EP2272993B1 - Method for producing a forged article from a gamma-titanium-aluminium base alloy - Google Patents

Description

The invention relates to a method for producing a forgings for turbine blades made of a gamma titanium-aluminum base alloy

Titanium alloy of 6 at.% Or 8 at.% And (alpha + beta) or near alpha structure are known from US Pat EP 1 127 953 known and are used for a production of poppet valves. This involves upsetting a rod material above the beta conversion and finish-forging the valve disc with an alpha structure in a heat.

Titanium-aluminum base alloys are essentially formed of titanium aluminide intermetallics and have a high melting point, low density, a high specific modulus of elasticity, good oxidation behavior and high specific tensile strength and creep resistance in the temperature range of 600 ° C to 800 ° C, So meet the ever-increasing demands on special materials such as for next-generation components of aircraft engines and internal combustion engines.

Titanium aluminide materials are not yet optimized with regard to their alloy composition and their production and processing.

An alloy that has good processability as well as balanced mechanical properties that can be created by suitable heat treatments includes the elements titanium, aluminum, niobium, molybdenum and boron and is therefore referred to in the art as TNM alloy.

Due to the intermetallic nature of the titanium aluminide alloys, and possibly also of the TNM materials, in other words their brittle behavior under inappropriate deformation conditions, especially the production of forgings such as turbine blades is critical and usually associated with high waste rates.

It is known to forge remoulding under isothermal conditions perform what a special high-temperature forging sink with inert gas atmosphere requires and therefore costly.

The object of the invention is to improve the difficult and expensive processing of titanium aluminide materials and has the task of creating a method of the type mentioned above for economic production.

This object is achieved in a method for producing a forging, in particular a turbine blade, from a gamma-titanium-aluminum base alloy, in which a cylindrical or rod-shaped starting or starting material in one or more steps at those points at which the forging to be formed or the turbine blade to be formed has a volume concentration, heated by electric current passage or by induction over the cross section to a temperature higher 1150 ° C and deformed by application of force, in particular upsetting deformed and such a forging blank is created with different cross-sectional areas over its longitudinal extent, which blank in one or more subsequent steps is final deformed, wherein the or the subsequent step (s) for the final deformation of the forging blank each of an at least partially coating the surface with a heat radiation and thereby the oberflä is formed from heating the forging blank to forming temperature, from a heat soak and from a reshaping of the same, in particular in a die, is formed.

The advantages achieved with the invention are essentially to be seen in an economic pre-material production for a turbine blade production with different cross-sectional areas in the longitudinal extent and in thus favorable material flow conditions in the final shaping of the forging. Although gamma-titanium-aluminum base alloys have a high specific stiffness, it has proved to be beneficial to use a cylindrical or rod-shaped starting material and to increase it to a higher temperature by induction or in particular by direct passage of current between terminal or terminal areas on the rod to heat as 1150 ° C. By this heating, despite the radiation from the surface, a distribution of the temperature over the Cross section formed uniformly, because obviously by a current displacement of the specific current flow and thus the heat development in the surface area are increased.

At room temperature, the alloy consists mainly of gamma-titanium-aluminum and alpha 2-titanium-aluminum and has only a possibly small proportion of beta-phase, which phase has ductile properties depending on the temperature. When heated to more than 1150 ° C, with advantage over 1250 ° C, the proportion of beta-phase increases in the material, which justifies an improvement in the ductility of the material.

With a upsetting, as mentioned above, with targeted and homogeneous heating over the cross-section of the rod to high temperature, a uniform and targeted volume concentration and a desired fine-grain structure of the same can be achieved.

If more than one area of enlarged cross-section of the special blade bar is desired, upsetting may be done at several points in the sequence.

In a forging furnace, in one or more subsequent step (s), esp. In a die, a forged blank produced according to the invention can now be finally deformed, with advantage being due to the volume concentrations, a Gesenkfüllung with less material flow and / or material use can take place.

Because now a transport of forging blank or intermediate product from the heating furnace to the deformation plant with the tool or with a die, esp. At time-consuming movement paths, can cause a critical cooling of the surface portion of the deformed part, in an embodiment of the invention, a method in which or the sequential step (s) of final deformation of the forging blank or intermediate product for turbine blade production from at least partially coating the surface with a heat radiation and thereby the superficial one Temperature decrease-reducing agent, a heating of the forging blank or intermediate product to forming temperature, a heat soak, a transfer and a forming thereof, esp. In a die is formed (be), advantageously feasible.

It has been found that coating the surface of the forging blank or intermediate product with a means for reducing the heat radiation even with a thickness of greater than 0.1 mm can significantly reduce a temperature loss of the edge zone in the unit time and thus a required high forming temperature of the workpiece in the surface area Prevention of cracking during forming remains intact.
According to the invention, the oxide phase acts as a heat-resistant insulating component, with one or more additive (s) or adhesives having smaller proportions connecting (bonding) and retaining (holding) the oxide grains. The liquid component (s) serve to homogenize the phases and to adjust a desired level of liquid for homogeneous application to the surface of the workpiece or part.

An agent in which the main component or oxide phase is formed of zirconium oxide in a proportion in wt .-% of greater than 70, preferably from 80 to 98, esp. From 90 to 97, has been in view of a significant reduction in heat radiation turned out to be particularly favorable.

Advantageously, in another embodiment of the invention, a method which can be carried out without error is advantageous in which the final deformation takes place in a die which has a temperature which is at least 300 ° C. lower than the forging blank or the intermediate product. As a result, plant-technical simplifications are achieved with improved efficiency.

A method according to the invention, in which the final deformation takes place in a die having up to 900 ° C, preferably up to 800 ° C, lower temperature than the forging blank or the intermediate intensifies the above advantages, because such a low mold temperature Use of commonly used hot working steels for thermally tempered dies allows for no danger the hard waste of the same must be feared in the operation.

A process in which the final deformation as a rapid forming with a deformation rate of> 0.3mm / sec, esp. From 0.5 to 5mm / sec., Takes place, provides both forging advantages and a significantly improved microstructure of the forging.

Advantageously, the method of manufacturing turbine blades, e.g. made of a TNM alloy, usable.

With reference to exemplary embodiments, which each represent only one process path, the invention will be explained in more detail.

Fig.1

in Ansicht und Fig. 2 im axialen Schnitt ein freies Aufstauchen eines Stabendes

Fig. 3

in Ansicht und Fig. 4 im axialen Schnitt ein Aufstauchen eines Stabendes in einer Form

Fig. 5

in einer Form aufgestauchte Endenbereiche von Stäben einer Ti-Al-Basislegierung bzw. Vormaterial für eine Gesenkschmiedung

Fig. 1 und Fig. 2

zeigen ein Aufstauchen eines Stabes 1 bei freier Breitung.

They show schematically:

Fig.1

in view and Fig. 2 in the axial section a free upsetting of a rod end

Fig. 3

in view and Fig. 4 in axial section an upsetting of a rod end in a mold

Fig. 5

in a mold upturned end portions of rods of a Ti-Al base alloy or starting material for a drop forging

Fig. 1 and Fig. 2

show an upsetting of a bar 1 with free expansion.

A power source (not shown) is connected to a terminal 2 and a slightly concave shaped flat caliper 3. For a forming a rod 1 is pressed in a press on the flat saddle 3, wherein between the flat saddle 3 and the terminal 2 electric current flows, which heats the rod in this area by the ohmic resistance.

A heating of a rod or rod part can also be done by means of an induction coil and alternating current.

By an upsetting force occurs after warming up of a rod part upsetting a rod end, in the given case with free expansion.

It has been found that titanium-aluminum base alloys have particularly good compression properties and are not prone to buckling. Furthermore, a rapid, targeted heating of a rod area is possible by a heat technology with electrical current passage or by induction, with a precise adjustment of the forming temperature in the so-called. Deformability window of the alloy can be achieved.

FIG. 3 and FIG. 4 show a puncture of one end of a rod 1 in a mold 3 to form a desired shaped end portion 11th

Thus, an accurate dimension of a forging blank for final forming can be made.

Blanks, as in FIG. 3 and FIG. 4 2, for a turbine blade forging, a rod having a diameter of 30mmφ and a length of 225mm was made of an alloy Ti-43.5Al- (Nb-Mo-B) 5 at%. The production length was 192mm with a head diameter of 45mm and a head length of 63mm.

The heating and compression time was 60 sec., With a heating current of 7740 A and a forming temperature of 1250 ° C had been set.

Fig. 5 shows in a form compressed blanks.

Claims (6)

1. A method of preparing a forged object, particularly a turbine blade, from a gamma-titanium/aluminium basic alloy, in which, in one or more steps, a cylindrical or bar-shaped starting or preliminary material is, at those sites where the object to be forged, or the turbine blade to be forged, respectively, has a volume concentration, heated to a temperature of more than 1150 °C upon dectrical power passage or upon induction throughout the cross-section and deformed, particularly deformed by upsetting, upon imposing force, thus preparing a forging biscuit having different cross-sectional areas along its longitudinal dimension, which biscuit is end-shaped in one or more subsequent steps, wherein the, or each, subsequent step of end-shaping the forging biscuit is formed by at least partially coating the surface with an agent decreasing heat radiation and thus surface temperature drop, heating the forging biscuit to a transformation temperature, through-heating and reshaping the same, in particular within a die.
2. The method of claim 1, wherein said agent decreasing surface temperature drop is formed by an oxide phase as the main component and one or more adhesive(s) as additive(s) as well as liquid components.
3. The method of any one of claims 1 to 2, wherein said coating agent is formed by zirconium oxide at a content of more than 70, preferably of from 80 to 98, and particularly of from 90 to 97, per cent by weight.
4. The method of any one of claims 1 to 3, in which said end shaping is conducted within a die having a temperature of at least 300 °C below that of said forging die.
5. The method of any one of claims 1 or 4, in which said end shaping is conducted within a die having a temperature of up to 900 °C, preferably of up to 800 °C, below that of said forging die or said intermediate.
6. The method of any one of claims 1 to 5, in which said end shaping is conducted in the form of rapid reshaping at a deformation rate of > 0.3 mm/sec, particularly of from 0.5 to 5 mm/sec.

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