JP2007031836A - Powder metal rotating components for turbine engines and process therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for producing turbine rotors and other large rotating components of power-generating gas turbine engines using powder metallurgy techniques. <P>SOLUTION: The process involves forming a powder of a gamma prime or gamma double prime precipitation-strengthened nickel-based superalloy whose particles are about 0.100 mm in diameter or smaller. The powder is placed in a can and consolidated to produce an essentially fully dense consolidation, which is then hot worked to produce a billet of a size sufficient to form a forging of at least 2300 kg. The billet is forged at a temperature and strain rate to produce a forging with a uniform fine grain of ASTM 10 or finer. Thereafter, the forging may undergo a heat treatment to achieve a desired balance of mechanical properties while retaining a uniform grain size of ASTM 10 or finer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing large forgings using metal powder as a starting material. More specifically, the present invention is directed to a method of manufacturing a turbine engine turbine rotor and other large rotating components using powder metallurgy.

  Currently, rotor components for some state-of-the-art gas turbine engines used in the power generation industry, such as the Applicant's H and FB class gas turbines, such as Alloy 718 and Alloy 706 Made of gamma double prime (γ ″) precipitation strengthened nickel-base superalloy. For example, the wheel and spacer are triple melt (vacuum induction melt (VIM) / electroslag remelt (ESR) / vacuum arc remelt (VAR)) having a diameter of about 27 to about 36 inches (about 70 to about 90 cm). This ingot is then billeted and formed by forging. Due to potential chemical or microstructural segregation and the expected hot working losses that occur from ingot to final forging, the weight of the starting ingot is about 1.5 to 3 times the weight of the final forging, and It should be about 2.5-7 times the weight of the final machined part. In addition to these large material losses, current best processing practices generally include billets (eg, ASTM 00 or greater) and final forgings (eg, ASTM 8.0 or greater) (overall Through non-uniform and relatively coarse grained microstructures within the standard scale established by the American Materials Testing Association). The billet particle size is too large to allow any proper ultrasonic inspection to identify potential life limit defects, so that ultrasonic inspection is not performed on currently used billets. Therefore, the final forging must be ultrasonically inspected for potential life-limiting defects and generally requires a minimum 0.25 inch (about 6 mm) thick sonic shape inspection jacket. The cover forms the final forged envelope.

  In contrast, aircraft gas turbine engine rotor components are often formed by powder metallurgy (PM), which provides a good balance of creep, tensile and fatigue crack growth properties. It is known to meet the performance requirements of aircraft gas turbine engines. In general, powder metal components are compacted in some form, such as extruded compacted metal powder, then isothermal or hot die forged the consolidated material to the desired contour, and finally the forged product is heat treated. Manufactured after final machining to complete the manufacturing process. Consolidation and forging process steps maintain a very fine particle size in the material, allowing high-resolution ultrasonic inspection of billets, minimizing mold load and improving final forging shape formation Designed to let you. Unlike state-of-the-art gas turbine engine turbine systems, PM rotor components in aircraft gas turbine engines typically have gamma prime (γ ') deposition that has the very high temperature and stress performance required for these components. It has been formed from a reinforced nickel-base superalloy. In order to improve fatigue crack growth resistance and mechanical properties at high temperatures, some of these alloys have been heat treated above their gamma prime solvus temperature (usually referred to as supersolvus heat treatment) to make the particles noticeable and Causes uniform coarsening. Nickel-based superalloy rotors used in large power turbines currently require neither heat-resistant gamma prime alloy nor this grain coarsening treatment to meet their mission and component mechanical property requirements. It can be expected in the near future that it will be necessary to increase turbine efficiency or extend component life.

Although powder metal nickel-base superalloys have been processed for use in aircraft engine turbine rotor forgings, which are typically lighter than 2000 pounds, the powder metal process can weigh over 5000 pounds (about 2300 kg). It has not been used to produce the very large forgings necessary for gas turbines used in the power generation industry. However, the ability to use powder metallurgy to produce large nickel-based superalloy forgings suitable for power gas turbine engine rotor components produces more near net shape forgings, thereby reducing material loss. Will bring the possibility to reduce. Until recently, these power turbine alloys have low alloy content, ie iron with three or four main elements that can be dissolved and processed relatively easily and with minimal chemical or microstructural segregation. Or it was nickel group. The powder metal versions of these alloys offer significant advantages to compensate for the higher base cost of PM in either ease of processing or characteristic gain compared to cast ingots that can be easily converted to rotor forgings. Will not bring. However, as more complex alloys such as alloy 718 and higher are preferred and the size of the forging continues to increase, convert chemical and microstructure segregation, coarse grain ingots to the final forging. Due to the high material loss associated with and the limitations of production capacity to process large and high strength forgings, higher reference cost PM alloys are becoming potentially more cost effective. Reduced processing losses, increased production capacity, improved inspection of fine particulate billets and parts, and the ability to produce more near net shape forgings are all from PM than with current casting plus forging practices It is a driving factor for achieving lower cost large rotor forgings.
US Pat. No. 6,315,846 US Pat. No. 6,531,002 US Pat. No. 5,413,752 US Pat. No. 5,529,643 US Pat. No. 5,571,345 US Pat. No. 5,584,947 US Pat. No. 5,584,948

  The present invention provides a method for manufacturing turbine rotors and other large rotating components of power generation gas turbine engines using powder metallurgy. The method significantly reduces the ratio of input weight to final forging weight by eliminating yield loss during the conversion from coarse particle ingots to fine particle forgings. The method also substantially eliminates chemical and microstructural segregation and results in a fine and uniform particle size (ASTM 10 or finer), which is the required acoustic wave size. There is the advantage of reducing the shape envelope and thus further reducing the final forged weight. In addition, the use of particulate PM billets has the potential to reduce the indentation force required to produce the final forging, thereby reducing capital equipment costs and expanding the potential supply base.

  The method of the present invention includes forming a precipitation strengthened (gamma prime or gamma double prime) nickel-base superalloy powder having a particle diameter of about 0.004 inches (about 0.100 mm) or less. The powder is placed in a can and the can is evacuated and sealed in a controlled environment, and then compacted at a temperature, time and pressure that produces an essentially full density compact. The compact is then hot worked at a temperature that produces a uniform particle size of ASTM 10 or finer and a sufficient size to form a billet that is at least 5000 pounds (about 2300 kg) in size. Is done. The billet is then forged at a temperature and strain rate selected to produce a forging having uniform fine particles of ASTM 10 or finer throughout. The forged product is then preferably subjected to a heat treatment designed to achieve a desired balance of mechanical properties while maintaining a particle size of ASTM 10 or finer.

  As a result of the above method, very large rotor components, previously limited to conventional casting and forging processes, now reduce material loss and achieve with this powder metallurgy process by powder metallurgy. It can be formed with the advantages of microstructural, compositional and mechanical properties.

  Other objects and advantages of this invention will be better appreciated from the following detailed description.

  The present invention provides a method for producing very large nickel-base alloy rotor forgings, typically over 5000 pounds, using powder metallurgy. A powder-based alloy is used to produce a nickel-based compact, which is then hot-worked into billets and then large turbine wheels, spacers or other dimensions that are suitable for large gas turbine engines used in the power generation industry Forged into rotating components.

  A particularly suitable alloy to demonstrate the advantages of the present invention is a gamma prime precipitation strengthened nickel base superalloy based on commercially available alloy 725. The superalloy identified herein as ARA725 is about 19 to about 23% by weight chromium, about 7 to about 8% molybdenum, about 3 to about 4% niobium, about 4 to about 6% iron, About 0.3 to about 0.6% aluminum, about 1 to about 1.8% titanium, about 0.002 to about 0.004% boron, up to about 0.35% manganese, up to about 0.00. It has a composition of 2% silicon, up to about 0.03% carbon, the balance nickel and associated impurities. US Pat. No. 6,315,846 to Hibner et al. And US Pat. No. 6,531,002 to Henry et al. Are particularly well suited for making very large forgings with powder metal. The properties of the conventional cast plus forged ARA 725 considered to be included include room temperature and high temperature tensile strength and ductility similar to alloy 718, with significantly improved resistance to time-dependent crack growth compared to alloy 718. No mechanical property data is available yet for the powder metallurgy version of ARA725, but properly processed powder metal forgings will have similar or in some cases better properties than casting plus forgings. is expected. Although the present invention will be described with reference to an ARA725 alloy, the teachings of the present invention include alloys 625, other gamma prime and gamma double prime precipitation strengthened nickel-base superalloys such as LC Astroloy (U700), Udimet 720, ARA054, ARA017, and alloys It can be applied to any other nickel-base superalloy that has excellent time-dependent crack growth resistance compared to alloy 718 with tensile properties equivalent to or better than 718.

  In interesting applications of the present invention, optimum processability and mechanical properties are achieved with a uniform particle size not larger than ASTM 10. Larger particle sizes than ASTM 10 can cause the presence of such particles to significantly reduce the low cycle fatigue resistance of the component, and other mechanical components such as tensile and high cycle fatigue (HCF) strength. Properties can be adversely affected, increasing hot working load requirements and undesirable in that they prevent thorough ultrasonic inspection of billets and thick forgings. Accordingly, a preferred embodiment of the present invention is to achieve a uniform particle size within the nickel-base superalloy, which prevents irregular grain growth within the nickel-base superalloy and is finer than that of ASTM 10 or finer. Try to produce maximum particle size.

  The method of the present invention includes the step of forming a melt whose chemical properties are those of the desired alloy (eg, ARA725). This is generally achieved by the VIM treatment method, but can also be done by adaptation of the ESR or VAR treatment method to form a lysate for subsequent atomization or other powder manufacturing methods. . Considering the reactivity of the elements contained in the preferred gamma prime and gamma double prime precipitation strengthened alloys (eg, aluminum and titanium), the melt is formed under vacuum or in an inert environment (hereinafter controlled environment). The While within the melting conditions and within the chemical specification range, the alloy is converted to a powder by atomization or another processing method suitable to produce approximately spherical powder particles. According to a preferred embodiment of the present invention, the particles are produced by the atomization process so that most of them have a diameter of 0.004 inches (about 0.100 mm) or smaller. The powder is then screened in a controlled environment to remove substantially all particles larger than 0.004 inches (about 0.100 mm) in order to reduce the likelihood of subsequent billet / forging defects. The Larger powder sizes may be acceptable if defective particles larger than 0.004 inches (eg, ceramics) can be removed by methods other than screening methods. it can. Because of the large amount of powder required to produce billets of the dimensions required by the present invention, for example, 5000-20000 pounds (about 2300-10,000 kg), it will accumulate enough powder to be used in the method of the present invention. It may be necessary to mix powders produced by multiple atomization steps. Any necessary storage of such powder is preferably in a controlled environment container.

  Once a sufficient amount of powder has been produced, the powder is placed in a suitable can, preferably a mild steel can, whose dimensions will meet billet size requirements after consolidation. The can is loaded in a controlled environment (inert gas or vacuum), after which the can is subjected to medium temperature heating (eg, about 200 ° F. (about 93 ° C. or higher)) to release moisture and any volatiles. While being evacuated, it is then sealed. The can and its contents are then consolidated at a temperature, time and pressure sufficient to produce a consolidated body having a theoretical density of at least about 99.9%. Consolidation can be achieved by hot isostatic pressing (HIP), extrusion, or other suitable consolidation methods.

  The powder compact is then hot worked by any of several methods, such as extrusion, upsetting and drawing, to produce the appropriate billet dimensions for forging. The conditions used to generate the input billet should produce a uniform ASTM 10 or finer particle size throughout to allow its ultrasonic inspection before forging into the final part shape. It is.

  Billets are then currently used to produce large industrial turbine alloy 706 and alloy 718 rotor forgings, but using known methods such as those modified to have the advantages of the fine particle billet method. And forged. Forging is performed at temperature and load conditions that allow complete filling of the final forged die cavity, prevent breakage, and generate or retain a uniform fine particle size that is not larger than ASTM 10 in the material. In particular, the ratio of the billet weight to the final forging weight, since chemical and microstructural segregation is virtually eliminated and very fine particle sizes can be achieved through the use of powder metal starting materials. Can be significantly reduced. For example, the weight of the starting billet can be as low as about 1.2 to about 1.5 times the weight of the final forging and about 1.8 to about 4 times the weight of the final machined rotor component. . This weight reduction is made possible by improving the processability of the fine particle billet and increasing its sound testability.

  The resulting rotor forging is preferably subjected to ultrasonic inspection for potential life-limiting defects. However, by enhancing the ultrasonic inspection of the billet, this step of component processing can be eliminated in some cases, which makes it possible to produce more near net shape forgings. In addition, the input weight can be further reduced.

  After inspection (if performed), final machining is performed by any suitable known method to produce the final machined rotor component. To achieve the required mechanical properties of the rotor components, prior to machining, the forgings are solution heat treated at temperatures and times that achieve a favorable balance of properties for long-term industrial gas turbine operation. And aging processing. An illustrative example of a suitable heat treatment method for the ARA725 alloy is a solution heat treatment at a temperature of about 1650 ° F. (about 900 ° C.) for approximately 4 hours, followed by two steps: about 1400 ° F. (about Aging at a temperature of about 760 ° C for about 8 hours, and then cooling to about 1150 ° F (about 620 ° C) at a rate of 100 ° F per minute (about 56 ° C) for about 8 hours. Followed by a step of air cooling.

  In addition to the preferred ARA725 alloy, the above method can be applied to a wide range of metal alloys whose composition and temperature performance meet various specific product requirements. For example, conventional reinforcements such as passive oxides, nitrides and / or carbides and / or alloys containing intergranular fixed or nanodispersoids may be desirable to provide long-term stability. Alloys containing higher levels of high temperature strengthening elements such as cobalt, tungsten, molybdenum, tantalum, niobium, etc., for applications that require operation at temperatures up to 1800 ° F. (about 1000 ° C.) or higher. This is desirable. In addition to direct melting and atomization of a specific alloy composition, mechanical alloying of two or more separately processed powders can also be used to obtain the desired properties of the rotor component. Can do.

  While the invention has been described in terms of a preferred embodiment, it is apparent that other forms can be adopted by one skilled in the art. Accordingly, the technical scope of the present invention is limited only by the claims.

Claims (10)

A method of manufacturing a component with gamma prime or gamma double prime precipitation strengthened nickel-base superalloy,
Forming the superalloy powder;
Filling the can with the powder and evacuating and sealing the can in a controlled environment;
Consolidating the can and the powder therein at a temperature, time and pressure to produce a compact;
Hot-working the compacted body to produce billets of sufficient dimensions to form at least a 2300 kg forging;
Forging the billet at a temperature and strain rate to produce a forging having uniform fine particles of ASTM 10 or finer throughout;
Including methods.   The nickel-base superalloy is 19-23% chromium by weight, 7-8% molybdenum, 3-4% niobium, 4-6% iron, 0.3-0.6% aluminum, Consists of 1.8% titanium, 0.002-0.004% boron, up to 0.35% manganese, up to 0.2% silicon, up to 0.03% carbon, the balance nickel and associated impurities The method of claim 1 having a composition.   The said forming step includes the steps of generating a melt of the nickel-base superalloy in a controlled environment and then rapidly cooling the melt to form the powder. Item 3. The method according to any one of Items 2.   The method of claim 3, wherein the forming step further comprises sieving the powder in a controlled environment to remove all particles having a diameter greater than 0.100 mm.   5. A method according to any one of claims 3 or 4, wherein the forming step further comprises mixing the powder with a second powder of the nickel-base superalloy.   6. A method according to any one of claims 1 to 5, wherein the compact formed by the consolidation step has a theoretical density of at least 99.9%.   The method according to claim 1, wherein the forging produced by the forging step has a weight of at least 2300 kg.   The method according to any one of claims 1 to 7, wherein the billet formed by the hot working step has a weight of 1.2 to 1.5 times the weight of the forged product.   The method according to any one of claims 1 to 8, wherein the billet formed by the hot working step has a weight of 1.8 to 4 times the weight of the rotor component.   The method of any one of claims 1 to 9, wherein the component is a gas turbine engine rotor component selected from the group consisting of a turbine wheel and a spacer.