RU2633679C1 - Cast heat-resistant nickel-based alloy and product made thereof - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: nickel-base heat-resistant alloy contains, wt %: carbon 0.05-0.15, chromium 11.9-12.7, cobalt 10.0-12.0, tungsten 4.0-5.2, molybdenum 1.5-2.1, titanium 3.2-4.2, aluminium, 3.2-4.0; tantalum, 1.5-2.9; boron, 0.001-0.015; zirconium, 0.008-0.08, cerium 0.002-0.02, yttrium 0.002-0.02, lanthanum 0.002-0.02, calcium 0.001-0.01, nickel is the rest.

EFFECT: alloy is characterised by high values of long-term strength, corrosion resistance, high phase stability and reduction of volume fraction of nonequilibrium phases precipitates.

3 cl, 2 tbl, 3 ex

Description

The invention relates to the field of metallurgy, in particular to the production of casting heat-resistant nickel-based alloys and products obtained from them with polycrystalline (equiaxial) or directional (single crystal) structures, for example, working blades of gas turbine units (GTU) and gas turbine engines (GTE) operating in aggressive environments at temperatures up to 900-1000 ° C.

From / RU 2131944 C1, 06/20/1999 /, a heat-resistant nickel-based alloy with a single crystal structure is known, intended for the manufacture mainly of directed crystallization of parts of high-temperature components of gas turbines with directional and single crystal structures with high yield of castings according to the macrostructure, the following chemical composition, mass . %:

carbon 0.005-0.12 chromium 13.5-14.5 cobalt 8.0-12.0 tungsten 3.0-5.0 molybdenum 1.5-2.5 titanium 3.4-4.3 aluminum 3.5-4.8 niobium 0.4-1.4 tantalum 0.2-1.0 hafnium 0.1-0.4 boron 0.001-0.02 yttrium 0.005-0.05 nickel rest

A disadvantage of the known alloy is the tendency to form harmful topologically tightly packed (hereinafter referred to as TPU) phases, the volume fraction of which in the structure of the material of a turbine blade of this alloy after 1000 hours of operation can reach 10%, which significantly reduces its further performance.

From / RU 2519075 C1, 06/10/2014 / a nickel-based heat-resistant alloy is known for casting parts of the hot path of gas turbine plants, for example, turbine rotor blades with polycrystalline (equiaxial) or directional (monocrystalline) structures operating in aggressive environments at temperatures up to 700-1000 ° C, the following chemical composition, mass. %:

carbon 0.08-0.10 chromium 8.85-9.15 cobalt 10.4-10.8 tungsten 5.60-5.85 molybdenum 0.20-0.30 titanium 3.0-3.2 aluminum 3.7-3.9 niobium 0.10-0.15 tantalum 3.9-4.1 hafnium 0.10-0.15 boron 0.08-0.012 yttrium 0.010-0.012 rhenium 2.9-3.1 cerium 0.01-0.012 lanthanum 0.010-0.012 magnesium 0.010-0.012 nickel rest,

the total content of cerium, yttrium, lanthanum and magnesium is not less than 0.40-0.048 mass. %, the total content of hafnium and niobium is 0.2-0.3 mass. %, and the total content of aluminum and titanium is 6.8-7.1 mass. % with a ratio of titanium to aluminum content of 0.81-0.825.

A disadvantage of the known alloy is its low corrosion resistance: the comparative corrosion resistance of log [metal loss (mm / 20 h)] is from -0.553 to -0.595, which limits the long-term performance of parts of this alloy in corrosive environments at temperatures elevated to 1000 ° C. Its disadvantages also include the increased (not less than 0.40 wt.%) Total content of cerium, yttrium, lanthanum and magnesium, as a result of which, segregating in the process of directed crystallization into single-dendritic regions of single-crystal castings of working blades, they lower the local liquidus temperature of the alloy , increasing the tendency of a liquid alloy to form foreign crystals during single-crystal casting, which impede further formation of a single-crystal structure of molded working blades, especially in places the passage from the pen to the shelf lock blades. In this regard, the alloy has a lack of manufacturability in the manufacture of gas turbine blades with a single crystal structure.

The closest analogue is a nickel-based foundry heat-resistant alloy, known from / JP 4911753 B2, 04/04/2012 /, intended for the manufacture of blades for industrial gas turbines with polycrystalline (equiaxed) and directional (columnar or single-crystal) structures of the following chemical composition, mass. %:

carbon 0.05-0.15 chromium 9-12 cobalt 9-11 tungsten 6-9 molybdenum less than 1 titanium 4-5 aluminum 4-5 niobium less than 1 tantalum less than 3 hafnium 0.5-2.5 boron 0.005-0.015 rhenium less than 3 zirconium less than 0.05 nickel rest

Additional studies have shown that increased to 2.5 mass. The% content of hafnium leads to the fact that it, segregating during casting into the interdendritic regions of the alloy parts, contributes to the formation of a significant number of nonequilibrium phases of eutectic origin such as Ni ₃ (Al, Hf) or Ni ₅ Hf with low melting points and thereby lowers the solidus temperature alloy. As a result, the risk of formation of significant porosity and crystallization hot cracks in the castings of products of complex geometry increases during crystallization. This can lead to the fusion of the interdendritic regions in the castings of alloy products during their heat treatment to a solid solution and / or barothermal treatment to eliminate casting porosity. The specified disadvantage of the prototype alloy, associated with the peculiarities of its alloying, leads to a decrease in manufacturability during casting, namely, the need for a long multi-stage thermal and / or barothermic treatment of parts. Another disadvantage of the prototype alloy is its low phase stability, which is manifested in the tendency to form TPU phases, the volume fraction of which in the structure of the material of a turbine blade of this alloy after 1000 hours of operation can reach 10% or more, which significantly reduces its further performance.

An object of the present invention is to provide a casting heat-resistant nickel-based alloy with enhanced physicochemical properties necessary to increase the operational characteristics of gas turbine blades operating in aggressive environments at temperatures up to 900-1000 ° C.

The technical result of the present invention is to increase the long-term strength, the relative corrosion resistance of a heat-resistant nickel-based alloy with an increase in its phase stability, as well as a decrease in the volume fraction of the precipitation of nonequilibrium phases and, as a result, the ability to obtain products of complex shape with polycrystalline (equiaxial) or directional (monocrystalline) structure, as well as conduct their thermal and / or barothermic treatment.

To achieve the technical result, a heat-resistant nickel-based alloy containing carbon, chromium, cobalt, tungsten, molybdenum, titanium, aluminum, tantalum, boron, zirconium, as well as cerium, yttrium, lanthanum and calcium is proposed in the following ratio of components, masses. %:

carbon 0.05-0.15 chromium 11.9-12.7 cobalt 10.0-12.0 tungsten 4.0-5.2 molybdenum 1.5-2.1 titanium 3.2-4.2 aluminum 3.2-4.0 tantalum 1.5-2.9 boron 0.001-0.015 zirconium 0.008-0.08 cerium 0.002-0.02 yttrium 0.002-0.02 lanthanum 0.002-0.02 calcium 0.001-0.01 nickel rest

The alloy may additionally contain rhenium in an amount of 0.9-3 mass. %

Also proposed is an article made of this nickel-based alloy having an equiaxed or single crystal structure.

The introduction of the proposed alloy of cerium, yttrium, lanthanum and calcium at the stated ratio of alloying elements leads to the fact that during the casting process, the above elements interact with impurities of sulfur, oxygen, nitrogen with the formation of sulfides, oxides and nitrides, which are concentrated in a profitable casting parts (sprues) of the casting part. As a result, the content of harmful impurities of sulfur, oxygen, and nitrogen in the volume of the alloy solid solution decreases and, as a result, the long-term strength increases. During thermal and / or barothermic treatment of alloy castings on the inner surfaces of inevitably founding and homogenizing micropores, the above elements interact with the remains of sulfur, oxygen, and nitrogen impurities to form dispersed sulfides, oxides, and nitrides inside the micropores. Thus, the formation of additional stress concentrators in the form of individual particles of sulfides, oxides and nitrides is reduced. As a result, the long-term strength and resistance of the alloy to corrosion are also increased.

Molybdenum and chromium, having distribution coefficients between the γ 'and γ phases equal to ~ 0.3 and ~ 0.2, respectively, are dissolved mainly in the γ-solid alloy solution. Therefore, increasing the molybdenum content to 1.5-2.1 mass. % and chromium to 11.9-12.7 mass. % in the proposed alloy with the claimed balanced total content of alloying elements causes an increase in the period of the crystal lattice of the γ-solid solution and thereby an increase in the relative difference between the periods of the crystal lattices of the γ- and γ'-phases (γ / γ'-misfit), which increases the long-term strength alloy.

Reduced to 4.0-5.2 mass. The tungsten content in the proposed alloy leads to a decrease in density and also helps to increase the high-temperature phase stability of the γ-solid solution and MeC-carbides and, therefore, to achieve higher values of long-term strength.

The exclusion from the chemical composition of the inventive alloy of the γ'-forming element of hafnium along with an increase in the content of γ-stabilizing elements of molybdenum and chromium contribute to a decrease in the volume fraction of precipitates of eutectic origin of the Ni ₃ (Al, Hf) or Ni ₅ Hf type in the cast alloy structure, which allows to obtain complex products with polycrystalline (equiaxial) or directional (monocrystalline) structure from it without the formation of foundry friability and hot microcracks during crystallization, as well as odit thermal and / or barothermal processing products in order to reduce their porosity without the danger of melting.

In addition, the ratio of the components of the proposed alloy — chromium, cobalt, tungsten, molybdenum, titanium, aluminum, tantalum, rhenium (if any), zirconium and nickel, provides an increase in phase stability, which eliminates the tendency of the alloy to form TPU phases.

где Z_i - концентрация i-го элемента, атомн. %, A_i - атомная масса i-го элемента, E_i - количество валентных электронов i-го элемента, n=9 или 10 - количество компонентов сплава (хром, кобальт, вольфрам, молибден, титан, алюминий, тантал, рений (при наличии), цирконий, никель) (Самойлов А.И., Морозова Г.И., Кривко А.И., Афоничева О.С. Аналитический метод оптимизации легирования жаропрочных никелевых сплавов // Материаловедение. 2000. №2. С. 14-17).It is known that to ensure phase stability, the value of the parameter ΔE characterizing it must correspond to the condition: 0.02≥ΔE≥-0.04. The specified parameter is calculated by the following formula:

where Z _i is the concentration of the i-th element, atom. %, A _i is the atomic mass of the i-th element, E _i is the number of valence electrons of the i-th element, n = 9 or 10 is the number of alloy components (chromium, cobalt, tungsten, molybdenum, titanium, aluminum, tantalum, rhenium (at availability), zirconium, nickel) (Samoilov AI, Morozova GI, Krivko AI, Afonicheva OS An analytical method for optimizing alloying of heat-resistant nickel alloys // Material Science. 2000. No. 2. P. 14 -17).

For the proposed alloy, this value is in the range from -0.007 to -0.032, while for the prototype alloy it is from -0.123 to -0.055, that is, beyond critical values. This indicates the lack of propensity of the proposed alloy to the formation of harmful TPU phases, as well as destabilizing solid-phase carbide reactions of the type MeC → Me ₆ C + γ '.

Products from the proposed alloy, for example, gas turbine blades with polycrystalline (equiaxial) and directional (monocrystalline) structures will have high indicators of long-term strength and corrosion resistance, providing increased reliability and service life.

Examples of implementation.

In a vacuum induction furnace, 4 melts of the proposed alloy and 2 melts of the prototype alloy were carried out. The melted alloys were remelted in vacuum units for equiaxial or directional crystallization to obtain products with a polycrystalline (equiaxial) or directional (single crystal) structure in the form of castings with a diameter of ~ 16 mm and a length of 70 and 160 mm, respectively.

The chemical composition of the proposed alloy and the prototype alloy are shown in table 1.

Further, samples were made from the obtained castings for differential thermal analysis and quantitative metallography, the results of which were used to determine the melting temperature and volume fraction of precipitates of the eutectic origin.

The obtained alloy castings were subjected to heat treatment, including homogenizing annealing and two-stage aging.

Samples were made from heat-treated castings in this way to determine the density and mechanical tests for long-term strength (sample length 70 mm, working base 25 mm, working diameter 5 mm), the results of which determined the time to failure at given temperatures and stresses.

Mechanical tests for long-term strength were carried out according to GOST 10145-81.

Testing of samples with a polycrystalline (equiaxial) structure was carried out in an atmosphere of air at a temperature of 900 ° C and a voltage of 260 MPa.

Tests of samples with a directed (single-crystal) structure were carried out in an atmosphere of air at a temperature of 1000 ° C and stresses of 200 and 140 MPa.

The corrosion resistance of the alloys was estimated by calculation, comparing the relative values of the mass loss of the alloy logjmetal loss (mm / 20 h)] obtained according to the well-known regression equation when the Na2S04 + NaCl salts were kept in the melt for 20 h at a temperature of 900 ° С (Harada N., Yamazaki M., Sakuma N. at al. Alloy design for nickel-base superalloys // In: Proc. Conf. "High Temperature Alloys for Gas Turbines 1982 @, held in Liege, Belgium, 406 Okt. 1982 / D. Reidel Publishing Co.)

The obtained characteristics of the compositions of the proposed alloy and alloy prototype are shown in table 2.

As can be seen from table 2, the proposed alloy has improved in comparison with the prototype alloy characteristics of long-term strength and corrosion resistance.

The alloy has a higher melting temperature of precipitates of a non-equilibrium phase of eutectic origin (by 14-52 ° C) and a lower volume fraction in the structure of castings of alloy products (2-4 times) than from an alloy taken as a prototype. In addition, the absolute values of the ΔE parameter characterizing the phase stability of the proposed alloy do not go beyond the critical values and range from -0.007 to -0.032, in contrast to the prototype alloy, in which the ΔE parameter values are from -0.123 to -0.055, which indicates an increase in the phase stability of the proposed alloy - the absence of a tendency to form harmful TPU phases, as well as destabilizing solid-phase carbide reactions of the type MeC → Me ₆ C + γ '.

The reduced volume fraction of precipitates of a non-equilibrium phase of eutectic origin provides the technological advantage of the proposed alloy, which consists in the possibility of producing articles of complex shape from it with a polycrystalline (equiaxial) or directional (monocrystalline) structure without the formation of cast friability and hot microcracks during crystallization, as well as thermal and / or barothermic processing of the product without the risk of reflow.

The described advantages will make it possible to use the proposed alloy for the production of gas turbine blades for gas turbine engines and gas turbine engines, which operate continuously in aggressive environments at temperatures up to 900-1000 ° C.

Claims (4)

1. A heat-resistant nickel-based alloy containing carbon, chromium, cobalt, tungsten, molybdenum, titanium, aluminum, tantalum, boron and zirconium, characterized in that it additionally contains cerium, yttrium, lanthanum and calcium in the following ratio of components, wt. %: carbon 0.05-0.15 chromium 11.9-12.7 cobalt 10.0-12.0 tungsten 4.0-5.2 molybdenum 1.5-2.1 titanium 3.2-4.2 aluminum 3.2-4.0 tantalum 1.5-2.9 boron 0.001-0.015 zirconium 0.008-0.08 cerium 0.002-0.02 yttrium 0.002-0.02 lanthanum 0.002-0.02 calcium 0.001-0.01 nickel rest 2. The alloy according to claim 1, characterized in that it further comprises rhenium in an amount of 0.9-3 wt. % 3. A product of a heat-resistant nickel-based alloy, characterized in that it is made of an alloy according to claim 1 or 2.