DE2010488A1 - Protective coatings for titanium bodies - Google Patents

Abstract

Titanium bodies (or Ti alloys), such as machine parts in a sliding contact with other parts, are anodically coated with a hard TiO2 layer (7.6 - 25 mu). The coating can be covered by a layer of a resinous material of thickness >=5 mu m (such as PTFE), which may contain finely dispersed particles of a solid material, e.g. a dry lubricant. Hard coatings, resistant to corrosion, abrasion and scratching are obtained.

Description

R e ctio n to the patent application pertaining to: Coated Titanium Articles and Processes for Their Manufacture The invention relates to new coated titanium articles.

They are coated in articles by anodic oxidation a specific aqueous alkaline bath. You can come with me a resinous material such as polytetrafluoroethylene or a thermosetting resin coated, this resinous material may contain solid particles to give the surface of the object the desired properties, such as e.g. sliding ability.

The present invention uses a novel aqueous alkaline Bath for anodic oxidation of titanium metal.

There. bath contains between 15 and 67.5 gXl sodium hydroxide, .15 to 60 g / l titanium dioxide, 7.5 to 37.5 g / l activated carbon and can contain 2 to 8 volume% sodium silicate solution contain.

Those made in the bath given above, with an oxide layer coated titanium objects have a hard surface which is suitable Forms the basis for a resin coating. The hardness of what is coated with the oxide layer Titanium object and / or the composite body subsequently coated with resin is increased when adding a ceramic material to the oxide-forming bath and, appropriately a vitreous material such as sodium silicate is added. The sodium silicate containing Coatings get their full hardness after firing at elevated temperatures The thickness of the oxide layers depends on the requirements.

It is usually between 7.6 and 25 µm. These coated Objects are corrosion-resistant and have abrasion-resistant surfaces. You are special suitable to bind a resinous material and thereby result in a titanium composite body With a resin coating that is securely and firmly bonded to the oxide layer.

The preferred resinous materials are the fluorocarbon polymers and copolymers and the thermosetting resins. For high temperature applications with low Friction are the thermosetting resins that are used at high temperatures can and contain dry lubricants dispersed in the resin, particularly suitable.

The inventive method is for the production of coated Suitable for titanium objects that can be made from many titanium alloys, like kneaded, cast and forged titanium alloys. The expression titanium here means items made of commercially available pure titanium, as well as the commercially available ones Titanium alloys such as the one commonly referred to as 6.4-titanium, the 6 parts Contains aluminum and 4 parts vanadium.

The titanium metal surface is first cleaned to remove dirt, impurities, Oxide coatings, etc. by suitable methods such as those described in the literature to remove. The cleaning conveniently comprises first physical cleaning, e.g. by a sand blower, or immersion in a steam room to remove dirt and surface oxides.

After cleaning the surface, the cleaned titanium becomes preferable dipped in a weak caustic that is used to activate the surface whereby, after the anodic oxidation, a rproduct is created that has a uniform Has parbe and uniform oxide surface. The acidic etch bath is preferred a hydrofluoric acid bath that is between 5 and 20 volumes and preferably between 10 and Contains 15% by volume of hydrofluoric acid.

B'in uniform oxia coating, which is firmly connected to the titanium surface is obtained by anodic oxidation as described in the following Titanium coated with an oxide layer serves as a suitable base for the desired Tightly bind surface coating material.

The thickness of the oxide coating depends on the process conditions used away.

The electrolyte used to form the oxide coating is an aqueous one Bath, which is between about 15 and 67.5g / l, advantageously about 30 to 45g / l, contains an alkali hydroxide (caustic soda). The bath also contains approximately. 15th up to 60g / l and advantageously 30 to 45g / l titanium dioxide, approximately 7.5 to 7.5 g / l and favorably between 7.5 and 22.5 g / l activated carbon. The sodium silicate ones Baths can contain between 2 and 8 volume% sodium or potassium silicate solution, with 2 to 4 volume% being preferred. Instead of using a silicate solution, men can also dissolve solid silicate in the aqueous bath.

The featen and largely insoluble components of the bath, dlh. the activated carbon and titanium dioxide particles should be very small so they ate while aer anodic oxidation with normally applied agitation in suspension. stay. Particles of about 1 / µm have been found to be suitable in this regard proven.

The anodic oxidation can be carried out in a wide temperature range from about 4 ° to more than 27 ° C. Higher temperatures lead to undesired gas development. One works favorably at a bath temperature between 18 and 270C for maximum production speeds and good quality of the end product.

The oxidation time changes depending on the one used Alloy, the current density and the applied voltage, the desired thickness aer Oxide layer, the i3d temperature etc. The applied voltage can be between a Vary minimums from about 20V to high voltages of more than 100V. It is advisable to gradually increase the tension, the one applied to the longest The maximum voltage should be in the range between approximately 50 and 70 V. With education The electrical resistance increases in the oxide layer and it increases for higher voltage necessary. In a preferred tension program, at least 5 min 20 V and then 5 to 10 V higher voltages each time for 5 minutes until the desired maximum voltage in the range of 50 to 40 V is reached that long is maintained until the desired Oxia layer thickness is reached. A very low current density at the applied voltage extends the time necessary to reach the desired thickness of the oxide layer. Too high a current density leads to "burning" of the object. At the specified The voltage program will have an initial current density between 0.5 and 1.5 amperes per dm2 preferred, giving excellent results at 0.5 to 1.0 amperes per dm2 will.

The total amperage does not need to be changed because the Tension is gradually increased.

The titanium object covered with the oxide layer becomes after removal rinsed from the electrolyte bath, advantageously with water of approx Room temperature. He is then with an organic solvent such as methyl ethyl ketone, ethyl alcohol and / or the halogenated hydrocarbons, such as dichlorodifluoromethane ("Freon"), cleaned.

The oxide surface formed in the bath containing titanium dioxide appears partly through oxidation of the original titanium surface and through the structure an oxide layer formed by the titanium dioxide particles from the bath, an oxide layer that is firmly bonded to the titanium body is created. Carbon particles as well as any other fine particles contained in the bath such as B. Boron nitride are also built into the oxide layer. Oxide layers containing carbon, produced in a bath that does not contain sodium silicate9 are unusual hard and tough surfaces. The application of a bath containing sodium silicate results Objects that are harder and tougher than the carbonaceous ones after firing Articles obtained without the use of sodium silicate. That touched make sure that from the one in the carbonaceous Oxschicht contained Sodium silicate forms a glass phase during firing.

Titanium objects coated with an oxide layer, manufactured in baths which contain sodium silicate but no carbon, a4nd before Doesn't burn much harder than those from the same bathroom without the Addition of sodium silicate have been obtained.

After firing, e.g. hardened at temperatures above 60,000 < however, the sodium silicate in the coating resulted in a substantial improvement the overall properties and hardness of the oxide surface.

The titanium objects with the oxide coating can then be coated with a resin are coated, producing an article that is resistant to corrosion and its surface properties differ from that used as a coating agent Resin depend. Polymers and copolymers made from fluorocarbons, e.g. Polytetrafluoroethylene, results in exceptional sliding properties and good corrosion resistance. Articles with good sliding properties at high temperatures, e.g. at 260 ° C and above, can can be made by using a solid lubricant such as graphite or molybdenum sulfite 8 built into the resin. The thermosetting resins, which become permanently rigid when hardened, are preferred for this application. The polymeric coatings generally have a thickness of at least 5 µm (0.0002 inch). They can also be much thicker depending on the requirements of use.

The impregnation of the anodically oxidized titanium parts with fluorocarbon polymers or copolymers is conveniently carried out in a liquid impregnation solution.

The titanium body is preferably heated to a temperature the above that of the material contained in the container, and then into the aqueous Dispersion immersed until a coating of the desired thickness is formed Has.

A preferred aqueous dispersion contains between about 10 and 30% by weight of the polymer material in water. Particularly inexpensive baths contain between 15 and 24,> polymer material, the best results being obtained with baths that contain between 18 and 22%. This corresponds to the density of the bath between about 7.5 ° and 9 ° Bé and conveniently about 8 ° Bé. Higher and lower Concentrations are also suitable, but have several disadvantages.

The polymer material should be finely divided so that it can be molecularly Attraction is absorbed and packed into the fine spaces and pores of the oxide layer will. For this purpose, relatively small particles, e.g. up to 4 µm used. Preferably, particles of about 2 µm or less are used.

The polymer drinking kettle can operate at temperatures @ between about 20 and more than 650, preferably between 32 and 45o, the cheapest Temperature is between 32 and 40 °. The immersion time is preferably at least 15 min and can be up to 30 min to get the desired surface of approximately 5 µm thickness.

Longer immersion times lead to a slow build-up of outer pits, which are often not required. If a coating thicker than 5 µm is desired it is pre-weighed to make it by working the polymeric material sprayed in a suitable carrier onto an air-dry coating that passes through Immersion in the soaking kettle has been obtained. The carrier can be a liquid be organic substance in which the resin is dispersed or dissolved.

This carrier is conveniently volatile. When spraying fluorocarbon polymers aqueous dispersions are preferred. The particle size used can be in the same area as used in the impregnation kettle, or one can use larger particles. # The parts coated in the soaking kettle will be then dried.

They are conveniently dried in the air, e.g. at temperatures from about 38 to 65 0C and then at I temperatures between about Fired 175 to about 400 C. Such treatment leads to the formation of a tough coating. A two-stage heating in which the coated parts first maintained at a temperature of about 3150 and then further to 4000C has to be heated to polymer coatings with excellent adhesion to the anodically oxidized titanium.

Resin or polymer coatings can also be used in other ways, e.g.

applied by spraying onto the anodically oxidized titanium surface will. The spray methods are particularly suitable for applying coatings that solid particles and especially dry lubricants such as molybdenum disulfide in the Resin dispersed included. The resin coatings can also be applied by rolling, dipping, Calenders, etc. are produced.

Thermoplastic ones are suitable for use at low temperatures Use resins. Use at high temperatures usually requires hot curing Resins. Suitable thermosetting resins are e.g. polyepoxy resins, butylated urea-formaldehyde resins, Epoxy phenolic resins, methylol phenolic ethers, etc.

The invention is illustrated in more detail by the following examples.

EXAMPLE 1 A polytetrafluoroethylene coating was applied a bolt with an elastic stop nut made of a titanium alloy, the 6 parts Containing aluminum and 4 parts vanadium. The parts were made with a fine sandblasted to avoid the common occurrence in all titanium alloys Remove oxide surface. They were then fixed in a titanium bracket and immersed in a weak hydrofluoric acid bath, the 60% hydrofluoric acid with 19 parts of water diluted to 5% by volume, immersed to activate the titanium surface.

The parts were then immersed in an aqueous electrolyte bath, the 33.8 g / l caustic soda (NaOH) 30 g / l titanium dioxide, 7.5 g / l activated carbon and 2 volume% Contained sodium silicate solution. The bath was stirred and kept at a temperature of Maintained 24 ° C. The parts were anodically oxidized, initially with a voltage of 5 was held at 20 V min. The amperage supplied by a transformer was 5 A at 20 V and was not further regulated during the oxidation process. After 5 minutes the voltage was increased to 35 V and held at this value for 5 minutes. The voltage was then increased by 5 V / min until 55 V was reached. procedure was maintained for 30 minutes.

This procedure gave an approximately uniform oxide coating 12.5 µm thickness on the parts. Thicker oxide coatings were produced by a continuous Increase in voltage achieved within the specified limits. Similar oxide coatings were created on a wide variety of commercially available titanium alloy parts, using baths with a concentration of approximately 41.3 g / l caustic soda, 33.8 g / L titanium dioxide and approximately 22.5 g / L activated carbon and approximately -3% by volume sodium silicate solution contained. The titanium parts were after they got out of the electrolytic bath removed for about 5 minutes in room temperature water, e.g. 20 ° C, washed and dried. The parts were then washed with an organic solvent cleaned, with various rroben cleaned with methyl ethyl ketone and ethyl alcohol became.

Example 2 The anodically oxidized and cleaned as in Example 1 Parts were placed in a boiling water bath of a pH between 6 and 1 for 1 min 6.5 given to raise the temperature of the parts to about 540C. they were then immersed in an aqueous Polytetrafluoräthylenimprägnierbad that had been obtained by 4-fold dilution of an aqueous dispersion containing 58% Contained pesticides, creating a bath that was 20% by volume of a 58% solution contained. This bath had a temperature between 32 and 38 ° C. The particle size of the polytetrafluoroethylene was approximately 2 µm. The parts were at least 15 min and some left in the bath for about 20 min. They were then about 5 min dried in a forced air oven at about 50 ° C. The parts were then under heated with an infrared heat lamp at about 4000C (+ 6 ° C) for about 20 minutes. the Parts had a polytetrafluoroethylene coating 5 µm thick.

The surface had a uniform brown appearance. The parts owned had good sliding properties and were resistant to scratches and abrasion.

EXAMPLE 3 The procedure of Examples 1 and 2 was followed with the exception that after the parts are impregnated with polytetrafluoroethylene and air dried at 50 ° C had been, another polytetrafluoroethylene coating was sprayed onto the impregnated parts. Then it was set to about 4000C heated, whereby a part was created, the polytetrafluoroethylene coating by 2.5 / was thicker.

EXAMPLE 4 The procedure of Example 3 was followed, with except that the part with a polymer of tetrafluoroethylene and hexafluoropropylene instead of the polytetrafluoroethylene was sprayed. The resulting coating was harder than that described in Example 3 and showed higher shear strength. It also had greater lubricity and greater abrasion resistance.

EXAMPLE Ij The procedure of Examples 1, 2 and 3 was followed a titanium plate was used, with the exception of the latte from the polytetrafluoroethylene impregnation bath had been removed and while it was still wet, diamond particles of in general spherical shape and a particle size of less than 1 / µm on the surface were applied.

These diamond particles were dry and were uniformly on the wet polymer surface applied, eo that they are bonded to the surface of the plate were when the P.olyner dried.

The diamond-containing surface was then coated with polytetrafluoroethylene sprayed and heated to approximately 400 ° C.

The resulting surface was firm and extremely hard.

Although the surface was somewhat rough, it had good sliding properties and wear properties.

EXAMPLE 6 A plate made from a commercially available titanium alloy was anodically oxidized according to Example 1. The cleaned parts were then heated and impregnated as described in Example 2, with the exception that the polymer in an impregnation vessel is a copolymer of tetrafluoroethylene and hexafluoropropylene instead of the polytetrafluoroethylene used in Example 2 was. the Parts were dried at approximately 50 ° C and allowed to reach a temperature of 15 minutes 315 0C erq. It was then heated to about 370 ° C for about 15 minutes. The resulting finished slats had a uniform blue color. The surface was very hard and had better wear resistance than the corresponding polytetrafluoroethylene product of the game 2.

EXAMPLE 7 The procedure of example 6 was applied with the exception that an additional coating of aem tetrafluoroethylene-hexafluoropropylene copolymer was sprayed on the part after the first impregnation had dried, to achieve a thicker coating. The coating thus obtained was in spite of it The dioker was not overall harder than that achieved in Example 6, It showed however, it was found that it was more difficult to penetrate the full thickness of the coating.

Example 8 A titanium part was prepared according to the method of Example 1 anodically oxidized, with a uniform oxide coating of approximately A thickness of 12.5 µm was created. A dispersion containing approximately 15% by weight molybdenum disulfide with a particle size between 4 and 10 µm in a liquid phenol-formaldehyde resin contains was spotted on the anodically oxidized part. Of the part coated in this way was then placed in an oven at a temperature of 230 ° C and cured for 60 min. The resulting hard coated part had a coating made of a resin containing molybdenum disulfide and approximately 5 μm thick. The part owned good lubricity and was for constant use at temperatures of about 2600C suitable. Higher temperatures could be applied to this part, though it was only used intermittently, Example 9 The procedure of Example 8 was followed used, with the exception that graphite with a particle size between 6 and 15 µm was used in place of the molybdenum disulfide. The product was ready for use at high temperatures e.g. about 5400C determined only by the working temperature of phenol-formaldehyde resin has been limited.

Parts were also coated with a resin, titanium disulfide and that is suitable for use at temperatures of about 400 is. Similar parts1 coated with a resin containing boron nitride, can be used at high temperatures between 760 and 815. semi-synthetic resin coatings, which contain solid particles of sodium silicate1 can be produced on titanium parts, will.

Hard composite bodies were also made from the preferred baths, the activated carbon content of at least 7.5 ″ / l has been omitted. The one with oxide coated objects were baked to achieve the desired hardness Others Samples were coated with resin and then fired.

Although all examples, the thermosetting resin coated parts describe solid particles such as molybdenum disulfide, Graphite etc. dispersed in the resin, it is evident that resin coatings are applied which do not contain solid particles, being also effective corrosion-resistant Coatings arise. Some of these coatings can be used for specific purposes be suitable, depending on the chosen coating in relation to hardness, lubricity , Wear resistance, etc. Suitable thermosetting resins include epoxy resins, Silicone resins, and melamine resins. The use of thermosetting resins is suggested in generally for high temperature purposes and for purposes that require a hard coating, preferred. For other application conditions, the use of thermoplastic Resin may be cheap or necessary, such as the fluorocarbon polymers described here ? olycarbonates, polyolefins, etc.

-Patent claims-

Claims (10)

Patent claims 1. Coated articles made of titanium, marked, by a hard coating layer of titanium oxide of approximately 7.6 to 25 μm thickness and optionally a cover layer of a resinous material of at least Thickness. 2.- Objects according to claim 1, characterized in that g e k e n n -z e i c h n e t that the resinous material is a fluorocarbon polymer or copolymer is. 3. Objects according to claim 1 or 2, characterized in that g e -k e n n z e i c h ne t that the resinous material is made of polytetrafluoroethylene or a copolymer Is tetrafluoroethylene and hexafluoropropylene. 4. Articles according to claim 1, characterized in that g e k e n n -z e i c h n e t that the resinous material is a thermoset resin. 5. Objects according to claim 1 to 4, characterized in that g e -k e n n z e i c That is, the resinous material evenly distributes small particles of a contains solid material. 6. Objects according to claim 1 to 5, characterized in that g e -k e n n z e i c That is, the resinous material disperses particles of a dry lubricant contains. 7. A method for producing the objects according to claims 1 to 6, by not showing a titanium object in a bathroom, the sodium or potassium hydroxide, suspended titanium dioxide, activated carbon and X or contains still other solids, anodic at a temperature of about 18-2700 oxidized, with a voltage of at least 20 V and a current density of at least 0.5 A / dm² is used and electrolyzed until an oxide layer of approximately 7.6 / um thickness has formed, whereupon this oxide surface with a Resin layer covers. 8. The method according to claim 7, characterized in that g e k e n n -z e i c h n e t, that an electrolyte bath was used that additionally contained 2 to 6% by volume of sodium silicate solution contains, and after the oxidation dries the object and by pricking the in or sodium silicate present on the oxide layer melts. 9. electrolyte bath for performing the method according to claim 7 or 8, g e k e n n n z e i c h n e t by switching from 15 to 67.5 £ l iatriurn- or Potassium hydroxide, 15 to 60 g / l suspended titanium dioxide, 7.5 to 37.5 g / l activated carbon. 10. Electrolyte bath according to claim 9, g e k e n n -z e i c h n e t through a content of 3G to 45 t sodium hydroxide, 30 to 45 g / l titanium dioxide, 7.5 to 22.5 g / l activated carbon and 2 to 4% sodium silicate solution.