Brazing alloys

Abstract

The present invention relates to a brazing alloy composition comprising, in wt. %: 80 to 97.98 Cu; 2.0 ≤ Ge ≤ 9.5; 0.02 < B ≤ 1.25; and accidental impurities. The brazing alloy composition contains no more than 0.4 wt.% Sn.

Description

field of technology

[0001] This invention relates to brazing alloys for hermetic high-temperature pistons and assemblies consisting thereof; brazed joints; and the process for producing brazed joints using the brazing alloys. General state of the art

[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 from the vacuum tube body may be offset through the ceramic insulator. The vacuum tube body 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 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 can be relatively high, producing electrons that can become the source of arcing and / or breakdowns.

[0005] High-voltage structures with an insulator forming part of a vacuum chamber are known from US4126803.

[0006] 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.

[0007] As highlighted in US20210134553, bonding an iron-nickel-cobalt or iron-nickel alloy to niobium may require a brazing alloy with a liquidus greater than approximately 900 °C to achieve the necessary wetting and brazing flux. The brazing material can be selected to achieve the desired wetting and brazing flux, such as a 50 / 50 Au / Cu blend, an 81.5 / 16.5 Au / Cu blend (Nicoro™-80), and an 82 / 18 Au / Cu blend (Nioro™).

[0008] 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.

[0009] 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), were used for vacuum brazing of copper-, steel- and nickel-based metals.

[0010] However, such an alloy exhibits a large range between its solidus and liquidus temperatures, known as the solidification temperature range (STR), which causes 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 alloy. It occurs when the alloy is heated slowly through this melting range, such as in furnace brazing, and it manifests as an unmelted bead of alloy that remains at the point where the brazing alloy was applied. This often results in poor joint strength due to the presence of a brittle intermetallic phase in the brazed joint. Segregation is usually evident in alloys that have a large STR.Brazing processes carried out within a furnace that exhibits temperature variations are also prone to segregation, especially if the brazing alloy includes a large STR.

[0011] 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.

[0012] SU564128 discloses a brazing alloy composition with good wettability properties at 1000 °C, comprising 9.5–11 wt.% Ge; 0.8–1.3 wt.% Sn; 0.03–0.15 wt.% elements from the group consisting of B, Co, and Fe; and the remainder Cu. By increasing the amount of Ge and reducing the amount of B, the composition overcame the shortcomings of the brazing alloy composition from SU255015, which, although suitable for brazing at temperatures between 1000–1040 °C, exhibited poor formability, with initial cracking occurring after rolling the starting ingots to a reduction value of only 14% for compositions in the range of 6.5–9 wt.% Ge; 0.1–2.5 wt.% Ni; 0.5–1.5 wt.% Sn; 0.05 to 0.25 wt% Co; 0.05 to 0.25 wt% B; and the remainder Cu.

[0013] While these brazing alloy compositions address some of the needs for alternatives to brazing alloys with a significant precious metal content, there remains a need for brazing alloys, brazing assemblies, and devices comprising components brazed together using alternative brazing materials that are sufficiently malleable to be formed into wires, foils, and preforms, and that do not rely on large proportions of precious metals. Additionally, the brazing alloys should have a sufficiently low STR to avoid or reduce the risk of segregation compared to conventional non-precious metal brazing alloys. Brief description of the invention

[0014] In a first aspect of the present invention, a brazing alloy composition is provided, comprising in wt%: 80 to 97.98 Cu; 2.0 ≤ Ge ≤ 9.5; 0.02 < B ≤ 1.25; and accidental impurities, wherein the brazing alloy composition does not contain more than 0.4 wt.% Sn.

[0015] The copper content may be greater than 85 wt.%, 87 wt.%, 89 wt.%, 91 wt.%, or 93 wt.% of the total weight of the brazing alloy composition. The copper content may not exceed 96 wt.%, 94 wt.%, or 92 wt.% of the total weight of the brazing alloy composition.

[0016] In some embodiments, the brazing alloy composition may further comprise a residue of additives, excluding Cu, Ge, and B. In another embodiment, the brazing alloy composition may further comprise 0 to 10 wt.% additives (or 0 to 5 wt.% additives) that do not include Cu, Ge, and B. In some embodiments, the additives are selected from one or more elements from the group consisting of rare earth metals and transition metals, with the exception of Cu. In some embodiments, the Sn content is not more than 0.2 wt.% or is present as an incidental impurity. In other embodiments, Sn is present as an optional additive.

[0017] In some embodiments, the additives constitute the remainder of the brazing alloy composition in addition to the Cu, Ge, B, and Sn. The additives may comprise more than 0.1 wt.% of the total weight of the brazing alloy composition.

[0018] The brazing alloy composition is typically crystalline. However, in some embodiments it may be at least partially amorphous.

[0019] In an alternative aspect, the brazing alloy composition in weight % includes: 2.0 ≤ Ge ≤ 9.5 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; 0 ≤ In ≤ 2.0; 0.02 < B ≤ 1.25; 0 to 5.0 additives; accidental impurities; and Rest 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.

[0020] The additives may include or consist of one or more additives (i.e., elements) selected from the group consisting of transition and rare earth metals.

[0021] The brazing alloy composition is preferably suitable for use in a vacuum tube and therefore possesses the required properties, including low vapor pressure and low magnetism. The need 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.%.

[0022] The brazing alloy compositions of the present invention provide a non-precious metal alternative, or an alternative with a low precious metal content, for high-temperature brazing, particularly in a vacuum environment. The applicants have identified a narrow compositional window for a brazing alloy with a desirable liquidus temperature and solidification temperature range (STR) with good formability, capable of forming hermetic seals within low-pressure environments.

[0023] For the purposes of the present invention, good formability means that the brazing alloy has a formability of at least 38%, as determined by the formability test described in this document, 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" can be used, although wires with larger diameters can be produced as required.

[0024] It is understood that in embodiments the brazing alloy composition may consist of the components defined above in weight percent. Thus, the first aspect of the present invention may also relate to a brazing alloy composition consisting in weight percent of: 2.0 ≤ Ge ≤ 9.5 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; and 0 ≤ In ≤ 2.0; 0.02 < B ≤ 1.25; 0 to 5.0 additives, preferably selected from the group consisting of transition metals and rare earth metals; accidental impurities; and Rest 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.

[0025] In one embodiment, the brazing alloy composition comprises, in weight %: 2.5 ≤ Ge ≤ 7.4 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; and 0 ≤ In ≤ 2.0; 0.25 < B ≤ 0.75; 0 to 3.0 additives, preferably selected from the group consisting of transition metals and rare earth metals; accidental impurities; and Rest 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.

[0026] In another embodiment, the brazing alloy composition comprises, in weight %: 3.0 ≤ Ge ≤ 6.2 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; and 0 ≤ In ≤ 2.0; 0.3 < B ≤ 0.70; 0 to 2.0 additives, preferably selected from the group consisting of transition metals and rare earth metals; accidental impurities; and Rest 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.

[0027] In another embodiment, the brazing alloy composition comprises, in weight %: 2.0 ≤ Ge ≤ 6.3 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; and 0 ≤ In ≤ 2.0; 0.02 < B ≤ 1.25; 0 to 5.0 additives; accidental impurities; and Rest 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.

[0028] In another embodiment, the brazing alloy composition comprises, in weight %: 2.0 ≤ Ge ≤ 9.5 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; and 0 ≤ In ≤ 2.0; 0.27 < B ≤ 1.25; 0 to 5.0 additives; accidental impurities; and Rest 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.

[0029] It is understood that in embodiments the brazing alloy composition may consist of the components defined within the description in weight percent.

[0030] Brazing alloys within this composition range exhibit a combination of low STR values ​​and high liquidus temperatures that are suitable for joining substrates, at least one of which comprises copper.

[0031] In some embodiments, the sum of Ge+B+Cu is greater than 85.0 wt.% or greater than 90.0 wt.% or greater than 95.0 wt.% or greater than 96.0 wt.% or greater than 97.0 wt.% or greater than 98.0 wt.% or greater than 99.0 wt.% or greater than 99.5 wt.% or greater than 99.7 wt.% of the total weight of the brazing alloy composition.

[0032] It should be noted that 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 content

[0033] Levels of elemental germanium below 2.0 wt.% result in the brazing alloy having a liquidus temperature too high to braze copper or copper-based alloys. In some embodiments, the brazing alloy comprises at least 2.2 wt.%, or at least 2.5 wt.%, or at least 2.7 wt.%, or at least 2.9 wt.%, or at least 3.1 wt.%, or at least 3.3 wt.%, or at least 3.5 wt.%, or at least 3.7 wt.%, or at least 3.9 wt.%, or at least 4.1 wt.%, or at least 4.3 wt.%, or at least 4.5 wt.%, or at least 4.7 wt.%. Higher levels of germanium above 10 wt.% correspond to a brazing alloy composition with a lower liquidus temperature.

[0034] Germanium levels above 9.5 wt% Ge encompass a higher solidification temperature range (STR), which is less desirable for brazing applications, particularly those involving step brazing. It has been found that Ge contents below 10 wt% provide an acceptable STR range for many applications, while increasing the liquidus temperature but remaining within the target liquidus temperature range for brazing, for example, copper (or a copper alloy) to a substrate such as stainless steel (e.g., 900 to 1050 °C).

[0035] In some embodiments, the Ge content is not more than 9.3 wt.% or not more than 9.0 wt.% or not more than 8.5 wt.% or not more than 8.0 wt.% or not more than 7.5 wt.% or not more than 7.2 wt.% or not more than 7.0 wt.% or not more than 6.5 wt.% or not more than 6.4 wt.% or not more than 6.3 wt.% or not more than 6.2 wt.% or not more than 6.1 wt.% or not more than 6.0 wt.% or not more than 5.8 wt.% or not more than 5.5 wt.% or not more than 5.2 wt.% or not more than 5.0 wt.%.

[0036] In one embodiment, the germanium content is in the range of 2.5 wt.% to 7.4 wt.%, or in the range of 3.0 wt.% to 6.5 wt.%, or in the range of 3.5 wt.% to 6.3 wt.%, or in the range of 3.8 wt.% to 6.0 wt.%, or in the range of 4.0 wt.% to 5.8 wt.%. It was found that germanium contents within these compositional ranges exhibit a combination of low STR values ​​and relatively good formability for a given boron content. Optional liquidus temperature reducers

[0037] Optional amounts of liquidus temperature reducers of aluminium, indium and silicon, as defined in the first aspects of the present invention, contribute to reducing the liquidus temperature of the brazing alloy while maintaining a relatively small solidification temperature range (STR).

[0038] It has been found that Al, In, and Si can lower the liquidus temperature of brazing alloy compositions in relatively smaller amounts than Ge. As a general rule, it is assumed that more Ge is required to reduce the liquidus temperature than any combination of Al, In, and Si based on wt.% (e.g., 2.5 wt.% Ge has the equivalent strength in lowering the liquidus temperature as 1.0 wt.% of Al, In, and Si). For example, instead of using 7.25 wt.% Ge, an alternative starting point might include 3.0 wt.% Ge and 1.7 wt.% In, or 5.5 wt.% Ge and 0.7 wt.% In.

[0039] As is understood by those skilled in the art, the exact equivalent amounts for lowering the liquidus temperature can vary depending on the specific liquidus temperature reducer used and the overall composition of the brazing alloy. It has also been found that relatively small amounts (compared to Ge) of combinations of Al, In, and Si can adversely affect the STR or the liquidus temperature of the brazing alloy composition. Therefore, Ge should preferably constitute at least 50 wt.%, or at least 60 wt.%, or at least 70 wt.%, or at least 80 wt.%, or at least 90 wt.%, or at least 95 wt.% of the total amount of liquidus temperature reducers (Ge, In, Si, and Al). boron content

[0040] It has been shown that the addition of elemental boron (e.g., boron > 0.02 wt.% or > 0.05 wt.% or > 0.10 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).

[0041] In some embodiments, the boron level is greater than 0.05 wt.% or greater than 0.10 wt.% or greater than 0.12 wt.% or 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 0.27 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.%.

[0042] 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. Additives

[0043] A range of elemental additives (preferably metallic) can be added to the alloy composition to improve wettability, 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, malleability, and / or vapor pressure of the brazing alloy; or the mechanical integrity or hermeticity of the resulting joint.

[0044] 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.

[0045] In some embodiments, the additives comprise one or both of the transition metals and rare earth metals. The additives may comprise one or more elements from the group consisting of transition metals. The additives may comprise one or more elements from the group consisting of rare earth metals.

[0046] 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 selected from the group consisting of transition metals and rare earth metals, excluding copper. 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.

[0047] In some embodiments, the additives comprise 0 or > 0 to 5 wt.% transition metals.

[0048] The transition metals and rare earth metals can include scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, 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.

[0049] In some embodiments, the additives may include wetting agents selected from the group consisting of Nb, Ni, Mo, W, Co and Fe.

[0050] In some embodiments, the brazing alloy composition may include one or more liquidus temperature reducers in the following concentration ranges: > 0 to 2.0 wt.%; or > 0 to 1.5 wt.%; or > 0 to 1.0 wt.%; or > 0 to 0.5 wt.% Al; > 0 to 1.0 wt.%; or > 0 to 0.5 wt.% Si; > 0 to 2.0 wt.%; or > 0 to 1.5 wt.%; or > 0 to 1.0 wt.%; or > 0 to 0.5 wt.% In.

[0051] Larger quantities of these elements can lead to a deterioration of the ductility and / or STR of the brazing alloy composition.

[0052] In some embodiments, the additives may include Ag or Zn to further increase the machinability of the brazing alloys.

[0053] Ti, V and / or Zr can also be added to aid in the bonding of the brazing alloy to ceramic surfaces.

[0054] Other transition metals, including noble and / or precious metals, may also be added to enhance functional performance. In some embodiments, the proportion of precious metals (combined or as any single elemental additive) is less than 4.0 wt.%, less than 3.0 wt.%, less than 2.0 wt.%, less than 1.0 wt.%, or less than 0.5 wt.%. While a small proportion of precious metals may provide some functional advantages, their addition is optional.

[0055] In one embodiment, the additives comprise one or more of Nb, Ni, Mo, W, Co, Cr, Fe, Ti, V, Zr, Au, Ag, Zn, Pt & Pd.

[0056] 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.%, 0.3 wt.%, or 0.1 wt.%.

[0057] Rare earth metals, such as Nd, Y, Yb and Ce, can be added to further improve strength and / or hermeticity through grain refinement.

[0058] In one embodiment, the additives comprise one or more of Nb, Ni, Mo, W, Co, Cr, Fe, Ti, V, Zr, Au, Ag, Zn, Pt, Pd, Y, Yb, Nd & Ce.

[0059] In another embodiment, the additives comprise one or more of Ni, Co, Cr, Fe, Zr, Au, Ag, Zn, Y and Nd.

[0060] In a preferred embodiment, the additives comprise Ni. In a preferred embodiment, the additives are selected from the group consisting of Ni, Co, Fe, Au, and Ag. In a preferred embodiment, the brazing alloy composition comprises at most 4.8 wt.% of the additives.

[0061] In a preferred embodiment, the brazing alloy composition comprises at most 1.0 wt.% of the additives. In a preferred embodiment, the brazing alloy composition comprises at least 0.2 wt.% of the additives.

[0062] It was found that the addition of tin (Sn) has a detrimental effect on both the structural strength (STR) and the malleability of the brazing alloy. Therefore, the addition of tin should be avoided and, if present, should be in amounts (additives + accidental impurities) not exceeding 0.4 wt.%, 0.3 wt.%, 0.25 wt.%, 0.2 wt.%, 0.15 wt.%, or 0.1 wt.% of the total weight of the brazing alloy composition. In some embodiments, the tin content in the brazing alloy composition is 0.05 wt.% or less, and more preferably 0.01 wt.% or less.

[0063] The additives preferably comprise 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.

[0064] 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, Ni, 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.

[0065] 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.

[0066] 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

[0067] 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.

[0068] Unless otherwise specified, accidental impurities may include any element or compound not already specified within the brazing alloy composition (e.g., excluding Ge, Cu, B, Al, In, Si, Sn, and the additives). Accidental impurities may include elements (and derivatives thereof) from Groups 1, 2, 3A (except B), 4A (except Sn and Ge), 5A, 6A, 7A, and 8A of the periodic table.

[0069] Elements of group 1 include H, Li, Na, K, Rb, Cs and Fr.

[0070] Elements of group 2 include Be, Mg, Ca, Sr, Ba and Ra.

[0071] The elements of group 3A include Ga and Tl.

[0072] The elements of group 4A include C and Pb.

[0073] The elements of group 5A include N, P, As, Sb and Bi.

[0074] The elements of group 6A include O, S, Se, Te and Po.

[0075] The elements of group 7A include F, Cl, Br, I and At.

[0076] The elements of group 8A include He, Ne, Ar, Kr, Xe and Rd.

[0077] In a preferred embodiment, the brazing alloy composition comprises less than 1.0 wt.% accidental impurities, or at most 0.5 wt.% accidental impurities, preferably at most 0.3 wt.% accidental impurities, and more preferably at most 0.15 wt.% accidental impurities. These small amounts of elements typically do not contribute to or modify the actual purpose and / or performance of the brazing alloy.

[0078] In one embodiment, the brazing alloy composition, preferably excluding oxygen, comprises 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 individual random impurity element.

[0079] Although accidental impurities (also known as unavoidable impurities) can vary depending on the purity of the raw material used, typical levels of accidental impurities are less than 0.8 wt%, less than 0.5 wt%, less than 0.2 wt%, less than 0.1 wt%, or less than 0.05 wt% of the total weight of the brazing alloy composition. Due to oxidation reactions, oxygen (O) may be present as an accidental impurity at levels as high as 1.0 wt%, 0.8 wt%, or 0.5 wt% of the total weight of the brazing alloy composition. Some applications require even stricter limits. For example, limits for each of Zn, Cd, Pb, C may be less than 0.1 wt.% or less than 0.05 wt.% or less than 0.01 wt.% or 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 elemental impurities (including metallic impurities) with a vapor pressure higher than 10. -7 mm Hg (1.33 × 10 -5 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.

[0080] Elemental impurities that have a vapor pressure lower than 10 -7mm 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.

[0081] A list of incidental impurities typically tested for includes Al, P, Pb, Cd, and Zn. For a duplicate analysis of Example 8 (Table 1), all incidental 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 each considered incidental impurities for this specific end-use application. Any use of ultrapure raw materials, such as those used in Example 8, does not reflect the typical levels of incidental impurities that may be used. Form of the brazing alloy

[0082] 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.

[0083] 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), or only up to 200 µm. Wire diameters are typically no more than 5.0 mm or 2.54 mm in diameter. 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 0.020" (500 µm) or greater can be produced. Applications

[0084] The brazing alloys can be used to form brazed assemblies in aircraft engines (OEM and repairs), fuel line assemblies in the aerospace industry, semiconductor process chamber components, vacuum tubes (including high-voltage vacuum tubes such as X-ray tubes), waveguide and klystron assemblies, power supply surge arresters, and automotive components.

[0085] In a second aspect of the present invention, a piston is provided comprising a first component and a second component, wherein a brazed connection (preferably hermetically) connects the first component and the second component together, wherein the piston comprises a brazing alloy composition of the first aspect of the present invention or a brazing assembly of the fourth aspect of the present invention.

[0086] It is understood that in other embodiments the brazing alloy composition may consist of the components defined above in weight percent.

[0087] 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).

[0088] "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.

[0089] "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 subjected 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.

[0090] Pistons, by their very nature, typically include at least one brazed joint, one of which must necessarily be formed as a blind joint. 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), often after the sub-subassembly components are in place within the piston. Therefore, the properties of the brazing alloy are crucial, firstly to form the brazed joint with the desired dimensions, which must be positioned immediately adjacent to the components to be joined. Secondly, the brazed joint should exhibit sufficient wettability and flowability to form a high-quality bond (e.g., without segregation) between the components via 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.

[0091] 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.

[0092] 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.

[0093] 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. In the vacuum tube, the bulb may further include an enclosed heat source, such as a cathode filament of the X-ray vacuum tube or a lamp head in a rapid heat treatment assembly within a semiconductor processing chamber. The heat source is preferably capable of heating at least a portion of the bulb's contents to at least 800 °C, 900 °C, or 1000 °C. The maximum operating temperatures of the bulbs are determined by the softening and liquidus temperatures of the materials used. At least a portion of the brazed connection is located opposite the inside of the bulb (e.g.,The inside of the vacuum tube is exposed, which can be subjected to high temperatures and high vacuum.

[0094] In one embodiment, 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 strike a target surface of the anode assembly and to form X-rays, wherein the X-ray 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 include 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 comprises a composition as defined in the first aspect of the present disclosure, wherein at least one section of the brazing joint is exposed to the interior of the X-ray tube bulb and wherein at least one of the first and the second components forms a part of one or more of the X-ray tube bulb, the anode assembly and the cathode assembly.

[0095] In one embodiment, a device is provided comprising a heat source and a piston, wherein the piston comprises a first component and a second component, wherein a brazed connection joins the first component and the second component together, wherein the brazed connection comprises a brazing alloy composition comprising in weight %: 2.0 ≤ Ge ≤ 9.5 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; and 0 ≤ In ≤ 2.0; 0.02 < B ≤ 1.25; 0 to 5.0 additives; less than 1.0 wt% random impurities; and Rest 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, and wherein the piston is hermetically sealed.

[0096] In another embodiment, the brazed joint comprises: 80 to 97.98 Cu; 2.0 ≤ Ge ≤ 9.5 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; and 0 ≤ In ≤ 2.0; 0.02 < B ≤ 1.25; ≤ 0.4 Sn; and accidental impurities.

[0097] In another embodiment, a device is provided comprising a piston and a heat source, wherein the piston comprises a brazing assembly, the brazing assembly comprising a first component and a second component connected to each other by a first brazing joint, the brazing joint comprising a solidification temperature range of not more than 90 °C, the brazing joint comprising a liquidus temperature in the range of 950 °C to 1060 °C and a precious metal content of less than 4.0 wt.% relative to the total weight of the brazing joint.

[0098] The heat source can be located inside the piston or form part of the piston.

[0099] 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 melting point above 1050 °C or above 1080 °C. The piston may further include a cooling system to dissipate heat from the system. The piston may also be under vacuum, as in a vacuum tube, or may contain a process gas (e.g., in a semiconductor processing chamber).

[0100] The first or second component may also include ceramic or a metallized ceramic (i.e., a ceramic that includes a metallized coating).

[0101] In embodiments where the piston forms part of a vacuum tube, the piston can comprise an anode and a cathode arranged opposite each other in a vacuum-sealed interior. The vacuum-sealed interior can be enclosed by a cylindrical metal piston, wherein the anode and / or the cathode are electrically insulated by means of an annular insulator (e.g., a ceramic or metallized ceramic component). The brazed joint can form a seal between the cylindrical metal piston and the annular insulator.

[0102] The brazed joint can comprise a ceramic (or metallized coated ceramic) component and a metallic component, wherein the brazed joint joins the ceramic / metallized coated ceramic and the metallic components together. In one embodiment, the brazed joint comprises a brazing alloy composition comprising, in wt.%: 2.0 ≤ Ge ≤ 9.5 and 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; 0 ≤ In ≤ 2.0; 0.02 < B ≤ 1.25; 0 to 5.0 additives, preferably selected from the group consisting of transition metals and rare earth metals; 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.

[0103] It is understood that in embodiments the brazing alloy composition may consist of the components defined above in weight percent.

[0104] The brazed joint can also comprise compositional variations of the brazing alloy according to any of the embodiments of the first aspect of the present invention.

[0105] The ceramic component may include a metallized coating, such as a molybdenum-manganese coating or nickel plating.

[0106] In a third aspect of the present invention, a vacuum tube assembly or a semiconductor processing chamber, such as a rapid heat treatment assembly, comprising a piston of the second aspect of the present invention, is provided. In some embodiments, the vacuum tube assembly or the rapid heat treatment assembly is operated at temperatures of up to 800 °C or more, or 900 °C or more, or 1000 °C or more.

[0107] 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.

[0108] The vacuum tubes of the present invention 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. These properties of brazing alloys allow for the fabrication of a versatile variety of vacuum tubes using a variety of different brazing techniques and conditions. Brazing alloy

[0109] 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); aerospace applications (such as engine components and repairs, and fuel line assemblies); gas turbine assemblies; semiconductor process chamber components, such as the power supply of a rapid heat treatment unit; power supply surge arresters; and automotive components.

[0110] 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.

[0111] The liquidus temperature of the brazing alloy composition is typically below about 1060 °C, or typically below 1055 °C, or below 1050 °C, or below 1045 °C. The liquidus temperature is typically at least 890 °C, or at least 900 °C, or at least 910 °C, or at least 920 °C, or at least 925 °C, or at least 950 °C. Therefore, the brazing alloys are particularly suitable for brazing substrates made of copper or copper alloy. 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.

[0112] 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.

[0113] 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. Substrates

[0114] The brazing alloys of the present invention are suitable for a range of brazing applications that includes, but is not limited to, assemblies comprising substrates comprising copper or copper alloys, Kovar™ (Ni-Co-Fe alloy), metallized ceramic components (e.g., molybdenum-manganese metallized or nickel-plated or copper-plated); steel comprising stainless steel; nickel and nickel alloys comprising Ni superalloys; and other refractory metals (e.g., molybdenum and alloys thereof) comprising a melting temperature that is preferably at least 20 °C or at least 50 °C above the liquidus temperature of the brazing alloy. solidification temperature range

[0115] To avoid segregation while promoting good brazing coverage over the joint, the brazing alloy preferably has a narrow temperature difference between the solidus temperature and the liquidus temperature (i.e., low STR values). In some embodiments, the boron and / or germanium content of the brazing composition is configured to achieve a temperature difference between the solidus temperature and the liquidus temperature of the brazing alloy of not more than 90 °C or not more than 88 °C or not more than 85 °C or not more than 82 °C or not more than 80 °C or not more than 75 °C or not more than 70 °C or not more than 65 °C or not more than 60 °C or not more than 55 °C or not more than 50 °C or not more than 45 °C or not more than 40 °C or not more than 35 °C or not more than 30 °C or not more than 25 °C or not more than 20 °C.The STR ranges mentioned above are considered to have low STR values.

[0116] In a fourth aspect of the present invention, a brazing assembly is provided, comprising a first connection and a second connection, wherein at least one of the connections comprises a brazing alloy composition according to the first aspect of the present invention. Alternatively, the brazing assembly can be part of a device, the device comprising a piston and a heat source, the piston comprising a brazing assembly, the brazing assembly comprising a first component and a second component connected to each other by a first brazing joint, the first brazing joint comprising a solidification temperature range of not more than 90 °C, the first brazing joint comprising a liquidus temperature in the range of 950 °C to 1060 °C and a precious metal content of less than 4.0 wt.% relative to the total weight of the first brazing joint.

[0117] In one embodiment, the assembly comprises two assemblies, each assembly comprising a brazing alloy composition according to the first aspect of the present invention. Each of the brazing alloys may be different. The first assembly may comprise a brazing alloy having a liquidus temperature below the solidus temperature of the second brazing alloy.

[0118] In one embodiment, the first and second brazing alloys comprise a brazing alloy composition according to the first aspect of the present invention. Preferably, the difference between the solidus temperature of the first compound and the liquidus temperature of the second compound is at least +15 °C or at least +20 °C. The first compound may comprise a brazing alloy composition with a solidus temperature of at least 950 °C or at least 990 °C, and the second compound may comprise a liquidus temperature of not more than 1017 °C, not more than 1000 °C, or not more than 980 °C.

[0119] 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.

[0120] Although the present invention includes step brazing using two brazing alloy compositions, the present invention also includes step brazing wherein only one of the brazing joints comprises a brazing alloy according to the first aspect of the present invention.

[0121] 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.

[0122] In some embodiments, the brazed joints are derived from the brazing alloy composition of the first aspect of the present invention. The derived brazed joints may have a lower boron content compared to the brazing alloy composition from which they are derived. Furthermore, the materials / components adjacent to the brazed joint may have a certain level of boron relative to the materials / components present before the brazed joint is formed.

[0123] 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 melting point of the brazing alloy is lower than the melting point 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 molten brazing alloy. However, fluxless brazing is preferred.

[0124] 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.

[0125] In some embodiments, the anode is a rotating anode. Rotating anodes subject the brazed joints within them to additional stresses, and therefore the strength of these brazed joints is of particular importance compared to brazed joints within vacuum tubes with static anodes.

[0126] In a fifth aspect of the present invention, a process for producing a brazed joint between a first component and a second component using the brazing alloy composition according to the first aspect of the present invention is provided.

[0127] The brazing process can include: a. optionally, hold the brazing alloy composition 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 brazing alloy composition to a brazing temperature above the liquidus temperature of the brazing alloy composition; and c. Cooling the brazing alloy composition below the solidus temperature of the brazing alloy composition to produce the brazed joint.

[0128] The process can involve 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 the present invention 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.

[0129] 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.

[0130] 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.

[0131] 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 -8 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.

[0132] In some embodiments, a two-stage brazing process is employed, comprising heating 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 heating 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 the second brazing temperature is kept below the solidus temperature of the first brazed joint.

[0133] 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.

[0134] A sixth aspect of the present invention provides a brazed joint produced or obtainable by the process according to the fifth aspect of the present invention. The brazing process enables the brazing alloy composition to have a sufficiently low liquidus temperature and sufficient flow and wettability properties to form a concealed joint by capillary action drawing the brazing alloy into the gap between the substrates to be joined. The cooled brazed joint may have a reduced boron content compared to the original brazing alloy composition. Thus, without the brazing process of the present invention, the brazing alloy composition could not have been obtained, as the liquidus temperature of the brazing alloy composition would have been higher. Performance of the brazed joint

[0135] The brazing alloys and derived compounds of the present invention are preferably hermetic, have good mechanical strength and exhibit a low vapor pressure.

[0136] The brazed joints of the present invention 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.

[0137] The brazed joints of the present invention preferably have a tensile strength of at least 900 MPa, at least 950 MPa, or at least 1000 MPa. The brazed joints of the present invention 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 method of standard AWS C.3.2M / C3.2:2019 for assessing the strength of brazed joints. The reference substrates for the test were 304 stainless steel joined to 100% copper.

[0138] The brazing alloy of the present invention 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).

[0139] For the purposes of this invention, a vacuum tube includes power tubes, X-ray tubes, magnetrons, traveling wave tubes, carcinotrons and klystrons.

[0140] 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.

[0141] For the purposes of the present invention, 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 the present invention can also be determined by applications in which 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.

[0142] Vacuum brazing is typically performed at approximately 1 × 10 -5 mm Hg (1.33 × 10 -3 Pa) carried out.

[0143] 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).

[0144] The total weight of all components in the brazing alloy composition should not exceed 100 wt.%. Theoretical total weights of combinations of components exceeding 100 wt.% should be disregarded.

[0145] Unless otherwise specified, references to quantities in wt.% are based on the total weight of the brazing alloy composition.

[0146] Additives exclude elements that are already defined within the scope of the brazing alloy composition (e.g. Cu, Ge, Sn, Al, Si, In and B).

[0147] For the purposes of the present invention, precious metals mean gold, silver, palladium and platinum.

[0148] References to boron, copper, germanium, and additives refer to these components in their elemental form (i.e., oxidation state = 0). Accidental impurities may be present in any permissible oxidation state, but preferably have an oxidation state of zero.

[0149] For the purposes of this invention, a brazing compound composition derived from a brazing alloy composition means that the brazing compound, although formed from a brazing alloy composition, may also comprise components from the associated substrates forming the joint, which may have diffused into the joint during the brazing process. Likewise, at least some components of the original brazing alloy composition may have diffused into the adjacent substrates (e.g., boron from the brazing alloy composition may have diffused at least partially into the adjacent substrates). Brief description of the characters

[0150] The present invention will now be described with reference to the figures in the accompanying drawings, which illustrate particularly preferred embodiments of the present invention, in which the following applies: Fig. Figure 1 is a schematic representation of an X-ray tube within the scope of the present invention. Fig. 2 is a scanning of sample 4 by dynamic differential scanning calorimetry (DSC). Fig. Figure 3 is a graph illustrating the influence of the boron content in the brazing alloy on the solidification temperature range. 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 by the brazing alloy composition of sample 14. Fig. 5 is a microstructure image of a cross-section of the brazed joint made of Fig. 4. Fig. 6A to 6F are photographs illustrating the malleability of samples 8 to 12; and C-6, respectively. Fig. Figure 7A is a photograph of a brazing alloy wire of the present invention in contact with two components, before brazing using the brazing alloy of sample 13. Fig. 7B and Fig. 7C are a photograph or a SEM image of the brazed joint made of Fig. 7A after brazing. Fig. Figure 8A is a photograph of a prior art brazing alloy wire in contact with two components prior to brazing using the commercially available brazing alloy GEMCO™. Fig. 8B and Fig. 8C are a photograph or a SEM image of the brazed joint made of Fig. 8A after brazing. Detailed description of a preferred embodiment of the present invention

[0151] Brazing alloys must possess ductility (the ability of the alloy to undergo plastic deformation without fracturing), particularly tensile strength, to be manufactured in various forms such as wires and foils. The production of a brazing alloy begins with mixing all the elements in the alloy in appropriate proportions and melting the mixture to a sufficiently high temperature, followed by casting to produce an ingot or billet in a solid form. The state of the alloy can be changed from its as-cast state to its forged state by cold or hot working processes such as rolling, drawing, and stamping.

[0152] 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 preforms are manufactured 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. During brazing, preforms are placed in a joint region 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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).

[0157] 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.

[0158] 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 housing include copper due to its high conductivity, the use of copper-based brazing alloys offers 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 the present invention can advantageously be 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.

[0159] As is evident from the sophistication of the setup, it is also crucial that the brazing alloys are positioned in and can flow into 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 the present invention are less prone to segregation.

[0160] Although the brazing alloys and compounds thereof of the present invention are particularly suitable for applications with high-temperature vacuum tubes, the brazing alloys are not limited to these applications.

[0161] For example, brazing alloys can be used in brazed joints within semiconductor process chamber components, such as components of a rapid thermal processing (RTP) chamber. RTP can be used in a range of industrial high-temperature processes that involve heating to temperatures exceeding 1000 °C for no more than a few seconds. During cooling, wafer temperatures must be reduced slowly to prevent dislocation and wafer fracture due to thermal shock. Such rapid heating rates are often achieved using high-intensity lamps or lasers. As with components of high-temperature vacuum tubes, RTP components are required to withstand high temperatures and incorporate highly conductive metals for the system's thermal management.Accordingly, a copper component is often used, typically brazed to other metal components, such as stainless steel. The RTP chamber typically includes a lamp head as a heat source and contains a flow of process gas, such as an inert gas like nitrogen, to facilitate the heat treatment process. Because purity is critical in wafer processing, the chamber must be hermetically sealed during operation. Examples of RTP assemblies and processes are provided in US8,698,049 and US20210348302. Examples

[0162] Test brazing alloys comprising copper, germanium, and boron with 0.25 wt% nickel in various compositions listed in Table 1 were prepared 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

[0163] 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. -1 The analysis was performed. The output is a curve representing the variation in heat flux density with temperature.

[0164] 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.

[0165] 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. The interpretation of the DSC data is carried out in accordance with the National Institute of Standards and Technology (NIST) Special Publication 960-15 entitled “DTA and Heat-flux Measurements of alloy melting and freezing”, WJ Boettinger, UR Kattner, KW Moon, JH Perepezko (November 2006). malleability

[0166] 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.

[0167] The formability of each composition was determined by measuring the deformation required to produce a fracture (as observed with the naked eye) when passed through 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 that can withstand cold rolling 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, with a reduction to 0.125 inches corresponding to 50% formability.

[0168] 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).

[0169] 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. Test results

[0170] A series of experiments were undertaken to evaluate the characteristics of brazing alloys with regard to their solidus and liquidus temperatures as well as their malleability.

[0171] It was found that the vapor pressures of the brazing alloys of the present invention in Table 1 are less than 1 x 10 -11 mm Hg (1.33 x 10 -9Pa). 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.

[0172] 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).

[0173] With reference to Fig. Figure 3 shows the effect of boron on brazing alloys with 2.5 wt% germanium (line A) and 4.8 wt% germanium (line B), demonstrating 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.

[0174] 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 invention 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 invention 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.

[0175] 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).

[0176] 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.

[0177] 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 less of an effect on 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.%.

[0178] 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. Table 1 Proben-ID Cu(Gew.%) Ge(Gew.-%) B(Gew.%) Sonstige(Gew.%) Ni(Gew.-%) Liquidustemp.(°C) Solidustemp.(°C) STR-Temp (°C) Formbarkeit % 1 96,75 2,5 0,5 0 0,25 1068 1008 60 100 2 96,45 2,5 0,8 0 0,25 1039 1002 37 68 3 96,0 2,5 1,25 0 0,25 1044 1008 36 43 C-1 95,25 2,5 2,0 0 0,25 1077 1008 69 36 4 94,81 4,2 0,84 0 0,15 1039 1032 7 84 C-2 94,95 4,8 0 0 0,25 1048 986 62 100 5 94,45 4,8 0,5 0 0,25 1015 1003 12 100 6 94,18 4,8 0,77 0 0,25 1035 1016 19 83 7 93,77 4,8 1,25 0 0,25 1010 986 24 40 C-3 92,95 4,8 2,0 0 0,25 989 951 38 35 8 92,3 7,2 0,25 0 0,25 1035 959 76 100 9 92,175 7,2 0,375 0 0,25 1034 959 75 100 10 92,0 7,2 0,55 0 0,25 1020 954 66 100 11 91,75 7,2 0,8 0 0,25 1040 962 78 60 12 91,30 7,2 1,25 0 0,25 1012 953 59 38 13 91,94 7,33 0,47 0 0,26 1028 947 81 - 14 91,82 7,4 0,53 0 0,25 1005 967 38 100 C-4 89,75 10 0 0 0,25 1005 902 103 100 15 89,25 10 0,5 0 0,25 974 905 69 100 16 88,95 10 0,8 0 0,25 974 906 68 56 17 93,00 6,5 0,25 0 0,25 1025 956 69 100 C-5 87,25 12 0,5 0 0,25 968 823 145 100 C-6 93,45 4,8 0,5 1,0 Sn 0,25 1010 837 173 20 C-7 92,00 6,5 0,25 1,0 Sn 0,25 1007 891 116 30 C-8 88,90 10 0,1 1,0 Sn 0 983 773 210 - 18 90,55 5,5 0,7 3,0 Co 0,25 1053 1003 50 - 19 87,60 7,5 0,1 0 4,8 1026 937 89 - 20 91,25 5,5 0,8 2,2 Fe 0,25 1059 1019 40 - 21 92,55 5,5 0,7 1,0 Ag 0,25 1012 970 42 - 22 90,75 4,5 0,7 3,8 Au 0 1037 998 39 - 23 95,5 4,0 0,5 0,45 Si0,2 Al 0,25 1007 920 87 100 C-9 81,5 8,5 1,0 0 9,0 1026 926 100 - C-10 91,45 2,5 0,8 5,0 Y 0,25 1077 983 94 - C-11 85,8 5,5 0,8 8,0 Ag 0,7 1006 775 231 - Effect of the addition of additives

[0179] 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 shown 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.

[0180] 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

[0181] 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 × 10⁻⁶ for closed vacuum assemblies. -8 atm.cc / s complied with the requirements for high-vacuum assemblies.

[0182] 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).

[0183] 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 brazing 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 Handelsmarke Au (Gew.-%) Ni (Gew.-%) Cu (Gew.-%) Ge (Gew.-%) Liquidustemp. (°C) Solidustemp. (°C) STR-Temp. (°C) Nicoro™ 35 3 62 - 1030 1000 30 Nioro 73,8 26,2 - - 1010 980 30 WESGO™50Au-50Cu 50 - 50 - 970 955 15 WESGO™35Au-65Cu 35 - 65 - 1010 990 20 GEMCO™ - 0,25 87,75 12 975 880 95

[0184] 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.

[0185] It is understood that modifications and variations can be made without deviating from the spirit and scope of the novel concepts of the present invention. 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

[0005] US 20210134553

[0007] SU 564128

[0012] SU 255015

[0012] US 8,698,049

[0161] US 20210348302

[0161] Cited non-patent literature

[0000] DTA and Heat-flux Measurements of alloy melting and freezing”, WJ Boettinger, UR Kattner, KW Moon, JH Perepezko (November 2006

[0165]

Claims

[1] Brazing alloy composition, comprising wt%: 80 to 97.98 Cu; 2.0 ≤ Ge ≤ 9.5; 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; 0 ≤ In ≤ 2.0; 0.02 < B ≤ 1.25; and random impurities, wherein the brazing alloy composition does not exceed 0.4 Sn. [2] Brazing alloy composition according to claim 1, further comprising a residue of additives, excluding Cu, Ge, Sn, Al, Si, In and B. [3] Brazing alloy composition according to claim 1, comprising 0 to 5.0 wt.% additives. [4] Brazing alloy composition according to claim 1, wherein the additives comprise or consist of one or more elements selected from the group consisting of transition metals and rare earth metals, with the exception of Cu. [5] Brazing alloy composition according to claim 1, wherein the additive content is less than 1.0 wt.%. [6] Brazing alloy composition according to claim 1, wherein the additives and impurities do not include Sn in an amount exceeding 0.25 wt.% of the total weight of the brazing alloy composition. [7] Brazing alloy composition according to claim 1, comprising a solidification temperature range of not more than 90 °C. [8] Brazing alloy composition according to claim 1, comprising a liquidus temperature in the range of 950 °C to 1060 °C. [9] Brazing alloy composition according to claim 1, comprising a formability of the brazing alloy composition of at least 38%, wherein the formability is determined when 5±1 grams of the brazing alloy composition is melted and formed into a knob with a height of about 0.25 in and is passed at room temperature through a rolling mill with two rollers, wherein the gap between the rollers is set to about a 10% reduction in the height of the knob, wherein the knob is repeatedly passed through the roller until a thickness of 0.002 in is obtained, which is considered to be 100% formability, or the formability is determined as the % thickness of the initial height at which a fracture point is observed with the naked eye. [10] Brazing alloy composition according to claim 1, wherein the addition of the additives does not result in the vapor pressure being greater than 1.0 × 10 - 8 mm Hg (1.33 × 10 -6 Pa) increased at 700 °C. [11] Brazing alloy composition according to claim 1, comprising a vapor pressure of less than 1 × 10 -11 mm Hg at 500 °C (1.33 × 10 -9 Pa). [12] Brazing alloy composition according to claim 1, wherein the random impurities comprise no more than 0.2 wt.% of any individual impurity element. [13] Brazing alloy composition according to claim 1, wherein the brazing alloy composition is in the form of a wire, a powder, a preform, a paste or a foil. [14] Brazing alloy composition according to claim 13, wherein the wire has a diameter in the range of 0.2 mm to 5.0 mm or 0.38 mm to 2.54 mm or [15] Brazing alloy composition according to claim 13, wherein the foil thickness is in the range of 25 µm to 500 µm. [16] Brazing alloy composition, comprising wt%: 2.0 ≤ Ge ≤ 9.5; 0 ≤ Al ≤ 2.0; 0 ≤ Si ≤ 1.0; 0 ≤ In ≤ 2.0; 0.02 < B ≤ 1.25; 0 to 5.0 additives; 0 ≤ Sn ≤ 0.4; less than 1.0 random impurities; and The remainder is Cu, wherein the additives consist of one or more elements selected from the group consisting of rare earth metals and transition metals, with the exception of Cu. [17] Brazing alloy composition according to claim 16, comprising at most 0.50 wt.% and preferably at most 0.30 wt.% and further preferably at most 0.15 wt.% of accidental impurities. [18] Brazing alloy composition according to claim 16, wherein the random impurities consist of any element other than Ge, B, Cu, Al, Si, In, Sn and the additives. [19] Brazing alloy composition according to claim 16, wherein the accidental impurities, with the exception of oxygen, comprise 0.2 wt.% or less of the brazing alloy composition of any individual impurity element and preferably comprise 0.10 wt.% or less of the brazing alloy composition of any individual impurity element. [20] Brazing alloy composition according to claim 16, comprising in wt%: 0.27 ≤ B ≤ 1.

25. [21] Brazing alloy composition according to claim 16, wherein the additives consist of one or more elements selected from the group consisting of Nb, Ni, Mo, W, Co, Cr, Fe, Ti, V, Zr, Au, Ag, Zn, Pt, Pd, Y, Yb, Nd & Ce. [22] Brazing alloy composition according to claim 16, comprising a solidification temperature range of not more than 90 °C. [23] Brazing alloy composition according to claim 16, comprising a liquidus temperature in the range of 950 °C to 1060 °C. [24] Brazing alloy composition according to claim 16, wherein the additives comprise or consist of one or more elements selected from the group consisting of transition metals and rare earth metals. [25] Brazing alloy composition according to claim 16, wherein the brazing alloy composition is in the form of a wire, a powder, a preform, a paste or a foil. [26] Brazing alloy composition according to claim 16, wherein the wire has a diameter in the range of 0.2 mm to 5.0 mm or 0.38 mm to 2.54 mm. [27] Brazing alloy composition according to claim 16, wherein the foil thickness is in the range of 25 µm to 500 µm. [28] Brazing assembly comprising a first component and a second component joined together by a brazing joint, wherein the brazing joint comprises a brazing alloy composition according to claim 1 or is derivable from a brazing alloy composition according to claim 1. [29] Brazing assembly according to claim 28, wherein the brazing joint is hermetic. [30] Brazing assembly according to claim 28, wherein the brazing joint undergoes a leak test with a gas tightness of 1 × 10 -6 consists of atm.cc / s or less (ASTM F2391 using helium gas). [31] Brazing assembly comprising a first component and a second component connected to each other by a first brazing joint and a second brazing joint, wherein at least one of the first and the second brazing joint comprises a brazing alloy composition according to claim 1 or a brazing alloy composition derivable therefrom. [32] Brazing assembly according to claim 31, wherein the first and the second brazing joint comprise a brazing alloy composition according to claim 1 or a brazing alloy composition derivable therefrom. [33] Brazing assembly according to claim 31, wherein the difference between the solidus temperature of the first brazing joint and the liquidus temperature of the second brazing joint is at least +15 °C. [34] Brazing assembly according to claim 31, 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 comprises a brazing alloy composition configured to achieve a liquidus temperature of not more than 1017 °C. [35] Device comprising a heat source and a piston, wherein the piston comprises a brazing assembly according to claim 28. [36] Device according to claim 35, wherein the heat source is enclosed within the piston or forms part of the piston. [37] Device according to claim 35, wherein the heat source is capable of heating at least a section of the contents of the flask to more than 800 °C. [38] Device according to claim 35, wherein the first or the second component comprises copper. [39] Device according to claim 35, wherein the first or the second component comprises ceramic or a metallized ceramic. [40] Device according to claim 35, wherein the first or the second component comprises stainless steel, copper, a copper alloy, a nickel alloy or a Ni-Co-Fe alloy. [41] Device according to claim 35, wherein the piston is under vacuum. [42] Vacuum tube assembly comprising the device according to claim 35. [43] Rapid heat treatment assembly comprising the device according to claim 35. [44] Process for producing a brazed joint between a first component and a second component using the brazing alloy composition according to claim 1, wherein the brazing alloy composition: a. optionally, held for at least 10 minutes at a temperature between 10 °C and 400 °C below the liquidus temperature of the brazing alloy composition; b. is heated to a brazing temperature above the liquidus temperature of the brazing alloy composition; and c. is cooled below the solidus temperature of the brazing alloy composition. [45] Process according to claim 44, comprising increasing the brazing 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. [46] Process according to claim 44, wherein the brazed joint is heated inside a brazing furnace. [47] Process according to claim 44, 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. [48] ​​Process according to claim 44, 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 and the second components to be joined, and heating the brazing alloy composition above the liquidus temperature of the brazing alloy composition and allowing the molten brazing alloy to flow between the first and the second components by capillary action to form the brazing joint. [49] Process according to claim 44, wherein the production of the brazed joint is carried out in a vacuum, a reducing atmosphere or a protective atmosphere. [50] Brazed joint produced or obtainable by the process according to any one of claims 44 to 49. [51] Brazing joint according to claim 50, wherein one or both of the first component and the second component comprise copper. [52] Brazing joint according to claim 50, wherein the brazing joint is a concealed joint. [53] Brazing joint according to claim 50, wherein the brazing joint comprises a lower proportion of boron compared to the brazing alloy composition and one or both of the first component and the second component comprise a detectable amount of boron derived from the brazing alloy composition.

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