JP2011089201A - Nickel-containing alloy, method of manufacture thereof and articles derived therefrom - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alloy exhibiting creep resistance, high heat corrosion resistance, castability and weldability, and used for both first stage and later stage turbine nozzle applications. <P>SOLUTION: Disclosed herein is a nickel-containing alloy, comprising: about 1.5 to about 4.5 wt.% aluminum; about 1.5 to about 4.5 wt.% titanium; about 0.8 to about 3 wt.% niobium; about 14 to about 28 wt.% chromium; about ≤0.2 wt.% zirconium; about 10 to about 23 wt.% cobalt; about 1 to about 3 wt.% tungsten; about 0.05 to about 0.2 wt.% carbon; about 0.002 to about 0.012 wt.% boron and about 40 to about 70 wt.% nickel. The atomic ratio of the aluminum to the titanium is about ≥0.5. Further, the alloy does not substantially comprise tantalum. The method for manufacturing the same and articles derived therefrom are also disclosed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nickel-containing alloy, a method for producing the same, and an article.

  Heat resistant alloys suitable for use in turbine nozzle and air foil applications typically exhibit properties such as high temperature strength, corrosion resistance, castability and weldability. Unfortunately, trying to optimize one characteristic usually reduces another characteristic. The process of alloy design typically compromises to achieve the best overall combination of properties that meet the various requirements of part design. In such a design process, one characteristic is hardly extracted to the maximum. Rather, by developing a balanced chemical composition and appropriate heat treatment, the best compromise of desired properties is measured.

  Cobalt-containing alloys are sometimes used for first stage turbine nozzle applications despite the tendency to generate thermal fatigue cracks. These alloys are accepted because they can be easily repair welded. However, it has been confirmed that the creep limit of the cobalt-based alloy in the latter stage nozzle is up to a point where the creep in the downstream direction of the nozzle results in an unreasonable reduction in the clearance of the turbine diaphragm. Cobalt-based alloys with suitable creep strength for these latter nozzle applications are available but do not have the desired welding characteristics.

  Accordingly, it is desirable to find another alloy that exhibits creep resistance, high thermal corrosion resistance, castability and weldability and can be used in first stage and latter stage turbine nozzle applications.

  The present invention includes about 1.5 to about 4.5 weight percent aluminum, about 1.5 to about 4.5 weight percent titanium, about 0.8 to about 3 weight percent niobium, about 14 to about 28 weight percent. % Chromium, about 10 to about 23% cobalt, about 1 to about 3% tungsten, about 0.05 to about 0.2% carbon, about 0.002 to about 0.012% by weight A nickel-containing alloy containing boron and about 40 to about 70 weight percent nickel, having an atomic ratio of aluminum to titanium of greater than about 1.0 and substantially free of tantalum.

  Another embodiment of the present invention relates to a method for manufacturing an article comprising the step of casting an alloy having the composition of the present invention and an article comprising the alloy composition.

It is a graph which shows the relationship between time and distortion at the time of applying a constant stress of 15 ksi at a temperature of 871 ° C. for two samples. It is a graph which shows the relationship between time and a creep strain about various alloy compositions.

The present invention is a nickel-containing alloy used in turbine applications. The nickel-containing alloy can advantageously be used for both first stage and latter stage turbine nozzle applications, and can also be used for large turbine buckets. The nickel-containing alloy includes nickel, chromium, cobalt, tungsten, aluminum, titanium, niobium and other essential elements. In particular, the nickel-containing alloy has a unique combination of aluminum and titanium concentrations compared to other similar alloys. As a result, the presence of undesirable phases such as the η phase of the formula M ₃ Ti (where M is a nickel or nickel alloy such as nickel-cobalt) having a hexagonal crystal structure is reduced or not. Such reduction of the η phase promotes an increase in creep resistance and makes the alloy metallurgically stable at high temperatures, eg, above 600 ° C. Usually, the η phase is present at a level of less than about 5% by volume, often less than about 2% by volume. In a preferred embodiment, the presence level of the η phase is less than about 0.5% by volume, for example, the alloy is substantially free of the η phase.

  Nickel-containing alloys of embodiments of the present invention also typically contain chromium at a level of about 14 to about 28% by weight, and in a preferred embodiment about 14 to about 24% by weight (more specific ranges are given below). .

  Furthermore, in a preferred embodiment, the nickel alloy should contain the main subgroup elements, namely aluminum, titanium and niobium. As will be described later, these elements play an important strengthening mechanism of the present composition due to the presence of the γ 'phase at the level of the present invention.

  Any metal that can be added to the nickel-containing alloy is cobalt, carbon, zirconium, tungsten, boron, hafnium, rhenium, ruthenium, molybdenum, or a combination of one or more of these metals. In a preferred embodiment, the alloy should contain at least the zirconium, cobalt and tungsten at the level of the present invention as additional components. In another preferred embodiment, the alloy composition must contain boron and carbon.

  In one embodiment, the nickel-containing alloy includes aluminum and titanium in an amount of about 2 to about 9 weight percent (wt%) relative to the nickel-containing alloy. Within this range, the total amount of aluminum and titanium used can be about 2.5 wt% or more, preferably about 3.0 wt% or more, more preferably about 4 wt% or more based on the nickel-containing alloy. Further, within this range, an amount of about 8.8 wt% or less, preferably about 8.6 wt% or less, more preferably about 8.0 wt% or less with respect to the nickel-containing alloy is desirable.

  The aluminum content of the nickel-containing alloy is about 1.5 to about 4.5 wt% with respect to the nickel-containing alloy. A preferred amount of aluminum is about 1.6 wt% or more, more preferably about 1.7 wt% or more. A preferred amount of aluminum is about 4.00 wt% or less, more preferably about 3 wt% or less, and particularly preferably about 2.5 wt% or less. The titanium content of the nickel-containing alloy is about 1.5 to about 4.5 wt% with respect to the nickel-containing alloy. A preferred amount of titanium is about 1.65 wt% or more, more preferably about 2 wt% or more, and particularly preferably about 2.25 wt% or more. The preferred amount of titanium is about 4 wt% or less, more preferably about 3.5 wt% or less, and particularly preferably about 3 wt% or less (the relative amounts of aluminum and titanium are in accordance with the following proportions of these two elements).

  In embodiments of the present invention, the atomic ratio of aluminum to titanium in the nickel-containing alloy needs to be about 0.5 or greater. In particularly preferred embodiments, the aluminum / titanium atomic ratio is greater than about 1.0. If the aluminum / titanium atomic ratio is within this range, the resistance to high thermal corrosion, weldability and castability are usually improved.

In another embodiment, it is desirable to control the total amount of aluminum, titanium and niobium present in the nickel-containing alloy to about 2 to about 13 weight percent, which is effective in maintaining the γ 2 phase. The preferred amount of γ ■ phase is 15 to 45% by volume. Strength in refractory nickel-containing alloys is usually due to several different mechanisms, such as precipitation strengthening of the γ 'phase, solid solution strengthening and carbide strengthening at grain boundaries. The γ ■ phase consists of [Ni ₃ (Al, Ti)]. Among these, precipitation strengthening of the γ ′ phase is the main strengthening mechanism of the nickel-containing alloy.

  In order to ensure the best compromise between alloy properties for gas turbine nozzle and airfoil applications, the content of the main precipitation strengthening elements, ie titanium, aluminum and niobium, is about 2 to about 13 wt% relative to the nickel containing alloy. To keep the amount of. Within this range, the amount of titanium, aluminum and niobium is usually about 4.35 wt% or more, preferably about 4.5 wt% or more, more preferably about 4.75 wt% or more based on the nickel-containing alloy. desirable. Further, within this range, an amount of about 11.5 wt% or less, preferably about 11 wt% or less, more preferably about 10 wt% or less with respect to the nickel-containing alloy is desirable. By maintaining the amounts of aluminum, titanium and niobium within the above limits, a good balance between creep resistance and weldability is achieved. In addition, the levels of carbon and zirconium (if present) are carefully balanced and controlled so that the castability of the nickel-containing alloy is improved.

  In other embodiments, the nickel-containing alloy does not include tantalum. Although tantalum is an important component in various nickel-based alloys, the presence of tantalum is undesirable in most embodiments of the invention. As shown in the examples, the absence of tantalum can significantly improve the creep strength. Furthermore, in many cases, the presence of tantalum, a relatively high density element, will unnecessarily increase the weight of parts made of alloys, and in parts such as aircraft turbine parts, even a little extra weight. May be a problem. In addition, tantalum is a relatively expensive element that may unnecessarily increase the cost of the alloy composition.

  In most embodiments of the present invention, it is generally desirable for niobium to be present in an amount up to about 3 wt% relative to the nickel-containing alloy. Within this range, the amount used can be about 2.5 wt% or less, preferably about 2.0 wt% or less, more preferably about 1.75 wt% or less. A specific amount of niobium is about 1.35 wt% with respect to the nickel-containing alloy.

  Chromium is typically present in an amount of about 14 to about 28 wt% relative to the nickel-containing alloy. Within this range, it is often desirable to use chromium in an amount of about 16 wt% or more, preferably about 17 wt% or more, and more preferably about 20 wt% or more with respect to (but not necessarily) the nickel-containing alloy. Further, within this range, an amount of about 27 wt% or less, preferably about 26 wt% or less, more preferably about 25 wt% or less is desirable with respect to the nickel-containing alloy. A specific amount of chromium is about 22 to about 23 wt% based on the total nickel-containing alloy.

  In the alloys of the present invention, nickel is present in an amount of about 40 to about 70 wt% based on the alloy. Within this range, the amount of nickel used is usually about 43 wt% or more, preferably about 44 wt% or more, more preferably about 46 wt% or more, relative to the nickel-containing alloy. Further, within this range, an amount of about 65 wt% or less, preferably about 60 wt% or less, more preferably about 55 wt% or less with respect to the nickel-containing alloy is desirable. A specific amount of nickel is about 45 to about 55 wt% with respect to the nickel-containing alloy.

  The amount of cobalt added is typically about 10 to about 24 wt% based on the total nickel-containing alloy. Within this range, the amount used can be about 14 wt% or more, preferably about 15 wt% or more, more preferably about 17 wt% or more based on the entire nickel-containing alloy. The amount used is about 23.5 wt% or less, preferably about 22.5 wt% or less, more preferably about 21 wt% or less based on the entire nickel-containing alloy. A specific amount of cobalt is about 18.5 to about 19.5 wt% based on the total nickel-containing alloy.

  The amount of carbon added is usually less than 0.15 wt%. The preferred amount of carbon is 0.05 to about 0.2 wt%. Carbon is usually alloyed with metals such as titanium and tungsten to form monocarbide. In many cases, carbide formation is important to improve the grain boundary strength of embodiments of the present invention. Usually, the amount of titanium and / or tungsten in the monocarbide is about 80 wt% or less of the carbide phase. A specific amount of carbon is about 0.02 to about 0.15 wt% relative to the nickel-containing alloy.

  Tungsten is present at a level of about 3 wt% or less relative to the nickel-containing alloy. In some cases, tungsten can be replaced with molybdenum, rhenium, ruthenium, or the like. However, the preferred embodiment often requires the presence of tungsten itself. A specific amount of tungsten is about 1.9 to about 2.1 wt% with respect to the nickel-containing alloy.

  Boron can also be present in an amount up to about 0.025 wt% relative to the nickel-containing alloy. A preferred amount of boron is from about 0.002 to about 0.012 wt% relative to the nickel-containing alloy. Boron typically reacts with metals in nickel-containing alloys to form metal borides, and in certain embodiments, metal borides are also important for improving creep strength and grain boundary strength. A specific amount of boron in the nickel-containing alloy is about 0.002 to about 0.006 wt% relative to the nickel-containing alloy.

  Zirconium can also be added in an amount of about 0.2 wt% or less relative to the nickel-containing alloy. In some embodiments, zirconium can be replaced with hafnium if desired. A specific amount of zirconium is about 0.01 wt% to about 0.2 wt% with respect to the nickel-containing alloy.

  The nickel-containing alloy can be processed by existing methods to form gas turbine components. Examples of such parts are rotating buckets (ie, blades), non-rotating nozzles (ie, vanes), shrouds, combustors, and the like. Preferred parts for using nickel-containing alloys are gas turbine nozzles and buckets. Turbine components can be produced in a wide variety of ways, including, but not limited to, powder metallurgy (eg, sintering, hot pressing or hot isostatic pressing, thermal vacuum compression, etc.), ingot casting followed by directional solidification, It can be formed by investment casting, ingot casting and subsequent thermal machining, near net shape casting, chemical vapor deposition, physical vapor deposition, or the like. The preferred method is ingot casting followed by directional solidification and investment casting.

  In one embodiment, in producing a gas turbine airfoil from the nickel-containing alloy, the components of the nickel-containing alloy in the form of powder, particles, etc. are heated to a temperature of about 1350 to about 1750 ° C. to melt the metal component. .

  Thereafter, the molten metal can be cast into a mold by a casting method to obtain a desired shape. Casting methods include investment casting and ingot casting. Investment casting is typically used to produce parts that cannot be produced by conventional production methods, such as complex shaped turbine buckets or turbine parts that need to withstand high temperatures. In order to manufacture a mold, a prototype is first made using a material such as a wax that can be removed by melting. The wax pattern is immersed in a refractory slurry, the wax pattern is coated, a film is formed, and this is dried. The dipping and drying process in the slurry is repeated until a strong thickness is obtained. Thereafter, the entire prototype is placed in an oven to melt the wax. This molds a mold that can be filled with a molten nickel-containing alloy. Since the mold is formed around a one-piece master (no need to be pulled out of the mold as in the conventional sand casting process), very complex shapes and undercuts can be produced. The wax prototype itself is manufactured by duplicating it using a model such as stereolithography manufactured with a master model of a computer solid model.

  Immediately before casting, the mold is preheated to about 1000 ° C. to remove the remainder of the wax and to cure the binder. In addition, the mold is completely filled by casting into a preheated mold. Casting can be done using gravity, pressure, inert gas or vacuum conditions. In a preferred embodiment, casting is performed in a vacuum. In another embodiment, ingot casting can be used to manufacture turbine components. After casting, the molten metal in the mold is directionally solidified. Directional solidification usually forms crystal grains extending in the growth direction. As a result, the creep strength of the air foil is further increased compared to equiaxed casting. Directional solidification can be more expensive than equiaxed casting. Depending on the specific requirements of the airfoil, it can be either equiaxed or directionally solidified. After directionality and / or equiaxed solidification, the casting is air cooled.

  If desired, a casting made of the present nickel-containing alloy can be subjected to different heat treatments to improve creep resistance and optimize strength. In one embodiment, the casting is heat treated at a temperature of about 1095 ° C. to about 1200 ° C. to optimize yield strength and improve creep resistance. Usually, this heat treatment is performed for about 1 to about 6 hours. A preferred heat treatment time is 4 hours. In another embodiment, the heat resistance cycle can be used to improve creep resistance. As an example, the heat treatment cycle can include heat treating the casting at a temperature of about 1150 ° C. for 4 hours, then 1000 ° C. for 6 hours, then 900 ° C. for 24 hours, and finally 700 ° C. for 16 hours. This heat treatment significantly improves the values of tensile strength and yield strength.

  In other embodiments, the material is solution heat treated at a temperature from 750 ° C to about 850 ° C. The solution treatment is usually performed for about 8 to about 36 hours. The specific time is about 24 hours. Usually, heat treatment and solution heat treatment are used to reduce the presence of undesirable phases such as the η phase.

  If desired, the casting can be hot isostatically pressed (HIP). Hot isostatic pressing is usually preferred because it can greatly reduce pores and facilitate shrinkage during the manufacture of such parts. Typically, hot isostatic pressing process conditions are selected so that the porosity of the final composite material is densified to less than about 10% by volume, more preferably less than about 2% by volume, relative to the total volume of the composite article. To do. This process typically applies high pressure and high temperature through a pressurized gas medium to remove internal pores and voids, thereby increasing the density of the resulting composite material and improving properties. Hot isostatic pressing is usually performed at a temperature of about 1000 ° C. or higher, and in some cases about 1050 ° C. or higher. In a preferred embodiment, the hot isostatic pressing is performed at a temperature of about 1150 ° C. or higher. The gas pressure used during hot isostatic pressing is usually about 100 MPa or more, preferably about 150 MPa or more, more preferably about 200 MPa or more. Preferred gases for use in this process include, but are not limited to, argon, nitrogen, helium, xenon and combinations including one of these.

  As described above, the nickel-containing alloy of the present invention is advantageous because it can be used for a large airfoil of a large turbine. By reducing undesirable phases such as η phase and increasing the volume fraction of γ ′ phase to about 15-45% by volume with respect to the nickel-containing alloy, the nickel-containing alloy has excellent creep resistance and high heat resistance. It exhibits corrosiveness and excellent castability and weldability.

  Hereinafter, although the composition and the manufacturing method of various embodiments of the nickel-containing alloy will be specifically described using various materials and apparatuses by way of examples, these are merely examples and do not limit the present invention. .

Example 1
This example was done to show that the properties of nickel-containing alloys containing no tantalum are improved relative to nickel-containing alloy samples containing comparative tantalum. Table 1 shows a sample having a comparative composition and a sample having a composition embodying the present invention. From Table 1, it can be seen that the comparative sample (sample No. 1) contains tantalum, and the other samples (samples No. 2 to 6) do not contain tantalum.

  Samples were prepared as follows. First, various components of the sample shown in Table 1 were prepared, heated to a temperature of 1550 ° C., made into a molten metal, and then cast. The casting was air cooled. This was annealed at 1150 ° C. for 4 hours and aged at 780 ° C. for 24 hours. The specimen was subjected to a creep test at a temperature of 1600 ° F. (871 ° C.) under a stress of 15 ksi using a tensile tester. The time taken to reach 1% strain was measured and recorded as a function of the ability of the sample to exhibit creep resistance. The sample is a cylindrical dockbone standard creep sample with a total length of 4 inches and a reference diameter of about 0.25 inches.

FIG. 1 shows the result of the creep test. The time taken to reach about 0.5% and 1% strain is compared for both samples. FIG. 1 shows that the creep of the sample not containing tantalum is improved by 200% compared to the comparative sample containing tantalum. Similarly, the creep of the 1% strain and tantalum free sample is improved by 220% compared to the comparative composition.

  Sample No. When the metallographic image analysis was performed on Nos. 2 to 6, it was found that each sample had almost the same amount of γ ′ phase and almost no undesirable η phase.

The above examples confirm that nickel-containing alloys that do not contain tantalum exhibit superior creep resistance properties compared to alloys that contain tantalum and can therefore be used advantageously in high temperature applications such as gas turbines. . Turbines containing nickel-containing alloys can be used on ships moving on and under water, such as aircraft and spacecraft, ground power systems and large ships, submarines, barges.
Example 2
This example demonstrates the effect of some embodiments of the present invention. Three samples were made as follows. The ingredients shown in Table 2 were mixed and melted at a temperature in the range of about 2700 ° F. (1482 ° C.) to 2800 ° F. (1538 ° C.). The molten alloy was then cast into a suitable ceramic mold by conventional investment casting.

  Table 2 below shows the compositions of Samples A, B, and C in weight percent (the aluminum / titanium ratio is shown in atomic percent) (Sample A is a commercially available alloy).

Sample A deviates from the technical scope of the present invention in several respects. For example, Sample A contained no tungsten or niobium. Furthermore, Sample A had an aluminum / titanium atomic ratio of less than 1. As explained, the Al / Ti atomic ratio is a key parameter and is usually independent of other component differences such as molybdenum and tungsten level differences (see Table 2). Sample B falls within the technical scope of embodiments of the present invention with an Al / Ti atomic ratio of about 0.5 or greater. However, Sample B deviates from the technical scope of the preferred embodiment of the present invention where the Al / Ti atomic ratio must be greater than about 1.0. Sample C was within the scope of the embodiments of the present invention.

  Sample A had a large amount of η phase that was undesirable in the present invention after thermal exposure to high temperature. Sample C had almost no η phase after as-cast and after heat exposure to high temperature. (Sample A also had insufficient levels of γ 'phase forming elements for the requirements of the alloy composition of the present invention).

  Test coupons were machined from the cast and heat treated alloy by wire electrical discharge machining (EDM) and polishing. The coupon dimensions were about 5 inches (12.7 cm) long and 0.75 inches (1.9 cm) in diameter. The coupons were tested for creep resistance properties according to ASTM creep test standard E139.

FIG. 2 is a graph showing the time to reach 1% creep strain at a temperature of 1600 ° F. (871 ° C.) and a similar stress level. As shown in the figure, the creep resistance of the sample C was greatly increased as compared with the sample B, and was significantly increased as compared with the sample A. The estimated time to reach 1% creep strain level for sample A was 110 hours, and the estimated time for sample B was 1450 hours. The estimated time to reach 1% creep strain level for Sample C was 3050 hours. (Sample C was also confirmed to be superior in creep resistance compared to other commercially available nickel-based alloys such as nickel-based alloys with insufficient levels of aluminum.)
These results were surprising for another reason. For example, comparing the compositions of Samples A and C, Sample C shows that the level (total amount) of precipitation strengthening elements, that is, aluminum, titanium, and niobium, increased by 89% relative to Sample A. The creep property increased by about 2800%.

  While the present invention has been described with reference to the exemplary embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit of the present invention, and that constituent elements can be replaced with equivalents. . In addition, many modifications may be made to adapt a particular situation or material to the present invention without departing from the spirit of the invention. Therefore, the present invention is not limited to the specific embodiment described above as the best mode for carrying out the invention, and the present invention includes all embodiments falling within the scope of the claims.

Claims (9)

1.5-4.5 wt% aluminum,
1.5-4.5 wt% titanium,
0.8-3 wt% niobium,
14-28% by weight chromium,
10-23 wt% cobalt,
1-3 wt% tungsten,
0.05-0.2 wt% carbon,
0.002 to 0.012 wt% boron and 40 to 70 wt% nickel,
The atomic ratio of aluminum to titanium is greater than 1.0;
Substantially free of tantalum,
Nickel-containing alloy.   The nickel-containing alloy according to claim 1, wherein the total amount of aluminum and titanium is 2 to 9% by weight based on the nickel-containing alloy.   The nickel-containing alloy according to claim 1, wherein the total amount of aluminum, titanium and niobium is 2 to 13% by weight based on the weight of the alloy.   The nickel-containing alloy according to claim 1, further comprising at least one element selected from the group consisting of zirconium, hafnium, rhenium and ruthenium.   The nickel-containing alloy of claim 1, comprising a η phase at a level of less than 5% by volume. (A) 1.5-4.5 wt% aluminum, 2.1-4.5 wt% titanium, 0.8-3 wt% niobium, 14-24 wt% chromium, 10-23 wt% Cobalt, 1 to 3% by weight of tungsten, rhenium, ruthenium, molybdenum, or a combination thereof, 0.05 to 0.2% by weight of carbon, 0.002 to 0.012% by weight of boron, and Casting an alloy containing 40-70 wt% nickel;
(B) including a step of solidifying the casting,
Article manufacturing method.   The method of claim 6 further comprising the step of directional solidification of the casting.   The method of claim 6, wherein the casting is an equiaxed casting. A turbine component manufactured from a material comprising the alloy of claim 1.