KR100317730B1 - Oxidation film of fomation method - Google Patents

Abstract

The present invention relates to a method for forming an oxide film, by presenting a concrete alternative for the porosity control of the nitride layer and the phase control of the oxide layer, the adhesion between the nitride layer and the oxide layer, which is a problem in the conventional plasma nitriding and oxidation process. Its purpose is to be able to form an oxide film that is greatly improved than conventional ones in wear characteristics. The present invention configured for this purpose is a step of removing an oxide film on the surface of the sample by a sputtering process, injecting a nitriding gas, but applying a voltage of less than 550V in a temperature range of 500 to 550 ° C to form a dense compound layer on the surface of the sample. In order to facilitate the diffusion of Fe and O ions after forming a compound layer on the surface of the sample, the amount of nitrogen is increased by 100 sccm or more, the temperature is increased by 10 to 20 ° C. and the voltage is increased by 10 V or more, at least 2 μm. Process of forming the above-mentioned porous nitride layer, process of injecting oxidizing gas consisting of oxygen and water vapor alone or a suitable mixture thereof as an oxygen supply source, plasma oxidation treatment by applying a voltage of 400 to 700V in an oxidizing gas atmosphere First oxidation process with oxygen or water vapor flow rate less than 200 sccm in the first half of the time. It includes a step of reducing the flow rate of oxygen or water vapor to be supplied to proceed with the oxidation reaction at a slow rate for 2/3 hours of the remaining process to form an oxide film and to inject nitrogen gas to cool the sample.

Description

OXIDATION FILM OF FOMATION METHOD

The present invention relates to a method of forming an oxide film, and in particular, to increase the supply of Fe ions or atoms by making the nitride layer have sufficient porosity, while controlling the oxidation reaction rate using hydrogen during the oxidation process, only the desired magnetite single phase can be formed. The present invention relates to an oxide film forming method.

In general, surface treatment is a treatment to give abrasion resistance, corrosion resistance, heat resistance, and lubricity to a surface of a sample (a surface treatment object, that is, a metal material to be heat treated, such as a tool steel or a mechanical part). And other adjustments for corrosion protection, plating, cleaning, coating, coloring and painting.

On the other hand, the above-mentioned hardening treatment of the sample surface includes heat treatment hardening methods such as carburizing, nitriding, nitriding, cyaniding, and metal impregnation. There is this. Here, the heat treatment refers to a heating and cooling process performed in order to obtain the mechanical properties required for use of the part or tool.

In the above-mentioned hardening treatment of the metal surface, carburization is one of the oldest surface hardening methods, and carbon is heated into a steel by heating to a high temperature in a state in which a low carbon steel is brought into contact with a material composed of carbon such as charcoal. To be absorbed.

Among the hardening methods of the metal surface, the nitriding method is used in all industries as a means of extending the life of mechanical parts because there is less deformation after treatment than other heat treatment hardening methods. Nitriding refers to the operation of hardening the surface by infiltrating nitrogen into a metal material. Nitriding using plasma involves hardening the active ions by plasma discharge into the metal surface and installing the metal material in the reactor. The surface of the metal material is heated by heating a vacuum reactor at a constant reaction temperature in one state, injecting a nitriding gas into the reactor, and applying a constant pulsed negative voltage to the metal material to generate a plasma. Curing

In particular, conventional techniques for producing a sample having excellent wear resistance, oxidation resistance and fatigue resistance using plasma are as follows.

First, the technique disclosed in Korean Patent Application No. 98-54911 uses a plasma to form a nitride layer on the surface of a sample and then subjects the oxidation process to a plasma state to form a magnetite (Fe ₃ O ₄ ) film to wear The present invention relates to a surface treatment method for making a sample having excellent properties, oxidation resistance and fatigue resistance. The above-mentioned technology of Korean Patent Application No. 98-54911 indicates that it is the same application as the applicant.

The technique of US Pat. No. 4,496,401 relates to a method of nitriding an unalloyed steel to form an ε-nitride layer and then oxidizing to form an oxide film composed of Fe ₃ O ₄ and cooling it in oil or water.

The technique of US Pat. No. 4,596,611 relates to a method of forming an epsilon compound on the surface of a sample through gas nitriding, cooling the sample, finishing it with surface polishing, and oxidizing it.

The technique of US Pat. No. 4,881,983 relates to a method of surface treatment by forming an oxide film composed of Fe ₃ O ₄ after generating an ε-nitride layer or an ε-carburized nitride layer on the surface of a part.

The technique of US Pat. No. 5,679,411 relates to a method of softening an iron material, activating it with plasma, and then oxidizing it to have corrosion resistance and wear resistance.

The technique of Korean Patent Publication No. 95-10239 uses ε-nitride containing an oxide layer and oxygen on the surface by oxidizing and nitriding steel parts simultaneously by directly injecting air or air and propane gas into ammonia gas. The present invention relates to a method for manufacturing a plating-replacement steel part for forming a layer or an ε-carburized nitride layer containing oxygen to finish the surface of a sample.

However, as described above, in the plasma nitriding (soft nitriding) and oxidation complex process, due to the compact structure of the plasma nitriding and soft nitriding layers, the amount of Fe supplied due to the decomposition of the compound layers (Fe ₃ O ₄ , Fe ₄ N) is small. In addition, the characteristics of the oxide film are not dense, and the corrosion property of hematite (Fe ₂ O ₃ ), which is relatively poor compared to the magnetite (Fe ₃ O ₄ ) phase, occurs.

On the other hand, in the problem of adhesion with the nitriding layer, there is a problem in that a phenomenon in which peeling occurs more easily than gas oxidation using water vapor on the porous nitride layer formed after gas nitriding.

The present invention has been devised to solve the above problems, and proposes specific alternatives for controlling porosity of the nitride layer, phase control of the oxide layer, and improving adhesion between the nitride layer and the oxide film, which are problematic in the conventional plasma nitriding and oxidation process. It is an object of the present invention to provide an oxide film formation method capable of forming an oxide film that is significantly improved in corrosion resistance and abrasion resistance than the conventional.

The present invention configured to achieve the above object is a step of removing the oxide film on the surface of the sample by the sputtering process by inert gas at the carburizing temperature, injecting nitriding gas into the chamber after the sputtering process in the temperature range of 500 ~ 550 ℃ In the process of forming a dense compound layer on the surface of the sample by applying a voltage of less than 550V, and the process of forming a dense compound layer to facilitate the diffusion of Fe and O ions after forming the compound layer on the surface of the sample, A process of forming a porous nitride layer by raising or increasing the voltage, injecting oxidizing gas composed of oxygen or water vapor alone or a suitable mixture thereof as an oxygen supply source in a chamber, and applying a voltage of 400 to 700 V in an oxidizing gas atmosphere. Plasma oxidation treatment, but the flow rate of oxygen or water vapor is 200sc In the process of primary oxidation with less than cm, reducing the flow rate of oxygen or water vapor supplied at the time of primary oxidation and proceeding the oxidation reaction at a slow rate for 2/3 hours of the remaining processes to form an oxide film and inside the chamber Nitrogen gas is injected to cool the sample having the nitride layer and the oxide film formed thereon.

In order to accelerate the nitriding reaction of the above-described nitriding process, a mixed gas containing ammonia (NH ₃ ) may be used instead of nitrogen (N ₂ ).

In the process of forming the porous nitride layer, the amount of nitrogen is increased by 100 sccm or more, the temperature is increased by 10 to 20 ° C. or more, and the voltage is increased by 10 V or more. In this way, a porous nitride layer of at least 2 μm or more can be formed.

Nitriding gas may be made of nitrogen (N ₂ ), hydrogen (H ₂ ), methane (CH ₄ ) alone or a mixture thereof.

Hydrogen gas may be further added to the oxidizing gas injection process as the oxygen supply source.

In the process of injecting the oxidizing gas, the flow rate of hydrogen is preferably in the range of 100 to 1000 sccm per unit volume (m ³ ) of the chamber, based on the processing pressure of several Torr.

Hereinafter, an oxide film forming method according to a preferred embodiment of the present invention will be described in detail.

In the method for forming an oxide film according to the present invention, first, a sample (oral cavity and a mechanical part) is placed in a chamber, vacuumed and evacuated at an appropriate vacuum pressure, and then heated to a suitable temperature of 500 to 570 ° C.

On the other hand, while heating the sample, while maintaining the inert gas at a predetermined pressure, a predetermined voltage is applied to the power supply device to sputter the surface of the sample to reduce the ion bombardment effect in the vacuum. Cleaning method by heating or sputtering after raising the temperature to the carburizing temperature to remove impurities such as an oxide film on the surface of the sample. At this time, the inert gas for sputtering consists of CO ₂ , CO, Ar, H ₂ gas alone or a suitable mixture thereof.

After sputtering the surface of the sample, a nitriding gas is injected into the chamber and a plasma is generated by applying a constant voltage to a supply device (or a pulsed power supply), while nitride is nitrided on the surface of the sample through nitriding and soft nitriding by plasma. The layer {ε phase (Fe _2-3 N) or γ 'phase (Fe ₄ N)} is formed. At this time, the nitriding and soft nitriding process by plasma is performed by the following two processes.

That is, it can be divided into a process for forming a compound layer on the surface of the sample and a process for forming a porous nitride layer. First, the process for forming the compound layer using a reaction gas consisting of nitrogen (N ₂ ), hydrogen (H ₂ ) or nitrogen (N ₂ ), hydrogen (H ₂ ), methane (CH ₄ ) alone or a mixture thereof However, in the temperature range of 500 to 550 ° C., the ratio of nitrogen and hydrogen is limited to 8: 2 or less, and a process for obtaining a dense compound layer in the voltage range as low as possible below 550V.

On the other hand, the process of forming the porous nitride layer is to increase the amount of nitrogen more than 100sccm, increase the temperature 10 ~ 20 ℃ or more than 10V or more voltage than the process for forming the compound layer in order to facilitate the diffusion of Fe and O ions It is a process for forming a porous nitride layer of at least 2㎛ higher.

At this time, in the process for forming the compound layer in the above-described process by using a mixed gas containing ammonia (NH ₃ ) as a nitrogen source in place of the nitrogen source to proceed the nitriding reaction quickly to form a porous nitride layer.

As described above, after performing the nitriding and soft nitriding process, a post-oxidation process is performed on the surface of the sample. The post-oxidation process is performed by injecting an oxidizing gas into the chamber, by performing a first oxidation treatment, and by forming an oxide film. .

In the process of injecting the oxidizing gas of the post-oxidation process into the chamber, oxygen or water vapor is injected into the oxygen supply source. At this time, hydrogen may be supplied in addition to steam or oxygen gas as an oxygen source for phase control of the oxide film. When hydrogen is supplied together with steam or oxygen gas, the oxidation reaction is controlled through a rate control function of hydrogen. It can progress slowly, and production of hematite (Fe ₂ O ₃ ) can be sufficiently suppressed.

After the oxidizing gas injection process, plasma oxidation treatment is performed by applying a voltage of 400 to 700 V in an oxidizing gas atmosphere, but the primary oxidation process is performed by reducing the flow rate of oxygen or water to less than 200 sccm in the first third of the entire processing time. Then, the flow rate of the oxygen or water vapor supplied is reduced than in the first oxidation process, and the second oxidation reaction is performed at a slow rate for 2/3 hours of the remaining processes to form an oxide film.

Then, nitrogen gas is injected into the chamber to cool the sample having the nitride layer and the oxide film formed thereon.

Referring to the oxide film forming method of the present invention in more detail as follows. In other words, in order to form the oxide film composite layer, three steps of sputtering, nitriding, and post-oxidation are performed. Considering that the nitride layer functions as an intermediate layer with the base metal, it is considered that the more dense and fine pores exist in the structure, the more favorable the oxidation reaction is in the case where the nitride layer is porous in the subsequent oxidizing atmosphere.

In other words, the more porous the nitride layer is, the more the actual area exposed to the oxidizing atmosphere increases, so that the supply of Fe atoms or ions is facilitated, and oxygen also penetrates deep into the pores to form an oxide film, thereby greatly improving the bonding strength between layers. Because.

Therefore, in the existing oxide film formation method, it is preferred that gas nitriding, which essentially has a porous structure, is preferred.

However, as mentioned above, in order for the nitride and oxidized composite layers to function as well as the formation of the oxide film, the nitride layer must have sufficient abrasion resistance and corrosion resistance as an intermediate layer. I can think of it.

In other words, the inner layer where the nitride layer is formed is treated with denseness to have sufficient mechanical properties, and the outer layer where the oxide film is formed increases the amount of nitrogen supplied to have sufficient microporousity with respect to 3 to 4 µm or increases the temperature or voltage. By raising, nitrification proceeds at high speed to finish the outer layer of the compound layer. By using ammonia (NH ₃ ) as a nitrogen source for plasma nitridation instead of controlling these process variables, it is possible to form a porous nitride layer with rapid growth rate, thereby promoting the formation of the magnetite film and reducing the time for the surface treatment process.

On the other hand, if hydrogen is supplied in addition to water vapor or oxygen gas as an oxygen source for phase control of the oxide film, the oxidation reaction can be slowed through the oxidation reaction rate control function by hydrogen and hematite (Fe ₂ O). ₃ ) generation can be sufficiently suppressed. At this time, the flow rate ratio of hydrogen and oxygen, hydrogen and water vapor used is influenced by the processing pressure, the area of the sample, the size of the chamber and the temperature, but can usually form a magnetite single phase if it is at least 9: 1 and 2: 1 or more. However, when the amount of hydrogen is too large, the oxidation reaction is suppressed to slow down the growth rate of the oxide film, so that the thickness of the film is rather thin at the same processing time.

It can be expected that the time when the oxide film is first formed and the situation in which Fe and O react with each other after the oxide film entirely covers the nitride layer and grows uniformly will be different. In other words, after the oxidation reaction, Fe atoms or ions diffuse through the oxide film of dense structure and react with oxygen on the surface of the sample. Therefore, the supply of Fe decreases from the beginning, so that the relative amount of oxygen increases when oxygen is continuously supplied in the same amount. Undesired hematite (Fe ₂ O ₃ ) can be formed together. After plasma oxidation for 10 minutes at pressure of 3 Torr, flow rate of oxygen and hydrogen at 100: 900 sccm, and then for 20 minutes, the amount of oxygen was reduced in half and tested at the same voltage, pressure and temperature conditions. The magnetite film of the structure was obtained. At this time, the treatment pressure, the flow rate ratio of oxygen and hydrogen, and the treatment time may be changed according to the combination of the remaining oxidation process parameters of the pretreatment process including the type and nitriding of the specimen.

As described above, the oxide film forming method according to the present invention can form an oxide film having high wear resistance and high corrosion resistance.

On the other hand, look at the relationship between the present invention and the prior art as follows. In other words, the oxidation process after nitriding is common with the prior art, whether it is a gas-based method or a plasma treatment. The process can be seen that the direct application of domestic patent No. 98-54911. However, in the conventional patent, due to the dense structure formed by the plasma process compared to the case of using gas nitriding and gas oxidation, the amount of Fe atoms or ions supplied is rather small, so that the structure of the oxide film is not dense and the corrosion characteristics are relatively poor. Hematite (Fe ₂ O ₃ ) is likely to be mixed and may be formed in a poor adhesion.

However, the present invention describes that the influence of the porosity of the nitride layer and the rate control of the oxidation reaction must be considered in order to obtain an oxide film capable of satisfying high abrasion resistance and high corrosion resistance characteristics, and a new process method necessary for this is specifically described. Presented as.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical idea of the present invention.

As described above, according to the present invention, it is possible to sufficiently increase the supply of Fe ions or atoms by increasing the processing voltage, the pressure, the temperature of nitrogen, etc. so as to have sufficient porosity, or rapidly nitriding the ammonia instead of nitrogen. have.

On the other hand, by controlling the oxidation reaction rate by using hydrogen during the oxidation process there is an effect that can form a desired magnetite single phase to have more excellent corrosion resistance.

Therefore, the oxide formed as described above has a dense structure due to the advantages of plasma nitriding and grows uniformly in the nitride layer, thereby exhibiting high wear resistance and high corrosion resistance characteristics than the oxide film treated with only water vapor, oxygen, or air. There is.

In addition, the present invention is not only the film properties but also the process itself is environmentally friendly and can be processed at low temperatures because it uses a plasma, less deformation and no post-processing can be expected economic effects.

Claims (6)

Removing an oxide film on the surface of the sample by a sputtering process using an inert gas at a carburizing temperature; Injecting nitriding gas into the chamber after the sputtering process and applying a voltage of less than 550 V in a temperature range of 500 to 550 ° C. to form a dense compound layer on the surface of the sample; Forming a porous nitride layer by increasing the amount and temperature of nitrogen or increasing the voltage than in the step of forming the dense compound layer to facilitate diffusion of Fe and O ions after forming the compound layer on the surface of the sample; Injecting an oxidizing gas composed of oxygen or water vapor alone or a suitable mixture thereof into an oxygen supply source into the chamber; Performing a plasma oxidation treatment by applying a voltage of 400 to 700 V in the oxidizing gas atmosphere, but performing primary oxidation with a flow rate of oxygen or water vapor less than 200 sccm in the first third of the entire processing time; Reducing the flow rate of oxygen or water vapor supplied during the first oxidation process to perform an oxidation reaction at a slow rate for 2/3 hours of the remaining processes to form an oxide film; And And injecting nitrogen gas into the chamber to cool the sample having the nitride layer and the oxide film formed thereon. The method of claim 1, wherein a mixed gas containing ammonia (NH ₃ ) is used instead of nitrogen (N ₂ ) to accelerate the nitriding reaction of the nitriding process. 3. The method of claim 2, wherein the amount of nitrogen in the process of forming the porous nitride layer is increased by 100 sccm or more, the temperature is increased by 10 to 20 DEG C or more, and the voltage is increased by 10 V or more. The oxide film according to any one of claims 1 to 3, wherein the nitriding gas comprises nitrogen (N ₂ ), hydrogen (H ₂ ), methane (CH ₄ ) alone or a mixture thereof. Formation method. 5. The method of forming an oxide film according to claim 4, wherein hydrogen gas is further added to the oxidizing gas injection step as the oxygen supply source. The oxide film according to claim 5, wherein the flow rate of hydrogen in the step of injecting the oxidizing gas is in the range of 100 to 1000 sccm per unit volume (m ³ ) of the chamber when the flow rate of hydrogen is based on a processing pressure of several Torr. Formation method.