Nickel-based braze alloy compositions and related processes and articles

Abstract

A nickel-based braze composition is described, containing nickel, palladium, and restricted amounts of boron and silicon. The composition can also contain tantalum, titanium, and zirconium, as well as aluminum, chromium, and cobalt. A method for joining two metal components, using the braze composition, is also described. The braze composition can also be used to fill cracks or other cavities in a component, e.g., a gas turbine part formed from a nickel-based superalloy. Articles of manufacture which contain the braze composition are also described.

Description

BACKGROUND OF THE INVENTION In a general sense, this invention relates to braze compositions. More specifically, it relates to braze materials suitable for repairing nickel-based superalloy articles, or for joining different sections of superalloy components. Nickel- and cobalt-based superalloys are very important in a number of industrial applications. These applications often involve extreme operating conditions, wherein the superalloys may be exposed to high temperatures, e.g., above about 750° C. Moreover, the alloys may be subjected to repeated temperature cycling, e.g., exposure to high temperatures, followed by cooling to room temperature, and then followed by rapid re-heating. Gas turbine engines are a prime example of components subjected to such an environment. It is frequently necessary to join various superalloy components together, and brazing techniques are often preferred to accomplish this objective. As an example in the case of power turbines, brazing may be used...

AI Technical Summary

Benefits of technology

As mentioned above, the nickel-based braze composition of this invention comprises about 10 to about 25 atom % palladium. Palladium is very effective as a melting point depressant for the composition. Its presence thus results in lower braze temperatures, which are highly desirable in many instances. Moreover, unlike melting point depressants such as boron and silicon, palladium exhibits a relatively high solubility in a nickel matrix. The high solubility prevents or minimizes the formation of brittle secondary phases in the nickel matrix.

The braze composition further comprises limited amounts of boron or silicon, or a combination of boron and silicon. The total amount of these elements should be at least about 0.1 atom %. It is believed that each of these elements may sometimes provide a degree of wettability and flow to the braze composition. These characteristics can be very helpful for ensuring that the braze material stays in intimate contact with the workpiece, and can readily fill cracks or other voids when necessary. Boron and silicon also help to reduce the melting point of the braze, as discussed previously.

However, it is important that the amount of boron and silicon be no greater than about 5 atom % (total). This limit on their presence substantially eliminates or minimizes the formation of secondary phases within the nickel microstructure, e.g., boride phases. In this manner, problems associated with those secondary phases are also eliminated or minimized, such as reduced ductility. High-temperature corrosion resistance and oxidation resistance, e.g., in the operating range of about 1800° F.-2100° F. (982° C.-1149° C.), can also be maintained.

Problems solved by technology

These types of parts are often subjected to high temperatures and high-oxidation conditions in service.

While each of the commercial compositions may be very suitable for a number of applications, most of them still exhibit some deficiencies when they are used in certain situations.

As technical requirements and other industrial needs increase, it is becoming more difficult to satisfy these general requirements for brazes.

However, significant levels of boron and silicon can be detrimental to the final braze product.

For example, these elements tend to form brittle, intermetallic phases in the braze microstructure.

Moreover, the Rabinkin patent describes other adverse effects caused by the use of boron and silicon metalloids.

If the components are subjected to brazing operations which contain the metalloids, the protecting film in the brazed region can be partially or completely damaged.

As a result, the brazed interface can act as a conduit for oxygen penetration, leading to oxidation-attack of the entire part.

Continuing developments in industry have made the search for improved braze compositions more problematic.