RU2656908C1 - Heat-resistant cast nickel-based alloy and article made therefrom - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, in particular to nickel-based alloys, and can be used for the manufacture of hot-run parts of gas turbine engines and installations that operate for a long time at temperatures of up to 1,000 °C. Heat-resistant cast nickel-based alloy comprises, wt%: carbon up to 0.15, chromium 12–15, cobalt 3–7, tungsten 5–9, molybdenum 0.5–2, aluminium 2–5, titanium 3–6, lanthanum up to 0.20, yttrium up to 0.20, cerium up to 0.20, praseodymium up to 0.20, rhenium up to 0.20, hafnium up to 0.10, barium up to 0.10, calcium up to 0.10, magnesium up to 0.10, boron up to 0.02, zirconium up to 0.10, nickel – the balance.

EFFECT: alloy is characterised by high characteristics of long-lasting strength at operating temperatures up to 1,000 °C and resistance of the alloy to corrosion in corrosive environments, as well as high phase-structural stability during prolonged operation (more than 500 hours).

2 cl, 2 tbl, 5 ex

Description

The invention relates to the field of metallurgy, in particular to corrosion-resistant heat-resistant alloys for parts of the hot tract of gas turbine engines and installations, long-term working in aggressive environments at temperatures of 750-1000 ° C.

Known heat-resistant alloy based on Nickel of the following chemical composition, wt.%:

carbon 0.08-0.11 chromium 14.6-15.1 cobalt 8.5-8.9 tungsten 6.5-6.9 molybdenum 0.3-0.6 aluminum 3.9-4.1 titanium 3.6-3.8 boron 0.01-0.013 calcium 0.01-0.20 flints ≤0.1 manganese 0.15-0.30 sulfur ≤0.005 phosphorus ≤0.005 magnesium 0.01-0.20 copper ≤0.05 nitrogen 10-20 ppm oxygen 10-15 ppm,

at least two elements selected from the group:

iron ≤0.2 vanadium ≤0.10 barium ≤0.01 nickel rest

(RU 2538054 C1, 01/10/2015).

The alloy has low characteristics of long-term and short-term strength, increased porosity in castings and reduced corrosion resistance.

Known heat-resistant alloy based on Nickel of the following chemical composition, wt.%:

carbon 0.05-0.09 chromium 15.4-15.8 cobalt 10.0-10.4 tungsten 5.0-5.3 molybdenum 1.6-1.8 titanium 4.3-4.5 aluminum 3.0-3.2 boron 0.06-0.09 zirconium <0.015 hafnium 0.2-0.3 silicon <0.1 iron <0.1 copper <0.05 sulfur <0.005 nitrogen <20 ppm oxygen <15 ppm cerium <0.015 niobium 0.1-0.2 yttrium <0.03 manganese <0.1 phosphorus <0.005 nickel rest

(RU 2539643 C1, 01.20.2015).

The alloy has a fairly high strength and plastic characteristics, but is characterized by reduced structural stability during long-term operation associated with the precipitation of the embrittling σ-phase, which significantly reduces the heat-resistant properties of the alloy and limits the life of the engine.

The closest analogue taken as a prototype is a heat-resistant nickel-based alloy for casting rotor blades of gas turbine plants, containing, wt.%:

carbon 0.07-0.12 chromium 12.9-13.5 cobalt 5.3-5.9 tungsten 6.7-7.3 molybdenum 0.8-1.2 aluminum 3.2-3.5 titanium 4.4-4.7 boron 0.010-0.015 copper ≤0.04 sulfur ≤0.005 phosphorus ≤0.005 nitrogen ≤15 ppm oxygen ≤15 ppm calcium ≤0.02 magnesium ≤0.02 manganese 0.01-0.30,

at least two elements selected from the group:

iron, silicon, ≤0.2 each, barium

at least two elements selected from the group:

yttrium, lanthanum, neodymium and samarium 0.005-0.05 each

nickel rest

(RU 2562202 C1, 09/10/2015).

The alloy taken as a prototype has satisfactory corrosion resistance in aggressive environments at operating temperatures of 750-1000 ° C and fairly high characteristics of short-term strength and ductility, but it has low characteristics of long-term strength when tested on the basis of 500-1000 hours, as well as low processability (suitable yield) when casting parts.

Thus, the known alloys at operating temperatures of 750-1000 ° C do not have the optimal combination of service properties (heat resistance, ductility, high-temperature corrosion resistance, structural and phase stability during operation), as well as high adaptability to casting parts.

The objective of the invention is to develop a heat-resistant cast alloy based on nickel with an optimized combination of service properties and high adaptability.

The technical result of the invention is to increase the characteristics of long-term strength at operating temperatures of up to 1000 ° C in combination with high resistance of the alloy to corrosion in aggressive environments, as well as increased phase-structural stability of the alloy during long-term operation (more than 500 hours).

To achieve a technical result, a heat-resistant nickel-based casting alloy is proposed containing carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, lanthanum, yttrium, barium, calcium, magnesium, boron, while it additionally contains cerium, praseodymium, rhenium, hafnium and zirconium in the following ratio of components, wt.%:

carbon up to 0.15 chromium 12-15 cobalt 3-7 tungsten 5-9 molybdenum 0.5-2 aluminum 2-5 titanium 3-6 lanthanum up to 0.20 yttrium up to 0.20 cerium up to 0.20 praseodymium up to 0.20 rhenium up to 0.20 hafnium up to 0.10 barium up to 0.10 calcium up to 0.10 magnesium up to 0.10 boron up to 0.02 zirconium up to 0.10

nickel rest

Also proposed is a product made of this alloy.

Compared with the prototype alloy, the proposed alloy contains small strictly regulated amounts of cerium, praseodymium, rhenium, hafnium and zirconium.

It was found that the complex introduction to the alloy containing lanthanum and yttrium, cerium and praseodymium further improved the corrosion resistance and operational reliability of the alloy at temperatures of 750-1000 ° C by creating a reliable protective barrier layer on the metal surface.

Complex alloying of the alloy with lanthanum, yttrium, cerium and praseodymium also made it possible to increase the long-term strength characteristics of the alloy due to additional hardening of the γ-solid solution with ultrafine nanoparticles up to 100 nm in size.

Rhenium additionally strengthens the γ-solid solution, slows down the diffusion processes during high-temperature creep, and thereby enhances the heat resistance. In addition, rhenium together with lanthanum, yttrium, cerium, and praseodymium can increase the structural stability of the alloy during operation and exclude the formation of embrittlement phases of the σ and μ type in the structure.

The introduction of hafnium and zirconium allows you to neutralize the harmful effects of impurities of sulfur, phosphorus, oxygen and others due to their binding to refractory, chemically stable compounds. In addition, hafnium and zirconium are part of the γ'-phase and additionally stabilize it, thereby providing an increase in long-term strength.

The proposed alloy can be used to obtain parts with both equiaxial, so with directional and single crystal structure.

Examples of implementation.

In the vacuum induction furnace, five alloys of the proposed composition and one alloy of the composition taken as a prototype were smelted. The obtained preforms were remelted in a directional crystallization unit and ceramic blocks with preforms were cast for samples with a single crystal structure with a crystallographic orientation.

After heat treatment, samples were prepared from billets for carrying out tests for long-term strength, as well as samples for testing for sulfide-oxide and chloride corrosion.

Long-term strength tests were carried out at a temperature of 870 ° C and voltages of 360 and 275 MPa on the basis of 100 and 1000 hours, respectively, at a temperature of 900 ° C and a voltage of 295 MPa on the basis of 500 hours, as well as at a temperature of 1000 ° C and a voltage of 120 MPa at base of 500 hours.

Corrosion tests were carried out in a cyclic mode. One test cycle included:

- creating on a hot surface of the samples of the salt crust of an aqueous solution of a mixture of salts of 75% Na ₂ SO ₄ + 25% NaCl (for sulfide-oxide corrosion) or a 3.5% aqueous solution of NaCl (for chloride corrosion);

- exposure of samples at T = 850 ° C for 1 hour in a heating furnace;

- air cooling.

The total test duration is 30 cycles.

The corrosion resistance of the samples was evaluated by the specific change (decrease) in the mass by weighing the samples every 5 cycles.

The content of components (wt.%) In the alloys and the test results for long-term strength and corrosion are shown in tables 1 and 2, respectively.

The obtained test results indicate that the durability of the proposed alloy when tested for long-term strength under all conditions significantly exceeds the durability of the prototype alloy, i.e. the proposed alloy has a higher level of heat resistance.

The proposed alloy has high corrosion resistance at a test temperature of 850 ° C in comparison with the prototype alloy: the specific change (decrease) in the mass of the samples with both sulfide-oxide and chloride corrosion is almost 2 times less than that of the prototype alloy.

The metallographic analysis of the structure of the destroyed samples after testing for long-term strength on the basis of 500-1000 hours did not reveal embrittlement TPU phases (σ, μ, etc.) in it, which indicates a high phase and structural stability of the proposed alloy.

When casting single-crystal turbine blades from the proposed alloy, its good processability was confirmed - the yield of the blades according to deviations from KGO was 85-90%.

Thus, the proposed alloy significantly exceeds the prototype alloy in terms of durability and corrosion resistance, has a high phase-structural stability, which allows to increase the service life and reliability of parts of gas turbine engines and plants that are used for a long time in aggressive environments at elevated temperatures and voltages.

Claims (6)

1. A heat-resistant nickel-based casting alloy containing carbon, chromium, cobalt, tungsten, molybdenum, aluminum, titanium, lanthanum, yttrium, barium, calcium, magnesium and boron, characterized in that it additionally contains cerium, praseodymium, rhenium, hafnium and zirconium in the following ratio of components, wt.%: carbon up to 0.15 chromium 12-15 cobalt 3-7 tungsten 5-9 molybdenum 0.5-2 aluminum 2-5 titanium 3-6 lanthanum before 0.20 yttrium up to 0.20 cerium up to 0.20 praseodymium up to 0.20 rhenium up to 0.20 hafnium up to 0.10 barium up to 0.10 calcium up to 0.10 magnesium up to 0.10 boron up to 0.02 zirconium up to 0.10 nickel rest 2. A product from a heat-resistant casting alloy based on nickel, characterized in that it is made of an alloy according to claim 1.