WO2000031313A1 - Material for producing a corrosion- and wear-resistant layer by thermal spraying - Google Patents

Abstract

The invention relates to a material for producing a corrosion- and wear-resistant layer on a substrate by thermal spraying. Said material consists of at least 20 wt.-% - preferably more than 30 wt.-% - magnetite (Fe3O4 and/or FeFe2O4). Preferably, the inventive material consists of pure magnetite or of magnetite and at least one other metallic material or at least one intermetallic compound.

Description

 DESCRIPTION

Material and method for producing a corrosion and wear-resistant layer by thermal spraying

The invention relates to a material and a method for producing a corrosion and wear-resistant layer on a substrate by thermal spraying.

Corrosion and wear protection layers are usually applied from powder mixtures of various types to surfaces to be protected in manufacturing or for maintenance. For this purpose, thermal spray processes or vapor deposition processes such as CVD (chemical vapor deposition) or PVD (plasma vapor deposition) are mainly used. With the CVD and PVD processes, thin corrosion and wear protection layers based on oxide or hard material can be applied, especially in mass production. Electrochemical or galvanic processes are also used.

Thermal spraying mainly creates layers with a layer thickness of more than 0.1 mm. The corrosion and wear-resistant layers produced by thermal spraying are mostly metallic or oxidic layers in which hard materials are stored for improvement.

One of the biggest problems with thermal spray processes is the production of layers of constant properties and quality. For this reason, thermal spraying processes on substrates or parts with high quality requirements could only be used to a limited extent in series production.

Experiments with selection of the material with regard to its chemical composition or its shape - for example on the one hand the wire diameter of a cored wire or on the other hand the grain size distribution and the grain form of wettable powder - did not lead to a sufficient increase in quality. Changes to the spraying systems also did not help to improve the quality.

Attempts were made to provide wear and corrosion protection using thermally sprayed layers of iron oxide or magnetite. In all experiments of this type, it was found that the quality of the respective layer could only be assured to a certain extent with great effort with regard to the layer structure.

Knowing these circumstances, the inventor has set himself the goal of improving the production of a constant wear-resistant and corrosion-resistant surface coating on an oxide basis by means of thermal spraying.

The teachings of the independent claims lead to the solution of this problem; the subclaims indicate favorable further training. In addition, all combinations of at least two of the features disclosed in the description, the drawing and / or the claims fall within the scope of the invention.

According to the invention, the layer material for producing the corrosion and wear-resistant layer has at least 20% by weight - preferably more than 30% by weight - magnetite iron (Fe ₃ 0 ₄ , also with additions of Fe 0 ₃ ); it can be pure magnetite (Fe ₃ 0 ₄ ) or a material made of magnetite and at least one further metallic material, possibly also magnetite and at least one intermetallic compound.

In addition, a material with an addition of carbide / s or nitride / s or silicide / s or boride / s or oxide / s has proven to be favorable or a material whose additions are mixtures of metals, intermetallic compounds, carbides, nitrides, suicides, Are borides and / or oxides.

The additions of up to 50% by weight, preferably up to 40% by weight, to the magnetic iron stone can be about Cr, CrNi or ferritic steels. Carbides, nitrides, suicides, borides and oxides have proven their worth as additives for hard materials. In the carbides, the carbide formers such as tungsten, chromium molybdenum, niobium, tantalum, titanium, vanadium or the like are suitable. The addition of the carbides should be limited to a maximum of 30% by weight, preferably 20% by weight. With borides and nitrides as additives at this level, improvements in properties are observed. Oxidic additions of chromium oxide (Cr ₂ 0 ₃ ) in the order of 1 to 40% by weight - preferably 5 to 30% by weight - also show good results.

In order to achieve high quality, the powdery spray materials must have a grain size of 0.05 to 150 μm - preferably 0.1 to 120 μm. When mixing different powdery materials, it is advisable to agglomerate or spray-dry to avoid segregation and to improve the flow behavior.

When using wire-shaped spray materials with a high magnetite content, a cored wire can be produced from a metallic sheath and magnetite powder.

To apply the wear and / or corrosion layer, according to the invention, all thermal spray processes, such as autogenous flame spraying, high-speed flame spraying (HVOF spraying), plasma spraying under air (APS), Shroud plasma spraying (SPS), vacuum spraying (LPPS ), high-performance plasma spraying (HPPS), autogenous wire spraying or arc wire spraying can be used.

The online control and control is carried out using a combination of different processes which allow the temperature of the particle or the degree of melting, the particle size, the speed, the impact of the same on the substrate and the heating of the layer and the substrate during the spraying process to eat. The measurement signals are then fed to the computer of a control system for the spraying system and the flame parameters and the power are adapted to the values. The inventor has thus found that it is possible to create a coating which meets the above-mentioned requirements if an iron-based oxide is used as the material, which - depending on the corrosion or wear problem to be solved - is used for metals, hard materials or intermetallic compounds. The material must be produced using a specific manufacturing process; According to the invention, a powder grain with good flow properties, which is produced from the powdery material mixture by spray drying, is proposed, as well as a detachable powder grain made from the powdery material mixture by means of an agglomeration process.

The spraying system is equipped with an online control system for monitoring in order to be able to produce layers with a high quality and consistent properties by spraying.

For this purpose, online control and control using an ITG camera directed at the spray jet, an LDA detector with LDA laser and an HSP head have proven to be cheap, or online control using an ITG camera directed at the spray jet and an HSP head of a measuring body.

The online control and control is conveniently used to measure the particle speed in the spray flame, for example by means of a laser Doppler anemometer using a beam emitted by a laser device, which is broken down into two partial beams by an optical transmitter.

According to another feature of the invention, the online temperature control monitors the particle temperature in the spray flame using a high-speed pyrometer. This is done using infrared thermography, for example.

It also turned out to be. It has proven to be advantageous to measure the amount of gas, for example a quantity of plasma gas, using the online control and control. Thanks to the online control and control, you are also able to evaluate a measured current-voltage characteristic or measure a quantity of powder supplied to the spray flame.

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments and from the drawing; this shows schematically in

Fig. 1: an online control and monitoring system for a plasma system;

2: a system for infrared thermography (ITG) and for high-speed pyrometry (HSP = High Speed Pyrometry) during thermal spraying;

Fig. 3: a scheme for infrared thermography (ITG);

4, 5: each a plant for high-speed

Pyrometry (HSP);

6: an embodiment of a laser Doppler anemometer (LDA);

Fig. 7: a sketch for particle shape measurement in flight

(PSI = Particle Shape Imaging);

8: a particle temperature measurement in flight (PTM = Particle Temperature Measurement);

Fig. 9: a sketch for measuring the particle temperature and speed.

All thermal spray processes are used to apply wear and / or corrosion layers - such as autogenous flame spraying, high-speed flame spraying (HVOF), plasma spraying under air (APS), so-called Shroud plasma spraying (SPS), plasma spraying in a vacuum (LPPS), high-power plasma spraying (HPPS), autogenous or arc wire spraying - applicable. The online control and control takes place by means of a combination of different processes, which allow the temperature of the particle or the degree of melting, the particle size, the speed, the impact of the same on the substrate as well as the heating of the layer and the substrate during the spraying process to eat. The measurement signals are then fed to the computer of the control part of the thermal spray system in order to be able to adapt the flame parameters and the power to the measured values.

An online control and monitoring system shown in FIG. 1 for the flame or the spray jet 10 of a spray gun or the like indicated at 12. Spray device 12 with its burner nozzle 14 upstream powder feed 16 - has an ITG camera 18 - ie an infrared thermography camera - and a laser Doppler anemometer (LDA - detector) 20 for one below the spray jet 10 via the spray jet 10 recognizable LDA laser 22; next to this, an HSP head 24 - HSP = high speed pyrometry - can be seen, which is connected to a coil-like measuring body 26.

To measure substrate temperature T _s and coating temperature T _c by means of infrared thermography, according to FIG. 3 there is a substrate 30 - to be provided with a coating 32 - in the recording area of an ITG camera 18. A glass fiber cable 36 extends from the latter one indicated at 42 indicated video PC card - 500 kHz. A computer 46 with a monitor 48 is connected to this, to which a temperature recording device 50 is assigned here.

In FIG. 4, for measuring the cooling rate or the coating temperature Tc by means of high-speed pyrometry (HSP), the coating 32 of the substrate 30 is connected to the HSP head 24, which has an AD converter 52 to a storage element 44 and monitor 48 - Computer 46 is connected. A high-speed pyrometer with HSP head 24, AD converter 52 and with a computer 46, which contains a user menu 54, a control menu 56 and graphics software 58, can be seen in FIG. 5. The process of laser Doppler anemometry (LDA) can be used to optimize the spray parameters with little time and effort. In the preferred two-beam technique, the beam 60 of an argon ion laser (λ = 514.5 nm, P = 150 mW) indicated at 62 is broken down into two partial beams 60 _a , 60 b of the same intensity by a transmission optics 64. Both partial beams 60 _a , 60 b are focused in a fixed measuring volume 66. There they intersect at a defined angle so that a stripe-shaped intensity-modulated interference pattern is created. A particle of the spray jet 10 that flies through this stripe pattern generates a time-periodically variable scattered light signal 68 for an optical receiving system with a photodetector 70. The modulation frequency of the scattered light signal 68 is proportional to the speed component of the particle perpendicular to the interference fringe system. The frequency of the LDA scattered light signals is a measure of the local density of the particles in the plasma spray jet 10. A locally resolved measurement of relevant particle parameters is possible by scanning the beam. Results such as speed distribution, trajectories and dwell times of the particles can be obtained from this.

Since an individual determination of the size and shape of a spray particle using LDA cannot be carried out, particle-shape imaging (PSI) is used according to FIG. 7, an imaging method for the spatially resolved determination of size and shape of individual powder particles in plasma spray jets 10. The measuring principle is based on a telemicroscopic image of the shadow of the particles. The advantages of the measurement method are a high light intensity compared to scattered light methods and at the same time a reduction to the desired image information. Similar to laser Doppler anemometry, the beam 60 of an Nd-YAG continuous wave laser 60 _a (λ = 532nm, P = 100 mW) is split on a beam splitter 72 with mirrors 74 into two equally intense partial beams 60 _a , 60b, which are generated by the Mirrors 74 in the object plane E of the long-range microscope objective of a long-range microscope 76 are crossed. Its use allows a safety distance of 600 mm to be observed. At a 1:10 scale, an optical resolution of 2.7 μm is still achieved. The image recording system consists of a CCD camera 78 with an upstream micro-channel plate (MCP) image intensifier with a minimum exposure time of 5 ns. The geometric dimensions of the 512 x 512 pixel CCD chip and the depth of field of the lens result in a measurement volume of 410 x 410 x 940 μm ³ .

In the event that a particle is located in the measurement volume exactly in the object plane E _, partial rays are generated from both beams 64, 64 _a , which completely overlap when they are imaged on the CCD chip and thus form a full shadow. Proportional to the distance of the particles from the object plane E, the partial shadows move apart in the image plane and the full shadow area decreases. With this effect, the position of a particle relative to the object plane E can be determined. The area and contour of the silhouette provide information about the size and shape of the particle. The LDA interference fringe pattern, also shown, provides the size scale. With the minimum exposure time of the MCP-CCD camera of 5 ns, a value of 500m / s results as the maximum particle speed at which the motion blur does not exceed the optical resolution.

In the so-called in-flight particle diagnosis method - to which reference is made to FIG. 8 - up to 200 individual particles per second can be measured simultaneously at each point of a spray jet for their surface temperature, speed and size, regardless of the spraying method . A non-reproduced travel unit additionally enables a plane to be scanned perpendicular to the spray jet 10, so that the distribution of the particles in the spray jet 10 can be determined precisely. The temperature is determined using two-wavelength pyrometery at 995 ± 25 μm and 787 ± 25 μm. The particles are treated as gray emitters so that knowledge of the exact emissivity is not necessary for the temperature measurement. The system comprises imaging a two-slit mask 80 with 25 μm × 50 μm — on a measuring head 82 — at a focal point at a distance of approximately 90 mm with a high depth of field. This creates a measurement volume which, according to the graphic representation in FIG. 10, is characterized by two visible and one shadow region in between. The measuring volume is approximately 170 x 250 x 2000 μm ³ . The natural radiation of individual particles that fly through this measurement volume is detected by two IR detectors recorded with two different wavelengths. The two partial measurement volumes result in two temperature peaks in a row. The time interval between the two peaks is a measure of the speed of the particle. The principle corresponds to that of the light barrier.

This procedure enables the determination of particle surface temperatures between 1,350 ° C and 4000 ° C. The measurable particle size essentially depends on the temperature of the particles. It has a lower limit of approximately 10 μm and an upper limit of approximately 300 μm and is determined by the absolute energy radiated by the particle, which is proportional to the square of the diameter. The measurable speed range is 30m / s - 1500 m / s.

The illustration in FIG. 9 follows on from that in FIG. 1 and illustrates the measurement of the particle temperature and the speed by means of an HSP head 24.

The procedure is further discussed using a few application examples:

EXAMPLE 1

A casting mold for aluminum casting should be provided with a layer that prevents caking and sticking in the mold.

For the tests, a 0.2 to 0.5 mm thick coating of a material composition of

95.5% by weight magnetite (Fe ₃ 0 ₄ ) 4.5% by weight iron oxide (Fe ₂ 0 ₃ )

selected; this should prevent sticking and caking in aluminum and its alloys. Other properties of the wettable powder were

Grain size> 5 μm

<45 μm with a grain size of the starting material> 1.5 μm.

The grain structure of the round grains was produced by agglomeration by means of spray drying.

The application was carried out by plasma spraying under air (APS) with a power of 60 KW and argon / hydrogen plasma, which was provided with an online control unit according to FIG. 1; The particle speed and particle temperature are measured there during the flight in order to control the plasma spray jet in such a way that the necessary degree of melting of the particle is achieved.

The mold surface to be coated was forced-cooled with CO ₂ with the aim of keeping the oxidation upon particle impact as low as possible.

The layer thus produced by thermal spraying was then ground and tested in an aluminum foundry. It was found that caking and sticking to the mold is prevented and the time-consuming spraying of the mold with a mold release agent can be avoided.

Example 2

An approximately 1.0 to 2.0 mm thick protective layer against wear and corrosion in aqueous solutions should be applied to the transport roller of a paper manufacturing machine. This protective layer must have a high density (at least 99% of the theoretical density) due to working in aqueous solution. A cored wire of the following composition was used as the spray material:

Filling: magnetite (Fe ₃ 0 ₄ )

Sheath: NiCr 80/20 with about

30% by weight of the cored wire.

The grain size of the starting material for the filling was> 1.0 μm. To spray the protective layer, an arc spraying system equipped with an online control and control system was used for processing cored wire, and a control system was a combination of the two systems shown in FIGS. 1 and 3. The forced cooling is done with C0 and air.

After coating, the 200 cm long roll was ground to a surface quality of Ra 0.4 μm. When checking the surface with a binocular magnifying glass with an enlargement of x = 20, no defects in the layer could be found.

After a test run of six months, the transport roller used in the paper machine was removed together with a chrome-plated roller, and the surfaces were examined. During this investigation it was found that no defects or attacks due to corrosion or wear could be found on the transport roller coated for the test by plasma spraying. The chrome-plated comparison roller showed the attack known for this runtime.

Example 3

For the piston rings of internal combustion engines, improvements in the coatings are constantly required during development. After several considerations, tests with a pure magnetite coating should now be carried out. The problem with such a coating made of pure magnetite (Fe3θ ₄ ) is the undesirable possibility that the magnetite could be oxidized to Fe ₂ θ3 during the spraying process, which would lead to a loss of the desired good properties.

Pure magnetite was used as the spray material. The grain size of the wettable powder was: <37 μm> 5 μm,

the grain size of the starting material

<0.5 μm.

The spray powder with a round grain shape was produced by agglomeration during spray drying.

A plasma system equipped with a gas shroud and an online control unit for plasma spraying under air (APS) with an output of 80 KW was used to apply the coating. The parameters to be kept constant for controlling the plasma system were:

• particle velocity;

• particle temperature;

• substrate temperature; • Melting the particle.

C0 _{2 was} used as forced cooling for the substrate and the layer during the spraying process. The Shroud used to protect against oxidation was operated with pure starch.

The piston rings coated with pure magnetite using this method showed high quality when checked and showed good results in the endurance test in engines.

Example 4

A dipping device for a salt bath working at 500 ° C. for the heat treatment of smaller parts shows high corrosion after approximately one week of operation.

An attempt should now be made to avoid wear and corrosion by applying a protective magnetite / carbide layer. A mixture of: 75% by weight magnetite,

25% by weight chromium carbide.

The thermal spraying process for applying the layer with a thickness of 80 μm was a high-speed flame spraying (HVOF), in which the control was carried out online. After spraying, the layer was polished.

The service life of the layer applied in this way was two weeks under the same conditions.

Example 5

A hydraulic cylinder for underground mining with a length of 1000 mm and a diameter of 200 mm should be provided with a protective layer against corrosion and wear. Until now, a galvanically applied hard chrome layer had been used as a protective layer, but due to the occurrence of hairline cracks in the layer, it had a service life of at most two months.

Now a protective layer of the composition

70% by weight Fe ₃ 0 ₄ (magnetite), 30% by weight Cr ₂ 0 ₃ (chromium oxide)

chosen, the grain size of the agglomerated spray material

> 5 μm, <37 μm

scam.

To apply the protective layer with a layer thickness between 1.0 and 1.5 mm, an HPPS (High Power Plasma) system with an output of 200 KW was used, which was used to maintain the exact spray parameters and avoid oxidation with an online control was provided. The protective layer thus prepared was checked after a period of two months, and it was found that the surface of the layer showed no attacks by corrosion or wear. The lifespan of the layer was nine months.

Example 6

The piston of a vacuum pump with a diameter of 20 mm and a length of 500 mm should be provided with a wear and corrosion protection layer. An agglomerated wettable powder with the composition:

80% by weight Fe ₃ 0 ₄ 20% by weight NiaAl

and one

Grain size> 5 μm

<45 μm

used.

An LPPS system with an output of 40 KW was used for coating, which was provided with an online control.

When used later, the coating produced in this way showed very good results compared to normal pistons.

Claims

PATENT CLAIMS 1. Material for producing a corrosion-resistant and wear-resistant layer on a substrate by thermal spraying, which has at least 20% by weight, preferably more than 30% by weight, of magnetic iron stone (Fe ₃ 0 ₄ and / or FeFe ₂ 0 ₄ ) . 2. Material according to claim 1, characterized in that it consists of pure magnetite. 3. Material according to claim 1, characterized in that it consists of magnetite and at least one further metallic material. 4. Material according to claim 1, characterized in that it consists of magnetite and at least one intermetallic compound. 5. Material according to claim 1, characterized by an addition of carbide / s or nitride / s or silicide / s or boride / s or oxide / s. 6. Material according to claim 1, marked by the addition of a mixture of metals, intermetallic compounds, carbides, nitrides, suicides, borides and / or oxides. 7. Material according to claim 1 or 3, characterized by magnetite and an addition of up to 50 wt.%, Preferably up to 40 wt.% Cr, CrNi, or a ferritic steel. 8. Material according to claim 1 or 5, characterized in that it consists of magnetite and carbides of W, Cr, Mo, Nb, Ta, Ti, V. 9. Material according to claim 8, characterized in that it is made of Magnetite with an addition of up to 30% by weight, preferably up to 20% by weight, of tungsten and / or chromium carbides. 10. Material according to claim 1 or 5 characterized by a mixture of magnetite and chromium oxide. 11. Material according to claim 10, characterized by a proportion of the chromium oxide between 1 and 40 wt.% Preferably between 5 and 30% by weight. 12. Material according to one of claims 1 to 1, 12, characterized by a grain size of the powdery spray material of 0.05 to 150 microns, preferably 0.1 to 120 microns. 13. Material according to one of claims 1 to 12, characterized by a cored wire as a wire-shaped spray material, the filling of which is made of magnetite and the jacket of which is made of an alloy. 14. Material according to one of claims 1 to 13, characterized by a powder grain produced from the powdery material mixture by spray drying with good flow properties. 15. Material according to one of claims 1 to 3, characterized by a powder grain produced from the powdery material mixture by means of an agglomeration process. 16. A method for producing a corrosion and wear-resistant layer on a substrate by thermal spraying, using a material based on iron oxide according to at least one of claims 1 to 15, characterized in that the application of the layer from the material by an online control and control system is monitored. 17. The method according to claim 16, characterized by an online controlled flame spraying process, in particular a high-speed flame spraying process, as a coating process. 18. The method according to claim 1 to 16, characterized by an online controlled plasma spraying process, in particular by plasma spraying in the air or in a vacuum, a high-performance plasma spraying process (HPPS), a Shroud plasma spraying process (SPS), as a coating process. 19. The method according to claim 16, characterized by an online controlled wire flame spraying process or an online controlled arc wire spraying process as a coating process. 20. The method according to any one of claims 16 to 19, characterized by an online control and control by means of an ITG camera (18) directed at the spray jet (10), an LDA detector (20) with an LDA laser (22) and an HSP head (24) (Fig. 1). 21. The method according to any one of claims 16 to 19, characterized by an online control and control by measuring the particle speed in the spray flame. 22. The method according to any one of claims 16 to 19 or 21, characterized by an online control and control by means of measuring the particle velocity in the spray flame by a laser Doppler anemometer using a beam (60) emitted by a laser device (62), which is broken down into two partial beams (60 _a , 60 _b ) by a transmission optics (64) (FIG. 6). 23. The method according to any one of claims 16 to 19, characterized by an online control and control by measuring the particle temperature in the spray flame by means of a high-speed pyrometer. 24. The method according to any one of claims 16 to 19 or 23, characterized by an online control and control, in which the particle temperature in the spray flame is measured by means of infrared thermography (Fig. 3). 25. The method according to any one of claims 16 to 19, characterized by an online control and control, in which the measured amount of gas is analyzed. 26. The method according to any one of claims 16 to 19 or 25, characterized by an online control and control, in which a measured amount of plasma gas is analyzed. 27. The method according to any one of claims 16 to 19, characterized by an online control and control, in which a measured Current-voltage characteristic is evaluated. 28. The method according to any one of claims 16 to 19, characterized by an online control and control, in which a quantity of powder supplied to the spray flame is measured. 29. A method for producing a corrosion- and wear-resistant layer according to one of claims 17 to 28, characterized in that an online-controlled plasma spraying method, which uses air as the plasma gas, is used as the coating method. 30. A method for producing a corrosion and wear-resistant layer according to one of claims 17 to 28, characterized in that an online-controlled, water-stabilized plasma spraying method is used as the coating method.