EP1024910B1 - Device for encapsulating blanks in high-temperature metallic alloys - Google Patents

Abstract

In a device for encapsulating blanks of metallic high temperature alloys, particularly TiAL alloys, which are subjected to forging or rolling for hot forming, at least a first inner envelope is supported on the blank in closely spaced relationship therefrom and a second envelope surrounds the first envelope and both envelopes consist of a metallic material.

Description

The invention relates to a device for encapsulation of blanks made of metallic high-temperature alloys, especially TiAl alloys used for hot forming be subjected to an extrusion, the Encapsulation at least from a first, the blank closely but spaced enclosing first inner shell consists.

From JP-A-01 027715 a device is known from which is a blank made of a metallic high-temperature alloy an encapsulation from a blank enclosing the blank Has shell. For example, the shell is made made of copper.

Metallic high-temperature alloys are used Manufacture of highly stressed or highly stressable Components used, for example as components for Use in turbines to power aircraft and like. To achieve the desired properties, e.g. height Strengths will be achieved for certain components basically required that they have been hot formed are. In the case of TiAl alloys as certain metallic high temperature alloy is a forming of the components also with regard to the setting certain structures are required, which are in other ways cannot be achieved by melt metallurgy. It has shown that hot forming of TiAl ingots Temperatures of 1100 ° C required, compare Y.-W. Kim, D.M. Dimiduk, J. Metals 43 (1991) 40. This is in many cases, for example in hot extrusion, because limiting die or die and receiver temperatures only possible isothermally. Since that Resilience and resistance to deformation of TiAl alloys are strongly temperature-dependent, the Blanks for extrusion are encapsulated to high Avoid loss of temperature. As capsule material So far there are Ti alloys or austenitic steels available, however, their resistance to deformation at the required temperatures is much smaller than that of the raw TiAl material to be formed or one corresponding blank from this material. One use of capsule materials with better adapted Resistance to deformation such as TZM molybdenum is eliminated Cost reasons.

The big differences in the resistance to deformation of capsule and Core material lead to uneven forming when extruding with undesirable variations in Degree of deformation over the length of the strand and also also for cracking in certain areas of the capsules. It an attempt was made to find the forming resistances between capsule and Core material through a cooling phase between the Warm up and adapt to the extrusion. model calculations the temperature profile of the capsule and core increasing hold time show that this way too small temperature differences can be achieved. Also at a low assumed heat transfer value that only with a thermal insulation layer (e.g. glass wool) what can be achieved is the achievable temperature difference not yet sufficient.

It is therefore an object of the present invention to Device for encapsulating metal blanks High-temperature alloys of the type mentioned at the beginning create with the heat loss of the blank avoided encapsulation due to longer waiting times between warming up and Extrusion with low temperature losses in the core to cool so far that capsule material and core material have almost the same deformation resistance, which is especially true Temperature differences of up to 500 ° K are necessary. The The device should be simple and inexpensive be educable and deployable.

The object is achieved according to the invention in that one enclosing the inner shell closely but at a distance second, outer shell is provided, the first and the second shell made of a metallic material consist.

The advantage of the solution according to the invention is that that an optimal shield against heat radiation from the blank, i.e. the core of the device will, which is fundamentally at the present temperatures the main cause of heat loss is whereby it is furthermore advantageously possible is an optimal heat conduction resistance Achieve vacuum insulation and finally advantageously to avoid convection as well as the Avoidance of material pairings, which in the case of a Extrusion of this type requires high temperatures lead to undesirable reactions.

It has been shown that for an effective radiation protection shield, which the inner shell forms sheet-shaped element as an inner shell is sufficient to this alone means a radiated emission reduced by 33% To achieve performance.

The outer shell of the device faces like experiments have resulted, preferably a wall thickness of 5 to 10 mm, with the outer shell basically made of steel or preferably a titanium alloy, e.g. Ti6Al4V, can be formed.

Studies have shown that the inner shell only a wall thickness in the range of 0.1 up to 1 mm, but particularly advantageously one Wall thickness of 0.3 mm is sufficient to reduce the Achieve radiation performance by 33%. Due to the high heating and processing temperature on the one hand but it is also advantageous for cost reasons as an inner shell sheets or foils made of molybdenum and / or tantalum to use, which have low emissivity have ε. This also makes material pairings avoided that applied to the high temperatures lead to undesirable reactions.

Basically, it is possible to be different appropriate way to ensure that the blank continuously spaced from the inner shell surrounding it is to have direct thermal contact between the Avoid blank and the inner shell largely. However, it has proven to be advantageous to Form blank so that this a plurality of projecting webs, which act as spacers act as the inner shell enveloping the blank. So can, for example, the webs in a simple manner essentially cylindrical in cross section Blank created by simply turning or milling become.

To in the same way as described above too to ensure that the inner shell opposite the outer shell a negligible thermal contact has, it is also advantageous to the outer Envelope with a plurality of protruding, on the inner Provide sheath-facing webs that act as spacers act to the inner shell. Here too in principle it is possible to use the webs, especially if it is is an outer hollow cylindrical cross section Wrapping acts, by unscrewing or suitable milling of the outer shell.

The webs are in the outer wrapping and the inner blank or core of the device preferably to train such that their contact surface with very small compared to the adjacent inner shell the remaining lateral surface is.

As already mentioned, the attachment can only be one inner shell that the radiation shield mentioned forms, to a reduction in the radiation power lead by 33%. The radiated power to decrease even further, it is with another advantageous embodiment of the device possible, to provide a third and a fourth shell, also each closely spaced between the first shell and the second shell and each of these are closely spaced. The choice of other covers will depend on the extent to which for the special Extrusion process depending on the one forming the blank Material is considered necessary, one same resistance to deformation of sheath and core material to reach.

As with the basic design described above the device with at least two sleeves can also in the configuration of the device described above be advantageous with four shells, the first, inner shell adjacent third shell with a Plurality of both the first and fourth shells Sheath-facing webs to provide the as Spacer to the adjacent first shell and fourth shell act. In this case, too Bridges by turning or milling the third shell are formed, the corresponding, Turning or milling the blank mentioned above or the outer second shell to form the there Webs, as described, remains unaffected or in the same manner as described can.

The third shell advantageously consists of the same material as the second shell, advantageously the fourth shell made of the same material how the first shell is made.

Overall, with a training of the device in the previously described sense with four envelopes Performance reduced to approx. 25% compared to the blank.

Finally, both for the design with two Envelopes and more envelopes make the outer envelope vacuum-tight be trained so that once heat conduction the gas in the spaces as well as convection in the Interstices are suppressed, on the other hand oxidation the metallic parts is prevented from doing so to obtain low emissivity ε of these parts.

Fig. 1

im Schnitt eine Vorrichtung gemäß der Erfindung mit zwei Hüllen, die einen Rohling aus einer metallischen Hochtemperatur-Legierung umschließen,

Fig. 2

eine Ausgestaltung der Vorrichtung der Erfindung gemäß Figur 1, bei der jedoch wenigstens in Teilbereichen der Rohling aus einer metallischen Hochtemperatur-Legierung von vier Umhüllungen umschlossen ist,

Fig. 3a-3b

den Verlauf eines minimalen und eines maximalen Durchmessers des Querschnittes des Kernes (Rohing) in der Vorrichtung über der Stranglänge bei verschiedenen Formen der Kapselung und Wartezeiten nach dem Anwärmen,

Fig. 4

den Kraftverlauf beim Strangpressen in einer Stahlkapselung mit Wärmeisolation nach einer Wartezeit von 25 sec nach dem Anwärmen und

Fig. 5

den Kraftverlauf beim Strangpressen in einer Stahlkapsel mit Wärmeisolation nach einer Wartezeit von 50 sec nach dem Anwärmen.

The invention will now be described with reference to the following schematic drawings or graphic representations using an exemplary embodiment and a modification thereof. In it show:

Fig. 1

on average a device according to the invention with two shells which enclose a blank made of a metallic high-temperature alloy,

Fig. 2

1 shows an embodiment of the device of the invention according to FIG. 1, in which, however, the blank made of a metallic high-temperature alloy is enclosed by four envelopes at least in partial areas,

3a-3b

the course of a minimum and a maximum diameter of the cross-section of the core (Rohing) in the device over the length of the strand with different forms of encapsulation and waiting times after heating,

Fig. 4

the force curve during extrusion in a steel encapsulation with thermal insulation after a waiting period of 25 seconds after heating and

Fig. 5

the force curve during extrusion in a steel capsule with thermal insulation after a waiting time of 50 seconds after warming up.

In Figures 1 and 2 is a device 10 according to the Invention shown, the extrusion too undergoing blank 11 from a metallic high temperature alloy, especially a TiAl alloy, essentially has a cylindrical cross section, accordingly, the device 10 also corresponds also essentially a cylindrical cross section having. At this point, however, it should be pointed out that this shape of the blank 11 or the device 10 by no means always has to be cylindrical, because they are also many other possible configurations of the blank possible, even before the final extrusion a roughly adapted to the shape to be taken later Can have shape. To understand the invention but because the construction principles of the device 10 apply generally, with reference to the representations of the device 10 according to FIGS. 1 and 2 with a substantially circular cross-sectional shape.

A blank 11 is arranged in the device 10 and of a first, inner shell 12 and a second outer shell 13 surrounded, compare in particular figure 1. The wrapping of the blank 11 in the design the device 10 of Figure 1 is complete, i.e. it is not just the outer, cylindrical surface here of the blank 11 surrounded by the sleeves 12, 13, but also the respective flat end faces of the blank 11.

The first, inner shell 12 encloses closely but at a distance the blank 11, the inner shell 12 for example a wall thickness of 0.1 to 1 mm, preferably 0.3 mm. The inner shell, which is sheet-shaped is preferably made of tantalum or molybdenum. Basically, however, all other are suitable Materials with low emissivity ε are used provided they do not match the material of the blank (11) or the outer shell (18) react.

The second, outer shell 13 has a much larger size Wall thickness than the inner shell 12, for example in Range from 5 to 10 mm. Both for the inner shell 12 as well as the outer shell 13 applies that also essentially flat end faces of the blank 11 with the same Cover structure, as described above, covered become.

The outer shell 13 can for example be made of steel or any other suitable material for this Purposes, for example TiA16V4.

The blank 11 has a plurality of projecting webs 110, which act as spacers to the inner shell surrounding the blank 11. These webs can be produced, for example, by milling or turning off the blank 11, for example by 0.3 mm, so that the webs thus formed have a width of approximately 1 mm at a height of 0.3 mm. This measure allows the necessary small distances d = d _isol - d _{mo to be maintained} between the first shell 12 serving as the first radiation protection _plate and the blank 11. To suppress direct heat conduction between the blank 11 and the second, outer shell 12, including the first, inner shell 12, the webs 110 on the blank 11 and the webs 131, which are likewise formed in an analogous manner on the second outer shell 13, staggered. All in all, the entirety of the casing made up of the first casing 12 and the second casing 13 acts as a double radiation protection shield, with the result that the power emitted by the blank 11 is reduced to approximately one third in comparison to the unprotected blank 11.

In the configuration of the device 10 according to FIG. 2, which basically have the same structure as that 1, is additional a third shell 14 and a fourth shell 15 are also provided. These sleeves 14, 15 are also closely spaced from one another closely spaced. In this case too has the one adjacent to the first, inner shell 12 third shell 14 a plurality of both to the first shell 12 as well as the fourth shell 15 facing webs 140 on. The webs 140 also serve as spacers to the adjacent first shell 12 and the also adjacent fourth shell 15. The third shell 14 can be made of the same material as that second shell 13 exist. The fourth shell 15 can consist of the same material as the first shell 12. Are factual in the design of the device 10 four radiation protection plates effective according to FIG. 2, namely the first shell 12, the second shell 13, the third shell 14, and fourth shell 15. In the embodiment the device 10 according to FIG radiated power compared to the unprotected blank 11 can be reduced to about 25%, with regard to an estimate of this reduction in radiated Performance based on a calculation below is referred.

Basically in the temperature range from 1000 ° to 1400 ° C for sleeves 13 and 14 steel or titanium alloys be used. At even higher temperatures should refractory metals for these shells (13 and 14) how to choose Mo or Ta. The sleeves 12 and 15 are made preferably made of Mo or Ta, even with even higher ones Temperatures than 1400 ° C. Basically, however also all other suitable materials with low Emissivity ε can be used, provided material pairings avoided, which lead to reactions. The first shell 12 and the fourth shell 15 are preferred thin-walled. It should be pointed out that the device according to the invention is not only limited to the extrusion of titanium aluminides, rather, reshaping is also possible by extrusion at temperatures above 1000 ° C for other metallic high-temperature alloys applied very successfully.

Encloses in the devices according to Figures 1 and 2 at least the first casing 12 makes the blank vacuum-tight, taking the necessary evacuation of the gaps between at least the first shell 12 and the blank 11 is achieved by having the lid and the bottom at least the first shell 12 by inexpensive Electron beam welding welded in a vacuum chamber. Overall, the manufacture of the device 10 can thus be designed relatively inexpensively. Also the other shells 13 to 15 of the device can if necessary, be vacuum-tight.

An estimate of the effectiveness of the invention with the device 10 proposed measures for Avoidance of heat loss due to radiation, should be based on the radiation power of non-insulated and extrusion blanks insulated by heat shields 11 are shown.

F - Oberfläche des Körpers

c - Stefan-Boltzmannsche Strahlungskonstante (c = 5.7·10^-8 Wm^-2 K^-4)

ε - Emissionsvermögen des Körpers

T - absolute Temperatur

According to the Stefan-Boltzmann law, a non-black body radiates the heat output in the cold room dQ s / dt = F ε c T 4 from. The names have the following meaning

F - surface of the body

c - Stefan-Boltzmann radiation constant (c = 5.7 · 10 ^-8 Wm ^-2 K ^-4 )

ε - body emissivity

T - absolute temperature

For bare metal bodies, ε = 0.3 often applies. An extrusion blank of  65 mm x 170 mm heated to 1300 ° C would initially emit a power of dQ _s / dt = 4.6 kW without insulation after removal from the furnace.

The resulting heat losses can be very effectively prevented at high temperatures by attaching one or more radiation shields (shells) which are introduced between the hot body or blank 11 and the cold environment. For the present geometry of a hot cylindrical blank 11, this is reduced with a radiation shield arranged concentrically around the body Q s, 1 = dQ s, 1 / dt = F ε c T 4 / (ε s / ε e + r k / rs ) With ε e = ε ε s / (1- (1 - ε s ) (1 - ε F k / F s )).

ε_s - das Emissionsvermögen

r_k - der Radius des heißen Körpers

r_s - der Radius des Strahlungsschutzschildes.

Here mean

ε _s - the emissivity

r _k - the radius of the hot body

r _s - the radius of the radiation protection shield.

According to Eq. 2 applies d Q s, 1 / dr k > 0, ie the effectiveness of the radiation protection shield is higher the smaller its distance from the hot body. If, to simplify the estimation, we continue to assume that ε = ε _s and r _k = r _s , the following applies dQ s, 1 / dt = 1/2 dQ s / Dt.

By attaching a radiation protection shield, the radiated power can already be reduced to 50%. When using n radiation protection shields, the same simplifying requirements apply dQ s, n / dt = (1 / (n + 1)) dQ s / Dt.

• Als Strahlungsschutzschilde (Hüllen) müssen nach Gl. 2 Werkstoffe mit geringem Emissionsvermögen ε verwendet werden. Aufgrund der hohen Temperatur und aus Kostengründen ist die Werkstoffauswahl auf Bleche bzw. Folien aus Mo oder Ta beschränkt. Allerdings sollten diese Werkstoffe eine möglichst glatte und oxidfreie Oberfläche haben.
• Der Abstand zwischen heißem Körper und dem ersten Strahlungsschutzschild und zwischen weiteren Strahlungsschutzschilden sollte nach G1. 2 möglichst klein gehalten werden.
• Wärmeverluste durch Konvektion bzw. Wärmeleitung müssen vermieden werden.

According to the conditions shown here, the encapsulation must be carried out according to the following principles to avoid heat loss through radiation:

• As radiation protection shields (envelopes) according to Eq. 2 materials with low emissivity ε can be used. Due to the high temperature and for cost reasons, the choice of materials is limited to sheets or foils made of Mo or Ta. However, these materials should have a surface that is as smooth and oxide-free as possible.
• The distance between the hot body and the first radiation protection shield and between further radiation protection shields should be according to G1. 2 should be kept as small as possible.
• Heat loss through convection or heat conduction must be avoided.

1. TiAl6V4- Kapselung ohne Wärmeisolation, 25 s Wartezeit

2. Stahlkapselung ohne Wärmeisolation, jedoch mit eingelegter Mo-Folie als Reaktionsbarriere, 25 s Wartezeit

3. Stahlkapselung mit Wärmeisolation wie erfindungsgemäß beschrieben (s. Abb. 1), 25 s Wartezeit

4. 3. Stahlkapselung mit Wärmeisolation wie erfindungsgemäß beschrieben (s. Abb. 1), 50 s Wartezeit

4 extrusion tests were carried out to test the extrusion capsule construction described. For this purpose, blanks 11 with a diameter of 65 mm, which consisted of the same TiAl alloy, were encapsulated in different capsules. Since the desired temperature difference between the encapsulation and the blank 11 increases with the above-described construction of the encapsulation due to an increased waiting time between heating and extrusion, the waiting time was also varied. The other test conditions (heating temperature 1250 ° C, predetermined stamp speed 20 mm / s) and the outer dimensions of the encapsulation were identical in all tests. The following forms of encapsulation and waiting times were selected:

1. TiAl6V4 encapsulation without thermal insulation, 25 s waiting time

2. Steel encapsulation without thermal insulation, but with inserted Mo foil as a reaction barrier, 25 s waiting time

3. Steel encapsulation with thermal insulation as described according to the invention (see Fig. 1), 25 s waiting time

4. 3. Steel encapsulation with thermal insulation as described according to the invention (see Fig. 1), 50 s waiting time

After the extrusion, the strands were cut open and the cross-sectional shape of the TiAl blank 10 was monitored over the length of the strand. In the ideal case - ie if the sheath and core material have the same resistance to deformation, circular cross sections of the TiAl raw ring 10 with a diameter of 22.9 mm should result with the selected transducer diameter of 85 mm and the die diameter of 30 mm. 3a-3d show the minimum and maximum diameters of the generally oval cross sections of the TiAl blank 10 after these tests. The results show that in the case of the TiAl6V4 capsule without thermal insulation, the most unfavorable conditions are present, i.e. the core cross-section shows the greatest differences between the minimum (d _min ) and maximum (d _max ) diameter and is due to the low deformation resistance of the TiAl6V4 alloy with the core material sometimes considerably above the ideal value of 22.9 mm. In addition, the cross section varies significantly over the length of the strand. In the case of steel encapsulation without thermal insulation, the cross-sections are more approximate to the circular shape and the diameter curve over the length is more uniform, but the values are above the ideal value of 22.9 mm. In contrast, the use of an encapsulation made of steel with thermal insulation leads to a diameter progression of 22.9 mm, whereby the most even progression is observed for the extended waiting time of 50 s. From these results it can be concluded that the thermal insulation is effective and that a good adjustment of the deformation resistance between the steel jacket and the TiAl blank 10 has already been achieved with waiting times of 50 s. The clear effect of the thermal insulation is also evident in the force curve during extrusion. As FIGS. 4 and 5 show, the initial die force when extruding encapsulations with thermal insulation after a waiting time of 50 s is considerably higher than after a waiting time of 25 s, which is due to the higher resistance to deformation of the capsule material due to the higher temperature drop. When using an encapsulation with thermal insulation, the above-mentioned tearing of the strands did not occur in the initial area, which can also be explained by the better adaptation of the resistance to deformation of the capsule and blank material. The aim aimed at by the invention was therefore achieved.

LIST OF REFERENCE NUMBERS

10

contraption

11

blank

110

web

12

first, inner shell

120

wall thickness

13

second outer shell

130

wall thickness

131

web

14

third shell

140

web

15

fourth shell

Claims (15)

1. Device (10) for encasing preforms (11) made of metallic high-temperature alloys, in particular TiAl alloys, that are subjected to extrusion in order to hot-reshape them, whereby the encasing consists of at least a first inner sheath (12) enclosing the preform (11) closely but separated from it by a space, characterized in that there is provided a second outer sheath (13) enclosing the inner sheath (12) closely but separated from it by a space, whereby the first and second sheaths (12, 13) consist of a metallic construction material.
2. Device according to Claim 1, characterized in that the inner sheath (12) is formed by an element in the form of sheet metal.
3. Device according to one or both of the Claims 1 or 2, characterized in that the inner sheath (12) has a wall thickness (120) in the range from 0.1 to 1 mm.
4. Device according to Claim 3, characterized in that the wall thickness (120) is 0.3 mm.
5. Device according to one or more of the Claims 1. to 4, characterized in that the inner sheath consists of molybdenum or tantalum.
6. Device according to one or more of the Claims 1 to 6, characterized in that the outer sheath has a wall thickness (130) in the range from 5 to 10 mm.
7. Device according to one or more of the Claims 1 to 6, characterized in that the outer sheath consists of steel.
8. Device according to one or more of the Claims 1 to 6, characterized in that the outer sheath (13) consists of TiA16V4.
9. Device according to one or more of the Claims 1 to 8, characterized in that the preform (11) has a plurality of projecting ribs (110) that act as spacers relative to the inner sheath (12) enclosing the preform (11).
10. Device according to one or more of the Claims 1 to 9, characterized in that the outer sheath (13) has a plurality of projecting ribs pointing towards the inner sheath (12) that act as spacers relative to the inner sheath (12).
11. Device according to one or more of the Claims 1 to 10, characterized in that there are provided a third sheath and a fourth sheath (15), each closely spaced relative to each other, between the first sheath (12) and the second sheath (13) and arranged closely spaced relative to these.
12. Device according to Claim 11, characterized in that the third sheath (14), separated from the first inner sheath (12) by a distance, has a plurality of ribs (140) pointing both towards the first sheath (12) and also towards the fourth sheath (15) that act as spacers relative to the neighbouring first sheath (12) and the fourth sheath (15).
13. Device according to one or more of the Claims 11 or 12, characterized in that the third sheath (14) consists of the same construction material as the second sheath (13).
14. Device according to one or more of the Claims 11 to 13, characterized in that the fourth sheath (15) consists of the same construction material as the first sheath (12).
15. Device according to one or more of the Claims 1 to 14, characterized in that at least the outer sheath (13) encloses the preform (11) in a vacuum-tight manner.

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