EP3269838B1 - High temperature resistant tial alloy, method for production of a composent from a corresponding tial alloy, component from a corresponding tial alloy - Google Patents

Description

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention relates to a highly heat-resistant TiAl alloy and a method for producing a component from such a TiAl alloy as well as a corresponding component.

STATE OF THE ART

TiAl alloys, which have titanium and aluminum as the main components - i.e. as chemical elements with the highest proportions in the composition - are used as materials for moving parts in engines and gas turbines, e.g. as Blades, used. An example of a TiAl alloy and its use in turbomachines, such as aircraft engines, is shown in WO 2009/052792 A2 which describes a TiAl material for a gas turbine component, which contains 42 to 45 at.% aluminum, 3 to 8 at.% niobium, 0.2 to 0.3 at.% molybdenum and / or manganese, 0.1 to 1 at .% Boron and / or carbon and / or silicon and the remainder titanium. This alloy is adjusted during production so that the material has a β-Ti phase and / or B2-Ti phase at room temperature, both of which will be referred to below as the β phase for short. The β - phase serves to avoid coarsening of the α - Ti grains at high temperatures at which in TiAl alloys with a correspondingly high aluminum part a substantial part of the material can be present as an α - Ti phase with high aluminum solubility, in order to achieve a homogeneous structure that is favorable for the ductility and creep resistance of the material with uniform, not too coarse microstructures. The β - phase stabilizes the grain boundaries of the α - Ti grains and thus counteracts any coarsening.

However, such TiAl alloys still have deficits in terms of creep resistance, so that there is a need for improvement in this respect in particular.

Other TiAl alloys are from the EP2851445A1 as well as from the article " Silicon distribution and silicide precipitation during annealing in an advanced multiphase γ-TiAl based alloy ", Klein, Thomas et al, ACTA MATERIALIA, ELSEVIER, OXFORD, GB, Vol. 110, March 23, 2016 (2016-03-23), pp 236-245 " known.

DISCLOSURE OF THE INVENTION OBJECT OF THE INVENTION

It is therefore the object of the present invention to provide a TiAl alloy and a method for producing a component from a TiAl alloy and a corresponding component, the TiAl alloy and the components made from it having a balanced profile of properties with sufficient strength, ductility and, in particular, creep resistance should have.

TECHNICAL SOLUTION

This object is achieved with a TiAl alloy with the features of claim 1, a method for producing a component made of a TiAl alloy with the features of claim 2 and a component made of a TiAl alloy with the features of claim 8 are the subject of the dependent claims.

In order to improve the creep resistance of TiAl alloys and / or components made therefrom, in particular for turbo engines, such as gas turbines and aircraft engines, the invention proposes to essentially dispense with the β phase to hinder the grain growth of α-Ti grains at high temperatures and that To hinder the growth of the α-Ti grains at high temperatures through the precipitation of silicides. The term “essentially without the β phase” or “essentially no β phase” means in this context that the β phase in the finished alloy is less than 5% by volume, preferably less than 2% by volume. -% and more preferably 0% by volume. By avoiding the β phase or restricting the β phase to minimal proportions in the structure, the creep resistance can be improved, while at the same time maintaining a homogeneous structure can be achieved with fine structures. For this purpose, the invention proposes to select a TiAl alloy which, in addition to the main alloy components titanium and aluminum, has at least niobium, molybdenum, carbon, boron and silicon and also has zirconium and / or tungsten, with silicon being provided for the formation of the silicides which the The aim is to hinder grain growth of the α-Ti grains at correspondingly high temperatures in order to counteract coarsening of the microstructure. The TiAl alloy should be selected in such a way that, given the chosen chemical composition of the TiAl alloy, there is an α-phase temperature range in whose temperature range there is essentially an α-Ti phase with silicides. A corresponding TiAl alloy, which is essentially in the form of α-Ti in a specific temperature interval for the given chemical composition, can be produced by means of simulation calculations with appropriate simulation programs that take into account a large number of thermodynamic data, and / or by producing appropriate Test melts or test alloys and metallographic examination of the test alloys are determined.

If a corresponding TiAl alloy with a certain chemical composition has been selected, which has an α-phase temperature range in which the corresponding TiAl alloy is essentially single-phase as an α-Ti phase, with only silicides additionally being present in the temperature range , in the process according to the invention, such a TiAl alloy with the selected chemical composition is melted and then cast in a further step into a semifinished product or atomized into TiAl powder, the semifinished product already being a near-net-shape intermediate product or a starting product for further forming into a Can be a preliminary product. For example, the cast semi-finished product can be formed into a preliminary product by forging. The TiAl powder can be used for further processing in powder metallurgical manufacturing processes, such as generative manufacturing processes, or compressed, joined and / or shaped by hot isostatic pressing (HIP) or the like in order to also create a preliminary product.

The cast semifinished product or a preliminary product produced from the semifinished product or from the TiAl powder is then cooled from a silicide start temperature in such a way that silicides can separate out in order to carry out precipitation stabilization. The cooling from the silicide start temperature can take place, for example, directly after the casting of the semifinished product when the casting is being cooled, or, if the semifinished product is unshaped after casting by hot forming into a preliminary product, by cooling from the forming temperature. Furthermore, the preliminary product can be heated to a silicide start temperature after its production and the intermediate product is cooled from the silicide start temperature in such a way that the desired silicides are eliminated. If the TiAl alloy is used as a powder for the powder-metallurgical production of a component, for example for the additive production of a component by layer-by-layer deposition of the powder particles or by vacuum-tight encapsulation and joining of the powder by hot isostatic pressing to form a pre-product, the pre-product produced by the powder can also be transferred to a Bred silicide start temperature and cooled by this in such a way that silicides can be excreted. In powder metallurgical production, too, the intermediate product can be cooled from a temperature already present during production, such as the HIP temperature, in such a way that silicide is precipitated. In this case, the HIP temperature is the silicide start temperature. In order to enable the silicides to precipitate, the cooling from the silicide start temperature must take place slowly enough to allow the silicides to precipitate.

Subsequently, in a further step of the method according to the invention, a heat treatment of the precipitation-stabilized semi-finished product or pre-product is carried out in the α-phase temperature range in which the semi-finished product or pre-product is essentially present as an α-Ti phase with precipitated silicides, the silicides having a coarsening of the Counteracting α - Ti grains. During this step, the existing β phase largely or completely dissolves. The heat treatment in the α-phase temperature range can be carried out for a period of 0.5 to 2 hours, in particular from 0.5 to 1 hour, the cooling being carried out in such a way that globular colonies of lamellae form from the α-Ti grains from α ₂ - Ti ₃ Al and γ - TiAl, the silicide precipitations previously generated during the precipitation stabilization of the material also being present. This results in a microstructure that has an excellent, balanced profile of properties with improved creep resistance.

The silicide start temperature to which a semi-finished product after casting or a pre-product formed after casting or a pre-product manufactured by a powder metallurgical process is heated during precipitation stabilization of the TiAl alloy can be at a temperature above a silicide dissolution temperature of the material, so that the Silicide start temperature the silicon is largely in solution in order to then enable a homogeneous precipitation of the silicides when the semi-finished product or intermediate product cools. That This coarser structure can be refined by forging, whereby fine silicides can be excreted by targeted cooling from the forging temperature. However, the silicide start temperature can also be below a silicide dissolution temperature if the silicide start temperature is the temperature during a deformation or compacting of a semi-finished product or a preliminary product. For example, when consolidating the powder by HIPing or when re-compacting a pre-product built up using powder metallurgy by HIPing, a temperature can be set well below the silicide dissolution temperature, so that silicides can form.

Correspondingly, the α-phase temperature range in which the subsequent heat treatment of the precipitation-stabilized semi-finished product or intermediate product is carried out can be below a silicide dissolution temperature of the TiAl alloy and above a γ-solvus temperature at which the entire γ-TiAl phase in α- Ti phase goes into solution, so that it is ensured that in the α phase temperature range, apart from the silicides present, essentially exclusively α Ti phase is present. In particular, the proportion of the α-Ti phase in the α-phase temperature range can be in the range of 95% by volume or more, in particular 98% by volume or more.

A corresponding TiAl alloy which has a suitable α-phase temperature range with a sufficiently high silicide dissolution temperature and a γ-solvus temperature at least 15 K, in particular at least 20 K lower, at which γ-TiAl components are no longer present, but exclusively The α-Ti phase has a chemical composition with 42 to 48 at.% aluminum, preferably 43 to 45 at.% aluminum, 3 to 5 at.% niobium, preferably 3.5 to 4.5 at.% niobium, 0, 05 to 1 at.% Molybdenum, preferably 0.85 to 0.95 at.% Molybdenum, 0.2 to 2.2 at.% Silicon, preferably 0.25 to 0.35 at.% Silicon, 0.2 to 0.4 at.% Carbon, preferably 0.25 to 0.35 at.% Carbon, 0.05 to 0.2 at.% Boron, preferably 0.05 to 0.15 at.% Boron as well as titanium and unavoidable impurities on, wherein titanium is provided in an amount that the sum of the chemical elements of the alloy is 100 at.%.

Alternatives according to the invention of the TiAl alloy, which are produced in particular by the production method described above or components made from this TiAl alloy, comprise at least one of the elements from a group comprising tungsten, zirconium and hafnium. With such alloys, the structures described can be achieved at room temperature or in the α-phase temperature range. In addition, the alloy components mentioned can give the alloys or the components produced with them additional properties.

According to an alternative according to the invention, the TiAl alloy contains, in addition to titanium and unavoidable impurities, 43.5 to 45 at.% Aluminum, 3.5 to 4.5 at.% Niobium, 0.1 to 0.5 at.% Molybdenum, 0, 4 to 1 at.% Tungsten, 0.25 to 0.35 at.% Silicon, 0.25 to 0.35 at.% Carbon and 0.05 to 0.15 at.% Boron, the alloy having precisely this composition may have or may include additional alloy elements. In any case, the proportion of titanium is chosen so that the sum of the chemical elements of the alloy is 100 at.%.

According to a further alternative according to the invention, the TiAl alloy contains, in addition to titanium and unavoidable impurities, 43.5 to 45 at.% Aluminum, 3.5 to 4.5 at.% Niobium, 0.85 to 0.95 at.% Molybdenum, 0 , 1 to 3 at.% Zirconium, 0.25 to 2.2 at.% Silicon, 0.25 to 0.35 at.% Carbon and 0.05 to 0.15 at.% Boron, the alloy being exactly these May have composition or may comprise additional further alloying elements. In any case, the proportion of titanium is chosen so that the sum of the chemical elements of the alloy is 100 at.%.

According to a further alternative according to the invention, the TiAl alloy contains, in addition to titanium and unavoidable impurities, 46 to 48 at.% Aluminum, 3.5 to 5 at.% Niobium, 0.1 to 0.5 at.% Molybdenum, 0.4 to 1 , 8 at% tungsten, 0.1 to 3 at.% Zirconium, 0.35 to 2.2 at.% Silicon, 0.25 to 0.35 at.% Carbon and 0.05 to 0.15 at.% Boron, wherein the alloy can have precisely this composition or can comprise an additional further alloy element, namely hafnium. In any case, the proportion of titanium is chosen so that the sum of the chemical elements of the alloy is 100 at.%.

In these alloys, for example, boron and carbon can both contribute to solid solution strengthening of the alloy and also produce borides and / or carbides, which positively affect the microstructure with regard to a homogeneous microstructure with suitable colony sizes and lamellar thicknesses or spacings of the α ₂ - Ti ₃ Al - and γ - TiAl - lamellae can influence.

In the method for producing a component from a TiAl alloy, the semi-finished product or intermediate product heat-treated in the α-phase temperature range can be subjected to a second heat treatment at a temperature below a γ-solvus temperature of Material are subjected to influence the formation of the lamellae from α ₂ - Ti ₃ Al and γ - TiAl from the α - Ti grains and to set the desired lamella thicknesses or spacings.

A corresponding TiAl alloy or a component made therefrom can thus have less than 5% by volume β phase and preferably no β phase at all in the TiAl alloy at operating temperatures of up to 1000 ° C., so that the creep resistance is improved.

The globular colonies with lamellae made of α ₂ - Ti ₃ Al and γ - TiAl can form 95% by volume or more, in particular 98% by volume or more, of the TiAl alloy at room temperature. The remainder can be formed by silicides, carbides and / or borides, the TiAl alloy being able to contain up to 5% by weight, preferably up to 2% by weight, of silicides, carbides and / or borides, their mean or maximum grain size can be less than or equal to 5 µm.

The globular colonies of α ₂ - Ti ₃ Al and γ - TiAl lamellae can have an average or maximum size of 50 to 300 μm, in particular 100 to 200 μm, the average lamellae spacing being in the range from 10 nm to 1 μm can. The lamella spacing is understood here as the distance between lamellae in the same phase, i.e. the distance from one γ-TiAl lamella to the next γ-TiAl lamella or the distance from one α ₂ -Ti ₃ Al lamella to the next α ₂ -Ti ₃ Al lamella.

BRIEF DESCRIPTION OF THE FIGURE

The attached drawing shows in a purely schematic manner the structure of a TiAl alloy according to the invention or a component made from a TiAl alloy.

EXAMPLE OF EXECUTION

Further advantages, characteristics and features of the present disclosure will become apparent from the detailed description below.

For a TiAl alloy consisting of 43.8 at.% Aluminum, 4 at.% Niobium, 0.9 at.% Molybdenum, 0.3 at.% Silicon, 0.3 at.% Carbon, 0.1 at .% Boron and the remainder titanium and unavoidable impurities, a structure can be formed through the corresponding heat treatments in the α-phase temperature range and a subsequent second heat treatment at a temperature below the γ-solvus temperature of the TiAl alloy, as shown in is shown in the accompanying drawing. The globular colonies 1 made up of α ₂ - Ti ₃ Al lamellae 2 and γ - TiAl lamellae 3 are equiaxed with similar sizes and spherical shapes, with silicides 4 and borides 5 and carbides 6 having separated at the borders of the colonies 1.

REFERENCE LIST

1

globular colonies

2

α ₂ - Ti ₃ Al - lamellae

3

γ - TiAl lamellae

4th

Silicides

5

Boride

6th

Carbides

Claims (12)

1. TiAl alloy which has a microstructure at room temperature that comprises globular colonies (1) of lamellae of α₂-Ti₃Al(2) and γ-TiAl (3) and silicide precipitates (4), wherein the β phase in the alloy makes up less than 5 vol.% and the alloy has one of the following compositions:

   (i) 43.5 to 45 at.% aluminum,

   3.5 to 4.5 at.% niobium,

   0.1 to 0.5 at.% molybdenum,

   0.4 to 1 at.% tungsten,

   0.25 to 0.35 at.% silicon,

   0.25 to 0.35 at.% carbon,

   0.05 to 0.15 at.% boron,

   0 to 3.5 at.% zircon,

   0 to 0.3 at.% hafnium,

   unavoidable impurities and
   titanium, wherein titanium is provided in such an amount that the sum of the proportions of chemical elements contained amounts to 100 at.%;

   (ii) 43.5 to 45 at.% aluminum,

   3.5 to 4.5 at.% niobium,

   0.85 to 0.95 at.% molybdenum,

   0.1 to 3 at.% zircon,

   0.25 to 2.2 at.% silicon,

   0.25 to 0.35 at.% carbon,

   0.05 to 0.15 at.% boron,

   0 to 2.0 at.% tungsten,

   0 to 0.3 at.% hafnium,

   unavoidable impurities and
   titanium, wherein titanium is provided in such an amount that the sum of the proportions of chemical elements contained amounts to 100 at.%;

   (iii) 46 to 48 at.% aluminum,

   3.5 to 5 at.% niobium,

   0.1 to 0.5 at.% molybdenum,

   0.4 to 1.8 at.% tungsten

   0.1 to 3 at.% zircon,

   0.35 to 2.2 at.% silicon,

   0.25 to 0.35 at.% carbon,

   0.05 to 0.15 at.% boron,

   0 to 0.3 at.% hafnium,

   unavoidable impurities and
   titanium, wherein titanium is provided in such an amount that the sum of the proportions of chemical elements contained amounts to 100 at.%;
2. Method for producing a component from a TiAl alloy according to claim 1, which method comprises the following steps:

   - selecting a TiAl alloy which comprises a chemical composition of the TiAl alloy according to claim 1, and which is present in the α-Ti phase with silicides in the chemical composition of the TiAl alloy to be selected in an α phase temperature range,

   - melting the TiAl alloy,

   - casting the TiAl alloy into a semi-finished product or atomizing the TiAl alloy to form powder,

   - precipitation-stabilizing the semi-finished product or a preliminary product produced from the semi-finished product or the powder by cooling the semi-finished product or the preliminary product from a silicide starting temperature in such a way that silicides are precipitated,

   - heat-treating the precipitation-stabilized semi-finished product or preliminary product in the α-phase temperature range in which silicide precipitates (4) are present for 0.5 to 2 hours and cooling, such that globular colonies (1) of lamellae of α₂-Ti₃Al (2) and γ-TiAl (3) are formed.
3. Method according to claim 2, wherein the precipitation stabilization takes place directly during solidification from the melt or during cooling after compaction or shaping, and/or the silicide starting temperature is above or below a silicide dissolution temperature.
4. Method according to any of claims 2 to 3, wherein the α-phase temperature range is below a silicide dissolution temperature and above a gamma solvus temperature and preferably includes a range of at least 15 K, in particular at least 20 K.
5. Method according to any of claims 2 to 4, wherein the α-phase temperature range, a silicide dissolution temperature and/or a gamma solvus temperature of the TiAl alloy is determined by simulation calculations and/or by test melts and metallographic examinations.
6. Method according to any of claims 2 to 5, wherein the TiAl alloy is selected such that the TiAl alloy exhibits peritectic solidification with α-Ti phase formation or solidification with β-phase formation.
7. Method according to any of claims 2 to 6, wherein the heat-treated semi-finished product or preliminary product is subjected to a second heat treatment at a temperature below a gamma-solvus temperature for a period of 2 hours to 24 hours.
8. Component made of a TiAl alloy according to claim 1, preferably for a turbomachine, wherein the TiAl alloy has less than 5 vol.% of β phase at operating temperatures of up to 900°C, and the globular colonies have an average or maximum size of 50 to 300 µm.
9. Component according to claim 8, wherein the TiAl alloy does not have a β phase at operating temperatures of up to 900°C.
10. Component according to any of claims 8 to 9, wherein the globular colonies of lamellae of α₂-Ti₃Al and γ-TiAl form more than or equal to 95 vol.%, preferably more than or equal to 98 vol.%, of the TiAl alloy.
11. Component according to any of claims 8 to 10, wherein up to 5 wt.%, preferably up to 2 wt.%, of silicides, carbides and/or borides are contained in the TiAl alloy, wherein the average or maximum grain size of the silicides, carbides and/or borides is smaller than or equal to 5 µm, in particular the diameter according to a circle-area equivalent is smaller than or equal to 5 µm.
12. Component according to any of claims 8 to 11, wherein the globular colonies of lamellae of α₂-Ti₃Al and γ-TiAl have an average or maximum size of 100 to 200 µm and/or the average lamellae spacing is in the range of from 10 nm to 1 µm.

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