SOLUTIONED TURBINE BLADE COMPONENT WITH SUBZERO COOLING

BACKGROUND

1. Field

[0001] The present disclosure relates generally to the field of materials technology, and more particularly, to additive manufacturing and braze repair methods for the repair of structural defects in superalloy components.

2. Description of the Related Art

[0002] Gas turbine engine hot gas path components are typically formed of superalloy materials in order to withstand the high temperature, high stress environment to which they are exposed during operation of the engine. 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. Such components are very expensive to manufacture, and in spite of their superior material properties, they are prone to various forms of degradation during engine operation. Degraded components are removed from the engine and replaced. Depending upon the type and degree of degradation, used components may be refurbished and reused at a cost lower than the cost of a new component.

[0003] Nickel based superalloys are generally considered to be difficult to weld due to their tendency to grain boundary cracking. Structural defects such as cracking typically occur when the material of the component cools after the weld procedure. One cause of the cracking is due to a phase change taking place in the material during the cooling, which induces a thermal mismatch between the different phases causing stress in the component, particularly at the grain boundaries. This stress leads to the development of cracks in the material.

[0004] Several methods have been utilized to in order to repair damage done to superalloy components, such as gas turbine blades or vanes. One such conventional method currently in use involves pre-heating the component to a very high temperature just below the melting temperature of the component in order to ensure that no change is induced by the additional heating that is applied during the weld procedure. Disadvantages of this method include the amount of time it takes to prepare the component for welding and that the component is very difficult to handle when heated to such high temperatures. [0005] Consequently, a need remains for alternate processes to structurally repair degradation and defects, such as cracks, in superalloy components.

SUMMARY

[0006] Briefly described, aspects of the present disclosure relate to a method of additively manufacturing or repairing a superalloy component and a system to additively manufacture or repair a superalloy component.

[0007] A first aspect provides a method of additively manufacturing or repairing a superalloy component. The method provides at least a double solution heat treatment including initially heating the tip of the superalloy component to a first temperature for a first time period and then cooling the component to ambient temperature. After the first solution heat treatment, a second heat treatment is performed including heating the tip of the superalloy component to a second temperature for a second time period and then cooling the component to ambient temperature. The tip of the superalloy component may then be laser braze repaired. The laser braze repair includes depositing a layer of braze material on an end surface of the tip at a temperature less than the melting temperature of the composition of the base material of the component. Following the laser braze repair, the deposited layer is sub-cooled.

[0008] A second aspect provides a system to additively manufacture or repair a superalloy component. The method described above may be performed utilizing the elements of the system. The system comprises a heating system operably configured to produce heat up to and beyond a grain boundary melting temperature of the base metal of a tip of the superalloy component, a laser energy source operably configured to direct a laser energy towards a braze material melting the braze material and forming a deposited layer of additive material on the tip, and a sub-cooling means for sub-cooling the deposited layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 illustrates an exemplary embodiment of an additive manufacturing process or a laser braze repair process utilizing a sintered weld rod to additively deposit a layer of braze material, and

[0010] Fig. 2 illustrates an exemplary embodiment of a component being heated by a heating system. DETAILED DESCRIPTION

[0011] To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are explained hereinafter with reference to implementation in illustrative embodiments. Embodiments of the present disclosure, however, are not limited to use in the described systems or methods.

[0012] The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present disclosure.

[0013] Additive Manufacturing, or 3-D printing, has recently been successfully used to ‘print’ or manufacture components directly layer by layer. This manufacturing technology enables the optimization of component design. Additive manufacturing of components includes a wide range of materials and process techniques. During one such additive manufacturing process, a powder material may be deposited onto a working surface. Many layers may be formed on top of one another in a sequence to achieve a net shape or a partial net shape component. A heat source, such as a laser beam, is directed onto the working surface. The deposited powder material is melted by the laser beam and fused to the working surface. [0014] The inventors thus propose a method and system of additively manufacturing or repairing a superalloy component in which the superalloy component undergoes at least a double solution heat treatment prior to a braze process that deposits a layer of braze material additively onto the superalloy component followed directly by sub-cooling the deposited layer. [0015] A turbine airfoil is one example of a superalloy component experiencing damage and degradation during operation of the gas turbine engine. The turbine airfoil may be the airfoil of a rotating blade or a stationary vane in a gas turbine engine. The tip of the turbine airfoil is particularly vulnerable to damage and degradation with the result that most of the damage and degradation occurs in the tip. For the purposes of the disclosure, the tip may be defined as 5 to 10% of its length extending radially inward from the end of the airfoil opposite the root which couples the turbine airfoil to a disc of the turbine engine.

[0016] Referring now to the drawings where the showings are for purposes of illustrating embodiments of the subject matter herein only and not for limiting same, Fig. 1 illustrates a system 100 for additively manufacturing or repairing a tip (t) of a superalloy component 110 utilizing a braze material 130. For exemplary purposes, the superalloy component 110 depicted in the disclosure is a turbine airfoil such as a turbine blade or vane, however, one skilled in the art would appreciate that the superalloy component may be any superalloy component having a tip.

[0017] The system 100 may include a heating system operably configured to produce heat up to and beyond a grain boundary temperature of the base metal of the tip (t) of the superalloy component 110. Fig. 2 illustrates an embodiment of a heating system 160 utilized to heat the tip (t) of a turbine airfoil 110 to a predetermined temperature. In the illustrated embodiment, an induction coil is utilized as the heating source 160. The induction coil 160 may surround the tip (t) of the airfoil 110 as shown.

[0018] The system 100 may also include a laser energy source 120 for emitting a laser energy 125. The laser energy 125 may be directed towards the braze material 130 so that the braze material 130 melts and additively forms a deposited layer 150 on the tip (t). The braze material 130 may be in the form of a sintered weld rod 130, as illustrated in Fig. 2, or a wire feed. The sintered weld rod 130 or wire feed may extend toward the tip (t) so that an end contacts the tip (t) of the superalloy component 110. In an embodiment, the laser energy source 120 may direct the laser energy 125 towards the end of the sintered weld rod 130 melting the sintered weld rod 130 or wire feed while in contact with the tip (t) forming the deposited layer 150 of additive material.

[0019] The method of creating a sintered weld rod 130 as well as its composition may be found in co-pending international (PCT) patent application number PCT/US18/19077 which is incorporated by reference herein. The sintered weld rod 130 may comprise a mixture of braze alloy powder and base metal powder, the base metal powder corresponding to the composition of the tip (t) of the superalloy component. The use of the sintered weld rod 130 or wire feed, allows better process control than conventional powder feeding into a laser weld pool. Additionally, a waste of the powder which may occur during a laser additive manufacturing process is eliminated.

[0020] The system 100 may include a means for sub-cooling 140 the deposited layer 150. In the context of the disclosure, sub-cooling may be defined as a cooling temperature range resulting in a cooling/freezing effect of the deposited layer after its deposit onto the base material of the tip (t). The sub-cooling temperatures may lie in a range between -l00-300°C. In an embodiment, the sub-cooling means 140 may comprise a stream of liquid nitrogen directed towards the deposited layer 150, as shown in Fig. 1. In an alternate embodiment, the sub-cooling may be accomplished by immersing the tip (t) into dry ice. The present inventors have recognized that sub- cooling the deposited layer 150 before, during, and/or after the layer 150 is deposited absorbs the heat quickly from the molten braze suppressing the formation of deleterious compounds that may cause cracking in the deposited layer 150.

[0021] Referring to Figs. 1 and 2, a method of additively manufacturing or repairing a superalloy component 110 is also provided. Prior to laser braze repairing the tip (t) of the superalloy component 110, the tip (t) undergoes at least a double solution pre-heat treatment at progressively higher temperatures in order to raise the grain boundary melting temperature and dissolve deleterious phases in the tip (t). In an embodiment, the at least double solution pre-heat treatment eliminates approximately 99% of the eutectic gamma prime phases.

[0022] With the tip (t) being heated by a heating source 160, which as described previously, may include a heating coil surrounding the blade tip (t), for example, a first heat treatment may begin and includes heating the tip (t) to a first temperature for a specified or predetermined time period. The first temperature may be the base metal solution treatment temperature plus l0°C. For example, in an embodiment, the first temperature may be l245°C when the base metal alloy is CM 247. The first temperature should be high enough to reduce or dissolve a portion, for example around 80%, of the deleterious phases of the component material that may cause cracking during welding. The first temperature should also be low enough to allow for subsequent heat treatments at temperatures higher than the first temperature. Once the first temperature has been attained, it should be held for a first time period. In the embodiment where the first temperature is l245°C, the first time period may be up to approximately 2 hours or until most of the eutectic gamma prime phases are dissolved. Following the first heat treatment, the tip (t) is cooled down to ambient temperature. The cooling may be performed under argon gas or other cooling means known in the art.

[0023] With continued reference to the figures, upon cooling to ambient temperature, the method may further include a second heat treatment by heating the tip (t) to a second temperature for a second time period. The second temperature may be a temperature below the grain boundary melt temperature but above the first temperature. The second temperature should be high enough to further dissolve the remaining deleterious phases in the tip (t). For example, with the second heat treatment, 50% of the remaining phases may be dissolved such that 90% of the deleterious phases are dissolved after the second heat treatment. In an embodiment, the second temperature may be l0°C above the first heat treatment temperature. For example, for the base metal alloy CM 247, the second temperature may be l255°C. Once the second temperature has been attained, it should be held for a second time period. In the embodiment where the second temperature is l255°C, the second time period may be up to approximately 2 hours or until a majority of the remaining eutectic gamma prime phases are dissolved. Following the second heat treatment, the tip (t) is cooled down to ambient temperature. Again, the cooling may be performed under argon gas.

[0024] Upon cooling, in an embodiment the tip (t) of the component 110 to ambient temperature after a second heat treatment, the tip (t) may be ready for depositing additive material or laser braze repair. In an alternate embodiment, the tip may undergo a third heat treatment to further dissolve any remaining deleterious phases in the material of the tip (t). For example, with the third heat treatment another 50% or more of the remaining eutectic gamma prime phases may be dissolved. The third temperature may be at least 5°C above the last heat treatment. Once the third temperature has been attained, it should be held for a third time period. The third time period may be up to approximately 2 hours or until a majority of the remaining eutectic gamma prime phases are dissolved. Following the third heat treatment, the tip (t) is cooled down to ambient temperature. Again, the cooling may be performed under argon gas. [0025] In an embodiment, after at least double solution pre-heat treatment, the tip

(t) is sub-cooled prior to a braze repair or additive manufacture of the tip (t). The sub- cooling may be accomplished by utilizing a stream of liquid nitrogen directed towards the deposited layer (150) or in an alternate embodiment, the sub-cooling may be accomplished by immersing the tip (t) in dry ice prior to the laser braze repair. [0026] The braze repair or additive manufacture of the tip (t) may be illustrated in

Fig. 1 where a layer of braze material 130 is deposited on an end surface of the tip (t) at a temperature less than the melting temperature of the base material of the tip (t). The braze repair utilizes a laser energy source 120 to melt a braze material while in contact with the tip (t) so that when cooled the melted braze material forms the deposited layer 150. In an embodiment, a sintered weld rod 130, as described previously, may comprise the braze material. In another embodiment, a wire feed comprises the braze material. In this step, it should be appreciated that the rod 130 or wire feed may be attached to a nozzle or other tool in order to be kept in contact with the tip (t) or the wire feed may be fed through a laser source tool. [0027] In an embodiment, illustrated in Fig. 1, directly following the laser deposition of the deposited layer, the deposited layer 150 is sub-cooled. In an embodiment, the deposited layer 150 may be sub-zero cooled as the sub-cooling may be accomplished with materials having below freezing temperatures. In an embodiment, to accomplish the sub-cooling, a stream of liquid nitrogen, as illustrated, or other liquid medium capable of cooling the deposited layer to a desired temperature range is used so that any heat from the deposited molten material may be released or removed. As an example, by using liquid nitrogen, the deposited material may be cooled down to a temperature less than -50°C. In an alternate embodiment, the sub- cooling is accomplished by immersing the tip in dry ice. Dry ice may be beneficial as it does not introduce any moisture into the process. The sub-cooling of the deposited layer 150 may suppress the formation of the deleterious phases in the tip (t) that cause cracking.

[0028] In an embodiment, a successive layer or a plurality of successive layers may be deposited or built on top of the deposited layer 150 after the sub-cooling. In this way, a plurality of layers may be additively built on the tip (t) of the component 110 so that an eroded portion of the tip (t) may be rebuilt, for example.

[0029] With continued reference to the figures, the method may include preparing the tip (t) for laser processing prior to the at least double solution heat treatment. Preparing the tip for laser processing may include, e.g., removing the component (damaged or otherwise) from an industrial machine, e.g., a turbo machine engine. The preparing steps may also include removing any damaged portions from the tip. The damaged portions may be removed by grinding, milling, or other means for removing damaged portions of a superalloy component known in the art. Upon removing any undesired portions from the tip, the component may be placed or removably secured to, e.g., a laser deposition fixture (not shown) or other type of securing means in, e.g., a chamber or other defined work area, for build-up and/or repair laser process with the embodiment of the sintered weld rod.

[0030] The disclosed method of additively manufacturing or laser braze repairing a superalloy component allows tip repair of turbine blades and vanes without recrystallization since only the tip of the blade or vane is exposed to high heat with the result that the properties at the tip will be different than the properties of the remaining portions of the blade or vane. The method accomplishes this though a super solution heat treatment to only the area of build-up and not the remaining area of the component. Laser braze repair lowers the deposition temperature by utilizing a braze material instead of base metal powder. Additionally, the method utilizes sub-cooling of the deposited layer as soon as the laser brazing is finished to minimize the grain boundary segregation and minimize the size of gamma prime phases forming during cooling on the additive layer and the heat affected zone. Utilizing this method and/or system, a deposited layer on a tip of a turbine airfoil cools without cracking or with minimal cracking to the newly deposited layer.

[0031] While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.