RU2297466C2 - Monocrystal nickel heat-resistant alloy - Google Patents

Abstract

FIELD: alloy metallurgy.

SUBSTANCE: invention relates to nickel-base heat-resistant alloys. Invention proposes nickel-base heat-resistant alloy used in monocrystal casting comprising the following components, wt.-%: chrome, 4.7-5.4; cobalt, 5.9-6.9; molybdenum, 0.6-0.7; tungsten, 5.3-6.1; rhenium, 4.8-5.6; tantalum, 6.2-7.2; aluminum, 4.8-5.6; titanium, 0.3-0.4; niobium, 0.8-0.9; hafnium, 0.009-0.0011; carbon, 0.007-0.009; lanthanum, 0.001-0.005; yttrium, 0.001-0.005, and nickel, the balance, in the content of detrimental impurities: iron, 0.5, not above; manganese, 0.2, not above; silicon, 0.2, nor above; phosphorus, 0.015, not above, and sulfur, 0.01, not above. Invention provides enhancing heat-resistance and phase stability of monocrystal nickel-base heat-resistant alloy and improving its technological indices. Proposed alloy can be used in making articles with monocrystalline structure, for example, gas turbine vanes working at high temperatures.

EFFECT: improved and valuable properties of alloy.

2 tbl, 1 ex

Description

The invention relates to metallurgy of alloys, namely, heat-resistant nickel-based alloys used for parts with a single crystal structure, for example, gas turbine blades operating at high temperatures.

Known heat-resistant nickel alloy for single crystal casting René N6 [US Patent No. 5270123 Int. C1. ⁵ C22C 19/05, C22F 01/10, 1993] composition, wt. %:

Chrome - 4.0 ... 6.5

Cobalt - 10 ... 15

Molybdenum - 0.5 ... 2.0

Tungsten - 5 ... 6.5

Rhenium - 5.1 ... 5.6

Ruthenium - 0 ... 6

Tantalum - 7 ... 9.25

Aluminum - 5 ... 6.25

Niobium - 0 ... 1

Hafnium - 0.1 ... 0.5

Carbon - 0.02 ... 0.07

Boron - 0.003 ... 0.01

Nickel - the rest

subject to the condition (Cr + Mo) = 4.6 ... 6.5.

A disadvantage of the known alloy is insufficient heat resistance: at a temperature of 1093 ° C and a voltage of σ = 141 MPa, the durability of the alloy is about 100 hours. This is due to the tendency of the alloy to form topologically tightly packed (TPU) phases in the operating temperature range of 1000 ... 1100 ° C. The negative effect of the TPU phases on the properties of the alloy is manifested in the fact that they serve as a source of nucleation and propagation of cracks leading to premature failure. In addition, TPU phases bind a significant amount of the main alloying elements (rhenium, tungsten, cobalt, chromium, molybdenum) and thereby not only deplete them in the γ-solid solution, reducing the efficiency of solid solution hardening of the alloy, but also reduce the amount and thermal stability of the hardening γ ' phase.

The closest analogue, taken as a prototype, is a nickel heat-resistant single crystal alloy CMSX-10 [US Patent No. 5366695 Int. C1 ⁵ C22C 19/05, 1994]. The heat-resistant nickel-based alloy contains chromium, cobalt, aluminum, tungsten, niobium, molybdenum, tantalum, rhenium, hafnium, titanium in the following ratio of the above components, wt.%:

Chrome - 1.8 ... 4.0

Cobalt - 1.5 ... 9.0

Molybdenum - 0.25 ... 2.0

Tungsten - 3.5 ... 7.5

Rhenium - 5.0 ... 7.0

Tantalum - 7.0 ... 10.0

Aluminum - 5.0 ... 7.0

Titanium - 0.1 ... 1.2

Niobium - 0 ... 0.5

Hafnium - 0 ... 0.15

Nickel - the rest

The alloy has the following characteristics of heat resistance: at a temperature of 982 ° C and a voltage of σ = 248 MPa, the durability of the alloy is τ = 239.8 ... 775.2 h; at a temperature of 1010 ° С and σ = 248 MPa, τ = 140.7 ... 354.4 h.

However, a disadvantage of the known alloy is a specific phase instability - the formation of a secondary reaction zone (SRZ), due to the high content of rhenium. SRZ is a three-phase region of a γ'-matrix with lamellar precipitates of the γ-phase and TPU of the P-phase of the Ni-Re-W system, the latter containing up to 50% rhenium and up to 20% tungsten.

In addition, the CMSX-10 alloy is prone to the formation of crystallization of excess phases of eutectic origin based on Ni ₃ (Al, Ta, Ti, Hf, Nb). The presence of eutectic phases in the cast structure of the alloy worsens the technological properties of the alloy, decreasing the temperature range of homogenizing annealing, which is equal to the difference between the local melting temperature and the temperature of complete dissolution of the strengthening γ'-phase. As a result, difficulties arise in performing heat treatment on a solid solution to dissolve excess phases and eliminate liquid segregation heterogeneity without the risk of melting, and the alloy has insufficiently high long-term strength at a temperature of 1000 ° C.

The problem to which the invention is directed, is to increase the heat resistance and phase stability of a single-crystal nickel heat-resistant alloy while improving technological characteristics.

The solution to this problem is achieved by optimal alloying of a single-crystal nickel heat-resistant alloy with cobalt, tungsten, molybdenum, rhenium and tantalum, which helps to reduce the risk of SRZ formation and increase heat resistance. Most preferred is the following ratio of components, wt. %:

Chrome - 4.7 ... 5.4

Cobalt - 5.9 ... 6.9

Molybdenum - 0.6 ... 0.7

Tungsten - 5.3 ... 6.1

Rhenium - 4.8 ... 5.6

Tantalum - 6.2 ... 7.2

Aluminum - 4.8 ... 5.6

Titanium - 0.3 ... 0.4

Niobium - 0.8 ... 0.9

Hafnium - 0.009 ... 0.011

Carbon - 0.007 ... 0.009

Lanthanum - 0.001 ... 0.005

Yttrium - 0.001 ... 0.005

Nickel - the rest

when containing harmful impurities:

Iron - no more than 0.5

Manganese - no more than 0.2

Silicon - not more than 0.2

Phosphorus - not more than 0.015

Sulfur - not more than 0.01.

A decrease in the concentration of molybdenum reduces the tendency of the alloy to release TPU phases and M ₆ C carbide phases with an unfavorable morphology. The introduction of carbon, lanthanum, and yttrium into the alloy composition further contributes to the expansion of the temperature range of homogenizing annealing, thereby reducing the risk of local melting during homogenization. A decrease in hafnium concentration helps to reduce the volume fraction of phases of eutectic origin based on Ni ₃ (Al, Ta, Ti, Hf, Nb), while also reducing the risk of local melting. As a result, the long-term strength of the alloy increases.

Concrete example

In a vacuum induction melting furnace UPPF-3M with an electrocorundum crucible with a capacity of 15 kg, 4 melts of the alloy of the proposed composition and one melting of the composition corresponding to the prototype alloy were prepared. As the initial charge materials were used:

Heat-resistant nickel alloy ZhS32 TU 1-92-177-91 Nickel electrolytic grade H0 GOST 849-97 Chrome aluminothermic grade X0 GOST 5905-79 Cobalt metal K1 brands GOST 123-98 Metal Molybdenum TU 48-19-73-86 Metal tungsten TU 48-19-76-90 Rhenium metal Re-2-RE TU 88-59 Tantalum bullion brand T-0 GOST 16400-70 Aluminum metal brand A99 GOST 11739-90 VT1-0 titanium GOST 19807-91 Metal niobium in NBSh000 GOST 16100-79 Hafnium iodide brand GFM1 TU 22517-77 Zirconium iodide TU 95-46-82 Ligature nickel-boron NB1 TU 1425-3-71 Carbon (electrode battle) GOST 4426-80

Calculation of the charge for the smelting of billets was carried out on the basis of preliminary studies of the fumes of alloying elements: for nickel, tungsten, molybdenum, chromium, vanadium, zirconium, rhenium, cerium, boron - according to the nominal calculation, for carbon, titanium and aluminum, taking into account fume -13%, 5% and 3%, respectively.

The charge was loaded into the crucible in the following sequence: 30% of ZhS32 and nickel alloys to the bottom of the crucible, then tungsten, molybdenum, chromium, cobalt, and the rest of the ZhS32 and nickel alloy on top. With a discharge of 9.33 Pa (7 · 10 ^-2 mm Hg), the furnace was turned on at low power for degassing and heating the charge, after 5 ... 10 min the power was increased. Tantalum, niobium, rhenium and carbon (electrode bout) were introduced into the liquid metal through a batcher. After complete melting, the temperature of the metal was raised to 1600 ° C, the metal was kept at this temperature for 10 ... 20 min until the boiling stopped, then the temperature decreased to 1510 ... 1540 ° C and additives were introduced at intervals of 3 ... 5 min in the following order: aluminum, titanium, zirconium, yttrium, lanthanum, nickel-boron ligature. After the introduction of the last additive, the metal was kept for 5 ... 10 min and, when the temperature reached 1510 ... 1530 ° С, it was cast in the form of a cylindrical type with a diameter of 70 mm for subsequent cutting under a measured workpiece.

Each heat was subjected to chemical and spectral analysis for all elements except boron and rare-earth metals. Boron and REM were determined only by spectral analysis.

Casting of samples and blades was carried out in shell molds made by investment casting.

Models were made from model mass MB, consisting of 50% model mass ZGV-101 (TU RB 0020-358-003-98) and 50% urea (GOST 2081-92). This model mass provides high accuracy and a clean surface of the model.

The ceramic mold was made by dipping the model block into a suspension, followed by sprinkling with electrocorundum and drying each layer in a vacuum-ammonia drying unit UVS-3. Electrocorundum was used as a refractory suspension filler; as a binder used hydrolyzed ethyl silicate ETS40 (GOST 51174-71). The viscosity of the refractory suspension for the first layer was 50 ... 60 s according to the VZ-4 viscometer (GOST 9070-75), for the next layers - 25 ... 30 s. To sprinkle the first layer of the ceramic form, we used electrocorundum fractions of 0.16 ... 0.25 mm, for subsequent layers - electrocorundum fractions of 0.5 ... 0.63 mm. 9 layers were applied to the model blocks, the last layer being a fixing layer, i.e. did not sprinkle with electrocorundum.

After drying of the last layer, the model mass was heated from the shell with hot steam at a temperature of 160 ... 170 ° C and a pressure of 0.7 ... 0.8 MPa on a boiler model 64501. Then, the shell was calcined at a temperature of 1025 ... 1075 ° C within 6 ... 8 hours in order to completely burn out the residual model mass and products of incomplete hydrolysis of the binder.

In order to ensure a regulated axial crystallographic orientation (CGO) [001], seeds were installed in the lower part of the ceramic mold — Ni-W alloy cylinders (67% Ni and 33% W) having a given axial CGO.

The calcined ceramic mold was placed in a mold heating furnace (PPF) of the UVK-8P high-speed directional crystallization apparatus. The temperature of the upper and lower PPF heaters was brought to 1540 and 1630 ° C, respectively, and kept at this temperature for 15 ... 20 min, bringing the vacuum in the furnace to 10.7 Pa (8 · 10 ^-2 mm Hg). After that, the measured billet of the alloy was melted, the melt temperature was brought up to 1590 ... 1610 ° С, kept for 1 ... 2 min and the melt was treated at high temperature, during which grade A argon was introduced into the chamber (GOST 10157-79), bringing pressure to 0.004 ... 0.005 MPa (30 ... 40 mm Hg), and the metal was overheated to 1730 ... 1750 ° C, held for 20 minutes and cooled to 1600 ° C. Next, the vacuum in the chamber was brought to 10.7 Pa (8 · 10 ^-2 mm Hg), the melt was cooled to 1540 ... 1560 ° C, poured into a mold and kept for 2.5 ... 3.5 minutes.

Filled molds to ensure directed heat dissipation and stabilization of the temperature at the crystallization front were moved at a speed of 10 mm / min from the initial position to the liquid metal crystallizer — a cast-iron bath with aluminum A5 (GOST 11069-74), having a temperature of 700 ° C, until the lock was completely immersed in the mold parts of the blades. Then, the filled molds were removed from the mold in PPF and, in order to reduce casting stresses, were thermostated for 10 min at a temperature of 1280 ... 1300 ° С. Then, the casting block was cooled together with PPF and, when the temperature dropped to 900 ° C, the mold was taken out of the furnace.

The obtained samples were subjected to heat treatment, including homogenizing annealing in the temperature range 1310 ... 1370 ° С followed by cooling in an argon stream, the first aging at a temperature of 1050 ... 1150 ° С for 8 hours and the second aging at a temperature of 850 ... 950 ° C for 20 hours.

The cast parts were subjected to inspection by the methods provided for in serial production for turbine blades: visual inspection, structure inspection, geometry verification, X-ray diffraction, luminescent inspection and color inspection.

KGO control was carried out on a DRON-3M diffractometer by X-ray photography from a cross section of a starter cone. A deviation of not more than 10 ° from KGO [001] was allowed.

Heat-treated samples were tested for short-term and long-term strength. Tests for short-term strength were carried out at 20 ° C, for long-term strength - at 1000 ° C.

Tests for static tension (tearing) were carried out according to GOST 1497-84 on a testing machine UTM-20 at room temperature. A load was smoothly applied to the sample, bringing the sample to rupture. The temporary resistance σ _{in was} determined by the formula:

where P _max is the maximum test load, MN;

F ₀ - the cross-sectional area of the sample before testing, mm ² .

After testing the samples, the elongation δ was determined:

where l ₀ is the estimated length of the sample before the test, mm;

l _to - the length of the sample after the test, mm

The initial calculated length l ₀ is the length of the portion of the working part of the sample on which the elongation was measured, before the start of the test, risks were limited with an error of not more than 1%. To measure the estimated length after rupture, l _{k, the} destroyed parts of the sample were tightly folded so that their axes formed a straight line. The estimated sample length before and after the test was measured with an error of ± 0.05 mm.

The relative narrowing of ψ was determined by the formula:

where F ₀ - the initial cross-sectional area of the sample, mm ² ;

F _to - the cross-sectional area of the sample after the test, mm ² .

The initial cross-sectional area of the working part of the sample F _{0 was} measured at room temperature before testing. After the fracture F _{k, the} cross-sectional area of the sample was calculated according to the arithmetic mean of the results of measurements of the minimum diameter at the gap in 2 mutually perpendicular directions. The measurement of samples after testing was carried out with an accuracy of ± 0.01 mm.

The test method for long-term strength corresponded to GOST 10145-81. The essence of the technique was to bring the sample to failure under the influence of a constant tensile load at a constant temperature (up to 1200 ° C). As a result of the tests, the time to failure at a given voltage at a constant temperature was determined.

Samples of a cylindrical type with a diameter of 5 mm with an initial calculated length of 25 mm were used; the deviation in the cross-sectional area did not exceed ± 0.5%. The permissible deviation of the diameter of the working part of the cylindrical samples is ± 0.2 mm, the roughness Ra <0.63 μm, the runout of the sample when checking in centers to 0.02 mm

To measure the temperature of the samples, 2 thermocouples were installed at the ends of their working part so that the hot junctions were in close contact with the surface of the sample. The hot junction of the thermocouple was protected from exposure to the hot walls of the furnace with asbestos.

The sample installed in the grips of the testing machine and placed in the furnace was heated to a predetermined temperature (heating time did not exceed 8 hours) and kept at this temperature for 1 hour. After heating the sample and holding at a given temperature, a load was smoothly applied to the sample. Time to failure at a given voltage value, i.e. load, referred to the initial cross-sectional area of the sample, was the main indicator of this type of test. After the destruction of the sample, the relative elongation δ (2) and the relative narrowing ψ (3) were determined.

The compositions of the alloys (wt.%) And test results are given in table. 1 and 2, respectively.

As can be seen from the table. 2, the proposed alloy surpasses the prototype alloy in long-term strength: at a test temperature of 1000 ° C and a voltage of 240 MPa, the durability of the inventive alloy is τ = 639 ... 662 hours versus 549 hours for the prototype alloy. This allows us to recommend this alloy for single-crystal casting of gas turbine blades, which are subject to increased demands on the service life at high temperatures.

So, the inventive alloy allows to achieve increased heat resistance and phase stability of a single-crystal nickel heat-resistant alloy with improved technological characteristics.

Table 1 The compositions of the alloys, wt.% No. Alloy Cr With Mo W Re That Al Ti Nb Hf FROM Y La Fe Mn Si R S Ni one Prototype 2,4 4.0 0.4 6.2 6.0 8.3 5.8 0.55 0.14 0,025 - - - 0.21 0,093 0.10 0.008 0.005 rest 2 The claimed 4.91 6.49 0.63 5.77 5.12 6.45 5.15 0.37 0.84 0.010 0.008 0.003 0.001 0.29 0.128 0.14 0.011 0.007 - ″ - 3 - ″ - 4.93 6.51 0.65 5.80 5.34 6.87 5.26 0.38 0.83 0.010 0.008 0.003 0.005 0.22 0,097 0.11 0.008 0.005 - ″ - four - ″ - 5.02 6.13 0.65 5.58 5.00 6.89 5.34 0.36 0.85 0.010 0.008 0.002 0.003 0.13 0.059 0,07 0.011 0.003 - ″ - 5 - ″ - 5.19 6.65 0.67 5.82 5.30 6.87 5.21 0.38 0.86 0.010 0.008 0.003 0.003 0.41 0.197 0.19 0.012 0.009 - ″ -

table 2 Test results Alloy Room temperature test results Test results at a temperature of 1000 ° C σ _B ²⁰ , MPa δ,% ψ,% τ at σ = 240 MPa, h δ,% ψ,% one 1175 7.0 10.7 549 13,2 15,5 2 1203 7.5 10,2 639 13.7 15.9 3 1212 7.2 9.5 650 14.2 15.3 four 1217 6.1 9.1 662 12.1 13.6 5 1225 6.0 8.1 647 13.3 14.5

Claims (1)

Monocrystal nickel heat-resistant alloy containing chromium, cobalt, molybdenum, tungsten, rhenium, tantalum, aluminum, titanium, niobium, hafnium, lanthanum, yttrium and carbon, characterized in that it contains components in the following ratio, wt.%: Chromium 4.7-5.4 Cobalt 5.9-6.9 Molybdenum 0.6-0.7 Tungsten 5.3-6.1 Rhenium 4.8-5.6 Tantalum 6.2-7.2 Aluminum 4.8-5.6 Titanium 0.3-0.4 Niobium 0.8-0.9 Hafnium 0.009-0.011 Carbon 0.007-0.009 Lanthanum 0.001-0.005 Yttrium 0.001-0.005 Nickel Rest when containing harmful impurities: Iron No more than 0.5 Manganese No more than 0.2 Silicon No more than 0.2 Phosphorus No more than 0.015 Sulfur No more than 0,01