Patent Application
20070102483
(1) Field of the Invention
The present invention relates to a method for repairing turbine engine components formed from a single crystal material and to a repair alloy composition used to effect said repairs.
Turbine engine components, such as high pressure and low pressure turbine blades, are often formed from a single crystal material such as a single crystal nickel-based superalloy. In use, these components will develop cracks which require repair. Currently, some repair techniques expose the components being repaired to temperatures of 2200 degrees Fahrenheit. Such exposures may produce a debit in 1600 degree Fahrenheit creep strength which is unacceptable.
A repair technique which does not adversely affect material properties would be highly desirable.
The present invention provides a repair technique was developed which does not adversely affect material properties.
In accordance with the present invention, a process for repairing turbine engine components broadly comprises the steps of providing a component with at least one crack, applying a repair alloy composition containing a single crystal nickel based alloy, a first nickel based braze alloy, and a second nickel based braze alloy to the crack(s), and subjecting the component with the applied repair alloy composition to a heat treatment to diffuse the repair alloy composition into the crack(s).
Further in accordance with the present invention, a repair alloy composition for use in repairing cracks is provided. The repair alloy composition broadly comprises a single crystal nickel based material, a first nickel based braze alloy, and a second nickel based braze alloy.
Other details of the low temperature diffusion braze repair of single crystal components of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the following drawing.
A process for repairing turbine engine components having at least one crack without adversely affecting material properties is provided by the present invention. The process may be used to repair turbine engine components formed from nickel-based superalloys, particularly those formed as a single crystal. Typical nickel-based superalloys which may be used for the components include, but are not limited to, those nickel base alloys having from 5 to 10 wt % chromium, from 5 to 10 wt % cobalt, from 5 to 6.2 wt % aluminum, up to 1.9 wt % molybdenum, from 4 to 6 wt % tungsten, from 8 to 12 wt % tantalum, up to 0.35 wt % hafnium, up to 3.0 wt % rhenium, and the balance nickel.
The process of the present invention utilizes a repair alloy comprised of three components. The three components are a single crystal nickel based material, a first nickel based braze alloy, and a second nickel based braze alloy. The single crystal nickel based material may be present in an amount from 5 to 50 wt %. The first nickel based braze alloy may be present in an amount from 40 to 60 wt %. The second nickel based braze alloy may be present in an amount from 10 to 35 wt %. The single crystal nickel based material and the first nickel based braze alloy additions provide alloy additions which are beneficial to the material forming the turbine engine component. The second nickel based braze alloy preferably allows the alloy mixture to melt in the 2025 degree Fahrenheit range. The three components may be mixed using any suitable means known in the art to form the repair alloy composition.
The single crystal nickel based material preferably comprises a single crystal nickel based alloy having a composition consisting of from 5 to 10 wt % chromium, from 5 to 10 wt % cobalt, from 1.5 to 3.5 wt % titanium, from 4.2 to 6.2 wt % aluminum, up to 1.9 wt % molybdenum, from 4 to 6 wt % tungsten, from 4.8 to 12 wt % tantalum, up to 0.5 wt % columbium, up to 0.35 wt % hafnium, up to 0.004 wt % boron, up to 3.0 wt % rhenium, up to 0.013 wt % yttrium, and the balance nickel.
The first nickel based braze alloy may be a braze alloy sold under the trade name DF-4B. This braze alloy has a composition consisting of 14 wt % chromium, 10 wt % cobalt, 3.5 wt % aluminum, 2.5 wt % tantalum, 2.75 wt % boron, 0.1 wt % yttrium, and the balance nickel. Other nickel based braze alloys may be used provided that the nickel content is greater than 50 wt %.
The second nickel based braze alloy may be a braze alloy sold under the trade name Nicobraz 150. This braze alloy has a composition consisting of 14.75 wt % chromium, less than 0.06 wt % carbon, 3.63 wt % boron, less than 1.5 wt % iron, and the balance nickel. Other nickel based braze alloys may be used provided that the nickel content is greater than 50 wt %.
After preparation of the repair alloy has been completed, the repair alloy formed from the three components may be applied to each crack in the component being repaired. The repair alloy may be applied to the crack(s) using any suitable technique known in the art.
After the repair alloy has been applied to the crack(s), the component is subjected to a thermal cycle which does not adversely affect the properties of the material forming the component. The thermal cycle comprises heating the component with the repair alloy applied to the crack(s) to a melt cycle temperature in the range of from 1950 to 2065° F., preferably from 2000 to 2050° F., for a time period such as 15 minutes, and then cooling the component with the applied repair alloy to a diffusion cycle temperature in the range of from 1950 to 2025° F., preferably from 1975 to 2025° F., and maintaining the temperature for a total time period in the range of from 5 to 20 hours, preferably from 8 to 12 hours, to effect the repair of the crack(s). The thermal cycle may be performed in a furnace at a vacuum of 5×10−4 Torr or lower. After the thermal cycle has been completed, the repaired component may be cooled at a rate of 35° F./minute or faster.
It has been found that cracks, when repaired with the braze alloy mixture of the present invention and exposed to the thermal cycle, yield a well filled, isothermally solidified structure.
Referring now to
A repair on a single crystal nickel based alloy component may also be made by removing all coatings from the component being repaired and cleaning the crack to be repaired. A repair alloy consisting of 50 wt % DF-4B, 25 wt % Nicobraz 150, and 25 wt % of a nickel based single crystal alloy having a composition consisting of 5 wt % chromium, 10 wt % cobalt, 5.65 wt % aluminum, 1.o9 wt % molybdenum, 5.9 wt % tungsten, 8.4 wt % tantalum, 0.10 wt % hafnium, 3.0 wt % rhenium, 0.013 wt % yttrium, and the balance nickel was prepared and applied over the crack. The component with the repair alloy may be placed in a furnace and heat treated in a vacuum of 5×10−4 Torr at a temperature in the range of 2035 to 2065° F. for 15 minutes. The component and the repair alloy may then be cooled to 1975° F. and held at temperature for 9 hours and 45 minutes. The repaired component may then be cooled at a rate of 35° F./minute or faster.
It is apparent that there has been provided in accordance with the present invention a low temperature diffusion braze repair of single crystal components which fully satisfies the objects, means, and advantages set forth hereinbefore. While the present invention has been described in the context of specific embodiments thereof, other unforeseeable alternatives, modifications, and variations may become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.
