WO2015031921A1

WO2015031921A1 - Method for surface treatment by means of gas dynamic cold spray

Info

Publication number: WO2015031921A1
Application number: PCT/AT2014/000167
Authority: WO
Inventors: Martin Kathrein; Dietmar Sprenger; Bernhard Lang
Original assignee: Plansee Se
Priority date: 2013-09-06
Filing date: 2014-09-04
Publication date: 2015-03-12
Also published as: AT14202U1

Abstract

The invention relates to a method for surface treatment by means of gas dynamic cold spray and the use of a gas dynamic cold spray system for such a method, wherein the method comprises: providing a blasting agent composed 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, and chromium, and accelerating the blasting agent (S) toward the surface of a substrate (14) by means of a process gas jet (T), wherein at least part of the substrate surface is cleaned, activated, roughened, structured, compressed, hardened, and/or smoothed by means of the blasting agent (S).

Description

METHOD OF SURFACE TREATMENT BY MEANS

KALTGAS SPLASH

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 such as

for example in DE 1020040S9716 B3. In this process, 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 a further developed method for

To provide surface treatment 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 sub-speech.

According to claim 1, a method for surface treatment by means of cold gas spraying is provided in which a blasting agent is accelerated toward the surface of a substrate by means of a process gas jet. The process gas is thereby 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 (or at least part of) the substrate surface. Unlike the above

described method of DE 102004 059 716 B3 is applied by the method claimed here by means of cold gas spraying no (or substantially no) material on the substrate. The blasting agent is accelerated so that the substrate is not (continuously) coated with the blasting agent, ie the blasting agent does not adhere to the substrate and no (closed) blasting agent layer is formed on the substrate As explained below, the claimed method is used for Surface treatment of a substrate, for example, before a coating or after a coating or for adjusting or generating 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).

For example, the blasting agent is made of Cr, Mo and / or W carbide.

An alloy or 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 prepared 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 SO.sub.MA% of the alloy. Alternatively, an alloy or a carbide based on refractory metal has a refractory metal content of greater than 80 ma%, preferably greater than 90 ma%, particularly preferably greater than 95 ma%. The abovementioned materials have a combination of properties (for example based on yield strength, hardness and modulus of elasticity) when they impinge on the substrate surface, which surprisingly results in the cleaning, activation, structuring, roughening, blasting of a cold gas spraying installation.

Make compaction, hardening and / or smoothing of surfaces suitable. In particular, blasting agents based on tungsten, which is the highest energy input due to the very high density, are suitable here.

When cleaning the substrate, material is removed from the substrate surface, i. the blasting abrasive is abrasive. For example, as a pretreatment 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 is through

Removal of inactive substances on the surface, e.g. Metal surface oxides increased. A cleaning or activation, for example, a sufficient

Ensuring wetting or adhesion of a subsequent coating of the substrate.

As a pretreatment for a subsequent coating, the substrate surface can be roughened to improve the adhesion of a subsequently applied layer, for example, by the higher roughness. For example, a substrate may consist of a Refractory metal or a refractory metal-based alloy, such as a tungsten or molybdenum substrate, may be roughened before the substrate is coated with tantalum to provide a diffusion barrier. Alternatively, a substrate after thawing with chromium, nickel or a chromium-nickel alloy, for example by means of

PVD process can be coated as corrosion protection. For example, that can

Cleaning or thawing also as a pretreatment of the substrate surface for various bonding techniques, e.g. Soldering processes are used.

By structuring (or enlargement) of the substrate surface can

For example, the thermal emission of the substrate can be increased. For example, the surfaces of rotating anodes, electrodes of high-power lamps,

Heaters and radiation shields are structured accordingly to the

Heat radiation emission to improve and thus the energy efficiency of the above components. Furthermore, the wetting of the substrate surface can be improved by structuring the surface. For example, the inner surface of

Evaporator crucibles are structured to improve the wetting with the material to be evaporated. As another example, the surface of rolls used in extreme ultraviolet (EUV) radiation sources may be patterned to enhance wetting of the rolls with liquid tin.

Due to the high momentum transfer occurring during cold gas spraying, the substrate surface can be further compacted, hardened and smoothed by the blasting medium without the blasting agent adhering to the substrate. That with the method can

Surfaces or near-surface areas to be aftertreated. So can

For example, with the inventive method in sintered steel components the

Residual porosity in near-surface areas to be greatly reduced or completely closed, whereby the susceptibility to fatigue cracks can be greatly reduced. The inventive method is also suitable for use in components by installation of

Compressive stresses and / or work hardening to increase the hardness. 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 efficiently treated in a short time and with little use of material. In addition, the method described advances the surface treatment by means of cold gas spraying beyond the simple coating of surfaces, so that a plurality of different surface treatments are provided as described above, such as the surface treatment of a substrate before coating, after coating, and the adjustment of Surface and boundary zone properties. Preferably, the blasting agent has a plurality of particles having a middle

Diameter of 5 microns to 2 mm, 10 microns to 500 microns, preferably less than 150 microns have. The values 5 μm and 10 μm represent laser-optically measured d ₅₀ values, while 2 mm, 500 μm and 150 μm represent the mesh size of sieves. For example, with a blasting agent consisting of tungsten (Tungrit®) having an average particle size of less than or equal to 150 μm, a substrate made of molybdenum or

Molybdenum-lanthanum oxide are structured, for example, as a pretreatment for the subsequent deposition of a layer, sintered steel components post-compacted or hardened steel components (hardness increase via work hardening). 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 Strahlnüttel be made of a refractory metal or a refractory metal-based alloy, reference being made to metals or alloys having a melting point greater than or equal to 1772 ° C (corresponding to the melting point of platinum). For example, For example, a tungsten substrate may be treated with a tungsten abrasive. Alternatively, the substrate and abrasive are made of related materials, e.g. one

Molybdenum substrate and a tungsten abrasive. In the surface treatment can (unintentionally) isolated particles of the blasting agent in the substrate 'stuck', wherein the use of identical or similar materials for substrate and blasting agent, the substrate is not contaminated with application-critical foreign elements becomes. This is particularly advantageous for high-temperature applications or when inserting the substrate or the surface-treated component below

High temperature conditions, since adhering foreign elements under these extreme conditions would form weak spots in the substrate.

Particularly preferably, the particles of the blasting medium are granular or rounded, in particular spherical, formed. For example, edge-rounded, rounded, rounded or well-rounded particles are used for compacting, hardening and / or smoothing the substrate surface in order to obtain a uniformly compacted, hardened or smoothed surface. The smaller the particles, the finer the surface structure created.

According to an alternative embodiment, the particles of the blasting medium are edged, in particular sharp-edged, formed. For example, can be roughened by this form of particles, a substrate surface more effective, structured or cleaned, since the edged particles remove more material than, for example, the above-described rounded particles.

Most preferably, the blasting agent is granules, i. a (fine-grained)

Starting material is removed by means of a granule production process (e.g.

Spray granulation) into particles of larger cross-section. For example, a molybdenum blasting abrasive has a laser-optically measured particle size d ₅₀ of 2 to 5 μm, or a blasting abrasive of tungsten has a laser-optically measured particle size d ₅₀ of 0.5 to 20 μm. In SprOhgranulierung using a binder such as paraffin, the (fine-grained) starting material to particles with larger

Cross-section connected. For example, the granules produced have a (mean) diameter of SO of up to 500 μm, preferably less than 150 μm.

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. By way of example, the diameter of the blasting agent jet can be adjusted via correspondingly adapted dimensions of a spray gun nozzle and / or a matched spray nozzle

Process gas flow can be adjusted. That is, by means of such a focused abrasive jet For example, the surface of a substrate may be partially treated, in particular, it is not necessary to mask substrate areas that do not need to be treated. Due to the focused use of the blasting medium and the high momentum transfer during 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 have a correspondingly high

Speed or pulse, which in turn, as described above, an effective treatment of the substrate surface is possible. For example, that will

Blasting agent added to the process gas jet before the process gas to a high

Speed, for example, supersonic speed has been accelerated, i. Process gas and blasting agents are accelerated together

Particularly preferred is the process gas jet with a temperature between

Room temperature to 1400 ° C, 400 ° C to 1000 ° C, preferably 500 ° C to 800 ° C provided. 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 spraying system is used for the surface treatment of a substrate, in particular according to a method as described above. For this purpose, the cold gas spraying system has a spray gun with a Laval nozzle to accelerate a process gas to a high speed, such as supersonic speed, a process gas supply line into the gun and a blasting agent supply line into the gun. The blasting agent is preferably supplied by means of a carrier gas. A supply line may for example comprise: pipe (s), pump (s) or other conveying means such as e.g. a screw conveyor for transporting the abrasive towards the gun.

Furthermore, a heating system for heating the process gas may additionally be provided. As described above, a blasting agent is accelerated by means of a process gas through the Laval nozzle to the surface of a substrate, wherein at least a part of the Substrate surface cleaned by the blasting agent, activated, roughened, structured, compacted, hardened and / or smoothed.

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 needed for acceleration can be reduced because the

Process gas and thus the accelerated abrasive are no longer braked by the air resistance. For example, as the process gas helium, nitrogen or a

Nitrogen-helium mixture used.

Individual features of the above-described embodiments of the method for

Surface treatment by means of cold gas spraying and the use of a

Kaltgasspritzanlage and features of the components described in the following embodiment and the method can be combined with each other in any way.

An embodiment of the invention will be explained in more detail with reference to the figures.

Show it:

1 is a schematic representation of a portion of a cold gas spray system,

Fig.2 blasting agent, and

Fig. 3a-b a comparison of two treated substrate surfaces.

Fig. 1 shows a schematic representation of a part of a cold gas spraying system 2 for explaining the principle of cold gas spraying. A spray gun housing 4 has a Laval nozzle 10 in order to accelerate a process gas T supplied through a process gas line 8 to the upper sound velocity. A blasting agent S, ie a large number of particles, is introduced into the process gas stream T via a blasting medium line 6 by means of a carrier gas, which particles are accelerated toward the substrate 14 by the process gas flow T and impact 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 spray system 2 is operated so that on the one hand by means of the particles

Substrate material can be removed (cleaning, structuring, activation, thawing) 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 stream. Additionally or alternatively, the type of particles used or of the blasting medium S can be adapted. For example, for a stronger

Material removal larger and / or edged particles are selected and for a

Compaction or hardening (or no material removal) can be used rounded or round particles. To contamination of the substrate 14 with

To avoid foreign materials, the beam center is made of the same material or similar materials (for example, molybdenum and tungsten)

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

FIGS. 3a-b each show a micrograph of two surface-treated substrates. FIG. 3a shows a tungsten sheet which has been cleaned with the described cold gas method using tungsten as blasting medium, ie substrate material has been removed. Fig. 3b shows a tungsten sheet which has been treated with a conventional sandblasting method using alumina (Al ₂ O ₃ ) as an abrasive. The deposits 16a-d of foreign material or Al ₂ O ₃ can clearly be seen in FIG. 3b. This means that unintentionally individual particles or grains of the blasting medium remain stuck in the substrate during the blasting process. This contamination with foreign materials is particularly in the use of the corresponding substrate or component in

High temperature applications are very critical because the impurities form weak spots in the substrate. In Fig. 3a can be clearly seen that the cleaned substrate surface is homogeneous. The use of tungsten as a blasting medium (or because blasting material and substrate are made of the same material), there is no risk of contamination

Foreign material.

LIST OF REFERENCE NUMBERS

2 cold gas spraying system

4 spray gun housing

6 blasting medium line

8 process gas line

10 Laval nozzle

12 blasting agent + carrier gas supply

14 substrate

16a-d foreign material (AI ₂ O ₃ )

S Blasting agent + carrier gas flow T Process gas flow

Claims

Claims 1. Process for surface treatment using cold gas spraying

providing a blasting agent (S), and

Accelerating the blasting agent (S) towards the surface of a substrate (14) by means of a process gas jet (T),

characterized in that

the blasting agent (S) is formed from at least one refractory metal, a refractory metal-based alloy or a refractory metal-based carbide, the refractory metal being selected from tungsten, molybdenum, chromium, and at least part of the substrate surface being cleaned and activated by means of the blasting agent (S), is roughened, structured, compacted, hardened and/or smoothed.

2. The method according to claim 1, characterized in that the blasting agent (S) striking the surface of the substrate (S) does not form a layer on the substrate (14), and / or that the blasting agent (S) striking the surface of the substrate (S). Blasting agent (S) does not adhere to the surface.

3. The method according to claim 1 or 2, characterized in that

Blasting media (S) has a large number of particles with a medium

Diameter of 5 μm to 2 mm, 10 μm to 500 μm, preferably

less than 150 μm.

4. The method according to claim 1, 2 or 3, characterized in that

Substrate (14) and the blasting agent (S) are made from the same material or from related materials, in particular a refractory metal or an alloy based on refractory metal.

5. The method according to any one of the preceding claims, characterized in that the blasting agent (S) has a large number of granular particles which are rounded, in particular spherical.

6. The method according to any one of claims 1 to 4, characterized in that the blasting agent (S) has a large number of particles which are angular, in particular sharp-edged.

7. Method according to one of the preceding claims, characterized in that the blasting agent (S) is granules

8. The method according to any one of the preceding claims, characterized in that the method involves generating a blasting agent jet with a diameter of 2 mm to 10 mm, 4 mm to 8 mm, preferably 5 mm to 6 mm, when it hits the substrate (14). includes

9. The method according to any one of the preceding claims, characterized in that the method comprises providing the process gas jet with a pressure between 10 bar to 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 at a temperature between room temperature to 1400°C, 400°C to 1000°C, preferably 500°C to 800°C.

11. Cold gas spray system for surface treatment of a substrate according to a method according to one of claims 1 to 10, wherein the system has: a spray gun housing (4),

a process gas supply line (8) into the housing (4),

a blasting agent feed line (6) into the housing (4), and

a Laval nozzle (10) connected to the housing (4) for accelerating a blasting agent (S) towards the surface of a substrate (14) by means of a process gas (T),

characterized in that

at least part of the substrate surface is cleaned, activated, roughened, structured, compacted, hardened and / or smoothed by means of the blasting agent (S).