JPH10500453A - Nickel-aluminum-base alloy between metals - Google Patents

Abstract

  (57) [Summary] The present invention relates to an intermetallic nickel-aluminum-based alloy whose structure consists mainly of a two-phase NiAl phase and further has the elements chromium and tantalum. The total content of elemental tantalum and chromium is at most 12 atomic%. Preferred contents are 0.3 to 3.8 atomic% tantalum and 1.0 to 9.0 atomic% chromium. This intermetallic nickel-aluminum-based alloy is distinguished by a high oxidation resistance, especially at high temperatures, for example of 1350 ° C. This alloy is therefore suitable for the production of components which are subjected to high-temperature continuous loads, for example gas turbine blades. Due to the high oxidation resistance, an additional oxidation protection film can be omitted if required.

Description

The present invention relates to an intermetallic nickel-aluminum-based alloy having two-phase NiAl. The invention further relates to the use of this intermetallic nickel-aluminum-based alloy. German Patent Application Publication No. 182,144 describes a method for producing a high strength nickel-aluminum material with good oxidation resistance. In this method, nickel powder is mixed with aluminum powder, followed by pressing and cold working to produce a self-supporting monolithic body having a fibrous or lamellar structure. The nickel component is at least 80% and the aluminum component is at most 20%. The monolith is subsequently hot worked at an elevated temperature. In this case, in addition to a solid solution of aluminum in nickel, in particular the compound Ni ₃ Al is formed. The solid solution and the compound Ni ₃ Al were confirmed by X-ray analysis. It is not clear from this publication whether other compounds can be obtained between nickel and aluminum in this way. An object of the present invention is to improve the thermo-mechanical properties of a nickel-aluminum alloy. This includes, in particular, heat resistance, oxidation resistance and thermal shock resistance. It is another object of the present invention to provide an application of such an improved nickel-aluminum alloy. According to the invention, the problem addressed by nickel-aluminum alloys is mainly that of two-phase NiAl and additionally chromium and tantalum, with the total content of chromium and tantalum being up to 12 at. The solution is an intermetallic nickel-aluminum-based alloy. The component amount of the two-phase NiAl is preferably 70 to 95 atomic%, especially 85 to 90 atomic%. The preferred content of tantalum or chromium is 0.1. It is 3 to 3.8 atomic% to 1.0 to 9.0 atomic%. Within this range, 0. It is advantageous to use 3 to 0.9 at% tantalum and 1.0 to 3.0 at% chromium to 1.7 to 3.0 at% tantalum and 6.0 to 9.0 at% chromium. is there. In this case, the ratio of tantalum to chromium is preferably less than 1: 3. With such a ratio, the concentration of the substitution element in NiAl becomes maximum. The addition of tantalum and chromium results in the deposition of coarse multilayer Laves phases in which the elements Ni, Al, Cr and Ta can participate in the grain boundaries of the two-phase NiAl of the intermetallic nickel-aluminum-based alloy. In addition, fine Laves phase and α-chromium precipitates are added in the NiAl particles. In this case, the structure advantageously consists of 5 to 11% by volume of Laves phase, 3 to 10% by volume of precipitates in NiAl and the balance NiAl. In particular, a structure with about 11% by volume of Laves phase and about 10% by volume of precipitates in NiAl and the balance of NiAl on the grain boundaries has been found to be advantageous. A further improvement of the specific properties is additionally when the alloy contains at least one element from the group of iron, molybdenum, tungsten and hafnium in an amount of up to 1 at.% Each and not more than 3 at. Is achieved. In addition, the alloy may have trace elements such as oxygen, nitrogen and sulfur, as well as manufacturing-related impurities. By adding tantalum and chromium at the respective contents described above, the above-mentioned coarse or fine multilayer Laves phase and α-chromium are formed. These precipitates are usually found on wedge points of various NiAl particles. If the amount of the alloying element tantalum or chromium is larger than the above-mentioned amount, the amount of the components of the precipitate may increase to an undesirable extent. Significant increases in the volume content of the Laves phase result in a cellular structure in which the Laves phase assumes the matrix function. Excessive amounts of Laves phase in the structure weaken and degrade the intermetallic alloy. By adding one or more elements from the group of iron, molybdenum, tungsten, niobium and hafnium to 1 at% each, and not exceeding 3 at% in total, the strength in the case of short-time loading is improved. Can be achieved. Of course, the creep resistance is reduced. The addition of hafnium results in an improved adhesion of the oxide film after the initial corrosion. The problem directed to the use of the alloys is solved according to the invention by producing components of gas turbines, in particular components subjected to high temperature loads, such as gas turbine blades, with NiAl-based alloys. Components of gas turbines, especially turbine blades, made from the base alloy are particularly suitable for continuous use at high temperatures, for example above 1100 ° C., in particular 1350 ° C., due to their high oxidation resistance. In each case, unlike a superalloy, an additional coating with a protective film can be omitted, if desired. Thus, turbine blades made from a unitary element without an additional film thereon are extremely easy to manufacture, and the coupling between the individual films is less than that of a turbine blade consisting of multiple films. The problem is solved. Intermetallic nickel-aluminum-based alloys are also generally suitable as materials for the manufacture of articles that need to exhibit high strength, high heat resistance, good toughness, good oxidation resistance and good thermal shock resistance. The strength in this case is 600 MPa or more at room temperature with a 0.2% elongation limit. The heat resistance is 800 ° C. at an extension limit of 200 MPa or more and 0.2%, and 1000 ° C. at 90 MPa or more. The toughness is at least 7 MPa / m and the oxidation resistance is of the order of 5 · 10 ⁻¹⁴ g ² c ⁻⁴ s The following examples illustrate the intermetallic nickel-aluminum-base alloy in detail. The composition of the tested alloys (atomic%) is shown in Table 1 below. Texture formation, ie, particle size, precipitate distribution and precipitate size, varies significantly with the manufacturing process. The distribution of Laves phase particles is homogenized by the use of thermodynamic processing, extrusion presses (SP) or powder metallurgy production routes (PM). The mechanical properties of the alloy also depend significantly on the manufacturing process chosen. The following production routes were performed for these alloys. -Directional hardening as a possibility to create a defect-free structure by casting techniques. The process parameters correspond to those of the superalloys (see Faudey Förtschlitzbergicht, No. 264, Waud Paul, Faudey Publishing). Powder metallurgy by dilution of the inert gas at 1250 ° C. and subsequent hot isostatic pressing. Extrusion press at 1250 ° C. for homogenizing the tissue and adjusting the size of the constant particle size. -Multiaxial stress conditions and pressure sintering at 1100 ° C. Directional cured samples have a distinctly higher strength, whereas, for example, extruded materials exhibit reduced or significantly lower strength. Table 2 below shows the 0.2% elongation limits in the squeeze tests for various alloys and NiAl. Table 3 shows the creep resistance (in MPa) of the tested alloys in the pressure test (second-order stationary creep resistance as a function of the elongation rate at 1000 ° C. and 1100 ° C. (fluorescent l / s)). . The creep resistance of these alloys is higher than the creep resistance of the intermetallic phase to be compared, for example higher than that of the two-phase NiAl or NiAlCr alloy. Table 4a shows a comparison of the 0.2% elongation limit (in MPa) in a pressure test of a conventional superalloy, a two-phase NiAl alloy and a NiAl-Ta-Cr alloy. The advantage of the alloy according to the invention at temperatures above 1000 ° C. is clearly evident for the 0.2% elongation limit. Pressurization test of superalloy, two-phase NiAl alloy and developed NiAl-Ta-Cr alloy It is shown in the following Table 4b. Compared to conventional superalloys, NiAl-Ta-Cr alloys have the advantage of having sufficient strength even at 1050 ° C to 1150 ° C or higher. The alloy does not experience a sudden loss of strength due to the dissolution of the hardened phase. Table 5 shows a comparison of the values known from the industrial data for various ceramics and NiAl-Ta-Cr alloys processed and produced by powder metallurgy. The toughness of the intermetallic NiAl-based alloy is clearly better than the measured data for two-phase NiAl and SiC. The alloy according to the invention has good oxidation resistance on the order of ^{5.10 14} g ² c ^-4 s. This is therefore equal to or better than the oxidation resistance of the two-phase NiAl. Therefore, a protective film made of, for example, a ceramic material is unnecessary even at a high temperature as compared with a superalloy. This solves the problem of bonding between the ceramic component and the metal component. In addition, sufficient thermal shock resistance is shown. At 1350 ° C., 500 temperature cycles have been achieved with this alloy without material damage.

────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventors Sauthof, Gerhard             Germany Day 40880 Latin             Gen Haselnusweg 1 (72) Inventor Tuoimer, Benedict             Federal Republic of Germany Day-40211 Deutz             Seldorf Schützienstraße 49

Claims (1)

[Claims] 1. An intermetallic nickel-aluminum-based alloy mainly composed of two-phase NiAl, having a structure containing chromium and tantalum, and having a content of both chromium and tantalum up to 12 atomic%. 2. 2. The alloy according to claim 1, wherein the total amount of the two-phase NiAl in the structure is 70 at.% To 95 at.%, Especially 85 to 90 at.%. 3. The alloy according to claim 1, wherein the alloy contains 3.0 to 3.0 atomic% tantalum and 1.0 to 9.0 atomic% chromium. 4. The alloy according to claim 3, wherein the alloy contains 0.3 to 0.9 atomic% tantalum and 1.0 to 3.0 atomic% chromium. 4. The alloy according to claim 3, wherein the alloy contains 5.0.7 at% to 3.0 at% tantalum and 6.0 at% to 9.0 at% chromium. 6. 6. The alloy according to claim 1, comprising tantalum and chromium in a ratio of 1: 3 or less. 7. 7. The method according to claim 1, wherein at least some NiAl grain boundaries have coarse Laves phase precipitates and at least some nickel-aluminum particles have fine Laves phase precipitates and α-chromium. The described alloy. 8. 8. The alloy according to claim 7, wherein the structure contains 5 to 11% by volume of a precipitate of a coarse Laves phase and 3 to 10% by volume of a precipitate of a fine Laves phase and α-chromium in NiAl. 9. 9. The alloy of claim 8, wherein the structure has about 11% by volume of Laves phase on grain boundaries and about 10% by volume of precipitates in two-phase NiAl. 10. 10. The method as claimed in claim 1, wherein at least one element from the group of iron, molybdenum, tungsten, niobium and hafnium is contained in an amount of up to 1 at% each and not more than 3 at% in total. The described alloy. 11. Gas turbine components such as runner blades and guide blades of gas turbines of intermetallic nickel-aluminum-based alloys mainly comprising two-phase NiAl and the elements tantalum and chromium, the total weight of tantalum and chromium being up to 12 atomic%. Use as. 12. High strength (0.2% elongation limit, 600Mp or more at room temperature), high heat resistance (0.2% elongation limit, 800 ° C at 200Mp or more, 1000 ° C at 90Mp or more), good toughness (K _K at least Mp) / M), a good oxidation resistance (about 5.10 ¹⁴ g ² c ^-4 s) and a good thermal shock resistance of the composition according to one of the claims 1 to 10 as a material for the production of articles having good thermal shock resistance. Alloy applications.