Process for the manufacture of wear resistant binding materials.

The invention relates to a method for producing wear-resistant composite materials on a substrate made of a metallic solid, wherein in a recipient a volatile compound of the hard-material forming metal is energized and applied as a wear-resistant coating on the substrate and the energy supply at least partially with a plasma CVD method.

The production of wear-resistant composite materials, which consist of a substrate or core of a metallic solid, in particular steel, hard metal, aluminum or titanium and have one or more surface layers, is of great importance in practice, for example for the coating of workpieces for production of particularly hard or wear-resistant wear layers. As practical examples, tools such as. B. Mills or drills are given, which are used for about machining.

The production of such composites is currently done using known technologies, including, for example, chemical or physical vapor deposition, which is referred to as CVD and PVD processes.

However, these known methods each have specific disadvantages that do not meet the requirements of practice.

In the case of the CVD processes in which the deposition takes place on the basis of a chemical reaction, it is true that the advantage is that the wear-resistant hard material can be applied to a substrate with a uniform layer thickness. The disadvantage here, however, that the end of the required reaction, high temperatures in the order of 1000 ° C are required. For example, when steel is used as the substrate, vapor deposition by CVD at high temperatures results in subsequent heat treatment of the steel substrate. The coating of precision tools made of steel is therefore not readily possible because warpage due to the heat treatment is virtually unavoidable.

In contrast, the PVD processes, which include, for example, sputtering and ion plating, operate at much lower temperatures. Normally, the upper limit for the temperatures used is about 5500 C, since this temperature value also represents the upper limit for tempered HSS steels or high-speed steels. However, the PVD method are not free of disadvantages, because it arises, for example, the difficulty to coat the respective workpieces with a uniform layer thickness In the specified variants of the PVD process also shadowing are very common because the vaporized metal atoms or hard material molecules from their source straight on the respective substrate zuliegen.

In order to take advantage of the advantages offered by the CVD process on the one hand and the PVD process on the other hand, namely uniform thickness on the one hand and low coating temperature on the other hand, the plasma CVD process has been developed in which the CVD processes Plasma, more specifically supported by the energy that is in the plasma.

Namely, in the plasma CVD method, the activating energy required for the reaction is not thermally supplied to the volatile gases and metal compounds which are in the recipient and serve to coat the respective substrate, but by the generation of a low-pressure plasma. Such a plasma can be generated either by dc glow discharges or by high-frequency discharges, wherein the high-frequency discharges are more universally applicable, as can be deposited in this way, non-conductive substances n Although the application of plasma CVD method is predominantly in the field of electronic and optical coatings, but also applications in the field of wear-resistant layers have become known. In this case, layers of the hard material titanium nitride have been deposited or deposited on a substrate using DC glow discharges.

Analogous to the conventional CVD process thereby titanium tetrachloride, hydrogen, nitrogen and possibly. Argon in the plasma generated by the DC glow discharge reacted, which is reflected on the substrates in the plasma, the substance titanium nitride Although it can be used with relatively low substrate temperatures of 3000 C - 5000 C, the known method is not free of serious disadvantages, because on the one hand chlorine is incorporated into the hard material layers, on the other hand, hydrogen chloride occurs as a corrosive by-product. The chlorine comes from the titanium tetrachloride, one of the few volatile titanium compounds, the need in the previous process was essential.

The object of the invention is therefore to provide a method for producing particularly high-quality wear-resistant composite materials and a long service life.

While the use of titanium tetrachloride or of titanium halides has heretofore been considered necessary, it has been found in the invention that the use of oxygen-containing titanium compounds leads to excellent results in the production of wear-resistant composites. Such oxygen-containing titanium compounds include the group of alkoxides and acetylacetonates. The titanium isopropylate (Ti (OPrl) 4) is the easiest to handle, since it has the highest vapor pressure of all compounds of this type.

Particularly useful in this case has proved the presence of hydrogen as a reducing agent.

The use of oxygen-containing titanium compounds to produce Ti-type (C, N) hard coatings has hitherto not seemed expedient, since titanium alkoxides are known to be used to produce corrosion-inhibiting titanium dioxide layers but, as relatively soft layers, have no increased wear resistance.

According to US Pat. No. 4,297,150, the formation of relatively soft titanium dioxide layers takes place by purely thermal excitation.

The reason for this is that the titanium dioxide is the thermodynamically most stable compound of the Ti / N / O / C / H system, with the titanium dioxide then forming, although only the activation energy necessary for the reaction can be applied.

Surprisingly, however, it was found within the scope of the invention that for temperatures above 2,000 K to 3,000 K, the formation of the hard materials TiN, TiC and TiO from the alkoxides becomes possible if hydrogen is present as the reducing agent.

Although the formation of TiN from the thermal conversion of titanium acetylacetonate, nitrogen and hydrogen has already been described in DE-PS 600 374, on the one hand temperatures of more than 1 2000 C are required, on the other hand, the formation of considerable amounts of undesired material has occurred , relatively soft titanium dioxide. The method described there was therefore unsuitable for practical application and has not been used for this reason.

Only in the context of the invention has surprisingly been found that the previously unthinkable reaction of the titanium alkoxide to hard titanium carbonitride is readily possible by the aid of a plasma which generates particles with an energy corresponding to a temperature of several 1,000 K.

The performance of the coating takes place in a vacuum recipient in which a plasma is generated with either a DC glow discharge or a high-frequency discharge. The metering of the gases argon (Ar), hydrogen (H2), nitrogen (N2) and methane (CH4) takes place via commercially available flow meters. The metering of the titanium alkoxide or titanium acetylacetonate is effected by the saturation of a gas stream, advantageously an inert gas stream. This gas stream bubbles through a heated container with the liquid alkoxide od. Like. And is cooled in a recooler to a defined temperature. Thus, a saturated gas stream can be produced which contains an amount of this substance which can be calculated via the vapor pressure of the alkoxide or the oxygen-containing volatile compound.

The solution according to the invention consists in using, as compound, an oxygen-containing volatile compound of the hard-material-forming metal and in that the reaction proceeds at a temperature of the order of from room temperature to about 600 ° C., in particular at about 5000 ° C.

In a further development of the process according to the invention it is provided that the oxygen-containing volatile compound Ti (OR) 4 is used, wherein for R the radicals -CH3, C -nC3H7, -iC3H7, -nC4Hg, -iC4H95 -tC4H9 or -CH2CH (C2H5) C4Hg can be used.

It is particularly advantageous if titanium isopropoxide used as the oxygen-containing volatile compound is used. In a further development of the process according to the invention, the volatile metal compound is an alkoxide and / or acetylacetonate of the elements Ti, Zr, Hf, V, Nb, Ta, Cr and / or W is used. The invention is therefore in no way limited to the use of titanium as a hard material-forming metal.

It is particularly advantageous if the reaction for reacting the oxygen-containing compound of the hard-material-forming metal proceeds in the presence of hydrogen as the reducing agent. The invention will be explained in more detail below, also with regard to further features and advantages, with reference to the description of an exemplary embodiment. The sole figure of the drawing shows schematically the structure of an arrangement for carrying out the method according to the invention.

In the drawing, the device is generally designated by the reference numeral 10, which may be a commercially available plasma nitriding. A recipient 12 is optionally provided with a heating device 14 and has in its interior a substrate holder 16, on which the respective samples can be arranged.

At the bottom of the recipient 12 can be seen an insulator 18; For generating the plasma in the recipient 12 supply lines 19 and 21 are provided which are connected to a power supply 20, for example a DC power supply, wherein the housing wall of the recipient 12 is connected as an anode and is at ground potential.

The recipient 12 can be evacuated via suction lines 23 and 25, possibly with the interposition of a separator 22, which may be a dust separator and / or a cold trap, with a pump which is indicated schematically by the arrow 24 , The supply of the respective substances in the interior of the recipient 12 is carried out with a line system, which is shown schematically in the drawing in the left area. In this case, supply lines 26, 28 and 30 are provided, which serve for example for the introduction of argon, nitrogen and hydrogen. In a container 32, which may be equipped with a heating device, not shown, there is a liquid, for example, consists of liquid alkoxide and through which the mentioned gas stream bubbles through, finally to get over the main feed line 50 into the recipient 12.

The valves in the respective lines are provided with the reference numerals 36, 37, 38, 39, 40 and 41, while pressure gauges are denoted by the reference numerals 43 and 44. Further, in the supply line from the container 32, a cooling device 34 is provided to the with the Alkoxide or the like.

saturated gas flow to a defined temperature.

To produce the wear-resistant composite materials with the method according to the invention, the samples to be treated, after thorough cleaning, in particular degreasing, are arranged on the cathode in the above-described commercial plasma nitriding system. This may be the substrate holder 16 schematically indicated in the drawing. After the evacuation of the recipient 12, hydrogen (H2) or argon (Ar) is first introduced, with a pressure of the order of about 1 mbar. The DC glow discharge is then ignited. The cathode heats up due to the electrical power supplied by the glow discharge including the samples of steel or carbide to the desired temperature.

The temperature control can be carried out in a manner not shown with a thermocouple, which is placed in a reference sample on the substrate holder. The pressure prevailing in the interior of the recipient 12 pressure is then increased gradually and gradually, for example, to a pressure of 5 mbar at a temperature of about 5000 C When the desired set temperature is reached, the influx of hydrogen or Interrupted argon and then introduced a defined gas mixture in the recipient, in one embodiment, a mixture of hydrogen (H2), nitrogen (N2) and titanium isopropoxide (Ti (OPrl) 4; in the ratio of 140: 20: 1 introduced via the heated main supply line 50 to just before the samples 12 located in the recipient.

The glow discharge is then maintained for a period of six hours at a temperature of 5000 C and a pressure of 5 mbar. Subsequently, the supply of the gas mixture is stopped and the DC voltage of the DC power supply 20 is turned off. After cooling the assembly to room temperature, the recipient 12 is vented and the samples taken.

On the samples is a reddish glossy layer, which was then examined more closely. The determination of the surface hardness resulted in a Vickers hardness of 1 900 HV ,, 015 for the wear-resistant composite material produced according to the inventive method. By comparison, the hardness of an uncoated substrate was determined to give a Vickers hardness of 260 HV 015.

Furthermore, a roentgenographic examination was carried out in order to obtain further information on the wear-resistant composite material produced according to the invention. The investigation revealed two reflections that coincide with the (111) and (200) planes of the TiC, TiN or TiO titanium insertion compound.

Further, a metallographic examination revealed that the applied wear-resistant coating had a coating thickness of 2-3 μm and showed good homogeneity.

An analysis of the film by a GDOES (Glow-Off Optical Emission Spectroscopy) method revealed 46 atomic% of Ti, 40 atomic N, 8 atomic% C, and 0 and Fe trace. Also, in the above-described embodiment, titanium isopropylate is used as the oxygen-containing volatile compound was used, the inventive method is by no means limited to such a substance. Other alkoxides as well as acetylacetonates can also be used. However, at the same mixing ratio, because of the lower vapor pressure, the temperatures of the evaporator and the pipeline to the recipient must be increased accordingly. It should also be noted that not only the volatile, oxygen-containing compounds of titanium are useful for forming the hard coatings, but others can Metals or oxygen-containing compounds of the hard-material-forming metals are used, such as, for example, the volatile alkoxides and / or acetylacetonates of the hard-material-forming elements Zr, Hf, V, Nb, Ta, Cr and / or Wo The reaction conditions are then adjusted accordingly. Meissner & Bolte Reference numeral 10 Device 12 Receiver 14 Heating device 16 Substrate holder 18 Insulator 19 Line 20 Power supply 21 Line 22 Separator 23 Suction line 24 Pump 25 Suction line 26 Supply line 28 Supply line 30 Supply line 32 Container 34 Cooling device 36 Valve 37 Valve 38 Valve 39 Valve 40 Valve 41 Valve 43 Pressure gauge 44 Pressure gauge 50 Main supply line - Empty side -