RU2325453C2 - Nickel-based heat resistant alloy - Google Patents

Abstract

FIELD: metallurgy; non-ferrous.

SUBSTANCE: said utility invention relates to a nickel-based heat-resistant alloy and may be used, in particular, for producing monocrystalline parts or parts with directionally crystallised structure, for example, gas turbine vanes. The alloy has the following chemical composition, % weight: 7.7-8.3 Cr; 5.0-5.25 Co; 2.0-2.1 Mo; 7.8-8.3 W; 5.8-6.1 Ta; 4.9-5.1 Al; 1.3-1.4 Ti; 0.11-0.15 Si; 0.11-0.15 Hf; 200-750, preferably, 200-300 ppm C; 50-400, preferably, 50-100 ppm B; the remaining being nickel and process foreign matters. The alloy has very high castability and high oxidation resistance.

EFFECT: obtaining nickel-based alloy with high castability and high oxidation resistance.

3 cl, 1 tbl, 5 dwg

Description

Technical field

The invention relates to the field of materials science. It relates to a heat-resistant nickel-based alloy, intended in particular for the manufacture of single-crystal parts (SX alloy) or parts with a directionally crystallized structure (DS alloy), such as gas turbine blades. However, the alloy according to the invention is applicable to traditionally cast parts.

State of the art

Mentioned heat-resistant nickel-based alloys are known. Single-crystal parts from such alloys have very good strength at high temperatures. As a result, it becomes possible, for example, to increase the temperature in the control stage of gas turbines, which increases the efficiency of the latter.

Nickel-based heat-resistant alloys intended for single-crystal parts, such as those known from US 4643782, EP 0208645 and US 5270123, contain alloying elements additionally strengthening the solid solution, for example, Re, W, Mo, Co, Cr, as well as forming γ'-phase elements, for example Al, Ta and Ti The content of refractory alloying elements (W, Mo, Re) in the main matrix (austenitic γ-phase) continuously increases with increasing temperature of loading of the alloy. So, for example, ordinary heat-resistant nickel-based alloys contain 6-8% W, up to 6% Re and up to 2% Mo for obtaining single crystals (data in wt.%). The alloys disclosed in the above publications are characterized by a high creep strength, good low and high cyclic fatigue, and also high resistance to oxidation.

These known alloys are designed for aircraft turbines and therefore are optimized for short and medium term applications, i.e. loading time is designed for about 20,000 hours. In contrast, parts for industrial gas turbines must be designed for loading times of up to 75,000 hours.

After loading for 300 hours, for example, the CMSX-4 alloy known from US 4,643,782, which was experimentally used in a gas turbine at temperatures above 1000 ° C, was characterized by a very strong coarsening of the γ 'phase, which was accompanied by a drawback in the form of an increase in the creep rate of the alloy.

Thus, there is a need to increase the stability of known alloys against oxidation at very high temperatures.

Another problem associated with known, for example, from US 5435861, heat-resistant nickel-based alloys, is that the casting properties in the manufacture of large parts, such as gas turbine blades longer than 80 mm, leave much to be desired. Casting a flawless, relatively large single-crystal, directionally solidified part from a heat-resistant nickel-based alloy seems extremely difficult, since most of these parts contain defects, such as small-angle grain boundaries, “dull spots” (defective areas caused by a chain of uniformly oriented grains with a high eutectic content ), equiaxed scattered boundaries, microporosity, etc. Such defects reduce the strength of parts at high temperatures, as a result of which the required the durability or operating temperature of the turbine. However, due to the fact that a perfectly cast single-crystal part is extremely expensive, a trend has been noted in the industry in which defects are allowed in an amount that does not reduce durability or operating temperature.

The most common defect is grain boundaries, which are especially harmful to the high-temperature properties of single-crystal products. If the small-angle grain boundaries in small parts have a relatively small effect on the properties, then they are of great importance for the casting properties and oxidizability of large parts made of SX or DS alloys at high temperatures.

Grain boundaries are regions of a large local defect in the crystal structure of the lattice, since neighboring grains border on these regions and cause a certain disorientation between the crystal lattices. The greater this disorientation, the larger the defect in the crystal structure, i.e. the greater the number of dislocations along the grain boundaries, which are necessary for the correspondence of both grains with each other. Such a crystal structure defect is directly related to the material properties at high temperatures. It weakens the material when the temperature rises above the equicohesion temperature (= 0.5 x Kelvin melting point).

The indicated effect is known from GB 2234521 A. Thus, for example, in a conventional single-crystal nickel-based alloy, the temporary resistance at a test temperature of 871 ° C was extremely reduced when the grain disorientation exceeded 6 °. This was also noted for single-crystal parts with a directionally solidified structure, as a result of which, on the whole, the opinion was formulated that disorientation above 6 ° should not be allowed.

From the aforementioned document GB 2234521 A, it is also known that due to the enrichment of heat-resistant nickel-based alloys with boron or carbon during directional solidification, structures characterized by equiaxial or prismatic grain structures are formed. Carbon and boron strengthen grain boundaries, since C and B cause the precipitation of carbides and borides along grain boundaries, which are stable at high temperatures. In addition, the presence of such elements reduces the diffusion process at the grain boundaries and along them, which is the main cause of weakening along the grain boundaries. Therefore, you can increase the disorientation to 10-12 ° and nevertheless achieve high properties of the material at high temperatures. Such small-angle grain boundaries negatively affect the properties of large single-crystal parts made of heat-resistant nickel-based alloys.

Disclosure of the invention

The aim of the invention is to remedy these shortcomings. The invention has the task of creating a heat-resistant nickel-based alloy having improved casting properties and higher resistance against oxidation compared to the known heat-resistant nickel-based alloys. In addition, this alloy should be suitable, in particular, for the manufacture of, for example, large single-crystal parts for gas turbines with a length of more than 80 mm.

According to the invention, this problem is solved due to the fact that the heat-resistant nickel-based alloy according to the invention has the following chemical composition (data indicated in wt.%):

7.7-8.3 Cr

5.0-, 25 Co

2.0-2.1 Mo

7.8-8.3 W

5.8-6.1 Ta

4.9-5.1 Al

1.3-1.4 Ti

0.11-0.15 Si

0.11-0.15 Hf

200-750 ppm C

50-400 ppm B

the rest is nickel and technological impurities.

The advantages of the invention are that the alloy has very high casting properties and, compared with the present prior art, is characterized by improved resistance to oxidation at high temperatures. A particular advantage is achieved with the following alloy composition:

7.7-8.3 Cr

5.0-5.25 Co

2.0-2.1 Mo

7.8-8.3 W

5.8-6.1 Ta

4.9-5.1 Al

1.3-1.4 Ti

0.11-0.15 Si

0.11-0.15 Hf

200-300 ppm C

50-100 ppm B

the rest is nickel and technological impurities.

This alloy is extremely suitable for the manufacture of large single-crystal parts such as gas turbine blades.

Brief Description of the Drawings

The drawings show an example embodiment of the invention in the form of quasi-isothermal oxidation diagrams. It is depicted on:

figure 1 the dependence of the change in the specific gravity of the control alloy VL1 on temperature and time,

figure 2 the dependence of the change in the specific gravity of the control alloy VL2 on temperature and time,

figure 3 the dependence of the change in the specific gravity of the control alloy VL3 on temperature and time,

figure 4 the dependence of the change in the specific gravity of the control alloy VL4 on temperature and time,

figure 5 the dependence of the change in the specific gravity of the alloy L1 according to the invention from temperature and time.

The ways of carrying out the invention

Below the invention is explained in more detail using an example of its implementation and figure 1-5.

We studied heat-resistant nickel-based alloys, the chemical composition of which is shown in table 1 (data are indicated in wt.%):

Table 1
The chemical composition of the investigated alloys VL1 (CMSX-11B) VL2 (CMSX-6) VL3 (CMSX-2) VL4 (René N5) L1 Ni rest rest rest rest rest Cr 12,4 9.7 7.9 7.12 7.7 With 5.7 5,0 4.6 7.4 5.1 Mo 0.5 3.0 0.6 1.4 2.0 W 5.1 - 8.0 4.9 7.8 That 5.18 2.0 6.0 6.5 5.84 Al 3,59 4.81 5.58 6.07 5,0 Ti 4.18 4.71 0.99 0,03 1.4 Hf 0.04 0.05 - 0.17 0.12 FROM - - - - 0.02 AT - - - - 0.005 Si - - - - 0.12 Nb 0.1 - - - - Re - - - 2.84 -

Alloy L1 is a heat-resistant nickel-based alloy for single-crystal parts, the composition of which is given in the claims of the present invention. In contrast, the VL1, VL2, VL3, and VL4 alloys are control alloys known in the art under the names CMSX-11B, CMSX-6, CMSX-2, and René N5. The latter differ from the alloy according to the invention in that they are not alloyed with elements C, B and Si.

Carbon and boron strengthen grain boundaries, in particular, small-angle boundaries oriented in the <001> direction in heat-resistant nickel-based alloys SX and DS, of which gas turbine blades are made, since these elements cause the precipitation of carbides and borides along grain boundaries, which are resistant at high temperatures. In addition, the presence of these elements at the grain boundaries and along them reduces the diffusion process, which is the main cause of weakening along the grain boundaries. As a result, the casting properties of long single-crystal parts, such as gas turbine blades with a length of about 200 to 230 mm, are significantly improved.

The addition of Si in an amount of from 0.11 to 0.15 wt.%, Especially in combination with Hf in approximately the same amount, leads to a significant increase in resistance against oxidation at high temperatures compared to previously known heat-resistant nickel-based alloys. This is shown in figures 1-5, in which, respectively, for control alloys VL1-VL4 (figures 1-4) and alloy L1 according to the invention (figure 5) isothermal oxidation diagrams are shown. For these alloys, a change in specific gravity Δm / A (data in mg / cm ² ) at temperatures of 800 ° C, 950 ° C, 1050 ° C and 1100 ° C and a duration of 0 to 1000 hours is shown. If we compare the characteristics of the curves, then, in particular, at high temperatures (1000 ° C) and a long time of natural aging, the superiority of the alloy according to the invention is noted.

If heat-resistant nickel-based alloys with a higher content of C and B (not more than 750 ppm C and not more than 400 ppm B) are selected according to claim 1, then details from them can also be cast in the traditional way.

Claims (3)

1. Heat-resistant alloy based on Nickel, characterized in that it has the following chemical composition, wt.%: Cr 7.7-8.3 With 5.0-5.25 Mo 2.0-2.1 W 7.8-8.3 That 5.8-6.1 Al 4.9-5.1 Ti 1.3-1.4 Si 0.11-0.15 Hf 0.11-0.15 FROM 200-750 ppm AT 50-400 ppm Ni and process impurities rest 2. The heat-resistant alloy based on Nickel according to claim 1, characterized in that it is intended, in particular, for the manufacture of single-crystal parts and has the following chemical composition, wt.%: Cr 7.7-8.3 With 5.0-5.25 Mo 2.0-2.1 W 7.8-8.3 That 5.8-6.1 Al 4.9-5.1 Ti 1.3-1.4 Si 0.11-0.15 Hf 0.11-0.15 FROM 200-300 ppm AT 50-100 ppm Ni and process impurities rest 3. The heat-resistant alloy based on Nickel according to claim 2, characterized in that it has the following chemical composition, wt.%: Cr 7.7 With 5.1 Mo 2.0 W 7.8 That 5.8 Al 5,0 Ti 1.4 Si 0.12 Hf 0.12 FROM 200 ppm AT 50 ppm Ni and process impurities rest

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