DE4200027A1 - Electrochemical prodn. of diffusion layer systems - by anodically heating workpiece in aq. soln., suspension or emulsion - Google Patents

Abstract

In the prodn. of layer systems on metal substrates in an electrochemical cell using aq. systems by anodic heating of the workpiece, the novelty is that multiphase layer systems of 5-90 microns thickness and greater than 700 HV0.05 hardness are produced even on unalloyed low carbon steels using an electrically conductive soln., suspension or emulsion consisting of conductivity salts, depassivating complex formers, diffusion element cpds. and dispersion layer-forming cpds. The process is carried out in the presence of a thin Fe, Al and/or Si oxide film in 2-10 mins. treatment time by means of (pulsed) d.c. voltage of 200-300V at 700-1100 deg.C. The resulting carbonitride, boride and/or sulphide layers act as corrosion and/or wear protection layers and the sintered Fe, Al and/or Si oxide layers act as catalyst layers. Appts. for carrying out the process is also claimed. USE/ADVANTAGE - The process is used esp. to produce protective or functional diffusion layers on ferrous metal parts in machine and electrical equipment construction, in the tool mfr. and machining industry and in reactor engineering. Diffusion layers, opt. with sintered dispersion layers, are produced rapidly and inexpensively in an easily operated appts.

Description

The invention relates to a method and an apparatus for Generation of layer systems on metal substrates, in particular Iron materials, through anodic treatment in aqueous electrolytes. The layer systems are preferably used as protective and Functional layers in machine and electrical system construction as well as in the tool manufacturing and machining industry and in the Reactor technology can be used.

It is known to use galvanic coating systems on metal substrates Deposition and / or thermal treatment, PVD and CVD Methods or in "electrolyte plasma" in time and / or material to generate complex one- and multi-stage processes. Are there the technical equipment for the production of diffusions layer systems often very cost-intensive and maintenance-intensive. The generation of diffusion layers with solid active media, such as e.g. B. by carburizing, alitizing, powder boronizing and nitriding etc., is due to large amounts of substance, high energy, labor and Characterized time expenditure. Another disadvantage is that insufficiently evenly formed layer with complicated molded parts. The proposed variants according to DE-OS 2 14 775 and DE-OS 24 29 948, in which borating agents are of various types applied, these disadvantages cannot be eliminated. The is particularly important for tools that are subject to high wear, highly disadvantageous.

When layering from the gas or vapor phase is the apparatus expenditure considerably and the uniformity of the Layer formation through "shadow formation" (gas flow profile training and / or temperature and / or concentration sub differ) on components with complicated shapes. Furthermore is the production of the raw materials for these processes, often very cost-intensive or with high occupational safety technology African effort, e.g. B. when using cyan, silane, borane bindings, coupled. Furthermore, a partial waiter surface treatment not possible or only with great effort.  

Also the application of the obvious methods of substrate heating in the cathodic or anodic "electrolyte plasma" for Generation of diffusion layers according to DD 1 52 144 or SU 6 21 799 show significant disadvantages, especially in the high substrate removal and thus in the achievable dimensional accuracy in which Uniformity of the layer formation, in the electrolyte together setting, the difficult to control temperature-time regime or Current-voltage-time regimes etc., can be seen.

It is also used to make these layers Device unsuitable for all-round practical use. The is also unsuitable for practical implementation Diffusion layer formation according to DD 1 51 330, since only local ones Diffusion islands formed and not homogeneous, even trained layer systems are aimed. By just one short-term reaction time from a few µs to only very small anode areas, as is typical for spark discharge, is the energetic effect only on the surface layer of the metal substrates limited. For this reason, the diffusion gene speed for diffusible particles smaller and the Treatment time longer than that of substrates that simultaneously and fully warmed or heated. For this reason this method, too, if you look at it more comparable Layer thicknesses, apart from the layer thickness distribution, layer composition, structure and structure, passivity behavior etc. ineffective.

The aim of the invention is to make diffusion layer systems layers or diffusion layers with fritted dis Persion layer in a simple way, quickly and in one easy manageable equipment with low technical and energetic Creating effort and eliminating the shortcomings shown.

The invention has for its object to use aqueous electrolytes with the help of an electrochemical cell arrangement to develop a method and an apparatus for producing layer systems on metal substrates, so that diffusion layers with a dispersed dispersion layer with specific properties, in particular for use as wear and tear and corrosion protection or catalyst support. According to the invention, the object is achieved in that the aqueous electrolyte is an electrically conductive solution, suspension or emulsion which consists of conductive salts, de-passivating complexing agents, compounds of the diffusion elements and / or dispersion-forming compounds and in an upwardly open double-walled cell arrangement according to FIG. 1 and FIG. 2 flushes the anodically polarized workpiece at voltages between 200 V and 300 V. In addition to pure DC voltage, pulsating DC voltage or DC voltage superimposed with pulses can also be used and the workpiece in the aqueous electrolyte or the electrolyte can be guided to the stationary workpiece. Ammonium compounds, such as NH₄F, NH₄CH₃COO, (NH₄) ₂CO₃, NH₄Cl, etc., come as conductive salts, especially tartrates, citrates, chelates, lactates, gluconates etc. as depassivating complexing agents and the compounds as donors of the diffusion elements N, C, B, S: NH₄OH, amines, urea, ketones, alcohols, alkanes, aromatics, HBF₄, dimethylhydroxiborin, methyl borate, (NH₄) ₂S, thiourea, NH₄SCN etc. and as a dispersion layer forming compounds, eg. B. Silicofluoride, silicosols, silicates, aluminates, etc. are used.

Surprisingly, the one-step Ver according to the invention shows drive an extremely high effectiveness, resulting in an extremely short treatment time from 2 min to 10 min and the formation of Layer systems with thicknesses of at least 5 µm to 90 µm reflect.

According to the invention, the layer systems are anodic Substrate heating to 700 ° C to 1100 ° C is formed.

It is surprisingly found that in the presence of iron and / or aluminum and / or silicon compounds in the com plexant-containing solution, suspension or emulsion which Layer system formation is influenced synergistically and increased Layer thicknesses (compared to iron, aluminum or silicon ver bond-free electrolytes) can be achieved.

This effect is achieved by the creation of a thin iron and / or aluminum and / or silicon oxide pore hem achieved that controls the layer system formation so that reactive capable partners in high concentration at the gas /  Solid bodies exist that quickly lead to multiphase diffusion lead layers.

According to the invention, the method is carried out in one device led, which as a double-walled, open cell with bottom inlet and outlet connection for the electrically conductive Solution, suspension or emulsion is formed, which inner tube carries the inlet connector and out with a cathode is preparing. A filter and a cooling system in the electrolyte servoir, as well as a pump for the electrolyte forced circulation and an optionally usable conveyor or lifting / lowering system for the Inclusion of the metal substrates to be treated and the powerful Generator complete the equipment.

According to the invention, when treating small parts, there is an endless one Belt in the form of a chain with workpiece holders on the individual Chain links for use. The chain is over current-carrying gears and sliding contacts anodically poled. The gears responsible for the feed or passage galvanically isolated from the driving gear motor. Likewise, the workpiece pick-up and release device and the out Plastic existing magazine system. The tension Feeding takes place at the gear axles via carbon brushes and the chain via sliding contacts made of a copper impregnation alloy. At Putting the device into operation becomes the inner tube of the galva African cell arrangement with electrolyte from the room temperature cooled electrolyte reservoir supplied, the electrolyte over the edge of the inner tube flows and gets into the outer tube, where it passes through the outlet nozzle and a filter the pump is returned to the electrolyte reservoir.

At the same time, the conveyor system is set in motion, whereby automatically the workpieces from those attached to the chain links brought recordings, electrically contacted and the electrolytic bath (inner tube with electrolyte) supplied be, the workpiece just completely into the electrolyte immersed and washed around. After going through the double wall Cell arrangement, the workpieces are removed from the clamping or clamping fixture automatically again. The treatment time can specified via the stroke rate that determines the cycle time will.  

The diffusion layer formation on large parts is dis continuous process (loading - sinking with tension add circuit - time-determining treatment - lifting with tension shutdown - removal). A vertical is used for this working conveyor system (lifting-lowering system), which is directly above the Cell arrangement is fixed. The lowering depth is according to the geometric shape of the workpiece is automatically limited so that the workpiece is being completely washed by the electrolyte. Operation can be in a single cell system, but also in parallel switched multi-cell system can be made, the Feed via a common drive at the same cycle times leads. The use of a common one is advantageous here Electrolyte stocks, but the use of cell-associated individual pumps for the electrolyte circuit.

A cell ventilation system is included when using electrolytes high vapor pressure necessary. Therefore, an exhaust pipe that is in the outer container system of the electrochemical cell arrangement is housed, coupled with a moisture separator (cyclone). The ventilation system is optionally switched on and off.

The invention is based on 3 exemplary embodiments are explained.

In the drawings Fig. 1 and Fig. 2 is a schematic representation of the device according to the invention.

Embodiment 1

The workpieces are in the form of clamps of quality C10 automatically fed to the conveyor system according to embodiment 3 and attached to the chain links at a distance of 75 mm brought clamp recordings recorded and electrically with a Working voltage of 250 V DC anodically loaded. To Entry of the workpiece (clamping bracket) into the electrically conductive Solution consisting of 80 g / l NH₄Cl, 5 g / l citric acid, 5 g / l Tartaric acid, 50 g / l NH₄OH, 25 g / l acetone, 3 g / l MgSiF₆ and 3 g / l AlCl₃, it passes under intense heating to the red heat of <900 ° C in cycle times of 2 s the 1.50 m distance of the 2 m long double-walled galvanic cell arrangement with a current Absorption of 60 A per 20 clamps within 5 minutes. To  Leaves from the electrolyte solution, which is cooled in the bottom inner tube opens upwards and over the edge into the outer tube flows and from the pump to the filter If an electrolyte reservoir with a capacity of 500 l is supplied, this is achieved treated workpiece for automatic removal. The free chain link pickup is again with a new train stirrup equipped and again in cycle times with 1 s feed (1 cm / s) and 1 s hold time supplied to the electrolytic bath.

The cross section on a tension bow treated in this way shows a multi-phase carbonitride layer with a thickness of µm50 µm. The hardness of the wear-reducing layer system is HV _0.05 ∼750 (RA: 25 µm) compared to a core hardness of HV _0.05 ∼150 and thus more than 3 times higher, so that the layer system also has a design-stabilizing effect on the tension bow. The fritted iron-aluminum-silicon oxide layer has a passivating effect, which is demonstrated by current density potential curves.

Embodiment 2

A worn creel of quality 80CrV3 of 1.60 m in length is on the vertically movable workpiece holder directly above the inner tube of the galvanic cell arrangement after execution Example 3 arranged and then when lowering into the cell with a DC voltage of between 230 and 250 V pulsing 100 Hz anodically loaded. After dipping the teeth down to 2/3 their height in the flowing electrolytes, the 50 g / l NH₄F, 17 g / l citric acid, 17 g / l tartaric acid, 5 g / l methyl borate, 5 g / l dimethylhydroxiborin, 50 g / l NH₄OH, 5 g / l silica sol, 5 g / l Contains aluminate and 25 g / l acetone, the material heats up a current flow of 60 A to the red heat.

After 4 minutes, the gate is disconnected from the voltage source, the heated teeth are quenched in the electrolyte and the gate is moved from the bath to the starting position. After a cooling time of 5 minutes, the gate is removed from the workpiece holder. After that, they are removed by setting and grinding the teeth. The layer structure is characterized by a multi-phase carbonitride boride layer with a thickness of <20 µm and a hardness of HV _0.05 ∼1030 (RA: 27 µm) with a core hardness of HV _0.05 ∼750.

The procedure allows gates to be approved several times in this way regenerate without significant loss of strength or Service life losses occur.

Embodiment 3

Fig. 1 and Fig. 2 show a schematic representation of the on device for the production of layer systems on metal substrates ( 23 ) in continuous and discontinuous operation. The inner tube ( 5 ) is equipped with the cathode ( 6 ) in a double-walled electrochemical cell arrangement ( 1 ) with a bottom-side inflow nozzle ( 2 ) and an outflow nozzle ( 3 ) for the electrically conductive solution, suspension or emulsion. A filter ( 7 ) with a coupled pump ( 8 ) for the electrolyte forced circulation and the electrolyte reservoir ( 9 ) with cooling system ( 10 ), as well as the optionally usable conveyor system ( 11 ) with workpiece clamp receptacles ( 12 ) on the transport chain ( 13 ) or lifting - Lowering system ( 14 ) with workpiece clamp ( 15 ) complete the equipment. The transport chain ( 13 ) is anodically polarized via current-carrying gears ( 16 ) and sliding contact ( 17 ). The magazin device ( 18 ) built of plastic, like the workpiece receiving and dispensing device ( 19 ), is galvanically separated from the electrochemical cell arrangement ( 1 ) and the conveyor system ( 11 ) or lifting / lowering system ( 14 ). A cell ventilation system consisting of an exhaust pipe ( 20 ) and a cyclone ( 21 ) as well as a workpiece catcher ( 22 ) complete the device.

List of the reference symbols used

1 double-walled electrochemical cell arrangement
2 inlet connections
3 outlets
4 electrically conductive solution, suspension, emulsion
5 inner tube
6 cathode
7 filters
8 pump
9 electrolyte reservoir
10 cooling system
11 conveyor system
12 workpiece clamp receptacles
13 transport chain
14 lifting and lowering device
15 workpiece clamps
16 current-carrying gears
17 sliding contacts
18 magazine system
19 Work piece dispenser
20 exhaust pipe
21 cyclone
22 workpiece catcher
23 metal substrates

Claims (3)

1. Process for the production of layer systems on metal substrates in an electrochemical cell with aqueous systems by anodic heating of the workpiece, characterized in that in an electrically conductive solution, suspension or emulsion consisting of conductive salts, entpassi-forming complexing agents, compounds of the diffusion elements and Dispersion layer-forming compounds exist, with the creation of a thin iron and / or aluminum and / or silicon oxide seam within 2 min to 10 min treatment time by means of direct or pulsating direct voltage in the potential range from 200 to 300 V and temperature range from 700 ° C-1100 ° C, multi-phase layer systems of 5 µm to 90 µm thickness and a hardness of <HV _0.05 700 also arise on unalloyed low-carbon steels, with carbonitride and / or boride and / or sulfide layers as corrosion and / or wear protection layers and the fritted Iron and / or aluminum and / or silicon moxide layers are formed as catalyst layers. 2. The method according to item 1, characterized in that the Conductive salts ammonium compounds such as NH₄F, NH₄CH₃COO, (NH₄) ₂CO₃, NH₄Cl etc., the de-passivating complexing agents, tartrate, Citrates, chelates, gluconates, lactates etc., the compounds the diffusion elements NH₄OH, amines, urea etc., for Carbon, HBF₄, BN, methyl borate, dimethylhy droxiborin etc., for boron, (NH₄) ₂S₄, thiourea etc., for Sulfur, NH₄SCN, for carbon, sulfur and nitrogen, the diffusion layer-forming compounds such as silicon fluorides, silicosols, silicates, aluminates, aluminum fluorides, Aluminosilicates, etc. 3. Device for carrying out the method according to items 1 to 4, characterized in that the double-walled upwardly open electrochemical cell arrangement ( 1 ) with bottom inlet spigot ( 2 ) and outlet spout ( 3 ) for the electrically conductive solution, suspension or emulsion ( 4 ) in the inner tube ( 5 ) is equipped with the cathode ( 6 ) and, via a filter ( 7 ), the pump ( 8 ) implements the electrolyte circuit into the electrolyte reservoir ( 9 ) with cooling system ( 10 ) and the conveyor system ( 11 ) with workpiece clamp receptacles ( 12 supplemented) in the transport chain (13) or the lifting-lowering device (14) with workpiece tensioners (15), the apparatus being made via gears (16) and sliding contacts (17), the Stomzuführung to the metal substrates (23), but the magazining ( 18 ), workpiece holder-dispenser ( 19 ) and the workpiece catcher ( 22 ) galvanically separated from the electrochemical cell arrangement ( 1 ) un d the conveyor system ( 11 ) or lifting-lowering system ( 14 ) is constructed.