AT14202U1 - Process for surface treatment by means of cold gas spraying - Google Patents

Abstract

The invention relates to a method for surface treatment by means of cold gas spraying and the use of a cold gas spray system for such a method, the method comprising: providing a blasting medium of at least one refractory metal, a refractory metal-based alloy or a refractory metal-based carbide, wherein the refractory metal is selected from tungsten, Molybdenum, chromium, accelerating the blasting agent (S) by means of a process gas jet (T) to the surface of a substrate (14), wherein at least a part of the substrate surface by means of the blasting agent (S) cleaned, activated, roughened, structured, compacted, hardened and / or smoothed.

Description

description

PROCESS FOR SURFACE TREATMENT USING COLD GASS PIPES

The invention relates to a method for surface treatment by means of cold gas spraying and the use of a cold gas spraying system for such a method.

Cold gas spraying systems are used for coating substrates as spielsweise disclosed in DE 10 2004 059 716 B3. In this case, a process gas and a coating material in powder form are accelerated by expansion in a Laval nozzle to very high speeds, typically in the supersonic speed range. Upon impact with a substrate, a dense and adherent layer is formed.

It is an object of the invention to provide an advanced method for Oberflächenbehand¬lung by means of cold gas spraying.

This object is achieved with the features of claim 1 and 11, respectively.

Advantageous embodiments are the subject of the dependent claims.

According to claim 1, a method for surface treatment by means of cold gas spraying is provided in which a blasting agent is accelerated by means of a process gas jet toward the surface of a substrate. The process gas is accelerated by expansion in a nozzle (for example Laval nozzle) to high speed, preferably at supersonic speed. The injection of the blasting agent, which is supplied by means of a carrier gas, preferably takes place in front of the nozzle. The high velocity accelerated abrasive cleans, activates, textures, roughens, densifies, cures and / or smooths the (or at least a portion of) substrate surface. In contrast to the method of DE 10 2004059 716 B3 described above, no (or substantially no) material is applied to the substrate by means of cold gas spraying with the method claimed here. The blasting agent is accelerated so that the substrate is not (continuously) coated with the blasting agent, i. the abrasive does not adhere to the substrate and no (closed) abrasive layer is formed on the substrate. As explained below, the claimed method of surface treatment of a substrate e.g. before a coating or after Beschich¬tung or for adjustment or generation of desired properties.

The blasting agent provided is made of at least one of a refractory metal, a refractory metal-based alloy, or a refractory metal-based carbide, wherein the refractory metal is selected from tungsten (W), molybdenum (Mo), and chromium (Cr). Beispielswei¬se is the blasting agent prepared from Cr, Mo and / or W-carbide.

An alloy or a carbide based on refractory metal contains at least 50% by mass (ma%) of one of the refractory metals such as W, Mo and / or Cr. Cr is produced by the known methods, preferably by aluminothermic reduction, and has a high microhardness. For example, the blasting agent contains a plurality of different refractory metals, which together form at least 50 ma% of the alloy. Alternatively, an alloy or a refractory metal-based carbide has a refractory metal content of greater than 80% by mass, preferably greater than 90% by mass, more preferably greater than 95% by mass. The abovementioned materials have a combination of properties (eg based on yield strength, hardness and modulus of elasticity) when they strike the substrate surface, which surprisingly they are used as abrasive in a cold gas spraying unit for cleaning, activation, structuring, roughening, compaction, hardening and curing / or make surface smoothing suitable. In particular, blasting agents based on tungsten, which is the highest energy input due to the very high density, are particularly suitable here.

When cleaning the substrate material is removed from the substrate surface, i. the blasting abrasive is abrasive. For example, as a pre-treatment of the substrate for a subsequent coating. In particular, the substrate surface can be activated by the cleaning, i. the reactivity of the substrate surface becomes inactive by removal

Substances on the surface, e.g. Metal surface oxides increased. Cleaning or activation can ensure, for example, sufficient wetting or adhesion of a subsequent coating of the substrate.

As a pretreatment for a subsequent coating, the substrate surface may be roughened to provide higher roughness, e.g. to improve the adhesion of a subsequently applied layer. For example, a substrate of a refractory metal or a refractory metal-based alloy, e.g. a tungsten or molybdenum substrate, are roughened before the substrate is coated with tantalum to provide a diffusion barrier. Alternatively, a substrate after roughening with chromium, nickel or a chromium-nickel alloy, for example by PVD method as corrosion protection beschich¬tet. For example, cleaning or roughening may also be used as a pretreatment of the substrate surface for various bonding techniques such as bonding. Soldering processes are used.

By structuring (or enlargement) of the substrate surface beispiels¬weise the thermal emission of the substrate can be increased. For example, the surfaces of rotating anodes, electrodes of high-power lamps, heating conductors and radiation shields can be patterned accordingly to improve the heat radiation emission and thus the energy efficiency of said components. Furthermore, the wetting of the substrate surface can be improved by structuring the surface. For example, the inner surface of evaporator crucibles can be structured in order to improve the wetting with the material to be vaporized. As another example, the surface of rolls used in extreme ultraviolet (EUV) radiation sources may be structured to enhance the wet-tin wetting of the rolls.

Due to the high momentum transfer occurring during cold gas spraying, furthermore, the substrate surface can be compacted, hardened and smoothed by the blasting medium without the blasting agent adhering to the substrate. That the process can be used to post-treat surfaces or near-surface areas. Thus, for example, with the method according to the invention in the case of sintered steel components, the residual porosity in areas close to the surface can be greatly reduced or completely closed, whereby the susceptibility to fatigue risers can be greatly reduced. The method according to the invention is also suitable for increasing the hardness in components by incorporation of compressive stresses and / or work hardening. This can be implemented in a particularly advantageous manner for components made of steel.

In summary, due to the high momentum transfer during cold gas spraying, a substrate surface can be treated efficiently in a short time and with little use of material. In addition, the surface treatment by means of cold gas spraying is further developed beyond the simple coating of surfaces by the described method, so that a multiplicity as described above of various surface treatments, such as surface treatment of a substrate prior to coating, after coating, and adjustment of surface and marginal zone properties.

Preferably, the blasting agent on a plurality of particles having a mean diameter of 5 pm to 2 mm, 10 pm to 500 pm, preferably less than 150 pm. The values 5 pm and 10 pm represent laser-optically measured d50 values, while 2 mm, 500 pm and 150 pm represent the mesh size of sieves. For example, with a blasting agent consisting of tungsten (Tungrit®) with an average particle size of less than or equal to 150 μm, a substrate made of molybdenum or molybdenum-lanthanum oxide may be structured, e.g. as a pretreatment for the subsequent deposition of a layer, sintered steel components nachverdichtet or hardened steel components (hardness increase on work hardening) wer¬den. Exemplary parameters for this surface treatment are the provision of the process gas jet at a pressure of 30 bar, a flow rate of 60 m 3 / h and a process gas temperature of 800 ° C.

According to one embodiment, the substrate and the blasting agent are made of the same material. For example, both the substrate and the blasting agent may be made of a refractory metal or a refractory metal-based alloy, referred to metals having a melting point equal to or greater than 1772Ό (equivalent to the melting point of platinum). For example, For example, a tungsten substrate may be treated with a Wolffam jet medium. Alternatively, the substrate and the blasting agent are made of related materials, e.g. a molybdenum substrate and a Wolffam blasting agent. During the surface treatment, isolated particles of the blasting agent can (unintentionally) get stuck in the substrate, whereby the use of identical or related materials for substrate and blasting agent does not contaminate the substrate with application-critical foreign elements. This is particularly advantageous for high-temperature applications or when the substrate or the surface-treated component is used under high-temperature conditions, since adhering foreign elements would form weak spots in the substrate under these extreme conditions.

Particularly preferably, the particles of the blasting medium are granular or rounded, insbeson¬dere spherical, formed. For example, edge-rounded, rounded, rounded, or well-rounded particles are used to densify, cure, and / or smooth the substrate surface to obtain a uniformly densified, cured surface. The smaller the particles, the finer the surface structure produced.

According to an alternative embodiment, the particles of the blasting medium are edged, in particular sharp-edged, formed. For example, this shape of the particles allows a substrate surface to be roughened, patterned or cleaned more effectively because the angular particles remove more material than, for example, the rounded particles described above.

More preferably, the blasting agent is granules, i. A (fine-grained) starting material is granulated by means of a granulate production process (for example spray granulation) to form particles having a larger cross-section. For example, a molybdenum abrasive has a laser-optically measured particle size d50 of 2 to 5 μm or a tungsten abrasive of a laser-optically measured particle size d50 of 0.5 to 20 μm. In the spray granulation, by means of a binder such as e.g. Parafin the (fine-grained) starting material to Parti¬keln connected with a larger cross-section. For example, the granules produced have a (mean) diameter of 50 pm to 500 pm, preferably less than 150 pm.

Preferably, a blasting agent beam is generated, which has a diameter of 2 mm to 10 mm, 4 mm to 8 mm, preferably 5 mm to 6 mm when hitting the substrate. For example, the diameter of the blast media jet can be adjusted via appropriately sized dimensions of a spray gun nozzle and / or an adapted process gas stream. That The surface of a substrate can be partially treated by means of a blasting agent beam focused in this way, in particular it is not necessary to mask substrate areas which do not have to be treated. Due to the focused use of the blasting agent and the high momentum transfer in cold gas spraying, a substrate surface can be treated precisely and efficiently in a short time and with little use of material.

According to one embodiment, the process gas jet is provided under a pressure between 10 bar to 100 bar, 20 bar to 60 bar, preferably 25 bar to 40 bar. In particular, the process gas jet is accelerated to supersonic speed by means of a Laval nozzle, whereby the particles of the blasting medium obtain a correspondingly high speed or pulse, which in turn enables effective treatment of the substrate surface as described above. For example, the blasting agent is added to the process gas jet before the process gas has been accelerated to a high speed, for example supersonic speed, i. Process gas and blasting agents are accelerated together.

Particularly preferably, the process gas jet is provided with a temperature between Raum¬ temperature to 1400 ° C, 400 ^ to ΙΟΟΟ'Ό, preferably 500 ° C to 800 ° C. In particular, the temperature of the process gas is (far) below the melting point of the material of the abrasive used.

According to one embodiment, a cold gas spray system is used for the surface treatment of a substrate, in particular according to a method as described above. For example, the cold gas spraying system includes a spray gun with a Laval nozzle to accelerate a process gas to a high velocity, such as supersonic velocity, a process gas feed into the gun, and a blast media feed into the gun. The Strahlmit¬tel is preferably supplied by means of a carrier gas.

A supply line may comprise, for example: pipe (s), pump (s) or other conveying means such. a screw conveyor for transporting the abrasive towards the gun. Wei¬terhin can be additionally provided a heating system for heating the process gas. As described above, a blasting agent is accelerated toward the surface of a substrate by means of a process gas through the Laval nozzle, wherein at least a part of the substrate surface is cleaned, activated, roughened, structured, compacted, hardened and / or smoothed by the blasting medium.

Preferably, at least the spray gun of the cold gas spraying system and a substrate to be treated are arranged in a vacuum chamber. In this way, the amount of process gas required for acceleration can be reduced because the process gas and thus the accelerated abrasive are no longer braked by air resistance. For example, helium, nitrogen or a nitrogen-helium mixture is used as the process gas.

Individual features of the above-described embodiments of the method for surface treatment by means of cold gas spraying and the use of a cold gas spraying system as well as features of the components described in the following embodiment and the method can be combined with each other in any desired manner.

Based on the figures, an embodiment of the invention will be explained in more detail.

Fig. 1 is a schematic representation of part of a cold gas spraying unit, Fig. 2 shows blasting means, and Fig. 3a-b shows a comparison of two treated substrate surfaces.

Fig. 1 shows a schematic representation of a part of a cold gas spraying unit 2 for explaining the principle of cold gas spraying. A spray gun housing 4 has a Lavaldü¬se 10 to accelerate a supplied through a process gas line 8 process gas T to supersonic speed. In the process gas stream T, a blasting agent S, i. introduced a plurality of particles, which are accelerated by the process gas flow T towards a substrate 14 and aufpral¬len there. The acceleration of the particles by the process gas stream and the particles are chosen so that the particles do not adhere to the substrate 14 upon impact.

The cold gas spraying installation 2 is operated in such a way that, on the one hand, substrate material can be removed by means of the particles (cleaning, structuring, activating, roughening) or, alternatively, the substrate surface can be compacted, hardened or smoothed. To achieve this, on the one hand, the operating parameters of Appendix 2 can be adjusted accordingly, i. Speed, pressure and / or temperature of the process gas flow. Additionally or alternatively, the type of particles used or of the blasting agent S can be adapted. For example, larger and / or more edgy particles may be chosen for greater material removal, and rounded or round particles may be used for densification or cure (or no material removal). In order to avoid contamination of the substrate 14 with foreign materials, the blasting agent is made of the same material or similar materials (e.g., molybdenum and tungsten).

2 shows a micrograph of individual particles or grains of a random abrasive produced from tungsten (Tungrit®) with a particle size (sieve fraction) between 36 and 150 μm.

Figures 3a-b each show a micrograph of two surface-treated substrates. Fig. 3a shows a tungsten sheet which has been cleaned by the described cold gas method using tungsten as a blasting medium, i. Substrate material was removed. Fig. 3b shows a tungsten sheet treated by a conventional sand blasting method using alumina (Al 2 O 3) as a blasting medium.

The deposits 16a-d of foreign material or Al 2 O 3 are clearly visible in FIG. 3 b. That During the blasting process, unintentionally individual particles or grains of the blasting agent remain stuck in the substrate. This contamination with foreign materials is particularly critical in the use of the corresponding substrate in high temperature applications, as the contaminants form weak spots in the substrate.

In Fig. 3a, it can be clearly seen that the cleaned substrate surface is homogeneous. The use of tungsten as a blasting agent (or since blasting agent and substrate are made of the same material) there is no risk of contamination with foreign material.

REFERENCE LIST 2 Cold gas spraying system 4 Spray gun housing 6 Blasting line 8 Process gas line 10 Laval nozzle 12 Blasting agent + carrier gas feed 14 Substrate 16a-d Foreign material (Al203) 5 Blasting medium + carrier gas flow T Process gas flow

Claims (11)

Claims 1. A method for surface treatment by means of cold gas spraying, comprising providing a blasting medium (S), and accelerating the blasting medium (S) by means of a process gas jet (T) to the surface of a substrate (14), characterized in that the blasting medium (S) is made at least one refractory metal, an alloy based on refractory metal or a carbide based on refractory metal, the refractory metal being selected from tungsten, molybdenum, chromium, and at least a part of the substrate surface being cleaned, activated, by means of the blasting agent (S), roughened, structured, densified, hardened and / or smoothed. A method according to claim 1, characterized in that the blasting agent (S) impinging on the surface of the substrate (S) does not form a layer on the substrate (14), and / or that the blasting medium (S) impinges on the surface of the substrate (S). S) does not adhere to the surface. 3. The method according to claim 1 or 2, characterized in that the blasting agent (S) has a plurality of particles with a mean diameter of 5 μιτι to 2 mm, 10 pm to 500 pm, preferably less than 150 pm. 4. The method of claim 1, 2 or 3, characterized in that the substrate (14) and the blasting agent (S) are made of the same material or of related materials, in particular a refractory metal or a refractory metal-based alloy. 5. The method according to any one of the preceding claims, characterized in that the blasting agent (S) comprises a plurality of granular particles which are rounded, insbeson¬dere spherical, are formed. 6. The method according to any one of claims 1 to 4, characterized in that the Strahl¬mittel (S) has a plurality of particles which are edged, in particular sharp, aus¬gebildet. A method according to any one of the preceding claims, characterized in that the abrasive (S) is granules. A method according to any one of the preceding claims, characterized in that the method comprises generating a blast media jet having a diameter of 2 mm to 10 mm, 4 mm to 8 mm, preferably 5 mm to 6 mm, when hitting the substrate (14). 9. The method according to any one of the preceding claims, characterized in that the method comprises providing the process gas jet at a pressure between 10 bar 100 bar, 20 bar to 60 bar, preferably 25 bar to 40 bar. 10. The method according to any one of the preceding claims, characterized in that the method comprises providing the process gas jet with a temperature between room temperature to 1400 ° C, 400 ° C to 1000 ° C, preferably 500'C to 800 ° C comprises. 11. cold gas spraying system for surface treatment of a substrate according to a method according to one of claims 1 to 10, wherein the system comprises: a spray gun housing (4), a process gas supply line (8) in the housing (4), a blasting agent supply line (6 ) in the housing (4), and connected to the housing (4) Laval nozzle (10) for accelerating a Strahlmit¬tels (S) by means of a process gas (T) to the surface of a substrate (14), characterized in that at least one Part of the substrate surface by means of the blasting agent (S) cleaned, activated, roughened, structured, compacted, hardened and / or smoothed. For this 2 sheets of drawings