WO2019014445A1

WO2019014445A1 - Method of repairing an article and associated article

Info

Publication number: WO2019014445A1
Application number: PCT/US2018/041822
Authority: WO
Inventors: Dheepa Nmn SRINIVASAN; Joydeep PAL
Original assignee: General Electric Company
Priority date: 2017-07-12
Filing date: 2018-07-12
Publication date: 2019-01-17

Abstract

Methods of repairing an article (100) are presented. A method includes depositing a material (135) using an additive manufacturing process on a portion (110,120) of the article (100) to form an additively manufactured section (130) in the article (100), wherein the additively manufactured section includes a directionally solidified microstructure.

Description

METHOD OF REPAIRING AN ARTICLE AND ASSOCIATED ARTICLE

BACKGROUND

[0001] Embodiments of the disclosure generally relate to a method of repairing an article using an additive manufacturing process and a repaired article including an additively manufactured section. More particularly, embodiments of the disclosure relate to a method of repairing an article and a repaired article, such that the additively manufactured section includes a directionally solidified microstructure.

[0002] Gas turbines include components, such as blades, nozzles, combustors, shrouds, and other hot gas path components that are exposed to extreme temperatures, chemical environments, and physical conditions during operation of the gas turbines. These components are generally serv iced at various points throughout their life cycle. Often, due to the operating conditions within the gas turbines, the servicing o the components may include removing and/or replacing a portion of the component.

[0003] For example, the servicing may include removing and replacing a bond coating and/or thermal barrier coating that was formed over the component during manufacturing. The servicing may also include removing and/or replacing portions of the substrate that form the component. However, the removing and replacing of portions of the substrate usually includes processing and/or post processing treatment of the serviced component, which may be costly, time consuming, and may increase down time for the gas turbine during servicing.

[0004] Additionally, when the portion of the component being removed is relatively large, replacing the removed portion may include welding a cast segment onto the component. This welding of the cast segment frequently results in distortion of the component, which is then reworked prior to being returned to service. The forming of the cast segment, processing of the serviced component, and reworking of the component may be both expensive and time consuming. Furthermore, the serviced/repaired components manufactured using conventional repair methods may have inferior performance characteristics and may further require servicing during future service cycles. While alternatively replacing the existing component with a new component may decrease service time, it also increases cost, increases component scrapping, and/or decreases component life cycle.

[0005] Accordingly, it would be desirable to have alternate methods for servicing gas turbine components. It may be further desirable to have serviced/repaired gas turbine components having the desired characteristics, e.g., enhanced life cycle.

BRIEF DESCRIPTION

[0006] In one aspect, the disclosure relates to a method of repairing an article. The method includes depositing a material using an additive manufacturing process on a portion of the article to form an additively manufactured section in the article, wherein the additively manufactured section includes a directionally solidified microstructure.

[0007] In another aspect, the disclosure relates to a method of repairing an article. The method includes removing a portion of the article to form an open section in the article. The method further includes depositing a material using an additive manufacturing process on the open section to form an additively manufactured section in the article. The depositing a material includes controlling a parameter of the additive manufacturing process to form a directionally solidified microstructure in the additively manufactured section.

[0008] In yet another aspect, the disclosure relates to a method of repairing a gas turbine nozzle. The method includes depositing a metal alloy using a direct metal laser deposition process on a portion of a trailing edge of the gas turbine nozzle to form an additively manufactured section in the gas turbine component. The additively manufactured section includes a directionally solidified microstructure.

[0009] These and other features, embodiments, and advantages of the present disclosure may be understood more readily by reference to the following detailed description.

DRAWINGS

[0010] These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein: [001 1] FIG. 1 illustrates an article for repair, in accordance with some embodiments of the disclosure;

[0012] FIG. 2 illustrates a method of repairing an article, in accordance with some embodiments of the disclosure;

[0013] FIG. 3 illustrates a method of repairing an article, in accordance with some embodiments of the disclosure;

[0014] FIG. 4 illustrates a trailing edge of a turbine nozzle, in accordance with some embodiments of the disclosure;

[0015] FIG. 5 illustrates a direct metal laser deposition (DMLD) process, in accordance with some embodiments of the disclosure;

[0016] FIG. 6 illustrates a repaired article, in accordance with some embodiments of the disclosure;

[0017] FIG. 7 illustrates a repaired article, in accordance with some embodiments of the disclosure;

[0018] FIG. 8 shows a creep curve for a cast component and a DMLD component, in accordance with some embodiments of the disclosure;

[0019] FIG. 9 shows a strain curve for a cast component and a DMLD component, in accordance with some embodiments of the disclosure; and

[0020] FIG. 10 shows optical micrographs of different sections of a turbine nozzle after the DMLD process, in accordance with some embodiments of the disclosure.

DETAILED DESCRIPTION

[0021 ] In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings. The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. As used herein, the term "or" is not meant to be exclusive and refers to at least one of the referenced components being present and includes instances in which a combination of the referenced components may be present, unless the context clearly dictates otherwise.

[0022] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value solidified by a term or terms, such as "about", and "substantially" is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Similarly, "free" may be used in combination with a term, and may include an insubstantial number, or trace amounts, while still being considered free of the solidified term. Here and throughout the specification and claims, range limitations may be combined and or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

[0023] As mentioned earlier, conventional methods for servicing/repairing turbine engine components may include welding pie-formed segments and. or replacing the entire components. These methods may be cost ineffective, increase service time, increase component scrapping, and/or decrease component life cycle. Furthermore, the serviced/repaired components manufactured using conventional repair methods may have inferior performance characteristics and may have reduced component life cycle. The methods described herein address the noted shortcomings in conventional repair methods, at least in part, through depositing a repair material using an additive manufacturing process directly on the component to be serviced. Further, by controlling the process parameters of the additive manufacturing process, a controlled microstructure is achieved in the component, which may enable increased life cycle.

[0024] In some embodiments, a method of repairing an article is presented. The method includes depositing a material using an additive manufacturing process on a portion of the article to form an additively manufactured section in the article, wherein the additively manufactured section includes a directionally solidified microstructure.

[0025] The article includes any component suitable for repair using an additive manufacturing process. In certain embodiments, the article includes a gas turbine engine component. A turbine engine refers to any engine in which the turbine is driven by the combustion products of air and fuel. In some embodiments, the turbine engine may be an aircraft engine. Alternatively, the turbine engine may be any other type of engine used in industrial applications. Non-limiting examples of such turbine engines include a land-based turbine engine employed in a power plant, a turbine engine used in a marine vessel, or a turbine engine used in an oil rig. The terms "gas turbine engine" and "turbine engine" are used herein interchangeably.

[0026] As used herein, the term "turbine engine component" refers to a wide variety of turbine engine (e.g., gas turbine engine) parts and components, which may require repair after normal engine operation. The methods described herein are particularly useful when applied to an engine component that includes one or more open sections, one or more areas of depleted thickness, and or an irregular surface formed during use of the engine component, though it will be appreciated that this is not a necessary limitation to the scope of methods. The term "open- sections" as used herein refers to one on more sections in the article that are formed in the article during use or during pre-processing of the article before the depositing step. For example, in some instances, portions of the article during use may be worn off, resulting in one or more sections in the article. In some other instances, the open sections may be formed by removing corresponding portions in the article before the depositing step. Non-limiting examples of turbine engine components that may be repaired by the methods disclosed herein include, but are not limited to, nozzles, blades, buckets, vanes, shrouds, combustors, or combinations thereof.

[0027] In certain embodiments, the gas turbine component includes a nozzle and the portion of the article includes at least a portion of a trailing edge of the nozzle. Turbine nozzles (e.g., stage 1 nozzles) may show some damage along the trailing edges after operation. These can be caused by corrosion and sometimes erosion. It may be difficult to weld a trailing edge to the damage component because of distortion during weld build up. Further, welding of components may result in compromised reliability of the nozzle due to excessive welding and resulting modification of material/component properties. Furthermore, welding of trailing edges followed by machining of the cooling holes may require additional time and may not be cost effective. Embodiments of the present disclosure may address these shortcomings at least, in part, by depositing the repair material directly on the nozzle to be repaired using a suitable additive manufacturing process. [0028] In some embodiments, the surface of, or, the entire portion of the article to be repaired may be subjected to a preparatory step, prior to the deposition step. For example, loosely adhered dirt and other debris may be mechanically removed by directing a jet of air or liquid onto the surface, by scraping or brushing, or by any other convenient technique. In some embodiments, the method further includes a preparatory step that includes applying a chemical preparation to the surface or the entire portion of the article, before the depositing step.

[0029] As mentioned earlier, the portion of the article to be repaired may include one or more open sections, one or more areas of depleted thickness, and'or an irregular surface formed during use of the article. Therefore, the method may further include performing additional preparatory steps on this portion of the article before the depositing step. These preparatory steps may include removing some of the material proximate to the portion of the article to be repaired (e.g., to form one or more open sections), smoothening the surfaces of the portion of the article to be repaired, or a combination thereof.

[0030] Referring now to FIG. 1, an article 100 suitable for repair according to the methods described herein is illustrated. In the illustrated example embodiment, the article 100 is a turbine nozzle employed in a gas turbine engine assembly. The article 100 includes a portion 110 that has an open section 101 formed therein, during use of the turbine nozzle. The portion 110 further includes an irregular surface 1 1 1 at the edges of the open section 101. In some embodiments, the method in accordance with embodiments of the disclosure may further including subjecting the article 100 to one or more preparatory steps before depositing the material using an additive manufacturing process. For example, removing at least some or all of the portion 110 prior to the depositing step. In some other embodiments, the depositing step may be performed directly on the surface of the portion 110, without any additional removal or smoothening preparator steps.

[0031] Referring now to FIG. 2, in some embodiments, a method 10 of repairing the article

100 includes removing some of the portion 110 of the article, at step 1 1, to form an open section 102 in the article 100. The open section 102 may be formed, for example, by cutting along the line 121 using any suitable cutting mechanism 150, shown in the FIG. 2. As illustrated in FIG. 2, after the removal step, the article 100 includes a portion 120 and an open section 102, formed at step 12. The method 10, further includes depositing a material 135 by an additive manufacturing process on some or all of the portion 120 of the article, at step 13. The additive manufacturing process may be performed using any suitable apparatus, e.g., a powder deposition assembly 400, described hereinafter. An additively manufactured section 130 is formed in the article after the depositing step, thereby forming a repaired article 200, at step 14.

[0032] In some other embodiments, as illustrated in FIG. 3, the method 20 of repairing the article 100 includes using the portion 1 10 as is, that is without any part removal, at step 21. The method 20 further includes depositing a material directly on a surface of the portion 110 through an additive manufacturing process, at step 22. The additive manufacturing process may be performed using any suitable apparatus, e.g., a powder deposition assembly 400, described hereinafter. In these embodiments, an additively manufactured section 130 is formed in the portion 1 10 after the depositing step, thereby forming a repaired article 200, at step 23.

[0033] The additively manufactured section 130 formed through the additive manufacturing includes any suitable desired shape and/or geometry. In some embodiments, the additively manufactured section 130 includes the shape of a trailing edge portion of a nozzle, as illustrated in FIG. 4. The trailing edge portion 130 includes a segment of an internal cavity 131 and a shaped outer surface 132. The trailing edge portion 130 may further include at least one cooling hole 133 formed therein. The cooling hole(s) may be formed in the trailing edge portion using the additive manufacturing process in some embodiments, or, alternatively, the cooling hole(s) may be formed in the trailing edge portion after the depositing using the additive manufacturing process is effected. The trailing edge portion shown in FIG. 4 may be entirely manufactured using the process steps as illustrated in FIG. 2 and the additively manufactured section 130 may have the shape and geometr of a trailing edge, in some embodiments. In some other embodiments, the trailing edge portion may be repaired using the methods illustrated in FIG. 3, wherein the additively manufactured section 130 may form a segment of the trailing edge portion.

[0034] The material deposited using the additive manufacturing process may be the same or different from the portion of the article 100 being repaired. The article 100 inc ludes any suitable material for continuous use in a turbine engine and/or within the hot gas path of the turbine engine. Suitable materials for the article 100 include, but are not limited to, a metal, a ceramic, an alloy (e.g., steel), a superailoy, or combinations thereof. In some embodiments, the turbine engine component includes an alloy, for example, a nickel-based alloy, an iron-based alloy, a cobalt-based alloy, or combinations thereof. In certain embodiments, the turbine engine component includes a superailoy, for example, a nickel-based superailoy, an iron-based superailoy, a cobalt-based superailoy, or combinations thereof.

[0035] For example, in some embodiments, the article 100 includes a cobalt-based alloy including, but not limited to, a composition, by weight, of about 29% chromium (Cr), about 10% nickel (Ni), about 7% tungsten (W), about 1% iron (Fe), about 0.7% Manganese (Mn), about 0.75% Silicon (Si), about 0.25% carbon (C), about 0.01 % boron (B), and balance cobalt (Co) (e.g., FSX414); about 20% to about 24% Cr, about 20% to about 24% Ni, about 13% to about 15% W, about 3% Fe, about 1.25% manganese (Mn), about 0.2% to about 0.5% silicon (Si), about 0.015% B, about 0.05% to about 0.15% C, about 0.02% to about 0.12% lanthanum (La), and balance Co (e.g., HAYNES^® 188); about 22.5% to about 24.25% Cr, about 9% to about 1 1% Ni, about 6.5% to about 7.5% W, about 3% to about 4% tantalum (Ta), up to about 0.3% titanium (Ti) (e.g., about 0.15% to about 0.3% Ti), up to about 0.65% C (e.g., about 0.55% to about 0.65% C), up to about 0.55% zirconium (Zr) (e.g., about 0.45% to about 0.55% Zr), and balance Co (e.g., Mar-M-509); about 20% Ni, about 20% Cr, about 7.5% Ta, about 0.1% Zr, about 0.05% C, and balance Co (e.g., Mar-M-918).

[0036] In some embodiments, the article includes a nickel -based alloy including, but not limited to, a composition, by weight, of about 9.75% Cr, about 7.5% Co, about 6.0% W, about 4.2% aluminum (Al), about 3.5% Ti, about 1.5% molybdenum (Mo), about 4.8% Ta, about 0.5% niobium (Nb), about 0.15% hafnium (Hf), about 0.05% C, about 0.004% B, and a balance of Ni (e.g., Rene N4); about 7.5% Co, about 7.0% Cr, about 6.5% Ta, about 6.2% Al, about 5.0% W, about 3.0% rhenium (Re), about 1.5% Mo, about 0.15% Hf, about 0.05% C, about 0.004% B, about 0.01% yttrium (Y), and a balance of Ni (e.g., Rene N5); between about 9%> and about 10% Co, between about 9.3% and about 9.7% W, between about 8.0% and about 8.7% Cr, between about 5.25%> and about 5.75% Al, between about 2.8% and about 3.3% Ta, between about 1.3% and about 1.7% Hf, up to about 0.9% Ti (for example, between about 0.6% and about 0.9%), up to about 0.6% Mo (for example, between about 0.4% and about 0.6%), up to about 0.2% Fe, up to about 0.12% Si, up to about 0.1% Mn, up to about 0.1% copper (Cu), up to about 0.1% C (for example, between about 0.07% and about 0.1%), up to about 0.1 % Nb, up to about 0.02% Zr (for example, between about 0.005% and about 0.02%), up to about 0.02% B (for example, between about 0.01% and about 0.02%), up to about 0.01% phosphorus (P), up to about 0.004% sulfur (S), and a balance of Ni (e.g., Rene 108); about 13.70% to about 14.30% Cr, about 9.0% to about 10.0% Co, about 4.7% to about 5.1% Ti, about 3.5% to about 4.1% W, about 2.8% to about 3.2% Al, about 2.4% to about 3.1% Ta, about 1.4% to about 1.7% Mo, 0.35% Fe, 0.3% Si, about 0.15% Nb, about 0.08% to about 0.12% C, about 0.1 % Mn, about 0.1 % Cu, about 0.04% Zr, about 0.005% to about 0.020% B, about 0.015% P, about 0.005% S, and a balance of Ni (e.g., GTD-1 11^®, available from General Electric Company): about 22.2 to about 22.8%> Cr, about 18.5 to about 19.5% Co, about 2.3% Ti, about 1.8 to about 2.2% W, about 1.2% Al, about 1.0% Ta, about 0.8% Nb, about 0.25% Si, about 0.08 to about 0.12% C, about 0.10% Mn, about 0.05% Zr, about 0.008% B, and balance Ni (e.g., GTD-222^®, available from General Electric Company); about 9.75% Cr, about 7.5% Co, about 6.0% W, about 4.2% Al, about 4.8% Ta, about 3.5% Ti, about 1.5% Mo, about 0.08% C, about 0.009% Zr, about 0.009% B, and a balance of Ni (e.g., GTD-444^®, available from General Electric Company); about 15.70% to about 16.30% Cr, about 8.00% to about 9.00% Co, about 3.20% to about 3.70% Ti, about 3.20% to about 3.70% Al, about 2.40% to about 2.80% W, about 1.50% to about 2.00% Ta, about 1.50% to about 2.00% Mo, about 0.60% to about 1.10% Nb, up to about 0.50% Fe, up to about 0.30% Si, up to about 0.20% Mn, about 0.15% to about 0.20% C, about 0.05% to about 0.15% Zr, up to about 0.015% S, about 0.005% to about 0.015% B, and a balance nickel (e.g., INCONEL* 738); about 9.3% to about 9.7% W, about 9.0% to about 9.5% Co, about 8.0% to about 8.5% Cr, about 5.4% to about 5.7% Al, up to about 0.25% Si, up to about 0.1% Mn, about 0.06% to about 0.09% C, incidental impurities, and a balance Ni (e.g., Mar- M-247).

[0037] In some embodiments, the article includes a iron-based alloy including, but not limited to, a composition, by weight, of about 50% to about 55% Ni and Co combined, about 17% to about 21% Cr, about 4.75% to about 5.50% Ni and Ta combined, about 0.08% C, about 0.35% Mn, about 0.35% Si, about 0.015% P, about 0.015% S, about 1.0% Co, about 0.35% to 0.80% Al, about 2.80% to about 3.30% Mo, about 0.65% to about 1.15% Ti, about 0.001% to about 0.006% B, about 0.15% Cu, and balance of Fe (e.g., INCONEL^® 718). Other suitable materials for the article include, but are not limited to, a CoCrMo alloy, such as, for example, 70Co-27Cr-3Mo; a ceramic matrix composite (CMC), or a combination thereof. "INCONEL" is a federally registered trademark of alloys produced by Huntington Alloys Corporation, Huntington, West Virginia. "HAYNES" is a federally registered trademark of alloys produced by Haynes International, Inc., Kokomo, Indiana.

[0038] Composition of the material 135 deposited using the additive manufacturing process is the same, substantially the same, or different from that of the article 100. For example, in some embodiments, the material 135 includes one or more of the alloys discussed above with regard to the article 100. In some embodiments, the material 135 includes tungsten carbide (WC) mixed with any one of the alloys discussed above with regard to the article 100. The addition of WC to the material 135 may strengthen the resulting article 200. In certain embodiments, the material 135 includes, by weight, of about 29% chromium (Cr), about 10% nickel (Ni), about 7% tungsten (W), about 1% iron (Fe), about 0.25% carbon (C), about 0.01 % boron (B), and balance cobalt (Co) (e.g., FSX414).

[0039] The portions 110 and 120 of the article 100 may be manufactured using any suitable technique, for example, investment casting, molding, additive manufacturing, or any suitable technique. In certain embodiments, the portions 1 10 and 120 of the article are formed by casting technique and may therefore be referred to as cast alloy sections 110 and 120, respectively.

[0040] According to the embodiments described herein, the material 135 is deposited using an additive manufacturing process. The additive manufacturing process forms net or near-net shape structures through sequentially and repeatedly depositing and joining material layers. As used herein the term "near-net shape" means that the additively manufactured section 130 is formed very close to the final shape of the section 130, not requiring significant traditional mechanical finishing techniques, such as machining or grinding following the additive manufacturing process. Suitable additive manufacturing processes include, but are not limited to, the processes known to those of ordinary skill in the art as direct metal laser melting (DMLM), direct metal laser sintering (DMLS), direct metal laser deposition (DMLD), laser engineered net shaping (LENS), selective laser sintering (SLS), selective laser melting (SLM), electron beam melting (EBM), fused deposition modeling (FDM), or combinations thereof.

[0041 ] In certain embodiments, the additive manufacturing process includes a direct metal laser deposition (DMLD) process. Referring now to FIG. 5, in some embodiments of the disclosure, the DMLD process is performed with a powder deposition assembly 400, which includes a powder delivery assembly 401 and the focused energy source 310. The powder delivery- assembly 401 includes one or more nozzles 403 and one or more material feeders 405. During the DMLD process, the one or more material feeders 405 deliver the powder material 135 and/or any other material to the one or more nozzles 403, which direct the powder material 135 towards a platform 407. The focused energy source 310 concurrently directs a focused energy beam 409 through the one or more nozzles 403, forming a gas atomized powder material 135 exiting the one or more nozzles 403. Next, the DMLD process includes directing the gas atomized powder material 135 towards the platform 407, and depositing the gas atomized powder material 135 on the platform 407.

[0042] During the directing of the powder material 135 and the focused energy beam 409, the DMLD process may include moving at least one of the nozzle 403 and the platform 407 relative to each other, the moving providing the shape and geometry of the additively manufactured section 130. To provide relative movement, the platform 407 may be fixed and the powder deposition assembly 400 may be moved, the powder deposition assembly 400 may be fixed and the platform 407 may be moved, or both the powder deposition assembly 400 and the platform 407 may be moved independently of each other. For example, in one embodiment, the platform 407 includes three or more axes of rotation for moving relative to the powder deposition assembly 400. In another embodiment, movement of the platform 407 and/or the powder deposition assembly 400 is controlled by software configured to automate the process and/or form the additively manufactured section 130 based upon a computer-aided design (CAD) model. In one embodiment, feedback sensors 142 may be employed to provide in-situ information during the additive manufacturing process, such as melt pool temperatures, layer thickness, laser power, laser track, or combinations thereof. The feedback sensors 142 may be communicatively coupled to a control system (not shown in Figures), for monitoring and controlling the additive manufacturing process by providing real-time feedback to the powder deposition assembly 400. The closed loop controls may provide increased control over microstructure and material properties of the additively manufactured section 130. In certain embodiments, the portion to be repaired is subjected to a coaxial laser that renders a net shape via a closed loop laser process, having minimal heat input and distortion. [0043] The one or more material feeders 405 and/or the one or more nozzles 403 are configured to provide any suitable composition of the atomized powder material 135. Suitable compositions include, but are not limited to, similar or substantially similar compositions between layers, differing compositions between layers, gradient compositions within the additively manufactured section 130, or a combination thereof. For example, gradient compositions within the additively manufactured section 130 may be formed by varying flow rate and/or compositions between material feeders 405, varying compositions within the material feeders 405, or a combination thereof. In one embodiment, the flow rate for the powder material 135 includes, for example, up to 5 g/min, between 0.1 and 5 g/min, between 0.5 and 4.5 g/min, or any combination, sub-combination, range, or sub-range thereof. In another embodiment, the directing of the focused energy beam 409 and the powder material 135 is shielded by a shielding gas such as argon. Suitable shielding gas flow rates, include, but are not limited to, between 1 and 15 1/min, between 2 and 10 1/min, or any combination, sub-combination, range, or sub-range thereof.

[0044] Suitable focused energy sources 310 for the DMLD process include any focused energy source 310 operating in a power range and travel speed for depositing the atomized powder material 135. Suitable focused energy sources include, but are not limited to, laser device, an electron beam device, or a combination thereof. The laser device includes any laser device operating in a power range and travel speed for melting the powder material 135, such as, but not limited to, a fiber-optic laser, a CO2 laser, or a ND-YAG laser. In one embodiment, the power range of the focused energy source 310 in the DMLD process includes, but is not limited to, between 100 and 3,000 watts, between 200 and 2,500 watts, between 300 and 2,000 watts, or any combination, sub-combination, range, or sub-range thereof. In another embodiment, the travel speed includes, but is not limited to, up to 300 mm/sec, between 1 and 300 mm/sec, between 4 and 250 mm/sec, or any combination, sub-combination, range, or sub-range thereof. For example, in a further embodiment, the focused energy source 310 operates in the power range of between 300 and 2,000 watts, at the travel speed of between 4 and 250 mm/sec. In another embodiment, a deposition rate for standard steels, titanium, and/or nickel alloys includes, for example, up to 1 kg/hour, up to 0.75 kg/hour, up to 0.5 kg/hour, between 0.1 and 0.5 kg/hour, up to 0.4 kg/hour, up to 0.3 kg/hour, or any combination, sub-combination, range, or sub-range thereof. [0045] As mentioned previously, embodiments of the present disclosure include forming an additive ly manufactured section 130 having a directionallv solidified microstnicture. In some embodiments, the depositing step using the additive manufacturing process includes selectively controlling a parameter of the additive manufacturing process to form the directionallv solidified microstructure. In some embodiments, controlling a parameter of the additive manufacturing process comprises real time monitoring and controlling of the parameter, for example, by using a closed loop control system described herein earlier. Non-limiting examples of suitable parameters are selected from the group consisting of a laser power, a powder feed rate, a scanning speed, a powder size, and combinations thereof In some embodiments, the laser power is selected in a range from about 150 W to about 2500 W, a powder feed rate is selected in a range from about 1 g/minute to about 100 g/minute, a scanning speed is selected in a range from about 200 mm/s to about 2500 mm s, and a powder size is selected in a range from about 1 micron to about 250 microns.

[0046] In the embodiments described herein, the additively manufactured section includes a directionallv solidified micro-structure in an as-deposited state, and may eliminate or require minimal post-deposition treatment to form the directionally solidified microstnicture. The term "as-deposited" as used herein refers to a stage of the additively manufactured section after the deposition step is completed and the required post-processing steps for the process have been performed. However, the as-deposited stage precludes any post-deposition steps (e.g., heat treatment etc.) that are performed to form the directionally solidified microstructure.

[0047] The term "directionally solidified microstructure" as used herein refers to a microstructure similar to a microstnicture developed in a section formed by a casting technique and subjected to a directional solidification processes/technique during the casting step itself or during post-processing. In a directionally solidified microstructure, the grains typically have a columnar orientation that are oriented in a particular direction. The directionally solidified microstructure is different therefore from an epitaxial microstructure formed using a conventional casting technique. The modified microstnicture may be single-crystal or polycrystalline. As mentioned previously, in the embodiments described herein, the additively manufactured includes a directionally solidified micro-structure in an as-deposited state, and may eliminate or require minimal post-deposition treatment to form the directionally solidified microstructure. In conventional turbine engine components that are manufactured using conventional casting techniques, the cast components may be typically subjected to multiple process steps to achieve the directionally solidified microstructure, thereby requiring additional time and cost.

[0048] In some embodiments, at least 50% of the grains in the additivelv manufactured section have a directionally solidified microstructure. hi some embodiments, at least 70% of the grains in the additively manufactured section have a directionally solidified microstructure. In some embodiments, at least 90% of the grains in the additively manufactured section have a directionally solidified microstructure. In some embodiments, at least 99% of the grains in the additively manufactured section have a directionally solidified microstructure.

[0049] The directionally solidified structure in the additively manufactured section 130 may include a plurality of columnar stuictures, in some embodiments. The plurality of columnar structures may be present as a plurality of dendrites, in some embodiments. In some embodiments, the directionally solidified microstructure includes a plurality of primary columnar structures having an average grain size in a range from about 1 micron to about 1000 microns. In some embodiments, the plurality of primary columnar structures having an average grain size in a range from, about 5 microns to about 750 microns, about 10 microns to about 500 microns, about 50 microns to about 250 microns, or any combination, sub-combination, range, or sub-range thereof. The term "primary columnar structures' as used herein refers to the columnar stnictures or dendrites formed proximate to the boundary between the additively manufactured section 130 and the section 110/120 of the article. The term average grain size as used herein refers the grain size measured in the longitudinal direction with respect to the columnar structures, that is, the primary or secondary columnar structures. An average grain size of the primary columnar structures is sometimes referred to in the art as primary dendritic arm spacing (PDAS).

[0050] In some embodiments, the directionally solidified microstructure further includes a plurality of secondary columnar structures having an average grain size in a range from about 0.5 microns to about 900 microns. In some embodiments, the plurality of secondary columnar structures having an average grain size in a range from, about 5 microns to about 750 microns, about 10 microns to about 500 microns, about 50 microns to about 250 microns, or any combination, sub-combination, range, or sub-range thereof. The term "secondary columnar structures' as used herein refers to the secondary arms of the columnar structures, dendrites typically formed from the primary columnar structures. An average grain size of the secondary columnar structures is sometimes referred to in the art as secondary dendritic arm spacing (SDAS).

[0051 ] Referring now to Figures 6 and 7, in some embodiments, an article 200 is presented.

The article 200 includes a cast alloy section 1 10/120 including a plurality of grains having an average grain size in a range from about 50 microns to about 5000 microns. The article 200 further includes an additively manufactured section 130 disposed adjacent to at least a portion of the cast alloy section 110/120. The additively manufactured section 130 includes a directionally solidified microstructure includes a plurality of primary columnar structures having an average grain size in a range from about 1 micron to about 1000 microns. In some embodiments, the plurality of primary columnar stractures having an average grain size in a range from, about 5 microns to about 750 microns, about 10 microns to about 500 microns, about 50 microns to about 250 microns, or any combination, sub-combination, range, or sub-range thereof.

[0052] In some embodiments, the directionally solidified microstructure further includes a plurality of secondary columnar stractures having an average grain size in a range from about 0.5 microns to about 900 microns. In some embodiments, the plurality of secondary columnar stractures having an average grain size in a range from, about 5 microns to about 750 microns, about 10 microns to about 500 microns, about 50 microns to about 250 microns, or any combination, sub-combination, range, or sub-range thereof.

[0053] As noted earlier, in some embodiments, the article 200 includes a gas turbine component. Non-limited examples of a suitable gas turbine component include a nozzle, a blade, a bucket, a vane, a shroud, a combustor, or combinations thereof. In certain embodiments, the article 200 is a gas turbine nozzle.

[0054] Without being bound by any theory it is believed that the directionally solidified structure in the additively manufactured section 130, may enable, at least in part, improved performance characteristics for the repaired article 200. For example, in some embodiments, a creep resistance of an article 200 after the step of depositing is greater than a creep resistance of an article 100 before the step of depositing, by a factor of at least 2. In some embodiments, a creep resistance of an article 200 after the step of depositing is greater than a creep resistance of an article 100 before the step of depositing, by a factor of at least 4, of at least 8, of at least 10, of at least 20, or any combination, sub-combination, range, or sub-range thereof. Without being bound by any theory, it is believed that the directional microstructure enables a lower modulus for the additively manufactured section, which in turn enables higher strain tolerance and therefore better creep resistance. The term "creep resistance" as used herein refers to the creep life (measured in time) at a particular creep percentage (e.g., 1% creep) for the article. The creep resistance of the articles 100, 120 as described herein may be measured at a temperature range of from about 1300 F to about 2000 F and at a pressure range from about 3 ksi to about 20 ksi, using ASTM (American Society for Testing of Materials) method E139-11.

[0055] Similarly, in some embodiments, a fatigue resistance of an article 200 after the step of depositing is greater than a fatigue resistance of an article 100 before the step of depositing by a factor of at least 1.5. In some embodiments, a fatigue resistance of an article 200 after the step of depositing is greater than a fatigue resistance of an article 100 before the step of depositing, by a factor of at least 2, of at least 5, of at least 10, of at least 20, or any combination, sub-combination, range, or sub-range thereof. The fatigue resistance of the articles 100, 120 as described herein may be measured at a temperature range of from about 70 F to about 2000 F using ASTM method E606-12. Enhanced performance characteristics such as improved creep and fatigue resistance may result in enhanced life cycle, thereby eliminating or minimizing the need to repair the component.

[0056] Further, embodiments of the present disclosure, in comparison to processes and articles not using one or more of the features described herein, may also enable decreasing scrapping of used components, increasing component life, permitting replacing larger portions of a component, decreasing or eliminating welding during the forming of the component, decreasing system down time, increasing efficiency of component formation, decreasing or eliminating formation of heat affected zones, decreasing cost of component formation, decreasing or eliminating post-formation processing of the component, permitting modification of component composition, decreasing or eliminating distortion of the component, increasing reliability of component formation, or combinations thereof.

EXAMPLES [0057] The following examples are presented to further illustrate non-limiting embodiments.

[0058] Example 1 Mechanical properties of Direct Metal Laser Deposited (DMLD)

Component versus Cast Component

[0059] A DMLD component was formed using a cobalt-based superalloy ( FSX414). The

DMLD component was subjected to solution heat treatment at 2100 F ± 25 F for about 2 hours to form Sample 1. The mechanical properties of Sample 1 were compared to that of a cast alloy component (Comparative Sample 1). The creep resistance of Sample 1 was measured at 1700F using 7 ksi stress. FIG. 8 shows the percentage creep (% creep) for Sample 1 as a function of time. Fig. 8 also shows a simulated creep curve for a cast FSX414 component (Comparative Sample 1). As shown in Fig. 8, the 1% creep life (shown in hours) of Sample 1 is about 4 times greater than that of Comparative Sample 1, thus indicating better creep resistance.

[0060] FIG. 9 shows the strain range (%) for Sample 1 as a function of cycles to initiation

(a strain curve). Fig. 9 also shows a strain curve for a cast FSX414 component (Comparative Sample 1). A shown in Fig. 9, the low cycle fatigue (LCF) of Sample 1 is greater than of Comparative Sample 1 , thus indicating better fatigue strength.

[0061] Example 2 Microstructure of a DMLD component deposited on a cast component

[0062] A turbine stage 1 nozzle that had been exposed to typical operational conditions of a gas turbine showed damage along the trailing edges. The nozzle included a cobalt-based superalloy (FSX414). The damaged part was removed and FSX414 was deposited on the remaining component using a DMLD process. A 1000W laser with a 2-mm laser bean diameter was used for the process. The powder size was in a range from about 35-95 microns and the powder feed rate was about 15 g/min. A scanning speed of about 8.33 mm/s was employed to deposit a DMLD section having a thickness of about 400 microns. X-ray microtomography was employed to detect presence of porosity and microcrack formati on in the DMLD region as well as in the DMLD-cast joint region. There were no significant voids and mic roc racks in the DMLD region as well as in the DMLD-cast joint region. [0063] Fig. 10 shows the optical micrographs of the cast alloy region, the DMLD-cast joint region, and the DMLD region. As shown in Fig. 10, the cast alloy section of the nozzle showed coarse dendritic structure with secondary dendritic arm spacing (SDAS) of around 70 microns. Further, columnar dendrites growing almost perpendicular to the boundary between the cast alloy region and the DMLD region were observed at the joint. The DMLD region showed a directionally solidified microstructure as shown in Fig. 10. The directionally solidified microstructure included columns breaking down into secondary arms after certain distance from the joint boundary. The primary dendritic arm spacing (PDAS) was around 7-9 microns.

[0064] The appended claims are intended to claim the invention as broadly as it has been conceived and the examples herein presented are illustrative of selected embodiments from a manifold of all possible embodiments. Accordingly, it is the Applicants^'' intention that the appended claims are not to be limited by the choice of examples utilized to illustrate features of the present disclosure. As used in the claims, the word "comprises" and its grammatical variants logically also subtend and include phrases of varying and differing extent such as for example, but not limited thereto, "consisting essentially of and "consisting of." Where necessary, ranges have been supplied; those ranges are inclusive of all sub-ranges there between. It is to be expected that variations in these ranges will suggest themselves to a practitioner having ordinary skill in the art and where not already dedicated to the public, those variations should where possible be construed to be covered by the appended claims. It is also anticipated that advances in science and technology will make equivalents and substitutions possible that are not now contemplated by reason of the imprecision of language and these variations should also be construed where possible to be covered by the appended claims.

Claims

1. A method of repairing an article (100), comprising: depositing a material (135) using an additive manufacturing process on a portion (1 10, 120) of the article (100) to form an additively manufactured section (130) in the article (100), wherein the additively manufactured section (130) comprises a directionally solidified microstructure.

2. The method of claim 1 , wherein the material (135) comprises a cobalt-based alloy, a nickel-based alloy, an iron-based alloy, or combinations thereof.

3. The method of claim 1 , wherein the directionally solidified microstructure comprises a plurality of primary columnar structures having an average grain size in a range from about 1 micron to about 1000 microns.

4. The method of claim 3, wherein the directionally solidified microstructure further comprises a plurality of secondary columnar stnictures having an average grain size in a range from about 0.5 microns to about 900 microns.

5. The method of claim 1, wherein the depositing a material using an additive manufacturing process comprises a direct metal laser deposition process.

6. The method of claim 1, wherein the depositing a material using an additive manufacturing process comprises controlling a parameter of the additive manufacturing process to form the directionally solidified microstructure.

7. The method of claim 6, wherein the parameter is selected from the group consisting of a laser power, a powder feed rate, a scanning speed, a powder size, and combinations thereof.

8. The method of claim 6, wherein the controlling a parameter of the additive manufacturing process comprises real-monitoring and control of the parameter of the additive manufacturing process using a closed loop control process.

9. The method of claim 1 , further comprising removing a portion of the article ( 100) to form an open section (120) in the article (100), and wherein the depositing a material (135) using an additive manufacturing process comprises depositing the material (135) on the open section (120) of the article (100).

10. The method of claim 1, wherein the depositing a material (135) using an additive manufacturing process comprises depositing the material (135) directly on a surface of the portion (110) of the article (100).

1 1. The method of claim 1, wherein the depositing a material (135) using an additive manufacturing process comprises forming the additively manufactured section ( 130) adjacent to a cast alloy section (1 10, 120).

12. The method of claim 1 , wherein a creep resistance of an article (200) after the step of depositing is greater than a creep resistance of an article (100) before the step of depositing, by a factor of at least 2.

13. The method of claim 1, wherein a fatigue resistance of an article (200) after the step of depositing is greater than a fatigue resistance of an article (100), before the step of depositing by a factor of at least 1.5.

14. The method of claim 1 , wherein the article (100) comprises a gas turbine component.

15. A method of repairing an article (100), comprising: removing a portion of the article (100) to form an open section (120) in the article (100); depositing a material (135) using an additive manufacturing process on the open section (120) to form an additively manufactured section (130) in the article (100), wherein the depositing a material (135) using an additive manufacturing process comprises controlling a parameter of the additive manufacturing process to form a directionaily solidified microstructure in the additively manufactured section (130).