KR0179194B1 - High-temperature brazing alloys for ceramic metal joints - Google Patents

Abstract

Au-Ni-Cr-Fe based alloys for ceramic-to-metal bonding have been developed for high temperature applications. The alloy exhibits low yield strength, high ductility and high tensile strength, which are essential for successful ceramic-to-metal bonding, and have bonding performance in combination with other bonding elements. This joining alloy is for forming high performance high performance joints and can be used for joints used in ceramic engines and high temperature combustors.

Description

Sintering alloys and bonding alloys for high temperature applications of ceramic-metal joints

1 shows a schematic diagram of a ceramic-metal junction according to the present invention,

2 shows a sintering process of the joined body according to the method of the present invention.

The present invention relates to a bonding alloy for high temperature applications of ceramic-metal joints and to a method of sintering the joints.

As such a bonding alloy for ceramic-to-metal bonding, various bonding alloys have been used depending on the application temperature, the shape of the bonding portion, the material of the substrate, and the like. Most of alloys for ceramic-metal joints, especially those used at high temperatures, are alloys based on precious metals such as gold (Au), silver (Ag), or palladium (Pd), which have high ductility, high oxidation resistance, and high melting point. . In the case of black, alloys in the form of solid solution with nickel (Ni) are predominant. In these alloys, the melting point of the alloy increases as the amount of Pd or Ni increases. However, alloys having high melting points such as Au-Ni, Pd-Ni, and Au-Pd-Ni are known to have inherently weak creep strength at high temperatures due to their microstructure and strengthening mechanisms such as solid solution strengthening. Therefore, the use temperature of such an alloy is not only limited to about 400 ~ 450 ℃ it is impossible to use for a long time.

With the development of ceramic materials, ceramic-metal joints are frequently required to be used for a long time under stress conditions such as rotation and high temperatures of 600 ° C or higher. In this case, the biggest problem of ceramic-to-metal joints is the generation of residual stresses due to the difference in coefficient of thermal expansion between different kinds of materials. In addition to the relaxation of residual stress, high toughness and ductility are required for rolling when the bonding alloy is used in the form of sheet. In addition, the junction must have a high temperature creep resistance in order for the junction to be used for a long time at a high temperature.

In order for the joined body to be used at a high temperature, one having a high melting point of the joined alloy is used.

However, the melting point of a suitable alloy must be considered first, since each joint component loses its stability near this melting point, thus losing the effect of using the alloy. For example, silicon nitride for automotive ceramic engines used in this experiment causes denitrification around 1200 ° C, which is characterized by the addition of highly reactive metals such as titanium (Ti) to the surface to improve the wettability of liquid bonded alloys. More prominent when coated. The low thermally expandable metal Incoloy 909, which is another member of the bonded body, greatly changes its microstructure and physical properties when subjected to heat treatment of 1200 ° C or higher, and therefore, the bonding process is preferably performed at 1200 ° C or lower.

Therefore, an object of the present invention is to effectively mitigate the influence of residual stresses that cause ceramic breakdown in the joint by inserting a material possessing ductility between the joints to make the joint.

It is another object of the present invention to ensure that the alloy has the low yield strength, high ductility and high tensile strength required for the ceramic-to-metal joint, thereby simultaneously maintaining harmonious bonding performance with other joining elements.

In order to obtain these properties, first, a system having a stable microstructure in solid solution form was found. This is for the ductility of the joining alloy, which is the first requirement of the joining, and the solid solution hardened alloy is inferior in creep resistance to the precipitate hardened alloy, but facilitates the formation of the joined body.

Second, we found a composition that can have a dual phase solid solution phase by having an immiscible region in the solid phase microstructure. This is because solid solution hardened alloys can be used as a way to increase weakened creep resistance. Third, the elements of the base material are diffused into the bonding material at the time of high temperature bonding, but the melting point is lowered due to the diffusion, so that various physical properties of the joint should not be deteriorated. It was to have.

In order to achieve the above object, according to the present invention, Au-Ni-Cr-Fe-based is selected as an alloying material for high-temperature ceramic-metal bonding. Such an alloy of Au-Ni-Cr-Fe can be used for a long time under the temperature and stress of 650 ℃, and also has a melting point of about 1050 ~ 1150 ℃.

EXAMPLE

The Au-Ni-Cr-Fe alloy material of the present invention was investigated for the ductility and wettability of various alloy compositions using an induction melting method in an argon atmosphere. Table 1 shows the ductility and wettability in the various compositions studied.

On the other hand, 2.5-10% Cr and 1.5-10% Fe were systematically added to Au-37-40% Ni system to measure the relative effects on the ductility and wettability of Cr and Fe in this alloy system. I could see the fact.

(1) Adding Fe to the Au-Ni system increases the creep resistance of the solid solution and does not interfere with the fluidity (wetting) of the good liquid metal of the Au-Ni system, but the ductility decreases as the amount of Fe increases.

(2) If more than 5% of Cr is added to Au-Ni system, creep resistance increases, but the flow characteristics of the liquid bonding material on the nickel alloy base material (Inconel 600) decreases as the alloy hardens.

(3) The ratio of Au and Ni plays an important role in increasing the ductility of the alloy.

In addition, studies have been made to increase the amount of high temperature strengthening elements in a range that minimizes the loss of other properties required for bonding. Among the alloy compositions, alloys in the Au-25-40% Ni-3-10% Cr-1-5% Fe region melted at 1050-1100 ° C. to meet the requirements for high temperature ceramic-metal bonding processes.

Based on the phase equilibrium and the results of these bonding experiments, 56% Au-37% Ni-4.8% Cr-2.1% Fe composition was determined as the final sheet composition. This alloy composition not only has excellent wettability and bonding properties, but also has excellent ductility compared to other compositions. Since this alloy melts in the vicinity of 1000 degreeC, it could join at 1050 degreeC considered to be the upper limit temperature of a ceramic-metal joining process.

For thin-film production of this composition, 120 g of alloy was placed in a boron nitride crucible and melted by induction heating at 1300-1400 ° C. and poured into a copper mold to form a rod of 2.0 × 0.75 × 0.25. After homogenization by heat treatment at 800 ° C. for 24 hours in an argon atmosphere, the film was rolled into a thick foil having a thickness of 0.002 with annealing at 800 ° C. for 2 to 4 hours in an intermittent vacuum atmosphere. The alloy was rolled successfully because of its good toughness and ductility.

Table 2 shows the results of the thin alloy composition analysis, and Table 3 compares the results of room temperature shear strength with other commercially-bonded alloys Au-18% Ni (Nioro) and Au-5% Pd-2% Ni. . High-temperature silicon nitride PY6 (Si3N4-6% Y2O3; Wesgo Inc., Belmont, CA) was used as the ceramic material, and Ni 200, which is the most preferred intermediate material, was used as the metal material. This test is a test that breaks at a given temperature after joining. Creep resistance cannot be measured, but it is suitable for checking the adequacy of alloys. The developed Au-Ni-Cr-Fe alloy shows shear strength similar to that of Au-18% Ni for medium temperature, and is better than Au-5% Pd-2% Ni provided for high temperature.

Indeed, an example of this material is the joining of a silicon nitride turbine used in ceramic automotive engines with an Incoloy 909 as a transmission material. Ni was used as an intermediate material to arrange PY6 / Ni / Incoloy 909 in order to form a conjugate as shown in FIG. The bonded alloy was inserted between PY6-Ni and Ni-Incoloy 909 to form a bonded body. The conjugate is first heated to 800 ° C. at a heating rate of 10 ° C./min, maintained at 800 ° C. for 10 minutes, and then again heated at a heating rate of 5 ° C./min according to the sintering process shown in FIG. 2. Produced according to a slow cooling process in the furnace through a vacuum brazing step at 1050 to 1100 ℃.

Since the temperature at which the junction is in contact with the ceramic engine is 650 ° C, the torsional strength is measured at room temperature and 650 ° C and compared with the torsional strength of the joint using Au-Pd-Ni. This result is as shown in Table 4. The results using the Au-Pd-Ni alloy is excellent at room temperature, but the Au-Ni-Cr-Fe of the present invention was remarkably excellent at 650 ° C.

On the other hand, the microstructure of this alloy, consisting of a solid solution of Au-Ni-Fe and Ni-Cr-Fe, has been shown to improve high temperature creep strength. The low creep resistance of commercial junction alloys such as Au-Ni, Au-Pd-Ni, and Pd-Ni is due to the presence of a solid solution in a single phase in the system. Brought.

As described above, the Au-Ni-based alloy of the present invention contains a high temperature solid solution reinforcing material such as Cr and Fe. This alloy has remarkable performance in bonding performance, strength and ductility. In particular, a dual phase microstructure consisting of a solid solution phase of Au-Fe-Ni-based and Ni-Cr-Fe-based shows a desirable high temperature creep resistance. Since the alloy has very good toughness and ductility, it is not only easy to process into a thin sheet by rolling, but also has an advantage that the alloy is inexpensive because the content of the precious metal is reduced (<60%). The alloy is suitable for forming high temperature, high performance, high performance joints and can be used in the production of ceramic-metal joints, especially used in ceramic engines and combustors for thermal power generation.

Claims (2)

In the bonding alloy of the ceramic-metal joint for high temperature application, the bonding alloy is an alloy having a composition ratio of Au-25 to 40% Ni-3 to 10% Cr-1 to 5% Fe (% by weight). Joining alloy of ceramic-metal joints. A method of sintering a ceramic-metal joint using the bonding alloy of claim 1, comprising the steps of: loading a bonding object in which the bonding alloy is placed between the ceramic and the metal; First heating step of heating the temperature of the furnace to 780 ~ 820 ℃; A holding step of maintaining the temperature of the furnace at 780 to 820 ° C. for a predetermined time; A vacuum brazing step of heating the furnace temperature to 1050 to 1100 ° C. and then performing vacuum brazing for 10 minutes; And a cooling step of cooling the temperature of the furnace.