FI66656C - FOERFARANDE FOER TILLVERKNING AV TITANNITRIDBELAEGGNING VID LAG TEMPERATUR MED HJAELP AV GLIMURLADDNING - Google Patents

Description

1 66656

METHOD OF PREPARING A TITANIUM NITRIDE COATING AT LOW TEMPERATURE USING A GLOW DISCHARGE

The invention relates to a gloss discharge method for producing a wear-resistant titanium nitride coating. The method can be used to create a thin layer of titanium nitride on the surface of the workpiece by vaporizing titanium in a vacuum chamber and conducting 5 rackets of nitrogen gas there.

Efforts have been made to manufacture wear-resistant coatings in many different ways. It is already known that the so-called titanium nitride coating is suitable for the production of so-called Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) methods. CVD processes are now widely used in industrial applications for coating carbide cutting blades. However, the CVD process requires quite high temperatures (up to 1000 ° C or more) because the coating is based on the generation of a coating by a chemical reaction from gaseous starting materials. In this case, for example, the coating of hardened steel becomes difficult and requires additional heat treatment to maintain the strength of the base material. In addition, process gases (e.g., chlorine) may react with the parent material and carbon loss may also occur at high temperatures.

Due to the above, a lot of attention has been paid to the development of PVD processes operating at lower temperatures. Despite significant advances, these methods have so far not become widespread for industrial use in the coating of wear-resistant parts. The most common PVD methods in titanium nitride coating are the so-called sputtering methods (Thornton, 1981), activated reactive evaporation methods (Bunshah, 1981), and ion plating methods (Matthews, 1980).

30 The problem with the application of PVD methods has been that, with a few exceptions, process variables have so far not been able to be controlled as required by industrial production. Piece size has also been a problem. It has mainly been possible to handle small specimens or small tools.

5 It is essential in the application of said PVD or glow discharge methods to utilize plasma to effect the reactions required to form the coating. In order to obtain a dense layer of titanium nitride on the surface of the workpiece at low temperature, an appropriately sized ion current density and a uniform coating growth rate must be obtained for the workpiece. To achieve this, the glow discharge must be intensified and the collision density of titanium ions and atoms must be equalized for different parts of the body. For example, if the growth rate of the coating is too high, porosity and hardness may remain low in the coating (Kennedy and Scheuermann, 1975).

Various methods have been used to enhance glow discharge, such as low-voltage electron beam electron emission (Moll and Daxinger, 1980), additional hot electrodes (Matsubara, 1976), and these combined with a magnetic field (Tisone and Cruzon, 1975). For the same purpose, the so-called the use of a negative filament in ion plating (Matthews, 1980). Said method differs from the above-mentioned hot electrodes in that a separate positive target (anode) is not used at all.

The present invention uses a negative filament to enhance the glow discharge and, in contrast to a conventional high voltage ion plating (e.g.

4 kV), the voltage of the workpiece in the method according to the invention is only 0 - 500 V. The workpiece itself acts as a cathode, and the glow discharge surrounds only the workpiece as closely as possible. In the method according to the invention, by adjusting the temperature of the filament, the negative voltage with respect to the body and the current, the amount of electron in the gas plasma is increased, so that the number of positive ions also increases and a high ion current is obtained for a cathode with a small negative voltage.

The arrangement according to the invention has an ionic current adjustable independently of the voltage of the workpiece (cathode), whereby this additional possibility of adjusting the voltage can be used for precise control of the power and the temperature of the workpiece during coating.

In order for the structure of the coating to be similar in different parts of the body 10 to be coated, the ratio of titanium and nitrogen atoms and ions entering the surface must be the same at different points. This is especially true when dealing with large paragraphs. In the method according to the invention, the flow of titanium can be controlled by a shield which prevents atoms coming directly from the source of evaporation-15 from entering the surface of the workpiece. The nitrogen to titanium ratio can be further compensated by feeding nitrogen from several different points in the vicinity of the evaporation source.

With the arrangements according to the invention, i.e. a negative glow-20 wire, a low voltage of the workpiece, a direct evaporation-preventing shade and a uniform flow of nitrogen, the structure of the coatings produced by ion coating and its uniformity in different parts of the workpiece can be decisively improved.

In the following, the invention will be explained in detail with reference to the accompanying drawing. Figure 1 schematically shows the apparatus.

In the method, the workpiece 1 is connected to the cathode of an external DC voltage source 2. In the vacuum chamber 3, a glow discharge is formed around the kappa 30 to be coated as the ionizing nitrogen or nitrogen and argon gases introduced into the chamber from the multi-hole nozzle 4. The glow discharge is intensified by 4 66656 and is expanded in the chamber by filament 5. Titanium vapor-by-electron beam evaporator 6. The cathode and filament are insulated from the walls of the chamber by means of bushings 7. The pressure 5 of the chambers of the coating and electron beam evaporator is regulated by means of vacuum pumps 8. Collision of titanium atoms advancing directly from the evaporation source into the workpiece is prevented by a shade 9 which can be placed at the potential of the body or cathode.

During the coating process, a Torr 10 (0/13 ... 1/3 Pa) pressure is maintained in the chamber at 1 ... 10 m and the titanium is vaporized evenly, aiming at a growth rate of approx. 0/5 ym / min. The chemical structure of the coating can be adjusted by adjusting the proportion of nitrogen in the chamber. With an ion current density of 2 mA / cm and a cathode voltage of -300 V, a dense, small-grained and hard TiN coating is obtained at a temperature of 400 ° C.

The method according to the invention differs from the previous ones in that it can control the temperature of the body to be coated by adjusting the voltage without changing other quantities of the process. Likewise, the ionic current density, the evaporation rate of titanium and the amount of nitrogen introduced into the chamber can be adjusted independently of each other, making it possible to control the chemical composition and microstructure of the coating. In addition, the method according to the invention provides a uniform coating on all surfaces of a workpiece of even complex shape.

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Claims (1)

A method for producing a titanium nitride coating using glow discharge, wherein the voltage of the workpiece (1) to be treated is low (0-500 V), characterized in that a negatively charged filament (5) is used to enhance the glow discharge, and directly from the evaporation source (6) entry into the workpiece is prevented by a shade (9). For the purpose of measuring the titanium nitride charge with the result of gluten charge, variables of the lowering object (1 to 5 V), the voltage to be measured with the power amplifier in the case of the negative (5) the titanium vapor charge is shown at the end of the operation (3) on the other side of the object.