RU2525883C1 - Refractory nickel-based alloy for casting gas turbine working blades - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed alloy comprises the following components in wt %: carbon 0.001-0.12, chromium 8.8-9.2, cobalt 4.8-5.2, tungsten 6.1-6.5, molybdenum 0.15-0.3, aluminium 3.7-3.9, tantalum 3.9-4.1, rhenium 3.4-3.6, boron 0.0003-0.01, niobium 0.10-0.20, cerium 0.002-0.012, yttrium 0.002-0.012, titanium 2.9-3.1, hafnium 0.15-0.25, manganese 0.002-0.12, nickel making the rest. This alloy contains cerium and yttrium at equal amounts while titanium-to-aluminium content is higher than 0.75.

EFFECT: higher long-term durability and oxidation resistance.

2 tbl

Description

The invention relates to metallurgy, in particular to heat-resistant casting alloys based on nickel with chromium and cobalt, and can be used for casting parts of the hot path of gas turbine units (GTU), for example, gas turbine blades with single-crystal, directional and equiaxial structures, working in aggressive environments at temperatures of 800-1000 ° C.

High strength characteristics of such alloys are achieved due to a significant amount (50-70 vol.%) Of the hardening γ'-phase (Ni ₃ Al) doped with niobium, titanium, tantalum, etc., as well as hardening of the solid solution (γ-phase ) cobalt, chromium, molybdenum, tungsten and rhenium. Increased corrosion resistance is ensured by a high chromium content (usually 6-10 wt.%) With a ratio of titanium to aluminum Ti / Al≥0.3, as well as the introduction of rhenium and rare earth elements. Oxidation resistance at elevated temperatures is provided by an increased content of aluminum and tantalum, a decrease in the content of chromium and, primarily, molybdenum, and also the introduction of rare earth elements.

Structural stability per resource (eliminating the formation of embrittleing phases) and limiting the formation of nonequilibrium phases during crystallization, in the place of which pores and cracks will arise after their decomposition during heat treatment, can be evaluated using the well-known FACOMP method.

The characteristics of long-term strength, the critical points of the alloy and its other physical and mechanical properties can also be evaluated by known methods.

(H. Harada et al., Sat. Superalloys, 1988; p. P. 733-742; Sat. Superalloys, 2000; p. P. 729-736.)

Known heat-resistant alloy based on Nickel for casting gas turbine blades with a single crystal structure containing cobalt, chromium, molybdenum, tungsten, tantalum, aluminum, titanium, hafnium, rhenium, in the following ratio, wt.%: Cobalt 9.3-10, 0; chromium 6.4-6.8; molybdenum 0.5-0.7; tungsten 6.2-6.6; tantalum 6.3-6.7; aluminum 5.45-5.75; titanium 0.8-1.2; hafnium 0.07-0.12, rhenium 2.8-3.2; nickel - the rest. The maximum carbon content in the known alloy is limited to 60 ppm, boron - 30 ppm, zirconium - 75 ppm, sulfur - 20 ppm, silicon - 400 ppm.

(US 4643782, C22C 19/05, published 02.17.1987.)

Cast gas turbine blades made of a known alloy have an increased volume of non-equilibrium eutectic γ'-phase (6-8%), which during casting can lead to significant porosity of the casting, as well as to a decrease in corrosion resistance and oxidation of the blades under aggressive exposure environment due to suboptimal ratios of alloying elements.

The closest is a heat-resistant nickel-based alloy for the manufacture by directional crystallization of gas turbine blades with directional and single-crystal structures. The known alloy includes carbon, chromium, cobalt, tungsten, molybdenum, aluminum, tantalum, rhenium, boron, niobium, cerium, yttrium, lanthanum, neodymium and nickel in the following ratio of components, wt.%: Carbon 0.05-0.12; chrome 5.0-6.0; cobalt 8.0-10.0; tungsten 6.5-7.5; molybdenum 0.8-1.5; 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 0.005-0.10; yttrium 0.0001-0.002; lanthanum 0.001-0.05; neodymium 0.0005-0.01; nickel rest.

(RU 2148099, C22C 19/05, published 04/27/2000.)

However, this known alloy at high rates of heat resistance has low corrosion resistance and reduced oxidation resistance due to the significant content of molybdenum.

The aim of the invention and its technical result is the achievement of: increased long-term strength of heat-resistant alloy for cast vanes of gas turbines in combination with high resistance to oxidation and corrosion; increased structural stability per resource; improving the technological characteristics of the alloy. In addition, the proposed alloy provides the production of working blades of gas turbines with single crystal, directional or equiaxial structures.

The technical result is achieved in that the heat-resistant nickel-based alloy for casting rotor blades of gas turbine plants contains carbon, chromium, cobalt, tungsten, molybdenum, aluminum, tantalum, rhenium, boron, niobium, cerium, yttrium, titanium, hafnium, manganese and nickel, in the following ratio of components, wt.%:

carbon 0.001-0.12 chromium 8.8-9.2 cobalt 4.8-5.2 tungsten 6.1-6.5 molybdenum 0.15-0.3 aluminum 3.7-3.9 tantalum 3.9-4.1 rhenium 3.4-3.6 boron 0.0003-0.01 niobium 0.10-0.20 cerium 0.002-0.012 yttrium 0.002-0.012 titanium 2.9-3.1 hafnium 0.15-0.25 manganese 0.002-0.12 nickel rest

while cerium and yttrium are contained in equal amounts, with a total aluminum and titanium content of 6.6-7.0 wt.% and the ratio of titanium to aluminum content> 0.75.

In the alloy according to the invention, the amount of hardening γ'-phase (Ni ₃ Al) is 56.7-58.9 at.%, Which provides a high and stable level of service characteristics, for example, heat resistance: 343-348 MPa for 10 ³ hours at 900 ° C.

The optimal content of tungsten, rhenium, tantalum gives increased heat resistance of the cast alloy, however, a further increase in their total content causes a significant increase in the temperature of dissolution of the γ'-phase, which can be compensated by an increase in the content of cobalt, but this increases the cost of the alloy.

Hafnium in combination with niobium in the declared concentrations provide sufficient ductility of the cast alloy for a long life and stabilization of carbides.

Moreover, the claimed ratios of the components in the alloy exclude the occurrence of embrittling phases during the running time and limit the release of the nonequilibrium eutectic γ'-phase, which provides a reduced volume of gas-shrink porosity and increases the resistance of the product to cracking. A high ratio of titanium to aluminum content> 0.75 in combination with a high chromium and rhenium content, the presence of rare earth metals and manganese contributes to an increase in the corrosion resistance of the proposed alloy.

The proposed alloy according to the invention by changing the content of carbon and boron allows you to get blades with single crystal, directional or equiaxial structures. In this case, the single-crystal structure is achieved when the content of carbon and boron in the alloy is predominantly in the ranges of 0.001-0.02 and 0.0003-0.002, respectively, and the directional and equiaxial structures are achieved when the content of carbon and boron in the alloy is mainly in the ranges of 0.04-0, 12 and 0.004-0.01, respectively.

In comparison with an alloy with a single-crystal structure, an alloy with directional and equiaxial structures will have approximately equal structural stability, but reduced characteristics of short-term and long-term strength. However, the advantage of alloys with directional and equiaxial structures is the lower cost of cast billets, mainly due to the increased yield.

To obtain cast working blades of a gas turbine from an alloy according to the invention, known methods and devices for casting turbine blades from heat-resistant alloys with single-crystal, directional and equiaxial structures are used. Heat treatment of cast billets involves homogenizing annealing at a temperature of about 1260 ° C for 3-10 hours.

The achievement of the technical result can be illustrated by the data from tables 1 and 2.

From the presented data it is seen that the alloy according to the invention with a single crystal structure (MK) at approximately equal values in heat resistance at temperatures of 800-950 ° C significantly (about an order of magnitude) surpasses the known alloy in terms of corrosion resistance. Alloys with directional (NK) and equiaxial (PC) have the expected lower service characteristics, but sufficient for the use of such alloys for the manufacture of casting working blades of the first stages of gas turbines.

The achieved increased resistance to aggressive environmental influences of the proposed alloy (compared with the known analogue) can increase the operational reliability and service life of products and, as a result, reduces the annual demand for metal. Moreover, the cost of the charge materials of the alloy according to the invention is ≈15% lower than that of the known one.

Narrow alloying intervals reduce the variation in the values of service characteristics and provide guaranteed strength and ductility values, which are laid down by the designers in the calculation of the product.

Table 1 The content of components, wt.% Famous alloy Alloy according to the invention CMSX-4 to US 4643782 according to RU 2148099 MK structure PC and NK structures carbon less than 60 ppm 0.08 0.01 0.08 chromium 6.5 5.5 9.0 9.0 cobalt 9.6 9.0 5,0 5,0 tungsten 6.4 7.0 6.3 6.3 molybdenum 0.6 1,1 0.25 0.25 aluminum 5,6 5.8 3.8 3.8 tantalum 6.5 4.9 4.0 4.0 rhenium 3.0 4.2 3,5 3,5 niobium - 0.8 0.15 0.15 titanium 1,0 - 3.0 3.0 cerium - 0.010 0.006 0.006 yttrium - 0.001 0.006 0.006 hafnium 0.10 - 0.20 0.20 manganese - - 0.05 0.05 silicon less than 400 ppm - - - boron less than 40 ppm 0.01 0.001 0.008 Lanthanum, Neodymium - at 0.001 - - nickel rest rest rest rest

table 2 Alloy characteristics Famous alloy Alloy according to the invention CMSX-4 to US 5270123 according to RU 2148099 MK structure PC structure NK structure 1. The strengthening γ'-phase 1.1. The volume of the γ'-phase, at.% 69.7 67.1 58.3 58.4 58.4 1.2. The total content of titanium and aluminum, wt.% 6.6 5.75 6.9 6.9 6.9 1.3. Solvus Tγ 'averaged, ° C 1290 1271 1255 1253 1253 1.4. Degree of legality of the γ'-phase 1,099 1,058 1,057 1.018 1.018 1.5. Ti / Al Ratio 0.18 - 0.79 0.79 0.79 1.6. Mismach at 900 ° C -0.001 -0.002 -0.003 -0.002 -0.002 1.7. The amount of non-equilibrium γ'-phase, inter-molten,% 6-7 1-2 2-3 1-2 1-2 2. The energy of stacking faults in the γ phase 1,353 2,157 0.870 1,186 1,186 3. The density of t / m ³ 8.72 8.78 8.70 8.68 8.68 4. Structural stability of FACOMP, 4.1. M _{dy crit} ≤0.928 averaged with TO 0.913 0.898 0.926 0.921 0.921 4.2. cast without maintenance: interax 0.907 0.911 0.888 0.883 0.883 5. Long lasting strength

one) $${\sigma }_{\mathrm{one}{0}^3}^{750^{\circ }C}$$

- - - 611 - 2) $${\sigma }_{\mathrm{one}{0}^3}^{850^{\circ }C}$$

497 510 484 341 437 3) $${\sigma }_{\mathrm{one}{0}^3}^{900^{\circ }C}$$

346 353 345 244 311 four) $${\sigma }_{\mathrm{one}{0}^3}^{\mathrm{one}000^{\circ }C}$$

184 184 182 - 163 6. Comparative corrosion resistance lg Metall loss (JN792 = -0.26) 0.982 0.569 -0.727 -0.776 -0.776 lg corros Rate (JN792 = 0.1) 0.186 0.402 -0.255 -0.235 -0.235 7. The relative cost of cast billet casting - - 1,0 0.45 0.75

Claims (1)

Nickel-based heat-resistant alloy for casting rotor blades of gas turbine plants containing carbon, chromium, cobalt, tungsten, molybdenum, aluminum, tantalum, rhenium, boron, niobium, cerium, yttrium and nickel, characterized in that it additionally contains titanium, hafnium and manganese in the following ratio of components, wt.%:
carbon 0.001-0.12 chromium 8.8-9.2 cobalt 4.8-5.2 tungsten 6.1-6.5 molybdenum 0.15-0.3 aluminum 3.7-3.9 tantalum 3.9-4.1 rhenium 3.4-3.6 boron 0.0003-0.01 niobium 0.10-0.20 cerium 0.002-0.012 yttrium 0.002-0.012 titanium 2.9-3.1 hafnium 0.15-0.25 manganese 0.002-0.12 nickel rest
however, it contains cerium and yttrium in equal amounts, and the ratio of titanium to aluminum content is> 0.75.