JPH10237699A - Method for removing titanium compound coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for perfectly removing or peeling titanium compound coating composed of TiC or TiCN applied on the surface of a metallic base material in a short time without damaging the metallic base material at the inside. SOLUTION: A member in which the surface of a metallic base material is applied with titanium compound coating composed of TiC or TiCN is immersed in an alkaline electrolyte of >=7.3pH preferably, of >=8.0pH, electric current is made to flow between the member as an anode and a reference electrode, and the potential difference between the member and the reference electrode is regulated to +0.1 to +1.0V (to silver-silver chloride electrode couple), by which the titanium compound coating is melted away.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of removing a titanium compound surface coating from a metal member having a titanium compound such as titanium carbide or carbonitride. is there.

[0002]

2. Description of the Related Art At present, the surface of a base material made of a metal material is
2. Description of the Related Art For the purpose of improving mechanical properties such as abrasion resistance and corrosion resistance or decorating, coating with a coating film of various metals or metal compounds by a plating method is generally performed. In particular, a coating film of a titanium compound such as titanium carbide or titanium carbonitride,
Due to its high hardness and excellent wear resistance and heat resistance, it is widely applied to various cutting tools, machine parts, dies, valves and the like.

The plating method used for forming a surface coating film made of such a titanium compound is roughly classified into a wet method and a dry method, and further includes an ion plating method, a vapor deposition method, a sputtering method, and the like. . In particular, many dry methods are widely used as means for easily obtaining a coating film of a metal compound by selecting a metal evaporation source and a reaction gas.

However, when a coating film is formed on the substrate surface by these methods, the metal member with the coating film may be defective due to an incorrect film forming condition or a trouble in the film forming apparatus. May be. Further, for example, in the case of a member such as a cutting tool with a coating film, the coating film is locally damaged in the course of its use, so that the life is often increased. In such a case, it is widely practiced to apply a coating film again on the surface of a member or a base material that has become a defective product or that has reached the end of its life, especially when the base material is expensive. Is effective.

However, when the coating film is reformed,
If the base material in which the coating film applied first remains is used as it is, the reformed coating film is likely to have cracks or missing portions, a difference in color tone, a change in dimensions, and the like. Therefore, when re-forming the coating film, it is common practice to remove or peel off the coating film that has been applied first, return to the original substrate state, and then re-coat.

[0006] The removal or peeling of the coating film is also performed by mechanical means such as polishing and grinding. Particularly, in the case of a member having a complicated shape, a material having a large coating film thickness, or a material having a large surface area, it is removed or stripped. Since stripping requires time and effort, removal or stripping by chemical immersion is widely used. For example, when the coating film is made of a titanium-based compound such as titanium nitride, as described in JP-B-63-53266, it is immersed in an aqueous solution containing hydrogen peroxide and an alkali agent. , Can be removed or stripped.

[0007]

[Problems to be Solved by the Invention]
Although the method described in Japanese Patent Publication No. 266 is effective for peeling off the coating film of titanium nitride, it is difficult to remove or peel off the coating film made of titanium carbide or carbonitride. It takes several times to several tens of times. This is because the coating film made of titanium carbide or carbonitride,
This is probably because the film is chemically more stable than the titanium nitride coating film.

Therefore, in order to remove or remove such a stable coating film of titanium carbide or carbonitride, an inorganic strong acid solution such as nitric acid or hydrofluoric acid, which is generally used as a stripping solution, is used. In this case, since the oxidizing power is too strong, the internal metal substrate is often damaged.

The present invention has been made in view of such conventional circumstances,
An object of the present invention is to provide a method for completely removing or peeling a coating film made of titanium carbide or carbonitride applied to the surface of a metal substrate in a short time without damaging the internal metal substrate. And

[0010]

In order to achieve the above object, a method for removing a titanium compound coating film provided by the present invention is to provide a method for removing at least one selected from carbides and carbonitrides of titanium on the surface of a metal substrate. A member provided with a coating film made of a kind of titanium compound is immersed in an alkaline electrolyte having a pH of 7.3 or more, and an electric current is passed between the member and a reference electrode using the member as an anode, thereby allowing the member and the reference electrode to contact each other. Potential difference between +0.1 and +1.
It is characterized in that it is controlled to 0 V (to silver-silver chloride electrode).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a member having a titanium compound coating film made of titanium carbide or titanium carbonitride on a substrate surface is immersed in an alkaline electrolyte having a pH of 7.3 or more, and this member is used as an anode. , Reference electrode (cathode)
By passing a current while maintaining a potential difference of +0.1 to +1.0 V between the substrate and the substrate, only the titanium compound coating film on the surface is dissolved and removed.

A member to which the present invention can be applied is one in which one or more coating films made of one or more of titanium carbide or carbonitride are formed on the surface of a metal substrate.
The method for producing the titanium compound coating film is not particularly limited,
The coating film formed by a known dry or wet plating method can be removed without any trouble.

The material of the substrate on which the coating film of the titanium compound is applied is not particularly limited as long as it is a metal material such as a pure metal material or an alloy material. In addition, even if the substrate contains titanium as an alloy component, if the titanium is uniformly dissolved, the substrate is not damaged by the method of the present invention. The shape and dimensions of the base material are also not limited. For example, cutting tools such as drills and chips, screws and nuts, and various types of mechanical parts, such as various mechanical parts, or molds and the like It may be large.

In the case of the electrolytic solution used in the present invention, the dissolution of the titanium compound coating film is recognized if it is alkaline.
If the pH is not higher than 7.3, the dissolution reaction is extremely slow and not practical. If the pH of the electrolyte is 7.3 or more, the higher the pH, the faster the dissolution reaction of the titanium compound coating film can be made even at the same potential difference, so that the removal of the coating film can be completed in a short time. Considering the practical processing time, p
H is preferably 8.0 or more, and more preferably pH 12.0 to 13.9.

The alkali source dissolved in the electrolytic solution is not particularly limited, but a hydroxide or an ammonium salt of an alkali metal is preferable, and handling is easy.
In order to stabilize the dissolution reaction or to prevent the dissolved coating film component from re-adhering to the member, a known complexing agent or surfactant can be added to the electrolytic solution.
Care must be taken not to reduce the excess.

The potential difference between the member and the control electrode is preferably in the range of +0.1 to +1.0 V, more preferably +0.2 to +0.8 V, with respect to the silver-silver chloride electrode.
When this potential difference is less than +0.1 V, the dissolution reaction of the titanium compound coating film is slow regardless of the pH of the electrolytic solution, and the time until the removal is completed becomes long. The larger the potential difference, the faster the dissolution reaction of the coating film proceeds, and the more efficiently the coating film can be removed in a short time. However, if the potential difference exceeds +1.0 V, the dissolution of the base material tends to occur, and It is not preferable because the surface of the material becomes rough or discoloration occurs.

The completion of the removal of the coating film can be known by monitoring a change in current during the potential difference control. That is, during the dissolution reaction of the coating film, there is a current flow accompanying the movement of the eluted ions. At the same time as the removal is completed, the value of this current becomes extremely low. You can know the completion. The value of this current varies depending on the amount (thickness and area) of the coating film, the material of the base material, the pH of the electrolytic solution, the value of the potential difference, and the like. Can be easily determined from this.

The control of the potential difference is performed by using a normal potential difference control device. Further, the measurement of the potential can be easily performed as usual by using the reference electrode and the potentiometer. As the reference electrode, a calomel electrode or the like can be used in addition to the silver-silver chloride electrode. For example, using a commercially available device such as a fully automatic polarization measuring device manufactured by Hokuto Denko Co., Ltd., the control of the potential difference and the monitoring and recording of the current value can also be performed simultaneously and fully automatically.

[0019]

EXAMPLE 1 A 2 .mu.m-thick titanium carbide (Ti) was coated on the surface of a high-speed steel SKH51 substrate by an ion plating apparatus.
C) A coating film was formed. The member having the TiC coating film formed on the surface of the base material was immersed in an electrolytic solution having a different pH as shown in Table 1 below, and the member was used as an anode, and electricity was passed between the control electrode and the control electrode. Table 1 shows the potential difference with the member
Controlled like A silver-silver chloride electrode was used as a reference electrode used for the potential difference measurement.

The composition and pH of each electrolytic solution are as follows. Electrolytic solution 1: 5.13 × 10 ⁻³ mol / l disodium hydrogen phosphate + 1.53 × 10 ⁻³ mol / l potassium dihydrogen phosphate mixed aqueous solution (pH 7.3) Electrolyte solution 2: 6.525 × 10 ⁻³ mol / l boric acid + 3.4
75 × 10 ⁻³ mol / l hydrochloric acid mixed aqueous solution (pH 8.
2) Electrolyte 3: 4.56 × 10 ⁻³ mol / l glycine + 5.
45 × 10 ^-2 mol / l sodium hydroxide aqueous solution (p
H12.0) Electrolyte 4: 0.6 mol / l sodium hydroxide aqueous solution (pH 13.1) Electrolyte 5: 2.5 mol / l sodium hydroxide aqueous solution (pH 13.6)

The test under each condition was performed for 3 hours, and the time until the TiC coating film was completely removed was examined. The results are shown in Table 1 below. In Table 1, "incomplete"
Indicates that the coating film could not be completely removed even after the treatment for 3 hours (180 minutes). In the case of "pitting", the coating film was completely removed, but at the same time, the base material was partially dotted. A member that has been corroded or removed.

[0022]

TABLE 1 electrolytic solution conductivity level difference (V; vs. AgAgCl electrode) No. pH +0.05 +0.1 +0.3 +0.45 +0.6 +1.0 +1.1 1 7.3 unfinished unfinished unfinished unfinished unfinished Unfinished unfinished 2 8.2 Unfinished Unfinished 170min 110min 45min 20min Pitting 3 12.0 Unfinished Unfinished 80min 50min 30min 10min Pitting 4 13.1 Unfinished Unfinished 50min 35min 20min Pitting with pit 5 13.6 Unfinished 150min 25min 15min 10min Pitting with pit

From the above results, if the pH of the electrolytic solution is 8.2 or more, a practical coating film can be removed by selecting the potential difference between the member with the TiC coating film and the control electrode, Further, it can be seen that more efficient removal is possible if the pH is 12.0 or more. Even when the pH of the electrolytic solution is 7.3, the TiC coating film can be completely removed by increasing the potential difference to near +1.0 V and energizing for 3 hours or more.

In each of the members in which the removal of the TiC coating film was completed and no pitting was observed, the surface roughness of the base material after the test was about 0.1 μm in Rmax in all cases. The surface roughness Rmax of the substrate before application of the film was 0.12 μm, which was almost unchanged, and no change in appearance such as spots or discoloration was observed.

Example 2 In the same manner as in Example 1, a member in which the surface of a base material of high-speed steel SKH51 was coated with titanium carbide having a thickness of 8 μm was prepared at pH 13.
9 was immersed in a sodium hydroxide solution and treated while controlling the potential difference between the control electrode and the member to + 0.45V. A silver-silver chloride electrode was used as a reference electrode in the potential difference measurement.

As a result, after the treatment for 40 minutes, the 8 μm thick TiC coating film was completely removed from the member surface.
The surface roughness of the substrate after removing the TiC coating film is R
The maximum value was around 0.1 μm, which was almost the same as the surface roughness Rmax of 0.12 μm before applying the coating film, and there was no change in appearance such as spots or discoloration.

Example 3 A coating film of titanium carbonitride (TiCN) having a thickness of 2 μm was formed on the surface of a cemented carbide chip by an ion plating apparatus. The chip made of cemented carbide provided with the TiCN coating film was immersed in a sodium hydroxide solution of pH 13.4, and the potential difference between the control electrode and the member at this time was controlled to + 0.6V. A silver-silver chloride electrode was used as a reference electrode for measuring the potential difference.

As a result, the TiCN coating film having a thickness of 2 μm was completely removed in 45 minutes. The surface roughness of the chip after removing the coating film was about 0.1 μm in Rmax, almost the same as the surface roughness Rmax of 0.12 μm before applying the coating film, and there was no change in appearance such as spots or discoloration. Was.

[0029]

Comparative Example A 2 μm-thick TiC coating film or a TiCN coating film having a thickness of 2 μm was formed on the surface of a high-speed steel SKH51 or a cemented carbide chip as a substrate by an ion plating apparatus.

Each of the members provided with the coating films was immersed in an aqueous solution containing hydrogen peroxide and an alkali agent in accordance with the method described in JP-B-63-53266. As a result, it took 20 hours for any of the members to completely peel off the coating film of TiC or TiCN.

[0031]

According to the present invention, a titanium compound coating film made of titanium carbide or titanium carbonitride applied to the surface of a metal substrate can be coated in a simple manner without damaging the internal substrate. It dissolves efficiently and can be completely removed in a short time.

Therefore, even in the case of a complex shape, a thick film or a large surface area, the coating film of the titanium compound can be efficiently and completely removed, and the base material from which the coating film has been removed is coated. If the film is reformed, a regenerated product with little deterioration in mechanical properties such as adhesion and the like in appearance can be obtained.

Claims (2)

[Claims] 1. A member in which a coating film made of at least one titanium compound selected from titanium carbide and carbonitride is formed on the surface of a metal substrate is immersed in an alkaline electrolyte having a pH of 7.3 or more. Then, a current is passed between the member and the control electrode using the member as an anode, and the potential difference between the member and the control electrode is increased by +
A method for removing a titanium compound-coated film, which is controlled at 0.1 to +1.0 V (to silver-silver chloride electrode). 2. The method for removing a titanium compound-coated film according to claim 1, wherein the pH of the electrolytic solution is 8.0 or more.