Patent Application
20140272450
This invention relates generally to the filed of materials technology, and more specifically to a braze material useful for the repair or joining of nickel base superalloy components
It is recognized that the repair of superalloy materials is made difficult due to their susceptibility to weld solidification cracking and strain age cracking. The term “superalloy” is used herein as it is commonly used in the art; i e, a highly corrosion and oxidation resistant alloy that exhibits excellent mechanical strength and resistance to creep at high temperatures. Superalloys typically include a high nickel or cobalt content. Examples of superalloys include alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g. IN 738, IN 792, IN 939), Rene alloys (e.g. Rene N5, Rene 80, Rene 142), Haynes alloys, Mar M, CM 247, CM 247 LC, C263, 718, X-750, ECY 768, 282, X45, PWA 1483 and CMSX (e.g. CMSX-4) single crystal alloys
Brazing processes are used to repair or to join superalloy materials in some applications While a braze joint is generally understood to be mechanically weaker than a weld joint and to have a lower acceptable operating temperature due to the relatively low melting temperature of the braze material, braze repairs may be acceptable in certain lower stress and/or lower temperature applications.
Typical braze materials using boron or silicon as the melting point depressant material are of limited value with superalloy substrate materials because they create deleterious phases which reduce the ductility of the joint and repaired region Boron and silicon free braze alloys incorporating hafnium or zirconium have been developed for which mechanical properties of up to 80% of the base superalloy properties are claimed U.S. Pat. No. 8,640,942, commonly assigned with the present application, discloses the repair of superalloy materials with titanium based, boron and silicon free braze alloys
The invention is explained in the following description in view of the drawings that show
The present inventors have successfully used high strength boron and silicon free braze alloys in powder form for the repair of superalloy materials However, the inventors have found that such high strength braze alloys may be difficult to fabricate as a foil because of their strength and brittleness
The sole figure illustrates a braze foil 10 which will have a desired high strength composition upon melting and which is suitable for use with superalloy materials, but which is formed as a sandwich of three layers 12, 14, 16, wherein each of the layers has a ductility sufficient to facilitate being fabricated as a foil For example, U.S. Pat. No. 8,640,942 describes near eutectic ternary alloys of Ni—Ti—Cr which are brittle in solid form, for example an alloy having a weight percentage composition of 20% Cr-20% Ti-60% Ni All composition percentages quoted herein are weight percent. In accordance with the present invention, such a composition may be formed of constituent parts which are each more ductile and more easily fabricated as a foil than the near eutectic alloy, such as when layers 12 and 16 are formed of 18-22% Cr-balance Ni, and layer 14 is formed of 100% Ti In this example, the chrome-nickel and titanium layers are relatively ductile compared to the ternary composition, and they can be rolled together to a desired thickness to form foil 10 which exhibits the desired composition upon melting The thickness of the various layers can be controlled to achieve the desired combined composition in the melted foil In one embodiment, each layer 12, 14, 16 has an equal thickness and the total thickness of the foil 10 may be less than 75 microns, although other relative and total thicknesses may be used for a particular application
Advantageously, the material of each layer is selected such that at the interfaces 18, 20 between the respective layers, the materials of the contacting layers 12/14, 14/16 diffuse and cooperate to form a desired eutectic or near eutectic composition, such that at or above the eutectic temperature, the foil 10 will begin to melt at each of the layer interfaces 18, 20. The term “near eutectic” is used herein to include any alloy having a melting temperature range of less than 25° C. Once melting is initiated, additional material from each of the layers 12/14, 14/16 contacting the puddles of melted material will add to the melt, thereby maintaining a relatively stable formulation in the puddles until the entire foil 10 is melted Accordingly, the compositions and thicknesses of the layers may be selected and manufactured in a manner that establishes a eutectic or near eutectic composition at the interfaces 18, 20 and then maintains the desired eutectic or near eutectic composition as the melt progresses.
The example of the figure includes three layers, but one skilled in the art may appreciate that other numbers of layers may be used in other embodiments so long as a desired formulation is established at each interface and is maintained as the layers melt For example, a two-layer foil may be formed by joining a layer of chrome-nickel alloy against a layer of pure titanium, hafnium or zirconium, such as may be envisioned by layers 14 and 16 alone of the figure Such a foil may be useful for filling minor surface cracks in a superalloy substrate by disposing the foil, alloy side down, on top of the substrate surface, then heating the assembly to melt the foil, thereby at least partially filling the cracks and recreating a crack-free surface.
Generally, pure metal layers tend to be more ductile than alloys of the metal, so for ternary alloys it may be useful to provide a middle layer 14 as a pure metal and to have an alloy of two other metals as top and bottom layers 12, 16. For example, a boron and silicon free braze alloy sandwich foil may be formed with layers 12 and 16 being Cr—Ni and layer 14 being titanium or hafnium or zirconium. When such a foil is used to braze two adjoined nickel-based superalloy substrates, the chrome-nickel layers are in contact with the superalloy substrates as the heating and melting progresses. Advantageously, this avoids contact between the pure metal layer and the superalloy substrates which might otherwise tend to form undesirable intermetallic compounds during the heating and melting process.
In one embodiment, shown in the photograph of
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only Numerous variations, changes and substitutions may be made without departing from the invention herein. Dimensions and compositions should be understood to be subject to typical manufacturing tolerances. For example, a composition expressed as a percentage will typically be understood to be within ±0 5% of the stated value, and “pure” is understood to include some trace impurities of inconsequential functional result.
This application claims benefit of the 14 Mar. 2013 filing date of U.S. provisional patent application No. 61/782,922
| Number | Date | Country | |
|---|---|---|---|
| 61782922 | Mar 2013 | US |
