DE1056450B - Process for the production of coatings from hard materials - Google Patents

Description

GERMAN

kl. 48b 11704

INTERNAT. KL. C 23 C

PATENT OFFICE

C 23 C 16/00 / C M27 211VI / 48b

REGISTRATION DATE: MAY 25, 1955

NOTICE THE REGISTRATION AND ISSUE OF THE EDITORIAL: APRIL 30, 1959

The carbides of the III. to VI. Group of the periodic table are very hard and resistant to corrosion. It has therefore already been proposed to use these hard materials as protective coatings against Use wear, corrosion and erosion. Furthermore, a number of procedures have become known to remove such coatings through reactions in the gas phase, especially on refractory metals, z. B. tungsten and molybdenum to be deposited. In almost all cases, the known method was used the base material is used in the form of relatively thin wires. Despite the known investigations, Coatings from the carbides of the metals of the III. to VI. To separate the group of the periodic table, often prepared the application of well-adhering coatings, especially for larger workpieces, clarified difficulties. While in one case the coatings adhered well to a material, In the other case, coatings that looked flawless at first could be obtained, but they were very strong tended to peel off. Since these difficulties also occurred when the with the coating too The workpieces provided are well cleaned before the coatings are applied and, in particular, all of them are removed Oxide residues were freed, the causes of the peeling off of the coatings were unknown.

It is known to clean the surface of workpieces that are to be provided with metallic or carbide coatings by subjecting them to a vacuum treatment, which can also be associated with a certain increase in temperature up to a maximum of 600.degree. This vacuum treatment has already been combined with an electrical discharge without increasing the temperature , which has also led to surface cleaning. In all of these cases only the skins formed by the adsorption of gases on the surface have been removed. However, this did not eliminate the malfunctions mentioned above when applying the coatings.

It has now been found that these disorders have their cause in the escape of gases that are dissolved in the base material and can be remedied by the fact that one with coatings of hard carbides, nitrides, borides, suicides of the metals of the III. to VI. Group of the periodic system, in particular the metals titanium, vanadium, tungsten, workpieces to be coated prior to gas plating, after they have been freed from adhering dirt and in particular from oxide residues, thoroughly degassed in a vacuum, with evacuation at workpiece temperatures of 800 to 1000 ° C is carried out until a vacuum of 10- ³ to 10- ⁴ Torr receive process for preparing
of coatings made of hard materials

Applicant:

Metallgesellschaft Aktiengesellschaft,
Frankfurt / M., Reuterweg 14

Wilhelm Ruppert and Gottfried Schwedler,

Frankfurt / M.,
have been named as inventors

remain. The inventive pretreatment of the base material prior to gas plating has to The result is that not only the gases adsorbed on the surface, but also those gases are removed, which are dissolved in the base material and those otherwise in the gas plating from the base material diffuse out to the surface, there with the deposited coatings with the formation of intermediate layers react, which increases the adhesive strength of the deposited coatings on the base material reduce quite significantly. This is the only way to ensure adequate adhesion in these cases Coatings that are applied by gas plating, especially for larger workpieces, achieved. When using the method according to the invention, it is not necessary to carry out the gas plating directly to be carried out after degassing, for example in one process step. Rather, it is possible according to the invention to cool treated degassed workpieces and to store them in the air for any length of time without that the gases once removed penetrate the material again.

The coatings deposited on the tool steels pretreated in the manner described Carbides of the III. to VI. Group of the periodic table, in particular from titanium carbon, adhere very firmly to the base material and even tend to under the extreme loads like them in the non-cutting deformation of metals, especially when drawing seamless tubes or Bar material, even occurring under unfavorable lubrication conditions, does not peel off.

Since the carbide coatings, in particular made of titanium carbide, adhere firmly to the base material and not tend to burst, they also offer due to their uniform and cohesive surfaces good protection against erosion and corrosion.

909 508/238

Since the method according to the invention involves degassing, be it nitrogen or oxygen or both, are also equivalent agents that bring about such a degassing Place of the "vacuum treatment or in addition to it in itself possible to achieve similar effects. So you can, for example, by a glow in hydrogen purified from nitrogen and oxygen or perform the degassing in a pure inert gas. However, these are much longer Treatment times and / or higher annealing temperatures are required to achieve sufficient degassing. Such gas treatments can also have adverse effects on the base metal exercise. For example, by annealing in hydrogen for a long time, decarburization can at least be achieved occur on the surface of steels. You can do that counteract by adding hydrocarbons to the hydrogen in such an amount that the Hydrocarbon partial pressure is the hydrogen-carbon equilibrium that is between the gas space and adjusts the carbon in the material.

Purely chemical methods can also be used to remove the gases absorbed in the material are, for example, annealing the workpieces in the presence of calcium and / or magnesium Temperatures from 800 to 1000 ° C, with nitrogen and oxygen forming oxides and nitrides Calcium and magnesium are bound. However, there is a risk that connections of the Magnesium and / or calcium precipitate on the metal surface and, in turn, the later Disrupt stratification.

The use of these is equivalent to these processes for pretreating the base materials Basic materials, their content of reactive nitrogen and / or oxygen through special alloying measures, for example by alloying titanium, or measures in the production, z. B. by melting in a vacuum, on similar low values as achieved by the pretreatment processes described.

The importance of such a pretreatment before applying a carbide layer is one thing Example explained in more detail. If you try a titanium carbide layer on cast iron without vacuum treatment To separate the gas phase, this is only possible occasionally with particularly dense types of cast iron, for example Centrifugal casting. Here, too, the liability is not always satisfactory. With ordinary cast iron In most cases it is not possible to remove firmly adhering titanium carbide coatings by reaction to apply the gas phase.

On the other hand we treat workpieces made of cast iron by first annealing in vacuum before, for example by heating to 950 ° C at a vacuum of 10 ^-3 to 10 ^-4 mm Hg, until this pressure is maintained even after switching off the pump, and then coating the so pre-degassed castings after any storage in air with a titanium carbide coating, for example, by titanium chloride, at temperatures above 900 ° C with a gas

brings mixture to reaction, in which hydrogen and volatile hydrocarbons are contained, so is obtained a firmly adhering even titanium carbide coating on the cast iron surface. On cast iron Such a treatment gives a particularly high-gloss titanium carbide coating. Other methods for applying such carbide coatings can also be used on im Apply firmly adhering titanium carbide coatings to vacuum pretreated cast iron surfaces.

The application of such layers after prior degassing is of particular importance Types of cast iron in which the carbon is wholly or largely in Spherolithic form, because this material has a higher gas content.

But also with materials that are denser per se, for example with steels, especially the usual ones Tool steels on which the application of firmly adhering carbide layers has not yet been possible with certainty was possible, it is particularly advantageous to use such a degassing pretreatment for the surface and to prepare the base material in order to obtain firmly adhering coatings. As well as alloyed steels as well as unalloyed steels, such as those used in particular for tool manufacture, can advantageously be pretreated in the manner according to the invention before a carbide coating is applied will.

Claims (1)

Claim: Process for the production of coatings from hard carbides, nitrides, bonds, suicides of metals of the III. to VI. Group of the periodic system, in particular the metals titanium, vanadium, tungsten by gas plating, characterized in that the workpieces to be coated are thoroughly degassed in a vacuum prior to gas plating, the evacuation being carried out at workpiece temperatures of 800 to 1000 ° C until a vacuum of 10-3 to ΙΟ- ⁴ Torr is maintained. Considered publications:
German patent specification No. 665 54O ¹ .