High-temperature active solders

Abstract

High-temperature active solders which comprise at least one vanadium- and / or niobium- and / or tantalum-based alloy, which may comprise Mo, W, Cr, Y and / or Al as further alloying elements, and which contains at least >0 to 7 at.% silicon and 2 to 10 at.% titanium and / or zirconium and / or hafnium and further comprises at least in some regions the intermetallic phase (V,Nb,Ta)3Si.

Description

[0001] The invention relates to the fields of technical ceramics and materials science and concerns high-temperature active solders, such as those that can be used for soldering oxide and non-oxide ceramics or ceramics with metals, which are then to be used at higher temperatures and under different ambient conditions.

[0002] Welding and soldering processes for joining ceramics and especially high-performance ceramics are known (Hesse, A. et al., Keramische Zeitschrift 3 (1994), pp. 147-150; Boretius, M. et al., VDI-Berichte, Volume 670, pp. 699-713, VDI-Verlag, Düsseldorf, 1988).

[0003] In these material-to-material joining processes, soldering is characterized by lower technological effort as well as higher reproducibility and reliability compared to (diffusion) welding.

[0004] Brazing is a thermal process for joining materials in which a liquid phase is created by melting the solder or by diffusion at the interfaces. This creates a surface alloy, but the workpiece is not melted at depth. The liquidus temperature of the base materials is not reached.

[0005] Ceramic or glass components can be joined to metal parts using glass solder or, if previously metallized, using metal solder. Active soldering is also a suitable alternative to prior metallization. In this process, an active element is alloyed into the solder or the joining partner is itself an active element alloy. The most common active metals are titanium, zirconium, or hafnium. These have an affinity for oxygen at elevated temperatures and react with the oxygen in the oxide ceramic during soldering.

[0006] Active brazing with metallic solders produces relatively strong bonds. When this process is used on PVD-metallized or laser-treated ceramics, the solder's wetting and flow properties are particularly favorable (Wielage, B. et al., VDI Reports, Volume 883, pp. 117-136, VDI-Verlag, Düsseldorf, 1991). In this process, the ceramic is metallized and then brought into contact with the solder in a furnace. The temperature is raised to above the melting temperature of the solder. In the molten state, the solders wet the metallized ceramic surface and, upon cooling, form a solid bond.

[0007] As is well known, active solders are already used for soldering oxide and non-oxide ceramics.

[0008] Such active solders usually consist of metal alloys containing titanium, zirconium, or hafnium as active elements. Vanadium-based alloys are also used.

[0009] From AT 285 187 B a vanadium-based alloy is known which consists of 0.1 to less than 2.8% Ti, Zr or Hf, as well as 0.1 to 2% Si and / or 0.5 to 4% germanium and the remainder vanadium, with 400 to 4000 ppm oxygen, 100 to 1500 ppm nitrogen, 100 to 1500 ppm carbon, oxygen and nitrogen and carbon but not more than 5000 ppm and small amounts of manufacturing-related impurities such as Ni, Fe, Cr, Cu.

[0010] According to AT 285 188 B, a vanadium-based alloy is known which consists of at least one of the alloying elements Ti, Zr or Hf with at least 0.1%, but not more than 5% Ti, not more than 1.2% Zr, not more than 1.2% Hf, 5 to 20% Cr and / or Mo and optionally 0.1 to 2% Si and / or 0.5 to 4% Ge, the remainder being vanadium with carbon and nitrogen contents of 100 to 1500 ppm each, oxygen of 400 to 3000 ppm, but in total not more than 4000 ppm carbon, nitrogen and oxygen, as well as small amounts of usual metallic impurities resulting from production, such as Fe, Ni, Cu.

[0011] According to US Pat. No. 3,576,621 B, a vanadium-based alloy is known that essentially consists of 60 to 80 wt.% vanadium, 15 to 25 wt.% molybdenum, 5 to 15 wt.% titanium, 0.1 to 1.0 wt.% yttrium, and 0.05 to 0.2 wt.% carbon. This alloy exhibits high strength and good processability. Strength can be improved by adding 0.2 to 0.75 wt.% silicon. The vanadium-based alloy is used as a structural material in instruments, pipelines, containers, etc.

[0012] Furthermore, WO 2017 / 032825 A1 discloses oxidation-resistant vanadium alloys for high-temperature stressed components. These alloys consist of 2 to 35 at.% Si and 3 to 50 at.% B, with the remainder V. The vanadium alloy contains at least one intermetallic phase consisting of vanadium, silicon, and boron. These vanadium alloys can be used as structural materials for fusion reactors or for applications in the field of energy conversion, e.g., in gas turbines.

[0013] However, such known vanadium alloys are not used as solder materials.

[0014] US 2019 / 0031570 A1 discloses a brazing alloy for joining or repairing ceramic components. It consists of 48 to 66 at.% Si, 1 to 35 at.% Ti, and another element from the group consisting of Al, Co, V, Ni, and Cr. The melting point of the alloy is at least 1300 °C. This brazing alloy is used, for example, in gas turbines.

[0015] EP 0 388 685 B1 discloses a method for joining oxide ceramic and metal and a tool produced thereby, in which a first metallic layer made of a titanium alloy is applied to the oxide ceramic, a second metallic layer is applied thereon, and the metallic component is soldered thereon to a third metallic layer containing nickel and titanium, the metallic component being made of a metal from subgroup 6, and a niobium foil being used as the second layer, and all of this together being subjected to a pressure of at least 0.2 MPa and a temperature which is at least the melting temperature of the materials of the first and third layers, and to a protective gas atmosphere.

[0016] Furthermore, US Pat. No. 3,903,585 A discloses a brazing process in which infusible metal alloys are used both as components and as brazing material for joining various parts and components made of materials based on infusible metals and compounds, ceramics, graphite, and the like. The alloys are based on hafnium, to which some elements from subgroup B of the first group of the periodic table and some elements with melting points above 600 °C from the third to eighth groups of the periodic table are added.

[0017] US 3,316,069 A discloses a method for joining tungsten, tantalum, molybdenum, niobium, and alloys thereof containing a predominant proportion of these metals, which are joined to themselves and to one another. A brazing alloy consisting of 4 to 50 weight percent vanadium, 20 to 96 weight percent niobium, and 0 to 60 weight percent tantalum is applied to the surfaces to be joined. The brazing alloy's composition falls within the range defined by triangle ABC in the adjacent figure. The bodies are then heated with the brazing alloy to a brazing temperature in the range of 1950°C to 2500°C in a non-oxidizing atmosphere, and the resulting brazed joint is subsequently cooled.

[0018] US 6,221,513 B1 also discloses a method for hermetically sealing ceramics to metallic surfaces, in which the metallic component is used in the form of a titanium-containing alloy and the metallic component is in contact with a metallic filler material consisting of a titanium-nickel material, wherein the filler material is additionally in contact with a ceramic component made of zirconium dioxide, whereby the titanium-nickel material is capable of melting at a temperature of less than 1100°C in the presence of the metallic component and the ceramic component.

[0019] And also from US 3,249,429 A a tantalum brazing alloy is known, which essentially consists of about 15 to 25 wt.% titanium, about 3 to 7 wt.% columbium and about 2 to 4 wt.% tungsten and the remainder tantalum.

[0020] Disadvantages of state-of-the-art active solder solutions include, on the one hand, that they are generally not suitable for high-temperature applications and, on the other hand, that they are uneconomical due to excessive material costs. On the other hand, their application with oxide and non-oxide ceramics is also difficult due to different thermal expansion coefficients.

[0021] The object of the present invention is to provide high-temperature active solders with which oxide and non-oxide ceramics can be soldered and which are long-term stable at high temperatures and / or aggressive environments and which realize a strong connection between the components to be joined during use.

[0022] The object is achieved by the invention defined in the claims. Advantageous embodiments are the subject of the dependent claims, whereby the invention also includes combinations of the individual dependent claims in the sense of an AND connection, as long as they are not mutually exclusive.

[0023] The high-temperature active solders according to the invention comprise at least one vanadium- and / or niobium- and / or tantalum-based alloy, which may comprise Mo, W, Cr, Y and / or Al as further alloying elements, and which contains at least >0 to 7 at.% silicon and 2 to 10 at.% titanium and / or zirconium and / or hafnium and further comprises at least in some regions the intermetallic phase (V,Nb,Ta)3Si.

[0024] Advantageously, the other alloying elements are present in a proportion of 0 to 20 at-% Cr, 0 to 2 at-% Y, 0 to 25 at-% Al.

[0025] Furthermore, 4 to 7 at.%, even more advantageously 6 to 7 at.% silicon are present.

[0026] And also advantageously 3 to 8 at.%, even more advantageously 4 to 6 at.% titanium and / or zirconium and / or hafnium are present.

[0027] It is also advantageous if 2 to 10 at.% titanium is present.

[0028] It is also advantageous if >0 to 20 vol.% intermetallic phase (V,Nb,Ta)3Si and / or Nb5Si3 is present.

[0029] It is also advantageous if V3Si is present as an intermetallic phase, advantageously with 7 to 10 vol.%.

[0030] It is also advantageous if the intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3 are largely homogeneously distributed in the solder.

[0031] The present invention makes it possible for the first time to provide high-temperature active solders with which oxide and non-oxide ceramics can be soldered and which are long-term stable at high temperatures and / or aggressive environments and which realize a strong connection between the components to be joined during use.

[0032] This is achieved with high-temperature active solders which contain at least one vanadium and / or niobium and / or tantalum-based alloy.

[0033] The use of vanadium as a construction material is widely known, but has so far been used little as a solder material.

[0034] Niobium and tantalum are also little or not at all known or used as solder materials.

[0035] By using high-melting solder materials, the operating temperature of soldered components can generally be increased.

[0036] In addition, vanadium, niobium and tantalum are significantly cheaper than precious metals, which have previously been widely used as high-temperature solder materials.

[0037] The respective base alloy of the high-temperature active solders according to the invention always contains at least > 0 to 7 at.% silicon.

[0038] The proportion of silicon in the high-temperature active solders according to the invention is of particular importance, since the comparatively small addition of silicon causes several metallurgical and rheological effects.

[0039] On the one hand, the addition of silicon to the base alloy lowers the melting point of the alloy. This has the advantage that the materials can be soldered at lower temperatures, but the overall application can be carried out at higher temperatures than before.

[0040] On the other hand, the addition of silicon enables the targeted creation of a two-phase region between the resulting melt and the vanadium / niobium / tantalum solid solution during melting of the materials. Subsequently, upon cooling of the high-temperature active solders, intermetallic phases are precipitated, while the melt formation during the soldering process can be specifically controlled by adjusting the amount of silicon added and the temperature.

[0041] Since the temperature influences the melting quantity of the solder, the melting quantity at the soldering point and the flow behavior of the solder can also be specifically controlled via the temperature.

[0042] Furthermore, oxidation of the ceramic materials also takes place during the soldering process, provided that ceramic materials are present as joining partners.

[0043] The escaping oxides increase the viscosity of the solder melt. According to the invention, this can be compensated for by increasing the silicon content and thus the melt quantity due to the temperature increase and the increased flowability of the solder melt.

[0044] In addition, silicon in the base alloy according to the invention also reduces the surface tension of the solder melt and thus also ensures better wetting of the surfaces to be joined.

[0045] The formation of the intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3 is of great importance according to the invention, since these intermetallic phases, which form in a temperature range of approximately 1700–2000 °C depending on the respective chemical composition and precipitate from the vanadium / niobium / tantalum solid solution in the two-phase region passing through during cooling, increase the overall high-temperature strength of the base alloy and prevent or hinder dislocation migration in the microstructure of the solders according to the invention. This increases the creep resistance of the solders according to the invention.

[0046] The presence of these intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3 has proven to be particularly advantageous.

[0047] Known high-temperature solders contain only pure solid solutions, which was considered particularly positive. However, it has been shown that such solders are very soft and thus lose their strength and creep resistance, especially at higher operating temperatures.

[0048] Therefore, while high-temperature solders containing intermetallic phases are known in the state of the art, these solders contain the intermetallic phases in a large number and in indeterminate quantities. Accordingly, the properties of these solders were not reproducible and could not be used, especially for long-term high-temperature applications.

[0049] Due to the composition according to the invention, the two-phase region between melt and solid solution of the base alloy materials is reached precisely during soldering of the material and passed through again during cooling of the melt, so that precisely the intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3 are formed.

[0050] A further advantage of the inventive solution is that the intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3 precipitate from the two-phase region in a finely distributed manner throughout the solder material upon cooling, thus ensuring a uniform, homogeneous distribution of the intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3. This also leads to the presence of the same properties throughout the solder material of a solder joint.

[0051] A further positive effect of the intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3 is achieved by the fact that before the formation of the intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3, the thermal stresses between the joining material and the solder material can be reduced via plastic flow during the cooling of the solder material, so that neither the diffusion zone of the solder material nor the joining materials are stressed.

[0052] Furthermore, according to the invention, the base alloy also contains at least 2 to 10 at.% titanium, zirconium and hafnium.

[0053] Titanium, zirconium and hafnium are known to be active elements that are able to enable the wetting of the ceramic with the solder.

[0054] In addition to the alloying elements (V, Nb, Ta) with (Ti, Zr, Hf) and Si according to the invention, further alloying elements known per se for improving other properties, such as Mo, W, Cr, Y and / or Al, can be components of the high-temperature active solders according to the invention.

[0055] The high-temperature active solders according to the invention have a thermal expansion coefficient, whereby these solder materials can also be used for joining aluminum, zirconium or silicon carbide ceramics or for joining ceramic-metal composites, such as for example for joining aluminum oxide with niobium.

[0056] The high-temperature active solders according to the invention can also be used in the temperature range above 1500 °C and exhibit high long-term stability there.

[0057] The high-temperature active solders according to the invention are available in compact or powder form.

[0058] The soldering process can be carried out in a furnace with moderate heating and cooling rates of, for example, 10 K / min. The soldering temperature depends on the chemical composition of the joining partners and the solder and is in the range of 1700 - 2000 °C.

[0059] Furthermore, the oxide joining partners can be joined using a laser-based brazing process. Heating rates of up to 25 K / s and cooling rates of approximately 6 K / s are possible when the brazing temperatures are between 1850 °C and 1900 °C.

[0060] The invention is explained in more detail below using an exemplary embodiment. Example 1

[0061] Two Al2O3 components with dimensions of 6 mm in diameter and 35 mm in length are to be soldered together at one end each. The two round surfaces at each end of the rods are the joining surfaces. Both rods are heated to a soldering temperature of 1900 °C using a 3 kW diode laser (808 nm and 940 nm). V is used as the solder material. 89,4 Si 6,6 A 5.8 mm diameter, 400 µm thick Ti4 foil is placed on the joining surface between the two Al2O3 components and heated. Heating takes place in a container that is evacuated (0.1 Pa) and then pressurized to an Ar atmosphere with a pressure of 0.1 MPa. For heating, the laser beam (1 cm focus diameter, 900 W laser power) is moved along a 35 cm circular path at 5000 mm / s through a scanner optics and reflected onto the joining zone by a copper mirror to evenly heat all sides of the joining zone. This achieves a heating rate of 25 K / s in the joining zone.

[0062] The holding time at soldering temperature is 10 seconds. After the holding time at soldering temperature, the joining zone is cooled to room temperature at 7 K / s.

[0063] The Al2O3 components are then firmly bonded together and 4-point bending strengths of 243 MPa have been achieved in the unground state of the joined Al2O3 bodies.

[0064] After soldering, the vanadium solid solution forms the matrix material within the brazing seam, with the intermetallic high-temperature phase V3Si embedded and evenly distributed within it. The resulting phases and the diffusion zone remain undamaged in the joining zone after aging for 4 hours in a protective gas at 1600 °C. Thus, the brazed components remain stable at high temperatures in an inert atmosphere and ensure a strong connection between the joined components. This allows the joined components to act as a drive shaft, transmitting torques and forces at high temperatures. Example 2

[0065] A SiC shaft with a diameter of 6 mm and a length of 50 mm is to be joined to a SiC hub with a thickness of 3 mm, an inner diameter of 6.4 mm, and an outer diameter of 12 mm. The components are inserted into each other such that the gap between the shaft and the hub is 0.2 mm. The assembly gap is filled with a solder paste made of Nb. 84,8 -Cr7-Al6-Zr2-Si 0,2 alloy and placed in a vacuum inert gas furnace. The SiC components are heated to 1000 °C under vacuum (0.1 Pa). From 1000 °C, 0.1 MPa of Ar is introduced into the furnace chamber, and the furnace is heated further to a brazing temperature of 1700 °C at 10 K / min. The holding time at 1700 °C is 10 minutes, after which the joined component is cooled to room temperature at 10 K / min.

[0066] The components are then joined together and can transmit mechanical torques via the shaft-hub connection at higher temperatures, depending on their function.

[0067] Within the solder joint, the intermetallic phases Nb5Si3 and Nb3Si are finely distributed in a Nb solid solution matrix to improve the high-temperature strength.

Claims

[1] High-temperature active solders which comprise at least one vanadium- and / or niobium- and / or tantalum-based alloy, which may comprise Mo, W, Cr, Y and / or Al as further alloying elements, and which contains at least >0 to 7 at.% silicon and 2 to 10 at.% titanium and / or zirconium and / or hafnium and further comprises at least in some regions the intermetallic phase (V,Nb,Ta)3Si. [2] High-temperature active solders according to claim 1, in which the further alloying elements are present in a proportion of 0 to 20 at-% Cr, 0 to 2 at-% Y, 0 to 25 at-% Al. [3] High-temperature active solders according to claim 1, in which 4 to 7 at.%, more advantageously 6 to 7 at.% silicon are present. [4] High-temperature active solders according to claim 1, in which 3 to 8 at.%, more advantageously 4 to 6 at.% of titanium and / or zirconium and / or hafnium are present. [5] High-temperature active solders according to claim 4, in which 2 to 10 at.% titanium is present. [6] High-temperature active solders according to claim 1, in which >0 to 20 vol.% of intermetallic phase (V,Nb,Ta)3Si and / or Nb5Si3 is present. [7] High-temperature active solders according to claim 1, in which V3Si is present as the intermetallic phase, advantageously with 7 to 10 vol.%. [8] High-temperature active solders according to claim 1, in which the intermetallic phases (V,Nb,Ta)3Si and / or Nb5Si3 are distributed largely homogeneously in the solder.