This application claims priority to German Patent Application DE102018212625.9 filed Jul. 27, 2018, the entirety of which is incorporated by reference herein.

The present disclosure relates in general to engine technology. In particular, the present disclosure relates to the production of engine parts with a complex geometrical structure. More particularly, the present disclosure relates to a production method for an engine component involving the application of force during a sinter joining process.

Joining is a suitable production method for complex parts or groups of parts, especially for parts in the aerospace sector which can be produced integrally only with difficulty, if at all. In this context, there are various joining techniques, e.g. welding, brazing, adhesive bonding but also screwed joints and mechanical joints designed in some other way. At the same time, however, it is not possible to join all workpieces because, for example, the materials used are insufficiently suitable for welding or brazing or because the joining methods can be made available only with additional weight, in the case of a screwed joint for example, or only with limited temperature stability, in the case of adhesive or brazed joints.

There may therefore be a need to implement joining methods specifically suitable for aeronautical applications in order to produce complex integral parts.

There may furthermore be a need, in the case of a joining process of this kind, to be able to implement further measures, thereby enabling a preferred joint and thus a joint with an enhanced joining quality to be implemented.

At least such a need may be met by the subject matter of the independent claims. Preferred embodiments will be found in the dependent claims and are explained in greater detail in the rest of the description.

According to a first aspect of the present disclosure, a method for producing a complex part is indicated, comprising making available a first component, having a thermal expansion coefficient of the first component, a first joining surface and a first bearing surface. A second component is furthermore made available, having a thermal expansion coefficient of the second component, a second joining surface and a second bearing surface. A jacket element is furthermore made available, having a thermal expansion coefficient of the jacket element and a jacket-element bearing surface. The first component, the second component and the jacket element are heated from a first temperature to a second temperature in order to carry out a joining process on the first component and the second component. During this process, the first component and the second component can be brought into contact in at least a partial area of the first joining surface and of the second joining surface, thus enabling a joint to be formed in the area of contact between the first joining surface and the second joining surface. In this case, the jacket element at least partially surrounds the first component and the second component and can be brought into contact by means of the jacket-element bearing surface with the first bearing surface and the second bearing surface. The thermal expansion coefficient of the jacket element is lower than the thermal expansion coefficient of the first component and/or the thermal expansion coefficient of the second component, wherein the thermal expansion coefficient of the jacket element and the thermal expansion coefficient of the first component and/or the thermal expansion coefficient of the second component are designed in such a way as to bring the jacket-element bearing surface into contact with the first bearing surface and the second bearing surface and to bring the first joining surface and the second joining surface into contact in the heated state while the joining process is being carried out, with the result that the first joining surface and the second joining surface are subjected to an opposing force action.

According to a second aspect of the present disclosure, a part, in particular for a gas turbine engine for an aircraft, more particularly a compressor-stator pair, that is to say two individual compressor-stators as a subassembly, wherein the stators can be joined, is made available, being produced by the production method according to the present disclosure.

According to a third aspect, a gas turbine engine for an aircraft is made available, having at least one part according to the present disclosure, produced by the production method according to the present disclosure.

Ideas and concepts in the present disclosure may be regarded as being based on the following observations and insights.

Sinter joining is a joining method in which two or more components in direct contact with one another at a joining surface are raised to a temperature suitable for a sinter joining process. During this process, the grain structures of a polycrystalline material coalesce. Typically, the sinter joining process is carried out at a temperature which is slightly below or even slightly above the melting temperature of the components to be joined or of the materials thereof.

Components for a sinter joining process are first of all produced in the context of a preparatory process, e.g. a metal powder injection molding process, in which a powdered material is mixed with a binder and processed into a molding in an injection molding process. A molding produced in this way is also referred to as a green compact. In a subsequent step, the binder is removed, being dissolved or removed by means of thermal treatment, for example. A resultant molding is referred to as a brown compact.

In a subsequent sintering process, the brown compact is raised to a temperature slightly below or slightly above the melting temperature of the materials thereof as explained above, resulting in a hardening reaction of the materials of the component and a simultaneous reduction in the dimensions thereof. A fully sintered part thus has reduced dimensions in comparison with the green compact and the brown compact. Typical shrinkage may be in the range of 10 to 30%.

During the sinter joining process described here, i.e. the heating of the component to the joining temperature, the thermal expansion coefficient of the material used leads initially to an increase in the dimensions or volumes of the components and the jacket element due to the expansion of the materials used and subsequently leads to the hardening of the joint. The above-described reduction in volume at the end of the joining process may take place to only a limited extent or not at all owing to pre-sintered components or fully sintered components.

The present disclosure relates to a method for applying force to join two or more subcomponents in a sintering process. Here, the application of force is advantageous for the quality of joining if the surfaces to be joined are subject to a contact pressure during sintering. Before sintering, the components to be joined are surrounded by a jacket structure, wherein the jacket structure is made from a material with lower thermal expansion than the components to be joined. Various combinations of materials for the jacket structure and the components are conceivable here, e.g. a ceramic jacket structure and a metallic component or, alternatively, jacket structures and components of the same material, such as a metallic jacket structure and a metallic component or a ceramic jacket structure and a ceramic component, with a higher melting temperature for the jacket structure than the components proving advantageous in the case of materials of the same kind. In this case too, the thermal expansion coefficient of the jacket structure is lower than the thermal expansion coefficient of the components to be joined.

Depending on the sintering temperature, the difference between the thermal expansion coefficients of the jacket structure and the components to be joined and the desired force to be applied to the joining surface, a gap can additionally be provided between the jacket structure and the components. In this case, the components to be joined can already be in the sintered state before sinter joining. As an option, a joining paste can be used between the subcomponents in order to compensate for slight irregularities in the surface or roughness during the sinter joining process.

Depending on the combination of materials for the jacket structure and components, it may be necessary to provide the jacket structure with a parting layer in order to counteract bonding between the jacket structure and the subcomponents.

Through a suitable choice of materials for the jacket structure and the metallic or alternatively, ceramic components to be joined with different thermal expansion coefficients, and taking into account the initial geometrical conditions or setting of the initial geometrical conditions before sinter joining through a suitable choice of a gap dimension between the jacket element and the components to be joined, it is possible to set the effective force during sinter joining. In this way, it is possible to implement a variable direction of action of force or a controlled force direction effect. Moreover, very high forces can be achieved by suitable dimensioning of the gap while taking into account the temperature expansion coefficients.

According to the disclosure, two components are introduced into a jacket element, wherein the jacket element at least partially encloses or surrounds the two components. In this arrangement, an opening in the jacket element is dimensioned in such a way that the two components can be introduced into the opening in the jacket element while being in contact with one another, for example. Here, the jacket element may have a gap with respect to the components.

Various developments of a sinter joining process produce a connection between two or more components by establishing a joint between joining surfaces that are in contact during the joining process, with the result that an integrally joined part is subsequently obtained from these two or more components. To form a preferred joint, it is helpful here if the components to be joined are pressed against one another with the use of a force, leading to a preferred material connection between the joining surfaces.

However, it is difficult to impose an external force on green compacts or brown compacts, in particular, owing to the porosity of the material composition of the green compact or the brown compact. In most cases, either only the weight of a component is used to press said component onto the other component during the joining process, or forces are introduced externally by means of elements in the form of small parts, e.g. “pin structures”, but this may not give uniform introduction of force and, in the worst case, may lead to a nonuniform joint or deformation of the green compact or the brown compact due to nonuniform application of force, making a component unusable after production.

However, in the context of the present disclosure, presintered or (almost fully) sintered components are preferably used since these may exhibit negligible shrinkage in comparison to the change in size due to the thermal expansion coefficient, as a result of which the change in size of the components during the sinter joining process is determined substantially by the thermal expansion coefficient itself.

According to one embodiment, a gap is formed between a partial area of the jacket-element bearing surface and at least a partial area of the first bearing surface and at least a partial area of the second bearing surface at the first temperature, wherein the gap is at least partially closed at the second temperature, thus enabling a force to be applied to the first component and the second component by the jacket element.

The jacket element at least partially encloses the first component and the second component and thus essentially provides support for the first component and the second component during the joining process. When heated, the jacket element expands less than the first component and/or the second component owing to the lower temperature expansion coefficient of said jacket element. Thus, the volume of the first component and the second component, or at least the extent in one particular dimension, increases more than that of the jacket element. A previously existing gap between the first component and the second component and the jacket element is thus substantially closed or reduced to zero, as a result of which the first component and the second component rest on the jacket element and obtain support from the latter. Heating is then continued and the first component and the second component expand further in relation to the jacket element. As a result, in turn, the joining surface between the first component and the second component is subjected to an opposing force and they are thus pressed against one another since the volume of the first component and the second component increases more than the volume of the jacket element.

At the second temperature, an opposing force action is provided between at least a partial area of the first joining surface and the second joining surface so as to form the joint.

If the first component, the second component and the jacket element are heated to the second temperature, the volumes of the first component and the second component increase disproportionately to the increase in volume of the jacket element. As a result, above a certain temperature the first component and the second component rest on the respective bearing surface relative to one another, as a result of which, in turn, when heated further and thus with a continued increase in volume, the first joining surface and the second joining surface are pressed onto one another.

According to another embodiment, the gap is dimensioned in such a way as to provide a directional force action.

In the case where the first component and the second component are introduced into an opening in the jacket element, the gap between individual sides of the components and of the jacket element can have different dimensions or be dimensioned differently, with the result, for example, that two gaps of relatively small dimensions provide a force action on a joining surface, while other gaps of larger dimensions are not yet providing a force action at a certain temperature. In this way, a directional force action can be obtained, e.g. exclusively a force action perpendicular to the joining surfaces, while a lateral force action or force action perpendicular thereto, parallel to the joining surfaces, is not effected or is effectively prevented through correspondingly larger dimensioning of the gap.

According to another embodiment, a joining paste is provided between the first joining surface and the second joining surface.

A joining paste can be composed of the same material as or a similar material to the first and the second component, for example, and can achieve a preferred joint between the first joining surface and the second joining surface as part of the joining process. In this context, the joining paste can, for example, compensate for irregularities in the surface of the joining surfaces which may arise because of inaccurate machining.

A joining paste can be composed of the same material as or a similar material to the first and/or the second component, for example, and can achieve a preferred joint between the first component and the second component as part of the joining process. In this context, the joining paste can, for example, compensate for irregularities in the surface of the first component and of the second component which may arise because of inaccurate machining. Here, the joining pastes can be adapted to the specific application, being identical in terms of material to the materials of the components to be joined, for example, or, alternatively, merely being similar in terms of material, e.g. having a smaller grain size and, as a result, being quicker to melt, for example. Formation of the joining paste from a different type of material is likewise conceivable, it being possible, by way of example, for the joining paste to comprise materials with a higher activation energy.

According to another embodiment, the jacket element may surround the first component and the second component over the full periphery in at least one section plane.

The first component and the second component are thus accommodated in a substantially internal opening in the jacket element, thereby resulting in a preferential force action of the jacket element on the first component and the second component since such a closed jacket element permits only slight deformations, in particular no nonuniform deformation, that could occur as part of the joining process when the first and the second component are supported on the jacket-element bearing surfaces.

According to another embodiment, the jacket element may not surround the first component and the second component over the full periphery in one section plane, in particular surrounding it in a U shape.

The first component and the second component are thus introduced into the interior of a jacket-element opening which is not closed fully or in the form of a ring. As a result, this may be deformed nonuniformly as part of a sinter joining process, e.g. the outer ends of the legs of the U may be pushed further apart than the sides situated further away from the base owing to the different lever forces. Moreover, support for the first component and the second component in cases where a jacket element that is closed over the full periphery is unsuitable owing, for example, to the geometrical shapes of the first component and/or the second component may be possible by means of such a jacket element that is not closed over the full periphery.

According to another embodiment, the joining method is a sinter joining method.

According to another embodiment, the first component and the second component may be formed from a sinterable material and may each be in a presintered or fully sintered state.

In the context of the present disclosure, the first component and the second component may be substantially fully sintered. It is likewise conceivable for one component to be composed of a presintered material and the other component to be composed of a fully sintered material. In this way, forces can be introduced preferentially into the components in order to provide a suitable force action on the joining surfaces relative to one another without endangering or prejudicing the structural integrity of the components. In the case of the use of a merely pre-sintered component, it must be ensured that the thermal expansion of the material overcompensates the shrinkage during the sinter joining process, thus enabling force to be applied, especially since the jacket structure likewise expands slightly.

According to another embodiment, the first component and/or the second component may be formed from a material from the group comprising a ceramic material, a metallic material, a material containing nickel, a material containing cobalt, IN713LC alloy, IN718 alloy, CM247 alloy, Haynes25 alloy and Hastelloy X alloy.

In this context, a nickel-based alloy or CM247LC alloy may, in particular, be composed as follows, based on % by weight: Ni: balance; Co: 9.25%; Cr: 8.2%; W: 9.52%; Al: 5.5%; Ta: 3.16%; Hf: 1.34%; Ti: 0.8%; Mo: 0.53%; B: 0.013%; C: 0.06%; Si: <0.01%; S: 0.0017%, Zr: 0.015%.

In this context, a cobalt-based alloy or Haynes25 alloy may, in particular, be composed as follows, based on % by weight: Co: balance; C: 0.05-0.15%; Ni: 9.0-11.0%; Fe: <=3.0%; Si: <=1.0%; Mn: 1.0-2.0%; Cr: 19.0-21.0%; W: 14.0-16.0%; P: <=0.03%; S: <=0.03%.

In this context, a nickel-chromium-molybdenum-tungsten alloy or Hastelloy X alloy may, in particular, be composed as follows, based on % by weight: Ni: balance; C: <=0.01%; Si: <=0.08%; Mn: <=1.0%; P: <=0.025%; S: <=0.01%; Co: <=2.5%; Cr: 14.5-16.5%; Fe: 4.0-7.0%; Mo: 15.0-17.0%; V: <=0.35%; W: 3.0-4.5%.

According to another embodiment, a parting layer or a parting material may be provided between the jacket element and the first component and/or the second component in order to prevent the formation of a bond between the jacket element and the first component and/or the second component.

Using the parting layer or parting material, the intention is thus to prevent the first component and/or the second component in turn forming a bond and thus entering into a joint with the jacket element as part of the joining process. It may thereby be possible to ensure that the first component and the second component can simply be released from the jacket element after the joining process.

According to another embodiment, the first component and/or the second component may be designed as a stator component or compressor stator component, in particular for a gas turbine engine for an aircraft.

Stator components or compressor stator components may have particularly complex geometrical structures, as a result of which it may only be possible to produce them integrally in a single production step with increased effort, if at all. Thus, stator components, compressor stator components or subassemblies comprising compressor stators (pairs) can preferentially be constructed from individual (sub)components.

According to another embodiment, the first joining surface and/or the second joining surface may have a joining surface geometry such that a positive connection is formed between the first component and the second component after the joining process has been carried out.

Here, a positive connection in addition to the nonpositive or bonded connection of the sintered joint may provide a joint between the first component and the second component which is capable of bearing particularly high loads.

