JPH07197275A - Surface treating method of metallic material by submerged discharge - Google Patents

Abstract

PURPOSE:To form a high quality covering layer on the surface of a metallic material by preventing a decomposed carbon generated by electric discharge from remaining a lumps in the covering layer. CONSTITUTION:An electroconductive fine ceramic such as WC, TiB2, TiN is mixed with a metal or metalloid(nonmetal) easy to form a carbide such as Ti or B and a metal to be treated or a metal easy to fuse with the fine ceramic as a binder respectively in a powdery state and the mixture is compression molded to form into a prescribed shape. The metal to be treated is electric discharge machined as one of electrodes in the machining solution, where the molding is used as a discharge electrode and a machining solution for forming carbon by decomposition caused by the generation of discharge is used as the machining solution. As a result, the surface layer composed of the electroconductive fine ceramic, the carbide, an uncarbonized part of the metal and a bonded metal is formed on the surface of the metal to be treated by allowing a part of the metal or metalloid easy to form the carbide to react to form the carbide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a metallic material by submerged discharge, and more specifically, a method for treating a metallic material made of steel, aluminum or an alloy thereof, zinc or an alloy thereof, copper or an alloy thereof, etc. The present invention relates to a surface treatment method in which a coating layer containing fine ceramics such as WC and TiC is coated on a surface having a shaped shape so as to have a strong adhesive force, and wear resistance of a mold, a gas turbine, etc.,
Suitable for improving heat resistance.

[0002]

2. Description of the Related Art Conventionally, a base material such as fine ceramics has been subjected to thermal spraying, physical or chemical surface treatment such as PVD or CVD, and plating.

However, the thermal spraying technique has a high film-forming rate and can easily obtain a thick film, but has poor adhesion, and the film is porous so that the hardness does not reach the original hardness of the coating material. There was a flaw. In many cases, PVD and CVD have good adhesion, but since the coating is performed by raising the temperature to a high temperature of about 1000 ° C., the dimensional change of the material is remarkable. Further, there is a drawback that only a thin film of 10 μm or less can be formed. Further, the plating has a drawback that a thick film is impossible and the adhesion is weak.

Further, in these techniques, the thermal spraying requires a vacuum device for low-pressure plasma, and PVD and CVD are performed in a vacuum tank, and plating is also performed in an electrolytic tank, resulting in poor workability. Automation is also difficult.

Therefore, the inventors of the present invention have proposed that these thermal spraying, P
As a technique for eliminating defects such as VD and CVD, Japanese Patent Application No. 3-329499 has proposed a discharge coating method. This method consists of coating the surface of a base material made of a metal material with a metal or non-metal material, and then remelting the deposits in minute regions by pulse electric discharge machining in a liquid, a gas, or a vacuum. And a coating material are diffused and mixed to form a dense coating layer on the surface of the base material.

This discharge coating method has a remarkably high adhesion of the coating layer as compared with the above-mentioned prior art, and is 10 to 100 μm.
It is possible to form a thick film, the dimensional accuracy and shape accuracy are equivalent to the machining accuracy of electrical discharge machining, the workability is remarkably good, and automation is easy. A comparison between the above conventional technique and the discharge coating method is shown in FIG. 1 and Table 1.

[0007]

[Table 1]

[0008]

However, the above-mentioned discharge coating method is a surface treatment technology which is very superior to the conventional thermal spraying method, PVD, CVD and plating, but on the other hand, the prior coating method (1 When the discharge deposition method in liquid (using an electrode that easily wears out) is performed as the next treatment), the carbon content generated by the decomposition of mineral oil in the working fluid due to discharge remains as carbon units in the coating layer. There is a case. Of course, secondary processing
It was found that although it was mostly solid-dissolved in the coating layer components by (remelting by pulse electric discharge machining), it could still be present in the coating layer as a fine lump.

The present invention eliminates the above-mentioned drawbacks of the discharge coating method, reduces the amount of decomposed carbon generated by discharge remaining in the coating layer as a lump, and forms a higher quality coating layer on the surface of a metal material. An object of the present invention is to provide a surface treatment method for a metallic material.

[0010]

Means for Solving the Problems As a means for solving the above problems, the present invention is to provide conductive fine ceramics with a metal or a semimetal (nonmetal) that easily forms a carbide, and as a binder to be treated. A process in which a metal or a metal in which the fine ceramics is easily fused is mixed in a powder state, compression-molded into a desired shape as an electric discharge electrode, and carbon is decomposed and generated by generating an electric discharge as a working liquid. By using a liquid to perform electric discharge machining with the metal to be treated as one electrode in the machining liquid, a portion of the metal or semimetal that easily forms the above-mentioned carbide is reacted and produced as the carbide, and the metal surface to be treated is electrically conductive. Metal material by electric discharge in liquid, characterized by forming a surface layer consisting of a porous fine ceramics, a carbide, a metal not partially converted to a carbide, and a binding metal The surface treatment method is the gist.

Another aspect of the present invention is that a non-conductive fine ceramic is provided with a metal or a semi-metal that easily forms carbide.
As the binding material, the metal to be treated and the metal that is easy to fuse are mixed in powder form, compression-molded into the desired shape, and used as the discharge electrode. By using a machining fluid to perform electric discharge machining using one of the metal to be treated as an electrode in the machining fluid, a part of the metal or semimetal that easily forms the above-mentioned carbide is reacted and produced as a carbide, and the metal surface is treated. A gist is a surface treatment method for a metal material by in-liquid discharge, which is characterized in that a surface layer composed of a non-conductive fine ceramics, a carbide, a metal not partially converted to a carbide, and a binder metal is formed.

Further, according to another aspect of the present invention, after the surface layer is formed by the above method, electric discharge machining is performed in liquid or air by using the electrode which is less likely to wear as one electrode, and the surface layer is remelted and solidified. The feature is to let.

[0013]

The present invention will be described in more detail below.

The present invention uses a discharge electrode containing another metal, fine ceramics or the like on the surface of a ferrous material such as steel, a non-ferrous material such as aluminum, zinc, copper or the like or an alloy thereof, and coating the same by in-liquid discharge. This is a method of performing surface coating of a metal material by melting and diffusing the material to form a strong and dense surface treatment layer. That is, the coating layer formed on the surface is remelted by utilizing the discharge energy and diffused in the base material to form a dense and highly adhesive coating layer.

Up to now, attempts have been made to improve the denseness and adhesion of the coating layer by irradiating the coating layer formed by the thermal spraying method with a laser beam or an electron beam to melt and diffuse the surface. . However, it has not been put to practical use due to the problems that beam streaks remain on the surface and the problem that it is difficult to apply it to an object of any shape.

The inventors of the present invention focused on pulsed discharge, which has been used as a conventional processing technique, and promote the remelting / diffusion of the coating material by the energy of the discharge, and it is possible to perform a dense and strong surface coating. It was found that there is.

The surface treatment process according to the present invention is based on the following mechanism. A coating layer of metal, carbide, nitride or the like is formed on the surface of the base material by a discharge coating method using a powder compact electrode. Next, the coating layer is remelted and diffused by discharge in liquid or air. If necessary, an electrode that is less likely to be consumed is then used as one of the electrodes for electrical discharge machining in liquid to finish it to the desired dimensions and finished surface roughness.

In order to form the coating layer on the surface in the first step, first, as the electrode, a material obtained by compression-molding the powder of the material of the coating layer to be formed or a sintered body is used, and an electric discharge is generated between the electrode and the base material. Wake up. Then, the material on the electrode side is melted and scattered by the energy of the discharge, and is deposited on the surface of the base material. Next, a pulse discharge is generated in a liquid such as kerosene or in air using a non-consumable electrode such as copper with the base material on which the coating layer is formed as one electrode. Due to the energy of the pulse discharge, a minute area near the surface of the coating layer momentarily becomes high temperature and high pressure, so that the coating layer is remelted and diffused into the base material. As a result, a dense and highly adherent surface coating layer is formed. The meaning of the air discharge is that it may be effective for the purpose of remelting, because it is more difficult to cool the air in the liquid than in the liquid. If necessary, in the subsequent process, the electrode is again subjected to in-liquid discharge using a material that does not easily wear out, such as copper, and finished to the desired dimensions, thickness, and finish roughness. Since this has a stronger impact force than the air discharge, it produces an effect like forging and forms a strong coating layer.

However, in the conventional discharge coating method, Co
In the present invention, it is used as a discharge electrode in view of the fact that it was insufficient to absorb and bond the decomposed carbon of the processing oil as a carbide because the binder was only added to the carbide as if they were simply mixed. A powder compact is obtained by adding an appropriate amount of a metal, which easily forms a carbide, as another component to the powder compact and mixing them. As a result, the added metal combines with the carbon generated by the decomposition of the processing oil at the time of discharge to form a carbide, so that the inclusion of carbon as a lump hardly occurs. By adding more steps, it is possible to obtain a coating layer in which carbon is not further present.

The reasons for limiting the manufacturing conditions in the present invention will be described below.

Discharge electrode: As the discharge electrode, a conductive or non-conductive fine ceramic is fused with a metal or semi-metal (non-metal) that easily forms a carbide and a metal to be treated or the fine ceramic as a binder. Easy metal,
The powders are mixed in a powder state and subjected to compression molding to obtain a desired shape.

Examples of the conductive fine ceramics include WC, TiC, TaC, ZrC, VC, TiB ₂ and Ti.
1 type (s) or 2 or more types of N are mentioned. Examples of non-conductive fine ceramics include Al ₂ O ₃ and Si ₃
One or more of N ₄ and ZrO ₂ may be mentioned.

Examples of metals that easily form carbides include:
One or more of Ti, Nb, W, V, Zr, Ta, Cr, Mo and Mn may be mentioned. Further, B is mentioned as a semimetal (nonmetal) that easily forms a carbide. In particular, Nb is an effective component for improving the toughness of the coating surface layer, and
It is recommended to add 10%. Other components are generally added with this added amount as a guide.

The binder may be a metal to be treated or a metal that easily fuses the fine ceramics, and an appropriate binder is selected depending on the material of the metal to be treated. For example,
When the metal to be treated is steel, it is selected from Fe, Co or Ni, when it is an aluminum material, it is selected from Al, Zn or Cu, and when it is a zinc material, it is selected from Cu, Al or Sn.

Electric discharge machining liquid: As a machining liquid used for electric discharge machining, a liquid that decomposes carbon by the generation of electric discharge is used.
For example, petroleum, fats and oils. Oil is a hydrocarbon (CnHm), so if pyrolyzed, C, H and Cn_x, Hm_y in the intermediate zone
Cause In a very short period of time, the metal that easily carbonizes collides with the decomposed carbon in a high temperature state through the machining gap and collides with the surface of the metal to be treated due to electric discharge. Since it is significantly activated due to the high temperature, 10% of this metal becomes carbide.

M ₁ + M ₂ + M ₃ → M ₁ + M ₂ C + M ₂ + M ₃ where M _{1 is a} fine ceramic M _{2 is a} metal or semimetal which easily forms a carbide M _{3 is a} binder metal M ₂ C is a carbide Easy metal or semi-metal carbide

Other electrical discharge machining conditions: Other electrical discharge machining conditions may be the same as in the previously proposed electrical discharge coating method, and pulse electrical discharge machining is desirable. For example, when electric discharge is generated several hundreds to tens of thousands times per second, the processed surface is a surface where small microscopic discharge marks are accumulated, and the discharge mark current density is a minute area. As high as tens of thousands of amperes / cm ² , high temperature and high pressure of tens of μs
It occurs in a short time of about 1000 μs. The surface temperature at the discharge point is the boiling temperature of the material, and the pressure at that point is several 1
It becomes 000 kgf / cm ² , and some of the melted part is scattered, but the remaining part is remelted and diffused into the base material. Since the discharge time is short, the discharge point is immediately cooled and the average temperature of the base material does not rise.

Preferable conditions of pulse electric discharge machining are power supply voltage: 60 to 100 V, pulse discharge current value (Ip): 1 to 1
00A, pulse width (τp): 5 to 2000 μs, rest time
(τr): 5 to 2000 μs. Generally, when the pulse discharge current value Ip is small, for example, Ip = 3A, τp
= 16 μs, when Ip is large, τp = when Ip = 50 A
When Ip is small like 2000τs, τp is short,
When Ip is large, τp is long.

In the case of performing the electrical discharge machining in liquid with one electrode which is less likely to be consumed in the process as the other electrode, only an electrode made of a material which is less likely to be consumed such as copper is used as the electrode. It may be almost the same as the in-liquid discharge condition.
However, since the purpose of the process is basically to process the coating layer thickness and the finished surface roughness to desired values, the process is always performed in liquid. Also note that some electrical conditions are also determined by the desired surface finish roughness.

An example of an apparatus used to carry out the present invention is shown in FIG. Place a metal to be treated (base metal) with a predetermined shaped surface in a processing tank containing a processing liquid that decomposes and produces carbon by the generation of electric discharge, while discharging a powder compression molded discharge electrode. It is held above the base material with a minute gap of several tens to 100 μm. The base material and the discharge electrode can be moved vertically and horizontally by a moving mechanism. Electric discharge machining is performed using the discharge electrode as a negative electrode. An electrode replacement mechanism is provided to replace the discharge electrode with an electrode that is less likely to wear.

[0031]

EXAMPLES Examples of the present invention will be described below.

[0032]

[Test Example 1] Fe consisting of WC powder (average particle size 3 μm) and pure iron
Powder (average particle size 9.8 μm) was mixed in a weight ratio of 1: 1 and compressed with a compression pressure of 4 ton / cm ² to obtain a powder electrode, while
The metal to be treated was carbon steel, and the electric discharge treatment (primary machining) was performed in an electric discharge machining oil (kerosene). The discharge conditions at this time were discharge current Ip = 20 A, discharge current pulse width τp = 16 μs, and the powder electrode was a negative electrode.

After this primary machining, the powder electrode was replaced with a non-consumable electrode (copper), and an electric discharge treatment (secondary treatment) was performed in the same electric discharge machining liquid. The discharge condition at this time is discharge current Ip = 10
A, τp = 1024 μs.

FIG. 3 shows a cross section of the surface analysis result by EPMA of the coating layer subjected to the primary processing and the secondary processing. (1)
Is a secondary electron image, (2) is W, (3) is C, and (4) is F.
It is the surface analysis result of e, and small holes are seen in the secondary electron image of (1), and it can be seen from the surface analysis result of C of (3) that it is a lump of carbon. As shown in the above-mentioned primary processing conditions, carbon lumps are present even though pure iron Fe powder is mixed. Iron and steel has a property that it is difficult to form carbides such that graphite is precipitated when the content of carbon is increased to form graphite cast iron. Of course, some will be cementite, but nonetheless it will leave the carbon as a lump.

The reason why the carbon lump remains is considered as follows. Like pure iron Fe powder, Co does not easily form carbide. Therefore, the same applies to the green compact of the mixture of WC + Co. Generally, the tendency to easily form carbides is as follows, and the elements on the left side are easier to form carbides. In particular, Ni, Co, and Si on the right side of Fe do not form an intrinsic carbide, but rather promote graphitization. Nb>Ti>V>W>Mo>Cr>Mn>Fe>Ni>Co> S
i

When the elements which easily form carbides are shown in the periodic table,
as below. IVB group: Ti, Zr, Hf VB group: V, Nb, Ta, VIB group: Cr, Mo, W VIIB group: Mn, Tc, Re Practically, those except Hf, Tc, Re It is an easily available material.

[0037]

[Test Example 2] Based on the results of Test Example 1, an element that easily forms a carbide was added as a constituent element of the powder electrode, and this powder electrode was used to perform in-liquid discharge. That is, in order to clearly indicate whether Ti is carbonized or not, Ti is selected as an element that easily forms a carbide, and Al which has no possibility of carbonization is also used to form a powder compact electrode composed of Ti and Al. The treated metal (base material) is also an Al material (aluminum die cast material AD
C12). At that time, an experiment was carried out so that the combination of carbon due to the decomposition of mineral oil was present only in the Ti carbide and the analysis was made clear. Also, TiC
It was made possible to analyze quantitatively the abundance ratio on the surface of. At this time, the mixing ratio of Ti and Al, the electric discharge machining conditions, etc. are as follows.

Electrode material: Ti: Al = 36: 64 (weight%) However, the purity of Ti is 99.5%, the purity of Al is 99.7%, both Ti and Al have a particle size of 44 μm or less and a molding pressure. Was 441 MPa. Machining oil: Kerosene for electric discharge machining Electric discharge machining condition: Discharge current Ip = 20A, Discharge current pulse width τp = 512μs Effective pulse width Rp (Duty factor) = 33% Here, when the rest time is τr, Rp = D = { τp / (τp + τr)} × 100 (%)

FIG. 4 is an X-ray diffraction pattern of the obtained base material surface coating layer, and the one generated on the surface of the base material Al material is Ti.
It can be seen that they are C and TiAl ₃ .

Further, of the electric discharge machining conditions, the discharge current pulse width τp was changed to examine the thickness of the coating layer and the volume ratio of TiC. The results are shown in FIG. Further, the results of examining the thickness of the coating layer and the volume ratio of TiC by changing the processing time tw are shown in FIG. From these test results, it is understood that the volume ratio of TiC in the coating layer is 50% or more, reaching about 70%.

As described above, the fact that most of Ti is TiC means that the carbon in the coating layer structure is sufficiently carbide,
It shows that it has a strong action that does not generate free carbon. The carbide thus produced has a sufficiently high hardness and a micro Vickers hardness of 500 to 1000 or more. Even with the bite materials already in practical use,
When TiC is added in addition to WC and Co, it exhibits excellent high-temperature wear resistance, and this coating layer also has excellent properties.

[0042]

[Test Example 3] Each powder of WC, Co and Ti was WC:
Co: Ti = 60: 20: 20 (wt%) was mixed to make a powder compact electrode, and this was used as a discharge electrode, and processing oil (kerosene) was used.
Electric discharge machining (primary machining) was performed inside. Carbon steel (S55C) was used as the metal to be treated. The electric discharge machining conditions at this time were a discharge current Ip = 20 A, a discharge current pulse width τp = 16 μs, and the powder electrode was a negative electrode.

After this primary machining, the powder electrode was replaced with a non-consumable electrode (copper), and an electric discharge treatment (secondary treatment) was performed in the same electric discharge machining liquid. The discharge condition at this time is discharge current Ip = 10
A, τp = 1024 μs.

From the result of X-ray diffraction of the base material surface coating layer obtained by the primary and secondary processing, TiC was generated as in Test Example 2. In addition, SEM image of the cross section (electron micrograph)
It was confirmed that no cavities were observed and no residual carbon was present. This coating layer is WC: Co without the addition of Ti.
The result was that the wear resistance of the cutting tool was about 10 times higher than that of the coating layer formed at a ratio of 80:20.
The cutting test condition at this time is that carbon steel (S55
Using the round bar of C), notch 0.5mm, feed 0.1mm / mi
The cutting speed was 100 m / min.

[0045]

As described in detail above, according to the present invention,
Since it is possible to reduce the amount of decomposed carbon generated by the discharge remaining as a lump in the coating layer, it is possible to form a higher quality coating layer on the surface of the metal material. It is suitable for improving the wear resistance and heat resistance of dies and gas turbines.

[Brief description of drawings]

FIG. 1 is a diagram showing a comparison of a film thickness and an adhesive force between a discharge coating method and another coating method.

FIG. 2 is a diagram illustrating an example of an apparatus used for implementing the present invention.

FIG. 3 is a photograph showing a cross section (particle structure) of the surface analysis result by EPMA of the coating layer obtained in Test Example 1, in which (1) is a secondary electron image, (2) is W, and (3) is C and (4) are Fe surface analysis results.

4 is an X-ray diffraction pattern of the surface of the aluminum die cast material obtained in Test Example 2. FIG.

FIG. 5 is a diagram showing the relationship between the change in pulse width and the average thickness of the coating layer and the volume ratio of TiC in Test Example 2.

FIG. 6 is a diagram showing a relationship between a change in processing time and an average thickness of a coating layer and a volume ratio of TiC in Test Example 2.

Claims (8)

[Claims] 1. A conductive fine ceramic is mixed with a metal or a semimetal (nonmetal) that easily forms a carbide and a metal to be treated or a metal that easily fuses the fine ceramic in a powder state as a binder. Then, by using a machining electrode that has been formed into a desired shape by compression molding as a discharge electrode, and using a machining liquid that decomposes and produces carbon as a result of electric discharge, the metal to be treated is discharged as one electrode in the machining liquid. By processing, a part of the metal or semimetal that easily forms the above-mentioned carbide is reacted and generated as a carbide, and the conductive fine ceramics and the carbide are formed on the surface of the metal to be treated, and the metal not partially turned into the carbide and the bonding metal A surface treatment method for a metal material by in-liquid discharge, which comprises forming a surface layer comprising 2. The conductive fine ceramics is WC,
The method according to claim 1, comprising one or more of TiC, TaC, ZrC, VC, TiB ₂ , TiN, and Ti ₂ N. 3. A non-conductive fine ceramic is mixed with a metal or semi-metal that easily forms a carbide and a metal that easily fuses with a metal to be treated as a binder, respectively, in a powder state, and compression molding is performed. By using an electric discharge electrode having a desired shape, using a machining liquid that decomposes and produces carbon by generating an electric discharge as the machining liquid, and performing electric discharge machining with one of the metals to be treated as an electrode in the machining liquid, A part of a metal or semimetal that easily forms carbide is reacted and generated as a carbide, and a surface layer composed of non-conductive fine ceramics and carbide, a metal that has not become a carbide and a binder metal is formed on the surface of the metal to be treated. A method for treating a surface of a metal material by in-liquid discharge, the method comprising: forming. 4. The non-conductive fine ceramics is Al ₂
The method according to claim 3, comprising one or more of O ₃ , Si ₃ N ₄ , and ZrO ₂ . 5. A metal which easily forms a carbide is Ti, Nb,
4. A compound of one or more selected from W, V, Zr, Ta, Cr, Mo, and Mn, wherein the semimetal (nonmetal) is B. 5.
The method described in. 6. The metal to be treated or the metal which easily fuses the fine ceramics is F when the metal to be treated is steel.
e, Co or Ni, Al for aluminum material,
It consists of Zn or Cu, and in the case of zinc material, Cu, Al or Sn.
The method according to claim 1 or 3, comprising: 7. Nb is 1 to 1 as a metal which easily forms a carbide.
The method according to claim 1 or 3, wherein 10% is added. 8. After forming the surface layer by the method according to claim 1 or 3, the electrode which is less likely to wear is used as one of the electrodes to perform electric discharge machining in liquid or in air to remelt and solidify the surface layer. A surface treatment method for a metal material by electric discharge, which comprises: