KR100217293B1 - Surface treatment method by liquid discharge - Google Patents

Abstract

Conventionally, the surface treatment method using the electric discharge process which forms the coating layer which has firm adhesive force and the outstanding property on metal surfaces, such as a cemented carbide, which could not form the coating layer which has strong adhesive force in the past can be obtained.

Using a powder containing a metal hydrogen compound powder as a discharge electrode, discharge is generated in a liquid in which carbon exists between the electrode and the workpiece to form a coating layer on the workpiece surface.

Description

Surface treatment method by discharge in liquid

1 is a diagram showing the principle of primary processing and secondary processing using a green compact of a mixture of WC + Co as an electrode;

2 is a photomicrograph of a cross section of a treatment layer of a treatment agent after the primary processing and after the secondary processing when the green compact is used for the electrode.

3 shows a comparison of abrasion test results.

* Explanation of symbols for main parts of the drawings

1 electrode 2 base material

[Purpose of invention]

It is an object of the present invention to obtain a surface treatment method by electric discharge machining which forms a coating layer having strong adhesion and excellent properties on the metal surface of a cemented carbide, which has not been able to form a coating layer having a firm adhesion.

[Technical field to which the invention belongs and the prior art in that field]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a technique for depositing and coating a material having a high wear resistance or corrosion resistance on a metal material or a conductive ceramic material based on high adhesion, and a surface treatment technology for imparting the above characteristics to a mold, a tool, or a mechanical part. .

The technique of depositing and coating the surface of a metal material by liquid discharge and giving corrosion resistance and abrasion resistance is already patented by us, and it is a known fact. The gist of these known techniques is as follows.

(1) In one method, liquid discharge is performed at a compression molded electrode by mixing powders of WC and Co. At this time, the coating material is deposited on the work piece once, and then the remelting and discharging processing of the coating material is performed by another electrode (for example, a coin electrode or a graphite electrode) to give the workpiece a high hardness and high adhesiveness.

(2) In the surface treatment method by other liquid discharge treatment, chemical reactions with carbon generated by the thermal decomposition of the processing liquid, such as titanium (hereinafter, Ti), cause Ti to be TiC (titanium carbide), resulting in high temperature and extremely hard materials. To form an electrode, and TiC is deposited on the surface of the workpiece (base material) using the electrode.

At this time, a metal that can be a binder such as Co (cobalt) is added to the compression molding material.

The conventional surface treatment technique will be described below with reference to FIG. 1.

Using a mixed compact electrode of WC-Co (tungsten carbide bite cobalt), discharge processing is performed in the liquid on the material (base material S50C) 2 to deposit WC-Co on the surface of the workpiece (primary processing).

Here, the green electrode is joined to the tip of the coin electrode 1 to form a discharge electrode. Subsequently, remelting (secondary processing) of the volume WC-Co layer is performed by a non-consumable non-consuming electrode such as the coin electrode 1.

The structure of the coating layer obtained by the deposition of the primary processing had a hardness of about Hv = 1410 and many voids, but the cavity of the coating layer disappeared by remelting of the secondary processing, and the hardness was improved to Hv = 1750. (Figure 2).

In these methods, the coated powder is well deposited on steel based on high adhesion, and exhibits a hardness of about 50% higher than that of the sintered cemented carbide alloy of the same component WC + Co or TiC + Co. For example, the hardness of normal carbide tools of WC70 and Co30 is Hv = 850 to 950, but on the surface of electric discharge machining of cemented carbide composed of such components, the hardness is Hv = 1710 after the secondary processing.

However, in the conventional method, it is difficult to form a coating layer having a firm adhesion on the surface of the sintered material such as an ultrahard alloy bite, and there is a large disturbance in the adhesion strength of the coating layer.

The reason why the prior art deposits the coating layer well on the steel surface, but the coating layer cannot be firmly deposited on the surface of cemented carbide or the like is explained.

Here, since deposition coating by Ti and its mixture becomes a main item of this invention, these phenomenon is demonstrated about Ti.

Ti is a metal having a melting point of 1800 ° C and a boiling point of 3000 ° C or higher.

Ti is covered with a thin dense oxide film (TiO ₂ ) in the air at room temperature and is scientifically stable. This is similar to that in which aluminum is covered with a dense oxide film AL ₂ O ₃ . Here, when the powder of Ti is compressed and used as an electrode for electric discharge machining (hereinafter referred to as green compact electrode), the following phenomenon occurs.

When discharge occurs between the electrode surface and the surface to be treated, the discharge point becomes the boiling point of the material, and at the same time, the processing liquid (mineral oil in this case) causes evaporative pyrolysis explosion, and the substance at the high temperature discharges.

Fugitives collide with the workpiece surface of the counterpiece workpiece, and usually about 50% of them are deposited on the workpiece surface.

Ti forms a thin oxide film in air, but discharge occurs.

This is because the oxide film is extremely thin and easily breaks down. Discharge generation is caused by insulation breakdown, and when the voltage is increased or the distance between the poles is shortened, the potential hardness (V / cm) generated between the poles becomes high, and insulation breakdown occurs, leading to discharge generation. It is also understood that the tunnel current flows when the high voltage transmission line causes a corona discharge or a thin oxide film. However, in order to increase the potential hardness in this way, when the distance is small, discharge occurs and the molten metal swells due to the discharge pressure. When the molten metal is in contact with the counter electrode before being detached from the electrode parent or the workpiece, a stop state of discharge called short circuit between the poles occurs. In short, an unstable phenomenon of discharge processing may occur. We have already experienced that the Ti electrode and the Ti green electrode have unstable discharge processing.

The carbon produced by decomposition of the processing oil and the high temperature titanium undergo a chemical reaction until the Ti collides, and the Ti deposits on the surface to be treated and the surface of the first deposited layer is covered with the next collided Ti. Becomes TiC. In this case, the material to be treated is easy to form an alloy with Ti, such as steel, and the melting point is relatively lower than that of cemented carbide (for example, in steel, melting point 1560 ° C and boiling point 2500 ° C). It is deposited by melting on or attaching to the base metal.

In the coating layer deposited once, the secondary electrode is changed by changing the electrode polarity or the discharge electric condition by the same electrode or another electrode, and the cavity formed by the first deposition is filled by remelting, and a high density coating layer is formed. Is as described in the previous application. To confirm again, a micrograph of the first deposited layer (secondary processing) and the tissue by secondary processing is shown in FIG.

By the way, for the material to be treated of cemented carbide (WC + Co, WC + Co + TiC small alloy), even if the coating by the Ti green electrode is deposited on the untreated surface, it is very likely to be peeled off and hardly deposited. . To understand this, it is better to infer from the welding of metal materials. Steel etc. can be arc welded.

It is impossible to weld arc between cemented carbides. Also, arc welding between cemented carbide and steel is impossible.

However, even in arc welding of steel, welding is impossible when the material surface is oxidized. Therefore, it is common sense to use an anti-oxidation flex for welding rods and welding wires. Also, such as aluminum, the melting point is low, and arc welding is difficult in normal conditions.

The reason is that the surface of the aluminum is always formed and covered with a dense film of thin aluminum oxide in the air, and it is known that welding can be performed if it is broken by an ultrasonic vibration.

The reason why the green compact electrode of Ti is not deposited even when Ti collides with the surface of the cemented carbide is described above. Since the powder surface of Ti is covered with a thin oxide film (TiO ₂ ), it is considered that this inhibits the bonding between the deposited layer and the base metal. In other words, as the particle size of Ti decreases, the proportion of the surface area increases with respect to the volume, so that the proportion of the Ti powder occupies the surface of the oxide.

This is similar to when the amount of oxide adhering to the surface oxidized or the workpiece in welding is significantly increased. This is shown next.

Find the ratio of the surface area and volume of the solid.

(1) Assuming powder is a sphere

Surface Area: S = π · d ²

Of the three-dimensional volume: S = π and d ^3/6 (stage, d is the diameter of the solid)

Ratio of surface area and volume: S / V = 6 / d

(2) Assuming powder is a cube

Surface Area: S = π · d ²

Volume of solids: V = d ³ (where d is the length of one side)

Ratio of surface area and volume: S / V = 6 / d

From the above considerations, it is understood that the smaller the powder is, the higher the ratio of the surface area to the volume is. As a result, when the surface is densely covered with an oxide film, the smaller the solid, the more the surface treatment is affected by the oxide film. In addition, the high melting point of the cemented carbide is considered to make welding difficult. This is because a high melting point makes it difficult for the weld fusion to flow. In contrast, weld fusions tend to flow in steel.

In addition, if the above-described three-dimensional oxide layer inhibits the fusion and bonding of the deposited layer to the workpiece, the compression-molded powder has a large influence of the oxide, and the effect increases as the particle size decreases. In contrast, since the ratio of the solid Ti metal titanium electrode occupies the surface of the oxide layer is small, it is possible to coat the metal Ti electrode with low efficiency. In the case of Ti solid electrodes, Ti deposits fairly well on the workpiece. In the case of a Ti electrode sintered or sintered in a vacuum furnace or the like, Ti is deposited very well. However, neither the Ti solid electrode nor the Ti sintered electrode had a small deposition amount (thickness) and the adhesion strength did not reach TiH ₂ which will be described later. That is, it is considered that the inhibitory factor of the oxide remains.

[Technical problem to be achieved]

As apparent from the above description, in the conventional surface treatment method using electric discharge machining, in the case of an electrode compression-molded with powder such as Ti, there is an oxide film (TiO ₂ ) that densely covers the powder surface. Even if separated from the powder surface, it is believed that the powder metal constituting the electrode is supported on the surface to be treated or fused with the counter metal. Further, since the pyrolysis temperature of TiO ₂ is extremely high (1800 ° C.), when the electrode body is scattered at the discharge pressure, there is a large number of shot collisions on the surface to be treated in the TiO ₂ state. In addition, since the gap between discharge generations becomes narrow (discharge becomes difficult due to the oxide film), short circuits occur in the surface treatment, and it is thought that the oxide film deteriorates the processing surface and hinders the processing efficiency.

The present invention has been made to solve the above-mentioned problems, and even for sintered cemented carbide, raw material powder is well deposited, its adhesion is strong, and there is almost no short circuit in processing, and the processing efficiency is high, and the finishing It is to provide a surface treatment method by electric discharge machining that the surface roughness is well processed.

[Configuration and Function of Invention]

In the surface treatment method according to the liquid discharge of the present invention, a raw material powder containing a hydrogen compound powder of a metal is used as a discharge electrode, and a discharge is generated between the electrode and the workpiece in a processing liquid in which carbon is present. It is to form a surface layer containing a compound of the metal on the surface.

An embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Embodiment 1 The surface treatment method of Embodiment 1 uses a TiH ₂ green compact electrode for electric discharge machining.

TiH ₂ green compact electrode is formed by a predetermined TiH ₂ powder of a predetermined particle size under compression conditions. The green compact electrode is usually formed on a disc of a predetermined diameter and thickness. The disk-like powder is bonded to the tip of a solid metal electrode such as a copper rod with a conductive adhesive to obtain a green compact electrode of TiH ₂ . TiH ₂ green compact electrodes are used for surface treatment of certain cemented carbides as workpieces.

In this treatment, a discharge is generated between the TiH ₂ green compact electrode and the cemented carbide under predetermined conditions in the processing liquid. The processing liquid contains carbon, or contains a polymer material that generates carbon by thermal decomposition. In particular, the polymer material is a mineral oil or a vegetable oil. Although such processing is different in processing conditions, it corresponds to the temporary processing of the conventional surface treatment.

Describes a TiH characteristic action of the surface treatment method of the present invention used as an electrode, by compression-molding the _two effects below. TiH ₂ starts to escape hydrogen at temperatures above 300 ° C. Since the surface of the discharge point is considered to be at the boiling point of the material until the discharge starts and ends (0.1 kPa to 1000 kPa in phase), TiH ₂ is completely decomposed.

At this time, Ti and decomposed hydrogen show extremely high chemical reactions.

That is, a hydrogen compound such as TiH ₂ is an unstable compound, and from the common sense of chemical change, it causes a high activity reaction.

In other words, the hydrogen of the generator strikes the surface to be treated to remove an oxide film or the like (the surface of a cemented carbide or steel, etc., which is dead or not, and an oxide exists).

In addition, since Ti does not contain any oxide and injection collisions to the surface to be treated as long as it has activity, Ti can be deposited with high adhesion.

In addition, since TiH ₂ is inherently a weak substance, it is thought to be made finer by discharge generation and thinner than the original particle size of TiH ₂ . For this reason, it is possible to obtain a better surface than the conventional WC-Co green compact when processed under the same electrical conditions. In the conventional electrode, the roughness of the finished surface is 30 to 40 µm Rmax, whereas in the electrode of the present invention, 6 to 12 µm Rmax can be obtained.

The surface to be treated is first cleaned with hydrogen of the generator and deposited on the metal surface of the clean workpiece to which TiH ₂ powder is applied. Once the treatment finishes the surface and most of the metal surface is coated with Ti or TiC, the surface of Ti or TiC (by compounding with carbon by hydrolysis) becomes the surface to be treated by subsequent discharge. Unlike the conventional art, there is no stereoscopically covered with Ti containing TiO ₂ . For this reason, the coating applied from the next time also becomes an extremely high adhesion layer. For this reason, it turned out that it shows remarkably high adhesiveness also about a cemented carbide and exhibits the ground-breaking wear resistance which was not acquired conventionally even in abrasion test.

In addition, welding of cemented carbide is impossible with normal arc welding. However, in discharge processing, the discharge point reaches the boiling point of the material, and the energy density is several times higher than that of arc welding. It seems to be close.

Example 1

A TiH ₂ green compact electrode was prepared as follows. First, TiH ₂ powder having a particle size of 10 GPa or less was compression molded under the following conditions.

Diameter: 15 mm

Load: 11.4Ton (about 6500㎏ / ㎠)

Thickness: about 5mm

The green electrode is adhered to the end of the copper rod with a conductive adhesive and used as a discharge electrode. As a material to be treated, cemented carbide (WC + TiC + Co: GTi30 Mitsubishi Material) is used. Then, discharge processing was performed between the TiH ₂ green electrode and the cemented carbide under the following conditions, and a deposition layer was formed on the surface of the workpiece. Here, the surface treatment by electric discharge machining uses only TiH ₂ green compact and corresponds to the primary machining of the conventional method.

(1) Machining conditions, hardness, roughness of finished surface, wear test results

1) Processing condition

Discharge Current: Ip = 3.5A

Pulse width: τp = 32㎲

Machining time: 2 minutes

Green Electrode Polarity: (-)

2) hardness, finish roughness

Vickers Hardness: Hv = 600 ~ 900 (Measurement Pressure 10g)

Volume layer thickness: 13㎛

Finish surface roughness: 10㎛Rz

3) Result of abrasion test (interlacing pin disk method)

Atmosphere: Atmosphere

Pin shape: φ7.98㎜ (0.5㎠)

Push force: 0.5㎏

Pressure part: 1kgf / ㎠

Friction Speed: 1㎧

Disc material: SKH-3

3 shows the frictional wear test results of the workpiece surface treated by the surface treatment method of Example 1 together with various comparative examples. The graph in FIG. 3 shows the result after the wear test travel distance of 25 km.

In the surface treatment by Example 1, as shown to (6) and (7) of FIG. 3, the wear amount Omg was obtained with respect to the to-be-processed object.

In addition, the wear amount of the cemented carbide material treated by another method for comparison with the wear test result of Example 1 is as follows.

Abrasion amount of cemented carbide (GTi 30) ground: 2.1 mg (1 and 2 in Fig. 3 or solid lines in the drawing indicate ① and dotted lines indicate ②)

Discharge coating surface by titanium metal electrode: 0.7-1.5 mg (3, 4 and 5 in Fig. 3)

TiN + Ti ₂ N (film thickness 2 μm) Ion mixing surface: 1.5 mg

Note] (The decomposition of the amount of wear is considered to be 0.1 mg.)

Although the hardness Hv = 600-900 obtained in Example 1 is only the grade corresponded to the hardness of quenched steel or tempering steel, its wear resistance is remarkably high.

On the other hand, the hardness of the cemented carbide, which is the base metal, is high at about Hv = 1500 to 1800. However, the cemented carbide only wears 2.1 mg as shown in the above results.

(2) Consideration of markedly improved wear resistance

1) Despite the low hardness, there is no clear interpretation of the high wear resistance until now, but the inventors think as follows. The surface of the deposition layer formed by the liquid inversion by the TiH ₂ powder electrode is made of Ti and TiC, and is in close contact with the surface of the cemented carbide of the base material without containing any oxide.

The reaction between the base material surface and the discharge causes the carbide surface to reach the boiling point of the material instantaneously, so that the deposited Ti and TiC can be diffused and fused to the base material side to some extent. The composition of components from the interface between the deposited layer and the base material to the surface of the deposited layer (in this case, about 13 µm) is also Ti and TiC, and the deposited layer does not contain any oxide and is in close contact with the base material.

The Ti component is oxidized in air to form TiO ₂ in the uppermost portion of the deposited layer, but the inside is made of Ti as active.

For this reason, in the abrasion test, it is considered that after the top surface portion of the deposition layer is abrasion removed when it comes in contact with the disk material Sk-3, the disk material is removed by fusing to the Ti deposition layer side and transferred to the surface to be treated. Since TiC also exists on the surface to be treated originally, it is considered that the disk material (Sk-3) to which the slightly soft Ti surface is attached is protected by attachment.

2) In consideration of the above, the theoretical difference between the adhesion of the electroplated surface and the adhesion by the surface treatment of the present invention, the cleaning effect by the decomposition hydrogen of the processing liquid by the discharge and the cleaning effect by the hydrogen of TiH ₂ State the logic differences with Electroplating The plated metal is deposited on the cathode. At this time, the cathode surface will also be cleaned by hydrogen of the generator by decomposition of the plating aqueous solution, but the adhesion to the base metal of the plating is not high. On the contrary, it is known that the base metal and the plating surface are weakened by hydrogen weakness. This may be considered that the plated base surface may be cleaned, but the plated metal cannot fuse and spread on the base material because the treatment is not performed at high temperature and high pressure.

3) In the case where the processing oil is decomposed by electric discharge machining, it is divided into carbon and hydrogen, and a large amount of carbon precipitates on the anode side. Therefore, hydrogen may collide and clean on the cathode surface.

This action cannot be ignored. When the metal powder of the WC + Co electrode is reliably deposited on the steel surface, a highly adhesive deposited layer is obtained. However, even when it was attempted to deposit on the cemented carbide surface, high adhesion was not obtained. Further, even if the titanium powder was simply deposited on steel with a green compact electrode of titanium powder, the deposition conditions could not be easily found. As a result of these experiments, in the cleaning with hydrogen decomposed by liquid discharge, it was impossible to deposit metal powder on cemented carbide, and thus, it is thought that the reduction effect of the surface covered with oxide film like titanium powder is impossible.

Example 2

A discharge was generated between the TiH ₂ green compact electrode and the cemented carbide as a workpiece under the following conditions different from the above to form a deposited coating layer on the surface to be treated. The TiH ₂ green compact electrode was formed from TiH ₂ powder in the same manner as in Example 1. Cemented carbide is also the same as in Example 1. Here, the surface treatment by discharge was performed only with the TiH ₂ green compact electrode.

This corresponds to the temporary processing of the conventional method. The test progress when the coating layer obtained by this process was tested and the discharge electric conditions were changed is shown below.

(1) When changing electrode polarity

1) Green electrode polarity: (-)

Discharge Current: Ip = 10A

Pulse width: τp = 32㎲

Machining time: 5 minutes

Hardness of surface to be treated: Hv = 670 ~ 900 (Measured pressure 10g)

2) Green electrode polarity: (+)

Electrical condition: same as 1)

Surface hardness: Hv = 1450-1550 (measured pressure 10g)

It was found from 1) and 2) above that the hardness of the surface to be treated also changes due to the change in the polarity of the electrode.

(2) When the discharge current is increased and the pulse width is made very small

Discharge Current: Ip = 45A

Pulse Width: τp = 0.5㎲

Machining time: 2 minutes

Green Electrode Polarity: (-)

Hardness of surface to be treated: Hv = 2000 ~ 3000 (Measured pressure 10g)

Hardness of surface to be treated: Hv = 1300 to 2000 (measured pressure 50g)

Deposit thickness: 2㎛

Finishing surface roughness: 6㎛Rz

If the measurement load is small, the hardness is large, the load is large, and the surface to be treated is slightly softened, and the deposited layer tends to have a hard surface and a slight light inside, and becomes inclined to the hardness. It is said that the deposited layer is strong against thermal expansion or impact during practical use.

(3) From the result of said (1) and (2), there are various means as a means which remarkably hardens the surface of a deposited layer, makes it soft enough so that it enters inside, and remarkably raises inclination. One is to perform the discharge machining under the condition of 1) of the above (1) and then the discharge machining under the condition of (2). Another method is to change the electrode polarity, for example, from minus (-) (condition of 1) to plus (+) (condition of 2).

Example 3

Steel material (SK-3) was used as a to-be-processed object. The surface of the steel was treated by primary discharge machining and secondary discharge machining as in the conventional method.

The coating layers obtained by these two treatments were tested respectively. The test results are shown below.

(1) As the primary processing, the discharge surface treatment (primary processing only) was performed on the steel material SK-3 using a TiH ₂ green electrode. The green compact electrode of TiH ₂ was the same as that of Example 1. Processing conditions are also the same as in Example 1.

Discharge Current: Ip = 3.5A

Pulse width: τp = 32㎲

Machining time: 5 minutes

Surface hardness: Hv = 900 to 1000 (measured pressure 10g)

Deposit thickness: 47㎛

Abrasion Test Result: 0mg

(2) After performing primary processing on the conditions shown in said (1), secondary processing was performed to steel material SK-3 using a graphite electrode. The conditions of secondary processing are as follows.

Discharge Current: Ip = 3.5A

Pulse width: τp = 4㎲

Machining time: 5 minutes

Polarity of Graphite Electrode: (-)

Hardness of surface to be treated: Hv = 1600 ~ 1750

From this, it can be seen that when the secondary processing is performed, the hardness of the surface to be treated is significantly increased. Similarly, the secondary processing with a coin electrode increased the hardness of the surface to be treated.

This is because in secondary processing, Ti or TiC does not newly deposit on the surface to be treated, but C (carbon) formed by decomposition of the processing oil is combined with residual Ti in the coated copper layer, so that the proportion of TiC in the coated layer increases. .

[Embodiment 2]

Embodiment 2 of the invention uses a green compact electrode formed by mixing TiH ₂ with another metal, carbide, nitride, or boride. These compounds further expand the above excellent properties of TiH ₂ . Many experiments were carried out to form various green compact electrodes by mixing the following with the powder of TiH ₂ , respectively.

(1) Metals that can be carbides by liquid discharge (eg Ta, Nb, V, Zr)

(2) carbides (e.g. TiC, TaC, NbC, VC, BC, B ₄ C)

(3) nitrides (eg TiN, HBN, CBN)

(4) borides (e.g. TiB ₂ , boric acid H ₂ BO ₃ , borax Na ₂ B ₄ O ₇ , 10H ₂ O)

(5) Etriors (e.g. Y ₂ O ₃ )

As a representative example of the above-described the things, by combining the TiN to TiH ₂ electrode a mixture of TiB ₂ in the electrode a mixture of TiH ₂ and TiN in TiH ₂ was tested as follows for each of the mixed electrode.

In the test, the same cemented carbide as in Example 1 was used as a workpiece.

The surface of this cemented carbide was treated by the primary discharge machining as in Example 1. In addition, this cemented carbide was further treated by secondary electric discharge machining as in Example 3. And the coating layer obtained in these two cases was tested, respectively. The test results will be described later with Examples 4 to 6.

Even when only the primary processing is performed, the hardness of the workpiece is greater than that of cemented carbide, but when secondary processing is performed with graphite electrodes (such as copper or tungsten), the hardness of the cemented carbide is further improved, and the surface hardness is increased. It turned out that it has the inclination to the hardness of the formula of ½ (more than Hv5000 equivalent to CBN) of diamond, and the inside becoming soft.

Example 4

Electrode material: TiH ₂ + TiB ₂ (7: 3 weight ratio)

1) A TiH ₂ + TiB ₂ green compact electrode was prepared in the same manner as the electrode of Example 1. Only the primary processing using the electrode yielded the following results under the following conditions.

Electric condition: Ip = 5.5A, τp = 32㎲

Machining time: 5 minutes

Hardness: Hv = 1850-2500 (load 10g)

Thickness: 24 ~ 28㎛ and Hardness: Hv = 1650 ~ 2500 (Load 50g)

As in Example 1, as a result of the abrasion test, the abrasion amount of the surface to be treated was 0 mg.

In addition, the above-described discharge treatment was performed on the one side and the front end surface of the cemented carbide bite (Mitsubishi Material Ti20) for 2 minutes, and the cutting test was performed by a lathe to investigate the adaptability to the cutting tool. The resultant bite showed a 1.9 times longer life than the bite not discharged under the cutting conditions shown below.

In addition, another test was performed by changing the discharge conditions as follows.

Electric condition: Ip = 8A, τp = 8㎲

Machining time: 5 minutes

The treated bite thus exhibited a long service life of 2.8 times as compared to the bite not discharged under the cutting conditions indicated below.

Cutting condition:

Material to be cut: S45C

Cutting: 0.5mm

Feed: 0.3㎜ / rev

Cutting speed: 160m / min

Dry cutting

Life judgment: wear width of front surface at cutting distance of 7km

(Usually denoted by VB)

2) After the primary processing described above, secondary processing was performed using a graphite electrode for 5 minutes under the following conditions.

Electrical condition: Ip = 3.5A, τp = 4㎲

Machining time: 5 minutes

Hardness: Hv = 2100-5100 (load 10g)

Green Electrode (-)

Hardness: Hv = 1500 ~ 3000 (Load 50g)

Thickness: 32 ~ 36㎛

The hardness Hv = 5000 is next to the diamond hardness Hv = 10000, which is comparable to the hardness Hv = 5000 of the CBN.

Also in this case, the coating layer exhibits an inclined hardness distribution that is very hard and gradually softens as it enters the interior, and is extremely useful because it has both surface hardness and toughness.

Example 5

Electrode material: TiH ₂ + TiN (7: 3 weight ratio)

1) Primary processing condition:

Electric condition: Ip = 5.5A, τp = 32㎲

Machining time: 5 minutes

Hardness: Hv = 1050-1800 (load 10g)

electrode : (-)

When only the primary processing is performed, the hardness of the coating layer is high, but not as much as that of the coating layer of Example 4 obtained from the electrode in which TiB ₂ is mixed with TiH ₂ .

2) The hardness of the coating layer at the time of tertiary processing with a graphite electrode after the said primary processing becomes about Hv = 1700-2300.

Example 6

Electrode Material: TiH ₂ + TiB ₂ + TiN (2: 1: 1)

1) Hardness only by primary processing

Machining conditions were the same as in Example 1 Machining time = 5 minutes

Hardness: Hv = 2000 ~ 2300 (Load 10g)

Thickness: 12-18㎛

2) Hardness when secondary processing is performed on graphite electrode

Machining conditions were the same as in Example 1 Machining time = 5 minutes

Hardness: Hv = 2550 ~ 6050 (load 10g)

Thickness: 14-18㎛

If the measured load is taken to be 50 g, the Hv is reduced to about 1800, so it is clear that this coating layer also has a gradient in hardness.

[Embodiment 3 of the Invention]

Embodiments 1 and 2 described above aim to increase wear resistance. In the primary processing of the TiH ₂ green compact, although the hardness is not so high, it is considered that the adhesion of the deposited layer is very strong, but a result of high wear resistance is obtained. When TiB ₂ or the like is added to TiH ₂ , the coating layer has high hardness and high wear resistance.

When the hardness is too high and there is a risk of weakening and breaking, it is known to add Nb, Ta, or NbC, TaC, etc. to TiH ₂ to give toughness (this is the knowledge known from the cemented carbide tool).

When Ta, Nb, and V were added to TiH ₂ by about 10%, the surface treatment was performed under the same conditions as in Example 1, and the results showed that the hardness did not increase from Ta and Nb to hardness Hv = 600 to 700 and V to hardness Hv = 900. However, even when hitting the surface of the coating layer with a hammer or the like, it is hard to fall off, which means that the quality has improved. The coating layer is deposited in a stable processing state at a thickness of 10 to 20 占 퐉 for 5 minutes.

Nb, TaC, VC, etc. are also effective in cutting tools to improve toughness for intermittent cutting. In this experiment, they were added to TiH ₂ at a weight ratio of about 10%.

As a result, the hardness is not so high as about Hv = 900 to 1050. However, the coating layer is processed for 5 minutes, and is deposited in a stable state at a thickness of 20 to 30 µm, and is also resistant to impacts.

[Mode 4 of implementation]

As described above, by applying a TiB _2, TiN or the like or TiH ₂ with a TiH ₂ groups TiH ₂ as the base material, it became clear that the surface deposition of the higher hardness is obtained. The reason why TiH ₂ is in close contact with the material to be treated is as described above in Embodiments 1 to 3 of the present invention. It is by being. It is also considered that the effective contact area to the base material is increased in order to reduce the size of Ti when discharge occurs. In addition, since the deposited structure becomes fine due to the refinement of Ti, the roughness of the polished surface is also very easily elaborated.

By extending this principle, hydrides of metals can be used for surface treatment.

The hydrides considered to be used for surface treatment are as follows.

ZrH ₂ , VH, VH ₂ , NbH, TaH, FeTiH ₂ , LaNi ₅ H ₆ , TiMnH ₂ , NaBH ₄

As an example, since ZrH ₂ was experimented, it is described as Example 7.

Zr is excellent in heat resistance and corrosion resistance, and it is used as a moderator of thermal neutron, and it is used in raw materials as well as in heat-resistant wear parts and pump parts of cutting tool bearings.

Example 7

The powder of ZrH ₂ was formed into a green compact under the same conditions as in Example 1 (compression pressure 6500 kg / cm 2), and the steel material SK-3 as a work was processed under the electrical conditions Ip = 5.5A and τp = 32 kPa.

As a result, the powder of ZrH ₂ deposits well in the processing state which is extremely stable with respect to the to-be-processed object. By 5-minute processing, the deposited layer had a thickness of 8 to 10 µm and a hardness of Hv = 660 to 690, which was not so high, but showed only high wear resistance.

When high hardness is required for the deposited layer, the hardness increases when secondary processing is performed with a graphite electrode or the like. Electrical conditions at the time of secondary processing are Ip = 3.5A, (tau) p = 4 kPa, a graphite electrode (-), and hardness Hv = 1350-2000-2350 is obtained in this case.

[Embodiment 5]

Aluminum, zinc, or steel (patented mild steel) may not be of high hardness, but may require a high wear resistance surface.

For example, if aluminum is the wear-resistant part of an aluminum engine, it is sometimes desired to give the surface of molds and shapes made of mild steel, which are shaped like zinc, and to provide wear resistance. In this case, when TiH ₂ powder is mixed with a powder of a metal requiring surface treatment, a discharge electrode is formed, and the metal surface is discharge-processed by these electrodes to form a surface coating having a high adhesion to the metal surface and a hardness higher than that of the base metal. .

As an embodiment, an example in which TiH ₂ + Al processed aluminum using a green compact electrode is described below.

Example 8

A green compact electrode having a weight ratio of 3: 7 of TiH ₂ to Al was used as powder (aluminum die-cast material containing 119 of Si) of the workpiece. As an electric condition, when the current Ip = 5A and? P = 260 mA, the hardness of the surface to be treated is also about Hv = 400 to 600, while when the electric conditions Ip = 20A and? P = 260 mA, the surface layer portion reaches about Hv = 1400. The same results can be obtained by treating zinc with an electrode of this composition.

[Embodiment 6]

Some nonferrous metals are called superalloys (superalloys), and this material is also subject to discharge surface treatment technology. In other words, a material in which 6% Al and 4% V is mixed with Ti has a tensile strength of about 100 kg / cm 2 and a Vickers hardness of about Hv = 260. Surface treatment was carried out with a green compact voltage of ZrH ₂ , and the electrodes were processed under the electric conditions Ip = 5.5A and τp = 32 kPa with an electrode having an area of 1.7 cm2. Sedimentary layer

Further, when secondary processing is performed on the surface of the workpiece with a graphite electrode, hardness Hv = 1350 to about 2000 is obtained.

By this surface treatment, discharge coating was carried out corresponding to the Ni-Al-Ti-Nb-Ta alloy to obtain the same result.

In the above invention, the material to be treated (materials generated opposite to the positive electrode) is composed of steel and special steel, cemented carbide, summit, aluminum and its alloys, lead and alloys thereof, copper and copper alloys, and Ni and Co as main components. Heat-resistant alloys (also called superalloys) are targeted. So-called nonferrous materials and nonferrous alloys are also covered.

[Effects of the Invention]

As described above, a hydride such as Ti, Zr, V, b, Ta, etc. is formed as a green compact and discharged in liquid to form a volume layer having a thickness of several micrometers to several ten micrometers having strong adhesion to the surface of steel cemented carbide or the like. It can be formed.

This volume layer is remarkably good in wear resistance. The roughness of the finished surface is also better than that of the other examples (WC + Co) performed under the same electrical conditions, resulting in roughness of ½ to ⅓.

In order to increase the hardness in the above hydride, the hardness can be further increased by mixing TiB ₂ , TiN, TiC, TaC, NbC, VC, or the like.

Toughness improves when metals of Ta, Nb, and V are added to the green component.

Secondary processing with graphite electrodes or coins increases the hardness from more than 50% to about 2 times.

Claims (1)

Using a raw material powder containing a metal hydrogen compound powder as a discharge electrode, a discharge is generated between the electrode and the workpiece in a processing liquid in which carbon is present, thereby forming the compound of the metal on the surface of the workpiece. A surface treatment method according to a liquid discharge, characterized in that to form a surface layer comprising.

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