RU2465359C1 - Heat-resistant alloy on nickel basis for monocrystalline casting - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to heat-resistant nickel-based alloys intended for manufacture of parts of high-temperature gas turbines of gas turbine engines and gas turbine plants by means of direct crystallisation method, mainly of monocrystalline blades and other components of hot turbine path, which operate continuously at temperatures exceeding 1000°C. Alloy contains the following, wt %: carbon 0.001-0.04, chrome 3.5-5.5, cobalt 8.0-10.0, tungsten 4.5-6.5, molybdenum 1.5-2.5, titanium 0.5-1.2, aluminium 5.5-6.2, tantalum 4.5-7.0, rhenium 3.5-5.0, cerium 0.005-0.01, yttrium 0.001-0.01, oxygen 0.0001-0.001, nitrogen 0.0001-0.001, silicon 0.005-0.2, manganese 0.01-0.2, iron 0.01-0.5, nickel is the rest when the following conditions are met: 11,0%≤W+Ta≤12.0%, 9.5%≤Ta+Re≤10.5%, 6.0%≤Al+Ti≤7.0%.

EFFECT: alloy is characterised with high level of heat resistance, phase stability and resistance of high-temperature corrosion at high characteristics of low-cycle fatigue and endurance limit.

2 cl, 2 tbl, 7 ex

Description

The invention relates to the field of metallurgy, in particular to nickel-based heat-resistant alloys, intended for the production by directional crystallization of parts of high-temperature gas turbines of gas turbine engines and gas turbine engines, mainly single-crystal workers, nozzle blades and other elements of the turbine’s hot path, which operate for a long time at temperatures exceeding 1000 ° FROM.

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

Carbon 0.05-0.12 Chromium 5.0-6.0 Cobalt 8.0-10.0 Tungsten 6.5-7.5 Molybdenum 0.8-1.5 Niobium 0.6-1.0 Aluminum 5.5-6.0 Tantalum 4.4-5.4 Rhenium 3.8-4.6 Boron 0.001-0.02 Niobium 0.6-1.0 Cerium 0.005-0.1 Yttrium 0.0001-0.002 Lanthanum 0.001-0.05 Underestimated 0.0005-0.01 Nickel rest

Subject to the conditions

9.5≤ (1 / 2W + 1 / 2Re + 1 / 2Ta + Mo + Nb) ≤10.5 (RF Patent No. 2148099).

In terms of heat resistance characteristics, it surpasses well-known alloys for blades with a directional structure, both domestic ZhS26, ZhS30, and foreign MarM200, MarM246 and other alloys. A high level of strength characteristics of the alloy is determined by its alloying with rhenium. However, the alloy is not phase stable. When the alloy contains rhenium at the level of 4–4.3% and tungsten at the level of 8.5–9%, lamellar precipitates of topologically densely packed phases form in the alloy at high temperatures. Topologically tightly packed (TPU) containing rhenium phases embrittlement and softening of the alloy; The result of phase transformations is high dispersion and a decrease in the long-term strength characteristics of the alloy. Precipitations of this type in the alloy can also form after heat treatment and technological heating in the manufacture of parts, which requires additional control and significantly increases the rejection of parts.

Known heat-resistant nickel alloy of the following chemical composition, wt.%:

Chromium 6.4-6.8 Cobalt 9.3-10.0 Tungsten 6.2-6.6 Molybdenum 0.5-0.7 Titanium 0.8-1.2 Aluminum 5.45-5.75 Tantalum 6.3-6.7 Rhenium 2.8-3.2 Hafnium 0.07-0.12 Carbon 0.01-0.08 Nickel the basis

(US Patent No. 5,549765).

The alloy is designed for casting vanes with a single crystal structure having a crystallographic orientation [001]; in this orientation, the alloy has a high level of heat resistance. The alloy is widely used for casting working and nozzle cooled single-crystal vanes of modern gas turbine engines. However, it is noted that its manufacturability is not high enough for single-crystal casting, that is, the yield of casting in structure. In addition, this alloy has low values of long-term strength in the [111] orientation, which limits the possibilities of its application.

Closest to the proposed technical solution and adopted for the prototype is an alloy of the following chemical composition, wt.%:

Chromium 4.0-6.0 Cobalt 8.0-10.0 Tungsten 6.5-8.0 Molybdenum 0.8-2.2 Titanium 0.1-1.0 Aluminum 5.4-6.2 Tantalum 4.0-7.0 Rhenium 2.7-3.7 Niobium 0.1-1.0 Boron 0.001-0.02 Cerium 0.015-0.05 Yttrium 0.001-0.002 Oxygen 0.0003-0.001 Nitrogen 0.0003-0.001 Carbon 0.001-0.04 Nickel rest

(RF patent No. 2318030).

The alloy is intended for casting GTE blades with directional and single-crystal structures that operate for a long time at high temperatures. The alloy has an insufficiently high level of heat resistance at temperatures exceeding 1000 ° C. The alloy does not have high phase stability during prolonged exposure to temperatures and voltages. When the content of W and Re in the stated ratio in the alloy, the formation of TPU phases is noted, which leads to a decrease in the characteristics of long-term strength (heat resistance), which along with insufficiently high corrosion resistance limits the use of products from this alloy by operating temperature and climatic conditions.

An object of the invention is the development of a heat-resistant nickel-based alloy for single-crystal casting of castings of GTE and GTU parts with a working temperature exceeding 1000 ° C, with a higher level of heat resistance, phase stability and high-temperature corrosion resistance while maintaining high MCU characteristics, endurance and processability.

To achieve the technical objective, a heat-resistant nickel-based alloy is proposed for single crystal casting containing carbon, chromium, cobalt, tungsten, molybdenum, titanium, aluminum, tantalum, rhenium, cerium, yttrium, oxygen, nitrogen, characterized in that it additionally contains silicon , manganese and iron in the following ratio of components, wt.%:

Carbon 0.001-0.04 Chromium 3,5-5,5 Cobalt 8.0-10.0 Tungsten 4,5-6,5 Molybdenum 1.5-2.5 Titanium 0.5-1.2 Aluminum 5.5-6.2 Tantalum 4,5-7,0 Rhenium 3,5-5,0 Cerium 0.005-0.01 Yttrium 0.001-0.01 Oxygen 0.0001-0.001 Nitrogen 0.0001-0.001 Silicon 0.005-0.2 Manganese 0.01-0.2 Iron 0.01-0.5 Nickel rest

subject to the following conditions

11.0% ≤W + Ta≤12.0% 9.5% ≤Ta + Re≤10.5%

6.0% ≤Al + Ti≤7.0%.

The heat-resistant nickel-based alloy may additionally contain, wt.%: Niobium 0.001-0.2 and boron 0.001-0.02.

Alloying the alloy with silicon in the specified range increases the resistance of the heat-resistant alloy to oxidation.

The introduction of iron and manganese in small amounts (0.01-0.5% and 0.01-0.2%) increases the manufacturability of the alloy when casting single-crystal parts of a gas turbine engine, in particular, the fluidity of the alloy when casting parts of a complex configuration.

The total content of titanium and aluminum 6.0-7.0% provides the optimal content of the primary eutectic γ'-γ phase (3-5%), which dissolves during heat treatment, increases the amount of hardening γ'-γ phase, thereby contributing to hardening alloy.

Compared with the prototype alloy, the proposed alloy has a lower tungsten content and an increased rhenium content, as the element that most effectively hardens heat-resistant alloys. The main difficulty arising in the development of rhenium-containing alloys is that, during high-temperature heating, phases may form in the alloys related to the discharge of topologically close-packed (TPU phases), which are formed, as a rule, in the axes of dendrites and are plates that are parallel to the planes of the {111} octahedron. TPU phase impairs the properties of the alloy, embrittlement and lowering the strength characteristics. A decrease in the tungsten content increases the structural stability of the alloy relative to the precipitation of TPU phases. The structural stability of rhenium-containing alloys relative to the formation of the TPU phase is determined mainly by the ratio of the content of Re, W, and Ta in the alloy. In addition, the restriction of the content of 11% ≤ (W + Ta) ≤12% ensures the absence of surface defects such as “jet” segregation and increases the yield of single-crystal castings suitable for the macrostructure.

Examples of implementation

In the VIAM-2002 vacuum induction furnace, seven alloy compositions of the proposed composition and one alloy taken as a prototype were smelted (Table No. 1). The metal mass of each heat was 10 kg. Single crystal billets of the [001] orientation with a deviation not exceeding 5 °, a diameter of 16 mm and a length of 180 mm were obtained by directional crystallization using a UVKN-9 unit with liquid metal cooling.

Single-crystal sample blanks were subjected to high-temperature homogenization at a temperature above the dissolution temperature of the secondary strengthening γ'-phase and below the solidus temperature of the alloys. Heating to the final homogenization temperature was carried out with intermediate stepwise isothermal extracts, which avoided the appearance of a local reflow structure. Cooling from the homogenization temperature was carried out at a rate of ~ 100 ° C / min. After cooling, the preform was subjected to two-stage aging.

Assessment of the level of heat resistance of the proposed compositions was carried out at test temperatures of 1000 and 1100 ° C in accordance with GOST.

The test results are presented in Table 2. The results obtained indicate that the proposed alloy provides a higher level of heat resistance than the prototype alloy. At close levels of durability, the destruction of samples of the proposed alloy occurred at higher voltages. The time to fracture during heat resistance tests of the investigated compositions of the proposed alloy was significantly longer than that of the prototype alloy.

A metallographic analysis of the structure of the samples of the investigated alloys destroyed at a test temperature of 1100 ° C and a voltage of 100 MPa did not reveal the formation of TPU-phase lamellae during testing, which indicates a high phase and structural stability of the proposed alloy.

The study of the resistance of the new heat-resistant alloy to sulfide-oxide corrosion (SOC) was carried out at a temperature of 850 ° C on cylindrical samples of ⌀10 mm, h = 15 mm according to the following regime: the coating of the salt crust of Na ₂ SO ₄ + NaCl was carried out by immersing the samples in salt solution, drying of samples, then exposure of samples with salt crust at a temperature of 850 ° C for 1 hour, cooling in air. The total test duration is 30 cycles.

Before the tests, the samples were degreased and weighed on an analytical balance with an accuracy of 0.0002 g. The tests of the samples placed in alundum crucibles were carried out in a resistance chamber furnace with an air atmosphere. To determine the kinetics of the RNS process, samples were weighed every 5 test cycles. At the end of the tests, the samples were subjected to special treatment to remove corrosion products in accordance with GOST 9.907-83. The sulfide-oxide corrosion rate of the new alloy was an order of magnitude lower than that of the prototype.

Tests for low-cycle fatigue (MCU) and multi-cycle fatigue (ISC - endurance limit) were carried out according to GOST 25.502-79. The tests at the MCU were carried out on the basis of N = 10 ⁴ cycles, T = 750 ° C and tensile stress on PSB10K servo-hydraulic machines with a “soft” cycle from zero axial loading (R = 0) of a triangular shape, cycle frequency f = 1 Hz. Tests at the ISTC based on 2 × 10 ⁷ cycles were carried out on MVPIAM machines at temperatures of 20 and 900 ° C on smooth samples with pure bending with rotation (σ _-1 ), the loading cycle was symmetric (R = -1), cycle frequency f = 50 Hz. 3-4 samples from each heat at various voltage levels. Based on the test results, a generalized durability curve was constructed (the dependence of the number of cycles before failure on the applied stress), which determined the endurance limit of the material at a given temperature (Table 2).

From the totality of the results it follows that the proposed alloy provides a level of heat resistance and resistance to high temperature corrosion, superior to the heat resistance and corrosion resistance of the prototype alloy, and the MCU and endurance limit at the level of the prototype. The alloy is technologically advanced in single-crystal casting and is suitable for producing castings of complex configuration.

Thus, the use of the proposed alloy will improve the resource and reliability of products, in particular working, nozzle blades and other elements of the hot path of the turbine engine and gas turbine, long working at temperatures exceeding 1000 ° C.

Table number 1 The content of alloying elements in wt.% No. p / p FROM Cr Co W Mo Ti Al That Re Xie Y Si Fe Mn O N Nb AT W + Ta Ta + Re Al + Ti one 0.001 5.5 8.0 4,5 2.5 0.7 5.80 6.5 4.0 0,025 0.001 0.01 0.5 0.01 0,0005 0,0008 - - 11.0 10.5 6.5 2 0.005 4,5 8.98 5,0 1,5 0.5 5.5 7.0 3,5 0.005 0.003 0.08 0.4 0.2 0.0001 0,0005 - - 12.0 10.5 6.0 3 0.02 3,5 9.3 6.5 1,5 1.2 5.7 4,5 5,0 0.01 0.01 0.005 0.3 0.1 0,0008 0.001 - - 11.0 9.5 6.9 four 0.01 4.3 10.0 6.0 1.8 1.0 5.9 6.0 4.3 0.005 0.004 0.15 0.15 0.05 0.001 0,0008 - - 12.0 10.3 6.9 5 0.04 5,0 9.0 5.8 2.2 0.8 6.2 5.5 4.0 0.008 0.005 0.2 0.01 0.15 0,0006 0.0001 - - 11.3 9.5 7.0 6 0.02 4,5 9.2 5.5 1.8 1,2 5.7 6.0 4.0 0.008 0.003 0.08 0.4 0.2 0.0001 0,0008 0.001 0.02 11.5 10.0 6.9 7 0.01 4.0 8.5 6.0 1.8 1.0 5.9 6.0 4.3 0.005 0.004 0.15 0.15 0.05 0.001 0,0005 0.02 0.001 12.0 10.3 6.9 prototype 0.02 5.2 9.3 7.0 0.8 0.8 5.8 6.0 3,7 0,03 0.002 0.001 0.001 0.8 0.005 Base - Nickel

Table number 2 No. p / p Structure Time to failure when tested for long-term strength (heat resistance) in hours The rate of cyclic sulfide-oxide corrosion at 850 ° C in g / m ₂ · h Low-cycle fatigue in MPa based on N = 10 ⁴ cycle. T = 750 ° C Endurance limit in MPa based on cycles of 2 × 10 ⁷ smooth samples Test temperature 1000 ° C, voltage 275 MPa Test temperature 1000 ° C, voltage 175 MPa Test temperature 1100 ° C, voltage 150 MPa Test temperature 1100 ° C, voltage 105 MPa Test temperature 20 ° C 900 ° C one The inventive alloy 116 860 98 975 3.0-4.0 1100 480 400 125 940 105 1025 2 157 1035 126 1140 3.5-4.5 1110 480 410 149 1290 143 1267 3 165 1120 154 1150 2.0-4.0 1100 470 400 180 1250 148 1300 four 148 1050 136 1040 1.9-2.5 1100 480 400 138 1150 142 1089 5 106 820 one hundred 960 4,5-6,0 1120 485 420 103 895 105 895 6 115 1015 98 985 9.0-10.0 1140 480 430 125 1105 107 1025 7 136 960 93 970 8.5-9.5 1135 480 430 125 1040 115 1015 8 Prototype 90 675 74 650 30-50 1050 420 400 80 725 82 720

Claims (2)

1. A heat-resistant nickel-based alloy for single crystal casting containing carbon, chromium, cobalt, tungsten, molybdenum, titanium, aluminum, tantalum, rhenium, cerium, yttrium, oxygen, nitrogen, characterized in that it additionally contains silicon, manganese and iron , in the following ratio of components, wt.%:
Carbon 0.001-0.04 Chromium 3,5-5,5 Cobalt 8.0-10.0 Tungsten 4,5-6,5 Molybdenum 1.5-2.5 Titanium 0.5-1.2 Aluminum 5.5-6.2 Tantalum 4,5-7,0 Rhenium 3,5-5,0 Cerium 0.005-0.01 Yttrium 0.001-0.01 Oxygen 0.0001-0.001 Nitrogen 0.0001-0.001 Silicon 0.005-0.2 Manganese 0.01-0.2 Iron 0.01-0.5 Nickel Rest,
subject to the following conditions:
11.0% ≤W + Ta≤12.0%,
9.5% ≤Ta + Re≤10.5%,
6.0% ≤Al + Ti≤7.0%. 2. The heat-resistant alloy based on Nickel according to claim 1, characterized in that it further comprises, wt.%: Niobium 0.001-0.2 and boron 0.001-0.02.