DE1056449B - Process for the production of coatings from hard carbides - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

INTERNAT. KL. C 23 C

C23C 16/00 / C

EXPLAINING EDITORIAL 1056 449

M 22308 VI / 48b

REGISTRATION DAY ·: 1 2. MAR Z 1 9 5 4

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

The present invention relates to a process for the production of coatings from hard carbides, for example the metals titanium, zirconium, vanadium and tungsten, by reaction of halogen compounds of the carbide-forming metal with gas mixtures of hydrogen and volatile hydrocarbons, thereby producing carbide coatings that are not elemental carbon or free Contain metal, but have an integral, fine-grained structure.

The hard carbides of the III. to VI. Group of the periodic table are characterized by excellent physical properties and chemical resistance. The connections therefore have in the last few years an increasing importance for the manufacture of tools and machine parts that are exposed to high levels of wear, corrosion or oxidation. Workpieces that mainly consist of carbides are manufactured using powder metallurgical processes, binder metals are added to the carbides, which increase the toughness of these carbide-containing Improve materials. When manufacturing workpieces from hard metal alloys, considerable amounts are omitted Expenses for the provision of the hard carbides and for the finishing by grinding. It was therefore desirable to produce workpieces from cheaper and more easily machinable materials and these then to be provided with carbide coatings.

A number of proposals are known from the incandescent lamp industry, hard carbides of the metals of the III. to VI. Group to be deposited by reaction of volatile metal halides with gaseous hydrocarbons in the presence of hydrogen on filaments made of refractory metals such as tungsten and molybdenum, or of carbon at high temperatures after the following reaction.

TiCl ₄ + CH ₄ - ^ TiC + 4 HCl.

However, the deposited carbide still contained free carbon, which significantly impairs its cohesion, so that such coatings even with minor stresses, especially in the case of friction and Impact loads, prone to cracking and peeling. About the annoying carbon separation / u avoid the gaseous hydrocarbons in the reaction gases replaced by carbon monoxide /. The deposition products are here, however J / contaminated to a greater or lesser extent with oxygen. / 1 Such separators heavily contaminated with oxygen / Invention products do not have the optimal mechanical properties of the pure or practically pure \ Titanium carbides.

45

Process for the production of coatings from hard carbides

Applicant:

Metallgesellschaft Aktiengesellschaft, Frankfurt / M., Reuterweg 14

Willy Ruppert, Frankfurt / M.,

and Gottfried Schwedler, Offenbach / M.,

have been named as inventors

It is also known, to avoid the deposition of free carbon, the hydrocarbonaceous Gases stronger, if not yet sufficiently diluted with hydrogen and the halide of the to add carbide-forming metal in large excess. But besides the carbide, it became free Metal or a carbide deposited with too low a carbon content, so that to achieve a If the carbon content in the coating is sufficient, subsequent carburization with hydrocarbons at temperatures above 2000 ° C was required. Such a process is not only uneconomical, it is considerable Quantities of unused metal halide leave the reaction chamber, but in larger systems also difficult to control as the escaping halides clog the exhaust pipes tend. ^

For all processes of the deposition of hard carbides by the reaction of halides of the carbide-forming metals with volatile carbon compounds were high temperatures of at least 1300 ° C required, which severely restricted the selection of suitable base materials. There were even recommended as the most favorable reaction temperatures are those above the melting point of the carbide-forming metal. In the case of the deposition of Ti C, there would be temperatures preferable above 1700 ° C. The deposited carbides were only at high reaction temperatures firmly grown together, while at low reaction temperatures they are in fine-grained form, however have only been preserved as loose, loosely connected crystal heaps.

It has now been found that coatings of high carbides of the metals of the III. to VI. Group of Periodic table, especially of the metals titanium,

Zircon, vanadium and tungsten, in principle, are formed at significantly lower temperatures can, if certain conditions are met. It was surprisingly found that such coatings with firmly interwoven, fine-grained structure and free of elemental carbon and unbound carbide-forming metal can be prepared in that a halogen compound of the carbide-forming metal with a gas mixture on the workpieces to be coated at temperatures from 900 to 1200 ° C is brought to reaction, with hydrogen and no more in the gas mixture volatile hydrocarbon compounds are included, as their equilibrium with carbon and Corresponds to hydrogen at the deposition temperature.

The process according to the invention has made it possible at a relatively low temperature and therefore coatings on materials that can be easily machined and manufactured cheaply from carbides and thus the mechanical and chemical properties of the surface of these To significantly improve materials and workpieces made from them. According to the invention The coatings * produced by the process are characterized by fine-grained and firmly intergrown coatings Structure and have only a low surface roughness of their own, which is the case with well prepared Base material is on the order of about 2 μ. The fine-grained, firmly grown coatings can be done by polishing, for example with diamond dust, boron carbide powder or by machining The graphite powder obtained can still be reduced significantly below 1 μ.

By the teaching given according to the invention to use a gas mixture in which hydrogen and no more volatile hydrocarbon compounds are contained than their equilibrium with Carbon and hydrogen corresponds to the deposition temperature, it is achieved that the deposited Coatings do not contain free carbon, but consist exclusively of carbide. This is based on the fact that a certain concentration of hydrocarbon is not exceeded when one adheres to this regulation. What concentration this is at the respective separation temperature, can be taken from known tables. It should be noted that at deposition temperatures from 900 to 1200 ° C all hydrocarbons are essentially split into methane and in addition higher hydrocarbons are only contained in negligible amounts.

However, it does not preclude the need that free carbon is not deposited with the carbide from that the coatings can be deposited on objects that contain elemental carbon in or contained on the base material. Even if this carbon reacts with the gas mixture, it works never enters the carbide coatings as free carbon and therefore does not affect their strength.

It is useful to check the concentration of the halide of the carbide-forming metal in the reaction mixture to be chosen so that it is not greater than that of the hydrocarbons used is equivalent. An excess of such halides over the stated amount is in accordance with the invention used deposition temperature of 900 to 1200 ° C is not harmful, but an excess superfluous because it goes into the exhaust gases and thus makes the process unnecessarily expensive.

Gas mixtures which meet the conditions according to the invention are preferably only produced in their composition in the reaction space itself. This can e.g. B. can be achieved by using hydrogen halide with or without hydrogen which allows the carbide (s) of the carbide-forming metal (s) to act. It then forms the or the corresponding metal halides, volatile hydrocarbon compounds and hydrogen. The production this gas mixture takes place at a temperature which is lower than the temperature at which the hard carbide is deposited on the surface to be treated. For example, one leads to manufacture of titanium carbide coatings hydrogen chloride, optionally together with hydrogen, in the Halide formation zone of the deposition apparatus at temperatures from 500 to 800 ° C over titanium carbide and the resulting gas mixture then passes to the deposition zone, which has a temperature from 900 to 1200 ° C. It is also possible to add hydrogen to the deposition zone initiate.

This procedure is possible because the equilibrium with increasing temperatures in the direction of the carbide formation is shifted, while it is at the lower temperatures in the halide formation zone is still on the side of the halide. The conduction of the gas from the at lower Temperature located halide formation zone in the carbide formation zone located at a higher temperature is preferably carried out with such a high flow rate that the carbide still not deposited in the transition zone, but only on the surfaces to be covered with the coating will.

Similar deposition conditions are also obtained by passing hydrogen halide over it with or without hydrogen via the metal whose carbide is to be deposited, for example Titanium, a gas mixture of hydrogen and metal halides, for example titanium halides, forms and in the carbide formation zone to the gas mixture containing halide vapors at the deposition temperature a mixture of hydrogen and volatile hydrocarbon compounds in equilibrium in at least such amounts that the hydrocarbon compounds at least are equivalent to the metal halide. This can be done by adjusting the flow velocities can be achieved. Such a gas mixture of hydrogen and volatile hydrocarbon compounds is preferably produced by hydrogen over carbon at a Conducts temperature which is at least as high as the temperature in the carbide formation zone. To this Gas mixtures produced in this way have proven particularly effective for producing the titanium carbide coatings.

There is already a known method in which

Diffusion layers on metals, for example chromium-plating layers on aluminum, in that the chromium is applied in the form of chromium halide is brought to the metal surface via the gas phase and with the formation of metallic Chromium reacts and diffuses into the surface layer. Although the halide of the Diffusion metal is formed in the reaction space, but this reaction does not lead to the application of carbide coatings used.

The method according to the invention can be used, for example, in the device shown in FIG

be performed. Solid titanium carbide is located in room 1. Through line 2 is hydrogen chloride initiated, the at a temperature of 500 to 700 ° C, which prevails in room 1, titanium tetrachloride and forms volatile carbon compounds. The ones with titanium tetrachloride and volatile carbon compounds Loaded gases pass through the narrow openings in the plate 3 at high speed and get into the enlarged space 4, in which the surfaces of the with the carbide coating covering workpieces. In this part of the reaction space 7 there is a temperature of about 900 to 1200 ° C. This creates the equilibrium between the metal halide and the volatile Carbon compounds, hydrogen and hydrogen chloride shifted to the side of carbide formation. The titanium carbide formed in this way is deposited on the surface of the workpieces to be coated. Hydrogen chloride, hydrogen and the equilibrium residues of metal halide, which are extremely small, leave the reaction furnace 5 in countercurrent to the incoming reaction gas through the nozzle 6. In doing so, they heat up the incoming gas.

It is particularly advantageous that in these embodiments of the invention it is possible to use the metal halide, for example titanium tetrachloride to be formed within the apparatus, be it from the metal and / or from a suitable compound of the metal, for example the carbide of the metal that is deposited should be, since in this way a carbide coating is possible, which is free from the Interferences that occur when using liquid titanium tetrachloride.

It is also possible when applying carbide coatings by the method according to the invention to use the metal halide or halides as such and to evaporate them into the reaction space and to bring into contact in the carbide formation zone with a gas mixture in which hydrogen and volatile carbon compounds in the ratio of the equilibrium between hydrogen, volatile Hydrocarbons and carbon at the deposition temperature and the required quantity ratio, based on the metal halide used, are located.

It is also possible to produce coatings using the method according to the invention, which are made from mixtures different carbides or mixtures of at least one carbide with at least one nitride of III metals to VI. Group of the Periodic Table. Have these mixed coatings properties similar to those of the carbide coatings. For the production of coatings from mixed Carbides can be a mixture of different metals and alloys in the halide formation zone the carbide-forming metals and / or compounds thereof, for example carbides, and the Halides with the help of hydrogen halide, as described for the production of the simple carbide coatings, generate and deposit carbides from them on the surfaces to be coated. But you can also subdivide the halide formation zone into individual separate areas and in each of these Areas that produce or halide only one of the carbide-forming metals and separate from feed the halide or halides of the other metals to the carbide formation zone.

If nitrides are also to be incorporated into the coatings, this can be done, for example, by that in the zone of formation of the coating the mixture of halides and volatile, im Equilibrium with hydrogen and carbon are carbon compounds nitrogen and / or nitrogen-releasing compounds or a gas containing such feeds. As such, connection can serve for example ammonia. In those cases in which nitrides are deposited in the coating should is free of oxygen and its volatile

ίο compounds, especially water vapor, to work. But you can also with all variations of the method according to the invention for generating the Halides of the carbide-forming metals or the hydrogen halide in the halide-forming zone partially by the halogens, especially bromine, replace. This is particularly advantageous when Carbide coatings of those metals are to be deposited whose halides are easily reduced by hydrogen will.

example 1

Drawing tools made of a steel with 12 to 13 vol of chromium and 1.9 to 2.5% carbon are said to have a Titanium carbide coating are provided. The drawing tools are prior to the application of the coatings, in particular on the work surfaces, finely machined, d. H. ground and polished to a high gloss. Then will they were placed in a quartz reaction crucible with the aid of a holding device and this was well sealed. The one in the reaction staircase! Any air present is pumped out and replaced with hydrogen. Of the The reaction chamber is now brought to the reaction temperature of 980 with the aid of an electrical heating unit heated up to 1000 ° C. During heating up and during the time it takes for the Workpieces at the reaction temperature is required, purified hydrogen is passed through the reaction crucible.

When the workpieces have reached the reaction temperature, pure hydrogen is used instead a mixture of hydrogen and hydrocarbons is initiated by passing over Hydrogen was produced over carbon at a temperature of 980 to 1000 ° C. IVIan receives such a gas mixture, for example, if you fill a quartz tube with carbon, this tube to 980 heats up to 1000 ° C, and at this temperature the hydrogen through the pipe over the carbon directs. The gas mixture obtained is used to deposit the titanium carbide coatings in the reaction crucible initiated.

After switching on the mixture of hydrogen and volatile hydrocarbons, the 2% titanium tetrachloride with hydrogen as the carrier gas is added to the reaction chamber. The emerging A gas mixture of titanium tetrachloride, hydrogen and volatile hydrocarbons acts on the surfaces of the drawing tools with the formation of a titanium carbide coating. The duration of treatment depends according to the thickness of the coatings desired. If the reaction is stopped after 3 hours by stopping the supply of titanium tetrachloride and volatile hydrocarbons and only hydrogen The reaction chamber is fed in, so after cooling the drawing tools in hydrogen to room temperature On the drawing tools, coatings with a thickness of up to 15 μ. These coatings are characterized by a very high surface quality. Their surface roughness is 1.5 to 2 μ and less.

After the coatings have been applied, the base material has a hardness which, depending on the cooling rate and the composition, is between HV _{30 kg} = 450 and 850 kg / mm ² .

After fine polishing of about 10 to 15 minutes, preferably on a belt polishing machine, the drawing tools can be used.

Example 2

It should be cylindrical machine parts made of a steel with about 1.5% chromium and 4% nickel, for example Bearing shells or pump cylinders, are provided with a titanium carbide coating. It becomes this chosen a process in which the titanium halides are only formed in the reaction crucible, namely using an apparatus as shown in the figure.

The reaction crucible is made of quartz. A narrower quartz tube is let into it, the one at the bottom is closed with a sieve plate. Titanium carbide lies on the sieve plate. Below the sieve chain a holding device is attached for the workpieces to be coated. For heating The system uses a two-part heating unit. One part of the heating unit is used for heating the halide formation zone, i.e. the zone in which is the titanium carbide. The other part of the heating unit has the carbide formation zone heat in which the coatings are deposited, i.e. the zone in which the workpieces are located. the The halide formation zone is maintained at a lower temperature than the carbide formation zone.

The machine parts are finely machined and then introduced into the reaction chamber with the holding device and the tube with the sieve plate and the titanium carbide inserted over it and then the apparatus tightly closed. After the air has been displaced from the reaction crucible, hydrogen is passed through the reaction crucible in such a way that the hydrogen flows first over the titanium carbide and then over the cylinders to be coated. The reaction crucible is then heated with the aid of the two heating units in such a way that the halide formation zone is brought to a temperature of 600 to 700.degree. C. and the carbide formation zone to a temperature of 980 to 1000.degree. After these temperature conditions have been reached, the hydrogen flow is throttled somewhat and about 10% hydrogen chloride is added to it. This gas mixture of hydrogen chloride and hydrogen reacts in the halide formation zone with the titanium carbide to form a gas mixture which consists of hydrogen chloride, hydrogen, titanium chlorides and volatile hydrocarbon compounds, some simple hydrocarbons, some chlorinated hydrocarbons. This gas mixture flows through the sieve plate into the carbide formation zone and there comes into contact with the surfaces of the machine parts to be coated, whereupon it heats up to the high temperatures. Firmly adhering, high-gloss titanium carbide coatings are deposited on the cylinders, and a gas mixture consisting predominantly of hydrogen and hydrogen chloride escapes from the carbide formation zone. After a reaction time of 4 hours, the supply of hydrogen chloride is switched off, rinsed for a short time with hydrogen and the reaction crucible is cooled to room temperature. After opening the reaction crucible, it is found that the workpieces are coated with titanium carbide coatings to a thickness of about 15μ. The coatings have a high gloss and a very low surface roughness of about V ₂ μ.

Claims (7)

Patent claims. 1. Process for the production of coatings from hard carbides of the metals of III. to VI. Group of the periodic system, for example the metals titanium, vanadium, tungsten, on metallic or non-metallic ^ jegengt änderTdurcrTReaTc ^ tion of halogen compounds of the metals concerned with hydrogen and hydrocarbons, characterized in that a halogen compound of the carbide-forming metal with a gas mixture on the workpieces to be coated is brought to reaction at temperatures of 900 to 1200 ° C, the gas mixture containing hydrogen and non-volatile hydrocarbon compounds than corresponds to their equilibrium with carbon and hydrogen at the deposition temperature. 2. The method according to claim 1, characterized in that no more, but preferably so much metal halide is reacted than the volatile hydrocarbon compounds is equivalent. 3. The method according to claims 1 and 2, characterized in that the halide of the carbide-forming Metal is formed in the reaction space. 4. Process according to claims 1 to 3, characterized in that the halides of the carbide-forming Metal by passing hydrogen halide and / or halogen over the carbide-forming Metal and / or a compound of the carbide-forming metal, in particular the carbide, is formed. 5. Process according to claims 1 to 4, characterized in that the halides and the Carbon-containing gas are fed separately from one another to the deposition zone. 6. The method according to claims 1 to 5, characterized in that one of hydrogen gas mixture consisting of volatile carbon compounds is used, which is caused by passing over from hydrogen over carbon at a temperature at least so is as high as the temperature in the deposition zone. 7. Device for performing the method according to claims 1 to 6, characterized through a covered reaction vessel (5) with a central over a substantial part of the length of the container extending gas inlet pipe (2), the preferably enlarged end thereof (4) serves to accommodate the objects to be coated with a carbide. Pamphlets considered;
U.S. Patent No. 1987,576; / S * i
British Patent No. 589,977;
Transactions of the Faraday Society, 1950, pp. 190-199.