HIGH-VOLTAGE VACUUM TUBES

Abstract

The present disclosure relates to a high-voltage vacuum tube comprising: a vacuum tube bulb comprising an interior; an anode assembly located inside the vacuum tube bulb; and a cathode assembly located inside the vacuum tube bulb that emits an electrode beam to strike a target surface of the anode assembly and form electromagnetic radiation. The high-voltage vacuum tube includes a brazed assembly, wherein the brazed assembly comprises a first component and a second component connected to each other by a first brazed joint, wherein the first brazed joint comprises a composition which in total includes not more than 18 wt.% of one or more precious metals selected from Au, Pd and Pt, wherein at least one section of the brazed joint is exposed to the interior of the vacuum tube bulb.

Description

field of technology

[0001] This disclosure relates to high-voltage vacuum tubes and, in particular, X-ray tubes; and the process for producing brazed joints therein. Background of the Revelation

[0002] High-voltage vacuum tubes comprise an anode and a cathode positioned opposite each other within a vacuum-sealed interior. This vacuum-sealed interior is typically enclosed by a cylindrical metal casing, with the anode and / or cathode electrically insulated by a ring-shaped insulator.

[0003] The high-voltage vacuum tube is a device that controls the flow of electric current in a high vacuum between electrodes, generating a significant amount of heat from both the filament (heating filament) and the electron bombardment of the anode. High-voltage applications of vacuum tubes include X-ray tubes, magnetrons, traveling-wave tubes, carcinotrons, and klystrons.

[0004] High-voltage vacuum tubes typically use ceramic insulators to offset a high voltage from a lower voltage. For example, an anode carrying a high voltage may be offset from the body of the vacuum tube through the ceramic insulator. The body of the vacuum tube is typically attached to a ceramic insulator. A metallic sealing ring may be brazed to an outer surface of the ceramic insulator to secure the body to the ceramic insulator. This attachment creates a triple junction between the ceramic insulator, the sealing ring, and a surrounding medium. An electric field at this triple junction may be relatively high, producing electrons that can become the source of arcing and / or breakdown. High-voltage structures with an insulator forming part of a vacuum chamber are known from US 4,126,803.

[0005] X-ray tubes for various applications are known to be operated with high applied DC and AC voltages between the anode and the cathode, and depending on the desired radiation intensity, the applied voltages can reach several hundred kV. In such X-ray tubes, the necessary insulating paths are predominantly arranged in the axial direction.

[0006] Brazing materials for the X-ray tubes can be selected to achieve the desired wetting and brazing flux, such as a 50 / 50 Au / Cu mixture, an 81.5 / 16.5 Au / Cu mixture (Nicoro™-80), and an 82 / 18 Au / Cu mixture (Nioro™).

[0007] Gold-copper brazing alloys are part of a larger family of high-temperature brazing alloys based on precious metals (palladium, platinum, gold, and silver) with nickel and copper additions. They possess good mechanical properties at elevated temperatures and good oxidation resistance. Cu-Ge-based alloys are often used as an alternative to precious metal brazing alloys (e.g., Au-Cu and Cu-Ag-based alloys) for vacuum brazing applications.

[0008] Non-precious metal alloys, such as Cu-Ge alloys (trade name Gemco™ with a nominal composition of 87.75% Cu, 12% Ge, and 0.25% Ni), have been used for vacuum brazing of copper-, steel-, and nickel-based metals. However, such an alloy exhibits a large range between its solidus and liquidus temperatures, known as the solidification temperature range (STR), which presents a segregation problem in brazing applications. Segregation in brazing is defined as the tendency of the lower-melting components of a brazing alloy to separate during heating and fly away from the higher-melting components of the brazing alloy. It occurs when the alloy is heated slowly through this melting range, as in furnace brazing, and manifests as an unmelted bead of alloy remaining at the point where the brazing alloy was applied.This often leads to poor joint strength due to the presence of a brittle intermetallic phase in the brazed joint. Segregation is typically evident in alloys exhibiting a high STR. Brazing operations performed within a furnace experiencing temperature variations are also prone to segregation, particularly if the brazing alloy has a high STR.

[0009] Another problem with high STR brazing alloys is their inability to be used in step brazing, where a lower-temperature alloy is used stepwise to braze complex joints. During step brazing, the liquidus temperature of the low-temperature brazing alloy is close to the solidus temperature of the high-temperature brazing alloy (due to the latter's high STR), causing dimensional shifts in the components.

[0010] There is still a need for high-voltage vacuum tubes that incorporate alternatives to conventional brazing alloys / joints with a high precious metal content. However, the brazing alloy must have a sufficiently low STR (Strength Ratio of Resistance) to avoid or reduce the risk of segregation compared to conventional non-precious metal brazing alloys. Furthermore, the brazing alloys must possess sufficient malleability to allow them to be precisely positioned adjacent to X-ray tube components, enabling capillary action to draw the alloy into the gap between the components during the brazing process. Summary of the Revelation

[0011] In a first aspect of the present disclosure, a high-voltage vacuum tube is provided, comprising: a vacuum tube bulb comprising an interior; an anode assembly located inside the vacuum tube bulb; and a cathode assembly arranged inside the vacuum tube bulb and emitting an electrode beam to impinge on a target surface of the anode assembly and to form electromagnetic radiation, wherein the high-voltage vacuum tube comprises a brazing assembly, the brazing assembly comprising a first component and a second component joined together by a first brazing joint, the first brazing joint comprising a composition configured to have a solidification temperature range of not more than 90 °C and a liquidus temperature in the range of 950 °C to 1060 °C; wherein the brazing joint in total does not exceed 18 wt.-% of one or more precious metals selected from Au, Pd and Pt, relative to the total weight of the first brazed joint, wherein at least one section of the brazed joint is exposed to the interior of the vacuum tube bulb and wherein at least one of the first and second components forms part of one or more of the vacuum tube bulb, the anode assembly and the cathode assembly.

[0012] In a variation of the first aspect of the present disclosure, an X-ray tube is provided, comprising: an X-ray tube bulb comprising an interior; an anode assembly located inside the X-ray tube bulb; and a cathode assembly arranged inside the X-ray tube bulb and emitting an electrode beam to impinge on a target surface of the anode assembly and to form electromagnetic radiation, wherein the X-ray tube comprises a brazed assembly, the brazed assembly comprising a first component and a second component joined together by a first brazed joint, the first brazed joint comprising a composition configured to have a solidification temperature range of not more than 90 °C and a liquidus temperature in the range of 950 °C to 1060 °C; wherein the brazed joint in total does not exceed 18 wt.-% of one or more precious metals selected from Au, Pd and Pt, relative to the total weight of the first brazed joint, wherein at least one section of the brazed joint is exposed to the interior of the X-ray tube bulb and wherein at least one of the first and second components forms part of one or more of the X-ray tube bulb, the anode assembly and the cathode assembly.

[0013] The anode assembly is a rotating anode assembly. Rotating anode assemblies are subjected to considerable forces during operation, and therefore the strength of the brazed joints is crucial.

[0014] In some embodiments, at least one of the first and second components forms part of the X-ray tube or vacuum tube bulb. In some embodiments, at least one of the first and second components forms part of the anode or cathode assembly.

[0015] High-voltage vacuum tubes preferably comprise a cathode and an anode capable of operating at at least 800 °C. Examples of high-voltage vacuum tubes include power tubes, magnetrons, traveling-wave tubes, carcinotrons, and klystrons, wherein the electromagnetic radiation emitted from the cathode assembly includes, but is not limited to, X-rays and microwaves. Brief description of the characters

[0016] The present disclosure will now be described with reference to the figures in the accompanying drawings, which illustrate particularly preferred embodiments of the present disclosure, in which the following applies: Fig. Figure 1 is a schematic representation of an X-ray tube according to the present disclosure. Fig.2 is a scanning of sample 4 by differential scanning calorimetry (DSC) according to the present disclosure. Fig. Figure 3 is a graph illustrating the influence of the boron content in the brazing alloy on the solidus / liquidus temperature range, according to the present disclosure. Fig. Figure 4 is a photograph of the results of a brazing flux test in a hydrogen atmosphere between a copper and a 304 stainless steel substrate, joined together by the brazing alloy composition of sample 14, according to the present disclosure. Fig. 5 is a microstructure image of a cross-section of the brazed joint made of Fig. 4 according to the present disclosure. Fig. 6A-6F are photographs illustrating the malleability of samples 8 to 12 and C-6 respectively, according to the present disclosure. Fig.7A is a photograph of a brazing alloy wire in contact with two components prior to brazing using the brazing alloy of sample 13 according to the present disclosure. Fig. 7B is a photograph of the brazed joint made of Fig. 7A after brazing according to the present disclosure. Fig. 7C is a scanning electron microscope (SEM) image of the brazed joint made of Fig. 7A after brazing according to the present disclosure. Fig. 8A is a comparative photograph of a conventional brazing alloy wire in contact with two components prior to brazing using the commercially available brazing alloy GEMCO™. Fig. 8B is a photograph of the brazed joint made of Fig. 8A after brazing according to the present disclosure. Fig. 8C is a SEM image of the brazed joint made of Fig. 8A after brazing according to the present disclosure. Fig. Figure 9 is a graph illustrating the solidification temperature range (STR) versus the Au content of the brazing alloys, according to the present disclosure. Fig. Figure 10 is a graph illustrating the liquidus and solidus temperatures relative to Ge in wt.% of the brazing alloys, according to the present disclosure. Detailed description of a preferred embodiment of the present disclosure Components of high-voltage vacuum tubes

[0017] It is understood that, in the context of the present description and claims, a piston means a hermetic high-temperature piston capable of operating at at least 500 °C or at least 800 °C, and capable of operating under vacuum or containing gases such that the brazed joints therein prevent gases from leaking into or out of the piston. Preferably, the hermeticity is such that the brazed joint passes a leak test with a gas tightness of 1 × 10⁻⁶ -6 consists of atm.cc / s or less (ASTM F2391 using helium gas).

[0018] "Piston" refers to a vessel, tube, or enclosure that defines an enclosed space containing enclosed components, fluid, vacuum, or gases. The piston separates or isolates the enclosed space from the space outside the piston.

[0019] "Hermetic" and its variations in this document refer to a sealed, gas-tight, and fluid-tight brazed joint, vessel, tube, or enclosure relative to the environmental conditions to which a housing or enclosure would normally be exposed relative to the environmental conditions to which a bulb described in this document would normally be subject. Hermetic can generally mean that a brazed joint is capable of isolating an environment on the outside of a device from the inside of the same device. The bulb may be part of an assembly, such as all or part of a high-voltage vacuum tube or a semiconductor process chamber component.

[0020] Pistons, by their very nature, typically incorporate at least one brazed joint, one of which must necessarily be formed as a hidden joint (i.e., the joint is not visible). This means a joint formed by drawing the molten brazing alloy into a gap (e.g., 5 µm to 500 µm or as narrow as 200 µm) between the two components to be joined (e.g., via capillary action, which avoids gas entrapment within the brazed joint), often after the subassembly components are in place within the piston. Thus, the properties of the brazing alloy are critical, firstly to form the brazing alloy composition with the desired dimensions, which is to be placed immediately adjacent to the components to be joined. Secondly, the brazed joint should exhibit sufficient wettability and flowability to create a high-quality joint (e.g.,(without segregation) between the components through capillary action. Third, the brazed joint requires sufficient hermeticity, corrosion resistance, high-temperature resistance, and strength to provide long-term functional integrity to the piston. At least some of the brazed joints within the piston (or other brazed assembly) should be concealed.

[0021] Furthermore, the joints of the many configurations cannot be inspected after manufacturing. This is particularly important because brazed joints require finite gaps for proper brazing. If manufacturing tolerances vary, maintaining a required gap becomes problematic because the final brazed gap is unknown and too large. Consequently, there is a need to maintain the stress-bearing capacity of the brazed joint and its ability to be inspected and produced with consistency.

[0022] The average thickness of a brazed joint typically ranges from 5 µm to 500 µm, 8 µm to 200 µm, or 8 µm to 100 µm. The depth of the brazed joint can range from 5 µm to 50 mm, 30 µm to 10 mm, or 40 µm to 5.0 mm. When forming concealed joints, the flowability of the brazing alloy is particularly important, especially as the distance over which the molten alloy must flow to achieve the required brazed joint depth increases.

[0023] Such assemblies are typically required to operate at high temperatures and / or with high precision using highly conductive components such as copper, which is an essential part of their system for effective thermal management. Within the vacuum tube, the piston may further include an enclosed heat source, such as a cathode filament from an X-ray vacuum tube. The heat source is preferably capable of heating at least a section of the piston's contents to at least 800 °C, 900 °C, or 1000 °C. The maximum operating temperatures of the pistons are determined by the softening and liquidus temperatures of the materials used.

[0024] The first or second component may comprise copper or a copper alloy exhibiting excellent conductivity. The first or second component may also comprise, but is not limited to, other metals, including stainless steel, copper alloys, or other metals or metal alloys with a liquidus temperature exceeding 1050 °C or 1080 °C. The piston may further include a cooling system to dissipate heat from the system.

[0025] The first or second component may also include ceramic or a metallized ceramic (i.e., a ceramic that includes a metallized coating).

[0026] The bulb comprises an anode and a cathode positioned opposite each other within a vacuum-sealed interior. This vacuum-sealed interior can be enclosed by a cylindrical metal bulb, with the anode and / or cathode being electrically insulated by an annular insulator (e.g., a ceramic or metallized ceramic component). A brazed connection can form a seal between the cylindrical metal bulb and the annular insulator.

[0027] The brazed joint can comprise a ceramic (or metallized coated ceramic) component and a metallic component, with the brazed joint connecting the ceramic / metallized coated ceramic and the metallic components.

[0028] The ceramic component may include a metallized coating, such as a molybdenum-manganese coating or nickel plating.

[0029] The wetting / binding additive(s), if present, may be selected to improve the wettability and / or bonding of the alloy to the first and / or the second component.

[0030] The vacuum tubes of the present disclosure can comprise a brazed joint formed from a high-copper brazing alloy with specific amounts of minor components, which can be varied to adjust the desired solidus temperature while maintaining a relatively narrow liquidus / solidus temperature range. Furthermore, the brazed joints typically exhibit excellent wettability and flowability over a range of base materials, including copper, nickel and alloys thereof, stainless steel, nickel-cobalt-iron alloys, and molybdenum-manganese metallized substrates.

[0031] These properties of brazing alloys allow for the formation of a versatile variety of vacuum tubes using a variety of different brazing techniques and conditions.

[0032] With reference to Fig. Figure 1 illustrates a bipolar rotating X-ray tube 10, which includes a hermetically sealed bulb 20 that maintains a high vacuum and, in addition, acts as an intermediate component to connect the cathode 30 and the anode 40. For high-voltage vacuum tubes (e.g., 150 kV), the bulb is typically made of stainless steel, heat-resistant steel, carbon structural steel, non-magnetic stainless steel, copper, or nickel-copper alloys. The bulb may include one or more welded seals W capable of hermetically sealing it.

[0033] Electrons are generated by heating the cathode filament 50 and, under the influence of the accelerated electric field between the cathode 30 and the anode, strike the target surface 60 at high speed, generating X-rays. The target surface is a tungsten rotating disk capable of withstanding the high temperatures generated by the impacting electrons. The induction motor 70 comprises bearings 80 and a rotor shaft 90, typically made of molybdenum, whose relatively low conductivity provides the motor with a degree of thermal insulation from the target surface 60. The stator (not shown) includes an array of magnets capable of driving the rotation of the rotor 90 from outside the piston 20.

[0034] Electron bombardment of the target surface releases a stream of X-rays, which can be selectively transmitted outside the bulb via an emission window 100. High-voltage wires 110, 120 are supplied to the cathode 30 and the anode 40, respectively, via feedthroughs 130, 140. The feedthrough includes conductors 110, 120, which are insulated from the bulb by metallized ceramic seals 150, 160.

[0035] Within this structure, there is a need for brazing alloys capable of joining various metal and / or ceramic components. For example, brazing joints B1 are required to hermetically seal the piston against the anode feedthrough 140 and a conductor 120 within the ceramic seal 160. A similar assembly is required at the cathode feedthrough using brazing joints B2. Furthermore, brazing joints B3 are required to hermetically seal the X-ray emission window 100 against the piston 20. Brazing joints B4 may also be required to join components of the rotating anode 40 or the cathode 30.

[0036] Since only 1% of the total energy is used to generate X-rays, with the remaining 99% being converted into heat energy, it is necessary that the X-ray vacuum tube consists of hermetically sealed components with varying degrees of conductivity and mechanical strength, which must maintain good dimensional stability under extreme temperature variations during commissioning.

[0037] The housing assembly (not shown) may further include a cooling fluid (e.g., oil) that assists in dissipating heat from the piston and maintaining temperatures within a target operating zone, typically up to 800 °C, 900 °C, 1000 °C, or higher. Since many of the metal components of the vacuum tube and outer casing include copper due to its high conductivity, the use of copper-based brazing alloys has the advantages of similar coefficients of thermal expansion and the ability to operate at the temperatures required within the vacuum tube. Thus, the brazing alloys of this disclosure can be advantageously used in the brazing joints of B1, B2, B3, and B4 to join metal to metal, metal to metallized ceramic, and / or metal to ceramic.

[0038] Brazing alloys for high-voltage vacuum tubes must exhibit deformability (the alloy's ability to undergo plastic deformation without fracturing), particularly ductility (under tensile stress), to enable their manufacture in various forms such as wires and foils. The production of a brazing alloy begins with mixing all the alloy's elements in appropriate proportions and melting the mixture to a sufficiently high temperature, followed by casting to produce a solid ingot or billet. The alloy's state can be modified from its as-cast state to its forged form by cold or hot working processes such as rolling, drawing, and stamping.

[0039] Rapid solidification processes (i.e., under extremely high cooling rates), such as melt spinning, can produce brazing alloys in thin foils. Milling brazing alloys into a casting mold, ingot mold, or any other shape, or using automation techniques, can be used to produce the alloy in powder form. Brazing alloys in preform shapes are produced by precision cutting a shaped and cold-drawn wire to form a ring, or by stamping the strip or foil from the alloy. Preforms provide an exact volume for the specific region of a given brazing joint. Preforms are placed in a joint region during brazing and melted to join the base materials to a solid state as they cool.In some embodiments, brazing is carried out under vacuum or under hydrogen or an inert gas, with the brazing temperature typically being at least about 20 °C above the liquidus temperature of the brazing alloy.

[0040] As is evident from the sophistication of the setup, it is also crucial that the brazing alloys are positioned and able to flow within tightly defined spaces to produce the required mechanical and hermetic integrity of the brazed joint. In contrast to brazing alloys with high STR values, the brazing process can employ a relatively low temperature increase, since the brazed joints of this disclosure are less prone to segregation. Form of the brazing alloy

[0041] The brazing alloy is preferably malleable enough to be processed as a standard alloy. It exhibits sufficient machinability, meaning it can be easily formed into required sizes and shapes using standard metal forming processes such as rolling, wire forming, wire drawing, and stamping.

[0042] In one embodiment, the brazing alloy can be produced as a wire with a diameter of only up to 0.030" (760 µm) or only up to 0.015" (380 µm). In another embodiment, the brazing alloy can be produced as a foil with a thickness of only up to at least 0.002" (50 µm) or less. In general, foils with a thickness in the range of 0.001" (25 µm) to 0.010" (250 µm) or greater can be produced. Brazing alloy

[0043] Brazing alloys generally exhibit excellent wettability and flow properties, enabling the creation of reliable hermetic seals at high temperatures. These alloys are particularly suitable for applications in high-temperature environments involving vacuum tubes (such as X-ray tubes, waveguides, and klystron assemblies).

[0044] A brazing alloy must melt to function. Its melting behavior is specified by its solidus and liquidus temperatures, with the initial melting temperature (the solidus) and the melting range (the difference between the two points) being the most significant for brazing. A brazing alloy should have a solidus temperature above the maximum temperature it will experience during its use, but below the solidus of the lowest-melting-point base material.

[0045] The liquidus temperature of the brazing alloy composition is typically below about 1060 °C and typically below 1050 °C. The liquidus temperature is typically at least 890 °C, at least 900 °C, or at least 950 °C. Therefore, these brazing alloys are particularly suitable for brazing substrates made of copper or copper alloys. In one embodiment, the brazing alloy comprises a liquidus temperature in the range of 950 °C to 1060 °C or in the range of 970 °C to 1050 °C. The brazing alloy composition is preferably configured to achieve the aforementioned liquidus temperature or ranges thereof.

[0046] Some brazing alloys have a narrow melting range, and some have a wide one. The melting range is often related to the flux, and this can guide the selection, as can the required heating rate. A brazing alloy with a narrow melting range (a small temperature range between the solidus and the liquidus) can be used with fast (e.g., more than 30 °C / minute or more than 40 °C / minute from the solidus to the liquidus temperature) or slow heating rates (e.g., in the range of 5 °C / minute or 10 °C / minute to 30 °C / minute from the solidus to the liquidus temperature). A slow heating rate, such as in furnace brazing, for a brazing alloy with a wide melting range can result in a considerable amount of time during which the solid and liquid phases are in equilibrium and coexist.This leads to segregation, whereby the first-formed liquid (with a specific composition differing from the bulk) flows into the bonding gap, thus becoming physically separated from the solid residue. The resulting chemical inhomogeneity can negatively impact the bond's strength and is often aesthetically undesirable.

[0047] In some brazing applications, the filler material (i.e., the brazing alloy) may need to flow to enter the joint gap, but even if it is pre-placed, flow characteristics can still be important to ensure that the entire joint gap is filled. More free-flowing alloys can penetrate smaller capillary gaps, but if an alloy is too free-flowing in larger gaps, it may not be retained in the joint, resulting in voids and reduced strength. The flow of an alloy is primarily determined by the relative amounts of solid and liquid present at the brazing temperature. If the alloy melts at a single point (e.g., a eutectic composition or a pure metal), then it will be completely liquid at the brazing temperature and will flow readily.In an alloy brazed within its melting range, a certain amount of solid and liquid is present; if it is largely molten, it flows well; if there is a significant solid content, the flow is sluggish. brazing compound composition

[0048] The brazing compound is configured to have a solidification temperature range of not more than 90 °C and a liquidus temperature in the range of 950 °C to 1060 °C, while comprising not more than 18 wt.% of one or more precious metals selected from Au, Pd, and Pt, relative to the total weight of the first brazing compound. The brazing compound may comprise at least 0.1 wt.%, or at least 0.3 wt.%, or at least 0.5 wt.%, or at least 0.8 wt.%, or at least 1.0 wt.%, or at least 1.2 wt.% of one or more of Pt, Pd, and Au. In some embodiments, the brazing compound comprises Au.

[0049] The desired solidification temperature range (e.g., not more than 90 °C) can be achieved with a brazing alloy comprising copper and preferably at least 70 wt.% Cu or at least 75 wt.% Cu or at least 80 wt.% Cu or at least 85 wt.% Cu.

[0050] It has been found that germanium is capable of reducing the liquidus temperature of the copper-based alloy without significantly increasing the solidification temperature range (STR). The brazed joint typically contains a germanium content of no more than 9.0 wt.% or 8.0 wt.%, as amounts above this level make the brazing alloy too brittle and difficult to form into wires, foils, or preforms used in the manufacture of the X-ray tube. Ge levels of at least 0.5 wt.%, 1.0 wt.%, 2.0 wt.%, or 2.5 wt.% may be required to sufficiently reduce the liquidus temperature.

[0051] The brazing alloy may also include other liquidus point reducers such as Au, Pt, Pd, B, Cr, In, Sn, Si, and Al. Au, Pt, and Pd were particularly advantageously added to the brazing joint to moderate the STR values, while improving the joint strength and wettability of the brazing alloy during manufacturing.

[0052] It may be necessary to limit the levels of B, Cr, In, Sn, Si, and Al in the brazing alloy to a combined amount of no more than 5.0 wt.%, 4.0 wt.%, 3.0 wt.%, 2.5 wt.%, or 2.0 wt.%, because the use of these components, as with germanium, can adversely affect the formability of the brazing alloy composition.

[0053] In some embodiments, the brazing alloy composition is free of one or both of boron and tin.

[0054] The brazed joint may further comprise one or more elements selected from the group consisting of transition metals and rare earth metals that are not already defined.

[0055] In one embodiment, the brazed joint comprises Cu, Ge, and one or more of Pt, Pd, Au, and boron. The brazed joint may comprise Cu, Ge, and at least 0.5 wt.% of the sum of one or more of Au + Pd + Pt, and the sum of Cu, Ge, and (Pt + Pd + Au) is greater than 90 wt.%, or greater than 95 wt.%, or greater than 98 wt.%, or greater than 99 wt.% of the total weight of the brazed joint.

[0056] In one embodiment, the brazed joint comprises, in weight %: 60 ≤ Cu ≤ 95; 0.5 ≤ Ge ≤ 9.5; 0 ≤ Sum of one or more of Cr, In, Sn, Si, Al ≤ 5.0; 0 ≤ B ≤ 1.25; 0 ≤ sum of one or more of Au, Pd and Pt < 18.0; and random impurities.

[0057] In one embodiment, the brazed joint comprises, in weight %: 60 ≤ Cu ≤ 95; 0.5 ≤ Ge ≤ 9.5; 0 ≤ Sum of one or more of Cr, In, Sn, Si, Al ≤ 5.0; one or both of 0 < B ≤ 1.25 and 0 < sum of one or more of Au, Pd and Pt < 18.0; and accidental impurities.

[0058] In some embodiments, the brazed joint comprises at least 0.02 wt.% B. In some embodiments, the brazed joint comprises at least 0.5 wt.% Au.

[0059] In some embodiments, the remainder of the brazed joint comprises transition metals or rare earth metals.

[0060] In some embodiments, the amount of tin in the brazed joint is limited to no more than 0.4 wt.%. This tin limitation is particularly preferred when the brazed joint composition includes B, as the combination of these elements has been found to be brittle.

[0061] In another embodiment, the brazing compound composition comprises (or consists essentially of) in weight %: 2.0 ≤ Ge ≤ 9.5; 0.02 < B ≤ 1.25; 0 to 5.0 additives; accidental impurities; and the remainder Cu, wherein the additives and impurities do not include Sn in an amount exceeding 0.4 wt.% of the total weight of the brazing alloy composition.

[0062] The additives may include or consist of one or more additives selected from the group consisting of transition and rare earth metals.

[0063] The brazing alloy composition is preferably suitable for use in a vacuum tube and therefore has the required properties, which include low vapor pressure and low magnetism.

[0064] In another embodiment, the brazing compound composition comprises, in weight %: 54 ≤ Cu ≤ 95.5; 0.5 ≤ Ge ≤ 10.0 and optionally 0 to 5.0 of the sum of Al, Sn, In, Si and B; 0.5 ≤ the sum of Au, Pd and Pt ≤ 30.0; and less than 1.0 random impurities.

[0065] In another embodiment, the brazing compound composition comprises, in weight %: 66 ≤ Cu ≤ 95.5; 0.5 ≤ Ge ≤ 10.0 and optionally 0 to 5.0 of the sum of Al, Sn, In, Si and B; 0.5 ≤ the sum of Au, Pd and Pt ≤ 18.0; and less than 1.0 random impurities.

[0066] In another embodiment, the brazing compound composition comprises, in weight %: 0.5 ≤ Ge ≤ 10.0 and optionally 0 to 5.0 of a sum of Al, Sn, In, Si and B; 0.5 ≤ a sum of Au, Pd and Pt ≤ 30.0; 0 to 5.0 additives selected from the group consisting of transition and rare earth metals, with the exception of Cu, Au, Pt, Pd and Ni; less than 1.0 random impurities; and Rest Cu.

[0067] The brazing alloys used to form the brazed joints within the high-voltage vacuum tubes provide a non-precious metal alternative, or a low-precious metal alternative (e.g., < 18.0 wt%), to high-temperature brazing, particularly in a vacuum environment. The applicants have found that low-precious metal brazing joints can be configured with a desirable liquidus temperature and solidification temperature range (STR) while exhibiting good formability, enabling the formation of hermetic seals within low-pressure environments.

[0068] For the purposes of this disclosure, good formability means that the brazing alloy has a formability of at least 38%, as determined by the formability test described herein, and / or that the brazing alloy is capable of being drawn into a wire with a diameter of only up to 0.030" (0.76 mm) and preferably only up to at least 0.015" (0.38 mm). Typically, wire diameters of up to 0.10" may be used, although wires with larger diameters may be produced as required.

[0069] As disclosed in this document, when it is stated that an element, compound, or other component has a content in a numerical range including zero or in a numerical range without a lower bound, the content of that element, compound, or other component may be zero. In other words, that element, compound, or other component may be absent and is therefore optional. Germanium and optional liquidus temperature reducer

[0070] Germanium and optional amounts of liquidus temperature reducers of aluminium, tin, indium, silicon, chromium and boron contribute to reducing the liquidus temperature of the brazing alloy while maintaining a relatively small solidification temperature range (STR).

[0071] In some embodiments, the germanium content is less than 9.0 wt.%, less than 8.0 wt.%, less than 7.5 wt.%, less than 7.0 wt.%, or less than 6.8 wt.% of the total weight of the brazing alloy. The brazing alloy composition may contain at least 0.5 wt.%, 1.0 wt.%, 1.5 wt.%, 2.0 wt.%, 2.2 wt.%, 2.5 wt.%, 2.7 wt.%, 3.0 wt.%, 3.5 wt.%, 4.0 wt.%, or 4.5 wt.% germanium.

[0072] In some embodiments, the germanium content is in the range of 2.5 to 8.0 wt.% or 3.0 to 7.5 wt.% or 3.5 to 7.0 wt.%. It has been found that this range of germanium content achieves a target liquidus temperature and target STR over a wide range of Pt, Pd, and Au contents.

[0073] In some embodiments, it has been found that for germanium contents of 2.0 wt.% or less, or 2.1 wt.% or less, or 2.2 wt.% or less, or 2.3 wt.% or less, or 2.4 wt.% or less, or 2.5 wt.% or less, or 3.0 wt.% or less, or 3.5 wt.% or less, or 4.0 wt.% or less, the liquidus temperature is typically outside a desired target range (e.g., less than 1060 °C), unless the sum of Au, Pd, and Pt is greater than 10.0 wt.%, and preferably greater than 11.0 wt.%, or greater than 12.0 wt.%, or greater than 13.0 wt.%.

[0074] The liquidus temperature can be further reduced by the addition of liquidus temperature reducers such as aluminum, tin, indium, silicon, chromium, and boron. If present (e.g., > 0.0 wt%), the boron content must not exceed 1.5 wt%, 1.0 wt%, 0.8 wt%, 0.6 wt%, 0.4 wt%, 0.2 wt%, or 0.1 wt%. Similarly, if present (e.g., > 0.0 wt%), the chromium content must not exceed 1.5 wt%, 1.0 wt%, 0.8 wt%, 0.6 wt%, 0.4 wt%, 0.2 wt%, or 0.1 wt%. If present, the aluminium content must not exceed 3.0 wt.% or 2.0 wt.% or 1.0 wt.% or 0.8 wt.% or 0.6 wt.% or 0.5 wt.% or 0.4 wt.%.The tin content, if present, may not exceed 1.5 wt%, 1.0 wt%, 0.8 wt%, 0.6 wt%, 0.4 wt%, 0.2 wt%, or 0.1 wt%. The silicon content, if present, may not exceed 3.0 wt%, 2.0 wt%, 1.0 wt%, 0.8 wt%, 0.6 wt%, 0.5 wt%, or 0.4 wt%. If present, the indium content must not exceed 3.0 wt%, 2.0 wt%, 1.0 wt%, 0.8 wt%, 0.6 wt%, 0.5 wt%, or 0.4 wt%. If present, the total amount of Al + Sn + In + Cr + Si + B must not exceed 4.0 wt%, 3.0 wt%, or 2.0 wt%.The levels of these components should not exceed -% or 1.0 wt.% or 0.5 wt.%. Higher levels of these components may adversely affect one or both of the STR and the machinability of the resulting brazing alloy composition. Gold, palladium and platinum

[0075] Relatively small amounts of gold, palladium, and platinum help to maintain the forgeability of the brazing alloy while maintaining a small STR.

[0076] If present, the gold, palladium, or platinum content preferably does not exceed 17 wt.%, 16 wt.%, 15 wt.%, 14 wt.%, 13 wt.%, 12 wt.%, 11 wt.%, 10 wt.%, 9 wt.%, 8 wt.%, 7 wt.%, or 6 wt.%. The gold, palladium, or platinum content may be at least 0.2 wt.%, 0.4 wt.%, 0.5 wt.%, 0.8 wt.%, 1.0 wt.%, 1.2 wt.%, 1.5 wt.%, 1.8 wt.%, or 2.0 wt.%.

[0077] The total amount of Au, Pd, and Pt preferably does not exceed 17 wt.%, 16 wt.%, 15 wt.%, 14 wt.%, 13 wt.%, or 13 wt.%. Lower amounts of Au, Pd, and Pt may result in poor machinability / forgeability of the brazing alloy. The brazing alloy preferably comprises at least 0.8 wt.%, 1.0 wt.%, 1.5 wt.%, 2.0 wt.%, 2.5 wt.%, or 3.0 wt.% of Au, Pd, and Pt. In some embodiments, the brazing alloy comprises Au and optionally one or both of Pt and Pd. The Pt and Pd may each be in the range of > 0 to 10 wt.%. In some embodiments, one or both of Pt and Pd are in the range of > 0 to 8.0 wt.% or 0.1 wt.% to 6.0 wt.% or 0.2 wt.% to 4.0 wt.%.

[0078] In one embodiment, the brazing alloy comprises 0.5 to 18.0 wt.% Au and optionally > 1.0 to 12.0 wt.%, and one or both of Pd and Pt are in the range of 0 to 10.0 wt.% or up to 8.0 wt.% or up to 6.0 wt.% or up to 4.0 wt.%.

[0079] In other embodiments, the brazing alloy composition includes no Au and one or both of Pd and Pt.

[0080] The brazing compound composition, due to its properties including low vapor pressure and low magnetism, is particularly suitable for use in vacuum tubes and similar applications. The requirement for low magnetism precludes the use of excessive amounts of Ni, Co, and Fe. In some embodiments, the combined amounts of Ni, Co, and Fe are no more than 4.0 wt.%, 3.0 wt.%, 2.0 wt.%, or 1.0 wt.%. boron content

[0081] It has been shown that the addition of elemental boron (e.g., boron > 0.02 wt.% or > 0.05 wt.% or > 0.1 wt.%) results in reduced STR values, while boron levels above 1.25 wt.% result in brazing alloys with insufficient formability, thus preventing the production of the desired forms of the brazing alloys (e.g., in wire or sheet / foil form).

[0082] In some embodiments, the boron level is greater than 0.15 wt.% or greater than 0.20 wt.% or greater than 0.23 wt.% or greater than 0.25 wt.% or greater than 0.26 wt.% or greater than 0.27 wt.% or greater than 0.28 wt.% or greater than 0.29 wt.% or greater than 0.30 wt.% or greater than 0.31 wt.% or greater than 0.32 wt.% or greater than 0.33 wt.% or greater than 0.34 wt.% or greater than 0.35 wt.% or greater than 0.37 wt.% or greater than 0.39 wt.%. In some embodiments, the boron level is not more than 1.2 wt.% or not more than 1.1 wt.% or not more than 1.0 wt.% or not more than 0.90 wt.% or not more than 0.80 wt.% or not more than 0.75 wt.% or not more than 0.70 wt.% or not more than 0.65 wt.% or not more than 0.60 wt.% or not more than 0.55 wt.% or not more than 0.50 wt.%.

[0083] In a preferred embodiment, the boron content is in the range of greater than 0.27 wt.% and not more than 0.80 wt.%. Within this range, the brazing alloys exhibit both good formability and low STR values. Nickel content

[0084] If present, the nickel content can be less than 14 wt%, less than 12 wt%, less than 10 wt%, less than 8.0 wt%, less than 6.0 wt%, less than 4.0 wt%, less than 2.0 wt%, or less than 1.0 wt%. For some applications, the amount of nickel may be dictated by the need for low magnetism. Additives

[0085] Additives exclude elements that already define the composition (for example, in some embodiments Cu, Ge, Sn, Al, Si, In, Ni, Au, Pt, Pd and B).

[0086] A range of elemental additives (preferably metallic) can be added to the alloy composition to improve wettability and flowability during brazing and / or the mechanical strength of the resulting brazed joint. The additives should be selected so as not to significantly impair the STR, liquidus temperature, machinability, and / or vapor pressure of the brazing alloy, or the mechanical integrity or hermeticity of the resulting joint.

[0087] As is obvious to those skilled in the art, small amounts of additives can be added to brazing alloy compositions, which may enhance the functionality of the brazing alloy composition within a given system or application, or at least not be detrimental to it. Determining the type and amount of additives would be within the competence of those skilled in the art, without requiring excessive experimentation. The scope of this disclosure covers such additions of additives.

[0088] In some embodiments, there are more than 0.0 wt.% additives (> 0.0 wt.% additives), which requires that the alloy composition include at least a certain additive content. For example, in some embodiments, the composition includes > 0 to 5.0 wt.% additives. In some embodiments, the additives are selected from the group consisting of transition and rare earth metals, with the exception of Cu, Ni, Au, Pd, and Pt. The upper limit of the total and individual additive components is limited by their ability to maintain the functional performance of the brazing alloy, while the lower limit is limited by the amount required to provide a functional advantage to the brazing alloy.

[0089] The transition and rare earth metal additives may include scandium, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, mercury, actinium, rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, darmstadtium, roenkium, copernicium, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

[0090] In some embodiments, the additives comprise > 0 to 5 wt.% transition metals and preferably at least 0.25 wt.% or at least 0.5 wt.%.

[0091] In some embodiments, the additives may include wetting agents selected from the group consisting of Nb, Mo, W, Co and Fe.

[0092] In some embodiments, the additives may include Ag or Zn to further increase the machinability of the brazing alloys.

[0093] Ti, V and / or Zr can also be added to aid in the bonding of the brazing alloy to ceramic surfaces.

[0094] In one embodiment, the additives comprise one or more of Nb, Mo, W, Co, Cr, Fe, Ti, V, Zr, Au, Ag and Zn.

[0095] In some embodiments, the additives comprise 0 or > 0 to 3 wt.% rare earth metals. The amount of rare earth metals may not exceed 2.0 wt.%, 1.0 wt.%, 0.5 wt.%, 0.1 wt.%, or 0.05 wt.%.

[0096] Rare earth metals, such as Nd, Y, Yb and Ce, can be added to further improve strength and / or hermeticity through grain refinement.

[0097] In one embodiment, the additives comprise one or more of Nb, Mo, W, Co, Cr, Fe, Ti, V, Zr, Au, Ag, Zn, Y, Yb, Nd & Ce.

[0098] The additives can include metals with a liquidus temperature of at least 500 °C, or at least 800 °C, or at least 900 °C, or at least 1000 °C. Due to the requirement for low vapor pressure and high temperature performance, additives with a high liquidus temperature are preferred.

[0099] In some embodiments, there are ≤ 4.0 wt.%, ≤ 3.0 wt.%, ≤ 2.0 wt.%, ≤ 1.0 wt.%, or ≤ 0.5 wt.% additives. In other embodiments, if present, the additive level may be ≥ 0.05 wt.%, ≥ 0.10 wt.%, ≥ 0.15 wt.%, or ≥ 0.20 wt.%. Additive levels below these amounts may not be sufficient to provide the desired functional effect, such as improved wettability or improved strength of the brazed joint. In some embodiments, the additives include or consist of a metallic wetting agent(s), which, if present, may be selected to improve the wettability of the brazing alloy on the substrate surfaces being joined (e.g., Nb, Co, and / or Fe). The wettability of the brazing alloy on the substrate is important to ensure a firm mechanical and hermetic connection.Due to the requirements of the brazing alloy to have a low vapor pressure in some applications, additives such as Cd and Zn are preferably not used.

[0100] In one embodiment, each additive has a vapor pressure of no more than 1.0 × 10 -7 mm Hg (1.33 × 10 -5 Pa) at 700 °C and preferably not more than 5 × 10 -8 mm Hg (6.65 × 10 -6 Pa) at 700 °C or not more than 1 × 10 -8 mm Hg (1.33 × 10 -6 Pa) at 700 °C. In another embodiment, the addition of the additives (which include wetting agents) does not result in the vapor pressure increasing to more than 1.0 × 10 -7 mm Hg (1.33 × 10 -5 Pa) at 700 °C or more than 5 × 10 -8 mm Hg (6.65 × 10 -6 Pa) at 700 °C or more than 1 × 10 -8 mm Hg (1.33 × 10 -6Pa) increased. These undesirable resulting vapor pressures would typically be higher than the vapor pressure of the brazing alloy without the addition of the additives. The brazing alloy preferably comprises no more than 0.5 wt.%, or no more than 0.4 wt.%, or no more than 0.3 wt.%, or no more than 0.2 wt.%, or no more than 0.1 wt.%, or no more than 0.05 wt.% of additives that do not meet this requirement.

[0101] It is understood that the brazing alloy composition can be derived from the composition of the brazing alloy and the composition of the substrates being joined, including any coatings on them. At least some, if not all, of the additives in the brazing alloy composition can be derived into the brazing alloy by diffusion from components in the substrates being joined. Accidental impurities

[0102] In the sense used in this document, accidental impurities refer to unavoidable traces of elements (including oxidized or reduced forms thereof) that occur during the production process of brazing alloys.

[0103] Unless otherwise specified, accidental impurities may include any element or compound not already specified within the brazing alloy composition. A list of accidental impurities typically tested for includes Al, P, Pb, Cd, and Zn. For a duplicate analysis of Example 14 (Table 1), all accidental impurities were measured as being below the limit of detection (wt%), namely Al < 0.001; P < 0.002; Pb < 0.001; Cd < 0.001; and Zn < 0.001. Although Cd and Zn are transition metals, for the application for which the brazing alloy is to be used (e.g., X-ray tubes), Cd and Zn are considered accidental impurities. The applicant's use of ultrapure raw materials does not reflect the typical levels of accidental impurities of these selected components.

[0104] The upper limit of the total amount of impurities can be 1.0 wt.%, preferably 0.5 wt.%, and more preferably 0.15 wt.%. These small amounts of elements typically do not contribute to or modify the actual purpose and / or performance of the brazing alloy. In one embodiment, the incidental impurities comprise no more than 0.5 wt.%, or no more than 0.2 wt.%, or no more than 0.15 wt.%, or no more than 0.1 wt.%, or no more than 0.05 wt.% of any impurity element (e.g., C or P).

[0105] Although accidental impurities (also known as unavoidable impurities) may vary depending on the purity of the raw material used, typical levels of accidental impurities are less than 0.8 wt.% or less than 0.5 wt.% or less than 0.2 wt.% or less than 0.1 wt.% or less than 0.05 wt.% of the total weight of the brazing alloy composition.

[0106] Some applications required even stricter limits. For example, limits for each of Zn, Cd, Pb, and C may be less than 0.1 wt.%, less than 0.05 wt.%, less than 0.01 wt.%, less than 0.005 wt.%, or less than 0.01 wt.% of the total weight of the brazing alloy composition. In one embodiment, Zn and Cd have limits of less than 0.002 wt.% or less than 0.001 wt.%. Pb and P may have limits of less than 0.01 wt.% or less than 0.002 wt.%. C may have limits of less than 0.05 wt.% or less than 0.01 wt.% of the total weight of the brazing alloy composition. All other metallic impurities with a vapor pressure higher than 10 -7 mm Hg (1.33 × 10 -5The concentrations of impurities with a vapor pressure lower than 10 Pa) at 500 °C are preferably limited to 0.1 wt.% or less, or 0.01 wt.% or less; or 0.005 wt.% or less, or 0.002 wt.% or less. Impurities with a vapor pressure lower than 10 -7 mm Hg at 500 °C are preferably limited to a total of no more than 0.2 wt.% or no more than 0.1 wt.% or no more than 0.075 wt.% of the total weight of the brazing alloy composition. Substrates

[0107] The high-voltage tubes of the present disclosure can comprise a variety of substrates suitable for joining and / or sealing using the previously defined low-precious-metal brazing alloy. The high-voltage vacuum tube can comprise brazing assemblies comprising substrates including copper or copper alloys, Kovar (Ni-Co-Fe alloy), metallized ceramic components (e.g., molybdenum-manganese metallized, nickel-plated, or copper-plated); steel including stainless steel; nickel and nickel alloys including Ni superalloys; and other refractory metals (e.g., molybdenum and alloys thereof) with a liquidus temperature preferably at least 20 °C, at least 35 °C, or at least 50 °C above the liquidus temperature of the brazing alloy, but not limited thereto. Solidus temperature range

[0108] To avoid segregation in the brazed joints of a high-voltage vacuum tube while promoting good brazing coverage over the joint, the brazing alloy used to produce the brazed joint preferably has a narrow temperature difference between the solidus temperature and the liquidus temperature (i.e., low STR values).In some embodiments, the brazing compound composition is configured to achieve a temperature difference between the solidus temperature and the liquidus temperature of the brazing alloy of no more than 90 °C, or no more than 88 °C, or no more than 85 °C, or no more than 82 °C, or no more than 80 °C, or no more than 75 °C, or no more than 70 °C, or no more than 65 °C, or no more than 60 °C, or no more than 55 °C, or no more than 50 °C, or no more than 45 °C, or no more than 40 °C, or no more than 35 °C, or no more than 30 °C, or no more than 25 °C, or no more than 20 °C. The STR ranges mentioned above are considered to be low STR values.

[0109] In a third second of the present disclosure, a brazing assembly of a high-voltage vacuum tube is provided, comprising a first connection and a second connection, wherein at least one of the connections comprises a composition as previously described in the section on brazing compound composition.

[0110] In one embodiment, the assembly comprises two compounds, each compound comprising a composition according to the first aspect of this disclosure. Each of the brazing alloys may be different. The first compound may comprise a composition having a liquidus temperature below the solidus temperature of the second brazing compound composition.

[0111] In one embodiment, the first and second brazed joints comprise a composition according to the first aspect of this disclosure. Preferably, the difference between the solidus temperature of the first joint and the liquidus temperature of the second joint is at least +15 °C or at least +20 °C. The first joint may comprise a brazing alloy composition with a solidus temperature of at least 950 °C or at least 990 °C, and the second joint may comprise a liquidus temperature of not more than 980 °C.

[0112] This type of assembly is ideally suited for a step brazing process, where the higher-temperature brazed joint is built up and cooled first, before the lower-temperature second brazed joint is built up. Since the solidus temperature of the first brazed joint is higher than the liquidus temperature of the second, the integrity of the first brazed joint should not be compromised if the brazing temperature of the second joint is kept below the solidus temperature of the brazing alloy used in the first joint.

[0113] Although the present disclosure includes step brazing using two brazing alloy compositions, the present disclosure also includes step brazing wherein only one of the brazing joints comprises a brazing alloy according to the first aspect of the present disclosure.

[0114] In some embodiments, the brazing process can result in the migration of boron from the brazed joint. The reduction of the boron content in this initial brazed joint can lead to an increase in the solidus and liquidus temperatures compared to the original brazing alloy composition, thus enabling the use of the same brazing alloy composition in a step brazing process. This increase in liquidus temperature can then allow the same initial brazing alloy to be used to subsequently braze an adjacent component (second brazing joint) at a brazing temperature below the solidus temperature of the first brazing joint.

[0115] The brazed joint may also include compositional variations compared to the brazing alloy composition used to form the brazed joint. In some embodiments, the brazed joints are derivable from the brazing alloy composition of the first aspect of the present disclosure. The derivable brazed joints may have a lower boron content compared to the brazing alloy composition from which they are derived. The materials / components adjacent to the brazed joint may also have a measured level of boron relative to the materials / components prior to the brazing joint being formed.

[0116] In the sense used in this document, brazing refers to a joining process of two (or more) materials using a brazing alloy that mixes with the materials to be joined upon melting. The liquidus temperature of the brazing alloy is lower than the liquidus temperature of the materials to be joined. The liquefied / molten brazing alloy interacts with the materials to be joined and forms the brazed joint as it cools. The interaction of the brazing alloy and the materials to be joined can be described by diffusion processes and the formation of intermetallic phases and other compounds. Brazing can be carried out in a vacuum, a reducing atmosphere, or a protective atmosphere (e.g., mixtures of hydrogen and nitrogen gases).A flux can be used during brazing to remove oxides from the brazing surfaces of the materials to be joined and to prevent oxide formation during brazing, thus allowing thorough wetting of the surfaces of the materials to be joined by the liquefied / molten brazing alloy. However, fluxless brazing is preferred.

[0117] High-voltage vacuum tubes comprise an anode and a cathode positioned opposite each other within a vacuum-sealed interior. This interior is typically enclosed by a cylindrical metal casing, with the anode and / or cathode electrically insulated by a ring-shaped insulator. These high-voltage vacuum tubes can operate at temperatures exceeding 800 °C, 900 °C, 950 °C, or 1000 °C. process

[0118] In a third aspect of the present disclosure, a process for producing a high-voltage vacuum tube of the first aspect of the disclosure is provided, wherein the brazing assembly forms the first component; wherein the second component and a brazing alloy composition comprise a total of not more than 18 wt.% of one or more precious metals selected from Au, Pd and Pt and are configured to encompass a solidification temperature range of not more than 90 °C and a liquidus temperature in the range of 950 °C to 1060 °C, wherein the brazing assembly is formed by: a. optionally, hold the brazed assembly for at least 10 minutes at a temperature between 10 °C and 400 °C below the liquidus temperature of the brazing alloy composition; b. Heating the brazed assembly to a brazing temperature above the liquidus temperature of the brazing alloy composition; and c. Cooling the brazing assembly below the solidus temperature of the brazing alloy composition to form the brazing joint that joins the first component and the second component together.

[0119] The process involves increasing the temperature between the solidus and liquidus temperatures at a rate of 1 °C / min to 30 °C / min between the solidus and liquidus temperatures of the brazing alloy. The temperature increase rate can be less than 28 °C / min, less than 26 °C / min, less than 24 °C / min, less than 22 °C / min, less than 20 °C / min, less than 18 °C / min, less than 16 °C / min, less than 14 °C / min, or less than 12 °C / min. In contrast to brazing alloys with a high STR (Strength of Solids), the brazing alloys of this disclosure are capable of being brazed at a lower heating rate without the same risk of segregation resulting in poor joint performance.The use of lower heating rates also avoids other disadvantages associated with faster heating rates, such as component distortion, spalling, and excessive degassing. This allows the brazing alloys to be used effectively in a wider range of brazing environments, including those involving the brazing of components where one component has such low conductivity (e.g., a ceramic) and / or a large thermally active mass that fast heating rates are difficult to achieve.

[0120] In some embodiments, the brazing cycle also includes holding the brazed joint and associated substrates at a temperature typically between 10 °C and 400 °C below the solidus temperature for between 10 and 30 minutes before brazing the brazed joint at the brazing temperature, typically between 15 °C and 60 °C above the liquidus temperature of the brazing alloy.

[0121] In other embodiments, double brazing is used, in which the brazed joint is cooled by approximately 100 °C (below the solidus temperature) between brazing cycles.

[0122] The brazed joint can be formed in a brazing furnace, which may include a vacuum furnace, a reduction furnace (e.g., hydrogen), or a protective gas furnace (e.g., nitrogen or argon). Brazing of concealed joints is particularly well-suited to being carried out in a brazing furnace or oven because the temperature and atmospheric conditions of the brazing process can be reliably controlled. The vacuum furnace can maintain an airless vacuum of less than 8 × 10⁻⁶. -4 mmHg (1.17 × 10 -3 Pa) and preferably less than 5 × 10 -4 mmHg (6.65 × 10 -2 Pa). The use of laser brazing in a controlled atmosphere may also be able to achieve the required levels of temperature and atmosphere control.

[0123] In some embodiments, a two-stage brazing process is employed, comprising brazing a first brazing alloy composition to a first brazing temperature and allowing it to cool in order to form a first brazed joint, and then brazing a second brazing alloy composition to a second brazing temperature and allowing it to cool in order to form a second brazed joint, wherein the solidus temperature of the first brazed joint is higher than the liquidus temperature of the second brazed joint, and wherein the second brazing temperature is kept below the solidus temperature of the first brazed joint (e.g. by at least 10 °C or at least 15 °C or at least 20 °C).

[0124] In one embodiment, the brazing joint is formed by placing the brazing alloy composition in the form of a wire, powder, paste or foil adjacent to two components to be joined, heating the brazing composition above the liquidus temperature of the brazing alloy composition and allowing a molten brazing alloy to flow between the two components via capillary action to form the brazing joint. Performance of the brazed joint

[0125] The brazing alloys and derived compounds of the present disclosure are preferably hermetic, have good mechanical strength and exhibit a low vapor pressure.

[0126] The brazed joints of the present disclosure preferably exhibit hermeticity with a maximum permissible leakage rate of closed vacuum assemblies of 1 × 10 -6 atm.cc / s or less, 1 × 10-7 atm.cc / s or less or 1 × 10 -8 atm.cc / s or less (ASTM F2391 using helium gas). In some applications, such as RTP assemblies, a lower sealing integrity may be sufficient, although the integrity of the brazed joint should be such that the process gases are contained within the process chamber and do not leak through the brazed joint.

[0127] The brazed joints of this disclosure preferably have a tensile strength of at least 900 MPa, at least 950 MPa, or at least 1000 MPa. The brazed joints of this disclosure preferably have a shear strength of at least 5.0 MPa or at least 7.0 MPa. The tensile and shear strength are measured according to the procedure of standard AWS C.3.2M / C3.2:2019 for assessing the strength of brazed joints. The reference substrates for the test were the joining of 304 stainless steel with 100% copper.

[0128] The brazing alloy of the present disclosure preferably has a vapor pressure of less than 1 × 10 -11 mm Hg at 500 °C (1.33 × 10 -9 Pa) or less than 1 × 10 -12 mm Hg (1.33 × 10 -10 Pa) at 500 °C or less than 1 × 10 -13 mm Hg (1.33 × 10 -11 Pa) at 500 °C or less than 5 × 10 -14 mm Hg (1.33 × 10 -12Pa) at 500 °C or less than 1 × 10 -15 mm Hg (1.33 × 10 -13 Pa) at 500 °C. At 700 °C, the vapor pressure of the brazing alloy is preferably less than 1 × 10 -8 mm Hg (1.33 × 10 -6 Pa) or less than 1 × 10 -9 mm Hg (1.33 × 10 -7 Pa) or less than 5 × 10 -10 mm Hg (1.33 × 10 -8 Pa) or less than 1 × 10 -11 mm Hg (1.33 × 10 -9 Pa).

[0129] A solidus temperature is the highest temperature at which a metal or alloy is completely solid. A liquidus temperature is the lowest temperature at which a metal or alloy is completely liquid.

[0130] For the purposes of this disclosure, high voltage means a voltage of at least 1 kV, or at least 10 kV, or at least 100 kV. The advantages of the brazing alloy of this disclosure may also be determined by applications where the voltage / distance ratio (V / d) is sufficiently high, for example, at least 0.5 kV / mm, or at least 1 kV / mm, or at least 10 kV / mm.

[0131] Vacuum brazing is typically performed at approximately 1 × 10 -5 mm Hg (1.33 × 10 -3 Pa) carried out.

[0132] Machinability and malleability are terms that are used interchangeably.

[0133] The notation "Rest Cu" means that the copper makes up the remaining part of the brazing alloy composition up to 100.00 wt.% (i.e. wt.% copper = 100.00 wt.% - amount of all other components (wt.%) in the brazing alloy).

[0134] The total weight of all components of the brazing alloy should not exceed 100 wt.%. Theoretical total weights of combinations of components exceeding 100 wt.% should be disregarded.

[0135] Unless otherwise specified, references to quantities in wt.% are based on the total weight of the brazing alloy composition.

[0136] For the purposes of this disclosure, precious metals means gold, silver, palladium and platinum.

[0137] References to the components of a composition are references to those components in their elemental form (i.e., oxidation state = 0). Accidental impurities can exist in any permissible oxidation state, but preferably have an oxidation state of zero. Examples

[0138] Test brazing alloys in various compositions listed in Table 1 were produced by heating the mixture of elemental components to approximately 1080 °C to form a homogeneous melt. The molten alloy was then cast into the form of an ingot, followed by cold working and annealing to produce the alloy in wire and / or foil form. Methodology: Solidus and liquidus temperature

[0139] Differential scanning calorimetry (DSC) was used to determine the melting behavior of these alloys. Liquidus and solidus temperatures were measured by DSC using small samples with a mass of approximately 20 mg, placed in an aluminum oxide crucible with a lid. After loading the sample, the chamber was evacuated and filled with argon gas. The analysis was performed in the temperature range of 298 K to 1373 K at a heating rate of 20 K min⁻¹. -1The analysis was performed. The output is a curve representing the variation in heat flux density with temperature.

[0140] With reference to Fig. 2. DSC measures physical and chemical changes within a material in response to temperature. It provides information about endothermicity (absorbing heat), exothermicity (releasing heat), and changes in heat capacity.

[0141] The DSC experimental setup (measured using a DSC instrument from Netzsch - model Jupiter STA 449 F3) involves two stages: heating and cooling, and the same cycle repeated a second time (second cycle of heating and cooling). Fig.Figure 2 is the DSC curve for the second heating-cooling cycle for sample 4. For better visibility, the DSC curve (which is continuous) has been split, with the lower curve being the heating curve (left to right) and the upper curve the cooling curve (right to left). The solidus temperature of 1032.4 °C is determined as the point on the heating curve immediately before an increase in heat flux density, indicating the onset of liquid phase formation. The liquidus temperature of 1039.3 °C is determined as the point on the cooling curve immediately before a decrease in heat flux density, indicating the onset of solid phase formation. malleability

[0142] The alloy compositions were prepared by melting 5 ± 1 grams (0.25 inches high) on a water-cooled copper hearth using a tungsten electrode in an argon gas atmosphere, producing hemispherical alloy ingots (buttons). Buttons with different compositions were subjected to cold rolling using a two-roll rolling mill to test their ability to plastically deform into a sheet shape.

[0143] The formability of each composition was determined by measuring the deformation required to produce a fracture point when subjected to the rolls at room temperature. At each stage, the roll gap is adjusted to the equivalent of up to a 10% reduction in the knob thickness. The formability of alloys capable of withstanding cold rolling down to a sheet only 0.002 inches (≈ 50 µm) thick is considered nearly ductile. The formability test defines that a reduction from 0.25 inches to 0.002 inches corresponds to 100% formability, while a reduction to 0.125 inches corresponds to 50% formability.

[0144] The compositions were considered somewhat brittle if an early onset of fracture occurred before the target thickness of approximately 50 µm was reached. This methodology was used to evaluate the ability of the various compositions of this alloy to produce pre-formed shapes of wire or sheet as filler material for brazing. Early onset of fracture means the visible appearance of fractures with the naked eye in the sample, as shown in Fig. 6d (60% malleability), 6e (38% malleability) and 6f (20% malleability) were observed, compared to Fig. 6a-c, which show no visible signs of fracture when the samples are processed to a thickness of 50 µm (100% malleability).

[0145] A formability percentage of at least 38% is considered practical for manufacturing preforms of brazing alloys, with a formability of at least 45%, 50%, 60%, 70%, 80%, 90%, or 100% being preferred. Accordingly, the boron content of the brazing alloy composition can be configured to achieve the aforementioned formability values ​​or ranges. Shear strength

[0146] Shear strength was measured according to the procedure of standard AWS C.3.2M / C3.2:2019 for assessing the strength of brazed joints. Shear strength was measured between substrates of 304 stainless steel and pure copper. It was observed that for each of the shear strength tests, the failure point was located at the copper substrate, indicating that the increase in the reported shear strength may be due to the diffusion of brazing elements of this disclosure into the copper substrate, thereby strengthening the copper substrate. Hermeticity

[0147] The hermeticity of the brazed joint was tested according to ASTM F2391 using helium gas. The hermeticity test was performed on all specimens that were tested for shear strength, and all specimens within the scope of disclosure passed the test by exhibiting an allowable helium leakage rate of 1 × 10⁻⁶. -8atm.cc / s or less. Test results

[0148] A series of experiments were undertaken to evaluate the characteristics of brazing alloys with regard to their solidus (S temperature) and liquidus (L temperature) temperatures as well as their malleability.

[0149] It was found that the vapor pressures of the brazing alloys of the present disclosure in Table 1 are less than 1 × 10 -11 mm Hg (1.33 × 10 -9 Pa). The vapor pressure of each alloy is estimated using the individual vapor pressure distribution of each element: Ptot=∑aiPi(i=1 to n) where ai is the activity and Pi is the equilibrium vapor pressure at liquidus temperature +50 °C.

[0150] The preferential evaporation of different alloying elements is a function of the element's volatility and its activity within the alloy. The partial contribution of each alloying element to the total equilibrium vapor pressure is a function of the equilibrium vapor pressure of the element in its pure form and its activity in the alloy, as described by equation (1).

[0151] With reference to Fig.Figure 2 shows the effect of boron on brazing alloys with 2.5 wt% germanium (line A) and 4.8 wt% germanium (line B), revealing that for each, there is an optimal boron content that yields a minimum STR value. For germanium contents of 2.5 wt% (samples 1, 2, 3, C-1), 4.2 wt% (sample 4), and 4.8 wt% (samples C-2, C-3, 5, 6, 7), the optimal boron content was in the range of approximately 0.5 to 1.25 wt% boron. Although a similar decrease in STR was observed at germanium levels of 7.2 wt% (a minimum STR was recorded at 0.55 wt% boron) and 10 wt% (a minimum STR was recorded at 0.80 wt% boron), the absolute minimum STR values ​​were not as low compared to the brazing alloys with lower germanium content.

[0152] However, a limitation of low Ge contents is that they exhibit elevated liquidus temperatures, which can be detrimental to applications involving the brazing of copper or copper alloy components. Brazing alloys with a Ge content of approximately 4.2 wt.% to 4.8 wt.% of the present disclosure have been found to exhibit an excellent combination of low STR values; liquidus temperatures within the desired range for brazing copper / copper alloy components; and good formability. The brazing alloy compositions of the present disclosure provide a variety of liquidus temperatures, favorable STR ranges, and acceptable formability to meet the functional requirements of many end-use applications, all without the use of significant amounts of precious metals.

[0153] For example, the melt profile of sample 4 is similar to that of the precious metal brazing alloy 35Au-65Cu (WESGO™), which has a liquidus temperature of 1010 °C and a STR of 20 °C (Table 2). Although other samples may have higher STRs than precious metal brazing alloy alternatives, they still offer improved performance relative to existing non-precious metal alternatives. For example, 50Au-50Cu (WESGO™) has a liquidus temperature of 970 °C and an STR of 15 °C (Table 2). Samples 15 and 16 have a comparable liquidus temperature but an STR of 68–69 °C. This is a significant improvement over the non-precious metal brazing alloy (GEMCO™ from WESGO™), which has a liquidus temperature of 975 °C but an STR of 95 °C (Table 2).

[0154] Although brazing alloys with a higher Ge content (e.g. 7.2 wt.% or more) may exhibit relatively high STR levels and lower liquidus temperatures (compared to brazing alloys with lower levels of Ge), these brazing alloy characteristics are still acceptable for some applications.

[0155] As shown in Table 1, the malleability of the brazing alloys tended to decrease with an increase in boron content, with a marked decrease when the boron content increased above 1.0 wt.%. Ge content appeared to have a lesser effect on malleability, with the malleability decreasing from 43 to 40 to 38 when, at a constant boron content of 1.25 wt.%, the Ge content increased from 2.5 wt.% to 4.8 wt.% to 7.2 wt.%. Fig.Figures 6A to 6F illustrate the films formed in samples 8 to 12 and C-6, with samples 11, 12 and C-6 showing visible signs of cracking while formability decreases. Effect of the addition of Au, Pd, Pt

[0156] As illustrated in Samples 22, 24 to 41, the addition of Au, Pd, and Pt provides brazing alloy compositions with desirablely low STRs and liquidus temperatures within the target range for brazing the interior of the X-ray tube, which is subject to high temperatures, vacuum, and, in some cases, high stress. Compared to conventional brazing alloys such as 50 Au 50 Cu with a shear strength of 1279 PSI, the brazing alloys containing Au exhibit improved shear strength and are therefore particularly advantageous for use in rotating anode assemblies within the X-ray tube. Table 1 ID Cu(Gew.-%) Ge(Gew.- %) B(Gew.-%) Tomorrow(Gew.- %) L-Temp. (°C) S-Temp. (°C) STR-Temp. (°C) Form.% Scherung (PSI) 1 96,75 2,5 0,5 0.25 Ni 1068 1008 60 100 - 2 96,45 2,5 0,8 0.25 Ni 1039 1002 37 68 - 3 96,0 2,5 1,25 0.25 Ni 1044 1008 36 43 - C-1 95,25 2,5 2,0 0.25 Ni 1077 1008 69 36 - 4 94,81 4,2 0,84 0.15 Ni 1039 1032 7 84 - C-2 94,95 4,8 0 0.25 Ni 1048 986 62 100 - 5 94,45 4,8 0,5 0.25 Ni 1015 1003 12 100 - 6 94,18 4,8 0,77 0.25 Ni 1035 1016 19 83 - 7 93,7 4,8 1,25 0.25 Ni 1010 986 24 40 - C-3 92,95 4,8 2,0 0.25 Ni 989 951 38 35 - 8 92,3 7,2 0,25 0.25 Ni 1035 959 76 100 - 9 92,175 7,2 0,375 0.25 Ni 1034 959 75 100 - 10 92,0 7,2 0,55 0.25 Ni 1020 954 66 100 - 11 91,75 7,2 0,8 0.25 Ni 1040 962 78 60 - 12 91,30 7,2 1,25 0.25 Ni 1012 953 59 38 - 13 91,94 7,33 0,47 0.26 Ni 1028 947 81 - - 14 91,82 7,4 0,53 0.25 Ni 1005 967 38 100 1041 C-4 89,75 10 0 0.25 Ni 1005 902 103 100 - 15 89,25 10 0,5 0.25 Ni 974 905 69 100 - 16 88,95 10 0,8 0.25 Ni 974 906 68 56 - 17 93,00 6,5 0,25 0.25 Ni 1025 956 69 100 - C-5 87,25 12 0,5 0.25 Ni 968 823 145 100 1299 C-6 93,45 4,8 0,5 1.0 Sn0.25 Ni 1010 837 173 20 - C-7 92,00 6,5 0,25 1.0 Sn0.25 Ni 1007 891 116 30 - C-8 88,90 10 0,1 1.0 Sn 983 773 210 - - 18 90,55 5,5 0,7 3.0 Co0.25 Ni 1053 1003 50 - - 19 87,60 7,5 0,1 4.8 Ni 1026 937 89 - - 20 91,25 5,5 0,8 2.2 Fe0.25 Ni 1059 1019 40 - - Table 1 (continued) ID Cu(Gew.-%) Ge(Gew.- %) B(Gew.-%) Monday(Gew.-%) L-Temp. (°C) S-Temp. (°C) STR-Temp. (°C) Form.% Scherung (PSI) 21 92,55 5,5 0,7 1.0 Ag0.25 Ni 1012 970 42 - - 22 90,75 4,5 0,7 3.8 Au 1037 998 39 - - 23 95,50 4,0 0,5 0.45 Si0.2 Al0.25 Ni 1007 920 87 - - 24 92,30 6,7 0 1.0 Au 1032 989 43 100 1628 25 89,40 5,3 0 5.3 Au 1049 1047 2 100 - 26 92,00 6,5 0,5 1.0 Au 1038 969 65 - - 27 86,50 3,0 0,5 10 Au 1039 984 55 75 - 28 86,50 3,0 0 10 Au0.5 Si 1057 1036 21 96 - 29 86,5 3,0 0,5 10.0 Au 1007 969 38 75 - 30 89,5 2,5 1,0 7.0 Au 1015 985 30 68 - 31 92,0 8,0 0 10.0 Au 1020 935 85 85 - 32 90,6 6,7 0 2.7 Au 1044 1013 31 100 1383 33 76,0 4,0 0 20.0 Au 1032 1002 30 100 1341 34 74,0 6,0 0 20.0 Au 978 927 51 - 1363 35 84,0 2,0 0 14.0 Au 1056 1031 25 - 1345 36 78,6 2,7 0 18.7 Au 1012 1004 8 - - 37 84,0 6,0 0 10.0 Au 1064 1041 23 100 - 38 80,0 10,0 0 10.0 Au 950 850 100 50 - 39 72,0 2,0 0 25.0 Au1.0 Sn 993 963 30 97 - 40 85,0 4,0 0 10 Au1.0 Ni 1028 1025 3 97 - 41 90,0 6,0 0 4.0 Pt 1023 1008 15 97 - 4.0 Pd C-9 81,5 8,5 1,0 9.0 Ni 1026 926 100 - - C-10 91,45 2,5 0,8 5.0 Y0.25 Ni 1077 983 94 - - C-11 85,8 5,5 0,8 8.0 Ag0.70 Ni 1006 775 231 - - C-12 46,0 6,0 0 48.0 Pd 1088 1059 29 21 -

[0157] As in Fig. As illustrated in Figure 9, the addition of a relatively small amount of Au to a Cu-Ge alloy containing approximately 6 wt% (5.3 to 6.5 wt%) Ge results in a substantial reduction of the STR of the resulting brazing alloy composition. A near-eutectic composition was obtained at an Au content of 5.3 wt%, after which a further increase in the Au content resulted in a gradual increase in the STR. Example 41, containing 4 wt% each of Pd and Pt (8 wt% combined) and 6 wt% Ge, achieves an STR of 15 °C, which is consistent with the STR value of an equivalent composition comprising 8 wt% Au (instead of 4 wt% each of Pd and Pt) when the STR is determined by interpolation of the data in Fig.9 is estimated. This result supports the notion that Pd and Pt have a similar effect on the STR as Au, with each of Au, Pt and Pd unexpectedly being able to provide high-quality brazed joints when present in relatively small quantities.

[0158] With reference to Fig. 10 highlights the variation of the liquidus and solidus temperature with the Ge concentration at a fixed Au concentration of 10 wt.%, that at this Au concentration the optimal Ge concentration is between about 2.5 wt.% and about 7.0 wt.%, with particularly low STR values ​​between about 3.5 and about 6.0 wt.%. Effect of the addition of additives

[0159] The majority of the examples contained 0.25 wt% Ni, added as a wetting aid to enhance the wetting of the brazing alloy against a stainless steel substrate. The brazing alloy composition tolerated Ni levels up to 4.8 wt% while still maintaining an acceptable STR value; however, it is expected that additive levels above 5.0 wt% may adversely affect the STR or the liquidus temperature, as indicated in Comparative Example 10 (C-10), which included 5.25 wt% additives. Higher levels of Ni and Ag (C-9, C-11) further confirmed this negative trend.

[0160] The effect of adding sulfur (Sn) was investigated by adding 1.0 wt% Sn to the composition for Example 5, which had a low STR of 12 °C. The resulting composition (C-6) showed a detrimental decrease in the STR value to 173 °C. Other Sn-containing compositions, C-7 and C-8, also exhibited high STR values ​​of 116 °C and 185 °C, respectively. Furthermore, the effect of Sn resulted in a significant decrease in the malleability of Example 5 (100% malleability), with the addition of 1.0 wt% Sn causing a dramatic reduction in malleability to 20%. Fig. 6f). Similarly, the malleability of sample 17 decreased from 100% to 30% (sample C-7) upon the addition of 1.0 wt% Sn. Performance of the brazed joint

[0161] With reference to Fig.4 & 5 it was found that the brazing composition (sample 13) is capable of flowing between a concealed joint 430, 530 of copper 410, 510 and 304 stainless steel 420, 520, with the arrow pointing in Fig. 4 indicates the flow direction. As shown in the cross-sectional image of the microstructure ( Fig. As stated in 5), the copper 510 and the 304 stainless steel substrate 520 are joined together by the brazed joint 530, which has an average thickness of approximately 10 µm. As shown in Fig. As illustrated in Figure 5, the brazed joint provides a continuous and clean interface between the substrates. No segregation was observed. Testing confirmed that the brazed joint met the maximum permissible leakage rate of 1 x 10⁻⁶ for closed vacuum assemblies. -8 atm.cc / s complied with the requirements for high-vacuum assemblies.

[0162] A similar performance without observed segregation was achieved when the brazing alloy was used to braze a strip of 304 stainless steel to a strip of copper in a “T” configuration (not shown).

[0163] Fig. Figure 7A illustrates a copper plate 700 on a 304 stainless steel substrate 710, with a wire made of a brazing alloy (0.030" diameter) 720 in contact with the two substrates. Fig.Figure 7B illustrates that after brazing (for 15 minutes at 1048 °C under vacuum), the brazing alloy forms brazing fillets 730 visible to the naked eye on all four edges of the square specimen of the concealed joint, indicating excellent brazing flux. A magnification (x30) of a section of the brazed joint combined with an EDS analysis reveals that the brazed joint 730 has a uniform smooth appearance immediately adjacent to 740 and distal to 750 to the copper plate 700 (i.e., no evidence of segregation), with the EDS spectrum confirming a uniform concentration of the brazing elements and also confirming the presence of the 304 stainless steel 760. Table 2 Trade market Au(Gew.- %) Ni(Gew.- %) Cu(Gew.-%) Ge(Gew.- %) Liquidstemp. (°C) Solid dust temp. (°C) STR-Temp. (°C) NicoroTM 35 3 62 - 1030 1000 30 NioroTM 73,8 26,2 - - 1010 980 30 WESGOTM50Au-50Cu 50 - 50 - 970 955 15 WESGOTM35Au-65Cu 35 - 65 - 1010 990 20 GemcoTM - 0,25 87,75 12 975 880 95

[0164] Fig.Figure 8A illustrates a copper plate 800 on a 304 stainless steel substrate 810, with a wire made of the commercial brazing alloy Gemco™ (0.030" diameter) 820 in contact with the two substrates. Fig. Figure 8B illustrates that after brazing (for 15 minutes at 1000 °C under vacuum), the brazing alloy forms a single brazing fillet visible to the naked eye at the edge where the wire was placed, resulting in restricted brazing flow and an inferior hidden joint compared to the brazed joint made of Fig.7B. Additionally, a magnification (x30) of a section of the brazed joint 830, combined with an EDS analysis, reveals that of the sections of brazed joint 840 and 850 with the copper plate 800, the section furthest from the copper plate 850 exhibited a rough appearance (i.e., evidence of segregation), with the EDS spectrum also confirming a variation in the elemental concentration of the brazing elements across this section. Due to the variation in the brazed joint composition, the functionality of the brazed joint would be expected to be impaired.

[0165] It is understood that modifications and variations can be made without deviating from the spirit and scope of the novel concepts of the present revelation. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 4126803

[0004]

Claims

[1] X-ray tube, comprising: an X-ray tube bulb comprising an interior; an anode assembly located inside the X-ray tube bulb; and a cathode assembly arranged inside the X-ray tube bulb and emitting an electrode beam to impinge on a target surface of the anode assembly and to form electromagnetic radiation, wherein the X-ray tube comprises a brazed assembly, the brazed assembly comprising a first component and a second component joined together by a first brazed joint, the first brazed joint comprising a composition configured to have a solidification temperature range of not more than 90 °C and a liquidus temperature in the range of 950 °C to 1060 °C; wherein the brazed joint in total does not exceed 18 wt.-% of one or more precious metals selected from Au, Pd and Pt, relative to the total weight of the first brazed joint, wherein at least one section of the brazed joint is exposed to the interior of the X-ray tube bulb and wherein at least one of the first and second components forms part of one or more of the X-ray tube bulb, the anode assembly and the cathode assembly. [2] High-voltage vacuum tube, comprising: a vacuum tube bulb comprising an interior; an anode assembly located inside the vacuum tube bulb; and a cathode assembly arranged inside the vacuum tube bulb and emitting an electrode beam to impinge on a target surface of the anode assembly and to form electromagnetic radiation, wherein the high-voltage vacuum tube comprises a brazing assembly, the brazing assembly comprising a first component and a second component joined together by a first brazing joint, the first brazing joint comprising a composition configured to have a solidification temperature range of not more than 90 °C and a liquidus temperature in the range of 950 °C to 1060 °C; wherein the brazing joint in its entirety does not exceed 18 wt.-% of one or more precious metals selected from Au, Pd and Pt, relative to the total weight of the first brazed joint, wherein at least one section of the brazed joint is exposed to the interior of the vacuum tube bulb and wherein at least one of the first and second components forms part of one or more of the vacuum tube bulb, the anode assembly and the cathode assembly. [3] High-voltage vacuum tube according to claim 2, comprising a voltage of at least 1.0 kV. [4] High-voltage vacuum tube according to claim 2, wherein the high-voltage vacuum tube is part of a power tube, a magnetron, a traveling wave tube, a carcinotron or a klystron. [5] High-voltage vacuum tube according to claim 2, wherein the electromagnetic radiation is in the form of X-rays or microwaves. [6] High-voltage vacuum tube according to claim 2, wherein the anode assembly is a rotating anode assembly. [7] High-voltage vacuum tube according to claim 2, wherein at least one of the first and second components forms part of the vacuum tube bulb. [8] High-voltage vacuum tube according to claim 2, wherein at least one of the first component and the second component forms part of the anode or cathode assembly. [9] High-voltage vacuum tube according to claim 2, wherein the first component or the second component comprises ceramic or a metallized ceramic. [10] High-voltage vacuum tube according to claim 2, wherein one or both of the first component and the second component comprise stainless steel, copper, a copper alloy, a nickel alloy or a Ni-Co-Fe alloy. [11] High-voltage vacuum tube according to claim 2, wherein the brazed joint comprises Au. [12] High-voltage vacuum tube according to claim 2, wherein the brazing joint comprises copper and not more than 8.0 wt.% germanium. [13] High-voltage vacuum tube according to claim 2, wherein the brazed joint further comprises one or more elements selected from the group consisting of transition metals and rare earth metals. [14] High-voltage vacuum tube according to claim 2, further comprising one or more of Pt, Pd, Au and B. [15] High-voltage vacuum tube according to claim 2, wherein the brazing compound comprises Cu, Ge and at least 0.5 wt.% of Au + Pd + Pt. [16] High-voltage vacuum tube according to claim 2, wherein the brazed joint comprises in wt.% relative to the total weight of the brazed joint: 60 ≤ Cu ≤ 95; 0.5 ≤ Ge ≤ 9.5; 0 ≤ Sum of one or more of Cr, In, Sn, Si, Al ≤ 5.0; 0 ≤ B ≤ 1.25; 0 ≤ sum of one or more of Au, Pd and Pt < 18.0; and accidental impurities. [17] High-voltage vacuum tube according to claim 2, wherein the brazing compound composition comprises B and not more than 0.4 wt% Sn. [18] High-voltage vacuum tube according to claim 2, wherein the distance between the first and second components comprising the brazed joint is not more than 150 µm to allow the brazed joint to form by capillary action. [19] High-voltage vacuum tube according to claim 2, further comprising a second brazed joint, wherein the difference between the solidus temperature of the first brazed joint and the liquidus temperature of the second brazed joint is at least +15 °C. [20] High-voltage vacuum tube according to claim 19, wherein the first brazing joint comprises a brazing alloy composition configured to achieve a solidus temperature of at least 950 °C and the second brazing joint composition configured to achieve a liquidus temperature of not more than 1017 °C. [21] High-voltage vacuum tube according to claim 2, wherein the first brazed joint comprises a composition configured to cover a solidification temperature range of not more than 50 °C. [22] Process for producing a high-voltage vacuum tube according to claim 2, wherein the brazing assembly is the first component; wherein the second component and a brazing alloy composition comprise a total of not more than 18 wt.% of one or more precious metals selected from Au, Pd and Pt and are configured to have a solidification temperature range of not more than 90 °C and a liquidus temperature in the range of 950 °C to 1060 °C, wherein the brazing assembly is formed by: a. optionally, hold the brazed assembly for at least 10 minutes at a temperature between 10 °C and 400 °C below the liquidus temperature of the brazing alloy composition; b. Heating the brazed assembly to a brazing temperature above the liquidus temperature of the brazing alloy composition; and c. Cooling the brazing assembly below the solidus temperature of the brazing alloy composition to form the brazing joint that joins the first component and the second component together. [23] Process according to claim 22, comprising increasing the brazing temperature between the solidus and the liquidus temperature at a rate of 1 °C / min to 30 °C / min between the solidus and the liquidus temperature of the brazing alloy. [24] Process according to claim 22, comprising a distance between the first component and the second component in a range of 10 µm to not more than 150 µm to allow the brazing joint to form by capillary action. [25] Process according to claim 22, wherein the brazing assembly is heated inside a brazing furnace. [26] Process according to claim 22, comprising heating a first brazing alloy composition to a first brazing temperature and allowing it to cool in order to form a first brazing joint, and then heating a second brazing alloy composition to a second brazing temperature and allowing it to cool in order to form a second brazing joint, wherein the first brazing alloy composition and the second brazing alloy composition are configured such that the solidus temperature of the first brazing joint is higher than the liquidus temperature of the second brazing joint, wherein the second brazing temperature is kept below the solidus temperature of the first brazing joint. [27] Process according to claim 26, wherein the second brazing temperature is kept at least 10 °C below the solidus temperature of the first brazing joint. [28] Process according to claim 22, wherein the brazing joint is formed by placing the brazing alloy composition in the form of a wire, a powder, a paste or a foil adjacent to the first component and the second component to be joined, and heating the brazing alloy composition above the liquidus temperature of the brazing alloy composition and allowing a molten brazing alloy to flow between the first component and the second component by capillary action to form the brazing joint. [29] Process according to claim 22, wherein the brazing alloy composition comprises a solidification temperature range of not more than 50 °C. [30] Process according to claim 22, wherein the brazing alloy composition has a vapor pressure of less than 1 × 10 -11 mm Hg at 500 °C (1.33 × 10 -9 Pa) includes. [31] Process according to claim 22, wherein the first component is a vacuum tube bulb and the second component is part of an anode assembly or part of a cathode assembly. [32] Process according to claim 22, wherein the second component is part of a rotating anode assembly. [33] Process according to claim 22, wherein the brazing alloy composition comprises at least 80 wt.% copper. [34] Process according to claim 22, wherein the brazing alloy composition comprises copper and not more than 8.0 wt.% germanium. [35] Process according to claim 34, wherein the brazing alloy composition further comprises one or more elements selected from the group consisting of transition metals and rare earth metals. [36] Process according to claim 34, wherein the brazing alloy composition further comprises one or more of Pt, Pd, Au and boron. [37] Process according to claim 22, wherein the brazing alloy composition comprises Au. [38] Process according to claim 22, wherein the brazing alloy composition is free of B. [39] Process according to claim 22, wherein the brazing alloy composition wherein the sum of Cu + Ge + Au is greater than 99 wt.% of the total brazing alloy composition. [40] Process according to claim 22, wherein the brazing alloy composition comprises Cu, Ge and at least 0.5 wt.% of Au + Pd + Pt and the sum of Cu, Ge and (Pt + Pd + Au) is greater than 90 wt.% of the total weight of the brazing joint. [41] Process according to claim 22, wherein the brazing alloy composition in wt.% relative to the total weight of the brazed joint comprises 60 ≤ Cu ≤ 95; 0.5 ≤ Ge ≤ 9.5; 0 ≤ Sum of one or more of Cr, In, Sn, Si, Al ≤ 5.0; 0 ≤ B ≤ 1.25; 0 ≤ sum of one or more of Au, Pd and Pt < 18.0; and accidental impurities.

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