JP4608220B2 - Discharge surface treatment electrode and discharge surface treatment method - Google Patents

Description

  The present invention uses a metal powder, a powder of a metal compound, or a green compact obtained by compression molding a ceramic powder as an electrode to generate a pulsed discharge between the electrode and the workpiece, Further, the present invention relates to a discharge surface treatment for forming a film made of an electrode material or a material in which the electrode material reacts with discharge energy.

It is necessary to coat or build up a material having strength and lubricity in a high temperature environment on the surface of an aircraft gas turbine engine such as a turbine blade. Since it has been known that Cr (chromium) and Mo (molybdenum) are oxidized to form an oxide in a high-temperature environment, it exhibits lubricity. Therefore, it is based on Co (cobalt) and contains Cr and Mo. The coating is thickened by welding or spraying the material.
Here, welding is a method in which the material of the welding rod is melted and adhered to the workpiece by electric discharge between the workpiece and the welding rod. Thermal spraying is a state in which a metal material is melted and sprayed onto the workpiece in a spray form. Is a method of forming
However, both the welding and thermal spraying methods are manual operations and require skill, so that there is a problem that it is difficult to line the operations and the cost is increased.
In particular, welding is a method in which heat concentrates and enters the workpiece. Therefore, when processing thin materials or materials that are easily broken such as directional control alloys such as single crystal alloys and unidirectionally solidified alloys, There is also a problem that cracking is likely to occur and the yield is low.

  On the other hand, although different from surface treatment methods such as welding and thermal spraying having strength and lubricity in a high temperature environment, other surface treatment techniques include surface treatment by electric discharge machining as shown in, for example, International Publication WO99 / 58744. Has also been established.

International Publication No. WO99 / 58744 (pages 7-8)

In the formation of a thick film by the discharge surface treatment, the method of supplying the material from the electrode side, melting the supplied material on the workpiece surface, and bonding with the workpiece material has the greatest influence on the coating performance.
It is the strength or hardness of the electrode that affects the supply of the electrode material.
In the electrode manufacturing method disclosed in International Publication No. WO99 / 58744, the electrode surface is hardened on the work surface by suppressing the supply of the electrode material by discharge while sufficiently melting the supplied material while the electrode has a certain degree of hardness. A ceramic film is formed. In this method, the film to be formed is limited to a thin film of up to about 10 μm.
However, there is a demand for the formation of a dense and relatively thick film (thick film of the order of 100 μm or more) for applications that require strength and lubricity in a high temperature environment.

  It is an object of the present invention to establish a dense and relatively thick surface treatment method that requires strength and lubricity in a high temperature environment.

  The discharge surface treatment electrode according to the first aspect of the invention is a metal powder, a metal compound powder, or a green compact obtained by compression-molding a ceramic powder, and is interposed between the electrode and the workpiece in the working fluid or in the air. In the discharge surface treatment in which a pulsed discharge is generated and a film made of the electrode material or a material obtained by reacting the electrode material with the discharge energy is formed on the work surface by the energy, 1.0 to 4.5 wt. % Boron, or 1.5 to 5.0% silicon by weight.

  According to the present invention, a dense film without pores can be formed by discharge surface treatment.

The electrode component used in the conventional discharge surface treatment contains a large proportion of materials that are likely to form carbides. For example, a material such as Ti chemically reacts by discharge in oil, and the material of the workpiece surface is Discharge surface treatment has been performed in which characteristics such as heat conduction and melting point change from steel material (when processed to steel material) to hard carbide called TiC (titanium carbide) which is ceramic.
According to experiments by the inventors, by adding a material that is not easily carbonized (hard to form carbides) to the electrode material, the material remaining in the film as a metal increases, and a film obtained by discharge surface treatment is added. It has been found that it can be thickened, and it has been found that the material conditions of the electrode are important for thick film formation.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1
The object of the present invention is to form a dense thick film by discharge surface treatment. First, the formation of a thick film by discharge surface treatment will be described.

In the conventional discharge surface treatment, the electrode contains a large proportion of materials that easily form carbides. For example, when a material such as Ti is included in the electrode, a chemical reaction occurs due to discharge in oil, It becomes a hard carbide called TiC (titanium carbide).
As the surface treatment progresses, the material of the workpiece surface changes from steel (when processed into steel) to TiC which is ceramic, and characteristics such as heat conduction and melting point change accordingly.
However, when a material that is not carbonized or hardly carbonized is added to the electrode, the film does not become a carbide, and a phenomenon occurs in which the material that remains in the film as a metal increases.
And, it has been found that the selection of the electrode material has a great significance for thickening the coating.

As shown in FIG. 1, a powder obtained by mixing Cr ₃ C ₂ (chromium carbide), which is a carbide, and Co (cobalt), which is a material that is difficult to form carbide, is compression-molded, and then heated to increase the electrode strength. When an electrode is manufactured, the ease of forming a thick film changes by changing the amount of Co that is difficult to form carbides.
FIG. 2 shows this state.

The powder used to produce the electrode was compressed so that the compression pressing pressure was about 100 MPa, and the heating temperature was in the range of 400 ° C to 800 ° C.
The heating temperature was increased as the amount of Cr ₃ C ₂ (chromium carbide) was increased, and the temperature was decreased as the amount of Co (cobalt) was increased.
This is because when the amount of Cr ₃ C ₂ (chromium carbide) is large, the manufactured electrode tends to become brittle and immediately collapses even when heated at a low temperature, whereas when the amount of Co (cobalt) is large, the heating temperature This is because the strength of the electrode was likely to increase even when the thickness was low.
At the time of pressing, a small amount (2% to 3% by weight) of wax was mixed with the powder to be pressed in order to improve the moldability. The wax is removed during the heating.

Cr ₃ C ₂ (chromium carbide) used powder with a particle size of about ₃ μm to 6 μm, and Co used powder with a particle size of about 4 μm to 6 μm. The base material is Cr ₃ C ₂ (chromium carbide).
The discharge pulse used has a waveform as shown in FIG. 3, and the pulse conditions are: peak current value ie = 10 A, discharge duration (discharge pulse width) te = 64 μs, rest time to = 128 μs, area of 15 mm × 15 mm A film was formed on the electrode of No. 5 in a treatment time of 15 minutes.
The polarity was negative for the electrode and positive for the workpiece.
In FIG. 3, when the electrode has a negative polarity and the workpiece has a positive polarity, the vertical axis is displayed on the upper side.

  When a film is formed based on such a pulse condition, the thickness of the film formed on the workpiece varies depending on the volume% of Co in the manufactured electrode. According to FIG. When the amount is low, the film thickness of about 10 μm gradually increases from the Co content of about 30% by volume, and increases from around the Co content of 50% by volume to about 10,000 μm. .

This will be described in more detail.
When a film is formed on the workpiece based on the above conditions, when Co in the electrode is 0%, that is, when Cr ₃ C ₂ (chromium carbide) is 100% by weight, The limit is about 10 μm, and the thickness cannot be increased further.
Moreover, the state of the thickness of the coating film with respect to the processing time when there is no material that hardly forms carbide in the electrode is as shown in FIG.
According to FIG. 4, at the beginning of the treatment, the film grows and thickens with time and saturates at some point (about 5 minutes / cm ² ).
After that, the film thickness does not grow for a while, but if the treatment is continued for a certain time (about 20 minutes / cm ² ) or more, the thickness of the film starts to decrease and finally the film height becomes minus, that is, changes to digging. .
However, the film is present even in the dug state, and the thickness itself is about 10 μm, which is almost the same as the state processed in an appropriate time. Therefore, the processing time between 5 minutes and 20 minutes is considered appropriate.

Returning to FIG. 2, it becomes possible to increase the thickness as the amount of Co, which is a material that is not easily carbonized in the electrode, and when the amount of Co in the electrode exceeds 30% by volume, the thickness of the formed film starts to increase, It has been found that when it exceeds 40% by volume, a thick film can be easily formed stably.
The graph of FIG. 2 shows that the film thickness increases smoothly from about 30% by volume of Co, but this is an average value obtained by performing a plurality of tests. Is about 30% by volume, there are cases where the film does not swell thickly, or even when it swells thickly, the film strength is weak, that is, it may be removed by rubbing strongly with a metal piece, etc. Not stable.
More preferably, the Co content exceeds 50% by volume.
By increasing the amount of the material remaining as a metal in the coating in this way, a coating containing a metal component that is not carbide can be formed, and a thick film can be easily formed stably.
The volume% here is a ratio of a value obtained by dividing the weight of each powder to be mixed by the density of each material, and is a ratio of the volume occupied by the material in the volume of the material of the whole powder.

FIG. 5 shows a photograph of the coating formed when the Co content in the electrode is 70% by volume.
This photograph illustrates the formation of a thick film.
In the photograph shown in FIG. 5, a thick film of about 2 mm is formed.
This film is formed in a processing time of 15 minutes, but if the processing time is increased, a thicker film can be formed.

In this way, by using an electrode containing 40% by volume or more of a material that is difficult to carbonize or not carbonized, such as Co, in the electrode, a thick film can be stably formed on the workpiece surface by discharge surface treatment. .
In the above description, the case where Co (cobalt) is used as a material that hardly forms carbides has been described. However, Ni (nickel), Fe (iron), and the like are materials that can obtain similar results, and are used in the present invention. Is preferred.

As described above, a thick film can be formed by adding a predetermined amount of a material that does not easily form carbides to the electrode. However, the film has a problem that there are many pores.
A method for reducing the pores will be described below.
In the following, a Co alloy, which is a material used as a thick film that actually exhibits lubricity and the like, was used instead of the electrode material for the test for forming a thick film as described above.

FIG. 6 shows a process for manufacturing an electrode used in the discharge surface treatment method of the first embodiment.
In the figure, 1 is a Co alloy powder having a particle size of about 1 to 2 μm, 2 is a B (boron) powder having a particle size of about 1 to 2 μm, 3 is a Si (silicon) powder having a particle size of about 1 to 2 μm, and 4 is a mold. The upper punch, 5 is the lower punch of the mold, and 6 is the die of the mold.
The mixing ratio of the Co alloy powder 1, the B powder 2 and the Si powder 3 is about 1.0 to 4.5% by weight of B (boron) in the electrode material, or 1.5 to 5.0% by weight of Si. % Or both.

Here, the Co alloy powder used was “Cr (chromium) 20 wt%, Ni (nickel) 10 wt%, W (tungsten) 15 wt%, Co (cobalt) residue”. Wt%, Ni (nickel) 10 wt%, W (tungsten) 7 wt%, Co (cobalt) residue "," Cr (chromium) 20 wt%, Ni (nickel) 10 wt%, W (tungsten) 15 wt% , Co (cobalt) remaining ”,“ Cr (chromium) 15 wt%, Fe (iron) 8 wt%, Ni (nickel) remaining ”,“ Cr (chromium) 21 wt%, Mo (molybdenum) 9 wt%, Ta (Tantalum) 4 wt%, Ni (nickel) residue "," Cr (chromium) 19 wt%, Ni (nickel) 53 wt%, Mo (molybdenum) 3 wt%, (Cb + Ta) 5 wt%, Ti (titanium) 0.8 weight , Al (aluminum) 0.6 weight%, may be of a material such as Fe (iron) remaining. "
In the present embodiment, the B powder 2 which is a material acting as a flux at a high temperature (about 1000 ° C.) with respect to the Co alloy powder 1 for forming a film on the workpiece, the flux at the same high temperature (about 1000 ° C.). By mixing the material Si powder 3 that acts as an electrode, it takes oxygen atoms at the time of film formation, and produces an electrode having a function for forming a metal film with less oxide and less porosity in the film. The method will be described.

Next, a specific electrode manufacturing process will be described.
A powder in which Co alloy powder 1, B powder 2 and Si powder 3 are sufficiently mixed is put into a mold and compression molded to form a predetermined shape.
At this time, it is more desirable to compress the powder after mixing the wax with the powder because the moldability of the green compact is improved.
However, since wax is an insulating material, if it remains in a large amount in the electrode, the electrical resistance of the electrode increases and the discharge performance deteriorates, so it is necessary to remove the wax.
This wax can be removed by placing the green compact electrode in a vacuum furnace and heating at about 300 ° C.
Moreover, the electrical resistance of an electrode can be lowered | hung or intensity | strength can be increased by heating.
Therefore, heating is meaningful even when no wax is mixed.

Now, FIG. 2 shows a state in which the discharge surface treatment is performed using the electrode made of the Co alloy powder 1, the B powder 2 and the Si powder 3 manufactured by the process as described above.
In the figure, 11 is an electrode made of Co alloy powder 1, B powder 2 and Si powder 3, 12 is a workpiece, 13 is a working fluid, 14 is a power supply for discharge surface treatment that generates a pulsed discharge, and 15 is a discharge power source. It is an arc pillar.

By realizing the discharge surface treatment shown in FIG. 7, a Co alloy film can be formed on the surface of the workpiece 12.
When B powder 2 or Si powder 3 was not mixed in the electrode 11, pores were formed in the formed film, and it was difficult to form a dense film. By adding 2 or Si powder 3 or both to the electrode, a dense film with few pores could be formed.
This is because, if B (boron) or Si (silicon) is present in the material supplied from the electrode 11 to the work 12 side, oxygen atoms in the oxide film of the powder constituting the electrode are changed to B (boron) or When Si (silicon) becomes hot during discharge, it becomes B ₂ O ₃ , SiO ₂ and dissolves and floats on the surface of the film, so that unnecessary oxygen atoms in the film disappear and adhesion between the powder materials is eliminated. I think it ’s better.

When B (boron) or Si (silicon) is not contained in the electrode, the amount of oxygen in the coating becomes high.
This indicates that oxygen in the powder constituting the electrode (mainly present in the oxide film) migrates directly into the film.
When the amount of oxygen is large when the electrode material becomes a film, the powders are prevented from adhering to each other, increasing the pores and thus decreasing the film strength.
When B (boron) or Si (silicon) is put in the electrode, such a phenomenon can be prevented, and a dense and strong film can be formed.

In the present embodiment, the electrode material is described as being about 1.0 to 4.5% by weight of B (boron) or about 1.5 to 5.0% by weight of Si.
If it is less than this, the effect of removing oxygen atoms in the material will be reduced, and if it is too much, B (boron) and Si (silicon) will remain in the material, causing problems such as reducing the film strength. It was.
Further, by adding B (boron) or Si (silicon) as an electrode component, the melting point of the electrode material can be lowered, and there is an effect of promoting the melting of the material.

In this embodiment, the method of adding B (boron) or Si (silicon) as a powder to the electrode material has been described. However, B (boron) or Si (silicon) may be mixed into the powder material as an alloy. .
In that case, B (boron) and Si (silicon) can be mixed uniformly, which is more desirable.

In this embodiment, a Co alloy is used as an electrode, but Ni alloy, Fe alloy, and the like are materials that can obtain similar results.
Further, although a Co alloy is used, this may be a mixture of powders of the respective component elements, not an alloy.
However, when mixing the respective powders, care must be taken because it may cause variations in the components of the coating unless the powders are sufficiently mixed.
In this embodiment, the metal-only electrode has been described, but ceramic powder may be mixed with the electrode in order to increase the hardness of the coating.
In this case, if the amount of ceramics becomes too large, it becomes difficult to form a thick film as described in the thick film formation. Therefore, it is necessary to set the amount to a predetermined amount or less. By increasing the metal density by adding boron) or Si (silicon), the film density can be increased.
As described above, the thickness of the coating can be increased as the amount of Co, which is a material that is difficult to carbonize in the electrode, is increased. If the amount of Co in the electrode exceeds 30% by volume, the thickness of the coating film increases. First, if it exceeds 40% by volume, a thick film can be easily formed stably.

  Japanese Patent Application Laid-Open No. 56-51543 discloses an invention for adding Si to an electrode material. This is an invention related to an electrode for ordinary electric discharge machining, and is intended to increase the machining speed, and forms a metal film. This is an invention in a field different from the present invention in which deoxidation is performed with Si so that the film is not oxidized.

  According to the present embodiment, by adding Si and B to an electrode containing 40% by volume or more of a material that is difficult to form carbide, Si and B are combined with oxygen atoms at the time of forming the coating for the discharge surface treatment. Since oxygen can be reduced, a dense and strong metal film with few pores can be formed.

The powder mixed and cr ₃ C ₂ and Co is a process diagram of compression molding. It is a figure which shows the quantity of Co in an electrode pillar, and the relationship of a film thickness. It is a figure which shows a discharge phenomenon. It is a figure which shows the relationship between processing time and a film thickness. It is a figure which shows the state of a film. It is a figure which shows one Example of 1st invention. It is a figure which shows one Example of 1st invention.

Explanation of symbols

  1 Co alloy powder, 2 B (boron) powder, 3 Si (silicon) powder, 4 upper die punch, 5 lower die punch, 6 die die, 11 discharge surface treatment electrode, 12 workpiece, 13 Machining fluid, 14 power source for surface treatment of discharge, 15 arc column of discharge.

Claims (6)

A metal powder, a metal compound powder, or a green compact obtained by compression molding a ceramic powder is used as an electrode to generate a pulsed discharge between the electrode and the workpiece in the machining fluid or in the air. In the discharge surface treatment to form a film made of a material in which the electrode material or the electrode material reacts with the discharge energy on the surface,
By adding boron powder or silicon powder to the electrode material, the electrode contains 1.0-4.5% by weight boron or 1.5-5.0% by weight silicon, and the powder particle size contributing to film formation is 3 μm or less. An electrode for discharge surface treatment. Using a green compact obtained by compression molding metal alloy powder as an electrode, a pulsed discharge is generated between the electrode and the workpiece in the machining fluid or in the air, and the electrode material or electrode material is discharged on the workpiece surface by that energy. In the discharge surface treatment to form a film made of a material that reacts with energy,
An electrode for discharge surface treatment, comprising 1.0 to 4.5% by weight of boron or 1.5 to 5.0% by weight of silicon as an alloy component, and having a powder particle size contributing to film formation of 3 μm or less. As alloy metal powder, “Cr 0 to 10 wt%, B 1.0 to 2.5 wt%, Si 1.5 to 3.5 wt%, C 0.25 wt% or less, Fe 4 wt% or less, Co 1 wt% or less, Cu 4 wt% or less , Ni residue ”,“ Cr 9 to 11 wt%, B 1.0 to 2.5 wt%, Si 2.0 to 3.5 wt%, C 0.5 wt% or less, Fe 4 wt% or less, Co 1 wt% or less, Ni residue ”,“ Cr 10 to 15% by weight, B 2.0 to 3.0% by weight, Si 3.0 to 4.5% by weight, C 0.4 to 0.7% by weight, Fe 5% by weight or less, Co 1% by weight or less, Ni remaining ”,“ Cr 12 to 17% by weight B2.5-4.0 wt%, Si3.5-5.0 wt%, C0.4-0.9 wt%, Fe5 wt% or less, Co1 wt% or less, Mo4 wt% or less, Cu4 wt% or less, Ni residue "," Cr 15-20 wt%, B 3.0-4.5 wt%, Si 2.0-5.0 wt%, C 0.5-1.1 wt%, Fe 5 wt% or less, Co 1 wt% or less, Ni remaining ”,“ Ni 10-30 wt% , Cr16-21% by weight, B1.5-4.0 wt%, Si2.0-4.5 wt%, C1.5 wt% or less, Fe5 wt% or less, Mo7 wt% or less, W10 wt% or less, Co residue "," Ni0-15 wt%, Cr19 24 wt%, B 2.0-3.0 wt%, Si 1.5-3.0 wt%, C 1.5 wt% or less, Fe 5 wt% or less, W 4-15 wt%, Co residue ”. The electrode for discharge surface treatment according to claim 2, wherein the electrode is for surface treatment. The discharge surface treatment electrode according to claim 1, wherein 30% by volume of Co, Ni, or Fe is contained as an electrode material or an alloy component. A metal powder, a metal compound powder, or a green compact obtained by compression molding a ceramic powder is used as an electrode to generate a pulsed discharge between the electrode and the workpiece in the machining fluid or in the air. In the discharge surface treatment to form a film made of a material in which the electrode material or the electrode material reacts with the discharge energy on the surface,
By adding boron powder or silicon powder to the electrode material, the electrode contains 1.0 to 4.5% by weight boron or 1.5 to 5.0% by weight silicon, and the powder particle size contributing to film formation is 3 μm or less. A discharge surface treatment method characterized in that a film is formed using a powder electrode. A metal powder, a metal compound powder, or a green compact obtained by compression molding a ceramic powder is used as an electrode to generate a pulsed discharge between the electrode and the workpiece in the machining fluid or in the air. In the discharge surface treatment to form a film made of a material in which the electrode material or the electrode material reacts with the discharge energy on the surface,
The film formation is carried out using a powder electrode formed by compression-forming an alloy powder containing 1.0 to 4.5% by weight of boron or 1.5 to 5.0% by weight of silicon and having a powder particle size of 3 μm or less that contributes to film formation. A discharge surface treatment method.

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