Patent Application
20110165012
This application claims priority under 35 U.S.C. §119(a)-(d) or (f) to prior-filed, co-pending Italian application number CO2009A000027, filed on Jul. 29, 2009, which is hereby incorporated by reference in its entirety.
1. Field of Invention
This invention relates to a new nickel-based superalloy and to a method to obtain it.
The invention also relates to a mechanical component made with the above mentioned superalloy, a piece of turbomachinery where the component will be fitted and a specific application method.
2. Description of the Prior Art
Usually in the field of materials technology, the problems related to the creation of mechanical components which work at high temperatures are solved by using cooling systems or thermal barriers in order to cool the material which they are made of, thus increasing the mechanical resistance. As a matter of fact, at a high temperature the life of the component is shortened if a cooling system is not planned adequately; it might be necessary to lower the temperature during use to extend the life of the component up to a standard value.
Many types of alloys, which are combinations of several elements in which at least one is a metal, have been developed in order to try to obtain a material which, at a high temperature when in use, will show high mechanical resistance and at the same time specific characteristics related to chemical resistance (against corrosion, erosion, or others) based on the specific application. More specifically, in case of turbomachinery components, the use of cooling systems entails complex production processes, and entails a decrease in performance of the specific piece of machinery; this proves that the choice of material which the components are made of is fundamental.
Nickel superalloys are special alloys developed to cope with high temperatures, designed to have good mechanical resistance coupled with high resistance against oxidation at temperatures of around 1000° C., and they are mostly used in the aeronautical and/or aero spatial fields (albeit not exclusively). These nickel-based superalloys include a very wide category of metal based alloys, which are constantly undergoing improvements and research, because the chemical elements involved can be associated differently, based on quantity and number, in a very malleable way, thus obtaining gradual differences based on the specific combination or mixture of elements.
Thus, currently, despite the progress in technology, this issue is still problematic and the necessity to create improved nickel-based superalloys is imperative. The need of superalloys having higher mechanical, chemical and thermal resistance in order to produce more cost effective and better performing pieces of machinery arises.
One of the purposes of the invention is creating a nickel-based superalloy which will allow operations at higher temperatures than the traditional ones, improving, at the same time, mechanical and chemical resistance and partially overcoming some of the above mentioned issues.
Further purposes of this invention are: the creation of a method to produce such superalloy, the creation of a mechanical component made of this superalloy and the creation of a piece of machinery in which said component will be fitted. These purposes and advantages are practically reached through a superalloy based on Claim 1, obtained through a method described in Claim 6 with a component as indicated in Claim 8, with a piece of machinery based on Claim 9 and with a specific application method as indicated in Claim 10.
The technical advantages of this invention are stated in the Claims listed below.
A main aspect of this invention is the production of a nickel-based superalloy suitable for the creation of mechanical components which will be used at high temperatures, around 1200° C., in a piece of turbomachinery. As indicated in the invention, this superalloy includes at least the following elements, in a quantity which is expressed in percentage by weight (below and in the attached claims the percentages indicated are per weight, if not indicated differently): Chromium (Cr) between 3% and 7%, Tunngsten (W) between 3% and 15%, Tantalum (Ta) between 4% and 6%, Aluminium (Al) between 4% and 8%, carbon (C) less than 0.8%, the remaining percentage of Nickel (Ni) and, in addition, possible impurities.
A very convenient application of the invention is the one in which the superalloy includes Yttrium(III) oxide, also called “Yttria” (chemical formula Y2O3), in a percentage by volume ranging from 0% to 15%, preferably from 0% to 7%, and even more preferably from 0% to 6% in order to enhance the mechanical resistance of the superalloy at high temperatures.
Yttrium(III) oxide is, in a few words, a whitish solid substance which is stable in air, used in several technological fields, such as, for example, in the production of microwave filters or superconducting metals (due to its capacity to become a superconductor at high temperatures), or for the production of some types of organometallic compounds (transforming it into Yttrium(III) chloride, chemical formula YCl3). In another convenient application of the invention, the superalloy includes Rhenium (Re) in a percentage by weight ranging from 0% to 10%, preferably from 3% to 7%, and even more preferably from 4% to 6% so that the mechanical resistance at high temperatures will be enhanced.
Rhenium, in a few words, is a rare, heavy white-silver metal, having a melting point among the highest of all elements, and lower only than the ones of tungsten and carbon. It is also one of the densest metals, surpassed only by platinum, iridium and osmium. Rhenium was the last naturally occurring element to be discovered. It is normally marketed in a powder, which can be compacted by pressure or void sintering, in a hydrogenated atmosphere. Rhenium is not free in nature, and it cannot be found in typical minerals. The quantity which can be found on the earth's crust is of around 0.001 ppm which is to say of around one milligram per ton. It is mainly extracted from the fumes produced by the roasting of minerals containing copper sulphide and of some minerals containing molybdenum, which happen to contain between 0.002% and 0.2% of Rhenium; it can be obtained, for example, from the reduction of ammonium perrhenate with hydrogen at high temperatures. Its purification process is difficult and expensive. The main applications of this element are: the creation of platinum-rhenium catalysts for gas production; the production of filaments and detectors of ions for mass spectrometers; additive for tungsten or molybdenum based alloys to create super conduction alloys; catalyst for hydrogenation processes, to create electric contacts, due to the good wear resistance and resistance against corrosion; an element in the production of thermocouple thermometers which measure temperatures up to 2200° C. and many other applications.
In a very convenient application of this invention, this superalloy includes tungsten in a percentage by weight ranging from 4% to 6% or from 9% to 11% based on the quantity of rhenium, please see below.
In another application the superalloy has at least one of the below mentioned elements in the following percentage by weight: chromium (Cr) between 4% and 6%, tantalum (Ta) between 4.5% and 5.5%, aluminium (Al) between 5% and 7%, carbon below 0.1%. In a specific application the above mentioned alloy, preferably of an equiaxial type, microadditions of hafnium (Hf), zirconium (Zr) and boron (B) might be performed, up to a maximum total of 2%, in order to improve the mechanical specifications based on the specific application.
From another aspect, this invention is related to a method to create a nickel-based superalloy, which includes a step in which the following elements are mixed in the quantity indicated below, (percentage by weight): chromium (Cr) between 3% and 7%, tungsten (W) between 3% and 15%, tantalum (Ta) between 4% and 6%, aluminium (Al) between 4% and 8%, carbon (C) less than 0.8%: the remaining percentage of nickel (Ni) and, in addition, possible impurities. Additional steps might include mixing the superalloy with at least one of the following elements:
In a very convenient application of this invention, this superalloy is obtained through “fusion”. “Fusion” refers to those productive processes also called “foundry works” which create casting spouts, for example in sand (called “sand work”), in metal (also called “in shell”) or under pressure (“die casting”) and many others.
In detail, this superalloy can be created through foundry works called “lost-wax microfusion” which consists in:
The thermal cycle at a high temperature might be performed following several heating procedures, such as free flame fusion, inductive fusion, fusion on a substrate heated by electric resistance, arc lamp fusion between tungsten electrodes in agglomerate, and many others thereof.
Casting might be carried out through gravity, through gas pushing the alloy, through depression, or also through centrifugal pushing and many others thereof. The solidification process, whether dealing with “lost-wax microfusion” or with any other foundry procedures, can be controlled in order to obtain a single crystal, an equiaxial or a directional solidification, as it will be explained below. In detail, a single crystal microfusion allows obtaining a superalloy with good specifications for all the grain boundaries phenomena (such as for example low creep) with high resistance against oxidation and against mechanical and chemical stress as well as against many other phenomena; on the other hand though, the procedure to obtain such results is complex and expensive. On the other side, the equiaxial fusion is such as to create a more cost effective superalloy which is also easier to produce, but having a lower resistance if compared to the one obtained through single crystal microfusion. Directional microfusion, on the other side, assures a better resistance based on the preferred grain direction. The main advantages of a foundry work, being it “lost-wax” or some other type, are that it is possible to control the cooling to obtain an alloy with good specifications, and at the same time it will be possible to create complex shapes without having to engage in elaborate mechanical works. The possible presence of microporosity, unevenness or undesired phase precipitates entails accurate checks both of the process and of the product.
In a very convenient application of this invention, this superalloy is obtained through “dust metallurgy”. “Dust metallurgy” is the production process through which metal (or ceramic) manufactured products are obtained through the thermo-mechanical treatment of their dusts.
In detail, this superalloy can be created through hot compression in order to compact the powders through a “sintering” process which mainly consists in:
The main advantages of dust metallurgy are that it minimizes or eliminates the need of mechanical work, it happens to be cost effective especially for geometrically complex shapes, and it is possible to obtain a wide choice of materials and final treatments with a good finish and a good reproducibility for each piece, characteristics which fit the requirements for chain production.
The disadvantages are, on the other side, mostly due to the lower mechanical specifications of the finished product and to the lower dimensional precision if compared to the products which are created by fusion. Both in case of foundry work and dust metallurgy, it is possible to include further treatments on the finished component, such as, for example, rectification, lapping, polishing, calibration or any other mechanical finishing treatments, as well as treatments to complete the shape (in case of geometrical restrictions which happen not to be compatible with matrix compression), or thermal treatments aiming at optimising the specifications of the material, as well as many other treatments.
Furthermore, protective coatings might be applied on this superalloy (or better on the finished product made of this superalloy) based on the specific use it is designed for. Another interesting aspect of this invention is the creation of a mechanical component of a piece of turbomachinery made of the above mentioned superalloy which can endure high temperatures while in use (up to about 1200° C. or slightly higher). Another aspect of this invention is the one regarding a piece of turbomachinery in which at least one mechanical component is created with the above mentioned superalloy, such as a gas turbine for example, or many others thereof.
It cannot be excluded that the above mentioned superalloy might be used in other applications or technological fields, where the use of materials which can endure high temperatures (up to about 1200° C.) is required or where high mechanical stress and oxidation and/or corrosion are involved.
Another aspect of this invention relates to a method created to improve the performances of a gas turbine, through the substitution of some parts of its statoric components, which might have created issues at high temperatures, with parts made of a superalloy, as indicated in this invention. Please refer to the description below.
One of the advantages in using a superalloy, as described in this invention, is that, if compared with the nickel-based superalloys, the one described in this document gives the opportunity to raise the temperature of use of a turbomachine component up to about 1200° C. thanks to its composition, which was created ad hoc.
Actually, such superalloy shows a good resistance against oxidation and a high mechanical resistance, at least up to the highest temperature indicated.
In detail, looking at its composition, this superalloy allows to improve at least the following characteristics:
Thus, it is possible to raise the typical temperature of use (which is not possible with the actual commercial alloys in the turbomachinery field) and to extend the life of the components on equal terms of use, or to reduce remarkably the cooling of the components; consequently the component is simplified and there is less request for a lower protection using thermal barriers.
The advantages arising from using materials characterized by specifications which allow their use at high temperatures are several and they can be summarized in the following list:
Each one of these technical aspects entails a corresponding economic benefit.
Another advantage is that this superalloy is very versatile, because it can be used either to create machinery or a newly designed component or to implement an improvement of an already existing machine or component. In general the invention can be used in all fields in which an adequate resistance against high temperatures is required, both in terms of mechanical specifications and in terms of resistance against oxidation and corrosion.
Further convenient specifications and ways to apply this method as well the devices indicated in the invention, are described in the attached claims, and will be described in detail below referring to some non limiting examples.
The numerous purposes and advantages of this invention will be more evident for the experts in this field if they refer to the schematic drawings attached, which show practical, non restrictive examples. In the drawings:
A first superalloy created as a first application of the invention was called Ni29 and includes at least the following elements: chromium (Cr) at 5% (in weight); tungsten (W) at 10%; tantalum (Ta) at 5%; rhenium at 0%; aluminium (Al) at 6%; carbon at 0.05% and eventually yttrium(III) oxide (Y2O3) between 0.5% and 2% (this last one in volume).
A second superalloy created as a second application of the invention was called Ni32 and includes at least the following elements:
chromium (Cr) at 5% (in weight); tungsten (W) at 5%; tantalum (Ta) at 5%; rhenium at 5%; aluminium (Al) at 6%; carbon at 0.05% and eventually yttrium(III) oxide (Y2O3) between 0.5% and 2% (this last one in volume).
In detail the quantity of tungsten can be balanced with the one of rhenium in an inverse proportion, for example setting 5% of tungsten when rhenium is at 5% and setting it at 10% when rhenium is not there. It cannot be excluded that a quantity of cobalt (Co) will be included, less than 5% (in weight), based on the specific application. Please note that the indication of the composition of the superalloys is only explicative and not limitative for the invention, because it can vary based on the specific application or procedures used in the application itself.
In detail, line 1A is related to the commercial cobalt based alloy FSX414; line 1B in related to the commercial nickel-based alloy GTD222; line 1C is related to the commercial SC Renè N4. Line 1D relates to alloy Ni32 created with the single crystal procedure; line 1E relates to alloy Ni29 created with the single crystal procedure, curve 1F relates to alloy Ni32 following the equiaxial procedure with micro-additions of Hf and Zr, point 1G relates to alloy Ni32 created through dust metallurgy followed by hot extrusion.
Please note, observing the graph, how the invention in its different forms, shows specifications of mechanical resistance almost comparable to the best commercial products and, at the same time, it shows a better resistance to oxidation (please see following figures as well). Furthermore, based on the specific necessities of the project, it is possible to enhance the specifications of the alloy by simply modifying the production process, for example single crystal, equiaxial process and many others thereof. In order to enhance mechanical properties, the production of the invention in its microfused single crystal form, is preferable.
From this graph it is possible to see how alloys created following the procedure implemented by the invention show a resistance against oxidation which is higher than the one of commercial alloys for high temperatures, exception made for alloy PM2000 which has very low mechanical specifications at high temperatures.
It seems evident, from this graph, that the specific production technology affects the resistance against oxidation. In detail, it is advisable to produce the invention through dust metallurgy to optimise the resistance against oxidation without excessively degrading the mechanical properties.
In detail, the first line 4A shows the behaviour of the equiaxial Ni29; a second curve 4B shows the behaviour of the equiaxial alloy Ni32; a third curve 4C shows the behaviour of alloy Ni29 containing less carbon (around 0.005%); a fourth curve 4D shows the behaviour of alloy Ni32 containing less carbon (about 0.005%); a fifth curve 4E shows the behaviour of microfused equiaxial alloy Ni29 which underwent hot isostatic pressing (HIP); a sixth curve 4F shows the behaviour of microfused equiaxial alloy Ni32 which underwent HIP; a seventh line 4G shows the behaviour of single crystal microfused alloy Ni29; an eight line 4H shows the behaviour of the single crystal microfused alloy Ni32.
Please note, in this graph, how the variations more or less substantial in the chemical composition within the intervals indicated in the invention, as well as the difference in the microfusion process, allow to create different specifications when undergoing cyclical oxidation.
In detail, a first line 6A shows the behaviour of alloy Ni29; a second line 6B shows the behaviour of alloy Ni32 containing 2% (in volume) of Y2O3; a third line 6C regarding the Ni32 alloy containing the 5% (in volume) of Y2O3; a fourth line 6D of alloy Ni32 showing 10% (in volume) of Y2O3; a fifth line 6E of alloy Ni32 containing 20% (in volume) of Y2O3; a sixth line 6F of alloy Ni32 containing 40% (in volume) of Y2O3.
Please note how a high concentration of Yttrium(III) oxide, exceeding 20%, decreases the resistance against oxidation.
In detail, the first line 7A shows the behaviour of alloy MA754; a second line 7B shows the behaviour of alloy MAR-M200; a third line 7C shows alloy MA956; a fourth line 7D alloy HA188; a fifth line 7E alloy PM1000; a sixth line 7F alloy PM2000 and a seventh line 7G alloy MA758. Point 7H shows the results achieved with single crystal Ni20 and point 7L the results achieved with single crystal Ni32 (almost overlapping the graph); point 7L shows alloy Ni29 created through dust metallurgy followed by hot extrusion and point 7M shows equiaxial alloy Ni29. Please note that the mechanical properties at high temperatures are comparable to the ones of commercial alloys showing, in the “single crystal” case, better specifications.
Cooling systems for the nozzles can also be implemented; these consist of a set of holes 116 through which cooling gas circulates from the inside towards the outside parts of this component so that the life of the component itself will be extended. Based on the procedure indicated in the invention, moulded insets 118 are included in the device—shown in an exploded view in
These insets 118 can be included in the project of a new component or, as an alternative, can be fitted in a used component to extend its life.
The mechanical system 100 is obviously shown as an exemplification, the alloy described in the invention is suitable to create other components or other mechanical systems based on the specific applications and needs.
It is agreed that the illustration is only an indication and that it does not, in any way, limit the possibilities of the invention, which can vary in form and ways always being pertinent to the foundation at the base of the invention itself. The possible presence of referral numbers in the claims has the only purpose to facilitate reading in the light of the previous descriptions and of the attached drawings and it does not limit, in any way, the scope of protection.
| Number | Date | Country | Kind |
|---|---|---|---|
| CO2009A000027 | Jul 2009 | IT | national |
