completed in a period of less than τ _C. It should be understood that this control circuit can be used to control both discharge and pressure application, or pressure can be applied after a discharge is detected. The former takes into account any mechanical time delay of die movement, so it can provide better control as the circuit timing can be selected to allow the force to be applied before or simultaneously with the discharge. . The latter is limited to pressure application after discharge, so any mechanical time delay will add to the total machining time.

  Although any suitable material can be used for the components of the RCDF forging device of the present invention, in one exemplary embodiment, the forging plate is not limited to copper, brass, and steel. Highly conductive electrodes can include, but are not limited to, copper and copper / beryllium. Similarly, although any detection and rapid actuation mechanism can be used, some exemplary methods of activating and applying force include, but are not limited to, air, hydraulic, or electrically sensed voltages. / Current and temperature detected by air, hydraulic pressure or electric power.

  In one embodiment of the invention, a stainless steel forging die is used to forge metal glass screws. The force is applied by a pneumatic piston with a 3/4 "diameter bore and equipped with a solenoid valve. The control circuit allows the circuit to be programmed with a coil such as a Rogowski coil as a current sensor. Consists of a microcontroller chip and a transistor, such as a Darlington transistor, that drives a solenoid.Before discharge, the die remains separated from the metallic glass.When discharge begins, a voltage is developed across the coil. Is amplified through an operational amplifier and fed to the microcontroller, which is programmed to hold the voltage for a period of time (a few milliseconds) before sending the voltage to the transistor. Open and urge the piston to move the forging die against the heated metal glass Make it.

To forge 10-32 screws from a 5 mm diameter rod of metallic glass (Zr ₃₅ Ti ₃₀ Cu _8.25 Be _26.75 ), two stainless steel dies were configured and aligned in the forging tool as described above. A 3.8 cm long BMG rod was clamped between two copper electrodes and heated with a current pulse generated using a capacitor bank with a 0.792 F capacitor. The capacitor bank was charged to 94 volts and delivered an energy density of 2100 J / cc. The tank connected to the solenoid valve was pressurized to 80 psi. The control circuit was programmed to start as soon as any current was detected. The resulting screw is shown in FIGS. 16a to 16c.

The screw is formed with extremely high accuracy. Inspection of the tread in a scanning electron microscope reveals that the material has preferably replicated a mold around the thread. The threading of the forged metallic glass appeared to be at least as accurate as stainless steel 10-32 screws, which were machined rather than forged as shown in FIGS. 17a to 17c. Small flashings can be formed during forging when some material inevitably flows out of the cavities between the closure plates. The flushing can be removed by polishing or cut using a saw. The removal of the flushing along with a small amount of threading does not change the operation of the screw.

(Equivalence)
The foregoing examples and description of various preferred embodiments of the present invention are merely illustrative of the present invention as a whole, and steps of the present invention and variations of various components are within the spirit and scope of the present invention. Those skilled in the art will understand that this can be done within. For example, additional processing steps or alternative configurations do not affect the improved characteristics of the rapid capacitor discharge forming method / apparatus of the present invention and do not result in a method / apparatus that is not suitable for its intended purpose. Will be apparent to those skilled in the art. Accordingly, the invention is not limited to the specific embodiments described herein, but rather is defined by the scope of the appended claims.

Claims (36)

A method of rapidly heating and forging amorphous material using rapid capacitor discharge,
Providing a sample of amorphous material having a substantially uniform cross section between at least two forged plates;
Uniformly discharging electrical energy quanta across the sample to uniformly heat the entire sample to a processing temperature between the glass transition temperature and the equilibrium melting point of the amorphous material;
Discharge is interrupted through the at least two forging plates to apply a deformation force and the heated sample is still heated while it is at a temperature between the glass transition temperature of the amorphous material and the equilibrium melting point. Forming a sample into an amorphous product,
Cooling the product to a temperature below the glass transition temperature of the amorphous material.   The method of claim 1, wherein the amorphous material has a resistivity that does not increase with temperature.   The method of claim 1, wherein the temperature of the sample is increased at a rate of at least 500 K / sec. The amorphous material has a relative change in resistivity per unit of temperature change (S) not greater than about 1 × 10 ⁻⁴ ° C. ⁻¹ and a resistivity (ρ ₀ ) at room temperature of about 80 to 300 μΩcm; The method according to claim 1.   The method of claim 1, wherein the electrical energy quantum is a discharge time constant of at least about 100 Joules and between about 10 μsec to 10 ms.   The method of claim 1, wherein the processing temperature is approximately between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy. The method of claim 1, wherein the processing temperature is such that the viscosity of the heated amorphous material is about 1 to 10 ⁴ Pas-sec.   The method of claim 1, wherein the sample is substantially free of defects.   The amorphous material is an alloy based on an elemental metal selected from the group consisting of Zr, Pd, Pt, Au, Fe, Co, Ti, Al, Mg, Ni, and Cu. The method described.   Discharging the electrical energy quanta generates an electric field in the sample, and the electromagnetic skin depth of the generated dynamic electric field is large compared to the radius, width, thickness and length of the charge, The method of claim 1.   The method of claim 1, wherein the forged plate is non-conductive.   The method of claim 1, wherein the forged plate is conductive.   13. The step of discharging the electrical energy quanta is performed through at least two electrodes connected to both ends of the sample, and the electrodes do not contact the forging plate. Method. Applying molding force
t _Fi > τ _RC and t _F0 <τ _C
Starting at time t _Fi and ending at time t _F0, where (τ _RC ) is the RC time constant of the discharge and (τ _C ) is the time for the metallic glass to crystallize at the processing temperature. The method of claim 12, wherein:   The method of claim 1, wherein the deforming force is applied to deform the heated sample at a sufficiently slow rate to avoid high Weber number flow.   The method of claim 1, wherein the heating and shaping of the sample is completed in a time of about 100 μs to 1 second. A rapid capacitor discharge device for rapidly heating and forging an amorphous material comprising a sample of an amorphous material having a substantially uniform cross section;
An electrical energy source;
Interconnecting the electrical energy source to the sample of amorphous material, and at least two electrodes attached to the sample such that a substantially uniform connection is formed between the sample;
A forging tool comprising at least two forging plates arranged in a formable relationship with the sample;
A timing circuit in signal communication with the electrical energy source and the forging tool;
With
The electrical energy source can discharge electrical energy quanta sufficient to uniformly heat the entire sample to a processing temperature between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy; The forging tool can apply sufficient deformation force to form the heated sample into a net shape product, and the timing circuit detects the discharge of the electrical energy and activates the forging tool And applying a deformation force to the heated sample through the at least two forging plates.   The apparatus of claim 17, wherein the timing circuit is configured to apply the force simultaneously with the discharging of the electrical energy.   The apparatus of claim 17, wherein the timing circuit is configured to apply the force after the electrical energy is discharged. The timing circuit is configured to apply the molding force, and the application of the molding force is:
t _Fi > τ _RC and t _F0 <τ _C
And starts at time t _Fi and ends at time t _F0 , where (τ _RC ) is the RC time constant of the discharge and (τ _C ) crystallizes the metallic glass at the processing temperature. The apparatus of claim 17, wherein the apparatus is time.   The apparatus of claim 17, wherein the timing circuit includes a Rogowski coil, a microcontroller chip, a Darlington transistor, and a solenoid valve.   18. The apparatus of claim 17, wherein the forming tool further comprises a temperature controlled heating element for heating the tool, preferably to a temperature around the glass transition temperature of the amorphous material.   18. The apparatus of claim 17, further comprising either one of a pneumatic or magnetic drive system in operable relationship with the forming tool to apply the deformation force to the sample.   The apparatus of claim 17, wherein the amorphous material has a resistivity that does not increase with temperature.   The apparatus of claim 17, wherein the temperature of the sample increases at a rate of at least 500 K / sec. The amorphous material has a relative change in resistivity per unit of temperature change (S) not greater than about 1 × 10 ⁻⁴ ° C. ⁻¹ and a resistivity at room temperature (ρ ₀ ) between about 80 and 300 μΩcm. The method of claim 17, comprising:   The method of claim 17, wherein the electrical energy quantum has a time constant of at least about 100 Joules and about 10 μs to 10 ms.   The method of claim 17, wherein the processing temperature is approximately between the glass transition temperature of the amorphous material and the equilibrium melting point of the alloy. 18. The apparatus of claim 17, wherein the processing temperature is such that the viscosity of the heated amorphous material is about 1 to 10 < ⁴ > Pas-sec.   The method of claim 17, wherein the sample is substantially free of defects.   18. The amorphous material is an alloy based on an elemental metal selected from the group consisting of Zr, Pd, Pt, Au, Fe, Co, Al, Mg, Ti, Ni, and Cu. The method described.   A controller for controlling a surface charge strain rate or displacement rate during discharge so that the heated sample deforms at a sufficiently slow rate to avoid high Weber number flow. Item 18. The method according to Item 17.   The method of claim 17, wherein the device is capable of forming the product from the sample at the room temperature in a time of about 100 μs to about 1 second.   The electrical energy source generates an electric field in the sample, and an electromagnetic skin depth of the generated dynamic electric field is large compared to a charge radius, width, thickness, and length. 18. The method according to 17.   The method of claim 17, wherein the at least two forged plates are conductive.   36. The method of claim 35, wherein the electrode does not contact the forging plate.