EP2165790A1 - Method for producing a workpiece from composite material and workpiece made of composite material - Google Patents

Abstract

The method for the production of structural element (50) made of a material composite, with a first output piece (10) made of sinter material, comprises partially subjecting second output piece (20) in a cavity of first output piece and then sintering. The first output piece exists in the form of a partially compressed sinter component, a green part or brown part. A connection (30) is produced between the output pieces and is formed on the basis of chemical connections between the materials of the output pieces in the form of an adhesive bond. The method for the production of structural element (50) made of a material composite, with a first output piece (10) made of sinter material, comprises partially subjecting second output piece (20) in a cavity of first output piece and then sintering. The first output piece exists in the form of a partially compressed sinter component, a green part or brown part. A connection (30) is produced between the output pieces and is formed on the basis of chemical connections between the materials of the output pieces in the form of an adhesive bond or based on increased shrinkage of the first output piece additionally in the form of a press fit. In the area of the connection, a diffusion layer is formed and the material fit is held freely by formed intermediate phases. A size of the diffusion zone is adjusted by a sintering duration. The connection is formed at the end of the sintering process. The output piece is produced by a powder metallurgical process such as powder injection molding, extrusion or uniaxial and/or isostatic pressing. The existing oxidation layers in the area of the connection are removed before or during the sintering under a reducing sintering atmosphere. After the sintering process, isotherm stop levels are intended during cooling process. An independent claim is included for a structural element made of composite material.

Description

State of the art

The invention relates to a method for producing a component from a composite material and in particular a manufactured by this method component from a composite material.

Composites offer the possibility to combine the advantages of different material groups and in this way to obtain components with outstanding properties compared to the base materials. Of particular interest for many applications is the combination of a hard, highly wear-resistant material (hard metal, cermet, ceramic) with a steel body of high toughness and ductility.

The joining of hard metals with steels has since been carried out via non-positive connections such as clamps, screw connections or shrinking or via integral connections such as soldering, welding, gluing or pouring.

Clamping and shrinking have the disadvantage that there is no positive connection between the two components. If the contact forces are too low or decrease over time, it may therefore lead to the separation of both components. Screw connections are only suitable for quite large components and also here the corresponding production cost for the production of the holes and threads is very high. Further disadvantages arise from stress concentrations on the screw connections, which can lead to failure long before the actual load capacity of the individual materials is reached. Furthermore, screw connections can become loose due to vibrations or cyclical loading.

In soldering, welding, gluing or pouring methods, a cohesive connection is created between the different materials. Due to the usually significantly different material properties of the weld line in comparison to the material pairs to be joined, however, this represents a weak point in the microstructure. In addition, the said methods are associated with a considerable manufacturing effort and sometimes high costs.

To produce a cohesive connection between steel and hard metal, various methods for diffusion welding with the aid of soft sheets (preferably copper or nickel) are known, as for example in the patent DE 10104632 C2 described. However, diffusion welding is limited to simple geometries in the connection plane and requires a very high surface quality of the workpieces to be joined.

In the patent applications EP 630713 A1 and EP 810051 A1 describes methods for diffusion brazing of steel and carbide components using various high temperature solders in powder or paste form. A disadvantage here proves to be the low strength of the solder joint compared to the base materials, partially by additional Force or positive connection must be compensated. In addition, a compensation of mechanical stresses due to temperature changes is limited.

In the patent application EP 1625896 A1 For example, a steel-cemented carbide composite roll is proposed for cold strip rolling of metal sheets. From a steel core and a hard metal outer layer, a composite body with high thermal shock resistance is realized by means of vacuum sintering or hot isostatic pressing. In this case, a thin cermet intermediate layer is applied between the steel core and the hard-metal outer layer. This then forms a metallurgical connection between the steel core and the hard metal under the influence of temperature.

Disclosure of the Invention Advantages

The invention is based on the object to propose a method with which components of different materials, in particular steel and hard metal components, without the use of other tools, such as brazing materials, interlayers or mechanical fasteners, are interconnected.

Furthermore, it is an object to provide a component made of a composite material, in particular the composite of a hard, highly wear-resistant material and a material with high toughness and ductility.

These objects are achieved according to the invention with a method for producing a component from a composite material and a component made of a composite material according to the characterizing features of the independent claims.

The method according to the invention therefore provides a first starting part made of a porous sintered material. The first output part is present as a partially compacted sintered component, green part or brown part. It is therefore not or not completely compressed, for example by a sintering process. Furthermore, the method according to the invention provides at least one second output part, which is introduced at least partially into a cavity of the first output part, preferably as a clearance fit. This is followed by a sintering process, in which the output parts are compressed under the influence of temperature. In this case, a connection between the starting parts is generated in at least partially filled by the second output part cavity. This compound forms due to chemical compounds, in particular of atomic bonds, between the materials of the starting parts in the form of a material bond. The material bond can be found at the points where both starting parts are in contact with each other.
Preferably, a contact formation of both output parts to one another during the sintering process is ensured by the expected sintering shrinkage of at least the first starting part. Provided is a sintering shrinkage, whereby a possibly present before the sintering clearance of the two output parts is bridged. The sintering process reduces the porosity and the volume of at least the first starting part. In the contact formation, the second output part to at least partially filled by him cavity of the first output part prefers a theoretical excess. This excess is compensated by material transport during the sintering process, which further favors a uniform and complete production of the compound of both starting parts.

Such an adhesion greatly favors a very stable connection of the starting parts. The formation of chemical compounds takes place in particular due to the active at the sintering temperature mass transfer due to diffusion, creep and viscous or plastic flow. Advantageously, no further aids are necessary for a connection of the starting parts, in particular in the form of a material bond.

A further advantage is that a compression of the material of at least the first output part as well as the generation of the compound in a process step take place. Thus, the present invention makes it possible to combine the two process steps of compaction and joining of steel-cemented carbide composites. This contributes greatly to a reduction in unit costs. In addition, in contrast to a conventional shrinking of a heated part to a non-heated part according to the invention all Augangsteile the same sintering temperature exposed. As a result, no thermal shock-induced material failure of the output parts at the point of connection is to be expected in an advantageous manner.

The measures listed in the dependent claims advantageous refinements and improvements of the features specified in the independent claims are possible.

Thus, a variant of the method provides that the connection is additionally formed in the form of a press fit. The press fit arises in particular during cooling after the sintering process due to different thermal expansion coefficients of the materials of the output parts. Here, the first output part should have a greater coefficient of expansion than the other output parts. Thus, upon cooling, there is a greater shrinkage of the first output member than at least the second output member.

Because the new method does not require low-melting solder materials, a composite material produced by this method has a high mechanical stability of the connection even at high temperatures. Such composite materials can be used in a variety of applications as materials for components used there. These components of a composite material can be used for various wear parts in which a material connection with a steel component or a component made of another material is advantageous (for example, drilling and cutting tools, rollers, pump parts). Also conceivable is the use in highly loaded assemblies from the automotive sector (for example, injection technology, exhaust gas turbocharger, rolling bearing, gearbox).

Brief description of the drawings

Fig. 1

einen Stahl-Hartmetall-Verbund in einer schemati-schen Darstellung vor einem Sintern

Fig. 2

den Stahl-Hartmetall-Verbund aus Fig. 1 nach einem Sintern als Verbundteil

Further advantages, features and details of the invention will become apparent from the following description Embodiments and with reference to the drawings. These show in:

Fig. 1

a steel-carbide composite in a schematic representation before sintering

Fig. 2

the steel-carbide composite Fig. 1 after sintering as a composite part

Embodiments of the invention

Fig. 1 shows schematically a steel-carbide composite before sintering according to the inventive method.

In this case, 10 denotes a first output part. The output part 10 is made of a sintered material, preferably a porous sintered material. The sintered material is at least partially in an uncompacted state, preferably in a non-compacted state before. This means that the first output part 10 has not yet undergone any or no complete sintering treatment by a temperature treatment. In general, non-compacted sintered components are also referred to as green parts (with organic binders) or brown parts (in the binder-free state).

The first output part 10 is in Fig. 1 designed as a hollow cylinder. In general, any part shape is possible for the first output part 10, wherein this part has at least one cavity 15. Such a cavity 15 is in in Fig.1 shown first output part 10, the inner bore with an inner surface 11 of the hollow cylinder. In the cavity 15 of the first output part 10, a second output part 20 is at least partially introduced. Preferably, the outer contour of the second output part 20 is formed complementary to the inner contour of the cavity 15. So that is in the Fig. 1 illustrated second output member 20 formed within the cavity 15 as a cylinder having an outer surface 21. In this case, a cavity 15 is possible in which the second output part 20 is surrounded on all sides by the first output part 10.

The preferred embodiment in Fig. 1 provides within the cavity 15 before a clearance between the first and the second output part 10, 20 before. In this case, a gap 16 is then present between the inner surface 11 of the first output part 10 and the outer surface 21 of the second output part 20.

In this state, the output parts 10 and 20 are then subjected to a sintering process. During the temperature treatment, the first output part 10 shrinks and consequently loses volume. Overall, the sintered material of the first starting part 10 thus undergoes compression. It is provided that the sintering shrinkage of the first output part 10 is so large that the gap 16 between the inner surface 11 and the outer surface 21 is closed. Due to the sintering shrinkage, a contact of both output parts 10 and 20 is to be ensured.

In Fig. 2 is made of steel-carbide composite Fig. 1 after sintering, shown as a composite part 50. Due to the sintering shrinkage, in particular of the first output part 10, at least partially the inner surface 11 of the first output part 10 and the outer surface 21 of the second output member 20 in contact with each other.

In this case, at the points of contact of the output parts 10, 20 to each other in the composite part 50, a compound 30 has been generated in the form of a material bond. As a result of the temperature treatment during the sintering process takes place in the starting parts 10 and 20 at their contact points to each other a brisk mass transfer. The reasons for the mass transfer are diffusion, creeping processes and viscous or plastic flow. This results in the formation of chemical bonds between the materials of the output parts 10 and 20 at the contact points. In addition, this also favors optimal geometric matching of the surfaces 11 and 21.

In order to ensure a material bond, existing oxide layers in the region of the compound 30 should be removed before or during sintering under a reducing sintering atmosphere.

In addition, in the composite part 50 in FIG Fig. 2 a connection 30 has been produced in the form of a press fit. Characterized in that the first output member 10 is selected with a larger coefficient of thermal expansion than that of the second output member 20, when cooling after the sintering process is a greater shrinkage of the first output member 10 in comparison to at least the second output member 20 before. By the resulting interference fit, the inner surface 11 and the outer surface 21 nestle well even in the presence of minor bumps together, creating a complete and uniform contact of the output parts 10 and 20 is ensured at the connection 30. A particularly uniform contact occurs at a roughness of the surfaces of the starting parts of Rz <100 microns. Alternatively, in the connection 30 after the sintering process, a transition fit or only a pointwise contact of the output parts 10 and 20 can be provided to each other.

It is important to ensure that in a press fit too much excess of the second output member 20 is avoided. Otherwise, this can lead to a disability of the compression of the first output member 10 in the radial direction. As a result, there may be a delay of the first output part 10. For this reason, the connection 30 of both output parts 10 and 20, in particular by the formation of the excess of the second output part 20 during the sintering process, should largely be generated only at the end of the sintering process. One possibility is to adapt the clearance of both output parts 10 and 20 to the expected sintering shrinkage of the output parts 10, 20 by the sintering process.

The sintering process is preferably carried out without pressure. As already described, this invention realizes a very stable connection between the output parts in a very cost-effective manner. Furthermore, other sintering methods, such as pressure sintering, vacuum sintering, hot isostatic pressing and field-assisted sintering, can also be used. As a result, in particular, pressure-assisted additionally a greater compression of the sintered materials and a better surface quality of the composite part 50 can be achieved in total. In principle, however, this involves a higher production cost.

An embodiment of the method according to the invention provides for the second output part 20 an already compacted, at least partially compressed state of a sintered material or a ceramic or a melt-metallurgically produced material, in particular a metal. Alternatively, the second output part 20 is made of a sintered material as a green part or brown part.

According to the invention, it is preferably provided that the composite part 50 is formed from a steel and a hard metal as materials of the output parts 10 and 20.

As sintered materials for the first and / or the second output part 10 and 20 in particular WC hard metals with Fe, Ni or Co binder metal (about 6-20 wt .-%) are proposed, said additional carbides based on Ti, Ta , V, or Nb. Likewise, sintered steels are used. In addition to the sintering materials mentioned sintered materials of ceramic hard materials, cermet or melt metallurgically produced materials are proposed alternatively. Preferably, steels having a carbon content ≥ 0.5 wt .-% in question, such as 100Cr6, X65Cr13. Thereby, excessive C diffusion during the sintering process can be suppressed, so that the steel is not deteriorated in its properties.

The production of the output parts 10, 20 from a sintered material is preferably carried out by a powder technology process, for example by means of powder injection molding. Advantageously, complex and near-net shape components can be produced in large quantities via this method. Equally advantageous is that at a first and a second output part 10, 20 as green or brown part, the shrinkage ratio of the two output parts 10, 20 can be adjusted to each other. Thus, it is ensured via the respective polymer fraction in the first output part 10 and in the second output part 20 that the first output part 10 has a greater shrinkage capacity than the second output part 20. Alternatively, the second output part 20 can have a boundary layer with a higher binder metal content (> 20 wt. ) contain. Possibilities for this are the use of a two-component material or a coating. As a result, an adaptation of the thermal expansion coefficients of the output parts 10, 20 to each other can be optimized.
Other powder technology processes, such as extrusion or uniaxial or isostatic pressing, can also be used for producing the starting parts 10, 20 from a sintered material.

• temperatur beeinflusst.
  Neben den η-Phasen kann sich je nach Zusammensetzung der Materialien der Ausgangsteile 10, 20 in der Verbindung 30 auch eine flüssige Phase bilden. Diese führt zwar im Allgemeinen zu einer vollständigen und porenfreien Anbindung, allerdings sind diese Schmelzen nach der Erstarrung meist spröde und daher unerwünscht.

In general, a concentration gradient of the respectively present alloying elements of the materials of the starting parts 10, 20 is formed by material exchange as a result of diffusion in a diffusion zone 31. In this case, the diffusion zone 31 is formed in the connection 30 and from there into the output parts 10 and 20. As a result of the concentration gradient, further material phases can form in the diffusion zone 31. Thus, for example, in the case of steel and carbide as materials of the starting parts 10, 20 so-called η-phases (M ₆ C or M ₁₂ C) are formed. However, such phases are very brittle and may degrade the mechanical properties of compound 30. Therefore, a very narrow diffusion zone 31 is sought in order to minimize or avoid the formation of these phases. How big is the diffusion zone 31 is formed by the setting of the sintering time and

• temperature influenced.
  In addition to the η-phases, depending on the composition of the materials of the starting parts 10, 20 in the compound 30, a liquid phase can also be formed. Although this generally leads to a complete and pore-free connection, but these melts are usually brittle after solidification and therefore undesirable.

In general, the method according to the invention provides that, in order to reduce residual stresses in the composite part 50 after the sintering process, several isothermal holding stages are run through during a cooling process. Such residual stresses can arise during the cooling process with large differences in the thermal expansion coefficients of the output parts 10, 20. Thus, steel has a thermal expansion coefficient of about 11-12 * 10 ^-6 / K and carbide a coefficient of thermal expansion of about 5-6 * 10 ^-6 / K. The radial shrinkage of the output member 10 made of steel, this leads to compressive stresses within the second made of hard metal output member 20. In the first place, these compressive stresses are unproblematic or even favorable due to the high compressive strength of the carbides. However, axial stresses also occur, which can then lead to the failure of the carbide. Several isothermal holding periods during the cooling process have a correspondingly favorable effect on a reduction of the residual stresses.

Claims (15)

A method for producing a component (50) from a composite material with a first output part (10) made of a sintered material, wherein the first output part (10) is in the form of a partially compacted sintered component, a green part or brown part
characterized in that at least a second output part (20) is at least partially introduced into a cavity (15) of the first output part (10) and both output parts (10, 20) are sintered and in at least partially filled by the second output part (20) cavity ( 15) then a connection (30) is produced between the output parts (10, 20), the connection (30) being formed in the form of a material bond due to chemical bonds between the materials of the output parts (10, 20). Method according to claim 1,
characterized in that the connection (30) due to a greater shrinkage of the first output member (10) is formed additionally in the form of a press fit. Method according to claim 2,
characterized in that in the region of the compound (30) a diffusion zone (31) is formed and the material bond is thereby kept substantially free of intermediate phases formed, wherein a size of the diffusion zone (31) is preferably adjusted by a sintering period. Method according to one of claims 1 to 3,
characterized in that the connection (30) is formed as far as possible at the end of the sintering process. Method according to one of claims 1 to 4,
characterized in that at least the first output part (10) is produced by a powder metallurgical process. Method according to claim 5,
characterized in that the powder injection molding, extrusion or uniaxial or isostatic pressing is used as powder-metallurgical process. Method according to one of claims 1 to 6,
characterized in that existing oxide layers in the region of the compound (30) are removed before or during sintering under a reducing sintering atmosphere. Method according to one of claims 1 to 7,
characterized in that after the sintering process a plurality of isothermal holding stages are provided during a cooling process. Component of a composite material, in particular according to a method according to one of claims 1 to 8, with a first output part (10) made of a sintered material
characterized in that at least a second output part (20) is arranged at least partially in a cavity (15) of the first output part (10) and after a sintering process the composite part (50) has a connection (30) in the cavity (15) at least partially filled by the second output part (20) ), wherein the compound (30) in the form of a material bond due to chemical compounds between the materials of the output parts (10, 20) is formed. Component according to claim 9,
characterized in that the connection (30) is additionally in the form of a press fit of the output parts (10, 20) is formed to each other. Component according to one of claims 9 to 10,
characterized in that the material bond is substantially free of intermediate phases formed. Component according to one of claims 9 to 11,
characterized in that at least the first output member (10) is a component manufactured powder technology. Component according to one of claims 9 to 12,
characterized in that the at least second output part (20) consists of a sintered material, a ceramic hard material, a cermet or a melt metallurgically produced material, preferably a metal. Component according to one of claims 9 to 13,
characterized in that the sintered material in the first output part 10 and / or the second output part 20 is a WC hard metal with Fe, Ni or Co binder metal (about 6-20 wt .-%), a cermet, a ceramic or is a melt metallurgically produced material. Use of a component (50) according to claims 1 to 14 as a wear-resistant component, in particular as a drilling and cutting tool, as a roller or pump part, and / or as a highly loaded component in the automotive sector, in particular in injection technology, in the exhaust gas turbocharger, in the rolling bearing or in Transmission.

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