CH705281B1 - Process for removing a layer system from a workpiece comprises applying a chromium- and aluminum-containing layer directly on the workpiece, and removing the coating on the workpiece using an alkaline solution - Google Patents

Abstract

Process for removing a layer system from a workpiece comprises applying a chromium- and aluminum-containing layer directly on the workpiece to improve the removal process, and removing the coating on the workpiece using an alkaline solution containing a strong oxidant. An independent claim is also included for a single chamber device for carrying out the process.

Description

Technical area

The invention relates to a method for detaching layer systems according to the preamble of claim 1, in particular for the detachment of chromium and aluminum-containing layers.

State of the art

Decoating process for the replacement of layer systems that have been applied to metallic materials, for example, with galvanic, PVD or CVD method are known from the prior art. For example, TiN layers can be easily solubilized with an aqueous hydrogen peroxide solution. However, if one wants to replace more complex, for example ternary or quaternary layer systems, which are particularly suitable for many applications in the tool or mechanical engineering industry due to their mechanical or chemical properties, one generally has to resort to more complex methods involving the use of a wide variety of sometimes expensive and / or environmentally harmful or toxic chemicals of concern include the electrical contacting of the workpieces for electrolysis or the like with and often still require a long for industrial manufacturing processes unacceptable treatment time.

In JP 3 320 965 a process for the detachment of TiAlN, ZrAlN, HfAlN and Si3N4 hard material layers is disclosed in the examples. Alkaline solutions containing permanganate and dichromate ions in different concentrations are used. However, the stated layers could be satisfactorily removed only at relatively high dichromate concentrations, high pH and temperatures above 40 ° C, or with additional use of electrolytic processes. The fastest decoiling times ranged from one to five hours. However, dichromates are known to have a high toxic potential due to the hexavalent chromium and are therefore applicable or disposable only under special precautions. Furthermore, the process causes the formation of small pores in the substrate, whereby a better layer adhesion is to be achieved. However, this is not desirable, for example, for polished substrates.

JP 02-285 081 discloses a method for stripping chromium or chromium oxide layers. The process is carried out in an aqueous solution with the addition of an etchant and an aromatic or fluorine-containing surfactant.

The patent application DE 4 339 502 describes the non-destructive stripping of carbide substrates, coated with u.a. TiAlN layers. The advantages over previous methods are given by the fact that in addition to the conventional complexing agents and stabilizers, inhibitors for the purpose of corrosion protection and other auxiliaries are used and the solution is adjusted to a pH, in conjunction with the other reagents, a release of Co from the Workpiece prevented. Disadvantages of this solution are the comparatively long stripping time for TiAlN or the like, the relatively high use of chemicals and the associated costs, the relatively complicated (because exactly to be observed) formulations and reaction conditions and the use of fluorine-containing reagents.

In WO 9 964 646 a de-coating process is described in which first a thin TiN layer is applied to a workpiece and only then the hard-to-remove TiAlN functional layer. The stripping then takes place with a hydrogen peroxide solution which dissolves the TiN intermediate layer through the pores in the cover layer. However, TiN layers have the disadvantage of a relatively lower temperature resistance compared to, for example, TiAlN or AlCrN. For example, in the case of TiN coatings in air, even at temperatures around 600 ° C, a damaging oxidation process takes place, which leads to complete failure of the coating system on prolonged exposure. In order to replace such high-temperature-resistant layers after possible errors in the manufacturing process or re-coating an expensive tool without damaging the sensitive workpieces, therefore, a whole range of more complex, including electrolytic, stripping, as in JP 3 320 965 or in WO 1999 -54 528 mentioned, developed.

Presentation of the invention

The invention is based on the object to provide a method for delamination of hard coatings available, in which the disadvantages of the prior art are avoided. In particular, this method should be easy and quick to carry out using harmless chemicals feasible. Another object of the invention is to provide a stripping method for layer systems which are also suitable for use at extremely high operating temperatures. For example, with TiAlN, oxidative damage only occurs at temperatures of approx. 800 ° C. However, the process is particularly good for AlCrN, Al2O3, (AlCr) 2O3 or (AlCr) xOyNz layers, in which failure of the layer or the layer / substrate composite can be detected only at temperatures above 1000 ° C.

These objects are achieved by the inventive features in the characterizing part of claim 1.

For this purpose, at least one aluminum and chromium-containing layer is applied directly to the workpiece to improve the detachment, since it has been found in extensive preliminary tests that such compared to other conventional stripping extremely resistant layers are completely surprising in an alkaline solution, the contains strong oxidizing agent, begin to dissolve at about 5 ° C and can be quickly and completely dissolve or dissolve at ambient temperatures. This is all the more astonishing since ternary titanium aluminum nitride layers are difficult to decoatle, for example with special complexing agents or electrolytic processes (see above), although TiN, in contrast to the chemically extremely resistant CrN, is easily soluble in dilute hydrogen peroxide, for example.

Suitable oxidizing agents are, for example, potassium permanganate, cerium ammonium nitrate, potassium peroxodisulfate or sodium peroxydisulfate.

Such layers may for example comprise at least one of the following materials: metallic AlCr, TiAlCr and other AlCr alloys and / or the nitridic, carbidic, carbonitridic, boridic or nitroboridic hard compounds of aluminum chromium or other AlCr alloys.

The layer can be constructed either as a substantially homogeneous single layer or as a multi-layer sequence of each aluminum and chromium-containing layers. Advantageously, an Al content of at least 30% atomic percent is selected in each layer, since otherwise the influence of the highly resistant CrN predominates and makes the detachment process more difficult. At the top, the Al content is advantageously limited to at most 80 atomic percent, since the coating process at the latest here, but usually from about 70 atomic percent, deposition of, for example, nitridic AlCr layers, relatively soft hexagonal phases arise due to the lower mechanical load capacity are less suitable for tasks in the field of wear protection.

Such layers can be replaced, for example, in a permanganate solution in a wide parameter range. For example, if one wishes to detach layers of hard metals which are sensitive to an all-too-alkaline environment, a high pH of about 7 is sufficient at high permanganate concentrations, such as 20 to 50 g / l, to detach the layers. Additionally, as is known to those skilled in the art, complexing agents such as, for example, potassium sodium tartrate tetrahydrate, sodium gluconate, EDTH, sulfonic acid derivatives of aliphatic or aromatic hydrocarbons, derivatives of a carboxylated aromatic hydrocarbon (eg a phenol) can be used to accelerate the dissolution process. et al., as well as inhibitors, such as mononuclear or polynuclear nitrogen-containing heterocycles (eg, morpholine, benzotriazole, ...), amine borates, Amincarboxylate, alkyl-aryl-sulfonamides, fatty acid amides, amine and sodium neutralized phosphoric acid esters of the solution to protect the sensitive substrate surface are added , The removal process can be carried out advantageously at temperatures between 5 and 70 ° C.

However, a higher pH range, preferably between 9 and 14, is recommended for stripping off workpieces which are insensitive to alkaline solutions, such as steel substrates and many other iron-containing alloys. A lower permanganate concentration, for example between 10 and 30, is generally sufficient g / l, in order to achieve a complete stripping of 2 to 10 microns thick AlCrN layers within 15 to 60 minutes even at room temperature, ie at about 15 to 30 ° C. However, here too an increase in the permanganate concentration above 30 g / l again accelerates the stripping rate. It is irrelevant whether the AlCrN layers are applied to the workpiece with a metallic AlCr intermediate layer or grow up without a metallic intermediate layer.

As is precipitated in the detachment process from the permanganate solution of brownstone, it may be necessary under certain circumstances, after the detachment process to remove MnO2 residues from the workpiece surface. This is especially true if the detachment process is carried out without the assistance of one or more ultrasound transmitters. For this purpose, a cleaning in aqueous solution is advantageously carried out, to which a weak acid or a buffer solution in the acidic to slightly alkaline range has been added. In this case, a pH between 2 and 9, preferably between 3 and 7, should be set. This can, as known to those skilled, for example, by the addition of phosphoric acid, of carboxylic or hydroxycarboxylic acids, in particular by the addition of formic, acetic, oxalic or lactic, malic, tartaric and / or their salts are caused.

The advantages achieved by the invention are also to be seen in the fact that in general complex layer systems, such as those required today for example for high performance cutting materials or the use of tools and components at high temperatures, can be easily and quickly replaced when on one or more cover layers of at least one hard material compound are applied to the AlCr-containing layer deposited directly on the workpiece. Examples of such layer systems are hard compounds of the IV, V and VI subgroup of the PSE (ie Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) or aluminum and / or silicon and one or more Non-metals such as C, N, B, O exist. In this case, the AlCr-containing layer is attacked by the pores of the cover layer and thus also the overlying cover layer detached.

Both PVD and CVD methods or hybrid methods, which combine both coating techniques, are suitable for the production of such layer systems. Since PVD processes always produce a certain number of pores, these methods are generally applicable and preferable. For CVD layers, the respective cover layer must be selected according to the criteria of a microporousness or so that the stripping solution can reach the AlCr-containing layer. This is for example given for Al 2 O 3 layers, since they usually have a fine crack pattern due to the cooling process.

As substrates ceramic and metallic workpieces, as well as hard metals, but preferably steels and ferrous materials can be stripped.

In the following the invention will be explained in more detail with reference to individual embodiment or comparative examples.

Coating of workpieces, coating systems

For the production of AlCrN layers were on various workpieces, especially on test drills, in an industrial coating plant type RCS the company Balzers, as for example in EP 1 186 681 in Fig. 3-6, Description page 12, line 26th to page 14, line 9, Cr layers deposited with different aluminum content. Depending on their diameter, the cleaned workpieces were mounted on two or, for diameters of less than 50 mm, on triply rotating substrate carriers and four powder metallurgy targets made of different AlCr alloys were installed in the cathodic arc sources attached to the walls of the coating system.

Subsequently, the workpieces were first brought by likewise mounted in the system radiant heaters to a temperature of about 450 ° C and the surface by applying a bias voltage of -100 to -200 V under Ar atmosphere at a pressure of 0.2 Pa subjected to an etching cleaning by Ar ions.

In the following, at a nitrogen pressure of 1 to 3 Pa and a substrate voltage of -50 V by operating four AlCr sources with a power of 3 kW for 120 minutes, an AlCrN layer was deposited. Basically, the process pressure in each of these steps can be set in a range of 0.5 to about 8 Pa, with either a pure nitrogen atmosphere or a mixture of nitrogen and a noble gas, such as nitrogen. Argon for nitridic layers, or a mixture of nitrogen and a carbon-containing gas, which is mixed with a noble gas if necessary, can be used for carbonitridische layers. Accordingly, for the deposition of oxygen- or boron-containing layers, oxygen or a boron-containing gas can be admixed as known.

Target composition, crystal structure of the layer, layer composition, layer thickness, layer hardness, wear resistance and adhesion and substrate bias and process pressure are listed in Table 1.

For layers in a transition region with an Al content between 60% and 75% by%, not only the preferred orientation, but also the basic structure of the crystal lattice can be set via the process parameters. Thus, for example, in Experiment B, a hexagonal structure is produced at a low pressure of 1 Pa and a substrate voltage of -50 V, while in Experiment A, a cubic face-centered structure is produced in a pressure range of 3 Pa and a substrate voltage of -50 V.

Table 1

[0025] <Tb> verse. Bez. <Sep> Al / Cr in the target <sep> crystal structure <sep> Al at% <sep> Cr at% <sep> layer thickness [Microns] <sep> HV0. 03 <sep> USubst. [V] <sep> PN2 [Pa] <Tb> A <sep> 3 <sep> kub <sep> 69.5 <sep> 30.5 <sep> 3.2 <sep> 3100 <sep> -50 <sep> 3 <Tb> B <sep> 3 <sep> hex <sep> 72.0 <sep> 18.0 <sep> 4.2 <sep> 2100 <sep> -50 <sep> 1 <Tb> C <sep> 1 <sep> kub <sep> 41.5 <sep> 58.5 <sep> 3.8 <sep> 2800 <sep> -50 <sep> 3 <Tb> D <sep> 12:33 <sep> kub <sep> 19.0 <sep> 81.0 <sep> 4.1 <sep> 2300 <sep> -50 <sep> 3

Furthermore, for comparative purposes, detachment tests were carried out with the following commercially available coatings from Balzers: Balinit A (TiN), Balinite C (WC / C with Cr / CrC adhesive layer), Balinit Futura Nano (TiAlN with a TiAl adhesion layer), Balinit D (CrN), Balinit DLC (DLC with Cr / CrC adhesive layer).

Attempts to delaminate

example 1

An aqueous solution with 100 g / l NaOH (pH 14.4) and 20 g / l KMnO4 and 10 g / l NaCl stripped at room temperature in about 15 to 35 min different as above under test designation A to D AlCrN-coated steel drill and tools.

Example 2

Solution with 200 g / l NaOH (pH 14.7) and 5 g / l KMnO4entschichtet in 2.5 hours AlCrN-coated steel drills, layer thickness 3 microns, deposition parameters according to experiment D.

Example 3

In a solution of 200 g / l NaOH and 5 g / l KMnO4 AlCrN-coated steel drills were stripped at 60 ° C in 35 to 50 minutes, layer thickness 3.5 microns, deposition parameters according to experiment A, B, C.

Example 4

In a solution of 20 g / l NaOH (pH 13.7) and 15 g / l KMnO4 and 20 g / l sodium bicarbonate and 20 g / l sodium carbonate, an AlCrN-coated steel drill was stripped in 40 to 55 minutes, layer thickness 3 microns, Deposition parameters according to experiment A, B, C.

Example 5

With an aqueous solution of 20 g / l NaOH and 20 g / l KMnO4 (pH 13.47) were at a temperature of 20 ° C AlCr / AlCrN coated HSS drill (6 mm), layer thickness AlCr 0.25, AlCrN 3.71 microns completely stripped in 30 minutes.

Example 6

For Example 6, two AlCr (70/30 and 50/50) and four TiAl (70/30 and 50/50) targets, respectively, were incorporated into a coating equipment as described above. Subsequently, with the two AlCr targets, under parameters as described under A or C, using argon instead of nitrogen, an approximately 0.3 μm thick AlCr layer was deposited on various workpieces. Finally, a known balinite futura nano-layer (TiAlN) with a layer thickness of 4 to 5 μm was applied as cover layer. These layer systems could also be removed with a solution according to Example 1 at room temperature within 30 to 60 minutes.

Example 7

In an equipped with targets as in Example 6 plant was first about 1 micron thick AlCrN layer without metallic interlayer, under as described under A and C parameters, and finally as a final layer again a balinit Futura nano Layer (TiAlN) applied with a layer thickness of 5 microns. Removal time with a solution according to Example 1, at room temperature 50 to 65 minutes.

Example 8

Here, the temperature dependence of the stripping was examined with a stripping solution with 2% KMnCM and 2% NaOH (pH 13.46). HSS drills were stripped at room temperature and at 5 ° C. It was found that the delamination at low temperatures, as expected, slower, but still significantly faster than most known Entschichtungsverfahren runs. For details see table 2 below.

Table 2

[0035] <Tb> Temp. (° C) <sep> tentschichtung (Min) <sep> dvorher (Microns) <sep> d10min (Microns) <sep> d20min (Microns) <sep> d30min (Microns) <sep> d40min (Microns) <Tb> 19 <sep> 20 <sep> 2:40 <sep> 1.65 <sep> 0 <sep> 0 <sep> 0 <Tb> 19 <sep> 20 <sep> 2:40 <sep> 1:45 <sep> 0 <sep> 0 <sep> 0 <Tb> 5 <sep> 40.0 <sep> 2:40 <sep> 1.95 <sep> 1.65 <sep> 1.25 <sep> 0.1

Comparative examples

Example 9

An applied with a 0.3 micron Cr intermediate layer DLC layer (Balinit DLC) with a layer thickness of 2 microns was replaced in a Permanganatlösung described in Example 1 of a steel drill in about 3 hours.

Example 10

In a solution of 200 g / l ceric ammonium nitrate and 32.5 g / l acetic acid coated with 3 microns AlCrN drills made of different steels were stripped in 2 hours. However, depending on the steel grade, a partial corrosive attack on the surface was found.

Example 11

In a solution according to Example 5 was trying to replace the following layers of 6-mm HSS drills at 20 ° C: Balinit A (TiN), layer thickness 5.1 microns; Balinite C (Cr / CrC / WC / C), layer thickness 1.4 p WC / C, 0.5 p Cr / CrC adhesive layer; Balinit Futura Nano (TiAlN with a thin TiAl adhesion layer), total layer thickness 4.4 μm; Balinit D (Cr / CrN), layer thickness Cr 0.5, CrN 3.2 μm.

In contrast to the AlCrN layer of Example 5, none of the layers could be stripped fast enough according to the needs of industrial manufacturing. So even after 8 hours, none of the drills could detect an exposure of the base material. For Balinit A coated drills, no layer removal was observed even after 10.5 hours, for Balinit Futura Nano only one tenth of a micron was measured after 10.5 hours, and for Balinit C coated drills the open area and phase were after 10.5 hours Although completely stripped, whereas in the flute only about 50% of the layer were detached. Only the relatively thin Balinit C layers could be completely removed after about 9 hours.

Example 12

A TiN / TiAlN-coated hob with a total thickness of about 6 microns (TiAl about 0.3 microns) and specimens with different thicknesses were in an alkaline 30% H2O2 solution, pH 14.2, at 30 ° C under Addition of a potassium sodium tartrate, a fluorosurfactant and other reagents analogously to Example 2 of DE 4 339 502 treated. Only after 24 hours had the substrate surface been exposed on specimens with a layer thickness of 2.2 μm. However, even with thicker layers, a significant reduction in the layer thickness could be measured. Complete stripping of the hob was only achieved after 48 hours. Due to the known high reactivity of such a solution, additional safety measures, such as a quick flush, rapid cooling or the like, are to be made.

Cleaning baths for removal of brown residue

In order to remove any adherent brownish residues, the debossed tools were dipped with adherent Braunsteinrückständen each 10 minutes at a temperature of 20 ° C in an aqueous solution.

Particularly well, as shown in Table 3 below, are weakly acidic solutions, with a pH between 3.5 and 7, since in this area a good solution of the residues can be done without attacking the workpiece surface of the steel. In the case of particularly sensitive hard metals, the addition of an inhibitor is recommended in all cases in order to prevent corrosive damage by the cleaning solution.

Experiment M was carried out with ultrasound support. Deconex 29 AC is a lactic acid-based industrial cleaner that also contains inhibitors (especially benzotriazole) to protect the metal surface, avoiding surface damage from the more acidic environment. Such cleaned workpieces can be readily charged after the usual rinsing and drying steps for recoating in a PVD or CVD coating system. If necessary, an additional micro-blasting process can be provided to compensate for any differences in surface finish, such as may arise from the use of tools after the first or previous coating.

A similar behavior results when the temperature of the cleaning solution is increased to 50 ° and the treatment time is shortened to 2 minutes. However, even in experiments K and L, a slight attack on the steel substrate can already be detected here.

Table 3

[0045] <Tb> verse. Bez. <Sep> Formulation <sep> pH <sep> Release Braunstein <sep> Attack stole (QRS) <tb> E <sep> 1% oxalic acid <sep> 1.6 <sep> fast <sep> large <tb> F <sep> 1% oxalic acid + NaOH <sep> 3.15 <sep> fast <sep> large <tb> G <sep> 1% oxalic acid + 1% NaAc + 1% Ac <sep> 3.75 <sep> ok <sep> low <tb> H <sep> 1% oxalic acid + 1% NaAc + 1% Ac + NaOH <sep> 6.9 <sep> slow <sep> none <tb> I <sep> 25% H3PO4 (85%) <sep> 0.5 <sep> fast <sep> large <tb> J <sep> 20% Deconex 33 SP <sep> 0.9 <sep> slow <sep> large <tb> K <sep> 1% K2S2O5 + 1% NaHCO3 + 1% Na2CO3 <sep> 7 <sep> ok <sep> none <tb> L <sep> 1% K2S2O5 + 1% NaHCO3 + 1% Na2CO3 + NaOH <sep> 9 <sep> slow <sep> none <tb> M <sep> 2% Deconex 29 AC <sep> 2 <sep> ok <sep> none

Cleaning solutions such as in Experiments H, K and M of the above table are preferable to hitherto conventional hydrogen peroxide-based solutions for removing manganese dioxide, since they do not require additional safety measures as mentioned under Example 12. For the sake of completeness, a recipe based on hydrogen peroxide is mentioned here: H2O235%, pH 3 to 8, cleaning time at room temperature approx. 5 min.

Claims (14)

1. A method for detaching a layer system of a workpiece, characterized in that directly on the workpiece to improve the detachment behavior at least one chromium and aluminum-containing layer is applied and the workpiece with an alkaline solution containing a strong oxidizing agent, is stripped. 2. The method according to claim 1, characterized in that the oxidizing agent is potassium permanganate, cerium ammonium nitrate, potassium peroxodisulfate, sodium peroxodisulfate or a mixture thereof. 3. The method according to claim 1, characterized in that the layer system is applied by PVD or CVD method. 4. The method according to claim 1, wherein the at least one layer comprises at least one of the following materials: metallic AlCr, TiAlCr and other AlCr alloys and / or the nitridic, carbidic, carbonitridic, boridic or nitridoboridic hard material compounds of the aluminum chromium or other AlCr alloys. 5. The method according to claim 4, characterized in that the at least one layer consists of a sequence of layers, each comprising at least one of said materials. 6. The method according to claim 1, characterized in that the proportion of chromium in the metal content of the layer is between 20 and 70%. 7. The method according to claim 1, characterized in that the proportion of aluminum in the metal content of the layer is between 30 and 80%. 8. The method according to any one of claims 1, 4 and 5, characterized in that in the layer system on the layer one or more outer layers of at least one hard material compound are applied, wherein the hard compound comprises at least one metal and at least one non-metal, the metal at least one of Elements of the IV, V, and VI subgroups of the Periodic Table of the Elements (in particular Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W), aluminum or Si and the nonmetal C, N, B or O. is. 9. The method according to claim 2, characterized in that the pH of the alkaline solution between 7 and 15, preferably greater 9, and a permanganate concentration of 1 to 50 g / l is set. 10. The method according to claim 2, characterized in that the stripping temperature of the permanganate solution between 0 and 30 ° C, but preferably at room temperature, is maintained. 11. The method according to claim 1, characterized in that after the detachment of the layer system, a cleaning in aqueous solution is carried out to solve any brownstone residues from the surface of the workpiece. 12. The method according to claim 11, characterized in that the pH of the aqueous solution between 2 and 9, preferably between 3.5 and 7, is set. 13. The method according to claim 12, characterized in that the aqueous solution contains phosphoric acid, a carboxylic acid or a hydroxycarboxylic acid. 14. The method according to claim 11, characterized in that the alkaline and / or the aqueous solution additionally includes an inhibitor for protecting the surface of the workpieces from corrosion.