Patent Application
20200032379
The present disclosure relates to a method for heat treatment of Alloy 282 which has been subjected to an initial solution annealing followed by cooling. Furthermore said alloy being heat treated according to the method and a component, a turbine exhaust case and a gas turbine engine made of said alloy are disclosed.
In applications such as aircraft jet engines, land based gas turbines, marine and automotive engines the present technical developments and demands regarding cost, fuel efficiency, engine performance and environmental aspects lead to the need of improving and further developing the materials used in different components used within the applications, e.g. the engine or turbine components. Especially, the recent developments have led to the turbine section of gas turbines being exposed to gases of higher temperatures, thereby putting special demands on the materials used in these sections. These parts therefore require high strength alloys which can withstand the extreme temperatures and harsh environments while still maintaining high strength and high durability required for these critical applications. Also, the weight of the components and the economic costs must be maintained within limits.
For the turbine section of an aircraft engine, especially the turbine exhaust case, different alloys can be used, depending on the temperature and strength requirements, while also factors such as weight and cost must be taken into account. As different parts of the turbine exhaust case are exposed to different temperature, an option might be to use different alloys in the different portions depending on temperature requirements, to thereby minimize weight and cost while meeting the requirements regarding heat resistance in the various portions. Also, by combining different materials in different parts of a component, the different requirements regarding strength and creep properties may be taken into account. However, a problem is that different alloys require different heat treatments in order to reach their optimum performance characteristics. Thus, a technological challenge is to join parts of different materials and subjecting them to a final heat treatment that meets both (or more) material individual requirements in terms of response to heat treatment and resulting properties.
Thus, there is a need for alloys with high strength for use at high temperature, which also allows fabricating components which meet other criteria regarding performance, durability, weight and cost. Especially the aircraft industry is subject to high standards regarding safety and environmental issues.
The present disclosure aims at, at least to a certain extent, alleviating the problems mentioned above.
A method is presented for heat treatment of alloys, the method being aimed at solving the problems mentioned above.
In a first aspect, a method for heat treatment of an Alloy 282 is presented. According to this aspect an Alloy 282, after having been subjected to an initial solution annealing followed by cooling, is subjected to the method comprising the steps of:
a) heating the Alloy 282 at a temperature between 954° C. and 1010° C. until the gamma prime phase is sufficiently dissolved, and
b) cooling the Alloy 282 to a temperature sufficiently low, and at a cooling rate sufficiently high, to suppress gamma prime precipitation.
These steps are referred to as solution treatment. By sufficiently dissolving the gamma prime phase (γ′) required tensile strength and yield strength properties can be achieved for the heat treated alloy. A faster cooling will lead to increased strength of the alloy. With this method, the resulting mechanical strength properties are improved compared to the solution treatment used in the heat treatment method conventionally applied to Alloy 282.
According to one embodiment, in step b) the Alloy 282 is cooled to a temperature below 594° C.
According to one embodiment the heating in step a) takes place during 0.5 to 2 hours.
According to one embodiment, the cooling in step b) is performed at a rate equal to or higher than 19° C./min.
According to one embodiment the cooling in step b) is performed at a rate of 19-25° C./min. According to one embodiment the heating as defined by step a) is performed at 954° C.
According to one embodiment the heating as defined by step a) is performed at 996° C. This further improves the mechanical properties of the Alloy 282.
According to one embodiment the method further comprises the steps of:
c) heating the Alloy 282 at 760° C. for 5 hours followed by cooling to 650° C., and
d) holding the alloy at 650° C. for 1 hour.
These steps are referred to as age-hardening. This part of the heat treatment method is particularly important for the resulting strength of the alloy.
According to one embodiment the cooling from 760° C. to 650° C. is performed at an average rate of 56° C.±8° C. per hour.
According to one embodiment, the Alloy 282 is joined together with an Alloy 718 prior to the heat treatment, whereby the combined unit is subject to the heat treatment.
According to one embodiment, the Alloy 282 and the Alloy 718 have been joined together by welding or by free-forming methods.
According to one embodiment, the Alloy 282 is joined together with an Alloy 718 by brazing during the heat treatment.
According to one embodiment, the Alloy 282 or the Alloy 718 or both have been formed into a shape by any of the methods wrought, cast, spray formed, powder metallurgy methods or free-forming methods. This gives the possibility of forming an alloy or combinations of alloys into a wide range of different shapes.
According to a second aspect an Alloy 282 which has been heat treated by the method for heat treatment according to the first aspect described. The Alloy 282 which has been heat treated with this method has improved strength characteristics compared to an Alloy 282 which has been heat treated according to a method conventionally used for Alloy 282.
According to a third aspect a component comprising an Alloy 282 according to the second aspect is described. Such a component benefits from the improved mechanical properties of the alloy.
According to one embodiment, the Alloy 282 is combined with an Alloy 718 prior to heat treatment according to the first aspect. This has the advantage that the multi-alloy component is subjected to a common heat treatment. As described in detail below, this heat treatment method is developed to result in optimized mechanical properties for both Alloy 282 and Alloy 718. The assembled component can therefore with good results be subjected to the common heat treatment.
According to one embodiment the Alloy 282 and the Alloy 718 have been joined together by welding or by free-forming methods.
According to one embodiment, the Alloy 282 is combined with an Alloy 718 by brazing during the heat treatment.
According to one embodiment of the third aspect the Alloy 282 and the Alloy 718 have been formed into shape by any of the methods wrought, cast, spray formed, powder metallurgy methods or free-forming methods. This gives the possibility of forming an alloy or combinations of alloys into a wide range of different shapes.
According to a fourth aspect a turbine exhaust case comprising a component according to the third aspect is described. This turbine exhaust case benefits from the improved mechanical strength properties resulting from the heat treatment method of the first aspect. Especially, by forming some portions of the turbine exhaust case from Alloy 282 and other portions from Alloy 718, as described in detail below, a turbine exhaust case which can withstand the very high temperatures of the exhaust gases which results from recent engine developments is achieved. By combining the different alloys, costs and weight of the turbine exhaust case can be maintained within limits while still achieving a turbine exhaust case having the required temperature characteristics and mechanical strength properties.
According to a fifth aspect a gas turbine engine comprising a turbine exhaust case according to the fourth aspect is described.
A heat treatment is described, where alloys of different character are selected that can be joined without difficulties like weld cracking (or post weld heat treatment) and where they can be given the same (hybrid) treatment with little or no reduction of the properties the alloys exhibit when used individually and heat treated according to their individual optimized heat treatment cycles.
Further, according to the method disclosed, fabricated components, comprising different alloys can be salvaged and repaired both during manufacture and in service.
A specific method for heat treatment applied to a nickel base alloy of the type 282 Alloy is presented. Such an alloy is for example known under the trade name Haynes 282. Alloy 282 is a material suitable for aircraft engines and gas turbines due to its high heat resistance. By using the disclosed heat treatment, the strength and ductility of an Alloy 282 can be increased compared to what has been reported when this alloy have been given other heat treatments, such as the heat treatment conventionally used for Alloy 282.
The method presented below can also be used for components comprising several different alloys joined together, where the different alloys are subjected to the heat treatment after being joined together.
In particular, the heat treatment described herein is developed for components and products which are formed by combinations of different alloys, such as Alloy 282 and Alloy 718, which have been joined together e.g. by welding. The heat treatment method is developed to balance the respective heat treatment requirements of the different alloys: During the solution annealing phase (steps a) and b)), the temperature should be set as high as possible for Alloy 718, which is the more heat sensitive material, while still maintaining its required strength properties, and at the same time achieving the optimum properties for Alloy 282, which requires higher temperatures for proper solution annealing. During the age hardening phase (steps c) and d)) the temperature must be set low enough that the required strength is achieved for both alloys. Alloy 718 cannot withstand the age hardening process conventionally applied to Alloy 282, but at the same time, an age hardening process must be provided which results in the required strength properties also for Alloy 282. Surprisingly, the method as described in detail below results in an Alloy 282 with improved strength properties compared to an Alloy 282 subjected to the heat treatment method conventionally applied to Alloy 282.
The present disclosure will hereinafter be further explained by means of non-limiting examples with reference to the appended figures where:
An aircraft engine is shown schematically in
At the end of the turbine section a turbine exhaust case (TEC) 12 is mounted. A turbine exhaust case is shown schematically in
While alloys of the type Alloy 718 have been conventionally used in turbine exhaust cases, the increase in temperature to which the turbine exhaust case is exposed as a result of engine developments leads to a need for use of other materials, since Alloy 718 is not suitable for these high temperatures due to a thermal instability occurring at higher temperatures. The development of the strength properties with time under exposure to these high temperatures would lead to unpredictable changes in strength of the Alloy 718. An Alloy 282 has higher heat resistance, i.e., it is thermally stable at these high temperatures, and could therefore be a suitable candidate for use in high temperature aircraft engine applications, such as turbine exhaust cases. However, Alloy 282 is not as strong as Alloy 718, especially not at somewhat less high temperatures. Therefore, if completely replacing the Alloy 718 components in a turbine exhaust case with Alloy 282 components, the dimensions, especially the thicknesses, of the components would need to be increased in order to reach the specified strength requirements. This would lead to an increase in weight and price of the turbine exhaust case. Alloys 718 and 282 will be discussed in more detail below.
One way to come around this problem, is to form only the parts of the turbine exhaust case that are exposed to temperatures in excess of what the Alloy 718 alloy can withstand from Alloy 282, while the other parts are made of Alloy 718. For example, the inner hub and portions of the outer case might comprise Alloy 718, while the vanes and the portions of the outer case to which the vanes are connected might comprise Alloy 282. The outer part of the turbine exhaust case is thereby made of an alloy adapted to withstand the highest temperatures, whereas for the inner part, which does not need to withstand as high temperatures, Alloy 718 can be used since it has the properties required for the inner parts. By using different alloys for different parts of a component, in the present embodiment Alloy 282 for certain portions and Alloy 718 for other portions of the turbine exhaust case, the different criteria regarding temperature requirements can be met, while at the same time meeting criteria related to engine performance and durability, and economics in cost and weight.
However, a challenge lies in the fact that different alloys need to be subjected to different heat treatment in order to reach their optimum performance. This is also the case for the alloys Alloy 282 and Alloy 718, where the known and conventionally applied heat treatment method for Alloy 282 differs from the known and conventionally applied heat treatment method for Alloy 718.
A description of what is meant with Alloy 282 and Alloy 718 will now follow. To begin with, Alloy 282 is defined in U.S. Pat. No. 8,066,938 B2. An example of such an alloy is known under the trademark Haynes 282, defined by AMS standard 5951, where the chemical compositions are given in Table 1 of the AMS standard 5951. Haynes 282 is a nickel base alloy, having the following nominal chemical composition (weight percent, w-%): Ni (57 w-%), Cr (20 w-%), Co (10 w-%), Mo (8.5 w-%), Ti (2.1 w-%), Al (1.5 w-%), Fe (1.5 w-%), Mn (0.3 w-%), Si (0.15 w-%), C (0.06 w-%), B (0.005 w-%). In the present disclosure, although Haynes 282 is advantageously used, the term “Alloy 282” is to be interpreted as any alloy having these specifications. The Haynes 282 alloy was developed for high temperature applications, such as aircraft engines and land-based gas turbines. For the Alloy 282 good strength properties have been shown for temperatures up to 927° C. (1700° F.).
After an initial solution-annealing which for Alloy 282 typically takes place at a temperature in the range of 1121 to 1149° C. (2050 to 2150° F.) followed by cooling, preferably rapid cooling or quenching, the Alloy 282 is formable into components and products. The initial solution-annealing could also be performed at lower temperatures. This initial solution-annealing usually takes place by heating at a temperature of 1121-1149° C. for approximately 1 hour, followed by rapid cooling or quenching. The piece of alloy is put into a furnace which is already at the desired temperature, and the temperature throughout the alloy material is allowed to equalize at this temperature. After reaching the desired temperature, it is held at that temperature for the set time, usually 1 hour. How long time it takes for the material to reach that temperature throughout its structure depends on its dimensions. With “rapid cooling” it is understood here that the cooling rate should be fast enough to result in clean grain boundaries and grain interiors free of secondary precipitations, i.e., that little, if any, gamma prime (γ′) phase is present after solution-annealing. In practice, the material is cooled as fast as possible, for example by cooling in a bath such as an oil bath. After this initial solution-annealing the alloy is soft and ductile and can be formed into a desired shape.
The particular example of Haynes 282 alloy is delivered in the solution-annealed condition. After component fabrication, the alloy can be subject to a heat treatment including a gamma prime solution treatment (also acting as a “carbide stabilization treatment”) followed by age hardening, in order to put the alloy into its high-strength condition. The known and conventionally applied age hardening treatment for Haynes 282 is to heat at 1010° C. (1850° F.) for 2 hours, followed by air cooling or rapid cooling and subsequently heating at 788° C. (1450° F.) for 8 hours, again followed by air cooling.
Secondly, the Alloy 718, which also is a nickel base alloy, is known under trade names such as INCONEL 718 and Allvac 718. INCONEL 718 has the following nominal chemical composition (weight percent, w-%): Ni (plus Co) (50-55, w-%), Cr (17-21, w-%), Fe (balance), Nb (plus Ta) (4.75-5.50, w-%), Mo (2.80-3.30, w-%), Ti (0.65-1.15, w-%), Al (0.20-0.80, w-%), Co (max 1.00, w-%), C (max 0.08, w-%), Mn (max 0.35, w-%), Si (max 0.35, w-%), P (max 0.015, w-%), S (max 0.015, w-%), B (max 0.006, w-%), Cu (max 0.30, w-%). Alloy 718 is defined by standards AMS 5662 (bar/forgings), AMS 5596, and AMS 5383 (castings) (see Table 1 of the respective standards for the chemical composition), and has been described in, e.g., U.S. Pat. No. 3,046,108. In the present disclosure, the term “Alloy 718” is to be interpreted as any alloy complying with these specifications. Alloy 718 has conventionally been used for various components, e.g., in aircraft engines and other gas turbines. However, as discussed above, Alloy 718 does not possess the temperature characteristics required by recent developments in engine applications, that is, an alloy 718 cannot withstand long-term exposure to the high temperatures to which certain parts of aircraft engines are exposed. Exposure of Alloy 718 to such temperatures will, with time, lead to microstructural instability due to the Alloy 718 not being thermally stable at these temperatures, leading to a reduction in the mechanical strength of the alloy. The higher the temperature the faster a loss in strength will occur. Thermal instability starts occurring at a temperature around 675° C., at which temperature microstructural changes occur relatively slowly such that it can withstand exposure to this temperature for on the order of magnitude some 1000 hours, while above 760° C. the microstructural changes occur rapidly leading to a critical decrease in strength within a few hours.
As discussed above, components might be formed by a combination of different alloys depending on, e.g., the different temperature requirements in different parts of the component. According to one embodiment, described in detail below, components can be formed by an Alloy 282 combined with an Alloy 718. Other combinations might be of Alloy 282 with Alloy 718 Plus or Alloy282 with C263. One area of application is in components for aircraft engines, such as turbine exhaust cases.
The method for heat treatment of a component comprising Alloy 282 and Alloy 718 according to a preferred embodiment is illustrated in
As illustrated in
As indicated schematically in
The solution treatment, as disclosed in
Although the heat treatment according to a preferred embodiment as described with reference to
Conventional heat treatment methods for Alloy 718, as also specified by the standards AMS 5596, AMS 5662 and AMS 5383, are described below.
For the Alloy 718, the solution treatment should be performed at a temperature of at least 915° C., more preferably at least 927° C., in order to dissolve the gamma double prime phase so that the material after cooling can be effectively hardened, and to control the delta phase which can limit grain growth. For Alloy 718 this step is preferably performed at 954° C. in order to optimize the mechanical properties of the alloy. Higher temperatures might lead to grain growth resulting in lower strength. The delta phase, which controls grain growth, is dissolved at approximately 980-1010° C. for Alloy 718, depending on the specific type of Alloy 718 and its thermo mechanical processing history. The solution treatment step of Alloy 718 should therefore, according to prejudices in the art, be performed below this temperature.
The conventional heat treatment method for Alloy 282 is specified e.g. in the standard AMS 5951. The main strengthening phase for Alloy 282 is the gamma prime phase, which corresponds to the gamma double prime phase in Alloy 718. The gamma prime phase starts being influenced at a temperature around 940° C. The gamma prime solvus temperature of Alloy 282 is approximately 995° C. Therefore, for Alloy 282, the solution treatment step should, according to the prejudice in the art, be performed at a temperature above 995° C., preferably at 1010° C., in order to ensure that the subsequent age-hardening step occurs effectively.
According to the method as disclosed here within, the solution treatment step is performed at a temperature within the range 954-1010° C. Preferably, it is performed at a temperature of 996° C. (1825° F.), in order to reach a balance between the preferred solution heat treatment temperatures for Alloy 282 and Alloy 718. In this way, the heat treatment is also adapted to optimize the resulting mechanical properties of a component comprising both Alloy 282 and Alloy 718 which are subjected to a common heat treatment after being worked together. In this way, the desired strength for the Alloy 282 can be ensured, while a detrimental effect on the strength of the Alloy 718 due to this somewhat elevated temperature is limited. The resulting strength of the Alloy 718 component is mainly depending on the rate of cooling from the solution temperature and on the age-hardening step, shown in
It is noted that the mentioned temperature values and time indications are subject to certain tolerances. According to these tolerances, time values are given with an accuracy of ±10 minutes, and temperature values are given with an accuracy of ±14 degrees, due to the accuracy of the furnace. The holding time indicated for the different temperatures in the heat treatment method relates to the time period during which the whole component is at the prescribed temperature. The total time that a component is kept at a certain temperature will therefore depend on the size of the component.
In Tables 1 and 2, comparisons are shown for mechanical strength values obtained for Haynes 282 alloy heat treated according to the conventional method known in the art and for Haynes 282 heat treated with the method as described here within.
As can be seen from Table 1 and Table 2 the ultimate tensile strength and the yield strength of Haynes 282 after treatment with the method as described here within are improved as compared to corresponding characteristics for Haynes 282 heat treated according to the conventional method for Haynes 282.
Correspondingly, the ultimate tensile strength and the yield strength characteristics of Alloy 718 are only negligibly decreased by the use of an increased solution annealing temperature as compared to the conventional heat treatment method for Alloy 718.
A special advantage of the heat treatment method as described above with reference to
The heat treatment as described here within can be applied to a turbine exhaust case comprising multiple alloys prior to mounting within the engine. The finished turbine exhaust case, after being formed by joining portions of Alloy 282 with portions of Alloy 718 in desired portions is subjected to the heat treatment according to the method as described with reference to
The method described herein is not limited to components for the type of aircraft engine illustrated in
Further modifications of the heat treatment method and products and components resulting from application of the heat treatment method to various alloys within the scope of the claims will be apparent to the skilled person.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1703222.8 | Feb 2017 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/054978 | 2/28/2018 | WO | 00 |
