Patent Application
20170232514
The invention relates to superplastic fabrication of superalloy material components for turbine engines, including steam and combustion turbine engines. More particularly, the superalloy turbine engine components are formed by sintering superalloy material powder into a preform, such as by laser sintering. The preform is inserted within a pressurized forming furnace, containing a mold with a mold cavity. A first side of the preform is in communication with the mold cavity. The preform is heated in the forming furnace, while fluid pressure is applied and increased on a second side of the preform. The preform superplastically deforms, in abutting contact with the mold cavity surface, forming the superalloy component. The superalloy component is extracted from the mold cavity and the forming furnace.
Application of nickel-, iron, or cobalt-based superalloy castings to gas turbines is largely limited to high value added components such as blades and vanes, due to fabrication challenges and cost. Extended application of such cast superalloy materials to other turbine components such as combustion baskets, associated resonators, pilot nozzles, and transition liners is limited by the inability to cast thin sheet or thin-walled component structures. Those high-strength superalloys are not easily formed into thin-walled components by traditional metal rolling, forging, or otherwise forming them into the precise shapes required for such aforementioned components.
Superplastic forming (“SPF”) by low strain rate, constant elevated temperature processing can shape fine-grained superalloys (such as IN-718 alloy) up to 250% without annealing. Fine grain structure in the range of American Society for Testing Materials (“ASTM”) grain size 10 to 13 is required for slippage of grain boundaries at low flow stress and strain deformation without fracture. Most cast or wrought materials have too large grain size to permit such processing. The fine grain structure in the ASTM grain size 10 to 13 can be achieved by precipitations in some alloys (e.g., heat treatment to precipitate delta phase needles in IN-718 alloy). Only a limited number of superalloys can benefit from precipitations to achieve fine microstructure. In addition to delta processing of alloy IN-718, it is possible to precipitate eta phase in alloy 901 and alloy A-286. However, many other superalloy material starter shapes needed for fabrication of turbine engine components must be made by powder metallurgy as the precursor to superplastic forming. Fine grain structure in the ASTM grain size 10 to 13 can be achieved by powder metallurgy processing (e.g. hot isostatic pressing or extrusion consolidation starting with powder). Conventional superalloy powder metallurgy processing is expensive, and of limited flexibility to provide useful SPF-precursor, starter shapes needed to form the relatively thin-walled, precise shapes of the aforementioned combustion baskets, associated resonators, pilot nozzles, and transition liners for turbine engines.
In exemplary embodiments described herein, superalloy material components for turbine engines, including steam and combustion turbine engines are fabricated by superplastic formation of a laser-sintered preform. Superalloy material powder is sintered into a preform, such as by an additive manufacturing process known as selective laser sintering (“SLS”), which in some embodiments exhibit a desired ASTM grain size 10 to 13. In some embodiments, the average grain size of the superalloy powder, prior to sintering, is 4 to 11 microns (μ). The preform is inserted within a pressurized forming furnace, containing a mold with a mold cavity defined by a mold cavity surface. The preform is heated in the forming furnace, and differential pressure is applied across the preform to deform it superplastically into abutting contact with the mold cavity surface, without fracturing the preform. The superalloy component is extracted from the forming furnace. In some embodiments, a first side of the preform is in communication with the mold cavity, while a second side of the preform is in communication with a pressurized fluid source. The preform is heated in the forming furnace, while fluid pressure is increased on the second side of the preform. The preform superplastically deforms, in abutting contact with the mold cavity surface, analogous to blow-molding polymer material into a bottle or other thin-walled vessel, forming the superalloy component. The superalloy component is extracted from the mold cavity and the forming furnace.
In some embodiments, the superalloy powder is a nickel-based superalloy powder (e.g., commercially available alloy powders sold under the designations Haynes 282, 263; Rene 41, 80; N4; Inconel 738, 939; CMSX 4, 6, 10; CM 247; PWA 1480, 1484) while in other embodiments, other powder material is used in the powder mixture to sinter the preform, such as iron (e.g., commercially available alloy powders sold under the designations A286; Incoloy 909, 925) or cobalt (e.g., commercially available alloy powders sold under the designations Haynes 25, 188; MarM 918) based superalloys, other element based alloys (e.g. titanium based alloys (e.g., Ti-6Al-4V, Ti-6Al-2Sn-4Zr-2Mo)), ceramics (e.g. silica, zirconia, alumina), oxide dispersion-strengthened material (e.g., commercially available ceramic powders sold under the designations MA758, 956), glasses (e.g. borosilicate, soda-lime silicate, phosphate) and polymers (e.g., silicone rubber, polyethylene terephthalate (PET), polyethylene succinate (PES), polyether ether ketone (PEEK)). In some embodiments, the selected powders used to form the preform are mixed with other structures, such as carbon fibers, or metals plus ceramics, during the sintering stage to produce composite preforms that are in turn superplastically formed into turbine engine components.
In some embodiments, powder material is preheated prior to laser sintering, in order to enhance particle sintering. In some embodiments, subsequent to laser sintering of the powder into the preform and its superplastic formation, various processes are performed, jointly or severally in any combination, on the preform. Post SPF processes include by way of example: heat treating the preform to enhance grain size and properties; diffusion bonding of a plurality of preforms, in order to fabricate composite components; hot isostatic pressing, in order to densify or modify grain microstructure within the component; machining; coating, and/or inspecting the preform.
Exemplary embodiments of the invention feature methods for forming superalloy components for turbine engines. Superalloy powder is sintered, by an additive manufacture, selective sintering process into a preform having first and second sides. The preform is inserted into a heated, pressurized forming furnace, which includes therein a mold with a mold cavity defined, by a mold cavity surface, and a chamber in communication with a pressurized fluid source, such as a pressurized inert gas source. The preform is heated in the forming furnace, and differential pressure is applied across the preform to deform it superplastically into abutting contact with the mold cavity surface, without fracturing the preform. The superalloy component is extracted from the forming furnace. In some embodiments, during the forming furnace insertion the preform's first side is in communication with the mold cavity, while the preform's second side is in communication with the chamber and pressurized fluid source. The preform is heated in the furnace. Increasing pressure is applied on the preform second side, with pressurized fluid from the pressurized fluid source. The preform is superplastically deformed in response to the increasing pressure, without fracturing the preform. Pressure is ceased on the preform second side after the preform first side is in abutting contact with the mold cavity surface, forming the superalloy component. Thereafter, the superalloy component is extracted from the forming furnace. In some embodiments, the heated preform surrounds a mold shape, and a differential pressure is applied to collapse the preform into the shape of the mold surface. Such collapsing differential pressure is generated by a vacuum generated between the mold surface and the inboard side of the preform, or an elevated pressure is applied outboard of the preform. This collapsing differential pressure approach is akin to using vacuum or external pressure to seal a storage bag tightly around an object—with the “bag” being a superalloy preform and “object” being the mold, with the process being conducted in a forming furnace.
Other exemplary embodiments of the invention feature methods for forming superalloy components for turbine engines by selective laser sintering (“SLS”) superalloy powder into a preform having first and second sides, without causing solidification cracking or reheat cracking in the preform. A heated, pressurized forming furnace is provided, which includes therein a mold with a mold cavity defined by a mold cavity surface, and a chamber in communication with a pressurized fluid source. The preform is heated in the forming furnace, and differential pressure is applied across the preform to deform it superplastically into abutting contact with the mold cavity surface, without fracturing the preform. The superalloy component is extracted from the forming furnace. In some embodiments, the preform is inserted into the forming furnace, with the preform first side in communication with the mold cavity and the preform second side in communication with the chamber and pressurized fluid source. The preform is heated in the furnace, below melting temperature of the preform material. Increasing pressure is applied on the preform second side with pressurized fluid from the pressurized fluid source, superplastically deforming the preform in response to the increasing pressure, without fracturing the preform. Pressure on the preform second side ceases after the preform first side is in abutting contact with the mold cavity surface, forming the superalloy component. The superalloy component is extracted from the forming furnace. In some embodiments the pressure differential across the preform is generated by decreasing pressure between the preform first side and the mold cavity surface, which in turn causes relative increased pressure of the pressurized fluid on the preform second side to deform the preform.
Additional exemplary embodiments feature a method for forming superalloy components for turbine engines, by selective laser sintering (“SLS”) superalloy powder into a preform having first and second sides, without causing solidification cracking or reheat cracking in the preform. A heated, pressurized forming furnace, is provided, which includes therein a mold with a mold cavity defined by a mold cavity surface, and a chamber in communication with a pressurized fluid source. The preform is inserted into the forming furnace, with the preform first side in communication with the mold cavity and the preform second side in communication with the chamber and pressurized fluid source. The preform is heated in the furnace to a temperature between approximately 900 to 1100 degrees Celsius, below melting temperature of the preform material. Increasing pressure is applied on the preform second side, with pressurized fluid from the pressurized fluid source. The pressure is increased, in order to deform the preform superplastically in response to the increasing pressure, to achieve strain rates in the range of approximately 0.02 to 1.0 per minute, without fracturing the preform. Pressure application is ceased on the preform second side, after the preform first side is in abutting contact with the mold cavity surface, which forms the superalloy component. The superalloy component is extracted from the forming furnace.
The respective features of the exemplary embodiments of the invention that are described herein may be applied jointly or severally in any combination or sub-combination.
The exemplary embodiments of the invention are further described in the following detailed description in conjunction with the accompanying drawings, in which:
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale.
In exemplary embodiments described herein, superalloy material components for combustion turbine engines, such as combustion baskets, associated resonators, pilot nozzles, main nozzles, and transition liners, are fabricated by superplastic formation of a laser-sintered preform. Such sintering of custom shape is accomplished by an additive manufacturing process, such as by selective laser sintering (“SLS”). Superalloy material powder is sintered into a preform, such as by laser sintering. The preform is inserted within a pressurized forming furnace, containing a mold with a mold cavity defined by a mold cavity surface. The preform is heated in the forming furnace, and differential pressure is applied across the preform to deform it superplastically into abutting contact with the mold cavity surface, without fracturing the preform. Thereafter, the superalloy component is extracted from the forming furnace. In some embodiments, a first side of the preform is in communication with the mold cavity, while a second side of the preform is in communication with a pressurized fluid source, such as an inert gas. The preform is heated in the forming furnace, while fluid pressure is increased on the second side of the preform. The preform superplastically deforms in response to the increasing fluid pressure, without fracturing, until it is in abutting contact with the mold cavity surface, forming the superalloy component. The preform's superplastic deformation process, within the mold cavity, is analogous to blow-molding polymer material into a bottle or other thin-walled vessel. In some embodiments, the pressure differential across the preform is generated by decreasing pressure between the preform first side and the mold cavity surface, which in turn causes relative increased pressure of the pressurized fluid on the preform second side to deform the preform. This collapsing differential pressure approach is akin to using vacuum or external pressure to seal a storage bag tightly around an object—with the “bag” being a superalloy preform and “object” being the mold, with the process being conducted in a forming furnace. After superplastic deformation, the superalloy component is extracted from the mold cavity and the forming furnace. While exemplary embodiments of the invention are used to fabricate superalloy components for combustion turbine engines, the same methods are applicable for fabrication of superalloy components for steam turbine engines.
The superalloy material powder 62 is sintered into the preform 60, such as by laser sintering. In some embodiments, selective laser sintering (“SLS”) or direct metal laser sintering (“DMLS”) is performed, to provide sufficiently fine grain size for the preform 60, so that it plastically deforms without fracturing, during subsequent shaping operations. In some embodiments, when employing superalloy powder with average pre-sintered grain size diameter of 4-11μ, the laser sintered preform 60 exhibits a desired post-sintered grain structure of ASTM grain size of 10 to 13, which facilitates slippage of grain boundaries at low flow stress and strain deformation without undesired fracture within the preform. Selective laser melting (“SLM”) can be utilized to form the preform 60 from small size powder, however, typical melt layers in SLM are about 20μ thick. The minimum approximately 20 micron thickness per-built up layer limitation has a fully melted structure, with grain solidification building epitaxially on the underlying substrate in a manner that tends to extend underlying grains in a columnar or elongated fashion. The columnar-like grains lengthen in each subsequent melt layer, which may then greatly exceed desired maximum grain size in the completed preform. As noted above, larger grain sizes increase potential risk of fracture in the preform during the superplastic forming of the component.
In some embodiments, subsequent to laser sintering of the powder into the preform 60, and prior to the superplastic formation various processes are performed, jointly or severally in any combination, on the preform, in order to prepare it for SPF into the finished engine component. For example, selective laser sintering, or other employed methods to form the preform 60 may or may not achieve sufficient material density between the powder particles. In some embodiments, intermediate hot isostatic pressing (“HIP”) operation may be used to increase the preform 60 density prior to SPF. HIP applies high pressure in all directions on the preform 60, to densify the sintered powder particles 62. Prior to the HIP process, the preform is packaged or encapsulated, so that pressure does not pass through the preform 60 without increasing particle densification. An external, HIP package can be utilized to encapsulate the preform 60. Alternatively, the preform 60 can be self-encapsulated by forming a melted skin on the preform during or subsequent to the SLS process.
In
Another exemplary embodiment of turbine component fabrication is shown in
The forming furnace 110 of
The forming furnace 110 and preform 90 are isolated from ambient air, and the furnace is selectively heated, in order to heat the preform 90. Heat, along with differential pressure applied within the chamber 118 cause superplastic deformation within the preform 90. More specifically, the preform 90 is heated in the forming furnace 110 below the preform's constituent superalloy melt temperature, while pressure is increased on the second side 96 of the preform. The preform 90 superplastically deforms, until its cylindrical first or outer surface 94 is in abutting contact with the mold cavity surface 114, forming the superalloy component 120, which is analogous to blow molding a polymer material bottle. The exemplary superalloy component 120 is a bellows component, for use within a turbine engine. After the SPF process is completed, the clamshell mold 112 segments are separated from the component 120. The component has an outer surface 122, an inner surface 124, and an internal cavity 126, which in this embodiment is open at both axial ends.
Turbine engine components fabricated in accordance with the exemplary methods of this invention are superplastically deformed without fracturing the preform during heating and application of the pressure differential. Preform fracture is avoided by balancing differential pressure increase rate, preform temperature, as well as any or all of preform constituent material composition, thickness and grain size, during the preform deformation cycle. Preform thickness is a function of the desired finished component thickness, which for turbine engine components is generally in the range of 0.5 to 12 millimeters. Preform grain size is influenced by average particle size of the alloy powder mixture used to fabricate the preform and any HIP or other grain densification processes applied to the preform. In some embodiments the preform heating temperature range is between approximately 900 to 1100 degrees Celsius and differential pressure increase is controlled to achieve strain rates in the range of 0.02 to 1.0 per minute.
After turbine engine component SPF process is completed, the component 80 or 120 is available for further fabrication processes. Exemplary post SPF processes include any one or more of heat treatment to enhance grain size and properties; diffusion bonding of a plurality of preforms, in order to fabricate composite components; hot isostatic pressing, in order to modify grain structure and increase component density; machining; coating; and/or inspection to confirm component conformity with design specifications. Exemplary heat treatments are chosen to optimize final component part properties and microstructure (e.g. grain size, carbides, gamma prime precipitation). For example, solution and double age hardening is widely applied as a final process step for optimizing material properties of nickel-based superalloys.
Finished turbine engine components, produced by the sintering and SPF process embodiments described herein, exhibit fine grain structure, and likely better fatigue strength than a comparable superalloy component that is manufactured through a selective laser melting (“SLM”) process or a general investment-casting process. As previously discussed, superalloy castings do not exhibit the small grain sizes or ability to form thin walled structures comparable to the present sintering/SPF processes. While it is possible to fabricate thin walled structures, using SLM, those components are more susceptible to solidification cracking during formation and reheat cracking during subsequent heat treatment. Both solidification and reheat cracking propensities are avoided in components produced by the sintering and SPF process embodiments described herein.
Although various embodiments that incorporate the invention have been shown and described in detail herein, others can readily devise many other varied embodiments that still incorporate the claimed invention. For example, the preform can be constructed in a flat, planar shape, a cylindrical shape, or any other three-dimensional shape that facilitates application of differential pressure on the preform, so that it is superplastically formed into contact with the forming furnace mold surface, in a fashion analogous to that of plastic blow molding bottles or other vessels.
The invention is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. In addition, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted”, “connected”, “supported”, and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical, mechanical, or electrical connections or couplings.
