RU2088684C1 - Oxidation-resistant alloy (variants) - Google Patents

Abstract

FIELD: metallurgy, alloys nickel-cobalt-iron. SUBSTANCE: alloy has, wt. -%: nickel, 25-50; cobalt, 5-50; aluminium, 5-10; niobium, 0.5-6; manganese + silicon + copper = ,0.14-2; and iron, 20-50. Variant of alloy, wt.-%: nickel, 25-70; cobalt, 5-50; aluminium, 4-15; and iron, the balance at total content of nickel and cobalt, 45-75. Alloy exhibits duplex structure. EFFECT: improved quality and property of alloy. 24 cl, 9 tbl

Description

 The invention relates to heavy-duty ductile alloys resistant to oxidation and, in particular, heavy-duty corrosion-resistant alloys with a low coefficient of thermal expansion, containing nickel and iron with cobalt.

Modern high-strength alloys with a low coefficient of thermal expansion, not containing chromium (US patent N 3157495, 4200459, 4487743 and 4685978), usually do not have the appropriate resistance to oxidation and corrosion at high temperatures. High-strength alloys Ni-Fe and Ni-Fe-Co with a low coefficient of thermal expansion not only have poor resistance to oxidation, but they are also subject to such phenomena as, for example, oxygen embrittlement of grain boundaries accelerated by stresses. This phenomenon is sometimes referred to as dynamic oxygen embrittlement or simply dynamic embrittlement. Modern heavy-duty chromium-free alloys usually do not have the required high strength at temperatures above about 600 ^o C. In addition, as a rule, in the known heavy-duty alloys with a low coefficient of thermal expansion, quick strengthening of grains at temperatures of about 1040 ^o C, which usually required for soldering products from these alloys.

 It is well known that the addition of chromium to these alloys can give the alloys resistance to oxidation and corrosion resistance, in addition, reduce the embrittlement of grain boundaries. However, in nickel, iron, and cobalt-based alloys, chromium also reduces ferromagnetism, the Curie point (the transition temperature from the magnetic state to non-magnetic) and, therefore, increases the thermal expansion of the material. When chromium is added in sufficient quantity to provide normal resistance to oxidation, then the material does not have a low coefficient of thermal expansion.

 It is also known that adding enough aluminum to nickel and iron based alloys can give them oxidation resistance and increase strength. However, according to modern technology for the production of heavy-duty alloys with a low coefficient of thermal expansion, it is believed that the addition of aluminum increases the tendency to oxygen embrittlement of grain boundaries, accelerated by stresses. So, for example, in US patent N 4685978, 4487743 and 4200459 indicated that the aluminum content should be as low as possible to reduce the tendency to oxygen embrittlement of grain boundaries, accelerated by stresses. Modern heavy-duty alloys with a low coefficient of thermal expansion contain aluminum only as an undesirable impurity.

When aluminum is present in very large amounts in the Ni ₃ Al intermetallic compound, an even more increased dynamic oxygen embrittlement is observed compared to the embrittlement of heavy-duty alloys with a low coefficient of thermal expansion. This occurs despite the exceptionally good resistance to oxidation of aluminum-containing intermetallic compounds. It is also known that an increase in the aluminum content in nickel-based alloys and in nickel-containing alloys will worsen dynamic oxygen embrittlement or low-temperature embrittlement especially in varieties of these alloys with low or no chromium content.

Outside the field of alloys having a low coefficient of thermal expansion, the applicant knows US Pat. No. 4,642,145 (Patent No. 145), which discloses nickel-iron-aluminum alloys and nickel-cobalt-aluminum alloys containing at least 8 atoms. aluminum and an intermetallic compound of type B-2 present in alloys. These alloys are obtained in such a way as to give them a microcrystalline structure with a crystal diameter in the range of 0.5-10.0 μm and, as indicated in the patent, such a particle size of the crystals is necessary to obtain a fine microcrystalline structure. Examples of alloys with a fine microcrystalline structure from patent No. 145 contain either cobalt or iron, but not both elements together. But, as the applicants are aware, the fine microcrystalline structure required in US Pat. No. 145 indicates the relatively poor mechanical properties of the alloy at temperatures above about 600 ^° C. Patent No. 145 does not disclose any specific characteristics of the claimed alloys and is generally silent about oxygen embrittlement of grain boundaries accelerated by stresses. In addition to patent No. 145, a technical report should be mentioned (Ionn et al. Microstructure and mechanical properties of rapidly quenched alloys in Ni-Al-Fe and Ni-Al-Co systems. Journal of Materials Science, 19 (1984), 3097 -3106). Here it was concluded that the wire obtained by quenching the melt in the Ni-Al-Fe and Ni-Al-Co systems will be ductile even if the compounds β ′ and γ ′ + β ′ are very brittle and usually in cured form.
Field and others are also featured in a technical article titled “Deformation of Ni-AL-Fe-gamma / Beta Alloy,” as part of the paper, “High-Temperature Ordered Intermetallic Alloys III,” at a Symposium held in Boston, Mass. With November 29 to December 1, 1988. In this article, Field and others described a test of a Ni-Al-Fe alloy identical in composition to alloy 14 of Example 11 in US Pat. No. 145. This material was melt-molded and then annealed for two hours. at 1100 ^o C for the preparation of essentially equiaxed microstructure with grains about 5 micrometers in diameter. After this treatment, the microstructure consisted of BzNiAl and gamma (a face-centered cubic phase structure with an ordered primary gamma phase inside the gamma phase grains. As in US Pat. No. 145, this technical article does not disclose any characteristics of the alloy at elevated temperatures or or data related to oxygen embrittlement of grain boundaries accelerated by stresses.

The aim of the present invention is a new alloy composition, which will eliminate many, if not all, of the disadvantages of the known alloys and obtain a new alloy with good oxidation resistance, resistance to dynamic oxidation of grain boundaries, ductility at room temperature, strength at temperatures above 600 ^o C and at the same time, with a relatively low coefficient of thermal expansion (CTE).

The features of the present invention are illustrated by drawings, in which:
figure 1 is a graph of the mutual dependence of the mechanical properties of the alloys at a temperature of 760 ^o C on the aluminum content;
figure 2 graph of the dependence of tensile strength under load of alloys at a temperature of 649 ^o C on the aluminum content;
figure 3 is a graph of the relationship of elongation and reduction of cross-sectional area together with resistance to fracture under load (figure 2) on the aluminum content in the alloys;
Fig. 4 is a photograph taken under an optical microscope of a double grain size structure of a typical alloy according to the present invention;
FIG. 5 is a photograph taken under an electron microscope and showing the uniformity of precipitation in one component of a dispersion hardening alloy with a double grain size according to the present invention;
FIG. 6 graphs showing the effect of niobium on the tensile strength under load, elongation and reduction of the cross-sectional area of the alloys according to the invention at a temperature of 649 ^o C, tested on combined smooth samples and notched samples (CT 3.6).

The present invention in particular relates to a oxidation-resistant alloy with a double grain size, containing in wt. about 36-44% nickel, 16-24% cobalt, about 5.5-6.5% aluminum, about 1.2-1.8% titanium, up to about 0.1% carbon, up to about 0.5 % in general manganese, copper and chromium, about 0.3% silicon, about 2% molybdenum, up to about 2% tungsten, 3-4% niobium, about 0.01% boron, the rest essentially iron in an amount of about 20-38% provided that when the iron content is less than about 24%, the cobalt content is at least 24%
To solve some problems of alloys having a composition within the specified limits, an oxidation-resistant alloy with a double grain size is proposed, containing in mass percent about 25-40 or 45% nickel, 25-38% cobalt, 4.8-6% aluminum, up to about 1.6% titanium, up to 0.1% carbon, 0.5% of the total amount of manganese and copper, up to about 6% chromium plus molybdenum, up to about 6% tungsten, about 0.5-6% niobium, 0.002-0 , 01% boron, the remainder is essentially iron in an amount of about 15-35%
In a broader sense, the present invention relates to alloys with double grain size, having:
1) as the first component, a matrix containing nickel, iron and cobalt, and nickel, iron and cobalt are present in the amount necessary to obtain an alloy with a low coefficient of thermal expansion (CTE) less than about 13x16 ^-6 at ^o C at a temperature of about 427 ^o C. This matrix transforms at approximately the deflection temperature from the paramagnetic gamma phase existing at a temperature above the deflection point to the ferromagnetic gamma phase present at a temperature below the deflection point;
2) the primary gamma phase (ideally Ni ₃ Al) inside the matrix of the first component, and
3) a second, independent component in close connection with the first component. This independent component contains nickel and aluminum and is believed to have an ideal body-centered cubic structure based on NiAl or FeAl and modified with cobalt, titanium or other alloy components. For the purposes of this description and the claims, the term "in close association with the first component" means that microscopic examination of crystals or mass-independent components shows that the independent component is substantially completely wetted by the first component after annealing. Electron microscopy studies of the alloys that were cooled after annealing show the separated phase, the primary gamma phase, which exists in the first (gamma) component, uniformly distributed in all grains, even close to grain boundaries with an independent component.

In general, the alloy can be contained in mass percentages of about 25-70% nickel, 5-45 or 50% cobalt, about 45-75% nickel + cobalt, 4 or 5-15% aluminum, 0-3% titanium, for example, 0- 10% 1-10% niobium or tantalum, 0-10% each molybdenum and tungsten, 0-3% vanadium, 0-2% silicon, 0-1% manganese, 0-1% copper, 0-6% chromium, 0 -2% hafnium or rhenium, 0-0.3% boron, 0-0.3% zirconium, 0.01% magnesium, calcium, yttrium and rare earth metals, 0.05% nitrogen, 0-0.3% carbon together with deoxidizers, additives, grinding grain, dispersoids and the like, which are common in the method of manufacturing an alloy with an iron content in the range of about 15-55%, provided that when the iron is less than about 24%, the cobalt content is at least 24% Sulfur, phosphorus and oxygen (except when they are present as dispersoid oxide) should be limited to a maximum of approximately 0.02% of each. Sometimes, due to the high content of aluminum and other active metal in the alloy, the oxygen content can be high, for example, 0.3%. By choosing the appropriate ratio of the contents of nickel, cobalt and iron in the alloys according to the present invention, it is possible to obtain an alloy with a relatively low coefficient of thermal expansion at a temperature of 427 ^o C, for example in the range of about 10.6-13x10 ^-6 / ^o C. The expansion coefficient is controlled mainly by the ratio of Ni-Co-Fe, and secondly, by the content of Al, Ti and Nb.

 In order to maintain the structure of the alloy with a double grain size (or even a more complex structure) according to the present invention, it is advisable to change this wide composition limit so that if the nickel plus cobalt content is high, i.e. approximately 75% nickel plus cobalt, the aluminum content in the alloy will be in a very narrow limit, i.e. about 8.0% If the nickel plus cobalt content in the alloy decreases to about 67%, the allowable amount of aluminum increases to about 7-15%. When the nickel plus cobalt content is further reduced, the allowable aluminum content limits to about 6-8% at 50 % nickel + cobalt and up to about 5.0 at 45% nickel plus cobalt. This interdependence of the nickel plus cobalt content suggests that nickel plus cobalt acts like nickel and that nickel plus cobalt, depending on the aluminum content, does not contain elements of the niobium, tantalum and titanium groups, which can increase the effect of aluminum in a limited amount. Thus, in alloys containing niobium-titanium and tantalum according to the present invention, the indicated relationship between the nickel plus cobalt content and the aluminum content can be changed by the combined effect of aluminum, niobium, titanium and tantalum, and not the aluminum content.

 A person skilled in the art will understand that the content of iron, nickel, cobalt and aluminum in the alloys according to the invention determines the basic property of any given alloy and that titanium, niobium, molybdenum, tungsten, tantalum, etc. usually increase the hardness and strength of the alloy in addition to the effect of aluminum. It has been found that cobalt improves fluidity and workability compared to alloys containing no cobalt, or containing it in very small amounts. In addition, the alloys of the present invention, which contain iron, nickel and cobalt, have improved high temperature properties, toughness when testing a notched specimen and resistance to hydrogen embrittlement.

The thermal expansion coefficients of the alloys according to the present invention were determined on alloys containing about 2-3% niobium and 1.3-2% titanium. If molybdenum is present in the alloy in an amount of, for example, about 5% together with niobium and titanium, as determined, then the coefficient of thermal expansion measured at 427 ^o C can be as high as, for example, 12.9x10 ^-6 / ^o C The elements of niobium (with bonded tantalum), molybdenum and titanium, contribute to the strength of the alloys, especially tensile strength and creep resistance at elevated temperatures, for example, above about 600 ^o C. It is preferable when the alloys according to the invention contain about 0.5- 5% niobium since niobium is dimomu increases the strength and ductility of the alloys at elevated temperatures, e.g., 600-800 ^o C. In addition, in alloys containing about 30% iron the presence of niobium in an alloy low in titanium appears pripyatstvy tendency to ohrupchivaemosti at room temperature after the alloy at finding temperature of about 600 ^o C for extended periods of time. It was found that in alloys containing aluminum between 5.0 and 6.5% niobium, apparently, increases the agglomeration and spheroidization of the second component of the microstructure of the alloys, i.e., the second globular element of the microstructure. It is believed that tantalum, when present on an atomic basis in the alloys of the invention, acts like niobium and can be used as a substitute for niobium.

 An additional advantage of the alloys according to the present invention is the relatively low density in comparison with the known heat-resistant alloys with a low coefficient of thermal expansion.

 When determining the composition of the alloys according to the present invention, it should be noted that each of the alloying ingredients, in percentage terms, as shown in the table. 1 can be used in combination with any other alloying ingredient, since the content of nickel, cobalt and iron is balanced to obtain a low coefficient of thermal expansion, as is known in the art, and the content of nickel and cobalt, as indicated, is interconnected depending on the aluminum content. In addition, in table. 1, together with the indicated limits of the components in the composition, it is shown that for each element the present invention provides not so much the specified limit, but also any limit that can be defined between two set values of a particular element.

 Although there are many specific limits of the individual elements indicated in the table. 1 is effective according to the present invention, however, it was found that it is possible to successfully apply the content limits of the alloying elements indicated in the table. 2.

Alloys with a limit A of the content of components indicated in the table. 2 have a predominantly high strength at high temperatures, for example, in the range of about 649 760 ^° C., while maintaining a favorable combination of a low coefficient of thermal expansion and good resistance to oxidation. The limits of B and C are respectively preferred, but the limits according to the present invention are more preferred. Alloys having a composition within B and especially within A and C typically have a tensile strength at room temperature in excess of about 900 MPa, yield strength in excess of 650 MPa, elongation in excess of about 10% and a decrease in cross-sectional area in excess of about 20% when experiencing tensile. Alloys having a composition within the same limits when tested in tension in air at a temperature of 760 ^° C. typically have a tensile strength of at least 550 MPa, a yield strength of at least 500 MPa, an elongation of about 5% and a decrease in area a cross section of at least about 30%. The limits D and E usually define alloys that are not embrittled at temperatures of about 600 ^° C, in which the second component of the alloy is formed as a result of isolation, and not as the primary casting product. In addition, alloys containing chromium and / or molybdenum within E are more resistant to salt corrosion in comparison with other known alloys containing no chromium and having a low coefficient of thermal expansion.

 The alloys according to the invention, as has been described, are successfully made by melting alloying ingredients in a vacuum induction furnace, casting and hot processing of an ingot, for example, by extrusion and rolling to obtain a hot-rolled bar. The compositions of such alloys obtained by hot working, according to the invention are indicated in wt. in table 3, and it is clear that the rest in the alloys is iron together with inevitable impurities.

 Although the specific alloys indicated in the table. 3 were obtained by casting and pressure treatment, however, within the scope of the present invention, alloys with the indicated composition limits can be obtained by any method known in the field of metallurgy. For example, the alloys of the present invention can be obtained by casting and used in cast form without any significant processing. Also, the alloys according to the present invention can be obtained in powder form and processed to a predetermined shape by a conventional pressing and sintering method, by casting and spraying, by flame or plasma spraying to form coatings, or by any other method known in powder metallurgy. The alloys according to the present invention can also be obtained by mechanical alloying techniques, as disclosed, for example, in US patent N 3785801 (in the name of Benjamin), especially when you want to include in them the phase of the oxide dispersoid, for example, a phase containing yttrium oxide. Then, the powder product of mechanical alloying is treated with powder metallurgy methods, as described, to obtain the desired products.

After the alloys according to the present invention are obtained by any suitable method, they are preferably heat treated by calcination at a temperature in the range of from about 980 ^° C. to a temperature below the solidus point of the alloy for about 12 hours, usually followed by cooling. Upon cooling after annealing, the primary gamma phase is released in the first component in a very thin discrete form, which is evenly distributed in the first component. The alloys according to the invention, when tested and reported, were heat treated at a temperature of about 760 ^° C. to avoid inconstancy when comparative tests were carried out on alloys that were outside the scope of the present invention. Annealing, especially at temperatures above about 1038 ^° C., can lead to at least partial dissolution of the second component of the alloys. Heat treatment of alloys, when some of the second component of the alloy has dissolved, carried out at a temperature of about 870 ^o C, can lead to re-isolation of the second component in a form different from that obtained by casting and hot pressure treatment.

 Tab. 4 contains data regarding the properties of two examples of dispersion hardening alloys according to the present invention in comparison with the properties of two known dispersion hardening alloys.

 As shown in the table. 4, the properties were determined on samples of alloys that were heat treated as follows.

Samples from examples 10 and 20 were held at a temperature of 1038 ^° C. for 2 hours, cooled in air, held at 760 ^° C. for 16 hours, and then cooled again in air.

Alloy X was held at a temperature of 1038 ^° C for 1 h, cooled in air, held for 8 hours at 774 ^° C, cooled in an oven to 621 ^° C, held for 8 hours, then cooled again in air.

Alloy Y was kept at a temperature of 1066 ^o C for 1 h, cooled in air, then kept at a temperature of 760 ^o C for 10 h, cooled in an oven to 621 ^o C and kept for the entire time, including the residence time at a temperature of 760 ^o C and the cooling time in the furnace, i.e. within 20 hours

The mass gain in the static oxidation test was measured in mg / cm ² as the result of the test, which consisted in heating the alloy samples in air at a temperature of 704 ^o C for 504 hours. The test was carried out on alloy X and on two alloys similar to alloys from examples 10 and 20, but containing 2.5 and 4.0% aluminum, respectively. Alloy X had a minimum increment of 7.1 mg / cm ² in mass, and a very porous, unprotected oxide film was formed on it, which strongly peeled off. All alloys according to this invention had a firmly bonded thin, non-peeling protective oxide film with a mass increment of less than 1.6 mg / cm ² . To ensure overall resistance to oxidation, it is only necessary that the alloy contains more than 2% Al, although an aluminum content of more than 5% is necessary for resistance against dynamic oxygen embrittlement.

 Properties, alloys indicated in the table. 4 relate to formulations with different grain sizes. The corresponding characteristics of alloys having a uniform fine grain size according to ASTM Standard N 8 (average grain diameter is 0.022 mm) are shown in Table. 5.

The alloys according to the present invention, tensile tested at a temperature of 760 ^o C, as indicated in the table. 2, and heat-treated, as described for examples 10 and 20, have ultimate tensile strength in the range of about 790,900 MPa, yield strength in the range of 725,790 MPa, elongation up to 40% and a decrease in cross-sectional area up to 88%. When examples of alloys According to the present invention, heat-treated in this way are tested for tearing at a temperature of 649 ^o C and under a load of 510 MPa, tearing resistance increases with increasing aluminum content from about 0.01 h at 4% aluminum content to 100,200 h at 6% -nogo content of aluminum. At elevated temperatures, the values of elongation and decrease in cross-sectional area increase simultaneously due to a decrease in dynamic oxygen embrittlement. Also, the elongation and reduction of the cross-sectional area, apparently, increase in value if the aluminum content increases from about 5 to 6% To obtain the best combination of properties such as tensile strength under load, the aluminum content in the alloys according to the invention containing about 3 , 0% niobium and 1.3 2.0% titanium, it is necessary to maintain in the range of about 5–6% or 6.5%. A comparatively insignificant effect of the aluminum content in the same alloys during similar heat treatment is observed during tensile tests. and room temperature. Strength at room temperature gradually increases to a small extent with an increased aluminum content, while a slight anomaly is possible with an aluminum content of about 4.8%. The curves of the elongation and reduction of the cross-sectional area at room temperature on the aluminum content are essentially flat.

The advantages of the alloys according to the present invention with respect to their resistance to oxygen embrittlement of grain boundaries accelerated by stresses at temperatures of 760 ^° C and 649 ^° C are shown in FIG. 1 3. A number of alloys from nine were obtained essentially in the same way as alloys from the examples indicated in the table. 3. The compositions of these nine alloys in wt. in which iron is used for equilibrium, are shown in table. 6.

When testing all the alloys indicated in the table. 6, the tensile strength at room temperature (under conditions after annealing and holding at 750 ^o C for 16 h and cooling in air), they showed ultimate strength in the range 1275 1655 MPa, yield strength 0.2% in the range 965 1138 MPa, elongation of approximately 30–40% and a decrease in cross-sectional area of approximately 30–45%. A slight tendency towards increasing strength and decreasing slightly ductility was noted, as was determined by a decrease in cross-sectional area with increasing aluminum content. However, when the alloys were tensile tested at a temperature of 760 ^° C., the results shown in FIG. 1, where it is shown that at the test temperature, when the aluminum content in the alloy exceeds about 4%, the elongation and reduction of the cross-sectional area increase significantly, even if the strength of the alloys remains essentially unchanged, FIG. 2 and 3 graphically confirm the surprising phenomenon shown in FIG. 1. FIG. 2 shows the results of tests for tensile strength in air at a temperature of 649 ^o C, when a combination of smooth samples with a notch (K _T 3,6) of the alloys indicated in table. 6. Alloys containing about less than 5% aluminum had a cut in the notch in 6 minutes or less, while alloys containing more than about 5% aluminum showed failure on smooth specimens and had a tensile strength of about 100 hours or more. The graph in FIG. 3, which represents in detail the values of elongation and decrease in cross-sectional area when testing samples for tensile testing under load, it clearly shows that at a temperature of 649 ^o C alloys (Table 6) containing less than 5% aluminum are susceptible to oxidation destruction along grain boundaries, accelerated stresses, while alloys containing more than 5% aluminum, show a percentage elongation of more than 30% and reduce cross-sectional areas of more than about 40%
The graphs of the dependence of the coefficient of thermal expansion at a temperature of 427 and 593 ^o C depending on the aluminum content show only the measured increase in the coefficient with increasing aluminum content, as described. Within the aluminum content of 4.0 to 7.5%, the deflection temperature of the alloys according to the invention remains relatively constant between 371 and 385 ^o C.

Alloys according to the present invention, which contain more than about 5% aluminum, have a double grain size structure or a more complex structure, which is not yet fully understood in this description. The microstructure of a material containing less than about 5% aluminum and annealed at a temperature of 1038 ^o C followed by isothermal processing at a temperature of 760 ^o C, images of which were obtained under an optical microscope, is similar to the microstructures of the known heavy-duty nickel-based alloys, and it has a matrix with a larger the grain size of one component containing the selected phase along with the precipitation of some secondary phases along the grain boundaries. However, a material containing more than about 5% aluminum and with the same heat treatment has a double grain size structure or a more complex microstructure, including the precipitation of very thin secondary phases along grain boundaries. The appearance of the secondary component and increased precipitation of the secondary phases along the grain boundaries is significant in that it coincides with the resistance of the material to oxygen embrittlement.

In FIG. 4 and 5 show the structure of a typical alloy according to the present invention. Preliminary X-ray diffraction analysis of alloy samples containing more than about 5% aluminum shows that the first component has a face-centered cubic structure. FIG. Figure 5 shows the phase (it is assumed that this is the primary gamma phase (Ni ₃ Al) isolated inside the phase with a graded cubic structure. Semi-quantitative analysis of the sample from Example 3 under a scanning electron microscope showed that the second component is richer in aluminum content. This analysis also showed that the second component is enriched to some extent with the content of nickel and titanium and, in addition, the content of iron and niobium is improved in comparison with the composition in the mass and the composition of the first component. with some assumptions affecting the role of Co and Ti, it suggests that the second component should be a phase with a body-centered cubic structure.The X-ray diffraction analysis and structural analysis under an electron microscope show that the phase with a body-centered cubic structure has a B2 structure at room temperature The presence of iron in the structure indicates that other types of structural ordering based on Fe ₃ Al are possible.

 Thus, the structure is very complex. However, it is possible that this is important for achieving resistance to oxygen embrittlement. In addition, it is believed that the formation of the second component in these alloys improves the hot working ability of the alloy and indeed it may be required to improve the hot workability of cast and malleable nickel-cobalt-iron alloys with a high aluminum content.

An outstanding feature of the alloys according to the invention is that they can be annealed at temperatures close to 1038 ^° C. for at least 2 hours without grain coarsening. At first glance, such alloys containing a small amount of aluminum or without aluminum, for example, alloy X has a significant enlargement of grains for such a minimum period of time as, for example, 1 hour at a temperature of 1038 ^o C, as indicated in table. 4. Thus, the alloys of the present invention can be used in structures obtained by high temperature brazing using relatively cheap brazing alloys.

Alloys according to the invention may contain, in addition to metal and secondary phases along grain boundaries, as described, up to about 2 wt. microfine-dispersed oxide phase containing yttrium oxide, lanthanum oxide, cerium oxide, alumina, or the yttrium oxide phase alumina, for example, garnet yttrium aluminum, which is formed by mechanical alloying and heat treatment. The alloys according to the invention may include dispersoids, for example, Be, B ₄ C, BN, C, SiC, TiB ₂ , TiN, W, WC, ZrB ₂ and ZrC.

A specific example of the composition of the alloy, which was obtained by mechanical alloying, consists of 42.58% nickel, 5.87% aluminum, 17.14% cobalt, 1.73% titanium, 2.78% niobium, 0.04% carbon, 0.37% yttrium in the form of J ₂ O ₃ (by itself or as an oxide containing J ₂ O ₃ ), 0.61% oxygen, the remainder is essentially iron. After pressing, sintering, hot working, annealing and aging at a temperature of 760 ^o C, this alloy obtained the following mechanical properties based on tests of combined smooth and notched samples.

Tensile test under a load of 510 MPa at a temperature of 649 ^o C (in air), resistance 859 h. Fracture failure.

Tensile test under a load of 241 MPa at a temperature of 761 ^o C (in air), resistance 307.4 hours. Notch fracture.

The niobium content in the alloys of the present invention can be of great importance. The niobium content in the alloys in accordance with the invention is mainly in the range of 2.5-4.0 wt. and if a relatively low ductility at a temperature of 649 ^o C is acceptable, the niobium content can be in the range of 1.5-4.0% or even 6% depending on the titanium content. FIG. 6 is based on a number of alloys, including examples 12 and 20, as indicated in the table. 3. In FIG. Figure 6 shows that when tested for tensile testing in air under a load of 510 MPa and a temperature of 649 ^o C, samples of alloys according to the invention containing 2.5% niobium or more had resistance for at least about 100 hours and at the same time they showed at least about 23% elongation and 40% reduction in cross-sectional area. The ductility in terms of elongation and reduction of the cross-sectional area seems to be maximized by about 3% (Example 20), and the tensile strength was over 100 hours. Those skilled in the art will understand that although the increase in tensile strength with increasing niobium content is essentially linear (Fig. 6), however, the tear resistance scale is logarithmic, moreover, at a 3% niobium content, the tear resistance is approximately two orders of magnitude higher than the resistance of a niobium-free alloy.

 According to the invention, alloys that have a high aluminum content, for example, above about 6% and which are obtained by conventional smelting and casting, contain the second component in cast form, and in such an amount and in such a form that the second component cannot be dissolved in the solid matrix during heat treatment.

 Products made from alloys according to the invention containing such a high amount of aluminum often have anisotropic mechanical properties due to differences in hot working characteristics between the matrix and the second component. In cases where the existence of anisotropic mechanical properties is undesirable in the processed alloy products, it is advisable to keep the aluminum content in the alloys according to the invention below about 6%, for example, in the range from about 4.3 to 6.0%, best in the range of 4.8- 5.8% Table 7 shows many examples of alloys having an aluminum content in the range of 5.0-6.2%. Each of these alloys (Table 7) was obtained in the same way as described for the examples in Table 3.

In the examples (table 7) are given alloys that were tested in various ways. For example, the alloys of Examples 23-28 were tested in order to show the effect of annealing and aging, as well as aging at 593 ^° C. for 100 hours at room temperature. It was found that when aging for 8 hours in an oven cooled to 718 ^° C, holding for 8 hours at 621 ^° C and then cooling in air, optimal results were obtained with alloys from Examples 23 and 27, which contain approximately 25% iron and 25% or more cobalt. In the example of alloy 23, satisfactory results are shown in a tensile test during annealing before aging for 1 h in the temperature range 982-1093 ^o C. In the example of alloy 29, satisfactory mechanical characteristics are shown at room temperature after aging and aging for 100 h at 593 ^o C only during annealing for 1 h in a narrower temperature range 1038-1093 ^o C. In the table. 8 shows the results of tensile tests at room temperature obtained with the alloys of examples 23 and 27.

In general, the alloys of examples 23-29 containing more than about 30% cobalt show insufficient ductility at room temperature after exposure at 593 ^° C. under the specified processing and test conditions. It has been found that when the iron content is greater than about 30%, aging stability at a temperature of 593 ^° C. or about 593 ^° C. can be achieved by reducing or removing titanium without changing the cobalt content in the alloy.

In contrast to the characteristics at room temperature, if annealing is carried out at 1038 ^o C, and aging either at 760 ^o C for 16 hours or at 718 ^o C for 8 hours and 621 ^o C for 8 hours (two-stage aging), or at a temperature of 899 ^° C for 4 hours, followed by aging at 718 ^° C for 8 hours and 621 ^° C for 8 hours, alloys 23-29 obtain satisfactory tensile properties at 649 ^° C. For example, alloy 25 which has undergone aging at 760 ^o C, shows a yield point of 924 MPa, a tensile strength of 1165 MPa, an elongation of 24% and reduced e cross-sectional area 50%
The alloys of examples 30-38 were obtained to study the effect of niobium and titanium on stability, as reflected by the ductility tensile test at room temperature, tensile after annealing, aging and aging at 593 ^o C. As a result, it was found that the presence of niobium is important for maintaining plasticity at room temperature after 100 hours at 593 ^° C. and that the presence of titanium is harmful (Table 9).

The data table. 9 show that in each alloy containing about 30% iron and not having niobium, there is a significant decrease in elongation at tension at room temperature and cross-sectional area after exposure at 593 ^o C. In addition, in the data presented in table.9, there is a trend indicating that even in the presence of niobium, the ductility in a tensile test at room temperature after holding at 593 ^° C. decreases with increasing titanium content, thus for alloys in accordance with the present invention, containing more than 30% iron, which can withstand temperatures of about 593 ^o C, the titanium content should be limited to a maximum value of about 0.5% Additional tests of the alloys of examples 30-38 at 649 ^o C show an increase in strength with an increase in the content of niobium and titanium separately and in aggregate. Similarly, niobium and titanium, taken separately or in combination, lead to a decrease in the coefficient of thermal expansion of the alloys. Alloys in accordance with this invention, containing about 25% or less of iron, still remain ductile although titanium reduces their ductility when tensile at room temperature after exposure to 593 ^o C. In contrast, alloys containing about 30% of iron and titanium are about more 0.5% do not maintain satisfactory ductility when tensile at room temperature after exposure at 593 ^o C.

The alloys of examples 39-47 were taken to study the effect of chromium and molybdenum in the alloys in accordance with the invention. These alloys were tested in salt spray for 720 hours in accordance with ASTM B117-85 (American Society for Testing Materials) using samples weathered at 1038 ^° C for 1 hour, air-cooled and aged at 760 ^° C. for 16 hours and chilled in air. The chromium-molybdenum alloy of Example 39 shows a corrosion rate of about 12 μm / year with a maximum pitting depth of about 165 μm. With an increase in the chromium and / or molybdenum content in general to 8%, the corrosion rate decreases to 0.76 μm / year and the maximum pitting corrosion depth decreases to less than 25 μm. The tensile test alloys of Examples 39-47, annealed for 2 hours at 1038 ^° C and aged for 16 hours at 760 ^° C, show satisfactory results at 649 ^° C with approximately a yield strength of 930 MPa and a limit of tensile strength 1158, elongation of 20% and a decrease in cross-sectional area of 30% At room temperature, tensile test results at elevated levels of molybdenum tend to slightly decrease elongation and decrease cross-sectional area, and Ia is also observed at 649 ^o C, although less severe at the elevated temperature. When testing smooth specimens and notched specimens (K _t equal to 3.6) at a temperature of 649 ^° C and a load of 510, tensile strengths were obtained, increasing from about 100 to 500 hours, elongation by about 30%, and reducing the cross-sectional area an average of 39% in molybdenum-free alloys, when the chromium content was increased from 0 to 4% instead of iron. At any given level of chromium, the addition of molybdenum reduces tensile strength. A more or less the same picture of an increase with increasing chromium content and a decrease with increasing molybdenum content was shown during impact tests of Charpy V-shaped notches at room temperature. The determination of thermal expansion coefficients in examples 39-47 shows an increase in the value of this characteristic with an increase either individually or in combination of chromium and molybdenum. Nevertheless, the thermal expansion coefficients were at least 10% lower than the thermal expansion coefficients of conventional heavy-duty alloys, such as, for example, Inconel 718 alloy.

In addition to these examples of alloys according to the invention, a number of alloys were obtained containing aluminum 5.9-6.2% titanium, approximately 1.5% niobium 3% boron, less than 0.01% iron 20-34% cobalt 18-40% and the rest nickel. The alloys were melted, cast, pressure treated and heat treated by holding for 2 hours at a temperature of 1038 ^o , cooled in air and kept at a temperature of 760 ^o C for 16 hours. When these tensile tests of the combination of smooth samples and notch under a load of 510 MPa at a temperature of 649 ^o C relate to the alloys represented by dots in the graph of the dependence of the iron content on the cobalt content, it is clear that alloys containing less than about 24% iron and 25 or 26% cobalt, show a gap in the notch, and they apparently susceptible to embrittlement as a result of oxidation at the grain boundary, accelerated by stresses. The maximum tensile strength of the alloy is observed when the alloy has an iron content of about 15-24% and cobalt 35-40% or more, as shown in the graph. The tensile strength under test conditions is reduced to zero in alloys containing more than 30% iron and 34% or the same amount of cobalt, although the ductility of these alloys is higher. The ductility, determined by the percentage reduction in cross-sectional area, seems to be appropriate or better for alloys having a cobalt content within the tested interval, provided that the alloys include over about 25% iron. When the iron content is less than 25%, adequate or good ductility is observed only in those alloys that contain more than 25 or 28% cobalt. Of the alloy compositions tested, the best resistance to fracture (438 h) and a 31% reduction in cross-sectional area were noted for the alloy containing 39.78% cobalt and 18.93% iron, but the thermal expansion coefficient increased as a result of the replacement of iron with cobalt. The worst results of this series of tensile tests were zero resistance and zero ductility in alloys containing cobalt 17.88% and iron 24.6% cobalt 23.04% and iron 24.06% cobalt 27.45% and iron 20.38% Specialists in the art will understand that the lines separating the good and bad compositions of the alloys based on the results of tensile tests under load at a temperature of 649 ^o C, are approximate, and they will slightly shift depending on changes in the composition of the alloy, from processing, heat treatment grain size as well as conditions tests (including the applied load, test temperature, notch sharpness, sample configuration) and other parameters. For example, if the alloy contains 30% iron, then an increase in the iron content will lead to a decrease in the coefficient of thermal expansion, and a reduced iron content seems to increase the stability and tear resistance of the alloy and reduces the formation of the beta phase, which, apparently, provides protection against embrittlement on grain boundaries accelerated by stresses.

 The invention has been described and shown using specific alloys as an example, however, one skilled in the art will understand that this description and illustration are not limited by the appended claims. The alloys according to the invention are suitable for any application in which high strength and ductility both at room and at elevated temperatures are criteria along with resistance to oxidation at grain boundaries, accelerated stress. Such application examples include components and parts for turbines operating at high temperatures, critical structural elements, for example, seals, rings, disks, compressor blades and casings, rocket engine parts, for example, pump parts for turbines operating on hydrogen fuel, and power heads. The alloy can also be used as a matrix material for composite materials with a metal or fiber matrix, a high-strength ferromagnetic alloy, gun barrels, high-strength fasteners, shells for semiconductors, in general, where good wear resistance and resistance to cavitation and erosion are required.

 Although the described examples of the alloys according to the invention were all cast and pressure-treated, it is possible to manufacture and use the alloys in cast form, in the form of a powder, and any other form known in the field of metallurgy.

Claims (18)

 1. The alloy is resistant to oxidation, with a low coefficient of thermal expansion, containing nickel, cobalt, aluminum, niobium, manganese, silicon, copper and iron, characterized in that it contains components in the following ratio, wt. Nickel 25 50
Cobalt 5 50
Aluminum 5 10
Niobium 0.5 6.0
The sum of manganese, silicon and copper 0.14 2.0
Iron 20 50
2. The alloy according to claim 1, characterized in that it contains up to 0.5 wt. silicon.  3. The alloy according to claim 1, characterized in that it further comprises one or more components, wt. Titanium Under 2
Carbon Up to 0.2
Chrome Up to 6
Sum of Molybdenum and Tungsten Up to 5
Zirconium Up to 0.1
Bor To 0.02
4. The alloy according to claim 1, characterized in that it contains at least 2 wt. niobium.  5. The alloy according to claim 1, characterized in that it contains 30 to 45 wt. nickel.  6. The alloy is resistant to oxidation, containing Nickel, cobalt, aluminum and iron, characterized in that it contains components in the following ratio, wt. Nickel 25 70
Cobalt 5 50
Aluminum 4 15
Iron 20 50
with a total content of Nickel and cobalt 45 75 wt. wherein the alloy has a duplex structure with a first crystalline component representing the γ phase with gaseous precipitates and a second component having a bcc type B2 structure enriched with aluminum compared to the first crystalline component.  7. The alloy according to claim 6, characterized in that it further comprises one or more components, wt. Titanium Under 3
Carbon Up to 0.3
Chrome Up to 6
Molybdenum Under 10
Tungsten Up to 10
Zirconium Up to 0.3
Bor To 0.3
Niobium Under 10
Tantalum Up to 10
Vanadium Under 3
Silicon Up to 2
Manganese Before 1
Copper Up to 1
Hafnium Under 2
Rhenium Under 2
The sum of magnesium, calcium, yttrium and rare-earth metals To 0.1
Nitrogen Up to 0.5
8. The alloy according to claim 6, characterized in that it contains at least 24 wt. cobalt when the iron content is less than 24 wt.  9. The alloy according to claim 7, characterized in that it contains at least 1 wt. niobium.  10. The alloy according to claim 7, characterized in that it contains at least 2.5 wt. niobium with a titanium content of less than 0.8 wt.  12. The alloy according to claim 7, characterized in that it contains 1.0 to 2.5 wt. titanium with an iron content of less than 30 wt.  13. The alloy according to claim 7, characterized in that it contains up to 5 wt. molybdenum plus tungsten.  14. The alloy according to claim 7, characterized in that it contains 25 to 40 wt. cobalt.  15. The alloy according to claim 14, characterized in that it contains 20.0 to 27.5 wt. gland.  16. The alloy according to claim 7, characterized in that it contains up to 2 wt. vanadium.  17. The alloy according to claim 7, characterized in that it contains 2 to 6 wt. chromium.  18. The alloy according to claim 7, characterized in that it contains 2 to 6 wt. molybdenum.  19. The alloy according to claim 7, characterized in that it contains 4 to 10 wt. molybdenum plus chromium.  20. The alloy according to claim 7, characterized in that it contains up to 0.3 wt. nitrogen.  21. The alloy according to claim 7, characterized in that it contains components in the following ratio, wt. Nickel 25 45
Cobalt 25 35
Aluminum 4.8 5.8
Iron 20 27
Titanium Up to 1.8
Carbon Up to 0.1
Silicon Up to 0.3
Sum of Molybdenum and Tungsten Up to 5
The sum of copper and manganese Up to 0.5
Niobium 0.5 4.0
22. The alloy according to claim 7, characterized in that it contains components in the following ratio, wt. Nickel 25 45
Cobalt 25 35
Aluminum 4.8 5.8
Iron 27.5 35.0
Titanium Up to 0.8
Manganese Up to 0.5
Silicon Up To 0.75
Molybdenum Under 2
Niobium Under 2
Boron 0.001 0.01
23. The alloy according to claim 6, characterized in that it further comprises up to 2 wt. dispersoid in the form of an oxide phase.  24. The alloy according to claim 6, characterized in that it further comprises 0.2 to 2.0 wt. yttrium or oxide phase in the form of a complex oxide.

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