SK282806B6 - Process for producing wear-resistant boride layers on metal material surfaces - Google Patents

Abstract

The invention concerns a process for producing wear-resistant boride layers on metal material surfaces. The process is characterized in that boron halide selected from the group comprising boron trifluoride, boron tribromide, boron triiodide and their mixtures is mixed with hydrogen and optionally argon and/or nitrogen in order to produce a reaction gas containing between 0.1 and 35 vol. % boron halide. The resultant mixture is activated by a plasma discharge such that boron can be transferred from the plasma to the metal surface.

Description

Technical field

The invention relates to a process for producing boride layers on surfaces of abrasion resistant metal materials.

BACKGROUND OF THE INVENTION

The production of abrasion-resistant boride layers is practically carried out mostly using solid boronizing materials, for example in the form of powders, pastes or granules.

These methods require disadvantageously high labor costs for packaging, unpacking and cleaning the parts. Cleaning is carried out using a combination of washing and brushing or throwing. Since powders, pastes and granules are only once to be used, problems also arise in the disposal of spent boronizing agent.

In addition, it is also known to use liquid boronizing agents, for example in the form of salt melts. However, not all these processes can be carried out due to the problems inherent in salt baths with regard to the safety of use, cleaning of parts after processing and disposal of the baths or their degradation products.

Accordingly, various boronization experiments were carried out with gaseous boronizing agents (CVD procedure). The use of organic boron compounds (borotrimethyl, bortrialkyl) is predominantly carburized instead of boration, and the use of diborane leads to safety-related technical problems due to toxicity and the risk of explosion.

The use of boron trichloride as the boron-providing medium cannot be enforced due to the operational problems of layer formation. The origin of these problems is the formation of hydrogen chloride occurring during boronization in BC1 ₃ - H ₂ mixtures.

The following basic reactions take place in the boronization of iron-based materials with boron trichloride:

BC1 ₃ + 3 H ₂ + 2 Fe-> 2 FeB + 6 HCl

BC1 ₃ + 3 H ₂ + 4 Fe -> 2 Fe ₂ B + 6 HCl.

Hydrogen chloride gas, produced by boron trichloride boronation, reacts with the iron of the base material to form a readily volatile ferrous chloride:

HCl + Fe -> FeCl ₂

The iron chlorides have high vapor pressures at treatment temperatures in the range of 500 ° C to 1200 ° C, which are considered in use, so that the iron chlorides evaporate constantly. This leads to the formation of holes between boride layer and the underlying material, which is always criticized as failing in the BC1 ₃ - process. Suppression of hole formation is only possible when a tightly sealed boride layer is produced within a short time at the start of the boration. This is so operationally and technically difficult that it has not been reliable and reproducible so far.

In addition to the purely thermal variant of CVD-boration, plasma-assisted boronation (PACVD-boration) experiments are also known. Here, only diborane and boron trichloride were used, with the disadvantages already known from the thermal CVD process. A summary of known procedures is found in the review of "Engineering the Surface with Boron Based Materials", Surface Engineering 1985, Vol. 1, no. 3, p. 203-217.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process for the production of abrasion-resistant boride layers on metal materials without the disadvantages of the aforementioned disadvantages.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a process comprising mixing at least one boron halide selected from the group consisting of boron trifluoride, boron tribromide and boron iodide with hydrogen and optionally argon and / or nitrogen as the boron carrier. % of the reaction gas containing 1 to 35% by volume of boron halide and the mixture thus obtained is activated by a plasma discharge so as to allow boron to pass from the plasma to the metal surface.

The reaction gas may additionally contain boron trichloride as the boron carrier.

Preferably, the reaction gas contains 5 to 20% by volume of boron halide, particularly preferably 5 to 15% by volume of boron halide.

Preferably, the reaction gas contains 20 to 90% by volume of hydrogen, particularly preferably 20 to 50% by volume of hydrogen.

Preferably, the reaction gas comprises boron trifluoride.

Boron trifluoride is particularly preferably used as the boron halide.

The reaction gas is fed to the treatment area in an amount of preferably 0.5 to 2 L per minute, particularly preferably about 11 / min.

The boration is preferably carried out at a pressure in the range of 0.1 to 1.0 kPa under the action of a plasma discharge, such as is known from a plasma coating apparatus.

The required processing temperatures, preferably 400 ° C to 1200 ° C, particularly preferably 850 ° C to 950 ° C, are achieved by means of plasma alone or, in particular, in the high temperature region above 900 ° C with the aid of additional heating.

The processing time is preferably 30 to 240 minutes, particularly preferably 30 to 120 minutes.

The thickness of the boride layer is usually governed by the processing time, and with increasing processing time the thickness of the layer also increases.

As further gases, the reaction gas may also contain argon and / or nitrogen. This can control boron transfer activity and achieve sufficient heating of the samples by plasma. The composition of the reaction gas can thus vary within wide limits, depending on the processing conditions and the boridized material.

The process of the present invention is particularly suitable for boronizing ferrous materials.

In the process of the present invention, the hydrogen molecules contained in the reaction gas are converted to atomic hydrogen by means of a plasma discharge. Atomic hydrogen reduces boron halide (BY ₃ ) and thus allows the transfer of hydrogen to the surface of the material to be treated. This transfer can be illustrated by the following reaction scheme:

ΒΥ ₃ + 3 H-> B + 3 BY

B + _x Me -> Me _x B.

It is also possible to convert BY ₃ to BY ₂ by plasma, whereupon the following reactions can take place:

BY ₂ -> B + 2 BY ₃

B + x Me-> Me _x B.

Following the boronization, the boronized material can be subjected to a post-treatment to convert eventually formed FeB to Fe ₂ B. time at processing temperature. The time of this diffusion treatment depends on the amount of FeB present and is usually 20 to 60 minutes.

The process according to the invention can be carried out, for example, in a known apparatus suitable for plasma coating. This consists essentially of the following components:

- From a vacuum reactor (reactor) for feeding workpieces. The reactor should be heatable and allow working at temperatures between 400 ° C and 1200 ° C.

- From a pump system to evacuate the reactor and adjust the working pressure.

Gas supply units for mixing and dispensing the reaction mixture.

From a pulse-plasma-current supply to produce and maintain the plasma discharge in a vacuum recipient, the power used may vary in pulse frequency or pulse width over a wide range.

- From the gas neutralization and disposal system as well as the system for managing and controlling the operating parameters that control and control the process.

Claims (5)

PATENT CLAIMS Method for producing boride layers on surfaces of abrasion-resistant metal materials, characterized in that boron trifluoride is mixed with boron trifluoride with hydrogen and optionally argon and / or nitrogen for the preparation of a reaction gas containing 1 to 35% by volume of halide of boron and the mixture thus obtained at a pressure of 0.1 to 1.0 kPa by means of a plasma discharge converts molecular hydrogen into atomic hydrogen and this reduces boron trifluoride, thereby allowing boron to pass from the plasma to the metal surface. The process according to claim 1, wherein the reaction gas contains 20 to 90% by volume of hydrogen. Process according to one or both of Claims 1 and 2, characterized in that the reaction gas is introduced into the treatment area in an amount of 0.5 to 2 l per minute. Process according to one or more of Claims 1 to 3, characterized in that the reaction is carried out at a temperature in the range of 850 to 950 ° C. Method according to one or more of Claims 1 to 4, characterized in that the processing time is 30 to 240 minutes. DETAILED DESCRIPTION OF THE INVENTION Example 1 After the 100Cr6 steel sample was fed to the reactor, a constant pulse frequency (4 kHz) DC mica discharge at 1.0 kPa pressure was performed in the plasma. Heating of the sample is performed additionally through the heating of the reactor, thereby reducing the heating time. The sample is heated and cooled in a 1: 1 mixture of argon and hydrogen. After reaching a treatment temperature of 850 ° C, the boron trifluoride support is added to form a reaction mixture of 45% hydrogen, 40% argon and 15% fluoride. boron. The gas mixture is fed to the recipient at 1 L / min. The plasma treatment time is 200 minutes. A metallographic cut revealed a boride layer with a mean thickness of 42 µm. The microhardness is around 1800 HV ₀₀₅ . The layer does not contain FeB. Example 2 After the sample from Hastelloy B was fed into the reactor, a constant pulse frequency (4 kHz) DC mica discharge was performed in the plasma. Using a plasma discharge at 1.0 kPa, the sample is heated to 850 ° C. The energy density is controlled over the pulse width. The sample is heated only through mica discharge. The sample is heated and cooled in a 1: 1 mixture of argon and hydrogen. After reaching the treatment temperature, the boron boron trifluoride support is added to form a reaction mixture of 45% by volume hydrogen, 45% by volume argon and 10% by volume boron trifluoride. The gas mixture is fed to the recipient at 1 L / min, the treatment time is 240 minutes. A metallographic cut revealed a boride layer with a mean thickness of 50 µm. The microhardness is around 2400 HVo.os.