JP3271844B2 - Surface treatment method for metallic materials by submerged discharge - Google Patents

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 metal material by electric discharge in a liquid, and more particularly, to a method for treating a metal material made of steel, aluminum or its alloy, zinc or its alloy, copper or its alloy, or the like. It relates to a surface treatment method in which a coating layer containing fine ceramics such as WC, TiC, etc. is coated on a surface having a shape so as to have a strong adhesive force.
Suitable for improving heat resistance and the like.

[0002]

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

[0003] However, the thermal spraying technique has a high film-forming speed and can easily obtain a thick film, but has poor adhesion, and the film is porous, and the hardness does not reach the original hardness of the coating material. There were drawbacks. PVD and CVD have good adhesion in many cases, 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 disadvantage that only a thin film of 10 μm or less can be formed. In addition, plating has a drawback that a thick film cannot be formed and adhesion is weak.

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

Therefore, the present inventors have developed these thermal sprays, P
As a technique for solving the disadvantages such as VD and CVD, a discharge coating method was previously proposed in Japanese Patent Application No. 3-329499. In this method, after coating a metal or non-metal material on the surface of a base material made of a metal material, the deposit is remelted for each minute region by pulsed 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.

In this discharge coating method, the adhesion of the coating layer is extremely high,
A thick film of about the same thickness is possible, the dimensional accuracy and the shape accuracy are equivalent to the machining accuracy of electric discharge machining, workability is remarkably good, and automation is easy. FIG. 1 and Table 1 show a comparison between the above conventional technique and the discharge coating method.

[0007]

[Table 1]

[0008]

However, the above-mentioned discharge coating method is a surface treatment technique which is much superior to the conventional thermal spraying method, PVD, CVD, and plating. When the discharge deposition method (using easily consumable electrodes) in the liquid is performed as the next treatment), the carbon content generated by the decomposition of the mineral oil etc. of the machining liquid by the discharge remains as a carbon unit in the coating layer as it is. May be. Of course, secondary processing
(Re-melting by pulsed electric discharge machining) caused most of the solid solution to form a solid solution in the coating layer components. However, it was found that there was still a case where fine solids were present in the coating layer.

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

[0010]

As a means for solving the above-mentioned problems, the present invention relates to a method for producing a conductive fine ceramic by adding a metal or semi-metal (non-metal) which is easy to form a carbide and a binder as a binder. A process in which a metal or a metal which is easy to fuse the fine ceramics is mixed in a powder state, and compression-molded into a desired shape is used as a discharge electrode. By performing electrical discharge machining with the metal to be treated as one electrode in a machining fluid using a liquid, a part of the metal or metalloid which is easy to form the carbide is reacted and produced as a carbide, and the surface of the metal to be treated is electrically conductive. Material by discharge in liquid characterized by forming a surface layer composed of conductive fine ceramics, carbide, metal not converted to carbide, and bonding metal The surface treatment method is the gist.

Another object of the present invention is to provide a non-conductive fine ceramic with a metal or semi-metal which easily forms carbide.
As a binder, a metal to be treated and a metal that is easy to fuse are mixed in powder form, and compression-molded to form a desired shape is used as a discharge electrode. Using a machining fluid to perform, by performing electrical discharge machining using one of the metal to be treated in the machining fluid as an electrode, a part of the metal or metalloid that easily forms the carbide is reacted as a carbide, and the surface of the metal to be treated is formed. The gist of the invention is to provide a method for surface treatment of a metal material by in-liquid discharge, which comprises forming a surface layer composed of a non-conductive fine ceramic, a carbide, a metal that has not partially turned into a carbide, and a binder metal.

Further, in another aspect of the present invention, after a surface layer is formed by the above-described method, electric discharge machining is performed in liquid or air using an electrode which is not easily consumed as one electrode, and the surface layer is re-melted and solidified. It is characterized by having

[0013]

The present invention will be described below in more detail.

The present invention uses a discharge electrode containing another metal or fine ceramics on the surface of a non-ferrous material such as iron, steel, aluminum, zinc, copper, or an alloy thereof, and performs coating by discharging in a liquid. This is a method of performing surface coating of a metal material by melting and diffusing a material to form a strong and dense surface treatment layer. In other words, the coating layer formed on the surface is re-melted using the discharge energy and diffused into the base material to form a dense and highly adherent coating layer.

Heretofore, attempts have been made to improve the denseness and adhesion of the coating layer by irradiating the coating layer formed by thermal spraying or the like with a laser beam or an electron beam to melt and diffuse the surface. . However, there is a problem that a streak of a beam remains on the surface and a problem that it is difficult to apply the method to an object having an arbitrary shape.

The present inventors have paid attention to pulse discharge which has been used as a conventional processing technique, promote remelting and diffusion of the coating material by the energy of the discharge, and can perform a dense and strong surface coating. I found something.

The surface treatment step 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 green compact electrode. Next, the coating layer is re-melted and diffused by liquid or air discharge. If necessary, thereafter, submerged electrical discharge machining is performed using the electrode that is not easily consumed as one of the electrodes to finish the electrode to the desired dimensions and finished surface roughness.

In order to form a coating layer on the surface in the first step, first, a material obtained by compression-molding a powder of the material of the coating layer to be formed or a sintered body is used as an electrode. 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, pulse discharge is caused in a liquid such as kerosene or in air using a non-consumable electrode such as copper, using the base material on which the coating layer is formed as one electrode. The minute area near the surface of the coating layer instantaneously becomes high temperature and high pressure due to the energy of the pulse discharge, so that the coating layer remelts and diffuses into the base material. As a result, a dense and highly adherent surface coating layer is formed. The meaning of aerial discharge is effective for the purpose of re-melting because air is harder to cool than liquid. If necessary, after that, in the process, the electrode is again subjected to submerged discharge with a material such as copper which is not easily consumed, so that the electrode is finished to the desired dimensions, thickness and finish roughness. Since the impact force is stronger than the air discharge, an effect such as forging is produced and a strong coating layer is formed.

However, according to the conventional discharge coating method, Co is set to Co.
In the present invention, it is used as a discharge electrode in view of the fact that it was not sufficient to absorb and bond the decomposed carbon of the processing oil as a carbide, since the binder was only added to the carbide, just as a mixture of An appropriate amount of a metal that easily forms carbide is added to the green compact as another component and mixed to obtain a green compact. As a result, the added metal is combined with carbon generated by the decomposition of the processing oil at the time of electric discharge and becomes a carbide, so that the inclusion of carbon as a lump hardly occurs. If a further step is added, a coating layer in which no further carbon is present can be obtained.

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

Discharge electrode: The discharge electrode is formed by fusing a metal or semi-metal (non-metal) that easily forms carbide with a conductive or non-conductive fine ceramic and a metal to be treated or the fine ceramic as a binder. Easy metal and
Each of them is mixed in a powder state and subjected to compression molding to obtain a desired shape.

Examples of conductive fine ceramics include WC, TiC, TaC, ZrC, VC, TiB ₂ , and Ti.
One or more kinds of N are mentioned. Non-conductive fine ceramics include, for example, Al ₂ O ₃ , Si ₃
One or more of N ₄ and ZrO ₂ are mentioned.

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

The binder may be a metal to be treated or a metal which is easy to fuse the fine ceramics, and an appropriate one is selected according to the material of the metal to be treated. For example,
When the metal to be treated is iron or 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 fluid: As a machining fluid used for electric discharge machining, a liquid which decomposes carbon by generation of electric discharge is used.
For example, petroleum, fats and oils and the like. Since oil is hydrocarbon (CnHm), if it is thermally decomposed, C, H and Cn_x, Hm_y in the middle zone
Is generated. In a very short time in which the easily carbonized metal collides with the surface of the metal to be processed through the machining gap in a high temperature state by electric discharge, a chemical reaction occurs with the decomposed carbon. Because of the high temperature, it is significantly activated, so that several tens of percent of this metal becomes carbide.

M ₁ + M ₂ + M ₃ → M ₁ + M ₂ C + M ₂ + M ₃ Here, M ₁ : Fine ceramics M ₂ : Metal or semi-metal easy to form carbide M ₃ : Binder metal M ₂ C: Carbide Easy metal or metalloid carbide

Other electric discharge machining conditions: Other conditions of electric discharge in liquid may be the same as those of the previously proposed electric discharge coating method, and pulse electric discharge machining is desirable. For example, when a discharge is generated at about several hundreds to several tens of thousands of times per second, the processed surface is a surface on which small microscopic discharge marks are accumulated, and the discharge mark current density is a small area. High tens of thousands A / cm ² , high temperature and high pressure several tens μs
It occurs in a short time of about 1000 μs. The surface temperature at the discharge point is the boiling point temperature of the material, and the pressure at that point is
000 kgf / cm ² , and some of the melted part is scattered, but the remaining part is re-melted 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 increase.

The preferred conditions of the pulse discharge machining are as follows: power supply voltage: 60 to 100 V, pulse discharge current value (Ip): 1 to 1
00A, pulse width (τp): 5-2000 μs, pause time
(τr): 5 to 2000 μs. Generally, when the pulse discharge current value Ip is small, for example, when Ip = 3 A, τp
= 16 μs, when Ip is large, τp =
When Ip is small, τp is short, like 2000τs,
When Ip is large, τp is lengthened.

When performing submerged electrical discharge machining using an electrode that is not easily consumed in the process as one electrode, only an electrode made of a material that is not easily 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 this step is to basically process the thickness of the coating layer and the roughness of the finished surface to desired values, the processing is necessarily performed in a liquid. Also note that some electrical conditions are determined by the expected roughness of the finished surface.

FIG. 2 shows an example of an apparatus used for carrying out the present invention. A metal to be treated (base material) having a surface having a predetermined shape is placed in a processing tank containing a processing fluid that decomposes and generates carbon by generation of electric discharge, and a discharge electrode obtained by compression-molding powder is used. It is held above the base material with a small gap of about several tens to 100 μm. The base material and the discharge electrode can be moved up, down, left, and right 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 be consumed.

[0031]

Next, examples of the present invention will be described.

[0032]

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

After this primary machining, the powder electrode was replaced with a non-consumable electrode (copper), and a discharge treatment (secondary treatment) was performed in the same electric discharge machining liquid. The discharge condition at this time is as follows: 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
This is the surface analysis result of e, and small holes are seen in the secondary electron image of (1), and it is understood from the surface analysis result of C of (3) that it is a lump of carbon. As shown in the above primary processing conditions, there is a lump of carbon in spite of mixing Fe powder of pure iron. Iron and steel have the property of not easily forming carbides, such that when the content of carbon increases, graphite precipitates and becomes graphite cast iron. Of course, some will be cementite, but still leave the carbon in clumps.

The reason why the carbon lump remains is considered as follows. Like pure iron Fe powder, Co is also difficult to form carbides. Therefore, the same applies to the green compact of the mixture of WC + Co. Generally, the tendency to form carbides is as follows, with the elements on the left being more likely to form carbides. In particular, Ni, Co, and Si located 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

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

[0037]

Test Example 2 Therefore, based on the results of Test Example 1, an element which easily forms a carbide was added as a constituent element of a powder electrode, and submerged discharge was performed using the powder electrode. That is, Ti is selected as an element that easily forms carbide, and in order to clearly show whether or not Ti has been carbonized, Al that is unlikely to be carbonized is also used, and a green compact electrode composed of Ti and Al is formed. The treated metal (base material) is also Al material (aluminum die-cast material AD)
C12). At that time, an experiment was conducted in which carbon compounds due to mineral oil cracking were not present except for Ti carbides, and consideration was given to clarify the analysis. Also, TiC
It was made possible to quantitatively analyze the ratio of abundance on the surface. At this time, the mixing ratio of Ti and Al, the electric discharge machining conditions, and the like are as follows.

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

FIG. 4 is an X-ray diffraction pattern of the obtained base material surface coating layer, wherein Ti formed on the surface of the base material Al is Ti.
It can be seen that the C and TiAl _3.

FIG. 5 shows the results of examining the thickness of the coating layer and the volume ratio of TiC by changing the discharge current pulse width τp among the electric discharge machining conditions. FIG. 6 shows the results of examining the thickness of the coating layer and the volume ratio of TiC while changing the processing time tw. From these test results, it is understood that the volume ratio of TiC in the coating layer is 50% or more and reaches about 70%.

As described above, the fact that most of Ti is TiC means that the carbon in the coating layer structure is sufficiently carbided,
This indicates that the compound 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 1,000 or more. Even with bite materials already in practical use,
This coating layer also has excellent properties, as well as excellent properties of high-temperature wear resistance when TiC is added in addition to WC and Co.

[0042]

Test Example 3 Each powder of WC, Co and Ti was used for WC:
A green compact electrode mixed at a ratio of Co: Ti = 60: 20: 20 (% by weight) was prepared, 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 pole.

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

According to 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. Also, SEM image of the cross section (electron micrograph)
No cavity was observed, and it was confirmed that no residual carbon was present. This coating layer is made of WC: Co without adding Ti.
= Abrasion resistance as a cutting tool was about 10 times higher than the coating layer formed at a ratio of 80:20.
The cutting test conditions at this time were as follows: carbon steel (S55
Using the round bar of C), cut 0.5mm, feed 0.1mm / mi
n, the cutting speed was 100 m / min.

[0045]

As described in detail above, according to the present invention,
Since the decomposition carbon generated by the discharge can be reduced from remaining as a lump in the coating layer, a higher-quality coating layer can be formed on the surface of the metal material. It is suitable for improving the wear resistance, heat resistance, etc. of molds, gas turbines, and the like.

[Brief description of the drawings]

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

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

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

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

FIG. 5 is a diagram showing a relationship between a change in pulse width, an average thickness of a coating layer, and a 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)

(57) [Claims] 1. A metal or semi-metal (non-metal) that easily forms a carbide and a metal to be treated or a metal that easily fuses the fine ceramic as a binder are mixed in a powder state with conductive fine ceramics. Then, a material having a desired shape by compression molding is used as a discharge electrode, a working fluid that decomposes and generates carbon by generating a discharge as a working fluid, and a metal to be treated is discharged as one electrode in the working fluid. By performing the processing, a part of the metal or metalloid that easily forms the above-mentioned carbide is reacted and generated as a carbide, and on the surface of the metal to be treated, the conductive fine ceramics and the carbide, and the metal that did not partially become the carbide and the bonding metal A surface treatment method for a metal material by discharge in a liquid, characterized by forming a surface layer comprising: 2. The method according to claim 1, wherein the conductive fine ceramic is WC,
TiC, TaC, ZrC, VC, TiB 2, TiN, The method of claim 1 comprising one or two or more of Ti ₂ N. 3. A non-conductive fine ceramic is mixed with a metal or semi-metal which is easy to form a carbide and a metal which is easy to fuse with the metal to be treated as a binder in a powder state, and compression-molded. By using a material having a desired shape as a discharge electrode, using a machining fluid that decomposes and generates carbon by generating a discharge as a machining fluid, and performing electrical discharge machining using one of the metals to be treated in the machining fluid as an electrode, A part of a metal or metalloid that easily forms carbide is reacted and produced as a carbide, and a surface layer made of non-conductive fine ceramics and carbide, a metal that has not been partially carbided, and a binder metal is formed on the surface of the metal to be treated. A surface treatment method for a metal material by discharging in a liquid, characterized in that the metal material is formed. 4. A non-conductive fine ceramic comprising Al ₂
O _3, Si ₃ N _4, The method of claim 3 consisting of ZrO ₂ 1 kind or 2 or more. 5. The metal which easily forms carbide is Ti, Nb,
4. The method according to claim 1, wherein the metalloid (non-metallic) is B, and is composed of one or more of W, V, Zr, Ta, Cr, Mo, and Mn.
The method described in. 6. When the metal to be treated or the metal which is easy to fuse the fine ceramics is steel, the metal to be treated is iron or steel.
e, Co or Ni, and aluminum, Al,
It is made of Zn or Cu. In the case of zinc material, it is made of Cu, Al or Sn.
The method according to claim 1, comprising: 7. Nb is used as a metal which easily forms carbide.
The method according to claim 1 or 3, wherein 10% is added. 8. After forming a surface layer by the method according to claim 1 or 2, a discharge process is performed in liquid or air using an electrode that is not easily consumed as one electrode, and the surface layer is re-melted and solidified. A method for treating a surface of a metal material by electric discharge.