RU2794496C1 - Heat-resistant nickel-based casting alloy and a product made from it - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to nickel-based cast heat-resistant alloys intended for casting parts of the hot path of gas turbine engines and installations, for example, turbine nozzles operating in a gaseous medium at high voltages and temperatures up to 1000°C. Nickel-based heat-resistant cast alloy contains, wt.%: cobalt 9.0-11.0, chromium 8.0-10.0, tungsten 6.5-7.5, aluminium 4.5-5.5, tantalum 3.0-5.0, titanium 2.0-3.0, molybdenum 1.0-3.0, hafnium 1.0-2.0, carbon 0.08-0.15, zirconium up to 0.10, boron up to 0.03, niobium up to 0.50, magnesium up to 0.05, lanthanum up to 0.05, yttrium up to 0.05, at least one element from the group: gadolinium and dysprosium up to 0.05, if necessary, erbium up to 0.05, nickel - the rest.

EFFECT: high long-term strength at temperatures of 900-1000° with a simultaneous increase in resistance to gas corrosion, as well as high structural stability of the alloy for a resource.

2 cl, 2 tbl, 8 ex

Description

SUBSTANCE: invention relates to the field of metallurgy, namely, nickel-based cast heat-resistant alloys intended for casting parts of the hot path of gas turbine engines and installations, for example, turbine nozzles operating in a gaseous medium at high voltages and temperatures up to 1000°C.

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

cobalt 9.0-10.0 iron 0.25 maximum chromium 8.0-9.0 aluminum 4.75-5.50 titanium 1.0-1.5 molybdenum 0-2.0 tungsten 6.0-9.0 carbon 0.12-0.18 zirconium 0.01-0.03 boron 0.005-0.015 tantalum 0.5-1.5 nickel and incidental impurities rest

(US 10533240 B2, 01/14/2020).

The alloy is characterized by reduced heat resistance, structural stability during operation and resistance to gas corrosion at temperatures of 900-1000°C.

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

chromium 7.25-7.75 molybdenum 0.6-1.0 tungsten 8.5-9.1 aluminum 6.0-6.4 titanium 0.6-1.0 carbon 0.06-0.10 boron 0.01-0.02 hafnium 0.4-0.6

at least one element from:

cobalt 8.6-9.6

And

tantalum 4.0-4.8

or

cobalt 8.6-9.4 tantalum 3.8-4.4

And

rhenium 0.4-0.6 nickel and impurities rest

(EP 3565914 A1, 11/13/2019).

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

chromium 9.5-10.0 cobalt 7.0-8.0 molybdenum 1.3-1.7 tungsten 5.75-6.25 tantalum 4.6-5.0 titanium 3.4-3.6 aluminum 4.1-4.3 niobium 0.4-0.6 hafnium 0.1-0.2 carbon 0.05-0.07 boron 0.003-0.005 nickel and incidental impurities rest,

(US 5399313 A, March 21, 1995).

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

chromium 9.0 cobalt 10.0 tungsten 7.0 molybdenum 2.0 aluminum 5.0 tantalum 3.5 titanium 2.5 carbon 0.1 boron 0.01 nickel rest

(Li-Kui Ning, Zhi Zheng, Feng-Quan An, Song Tang, Jian Tong, Hui-Si Ji, Hui-Wen Yu. Thermal fatique behavior of K125L superalloy, DOI 10.1007/s12598-014-0254-y, 23.05. 2014, page 2).

These alloys have low characteristics of long-term strength and reduced resistance to gas corrosion at operating temperatures.

The closest analogue is a nickel-based heat-resistant alloy of the Rene 125 brand, but with a reduced level of some elements (Zr, B, P, S, Si and, to a lesser extent, Ti and Hf), intended for the manufacture of some complex parts, for example, blades of aircraft gas turbine engines , containing, wt. %:

cobalt 9.50-9.90 chromium 8.70-9.00 tungsten 6.65-7.05 tantalum 3.67-3.87 carbon 0.10-0.12 molybdenum 1.77-1.97 aluminum 4.80-5.00 hafnium 1.48-1.52 titanium 2.28-2.33 boron 0.005-0.01 zirconium up to 0.007 nickel rest,

while the alloy may contain

phosphorus 0-0.001 sulfur 0-0.001 nickel ≥59.83 total titanium content, hafnium and aluminum up to 8.77

(FR 2980485 B1, 07/04/2014).

The alloy, taken as a prototype, has moderate characteristics of long-term strength, resistance to gas corrosion, as well as reduced structural stability during operation at operating temperatures of 900-1000°C.

Thus, the known alloys at operating temperatures of 900-1000°C do not have the optimal combination of service properties (long-term strength, resistance to high-temperature gas corrosion, structural stability during operation).

The objective of the proposed invention is to develop a high-temperature nickel-based cast alloy with an increased combination of service properties.

The technical result of the proposed invention is to increase the long-term strength and structural stability of the alloy for a resource at temperatures of 900-1000°C with a simultaneous increase in resistance to high-temperature gas corrosion (heat resistance).

To achieve a technical result, a nickel-based heat-resistant cast alloy containing cobalt, chromium, tungsten, aluminum, tantalum, titanium, molybdenum, hafnium, carbon, zirconium, boron is proposed, while it additionally contains niobium, magnesium, lanthanum, yttrium, at least at least one element from the group: gadolinium and dysprosium, with the following ratio of components, wt. %:

cobalt 9.0-11.0 chromium 8.0-10.0 tungsten 6.5-7.5 aluminum 4.5-5.5 tantalum 3.0-5.0 titanium 2.0-3.0 molybdenum 1.0-3.0 hafnium 1.0-2.0 carbon 0.08-0.15 zirconium up to 0.10 boron up to 0.03 niobium up to 0.50 magnesium up to 0.05 lanthanum up to 0.05 yttrium up to 0.05

at least one element from the group:

gadolinium and dysprosium up to 0.05 nickel rest.

The alloy may further contain up to 0.05 wt. % erbium.

A product made of this alloy is also proposed.

Compared with the prototype alloy, the proposed alloy contains strictly regulated amounts of microalloying elements of niobium, magnesium, lanthanum, yttrium and at least one element from the group: gadolinium and dysprosium.

It was found that the introduction of lanthanum, yttrium and at least one element from the group: gadolinium and dysprosium into the alloy of rare earth metals (REM) in given amounts makes it possible to increase the resistance of the alloy to high-temperature gas corrosion (heat resistance). These additives create a protective barrier layer on the metal surface due to their oxidation and thereby inhibit the diffusion fluxes of oxygen ions from the surface deep into the metal. In addition, these REMs contribute to the separation of ultrafine nanoparticles of the γ'-phase up to 100 nm in size from the γ-solid solution. Nanoparticles prevent the movement of dislocations during high-temperature creep, thereby providing an increase in heat resistance.

It was found that the introduction of magnesium into the melt before the addition of rare-earth metals makes it possible to increase and stabilize the degree of assimilation of these elements.

The presence of a strictly limited content of niobium in the alloy makes it possible to increase the temperature of complete dissolution of the γ'-phase, thereby providing an additional increase in heat resistance. With an increased content of niobium in the structure of the alloy during operation, topologically close-packed (TPU) phases are released, which reduce the long-term strength.

A balanced combination of alloying elements with the simultaneous introduction of REMs (lanthanum, yttrium and at least one element from the group: gadolinium and dysprosium) into the alloy makes it possible to increase the structural stability of the alloy for a resource by slowing down diffusion processes during high-temperature creep and eliminating the appearance of brittle TPU during operation phases.

It was found that when introduced into the alloy up to 0.05 wt. % of erbium provides an additional increase in long-term strength due to the release of ultrafine nanoparticles of the γ'-phase up to 50 nm in size from the γ-solid solution, which create an additional obstacle to the movement of dislocations in the process of high-temperature creep. In addition, the introduction of erbium strengthens the protective barrier layer on the metal surface, and thereby increases the resistance of the alloy to gas corrosion.

The proposed alloy can be used to obtain parts with a polycrystalline equiaxed or directional structure.

Implementation example.

Eight melts of the proposed alloy and one melt of the alloy taken as a prototype were carried out in a VIM-12 vacuum induction furnace. The mass of each heat was 13 kg. All melts were remelted in a UPPF-U vacuum melting and pouring unit and cast into blocks with blanks for samples with a polycrystalline equiaxed structure.

After heat treatment, samples were made from blanks for long-term strength tests at high temperatures and high-temperature gas corrosion tests (heat resistance).

The compositions of the alloy samples are shown in Table 1.

Long-term strength tests were carried out according to GOST 10145-81 at a temperature of 900°C and stresses of 330, 240 on the basis of 100-1000 hours, as well as at a temperature of 1000°C and a stress of 90 MPa on the basis of 500-2000 hours. From each heat, two samples were tested.

Tests for high-temperature gas corrosion were carried out according to GOST 6130-71 at a temperature of 1000°C. One test cycle included:

- loading samples into a hot oven in air;

- exposure of samples for 20 hours in an oven;

- extraction of samples and weighing.

The total duration of the tests is 5 cycles (100 hours).

The resistance of samples to high-temperature gas corrosion (heat resistance) was assessed by the specific change (loss) in mass.

The tests were carried out on 5 samples, after which the average value of their heat resistance (gas corrosion) was calculated.

The results of tests for long-term strength and heat resistance (high-temperature gas corrosion) of alloy samples are shown in table 2.

The results obtained show that the time to destruction of the proposed alloy during tests for long-term strength in all modes exceeds the time to destruction of the prototype alloy, i.e. the proposed alloy has a higher level of heat resistance.

The value of the change in the mass of samples for 100 hours of testing for heat resistance at a temperature of 1000°C for the proposed alloy (without erbium): approximately 70-90% lower than that of the prototype alloy, i.e. resistance to gas corrosion of the proposed alloy is superior to the prototype alloy.

The introduction of erbium into the alloy made it possible to further increase the durability of the alloy at T=900°C and a stress of 330 MPa from 121-142 h to 148-171 h, at T=900 and a stress of 240 MPa from 955-1030 h to 1189-1255 h, at Т=1000°С and voltage 90 MPa from 1101-1352 h to 1689-1854 h. In addition, the resistance of the alloy to gas corrosion increases: the corrosion rate (heat resistance) decreases from 0.0395-0.0442 to 0.0312-0 .0333 g/m ² ⋅ h.

Metallographic analysis of the structure of the destroyed samples after tests for long-term strength at temperatures of 900 and 1000°C and stresses of 240 and 90 MPa, respectively, on bases of 1000-2000 hours (Table 2) did not reveal the formation of embrittling TPU phases (σ, μ, etc.) , which confirms the high phase and structural stability of the proposed alloy.

Thus, the proposed alloy significantly surpasses the prototype alloy in terms of heat resistance and resistance to high-temperature gas corrosion (heat resistance), has phase stability, which makes it possible to increase the service life and reliability of aircraft gas turbine engines that operate for a long time in a gas (atmospheric) medium at elevated temperatures and stresses. .

Claims (5)

1. Nickel-based heat-resistant cast alloy containing cobalt, chromium, tungsten, aluminum, tantalum, titanium, molybdenum, hafnium, carbon, zirconium, boron, characterized in that it additionally contains niobium, magnesium, lanthanum, yttrium and at least one element from the group: gadolinium and dysprosium, and, if necessary, erbium, in the following ratio of components, wt.%: cobalt 9.0-11.0 chromium 8.0-10.0 tungsten 6.5-7.5 aluminum 4.5-5.5 tantalum 3.0-5.0 titanium 2.0-3.0 molybdenum 1.0-3.0 hafnium 1.0-2.0 carbon 0.08-0.15 zirconium up to 0.10 boron up to 0.03 niobium up to 0.50 magnesium up to 0.05 lanthanum up to 0.05 yttrium up to 0.05 at least one element from the group: gadolinium and dysprosium up to 0.05 if necessary, erbium up to 0.05 nickel rest 2. A product made of a heat-resistant nickel-based cast alloy, characterized in that it is made of an alloy according to claim 1.