KR100646718B1 - Die cast nickel base superalloy articles - Google Patents

Abstract

A die cast article composed of nickel base superalloy IN 718 is disclosed. The microstructure is characterized by an absence of flowlines and includes a fine average grain size, e.g., ASTM 3 or smaller. A method of heat treating the articles is also disclosed. Exemplary articles include gas turbine engine components, such as blades, vanes, cases and seals. <IMAGE>

Description

Die Casting Nickel-Based Superalloy Products {DIE CAST NICKEL BASE SUPERALLOY ARTICLES}             

1 illustrates a die cast product composed of IN 718 according to the present invention.

2 is an optical micrograph illustrating the microstructure of a test bar comprised of die casting IN 718 according to the present invention.

3 is an optical micrograph illustrating the microstructure of an airfoil composed of die casting IN 718 according to the present invention.

FIG. 4 is an optical micrograph of the wing of FIG. 3 after hot isostatic compression molding (HIP). FIG.

FIG. 5 is an optical micrograph illustrating the microstructure of a wing composed of forged IN 718. FIG.

6 and 7 illustrate the properties of die casting IN 718 products and corresponding forged products according to the invention.

8 and 9 are schematic diagrams of a die casting machine used in the manufacture of a product composed of IN 718.

10 is a process flow diagram illustrating a die casting process of IN 718 according to the present invention.

FIG. 11 is a graph illustrating average particle size and percent segregation versus heat treatment temperature of a die cast IN 718 product according to the present invention. FIG.

12 is an optical micrograph illustrating the microstructure including elemental segregation of a die cast IN 718 product.

13 is an optical micrograph illustrating that segregation is reduced after HIP and heat treatment in accordance with the present invention.

The present invention relates generally to articles made from superalloy materials, more particularly articles made from nickel-based superalloys and to methods of heat treatment of said alloys. Such alloys typically have high melting points in excess of 1260 to 1371 ° C (2300 to 2500 ° F). Nickel-based superalloys are used in applications that require high strength-to-weight ratios, corrosion resistance, and use at relatively high temperatures, such as at or above about 1093 ° C. (2000 ° F.).

In gas turbine engines, for example, these superalloys are typically used in turbine parts, and sometimes non-limiting examples include blades and vanes, as well as stationary structures such as intermediate and compressor cases, compressor disks, turbine cases, turbine cases and turbine disks. Used at the end of the compressor portion of the engine, including elements. Typical nickel-based superalloys used in gas turbine engines are Inconel 718 (IN 718), about 0.01 to 0.05 weight percent carbon (C), 13 to 25 weight percent chromium (Cr), 2.5 to 3.5 weight % Molybdenum (Mo), 5.0-5.75 weight percent Cb (Cb) (also called niobium (Nb)) + tantalum (Ta), 0.7-1.2 weight percent titanium (Ti), 0.3-0.9 weight percent It has a composition consisting of aluminum (Al), up to about 21% by weight of iron (Fe), and nickel, the majority of the balance.

In the gas turbine engine industry, forging is used to fabricate parts with complex three-dimensional shapes such as blades and vanes. Nickel-based superalloys have traditionally been forged precisely to produce parts that have a fine average particle size and are balanced with high strength, low weight, and good high cycle fatigue resistance. These parts exhibit a balance of high strength, low weight and durability when properly produced.

Briefly, in order to forge parts, such as blades of vanes, first an ingot of material having a composition corresponding to the desired composition of the finished element is obtained. The ingot is converted into a billet form, typically cylindrical for blades and vanes, and then thermomechanically processed, for example by heating and stamping several times between dies and / or hammers that can be heated, and the material In order to plastically deform and flow in the form of the desired element, it is gradually formed similarly to the desired form. Each element is typically heat treated to achieve the desired properties such as hardening / reinforcement, stress relief, resistance to crack nucleation, and to a certain level of HCF resistance, and also to ensure that the element has the correct shape, dimension or shape. Finishing, such as machining, chemical grinding and / or intermediate finishing, is required as provided.

The production of elements by forging is an expensive and time consuming process and therefore typically only tolerated for elements requiring a special balance of properties such as high strength, low weight and durability at both room temperature and elevated temperature. With regard to obtaining forging materials, some materials require long pretreatment times, sometimes months. Forging typically involves a series of processes, each requiring a separate die and associated equipment. Post-forging finishing processes, such as machining the base portion of the blade and providing a suitable surface finish, constitute a significant part of the overall production cost of the forged part, and also a large part of the parts to be discarded.

During forging of the element, much of the original material is removed (up to about 85%) and does not form part of the finished element (eg discarded). The complex shape of the element to be manufactured adds to the effort and expense required to manufacture the element, which is even more consideration for gas turbine engine elements having a particularly complex shape. Nickel-based superalloys such as IN 718 also exhibit significant springback (eg, the material is elastic), which should be taken into account during forging, ie the parts should typically be “over-forged”. As mentioned above, the finished elements may still require extensive post-forging processes. Moreover, because of the use of computer software to apply numerical fluid dynamics in order to analyze and be more aerodynamically efficient wing shapes, such wings and elements have even more complex three-dimensional shapes. Correspondingly, it is more difficult or impossible to precisely forge superalloys into these advanced and more complex forms. For example, due to its slightly elastic properties, many materials appear during forging, which adds to the cost of the element further, or makes the element too expensive to pioneer certain advances in engine technology or to some components. The use of certain alloys makes it economically infeasible.

Forged elements also often exhibit significant levels of defects, such as defects including inclusions and carbides, which vary considerably from element to element. Elements with higher CB content, such as IN 718, also tend to element segregation, as well as to form phases such as Rave and other morphologically close packed phases. The presence and extent of these defects adversely affect the mechanical properties, especially at elevated temperatures. The extent of these defects typically depends on the material composition and the length of time the elements are exposed to elevated temperatures, for example during the forging process. Thus, the product is heat treated, such as a homogeneous heat treatment, to reduce or eliminate the defect, which heat treatment is performed as a separate step in addition to any other processing steps performed on the product. Heat treatment typically involves exposing the product to relatively high temperatures, such as 1093 ° C. (2000 ° F.) for several hours. The temperature is high enough to reduce segregation, but may be too high or too long to cause significant particle growth.

Casting has been used extensively to make relatively nearly finished molded articles.

Investment casting can be used to make such a product, in which the molten metal is poured into a ceramic shell having a cavity in the form of the product to be cast. However, investment casting produces products with very large particles (relative to the small average particle size that can be achieved by forging) and in some cases the entire part consists of one particle. In addition, the rate of solidification may result in unacceptably large amounts of elemental segregation (variable from part to part) as a result of the test, or the presence of a brittle phase, which may reduce properties. Furthermore, the process is expensive since individual molds are made for each part. Reproducing very precise dimensions from part to part is difficult to perform. In addition, the molten material is melted, injected and / or solidified in air or other gases to produce parts with undesirable properties such as inclusions and porosity, especially for materials containing reactive elements. The pores must be removed, for example, by heating the product and applying pressure to the product. For IN 718, the product is typically HIP for several hours at a temperature of 982 to 1024 ° C. (1800 to 1875 ° F.), and a pressure of 105 to 154 MPa (15 to 22 ksi). Fracture of the ceramic shell also contributes to the generation of inclusions and impurities in the mold article.

Permanent mold casting has also been used to cast parts in general, in which the molten material is poured into a multi-part reusable mold and only flows into the mold under gravity (e.g. to Colvin). US Patent No. 5,505,246). However, permanent mold casting has a number of disadvantages. For thin castings, such as wings, the gravity may be insufficient to compress the material into thinner parts, especially when high melting point materials and low overheating are used, so that the mold cannot be consistently filled and It must be scraped off. Dimensional tolerances must be relatively large, correspondingly more post-casting work is required, and repeatability is difficult to achieve. Permanent mold casting also produces a relatively poor surface finish, which also requires more post-casting operations.

In the past, die casting that injects molten metal under pressure into a reusable die has been successfully used to mold such products from materials having a relatively low melting point, such as a Tm of less than about 1093 ° C. (2000 ° F.).

One type of die casting machine is disclosed in US Pat. No. 3,791,440. In this patent, the machine comprises a fixed die element 11 and a movable die element 12. Briefly, molten metal is poured through spout 22 and sprue 21 and flows into injection cylinder 30 in communication with die cavity 15. Sufficient molten material is poured to fill a portion of the injection cylinder 30 and the spout 21, thus exhausting air from the injection cylinder (see for example column 6, lines 7 to 17). The injection plunger 38 pushes the material from the injection cylinder 30 into the die cavity 15. The ball lock cylinder and the connecting plunger 35 may seal the ball 21 during injection, for example. The injection cylinder 30 is embedded in one of the die plates to prevent the cylinder from twisting when high melting point molten material is injected into the injection cylinder. The crossover machine does not use a vacuum environment, but rather completely fills the cylinder to prevent air from being injected into the die.

Such a machine is expensive. Moreover, this type of machine is not readily available and correspondingly expensive to refurbish and repair as needed. For example, attaching a vacuum system to the machine is difficult and expensive at best because the sleeve tube is buried in the plate and not easily accessible. Moreover, it will be difficult to move the molten material from the melting unit to the spout 22 in a vacuum environment. Controlling the temperature of the die can also be difficult due to the physical size of the plate / buried die combination as well as the thermal size of such a combination. The shape of the machine can also make it difficult to release the part in a vacuum environment.

Another type of die casting machine is a "cooling chamber" type. As disclosed, for example, in US Pat. Nos. 2,932,865, 3,106,002, 3,532,561, and 3,646,990, conventional cooling chamber die casting machines have multiple part dies, such as fixed and moving plates that cooperate with one another to define a die cavity. And a slotted sleeve tube mounted on a plate of one (typically fixed) of a two-part die comprising a. The launch sleeve tube can be oriented horizontally, vertically or inclined between horizontal and vertical. The sleeve tube communicates with a runner of the die and includes an opening through which molten metal is injected on top of the sleeve tube. The plunger is positioned as the sleeve tube moves and pushes the molten metal present in the sleeve tube into the die. In a "cooling type" machine, the firing sleeve tube is oriented horizontally and not heated. Casting is typically carried out under atmospheric conditions. That is, the device is not placed in a non-reactive environment such as a vacuum chamber.

Disadvantages of such machines are, in particular, inability to use such machines for casting higher melting materials (Tm above about 1093 ° C. (2000 ° F.), such as nickel-based, cobalt-based and iron-based superalloys. In this regard, it is disclosed in US Pat. No. 3,646,990. In a typical cooling chamber machine, the firing sleeve tube is not vented and the plunger also pushes air into the die, creating undesirable and unacceptable pores in the die cast product. Thus, to avoid introducing bubbles into the molten material, the firing sleeve tube is filled as completely as possible or tilted to prevent any air in the molten material from escaping from the die prior to injection.

Moreover, since the firing sleeve tube is not heated, the skin or “can” of molten metal solidifies on the inside of the firing sleeve tube and moves the plunger through the sleeve tube to inject molten metal into the die. In order to do so, the plunger must scrape the epidermis from the sleeve tube and crush the can. However, if the can forms a structurally strong member, such as a cylindrical member supported by a sleeve tube, the plunger and / or the associated structure for moving the plunger may be damaged or destroyed. If the sleeve tube is thermally distorted to match the plunger shape, or if the plunger is distorted to match the sleeve tube shape, the plunger can passes a metal ("blowback") between the plunger and the sleeve tube. Any trapped gas is passed between the plunger and the sleeve tube, all of which have a detrimental effect on the quality of the resulting product (see also US Pat. No. 3,533,464 to Parlanti et al.).

Despite extensive efforts, conventional "cooling chamber" die casting apparatus has not been used successfully in the manufacture of products consisting of high melting point materials, such as nickel-based superalloy alloys. Partial attempts at die casting of high melting point materials such as superalloys resulted in failures of die casting machines, as well as products characterized by inferior qualities such as impurities, excessive porosity and segregation, and relatively poor strength and high and low cycle fatigue. It became.

It is a general object of the present invention to provide a die cast product composed of a high melting point material such as a nickel-based superalloy.

It is a further object of the present invention to provide a die cast superalloy product having properties comparable to the corresponding forged product.

A more particular object of the present invention is to provide a superalloy product having strength, durability and fatigue resistance comparable to the corresponding forged superalloy product.

Still another object of the present invention is to provide such a product having a complex three-dimensional shape that is difficult (if not impossible) to forge.                         

Another general object of the present invention is to reduce or eliminate any element segregation in die cast superalloy articles.

A more particular object of the present invention is to provide a heat treatment for reducing or eliminating elemental segregation and TCP phase in die casting IN 718 products.

It is another object of the present invention to provide a heat treatment that can also include suitable HIP parameters to reduce or remove any residual pores.

Further objects will be apparent to those skilled in the art based on the following description and drawings.

In accordance with one aspect of the present invention, a die cast article consisting of a nickel-based superalloy such as IN 718 is disclosed. The article preferably satisfies at least the strength, low crack growth rate and stress fracture resistance requirements of the corresponding forged article according to eg AMS 5663 or AMS 5383. Examples of such products are blades or vanes for gas turbine engines. Each article has a microstructure similar to that of a forged material, and is characterized by more uniform particles, and a fine average particle size, such as about ASTM 3 or less, more preferably ASTM 5 or less, for cast articles. The microstructure is further characterized as preferably free of flow lines. In the case of rotating elements, such as gas turbine engine blades, the preferred average particle size is smaller, such as preferably less than or equal to ASTM 5, more preferably less than or equal to ASTM 6.

In accordance with another aspect of the present invention, a method of heat treating a die cast superalloy product having pores and elemental segregation as a mold is disclosed. The method includes heating the product at a temperature of about 982 to 1121 ° C. (1800 to 2050 ° F.), preferably at about 982 to 1023 ° C. (1800 to 1875 ° F.) for about 1 to 24 hours to reduce the segregation. do. More preferably, the pores are substantially removed simultaneously with the above by applying a pressure of about 105 to 154 MPa (15 to 25 ksi) to the product during the heating step.

The product has yield strength and ultimate tensile strength comparable to forged parts composed of the same material at both room temperature and elevated temperature, and also has similar high and low cycle fatigue.

An advantage of the present invention is that die casting is ingot from the ingot, since it is not necessary to produce specially tailored steel strips of material or ceramic clad shells and the casting can be carried out extensively in a single step as opposed to many forging processes or shell manufacturing. This significantly reduces the time required to manufacture the part, up to the finished part. Die casting can also produce multiple parts in a single casting. Die casting also makes it possible to manufacture parts with more complex three-dimensional shapes, thereby making wings and other elements more aerodynamically efficient than forging. The present invention will enable the manufacture of articles using materials having forms that are difficult or impossible to forge. Moreover, die cast parts have greater production reproducibility compared to forged or investment molded products, and can be manufactured in a form closer to their finished form with an excellent surface finish that minimizes post forming finishing processes. All of these also reduce the manufacturing cost of such components. Further advantages will be apparent from the following figures and detailed description.

1, a die cast nickel-based superalloy product according to the present invention is generally represented by reference numeral 10. FIG. In the illustrated embodiment, the article comprises a blade 10 consisting of IN 718, which is used in a gas turbine engine. The product includes wings 12, stages 14, and base 16. The invention can be applied to a wide variety of applications and is not intended to be limited to any particular product or use in gas turbine engines. Preferably, die casting elements for use in a gas turbine engine are issued by SAE International (SAE Int'l, Warrendale, PA) and are referred to herein by reference to die casting elements for other applications. Cited Aerospace Material Specification AMS 5663 (Rev. J, publ. September 1997) (for corresponding forged elements) or AMS 5383 (Rev. D, publ. April 1993) The strength, low crack growth rate and high stress fracture resistance disclosed in (for use of lower strength compared to AMS 5663 for corresponding investment casting elements).

As disclosed above, a typical nickel-based superalloy used in gas turbine engines is Inconel 718 (IN 718), which is nominally about 19 weight percent Cr, 3.1 weight percent Mo, about 5.3 weight percent (Cb + Ta) , 0.9 wt% Ti, 0.6 wt% Al, 19 wt% Fe and the balance. More broadly, IN 718 comprises about 0.01 to 0.05 weight percent carbon (C), about 0.4 weight percent manganese (Mn), about 0.2 weight percent silicon (Si), 13 to 25 weight percent chromium (Cr ), About 1.5% by weight or less of cobalt (Co), 2.5 to 3.5% by weight of molybdenum (Mo), 5.0 to 5.75% by weight of cadmium (Cb) + tantalum (Ta), 0.7 to 1.2% by weight of titanium (Ti) ), 0.3 to 0.9% by weight of aluminum (Al), up to about 21% by weight of iron (Fe), and the balance essentially includes nickel. Even more preferably, IN 718 is about 0.02 to 0.04 weight percent carbon, about 0.35 weight percent manganese, about 0.15 weight percent silicon, 17-21 weight percent chromium, about 1 weight percent cobalt, 2.8 to 3.3 wt% molybdenum + tungsten + rhenium, 5.15 to 5.5 wt% cadmium + tantalum, 0.75 to 1.15 wt% titanium + vanadium + hafnium, 0.4 to 0.7 wt% aluminum, up to about 19 wt% iron And the balance essentially contains nickel and trace amounts of other elements.

The composition change for IN 718, for example, can increase the Nb content of the material to be cast, as well as increase the content of other reinforcing elements to increase strength and capacity.

Applicants have produced die cast products consisting of nickel-based superalloys using die casting machines of the type shown and disclosed, for example, in US Pat. Nos. 3,791,440 and 3,810,505 to Cross. Applicants also die cast such products as disclosed in U.S. Patent No. 3,791,440 above, typically in a "cooling chamber type" die casting machine having an unheated firing sleeve tube. Applicants then used the "cooling chamber" machine in connection with the present invention and preferred the use of the machine, because at least the machine was less expensive, more readily available, and had a higher melting point. The machine may be reworked as needed for use in die casting of materials and is generally less expensive to perform the necessary repairs.

Briefly, according to the present invention, at least a single charge of a material is melted in such a way as to minimize contamination resulting from the reaction of one or more elements of the material or in connection with the melting apparatus. Thus, the alloy is heated and melted under an inert or preferably vacuum environment maintained at a non-reactive, such as preferably at a pressure below 100 μm, more preferably below 50 μm. The alloy is also preferably used using a non-pollution melting apparatus, for example, typically within 38-93 ° C. (100-200 ° F.) above the melting point of the alloy, more preferably 10-38 ° C. (50-100 ° F.). Heating to limited overheating. Applicants prefer ceramic-free melting systems, such as inducto-skull melting units. The material is overheated sufficiently to remain molten until injected into the die, but not to hinder the high speed solidification of the molten material after injection. The molten alloy is then transferred to a horizontal launch sleeve tube (preferably placed under a vacuum environment) of the machine and the molten material is injected into a reusable mold under pressure. The process involving the injection and injection of the molten material should not exceed several seconds in a die casting machine with an unheated firing sleeve tube, wherein the injection should preferably be carried out in one or two seconds.

It should be appreciated that the product may optionally be thermomechanically processed after casting. In other words, the product may be forged after die casting. For example, the die cast product may serve as a preform for use in the forging process. Applicants prefer to mold die cast products close to their final form, minimizing the post-casting operations and associated costs performed on the product.

The products made according to the invention are characterized by a microstructure with a fine and uniform average particle size and free of flow lines, especially for cast products. See FIGS. 2 and 3, respectively, illustrating the microstructure of die casting IN 718 test rods and wings, and FIG. 5, illustrating the microstructure of a conventional forged IN 718 wing. In Figure 2, the average particle size is approximately ASTM 6. In Figure 5, the average particle size is approximately ASTM 10.

The product of the invention is characterized by a small average particle size of less than or equal to ASTM 3, more preferably less than or equal to ASTM 5 for non-rotating gas turbine engine elements such as cases and seals. In the case of rotating elements such as gas turbine engine blades, the preferred average particle size is smaller, for example preferably at most ASTM 5, more preferably at most ASTM 6. The preferred average particle size and the maximum allowable particle size will vary depending on the use of the part, such as the product's use in gas turbine engines versus other applications, whether it is used in rotating versus non-rotating parts and whether it is operating in a lower temperature vs. higher temperature environment. . Such products have properties that are comparable to, preferably higher than, corresponding products made of forged materials.

Examination of die casting products, such as die casting IN 718, surprisingly showed that at least some rave phases and other TCP phases exist as well as elemental segregation. Surprisingly, the presence of such defects makes the rate of cooling of molten material into the mold relatively fast (relative to investment casting). As discussed above, the presence of these defects reduces the mechanical properties of the article. Depending on the intended use of the product, these defects must be reduced or eliminated. Typical heat treatments for reducing or eliminating these defects are discussed in connection with FIGS. 12 and 13.

As disclosed above, the present invention is capable of die casting articles with excellent strength as well as other properties comparable to or better than corresponding forged elements, such as low crack growth rates and high stress fracture resistance. Die casting IN 718 samples according to the present invention were tested to determine the yield strength and ultimate tensile strength, as well as durability and impact strength. For tensile, samples of die cast IN 718 products were tested at both room temperature (about 70 ° F.) and elevated temperatures (eg, about 650 ° C. (1200 ° F.)) (maintained for some time before testing). The sample was subjected to a stress strain rate of 0.076 to 0.178 mm / mm / min or 0.003 to 0.007 in / in / min through yield strength, which was then increased to break after about 1 minute. As shown in Figures 6 and 7, the die cast product is characterized by comparable 0.2% yield strength, ultimate tensile strength, elongation at break and impact strength at room and elevated temperatures.

More specifically, in the case of blades and vanes such as rotating elements, the die cast part requires at least the same strength and impact properties as exhibited by the corresponding forged product. Blades, vanes and rotating elements comprised of IN 718 have a 0.2% yield strength of at least 1 MPa (140 ksi), more preferably at least 1.05 MPa (150 ksi) and most preferably at least 1.12 MPa (160 ksi); And a yield strength of at least 805 kPa (115 ksi), more preferably at least 875 kPa (125 ksi) and most preferably at least 945 kPa (135 ksi) at 650 ° C. (1200 ° F.). Such articles have an ultimate tensile strength of at least 1.23 MPa (175 ksi), more preferably at least 1.3 MPa (185 ksi), most preferably at least 1.37 MPa (195 ksi) at room temperature; And ultimate tensile strength at 650 ° C. (1200 ° F.) of at least 1 MPa (140 ksi), more preferably at least 1.05 MPa (150 ksi), most preferably at least 1.12 MPa (160 ksi).

In addition, standard and smoothed and notched stress fracture test specimens (including materials prepared according to the present invention), such as those in accordance with ASTM E292, were tested. The specimens were maintained at about 650 ° C. (1200 ° F.) and subsequently loaded with an initial axial stress of about 735-770 MPa (105-110 ksi). In the case of materials used for blades and vanes, the specimens were not destroyed after at least 23 hours. The values are comparable to those found in AMS 5663, referenced above.

Finished and notched stress fracture test specimens (including materials prepared according to the present invention), such as those according to ASTM E292, which are similar standard combinations, were also tested at about 704 ° C. (1300 ° F.). The samples were loaded continuously, after which an initial axial stress of about 420-455 MPa (60-65 ksi) was generated. In the case of materials used for blades and vanes, the specimens were not destroyed after at least 40 hours.

Creep properties were also evaluated at about 650 ° C. (1200 ° F.). The specimen was maintained at about 650 ° C. (1200 ° F.) and loaded to produce an axial stress of at least about 560 MPa (80 ksi). The time to plastic deformation of 0.1% is measured and for materials used for blades and vanes the time should exceed about 15 hours. In addition, the specific requirements will depend on the particular application for which the product is placed.

For non-rotating parts such as cases, flanges and seals such as rings, these values exceed the required values. More specifically, non-rotating parts such as rings and seals made of IN 718 yield 0.2% yield of at least 910 MPa (130 ksi), more preferably at least 1 GPa (140 ksi) and most preferably at least 1.05 GPa (150 ksi) at room temperature. burglar; And a yield strength of at least 735 MPa (105 ksi), more preferably at 805 MPa (115 ksi), and most preferably at least 875 MPa (125 ksi) at 650 ° C. (1200 ° F.). Such articles have an ultimate tensile strength of at least 1.16 GPa (165 ksi), more preferably at least 1.23 GPa (175 ksi) and most preferably at least 1.3 GPa (185 ksi) at room temperature; And ultimate tensile strength at 650 ° C. (1200 ° F.) at least 875 MPa (125 ksi), more preferably at 945 MPa (135 ksi), most preferably at least 1.02 GPa (145 ksi).

In addition, standard combinations of finished and notched stress fracture test specimens (including materials prepared according to the present invention), such as those according to ASTM E292, were tested. The sample was maintained at about 650 ° C. (1200 ° F.), loaded continuously, and then generated an initial axial stress of about 735-770 MPa (105-110 ksi). In the case of materials used for blades and vanes, the specimens were not destroyed after at least 23 hours and the elongation was at least about 6%.

Finished and notched stress fracture test specimens (including materials prepared according to the present invention), such as those according to ASTM E292, which are similar standard combinations, were also tested at about 704 ° C. (1300 ° F.). The samples were loaded continuously, after which an initial axial stress of about 420-455 MPa (60-65 ksi) was generated. In the case of materials used for blades and vanes, the specimens were not destroyed after more than 85 hours.

Creep properties were also evaluated at about 650 ° C. (1200 ° F.). The specimen was maintained at about 650 ° C. (1200 ° F.) and loaded to produce an axial stress of at least about 560 MPa (80 ksi). The time to plastic deformation of 0.1% is measured and for materials used for blades and vanes the time should exceed about 15 hours. In addition, the specific requirements will depend on the specific application for which the product is placed.

AMS 5663 requires the following characteristics:

Property Room temperature 1200 ℉ ± 10 Tensile strength 1.26 GPa (180 ksi) 1 GPa (140 ksi) Yield strength, 0.2% offset 10.5 GPa (150 ksi) 875 MPa (125 ksi) 4D minimum elongation 10% 10% Minimum area reduction 12% 12%

AMS 5383 requires the following characteristics:

Property Room temperature Tensile strength 840 MPa (120 ksi) Yield strength, 0.2% offset 735 MPa (105 ksi) 4D minimum elongation 3% Minimum area reduction 8%

As shown in AMS 5663, the properties of the forged material depend on whether the sample is tested longitudinally or horizontally. For example, these properties are not isotropic and the values generated during the transverse test are smaller.

In addition, standard combinations of finished and notched stress fracture test specimens (including materials prepared according to the present invention), such as those according to ASTM E292, were tested. The specimens were maintained at about 650 ° C. (1200 ° F.) and subsequently loaded with an initial axial stress of about 735-770 MPa (105-110 ksi). The specimens were destroyed after at least 23 hours. These values satisfy the requirements disclosed in AMS 5663.

Finished and notched stress fracture test specimens are tested for products of lower strength, ie, products that meet the requirements of the AMS 5383 standard combination. After the samples were maintained at 704 ° C. (1300 ° F.) and loaded continuously, an initial axial stress of about 462 MPa (65 ksi) was generated. The specimens were not destroyed after at least 23 hours.

8, 9 and 10, nickel-based superalloys such as IN 718 are preferably melted and cast in a non-reactive environment such as inert gas or more preferably in a vacuum environment. Preferred methods of die casting an article are disclosed in co-pending applications filed on the same day as the present application under the headings "Method for Making Die Casting Products of High Melting Point or Reactive Materials" and "Die Casting Apparatus of High Melting Point Materials". Each of which is incorporated herein by reference. Preferably a single charge or small batch (about 4.5 kg / 10 lb) of material is prepared (FIG. 10, step 44). The charge is melted to melt at high speed without contaminating the material. The molten material is then injected into the sleeve tube to partially fill the horizontal firing sleeve tube of the die casting apparatus (also preferably vented) of the cooling chamber type. The molten material is then injected into a die (preferably not heated), where the material solidifies to form the desired product.

Initially, the die cast material is melted in the apparatus 18 illustrated in FIGS. 8 and 9 (FIG. 10, step 46). When casting a reactive material, such as a superalloy containing reactive elements, it is important to melt the material in a non-reactive environment to prevent any reactions, contamination or other conditions that may adversely affect the quality of the resulting product. Do. Since any gas in the molten environment may be trapped into the molten material and create excessive pores in the die cast product, it is desirable to melt the material in a vacuum environment rather than under an inert environment such as argon. More preferably the material is melted in a melting chamber 20 coupled to a vacuum source 22, wherein the chamber is maintained at a pressure of less than 100 μm, preferably less than 50 μm.

A nickel-based superalloy such as IN 718 is a crucible (single charge of cast material, such as about 25) made by induction skull remelting or melting (ISR) 24, such as Consarc Corporation, Rancocas, NJ. melting of less than lb material can be neatly melted at high speed). In ISR, the material is melted in a crucible defined by a number of metal (typically copper) fingers held in positions adjacent to each other. The crucible is surrounded by an induction coil connected to a power source 26. The fingers include a passage for circulating cooling water from a water source (not shown) back to the source to prevent melting of the fingers. The electric field generated by the coil passes through the crucible and heats and melts the material disposed within the crucible. The electric field also serves to agitate the molten metal. A thin layer of material is frozen on the crucible wall to form a skull to minimize the ability of the molten material to attack the crucible. By appropriately selecting the crucible and coil, and the power and frequency applied to the coil, molten material can segregate and actually float from the crucible.

Since some elapsed time will be required between the melting of the material and the process of injecting the molten material into the die, the material is sufficiently high enough to remain substantially molten until the material is at least injected, but for example Melt with superheat low enough to cause rapid solidification upon injection so that small particles can form. For superalloys, it is desirable to limit the overheat to within about 93 ° C. (200 ° F.) above the melting point, more preferably below 38 ° C. (100 ° F.), most preferably below 10 ° C. (50 ° F.).

It is preferred to melt a single charge of the material using an ISR unit, but the material may also be melted in other ways, such as by vacuum induction melting (VIM), electron beam melting, resistance melting or plasma arc. Moreover, it does not exclude the melting of bulk materials, such as multiple charges of material, at once in a vacuum environment, and then moving the single charges of the melted material from the launch sleeve tube into the die for injection. However, because the material melts under vacuum, any device used to move the molten material typically must be able to withstand high temperatures and must be placed in a vacuum chamber, resulting in a relatively large chamber. Additional devices add cost and the correspondingly larger vacuum chambers take longer to vent, adversely affecting cycle times.

In order to move the molten material from the crucible to the firing sleeve tube 13 of the device (FIG. 10, step 48), the crucible is moved (FIG. 9, arrow 42) and also the pivot movement around the injection axis (not shown) 8, arrow 33), which in turn rotates the crucible to inject molten material from the crucible through the injection hole 35 of the firing sleeve tube 30 with or without an injection cup or funnel. Load on a motor (not shown). The movement takes place between a melting chamber 20 that melts the material and a position in a separate vacuum chamber 34 in which the firing sleeve tube is disposed. The injection chamber 34 is also maintained as a non-reactive environment, preferably a vacuum environment, with a pressure of less than 100 μm, more preferably less than 50 μm. The melting chamber 20 and the injection chamber 34 are separated by an inlet valve or other suitable means (not shown) so that when one chamber is exposed to the atmosphere, for example to access an element in a particular chamber, Minimize losses.

As disclosed above, the molten material is moved into the firing sleeve tube 30 through the injection hole 35 in the crucible 24. The launch sleeve tube 30 is coupled to a multi-part reusable die 36, which defines the die cavity 38. A sufficient amount of molten material is injected into the firing sleeve tube to fill the die cavity (which may include one or more than one portion). In the present invention, for example, as many as 12 parts were successfully cast in one shot using 12 cavity dies.

The illustrated die 36 comprises two parts 36a, 36b, which cooperate to define a die cavity 38, for example in the form of a compressor blade for a gas turbine engine. Die 36 may also be coupled to a vacuum source to evacuate the die prior to injecting molten metal and close the die in a separate vacuum chamber. One of the two parts 36a, 36b of the die is fixed, while the other part is movable relative to the one part, for example by a hydraulic assembly (not shown). The die preferably includes a discharge pin (not shown) to facilitate the discharge of solidified material from the die.

The die can be composed of various materials, must have good thermal conductivity and be relatively resistant to chemical attack and corrosion by injection of molten material. A comprehensive list of possible materials can be very extensive and include materials such as metals, ceramics, graphite and metal matrix composites. With respect to the die material, the present invention refers to "Moldmax" which is a tool steel, such as H13 and V57, molybdenum and tungsten-based materials such as TZM and Anviloy, copper-based materials such as copper beryllium alloys. (High hardness), cobalt-based alloys such as F75 and L605, nickel-based alloys such as IN 100 and Rene 95, iron-based superalloys and mild carbon steels such as 1018 have been used successfully. The choice of die material is important for economically manufacturing the product and depends on the complexity and quantity of the material being cast as well as the market price of the element.

Each die material has the properties that make it desirable for a variety of applications. For inexpensive die materials, mild carbon steel and copper beryllium alloys are preferred because of their relative ease of machining and assembling the die. Heat resistant metals such as tungsten and molybdenum-based materials are preferred for higher cost and higher capacity applications due to their good strength at high temperatures. Cobalt-based and nickel-based alloys and more highly alloyed tool steels provide a compromise between these two groups of materials. The use of coatings and surface treatments may be used to improve device performance and quality of the resulting parts. The die may also be coupled to a coolant source such as water or a heat source such as oil (not shown) to thermally control the die temperature during the process. Die lubricants may also be used in one or more selected parts of the die or die casting apparatus. Any lubricant should generally improve the quality of the resulting cast product and, more specifically, be resistant to thermal breakage so as not to contaminate the material being injected.

The molten metal is then moved from the crucible to the firing sleeve tube. A sufficient amount of molten metal is injected into the firing sleeve tube to fill the die cavity and associated mandrel, biscuits, and other cavities. The IN 718 can fill the firing sleeve tube as it does not "form" a can to the extent of the titanium alloy. However, in the present invention, good quality castings were produced when the sleeve tube was filled to less than 50%, filled to less than about 40%, and filled to less than about 30%.

An injection device, such as the plunger 40, cooperates with the firing sleeve tube 30, and a hydraulic or other suitable assembly (not shown) drives the plunger in the direction of the arrow 42 to direct the plunger to the position indicated by the solid line and dotted line. The molten material is ejected from the sleeve tube 30 into the die cavity 38 by moving between the positions indicated by (Fig. 10, step 50). In the position indicated by the solid line, the plunger and the sleeve tube define a capacity which is substantially greater than the amount of molten material to be injected in cooperation. Preferably, the dose is at least two times, more preferably at least about three times, the dose of the material being injected. Thus, the dose of material is transferred from the crucible to the sleeve tube. If the sleeve tube is only partially filled, any material or skin solidified on the sleeve tube forms only a partial cylinder, such as an open arcuate surface, which is more easily scraped or crushed and melted during metal injection. It is incorporated back into. For injection, Applicants used a plunger speed of about 0.77 m / s (30 in / s (ips)) to 7.7 m / s (300 ips), and in the present invention about 1.3 to 4.5 m / s (50 to 175 ips) It is preferred to use a plunger speed of. The plunger typically travels at a pressure of at least 8.4 MPa (1200 psi), more preferably at least 10.5 MPa (1500 psi). As the plunger reaches the end of its stroke as the die cavity is filled, the pressure begins to move towards the metal. The pressure applied to the metal is then strengthened, preferably at least 3.5 MPa (500 psi), more preferably at least about 10.5 MPa (1500 psi) to completely fill the mold cavity. Strengthening is also performed to minimize pores and reduce or eliminate any material shrinkage during cooling. After sufficient time has elapsed to allow the material in the die to solidify, drain pins (not shown) are actuated to eject the parts from the die (FIG. 10, step 52).

As is known in the art, product casting and in particular die casting generally tend to include some pores, generally up to several percent of pores. Therefore, in particular when such products are used for more demanding applications, for example in compressor blades for gas turbine engines, it is necessary to reduce, preferably eliminate, or otherwise process them as necessary. (FIG. 10, step 54). The parts are therefore hot isostatically pressed (HIP) as described above to reduce and substantially eliminate any pores in the parts during casting. For nickel-based superalloys such as IN 718, about 105 to 175 MPa for at least about 4 hours at a temperature of about 982 to 1093 ° C. (1800 to 2000 ° F.), more preferably at about 982 to 1023 ° C. (1800 to 1875 ° F.) HIP at a pressure of (15-25 ksi) is preferred.

If desired, each product may then be heat treated. For wings composed of die casting IN 718, the heat treatment includes standard and commercially acceptable treatments as disclosed, for example, in AMS 5663.

Actual heat treatment and HIP parameters may vary depending on the desired properties and uses for the product, and the target cycle time for the process, but the temperature, pressure, and time used during HIP will substantially eliminate all pores and remove any residual casting. It should be sufficient to homogenize segregation but not to allow significant grain growth.

The parts are inspected using conventional inspection techniques such as fluorescence transmission (FPI), radiography, visual inspection (FIG. 10, step 56), used after passing the inspection, or optionally further processed / reprocessed. May be done (FIG. 10, step 58).

Returning to the heat treatment, the applicants determined that segregation and TCP phases can be reduced or substantially removed at significantly reduced temperatures compared to existing products, and therefore it is also possible to deal with the presence of elemental segregation at the same parameters as HIP. The heat treatment includes heating the material at a pressure of about 105 to 175 MPa (15 to 25 ksi) for about 1 to 24 hours at a temperature of about 982 to 1121 ° C. (1800 to 2050 ° F.) when removing porosity. The treatment is preferably carried out in an inert environment such as argon. Actual parameters may vary depending on the intended cycle of use for the product and the target cycle time for the process, but temperature, pressure and time will substantially eliminate all pores and reduce segregation in the cast product but will not allow significant grain growth. Should be enough. FIG. 13 illustrates die casting IN 718 material after heating without pressurization at a temperature of about 1010 ° C. (1850 ° F.) for 2 hours to illustrate segregation reduction. Application of a suitable HIP pressure during this time closes the existing pores.

The temperature and time will affect the resulting particle size of the product. For example, referring to FIG. 11, the die cast IN 718 product has an average particle size of about ASTM 9 and a segregation percentage of about 30% (see left side of the curve in the figure). The sample is treated at a temperature of about 954-1121 ° C. (1750-2050 ° F.), and the treated article has an average particle size and reduced segregation that increases with increasing temperature. The increase in average particle size is improved especially when longer times are used at high temperatures. The curve illustrated in FIG. 11 is for die casting IN 718, and other materials may exhibit similar aspects. See, eg, co-pending application under the heading “Die Casting Superalloy Product”.

As a result of this study using nickel-based superalloys, several conditions are considered important for producing good quality castings. Melting, injection and injection of materials, in particular reactive materials, should be carried out in a non-reactive environment, and these processes are preferably carried out in a vacuum environment maintained at a pressure of less than 100 μm, more preferably less than 50 μm. Do. The degree of superheat remains substantially completely molten from the time the material is injected until it is injected, but should also be sufficient to allow rapid cooling to form small particles once injected. Due to the relatively low overheating, the movement and injection of the molten metal must be fast enough to be carried out before the solidification of the metal. The resulting microstructures, such as particle size, seem to correspond to the cross-sectional thickness of the part being cast as well as the die material used and the overheating used. In other words, the thinner the cross-section, the smaller the particles, and the thicker the cross-section (particularly the inner portion of the thicker cross-section) tends to contain larger particles. Higher thermal conductivity results in products with smaller particles, such as when using less superheat. This result is believed to result from the relative cooling rates of these cross sections. The speed at which the plunger travels and correspondingly the rate at which material is injected into the mold appears to affect the surface finish of the cast product, although not only the exit design but also the die material may also play a role in the injection rate. Careful control of the post-cast thermal process is necessary to fully achieve the benefits provided by the relatively fine die casting microstructure.

Die casting offers forging and other significant advantages. The time required to manufacture the finished part from the ingot is considerably reduced because it is not necessary to manufacture steel strips of specially tailored materials and the casting is performed extensively in a single step, as opposed to many forging processes. In die casting, multiple parts can be manufactured in a single casting. Die casting makes it possible to manufacture parts with more complex three-dimensional shapes, which enables new software design techniques to be applied and used in applications such as gas turbine engines, enabling more efficient manufacture of vanes and other elements. . Die casting will enable the manufacture of articles using materials with complex shapes that are difficult or impossible to forge. Furthermore, die cast parts can be manufactured in a form closer to their finished form and with a better surface finish that has greater production reproducibility than forged or investment molded products and minimizes post forming finishing processes. All reduce the manufacturing cost of such parts.

The heat treatment of the present invention provides advantages. The heat treatment eliminates the adverse effects of casting, such as porosity, rave segregation and other unnecessary TCP phases, while maintaining fine particle sizes that provide better mechanical properties. Furthermore, the treatment allows to eliminate all of the above adverse effects in a single step, thereby saving cost, time and effort.

Although the present invention has been described in detail above, various changes and substitutions can be made without departing from the spirit or scope of the claims. Therefore, it is a matter of course that the present invention is disclosed by way of example and not by way of limitation.

Claims (28)

15 to 25 weight percent Cr, 2.5 to 3.5 weight percent Mo, 5.0 to 5.75 weight percent (Cb + Ta), 0.5 to 1.25 weight percent Ti, 0.25 to 1.0 weight percent Al, 21 weight percent Fe or less And a die casting product whose balance is made of nickel. The product of claim 1, wherein the product is characterized by a microstructure that has no free flow lines and has strength, crack growth rate and stress fracture resistance according to AMS (Aerospace Material Specification) 5663. Die casting products. The die casting product of claim 1, wherein the article comprises a gas turbine engine element. delete 2. The die cast product of claim 1 wherein the average particle size is less than ASTM 3. delete 2. The die cast product of claim 1 wherein the article is free of cross-flow lines and has a microstructure with strength, crack growth rate and stress fracture resistance according to AMS 5383. delete The die casting product of claim 1 comprising a gas turbine engine element. delete delete delete delete 15 to 25 weight percent Cr, 2.5 to 3.5 weight percent Mo, 5.0 to 5.75 weight percent (Cb + Ta), 0.5 to 1.25 weight percent Ti, 0.25 to 1.0 weight percent Al, 21 weight percent Fe or less And the remaining amount is a method of heat-treating the super alloy cast product having a composition consisting of nickel, having pores and elemental segregation during casting, Said article is heated at a temperature of 982-1121 ° C. (1800-2050 ° F.) for 1-24 hours to reduce the segregation. 15. The method of claim 14 wherein the pores are removed by applying a pressure of from 105 to 175 MPa (15 to 25 ksi) during the heating step. delete delete 15. The method of claim 14, wherein said article exhibits elemental segregation greater than 0% and up to 40%. The method of claim 14, wherein the article exhibits a microstructure having an average particle size of ASTM 3 or less. 15 to 25 weight percent Cr, 2.5 to 3.5 weight percent Mo, 5.0 to 5.75 weight percent (Cb + Ta), 0.5 to 1.25 weight percent Ti, 0.25 to 1.0 weight percent Al, 21 weight percent Fe or less And the remaining amount is a method of producing a superalloy cast product having a composition consisting of nickel, having pores and elemental segregation during casting, Die casting the product; Heating the product at a temperature of 982 to 1121 ° C. (1800 to 2050 ° F.) and a pressure of 105 to 175 MPa (15 to 25 ksi) for 1 to 24 hours to reduce the segregation. delete delete delete 21. The method of claim 20, wherein the article exhibits elemental segregation greater than 0% and up to 40%. 21. The method of claim 20, wherein the article exhibits a microstructure having an average particle size of ASTM 3 or less. 0.02 to 0.04 wt% C, 17 to 21 wt% Cr, 1 wt% or less Co, 2.8 to 3.3 wt% Mo + W + Re, 5.15 to 5.5 wt% Cb + Ta, 0.75 to 1.15 wt% Ti + V + Hf, 0.4 to 0.7% by weight of Al, less than 19% by weight of Fe and the remainder of the composition is a super alloy die casting product having no porosity and reduced segregation compared to the die casting product. delete delete

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