EP2742162B1 - Method for producing forged tial components - Google Patents

Description

FIELD OF THE INVENTION

The present invention relates to a method for producing forged components from a TiAl alloy, in particular components for gas turbines, preferably aircraft turbines and in particular turbine blades for low-pressure turbines. Moreover, the present invention relates to corresponding components.

STATE OF THE ART

Due to their low specific weight and their mechanical properties, components of titanium aluminides are of interest for use in gas turbines, in particular aircraft turbines. However, for titanium aluminide materials, the microstructures must be precisely adjusted to achieve the desired mechanical properties.

This results in the difficulty that special process routes must be selected in order to make the desired microstructural settings. At the same time, however, the production and processing of corresponding TiAl components in industrial processes should be economically feasible. Accordingly, there is a continuing need to optimize microstructural settings and production paths and parameters for the production of titanium aluminide components.

A method for producing forged components from a Ti-43Al-4Nb-lMo-0.1B alloy is known from " Microstructural and Tensile Ductility of a Ti-43Al-4Nb-1Mo-0.1B Alloy "- Laura, M. Droessler et al, Mater.Res.Soc.Symp.Proc, vol 1128, 2009 Materials research Society, pages 121-126 , known.

DISCLOSURE OF THE INVENTION OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a manufacturing method for the production of components made of titanium aluminide materials, which in gas turbines, in particular Air turbines, preferably in the field of low-pressure turbine, can be used, with an economically feasible production is possible.

TECHNICAL SOLUTION

This object is achieved by a method having the features of the claim.

Advantageous embodiments are the subject of the dependent claims.

In the method of manufacturing forged Ti-Al alloy components of the present invention, the components are subjected to a two-stage heat treatment after forging, wherein the first stage of the heat treatment provides recrystallization annealing below the γ / α transformation temperature for a period of 50 to 100 minutes , The annealing at a temperature below the γ / α transformation temperature at which α-titanium is converted into γ-TiAl in accordance with the phase diagram for the TiAl alloy used may take place as close as possible to the γ / α transformation temperature, with a temperature of 15 ° C, in particular 10 ° C, below the γ / α - conversion temperature should not fall below.

The recrystallization annealing may preferably be carried out for 60 to 90 minutes, especially 70 to 80 minutes.

The first stage of the heat treatment with the recrystallization annealing is followed by a second stage of the heat treatment with stabilizing annealing in the temperature range of 800 ° C to 950 ° C for 5 to 7 hours.

The stabilization annealing can be carried out in particular in the temperature range from 825 ° C. to 925 ° C., preferably from 850 ° C. to 900 ° C., with a holding time of from 345 minutes to 375 minutes.

The cooling in the recrystallization annealing can be carried out by air cooling, wherein in the temperature range between 1300 ° C and 900 ° C, the cooling rate ≥ 3 ° C per second should be to set a fine-lamellar microstructure of α ₂ -Ti ₃ Al and γ-TiAl in the corresponding α ₂ - and γ-phase, which ensures the required mechanical properties.

The cooling in the second heat treatment stage, so the stabilization annealing, can be done with correspondingly lower cooling rates in the oven.

For the adjustment of the microstructure and reproducibility of a corresponding structural adjustment, it is important that the heat treatment steps are carried out as accurately as possible at the corresponding selected temperature. However, an increasingly precise adjustment of the temperature and holding the components at the appropriate temperatures associated with increasing effort, so that a compromise must be found for an economically meaningful processing. For the heat treatment of forged TiAl components, a temperature adjustment with a deviation in the range of 5 ° C to 10 ° C up and down from the target temperature has been found to be advantageous. Accordingly, the selected target temperature for the heat treatment steps of the present invention can be set and maintained in a corresponding temperature window of 5 ° C to 10 ° C deviation from the target temperature up and down.

For the production of forged components from TiAl alloys, in particular for gas turbine components, such as, for example, low-pressure turbine turbine blades, titanium-titanium aluminide alloys alloyed with niobium and molybdenum can be used in particular. Such alloys are also referred to as TNM alloys.

For the present process, an alloy of 42 to 45 atomic percent aluminum, 3 to 5 atomic percent niobium and 0.5 to 1.5 atomic percent molybdenum is used.

In particular, the aluminum content may be selected in the range of 42.8 to 44.2 atomic percent aluminum, while 3.7 to 4.3 atomic percent of niobium and 0.8 to 1.2 atomic percent of molybdenum may be alloyed.

In addition, the alloy may be alloyed with boron in the range of 0.05 to 0.15 atomic percent boron, more preferably 0.07 to 0.13 atomic percent boron.

Further, the alloy may include unavoidable impurities such as carbon, oxygen, nitrogen, hydrogen, chromium, silicon, iron, copper, nickel and yttrium, the content of which is ≦ 0.05% by weight of chromium, ≦ 0.05% by weight of silicon, ≦ 0.08 wt% oxygen, ≤ 0.02 wt% carbon, ≤ 0.015 wt% nitrogen, ≤ 0.005 wt% hydrogen, ≤ 0.06 wt% iron, ≤ 0.15 wt% copper, ≤ 0.02 wt% nickel, and ≤ 0.001 wt% yttrium , Further constituents may be contained individually in the range of 0 to 0.05 percent by weight or in total from 0 to 0.2 percent by weight.

The forging of the corresponding components can be carried out by drop forging in the α-γ-β-temperature range, which can be used as a starting material for forging cast and / or hot isostatically pressed blanks.

The blanks themselves can be produced by melting in vacuo or inert gas with self-consumable electrodes or in the cooled crucible by means of plasma arc melting, wherein a single or multiple remelting of the alloy can be performed. The remelting may be by vacuum induction melting or vacuum arc remelting (VIM vacuum induction melting), and the cast material may be hot isostatically pressed using temperatures ≥200 ° C at a pressure ≥ 190 MPa and a holding time ≥ 4 hours can.

According to the invention, a component made of a TiAl alloy, in particular a component of a gas turbine, preferably an aircraft turbine, which is produced in particular according to the above-described method, is provided, which has a triplex structure with a globulitic γ-TiAl phase, a B2-TiAl Phase (cubic body-centered phase) and a lamellar α ₂ -Ti ₃ Al and γ-TiAl phase is constructed. The proportion of the γ-phase is in this case 2 to 20 percent by volume, the proportion of the B2 phase 1 to 20 percent by volume and the proportion of the γ-phase together with the B2 phase 5 to 25 percent by volume.

In particular, the proportion of the γ-phase 5 to 15 volume percent and the proportion of B2 phase 3 to 15 volume percent and the proportion of the two phases together amount to 8 to 20 volume percent.

The size of the γ-phase or the γ-grains may be set so that a circumscribed circle has a diameter ≤ 40 μm. The same applies to the B2 phase or B2 grains.

The lamellar microstructure areas of α ₂ and γ phase have a size in which the equivalent area of a circle has a diameter of ≤ 100 μm.

The aspect ratio of the lamellar α ₂ and γ phase, ie the ratio of the length to the width of the lamellae, can be ≦ 3: 1.

The structure may additionally have borides.

Embodiment

Further advantages, characteristics and features of the present invention will become apparent in the following description of an embodiment.

A TiAl alloy having an aluminum content of 28.1 to 29.1 weight percent, a niobium content of 8.5 to 9.6 weight percent, a molybdenum content of 1.8 to 2.8 weight percent, a boron content of 0.019 to 0.034 weight percent, a A carbon content of 0 to 0.02 weight percent, an oxygen content of 0 to 0.08 weight percent, a nitrogen content of 0 to 0.015 weight percent, a hydrogen content of 0 to 0.005 weight percent, a chromium content of 0 to 0.05 weight percent, a silicon content of 0 to 0.05 weight percent, an iron content of 0 to 0.06 weight percent, a copper content of 0 to 0.15 weight percent and a nickel content of 0 to 0.02 weight percent and an amount of yttrium of 0 to 0.001 weight percent and the balance titanium and others individual constituents in a proportion of 0 to 0.05 percent by weight or together with a total of 0 to 0.20 percent by weight, is in a vacuum or under inert gas with a selbstverzehre The electrode was melted and remelted at least once in the same way. The thus molten material was hot isostatically compacted at a temperature of> 1200 ° C and a pressure of greater than 190 MPa for a holding time of more than 4 hours, and then forged in a die forging at a temperature in the α-γ-β phase region , Subsequently, a heat treatment was carried out with recrystallization annealing below the γ / α transformation temperature for 75 minutes with air cooling at a cooling rate of more than 3 ° C per second. Subsequently, the corresponding component was subjected to stabilization annealing at 920 ° C. for 6 hours and then cooled in the oven.

Such a component, such as a turbine blade for a low-pressure turbine in an aircraft engine, has a triplex structure according to the invention with corresponding proportions of γ phase, B2 phase and lamellar α ₂ and γ phase. In a hot tensile test at 300 ° C., such a component has a yield strength (0.2% proof strength Rp _0.2 ) of more than 670 MPa and a tensile strength R _m of more than 840 MPa for a total elongation (elastic and plastic elongation to breakage) ) A _dead higher than 1.7%. In a hot tensile test at a temperature of 750 ° C, a yield strength Rp _0.2 of more than 500 MPa and a tensile strength R _m > 730 MPa is still achieved. At a creep temperature of 750 ° C. and a test voltage of 150 MPa and a creep time of more than 200 hours, the creep properties are characterized by a total plastic strain A _p of ≦ 1%.

Although the present invention has been described in detail with reference to the exemplary embodiment, it is obvious for a person skilled in the art that the invention is not limited to this example, but that modifications are possible in such a way that individual process and material parameters are omitted or other combinations of process and material parameters. and material parameters can be selected without departing from the scope of the appended claims. The disclosure of the present invention comprises in particular all individual process steps and process and material parameters.

Claims (9)

1. A method for producing forged components from a TiAl alloy, in particular turbine blades, in which the components are forged and after forging are subjected to a two-stage heat-treatment, wherein the first stage of the heat-treatment comprises recrystallization annealing for 50 to 100 minutes at a temperature below the γ/α - transition temperature, namely in the temperature range between 1300°C and 900°C, in particular a recrystallization cooling temperature between 1200°C and 1300°C, and the second stage of the heat-treatment comprises stabilization annealing in the temperature range of 800°C to 950°C for 5 to 7 hours, and wherein a TiAl alloy having 42 to 45 at. % aluminium, 3 to 5 at. % niobium and 0.5 to 1.5 at. % molybdenum is used, characterised in that the rate of cooling in the first heat-treatment stage is greater than or equal to 3°C/s in order to set a fine lamellar structure of α₂-Ti3Al and γ-TiAl in a corresponding α₂-and γ-phase.
2. A method according to claim 1,
   characterised in that
   the recrystallization annealing is carried out for 60 to 90 minutes, in particular 70 to 80 minutes, and/or the stabilization annealing is carried out in the temperature range of 825°C to 925°C, in particular 850°C to 900°C, and/or for 345 to 375 minutes.
3. A method according to one of the preceding claims,
   characterised in that
   the temperature during the heat-treatment is set and held with an accuracy of a 5°C to 10°C upward and downward deviation from the desired temperature.
4. A method according to one of the preceding claims,
   characterised in that
   during the recrystallization annealing there is no fall below a temperature of 15°C, in particular 10°C, below the γ/α transition temperature.
5. A method according to one of the preceding claims,
   characterised in that
   an alloy having C.05 to 0.15 at. % boron is used.
6. A method according to one of the preceding claims,
   characterised in that
   the component is produced by drop-forging in the α-γ-β-temperature range.
7. A method according to one of the preceding claims,
   characterised in that
   cast or hot-isostatically pressed blanks are used as the starting material for the forging.
8. A method according to one of the preceding claims,
   characterised in that
   after the second stage of the heat-treatment the component has a triplex structure, with a glabulitic γ-TiAl phase, a B2-TiAl phase and a lamellar α₂-Ti₃Al and γ-TiAl phase.
9. A method according to claim 8,
   characterised in that
   the proportion of the γ-phase is 2 to 20 percent by volume, the proportion of the B2-phase is 1 to 20 percent by volume, and the proportion of the γ-phase together with the B2-phase is 5 to 25 percent by volume.