DE102004052135A1 - Coated metal substrate especially a hard metal with a wear protection layer consisting of high purity Al2O3 nanocrystals and containing residual pressure stresses useful in tool production - Google Patents

Abstract

Coated metal substrate (1) especially a hard metal with a wear protection layer (2) with residual pressure stresses, where the wear resistant layer contains gradient-like element (3) from which the substrate or an intermediate layer (4) is obtained, with which the residual pressure stresses during layer deposition can be regulated (sic) by a wet chemical process directly in the wear protection layer. An independent claim is included for a method of producing the substrate involving wet chemical, combustion and sol-gel processes.

Description

The The invention relates to a coated metal substrate, in particular made of carbide, with a wear protection layer, which compressive stresses and a method for its preparation.

Hard coatings are used to reduce wear, especially in tools to increase the service life applied.

In the case of coated cemented carbide substrates, the functional layers are often subject to tensile stresses due to different coefficients of thermal expansion of the wear protection layer material and the substrate material. As the tensile stresses increase, the intended increase in wear resistance decreases. Often too high tensile stresses even lead to the detachment of the layers from the substrate. This also applies to the material combination carbide substrate / oxide ceramic layer, in particular Al ₂ O ₃ layer.

The hard material layers are applied to the substrate by classical methods of PVD (physical vapor deposition) or CVD (chemical vapor deposition). It is disadvantageous that tensile stresses occur in particular in the combination of cemented carbide substrate / Al ₂ O ₃ layer.

With various methods known in the art have been attempted to counteract the effects of these tensions.

To DE 101 15 390 A1 For example, a high abrasion resistant coated cutting tool is known for high speed cutting of steel having a hard sintered substrate and a hard coating applied to the surface of the substrate. In this case, the hard coating has a layer of hard material as inner layer with an average thickness between 0.1 .mu.m and 10 .mu.m and a remanent compressive stress applied by physical evaporation, and an aluminum oxide layer as outer layer with a thickness between 0.1 .mu.m and 5 microns, which is applied by chemical vaporization at medium temperatures.

Furthermore, in DE 34 43 329 A1 a method for producing corrosion-resistant wear protective layers with chromium end layer specified consisting of a 5 to 30 .mu.m thick nickel intermediate layer and a 10 to 40 .mu.m thick final chromium layer, wherein on the carrier material, the nickel intermediate layer is applied so that they under a compressive residual stress of 20 to 60 MPa and then the final chromium layer is applied in a known manner.

The Compressive stresses in these two methods, however, in an intermediate layer and not in the actual functional layer, namely the wear protection layer generated.

In DE 101 23 554 A1 is the generation of compressive stresses described by subsequent blasting. This method is used to increase the compressive residual stress or to lower the inherent tensile stress of an outer or an outermost, by CVD, PCVD or PVD on a hard metal, cermet, or Keramiksubstratkörper applied hard material layer in which the coated substrate body after the coating of a dry jet treatment using a granular blasting medium is subjected. The blasting agent in this case has a maximum diameter of 150 .mu.m, preferably of at most 100 .mu.m.

The Hard material layers to reduce wear, so that to increase the life of tools, in particular, are classic Process of PVD (physical vapor deposition) or CVD (chemical vapor deposition) applied to the substrate.

Of the Invention is based on the object, a coated metal substrate and to provide a method for its production, wherein the layer according to the production has compressive stresses and a high adhesive strength.

According to the invention Task with a substrate, which specified in claim 1 Features and with a method, which specified in claim 13 Has features solved.

advantageous Embodiments are specified in the subclaims.

The process according to the invention uses wet-chemical process steps, for example the sol-gel technology, for the production of oxide-ceramic hard material layers, preferably Al ₂ O ₃ . Here, a precursor of the oxide (as sol or gel) is applied to the substrate by dipping, spraying, or other suitable methods. Subsequently, the gel is converted by a two-stage firing process into the desired hard material modification.

It has been found that the layer then has a good adhesive strength when ent neither the substrate nor an additionally applied intermediate layer has suitable elements which diffuse into the wear layer. At the same time, these elements cause the generation of residual compressive stresses in the functional layer.

About the Duration of the burning process is the absolute height of the voltages up to one selectable range. An afterthought Treatment of the layer is not necessary. Also is not the application an intermediate layer with residual compressive stresses necessary.

• 1. Wegen der Reinheit der Ausgangssubstanzen, die für das Verfahren eingesetzt werden, ist die Schicht chemisch an allen Stellen des Substrates hochrein an Al₂O₃, so dass eine hochqualitative Oxidkeramik entsteht.
• 2. Die Zusammensetzung der Schicht ist in Bereichen über den thermischen Prozess steuerbar (Verhältnis von α/γ-Al₂O₃), während dies beim CVD-Verfahren nur über chemische Beimengungen möglich ist.
• 3. Verfahren ist einfach und bedarf außer einem Schutzgas- bzw. Vakuumofen keiner teuren Anlagen. Es kann daher auch von kleineren Unternehmen zur Beschichtung verwendet werden.
• 4. Im Gegensatz zu CVD- und PVD-Verfahren können auch große Oberflächen beschichtet werden.
• 5. Während die Beschichtung von inneren Oberflächen für die klassischen Verfahren an das Verhältnis von Durchmesser zu Tiefe gebunden ist, sind infolge des nasschemischen Verfahrens auch kleinste Bohrungen mit großer Länger beschichtbar.
• 6. Die Schicht ist nicht texturiert und besitzt keine säulenartige Kristallstruktur
• 7. Mit dem Beschichtungszyklus können gleichzeitig Werkzeugstähle gehärtet werden. Ist das Sol auf bereits gehärteten und/oder angelassenen Stählen aufgebracht, wird eine partielle Wärmebehandlung der Schicht beispielsweise mit einem Laserstrahl notwendig.

The invention is characterized by a number of advantages. These include in particular:

• 1. Due to the purity of the starting materials used for the process, the layer is chemically highly pure Al ₂ O ₃ at all points of the substrate, so that a high-quality oxide ceramic is formed.
• 2. The composition of the layer is controllable in areas by the thermal process (ratio of α / γ-Al ₂ O ₃ ), while in the CVD process this is only possible via chemical admixtures.
• 3. The process is simple and requires no protective gas or vacuum furnace no expensive equipment. It can therefore also be used by smaller companies for coating.
• 4. In contrast to CVD and PVD processes, even large surfaces can be coated.
• 5. While the coating of inner surfaces for the classical methods is bound to the ratio of diameter to depth, even the smallest bores can be coated for a long time due to the wet-chemical process.
• 6. The layer is not textured and does not have a columnar crystal structure
• 7. The coating cycle can simultaneously harden tool steels. If the sol is applied to already hardened and / or tempered steels, a partial heat treatment of the layer, for example with a laser beam, becomes necessary.

The Invention will be explained in more detail below with reference to an embodiment.

In the associated Show drawing:

1 a section through a coated arrangement with an additional intermediate layer and

2 a section through a coated arrangement without intermediate layer,

As a coating material here Al ₂ O _{3 was} chosen. This substance is characterized by high hardness and by a relatively low thermal conductivity compared to coating materials with a high metallic bond content. These properties are very beneficial for coatings designed for high speed machining.

The Deposition of the substance with conventional coating methods, CVD or PVD, are not easy.

When Substrate was used carbide. The layer thickness should be in Range of 0.5 to 6 microns are. On the direct sol-gel process, these thicknesses are only a multiple coating reachable.

at the sol-gel technique turns precursor solutions into the liquid sol, the starting substance, prepared. About the process of hydrolysis A gel is created by a subsequent multi-stage heat treatment is converted into an oxide ceramic.

When Starting material for the layer production can also by a over the Sol-gel be prepared product redispersed.

to Production of an oxide ceramic layer, it is necessary that Substrate with the liquid Sol to moisten. This process can be done with all known methods for coating from the liquid Condition done.

There the carbide substrate not over has the appropriate elements, with which the compressive stresses can be set, the carbide surfaces must be present the actual coating to be coated with an additional layer. This can over applied to the PVD process or by the sol-gel technique itself become.

These Elements are distributed in gradient form from the substrate / layer interface or intermediate layer / layer into the wear protection layer (elemental gradient).

Prefers are the dip-coating and the spray-coating process applied.

through dip-coating can very homogeneous and reproducible thicknesses can be generated even over large areas. In spray-coating, the advantages are in the coating of complex Part geometries.

After applying the Ausgangsubs dance is a thermal treatment (dry, calcination, burning) necessary. This serves to convert the starting substance into the nanocrystalline ceramic layer and to connect to the substrate.

The boundary conditions of the overall process can significantly influence the properties of the layer and of the layer / substrate composite:
In the coating of hard metals, the choice of the elements of the intermediate layer and the thermal treatment already during the production of the layer set the compressive stress state in the layer. Subsequent treatment, such as blasting the surface, is not required.

The corundum layer (α-Al ₂ O ₃ ) is the modification of the highest hardness Al ₂ O ₃ . However, corundum also has a tremendous brittleness. By lowering the actual firing temperature, it is advantageously possible to set a gradient of α- / γ-Al ₂ O ₃ in the layer. The service life of these layers increases significantly over layers with a pure corundum phase. This phase gradient can also be influenced by the layer thickness or by the number of individual coatings in the case of multiple layers.

The Ceramic layers are mostly nanocrystalline and have none Fiber textures.

The Adhesive strength of these layers is high. The layers are reproducible safe to produce with the same properties on all layer areas and compared to all parts coated with this method become.

1

metal substrate

2

Wear protection layer

3

Elementegradient

4

interlayer

Claims (17)

Coated metal substrate ( 1 ), in particular of hard metal, with a wear protection layer ( 2 ), which has residual compressive stresses, characterized in that the wear protection layer ( 2 ) gradient-like elements ( 3 ) from the substrate ( 1 ) or from an intermediate layer ( 4 ), with which the residual compressive stresses during the production of the layer can be set with a wet-chemical process directly in the wear-resistant coating. Coated metal substrate according to claim 1, characterized in that the wear protection layer ( 2 ) consists of an oxide ceramic material. Coated metal substrate according to claim 1 or 2, characterized in that the wear protection layer ( 2 ) consists of highly pure nanocrystalline Al ₂ O ₃ and was prepared by a sol-gel process. Coated metal substrate according to claim 3, characterized in that the wear protection layer ( 2 ) consists of α-Al ₂ O ₃ . Coated metal substrate according to claim 3, characterized in that the wear protection layer ( 2 ) consists of γ-Al ₂ O ₃ . Coated metal substrate according to claim 3, characterized in that the wear protection layer ( 2 ) consists of a gradient of α-γ-Al ₂ O ₃ . Coated metal substrate according to one of claims 1 to 6, characterized in that the wear protection layer ( 2 ) on a thin intermediate layer ( 4 ) is applied. Coated metal substrate according to claim 7, characterized in that the intermediate layer ( 4 ) is a metal layer. Coated metal substrate according to claim 8, characterized characterized in that the metal layer consists of titanium. Coated metal substrate according to claim 7, characterized in that the intermediate layer ( 4 ) is a sol-gel layer. Coated metal substrate according to claim 10, characterized in that the intermediate layer ( 4 ) is a sol-gel layer containing metal particles. Coated metal substrate according to one of Claims 1 to 11, characterized in that the substrate ( 1 ) made of hardened steel, preferably tool steel. Process for producing a coated metal substrate according to one of Claims 1 to 12, characterized in that the elements ( 3 ) are introduced adjustably during the layer production with a wet-chemical process and a firing process. A method according to claim 13, characterized in that for the production of oxide-ceramic hard coatings, a sol or gel on the Metal substrate ( 1 ) and then converted by a two-stage firing process in a hard material modification, wherein an in-diffusion of elements of the metal substrate ( 1 ) or an intermediate layer ( 4 ) in the wear layer ( 2 ) he follows. A method according to claim 14, characterized in that by the burning process in the wear layer ( 2 ) Compressive stresses are generated whose height is selected by the duration of the firing process and the firing temperature. Process according to claims 10 and 13 to 15, characterized characterized in that inner surfaces are coated. Process according to claims 10 and 13 to 16, characterized characterized in that the inner surface is the area of a bore whose diameter between 0.1 and 6 mm, preferably between 0.25 and 2 mm.