FR2899599A1 - Refractory composition useful for variety of turbine engine components and other machinery, comprises niobium and silicon - Google Patents

Abstract

A refractory composition comprises niobium and silicon. The silicon is present at less than 9 at.% based on total atomic percent. An independent claim is also included for turbine engine component formed of a material comprising an alloy of niobium and silicon (less than 9 at.% based on total atomic percent);and#niobium-silicide based composition comprising niobium, silicon, and titanium, hafnium, chromium, and/or aluminum; the composition comprises a metallic niobium-base phase and metal silicide phase(s) of the formula M3Si or M5Si3 M : Nb, Hf, Ti, Mo, Ta, W, and/or platinum group metal.

Description

Compositions comprising niobium and silicon, and components thereof

  The present invention relates generally to metals and metal alloys for use in high temperature applications. More specifically, this invention relates to niobium and silicon based compositions useful in various turbine engine components. For equipment operating at high temperature, for example turbine engines and other machines, various types of metals and metal alloys are used. The choice of a particular metal depends largely on the temperature conditions at which the component is projected to be exposed, as well as other specific requirements imposed on that component, with respect to its mechanical strength, creep resistance, resistance to creep, oxidation, its resistance to the surrounding environment, its weight, etc. Gas turbine engines are a good example of how the demands of a component can vary within a single complex piece of equipment. In a typical gas turbine engine, air is compressed in a compressor and mixed with a fuel, and the mixture is ignited in a combustion chamber to give very hot combustion gases. These gases pass downstream in a high-pressure turbine (HPT) comprising one or more stages, comprising a turbine distributor and rotor blades. The gases then pass into a low pressure turbine (LPT) which typically has several stages, each with its turbine distributor and rotor blades. For the "hot" areas of the turbine, where the metal is typically heated to temperatures as high as about 1150 C, nickel-based superalloys are often the materials of choice. On the other hand, in the compressor zones of turbine engines, where the temperatures are lower, for example below about 600 ° C., titanium alloys, which are lighter than nickel alloys, are often used.

  To meet higher performance requirements, it is necessary to increase the operating temperatures of turbine engines, and thus to develop new materials that can withstand being placed in a higher temperature environment. . Examples of such new materials include RMIC materials, inter-metal composite materials based on refractory metal, many of which are based on niobium and silicon, such as those described for example in US Patent No. 5,932 033 (Jackson & Bewlay), 5,942,055 (Jackson & Bewlay), and 6,419,765 (Jackson, Bewlay & Zhao). RMIC composites usually have a multi-phase microstructure. For example, this microstructure may comprise a niobium-based metal phase and one or more intermetallic metal silicide phases. As described by Bewlay & Jackson in US Pat. No. 5,833,773, there are sometimes, among the metal silicide phases, a silicide M3Si and a silicide M5Si3, the metal represented by M being niobium, titanium or hafnium. These materials are considered to be composites in which high strength, low tenacity silicides and a less resistant and tenacious niobium metal phase are combined. Their melting temperatures are up to about 1700 C, and they are less dense than many nickel alloys. These properties make them very promising materials for potential use in applications where temperatures exceed the current service limit of nickel-based superalloys. As mentioned above, certain sections of a turbine engine do not require the very high temperature resistance capabilities of many niobium-silicide alloys. For example, the low-pressure sections of a turbine are often exposed to temperatures of about 600 to 1000 C. These temperature conditions are not as severe as in the case of the hot areas of the turbine, but other properties of the components may become more important. For example, for low-pressure turbine components, there may be higher damage tolerance requirements than can be achieved by the typical niobium-silicide alloys contemplated for hot sections. In addition, the low temperature components may still require a relatively high level of mechanical strength, as well as other characteristics such as satisfactory oxidation resistance and creep resistance. It therefore appears that new niobium-silicide alloys, having a balance of properties more suitable for certain applications selected according to their operating temperature, would be welcome in the art. These compositions should provide good performance at intermediate operating temperatures, for example, from about 600 to about 1000 C, with respect to one or more properties, such as strength, ductility, and creep resistance. In addition, these compositions should be lighter than many of the nickel-based superalloys employed at operating temperatures of BPT and HPT. One of the objects of the present invention is a refractory composition comprising niobium and silicon, wherein the amount of silicon is less than about 9%, atomic percent based on the total composition. In certain embodiments of the invention, this composition is characterized by a microstructure comprising a niobium-based metal phase and at least one metal silicide phase of formula M3Si or M5Si3, where M represents at least one element selected from niobium, hafnium, titanium, molybdenum, tantalum, tungsten and platinum group metals as well as combinations of these elements. Another object of the invention is a turbine engine component, for example a gas turbine, consisting of an alloy based on niobium and silicon in which the amount of silicon represents less than about 9%, as a percentage atomic ratio to all the alloy. As used herein, the term "alloy" refers to a solid or liquid mixture of two or more metals, or one or more metals and one or more non-metallic elements.

  The following description provides further details of the various features of the present invention. The refractory composition of the invention comprises niobium and silicon. Silicon is present therein at an atomic percentage of less than about 9%, based on the entire composition. In some embodiments, there is at least about 0.5% silicon atoms. In other preferred embodiments, the atomic percentage of silicon is about 1 to 8.5%, and more preferably about 5 to 8.5%. But in other preferred embodiments, it is about 1 to 5% silicon atoms. In general, for some applications to turbine components, it appears that the presence of silicon in these relatively low proportions leads to significant improvements in component ductility and damage tolerance, when implemented in the intermediate temperature ranges, for example ranging from approximately 600 to 1000 C. In some preferred embodiments, the refractory composition of the invention further comprises at least one element selected from the group consisting of titanium, hafnium , chromium and aluminum. The choice of one or more of these elements and their amounts introduced into the composition depends on various factors, the most important of which are usually the performance requirements offered in a particular end use. It is usually to improve the resistance to oxidation at high temperature that titanium is used. The presence of titanium can also improve the intrinsic ductility of the metal phase. If there is, titanium is usually about 5 to 45 atomic percent of the entire composition. In some preferred embodiments, about 10 to 30% of titanium atoms are present. In some particularly preferred embodiments, there is about 15 to 25 atomic percent of titanium. Hafnium can serve as an element bringing, in solid solution, the mechanical resistance to the niobium-based metal phase. Hafnium can also reduce internal oxidation of the metal phase, as well as improve creep resistance. If there are any, the hafnium usually represents about 1 to 20 atomic percent of the total composition. In some preferred embodiments, there is about 2 to 15 atomic percent of hafnium. In certain particularly preferred embodiments, there is about 2 to 10 atomic percent of hafnium. Chromium is usually used to improve the resistance to oxidation. In the niobium-silicide compositions of the present invention, the presence of chromium can promote the formation of a silicon-modified chromium Laves phase of the type disclosed in Jackson et al US Patent No. 5,942,055. . The presence of a Laves phase may be desirable from the point of view of oxidation resistance. If there are, the chromium is usually about 1 to 25 atomic percent of the entire composition. In some preferred embodiments there are about 5 to 15% chromium atoms. In some particularly preferred embodiments, there is about 5 to 10% chromium atoms. As indicated above, there may also be aluminum in the niobium-silicide compositions of the invention. Aluminum can also improve the resistance to oxidation. If there is, aluminum usually represents about 1 to 20 atomic percent of the total composition. In some preferred embodiments, there is about 5 to 15% aluminum atoms. In some particularly preferred embodiments, there is about 5 to 10% aluminum atoms. In some cases, the refractory composition described herein further contains at least one platinum group metal. As used herein, the term "platinum group metal" refers to the following metals: rhenium, osmium, iridium, platinum, ruthenium, rhodium and palladium. Platinum-bearing metals can be used to improve various properties, such as strength, eg tensile strength, oxidation resistance, workability, ductility, toughness, fatigue resistance and creep resistance. The proportions of metals in the platinum group may vary significantly depending on the requirements imposed by the end use, for example as these requirements relate to the properties mentioned above. Usually there is about 1 to 30% metal atoms of the platinum group. In some preferred embodiments, there is about 1 to 25% metal atoms of the platinum group. In certain particularly preferred embodiments, there is approximately 1 to 15 atomic percent. Of the platinum group metals, platinum, rhenium and ruthenium are a preferred subset. Rhenium and ruthenium are sometimes particularly interesting because of their ability to significantly increase the mechanical strength of these low silicon content compositions, while providing them with acceptable ductility. Rhenium is a particularly preferred platinum metal for some embodiments of the present invention. The proper proportion of rhenium depends on the factors mentioned above. If present, rhenium usually represents up to about 20 atomic percent of the total refractory composition. In many embodiments, there is preferably about 1 to 15% rhenium atoms, and more preferably about 1 to 12% rhenium atoms. In some embodiments, the refractory composition of the invention further comprises at least one member selected from the group consisting of tungsten, tantalum and molybdenum. These elements often help to increase the tensile strength of the metal phase, and the creep resistance of both the metal phase and the intermetallic phase. But their presence may also result in increasing the weight of the alloy produced, particularly in the case of tantalum and tungsten. In addition, at certain levels, these metals can reduce the resistance to oxidation. Therefore, the appropriate amount of each of these elements depends on various requirements imposed by the end use. Usually, tungsten, tantalum and molybdenum each represent less than about 30 atomic percent of the total composition. In some preferred modes of

  7, there is approximately 1 to 25 atomic percent. In some particularly preferred embodiments, there is about 1 to 20 atomic percent of each. Together, their total amount is usually less than about 40 atomic percent, and most often less than about 30 atomic percent of the composition. In some embodiments, the refractory composition further comprises at least one rare earth element, namely lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium, the latter being here also considered to be part of the rare earths group. The rare earth elements can improve the oxidation resistance, for example the resistance to internal oxidation, as well as the adhesion of the oxide particles to the parent component. They can also improve ductility. Rare earth elements are usually used in relatively small amounts, for example, less than about 10 atomic percent of the total composition. In some preferred embodiments, there is about 0.1 to 5 atomic percent of each of the rare earth elements present. For some embodiments, it is preferred to use, among all rare earth elements, yttrium, terbium, dysprosium and erbium. The refractory composition may also contain other elements, for example at least one of the elements boron, carbon, germanium, zirconium, vanadium, tin, nitrogen, iron and indium. These elements are usually employed in amounts which represent, for each of them, about 0.1 to 15 atomic% of the total composition, the proportion of zirconium being up to about 20% by weight. atoms. These elements improve, by their presence, one or more characteristics. For example, an interstitial element such as boron can improve oxidation resistance, as can vanadium. In addition, carbon can improve creep resistance as well as tensile strength. Nitrogen addition can help stabilize an Nb5Si3 phase within the alloy, as described in US Patent Application Serial No. 2006/0042725 No. 10/932128 (RD-27,311-1), filed on Aug. name of Bernard Bewlay et al. Some of these elements may also enhance the temperature range in which one or more phases are stable within the refractory product. For these elements, the following ranges of proportions can be given by way of nonlimiting examples, expressed in atomic percentages relative to the entire composition: up to about 9% in boron atoms; up to about 9% carbon atoms; up to about 12% germanium atoms; up to about 15% zirconium atoms; up to about 7% vanadium atoms; up to about 6% tin atoms; up to about 10% nitrogen atoms; up to about 12% iron atoms; and up to about 6% indium atoms. Furthermore, it is well known to those skilled in the art that other elements are inevitably present in the compositions of the invention in minute amounts as impurities from, for example, commercially available alloys or implemented. The compositions containing these additional impurities may also be considered as part of the invention, insofar as these impurities do not adversely affect the characteristics of the compositions described herein.

  In what follows, some particular compositions of the present invention are preferred in some embodiments. All proportions indicated are percentages by atoms, the total of 100% by atom corresponding to the overall composition. Each of the compositions may contain other elements than those indicated. Composition I: approximately 1 to 8.5% of silicon, approximately 10 to 30% of titanium, approximately 1 to 25% of chromium, approximately 1 to 20% of aluminum, approximately 1 to 15%, in total, of platinum group metals, approximately 2 to 10%, in total, of tungsten, tantalum and molybdenum, and the niobium supplement.

  Composition II: about 1 to 8.5% silicon, about 10 to 30% titanium, about 1 to 10% hafnium about 1 to 25% chromium, about 1 to 20 About 1 to 15% of aluminum, about 1 to 15%, of platinum group metals, about 2 to 10%, in total, of tungsten, tantalum and molybdenum, and the niobium supplement.

  Composition III: about 1 to 8.5% silicon, about 15 to 25% titanium, about 2 to 15% chromium, about 2 to 15% aluminum, about 1 to about 15% 12% platinum group metals, and the niobium supplement. Composition IV approximately 2 to 8.5% of silicon, approximately 12 to 30% of titanium, approximately 5 to 10% of chromium, approximately 5 to 10% of aluminum, approximately 2 to 15% zirconium, about 0.1 to 5% iron, about 1 to 12% rhenium, about 0.1 to 6% tin, about 0.1 to 5% of carbon, and the complement of niobium. Composition V about 2 to 8.5% silicon, about 12 to 30% titanium, about 1 to about 0% hafnium about 5 to 10% chromium, about 5 to 10% % aluminum, about 2 to 15% zirconium, about 0.1 to 5% iron, about 1 to 12% rhenium, about 0.1 to 6% tin, about 0.1 to 5% carbon, and the niobium complement. As mentioned above, the refractory compositions or alloys of this invention are sometimes characterized by a multi-phase microstructure. In general, this microstructure comprises a niobium-based metal phase and at least one metal silicide phase of formula M3Si or M5Si3, where M represents at least one element selected from the group consisting of niobium, hafnium, titanium, molybdenum , tantalum, tungsten and platinum group metals, and combinations of these metals. Very often, the metal silicide phase comprises a Nb3Si phase or a Nb5Si3 phase, or a combination of these two phases. But some of the alloys described in this document also include other phases. For example, they may include a silicon-based Laves phase based on chromium. Such a phase promotes oxidation resistance, as disclosed in Jackson & Bewlay US Pat. No. 5,932,033. By the choice of phases and constituent elements of the alloys obtained from the refractory compositions, it is intended to achieve an equilibrium of the properties which are important for a particular end application. Primary properties, such as strength (tensile strength and impact strength), toughness, density, oxidation resistance and creep resistance, have been reported above. As stated in U.S. Patent No. 5,833,773, all the elements mentioned above are distributed at various degrees between the different phases of the alloy. The processes for preparing the refractory compositions and alloys of the present invention are well known in the technical field under consideration. There are non-limitative illustrations

  The processes for preparing the refractory compositions and alloys of the present invention are well known in the art. Non-limiting illustrations of these preparation techniques are found in the examples of the following patents: US 6,419,765 to Jackson et al. ; U.S. 5,833,773 to Bewlay et al. ; and US 5,741,376 to Subramanian et al. The constituents of the alloy, in elemental form, are often combined by melting them in a crucible using a suitable technique, such as arc fusion, electron beam melting, plasma fusion, and induction melting. . But other techniques or combinations of techniques can be employed to prepare the alloy compositions. It is possible, for example, to use powder metallurgy techniques such as grinding or atomization, for example gas atomization, as well as deposition techniques from a vapor phase. According to various techniques, the alloy product can be processed and shaped into the desired part. For example, the molten alloy can be cast in a suitable apparatus. Casting mold assemblies are well known in the art. An example of this can be found in U.S. Patent No. 6,676,381 to Subramanian et al. But we can use many casting techniques. Moreover, specialists in this field are familiar with the various operational details concerning any particular casting technique. In some preferred embodiments, the molten metal is solidified according to a directional solidification technique. These directional solidification techniques are well known to those skilled in the art, such as the Bridgman technique, and are described, for example, in US Pat. Nos. 6,059,015 and 4,213,497 to Sawyer.

  Various other techniques, used alone or in combination, can be used to process the alloy products. By way of non-limiting example, mention may be made of extrusion, for example hot extrusion, forging, hot isostatic pressing and rolling. It is familiar to those skilled in the art. Refractory compositions with low silicon content can be formed into various components. Many of these can be used in turbines, for example, land-based turbines, marine turbines and aeronautical turbines, but they can also be used elsewhere than in turbines. These components can greatly benefit from the improvements provided by the invention with respect to mechanical strength, ductility and creep resistance at selected operating temperatures. Such components therefore constitute another object of this invention.

  Particular examples of turbine components include, but are not limited to, nozzles, nozzles, vanes, rotors, vanes, stators, fairings and combustion chambers. In the foregoing, certain preferred embodiments of the invention have been indicated merely as illustrations, without limiting the scope of the invention. Therefore, one skilled in the art may consider various modifications or adaptations without departing from the scope of the present invention.

Claims (12)

  A refractory composition comprising niobium and silicon, wherein the amount of silicon is less than about 9 atomic percent of the total composition.   The composition of claim 1, further comprising at least one member selected from the group consisting of titanium, hafnium, chromium and aluminum.   The composition of claim 2 wherein the amount of titanium is from about 5 to about 45 atomic percent of the total composition.   The composition of claim 2 wherein the amount of hafnium is from about 1 to 20 atomic percent of the total composition.   The composition of claim 2 wherein the amount of chromium is from about 1 to 25 atomic percent of the total composition.   The composition of claim 2 wherein the amount of aluminum is from about 1 to about 20 atomic percent of the total composition.   The composition of claim 2, further comprising at least one platinum group metal selected from the group consisting of rhenium, osmium, iridium, platinum, ruthenium, rhodium and palladium.   The composition of claim 2, further comprising at least one member selected from the group consisting of tungsten, tantalum and molybdenum.   The composition of claim 2 further comprising at least one rare earth metal.   The composition of claim 2, further comprising at least one element selected from the group consisting of boron, carbon, germanium, zirconium, vanadium, tin, nitrogen, iron and indium.   11. Composition according to claim 1, characterized by a microstructure comprising a niobium-based metal phase and at least one metal silicide phase of formula M3Si or M5Si3, where M represents at least one element selected from the group consisting of niobium, hafnium, titanium, molybdenum, tantalum, tungsten and platinum group metals, and their combinations.   12. turbine engine component, formed of a material comprising a composition according to one of claims 1 to 11.