JP5012384B2 - Surface treatment method - Google Patents

Description

  In the present invention, a pulsed discharge is generated between a conductive electrode and a material to be processed, and the electrode material is applied to the surface of the material to be processed by the pulsed discharge energy. The present invention relates to a surface treatment method for forming a film containing a substance obtained by reaction.

  There is a surface treatment method in which a coating based on the material of the discharge electrode is formed on the surface of a material to be treated by electric discharge in insulating processing oil. In this surface treatment method, the surface of the material to be treated is obtained by applying a voltage between the material to be treated in a liquid containing carbon by using a powder containing metal hydride powder as a discharge electrode. A surface layer containing the metal compound is formed thereon. As a result, a surface layer having strong adhesion, good wear resistance, and beautiful finished surface roughness can be obtained (see, for example, Patent Document 1).

JP-A-9-192937 (first page)

  By the surface treatment method described above, for example, the surface of a material to be treated made of a metal material such as aluminum or an aluminum alloy can be coated with a metal different from aluminum to give corrosion resistance and wear resistance. However, with the harsh and diversified usage environment, coating materials that can withstand more severe usage conditions are required. Therefore, when the surface treatment is performed by the above-described conventional method using a precipitation hardening type metal material capable of expressing high strength by precipitation hardening as the material of the discharge electrode, the coating formed on the material to be treated becomes brittle. The problem of becoming.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a surface treatment method capable of forming a film having high strength at high temperatures.

  The surface treatment method according to the present invention generates a discharge by applying a voltage between a discharge electrode formed using a precipitation hardening type alloy material in a processing oil and the material to be treated. A discharge surface treatment process for forming a first film on the surface of the first film, a carbon removal process for removing carbon on the surface of the first film, and a precipitation hardening process after annealing the first film from which the carbon has been removed. And a heat treatment step for obtaining a second film.

  A precipitation hardening type alloy material is used as the material of the discharge electrode, and after removing carbon on the surface of the first film formed on the material to be treated by the discharge surface treatment in the processing oil, the first film is formed. Heat treatment. Therefore, it is possible to prevent carbon existing on the surface of the first film by heat treatment from precipitating carbides with Cr and Fe, thereby reducing the strength of the first film and causing embrittlement. An expressed second coating can be obtained.

Embodiment 1 FIG.
In the surface treatment method according to the first embodiment of the present invention, a voltage is applied between a discharge electrode formed using a precipitation hardening type alloy material and a material to be treated in processing oil, and the discharge electrode and the material to be treated are thus treated. A heat treatment in which a discharge is generated between the material and the first material to form a first film on the surface of the material to be treated, carbon on the surface of the first film is removed, and annealing treatment is performed, followed by precipitation hardening. To obtain a second coating.

  The precipitation hardening type alloy used for the discharge electrode according to the present embodiment is a material in which the material is hardened by solid solution treatment and subsequent aging treatment (that is, precipitation hardening treatment), and exhibits high strength. An alloy that can be subjected to a heat treatment method utilizing the precipitation phenomenon in which fine particles are precipitated and hardened by subsequent aging treatment, for example, there is a Ni-based alloy having the composition shown in Table 1.

  As shown in Table 1, the Ni-based alloy contains Ni as a main component and contains Cr and Fe. Examples of the precipitation hardening type alloy include stainless steel, aluminum alloy, and copper alloy.

FIG. 1 is an optical micrograph showing a cross section of a coating containing a Ni-based alloy, which is a first coating formed by discharge surface treatment using a Ni-based alloy as a discharge electrode in the present embodiment. Is the carbon amount by the distance from the surface of the first coating (the Ni-based alloy-containing coating) in FIG. 1 to the inside of the first coating, and the carbon amount on the surface of the first coating 1 is 100. FIG.
Hereinafter, the first film, which is a film containing a Ni-based alloy, is simply referred to as a first film.
As shown in FIG. 1 and FIG. 2, when the discharge surface treatment is performed in an insulating processing oil using the discharge electrode according to the present embodiment, the processing oil is decomposed due to the occurrence of electric discharge to generate carbon. The carbon penetrates into the first coating 1 formed by the massive particles.
As shown in FIG. 2, in the first coating 1 obtained by the discharge surface treatment in the present embodiment, a large amount of carbon is present on the surface, and the carbon present on this surface is called carburizing and is formed on the surface of the massive particles. This suggests that carbon derived from processing oil is attached.

  Table 2 shows the result of quantitative analysis of the amount of carbon on the surface of the first coating 1 obtained by the discharge surface treatment according to the present embodiment, using an electron probe microanalyzer. It can be seen that the amount of carbon on the surface of the coating 1 is about 300 times greater than the amount of carbon in the Ni-based alloy of the discharge electrode (shown in Table 1).

As described above, when the Ni-based alloy of the above-described precipitation hardening type alloy is used as the discharge electrode, carbon which is a decomposition product of the processing oil is taken into the first coating 1 by the discharge surface treatment in the processing oil. It is easy and exists especially on the surface. In addition, Cr contained in the Ni-based alloy is easily segregated on the surface in the discharge surface treatment, and carbon and carbide are easily formed in the aging treatment at a high temperature in the subsequent precipitation hardening treatment. In this way, the carbon existing on the surface precipitates carbides with Cr and Fe, and makes the portion where the concentration of Cr and Fe in the periphery is reduced easily oxidized. In other words, the carburization causes oxidation and corrosion to progress inside along the mesh-like carbide, thereby reducing the strength of the alloy of the second coating and causing embrittlement.
From the above, it has been found that the removal of carbon on the surface of the first coating 1 is indispensable in order to develop a high strength by the subsequent precipitation hardening treatment.

Therefore, in the present embodiment, since the precipitation hardening type alloy material is used for the discharge electrode, the first coating 1 formed by the discharge surface treatment is subjected to the heat treatment for expressing the high strength. By removing the carbon on the surface, it is possible to prevent Cr and carbon segregated on the surface of the first coating 1 from reacting and embrittlement due to carburization.
As a method for removing carbon on the surface of the film according to the present embodiment, ion etching, photoexcitation is used to ionize a target material or chemical bonds are cut, or high thermal energy is accumulated to melt or evaporate. There is a laser ablation method that causes.

In the present embodiment, annealing treatment is performed after removing carbon on the surface of the first coating 1. Since the discharge surface treatment in this embodiment involves local dissolution of rapid heating and quenching, some deformation or shrinkage occurs, and internal stress tends to remain at the interface between the material to be treated and the coating. Therefore, the annealing treatment according to the present embodiment is performed to remove such residual stress and increase the strength at high temperature. In addition, this annealing treatment relaxes the residual stress generated between the lumps forming the inside of the first coating 1, acts in the direction in which the vacancies in the first coating 1 disappear, and the first coating 1 It also plays a role in improving precision.
In the present embodiment, since carbon on the surface of the first coating 1 is removed, the precipitation hardening treatment performed after the annealing treatment prevents the embrittlement and the surface has high strength at high temperatures. A treated film can be obtained.

  In addition, as shown in FIG. 1, in the inside of the 1st film | membrane 1 in this Embodiment, since adjacent lump particles make a closed pore and do not touch external air directly, the 1st film | membrane 1 is carburized by carburization. Even if carbon is present inside, since it does not react with Cr segregated on the surface, corrosion such as oxidation does not proceed, so that no major problem is caused.

Embodiment 2. FIG.
In Embodiment 2 of the present invention, a carbon removal step and a heat treatment step performed thereafter in the surface treatment method of Embodiment 1 will be specifically shown.
First, in the same manner as in the first embodiment, the first film 1 is formed on the material to be processed by the discharge surface treatment. Next, the surface of the first coating 1 is ion-etched to remove carbon on the surface of the first coating 1.
FIG. 3 is a characteristic diagram showing the relationship between the ion etching processing time according to the present embodiment and the carbon content of the surface of the first coating 1 obtained by the discharge surface treatment. The ion etching is performed in an Ar atmosphere. In this case, the applied power is 500 W. In addition, 0 minutes of ion etching treatment time is the 1st film | membrane 1 as formed by discharge surface treatment.
As shown in FIG. 3, when the ion etching treatment is performed for 4 minutes or more, the carbon content on the surface of the first coating 1 is almost the same as the carbon content in the Ni-based alloy (shown in Table 1). It can be seen that

FIG. 4 shows the relationship between the ion etching processing time and the amount of carbon on the surface of the first coating 1 of the Ni-based alloy when the ion etching according to the present embodiment is performed with an input power of 500, 1000, or 1500 W. In the characteristic diagram showing the relationship, a, b, and c in FIG. 4 are characteristics when the input power is 500, 1000, and 1500 W.
As shown in FIG. 4, it can be seen that the processing time can be shortened by increasing the input power.

FIG. 5 is a characteristic showing the relationship between the ion etching treatment time and the carbon content of the surface of the first coating 1 when the ion etching according to the present embodiment is performed with the etching atmosphere being Ar, Kr or Xe. In the figure, the input power during ion etching is 1500 W. In FIG. 4, x, y, and z are characteristics when the etching atmosphere is Ar, Kr, and Xe.
As shown in FIG. 5, the Kr or Xe atmosphere can reduce the amount of carbon contained in the coating earlier than when Ar is used.

Next, a process of obtaining a second film by heat-treating the first film 1 from which carbon on the surface has been removed as described above will be described.
FIG. 6 is a diagram showing conditions for the heat treatment according to the present embodiment. Since the discharge surface treatment involves rapid melting and rapid local melting, a certain amount of deformation or shrinkage occurs, and internal stress tends to remain at the interface between the material to be treated and the first coating 1. As a first stage of the heat treatment, an annealing process p for removing the residual stress is performed. The temperature of the annealing treatment p is 700 ° C. and the holding time is 2 hours based on the result of 0.2% proof stress measurement shown in FIG.
In the solid solution treatment q of the precipitation hardening treatment performed after the annealing treatment p, the holding time at 980 ° C. is 1 hour. As the subsequent aging treatment, the first stage aging treatment r1 has a holding time at 720 ° C. of 8 hours, and the second stage aging treatment r2 has a holding time at 620 ° C. of 8 hours. The cooling rate from 980 ° C. during the solution treatment q to 720 ° C. during the first bullet aging treatment r1 and the cooling rate from 720 ° C. during the first stage aging treatment r1 to 620 ° C. during the second stage aging treatment r2. Both speeds were 55 ° C./hour.

FIG. 8 is a characteristic diagram showing the relationship between the tensile strength at 600 ° C. of the second coating according to the present embodiment, the carbon content of the surface of the first coating 1, and the processing time of the ion etching process. In addition, 0 minutes of the ion etching treatment time is a Ni-based alloy film as formed by the discharge surface treatment.
As shown in FIG. 8, when the ion etching time in the Ar atmosphere is 4 minutes or longer, the amount of carbon on the surface of the first coating 1 is small, so that it is difficult to cause embrittlement due to oxidation. The tensile strength of the second coating is increased, resulting in a coating with high strength at high temperatures.
The above tendency is desirable because the temperature of the annealing treatment p is observed between 400 to 800 ° C., and the longer the holding time of the annealing treatment p can be removed.

FIG. 9 is obtained in the present embodiment by performing an ion etching process for 10 minutes to remove the carbon on the surface of the first coating 1, and then performing a precipitation hardening process after annealing at 700 ° C. It is a figure which compares and shows the tensile strength in 600 degreeC with respect to the 2nd film and the film obtained by carrying out the precipitation hardening process, without performing an annealing process, and "on" in a horizontal axis is annealing. A film with treatment, "None" indicates a film without annealing treatment.
From FIG. 9, it was found that when the annealing process for removing the residual stress was omitted and the heat treatment was performed, the strength of the coating at a high temperature was remarkably lowered.

Embodiment 3 FIG.
The surface treatment method of the third embodiment of the present invention is the same as that of the second embodiment, except that the discharge electrode having the density of 2.7 to 5.0 g / in the second embodiment and the etching time is 10 minutes. The surface treatment is performed to obtain the second coating.
FIG. 10 is a characteristic diagram showing the relationship between the density of the discharge electrode according to the present embodiment, the tensile strength of the second coating film according to the present embodiment at 600 ° C., and the amount of carbon in the coating film.
That is, as in the second embodiment, a first film is produced by a discharge surface treatment, and is ion-etched for 10 minutes in an Ar atmosphere with an input power of 500 W, and is present on the surface of the first film 1. After removing the carbon, the heat treatment shown in FIG. 6 was performed to obtain a second coating, and the tensile strength of the coating at 600 ° C. and the amount of carbon in the coating were measured.
As shown in FIG. 10, when the density of the discharge surface treatment electrode is in the range of 3.0 to 5.0 g / cm ³ , the carbon content in the second coating is small, the toughness is excellent, and the tensile strength is high. Moreover, the discharge surface treatment can be performed stably.
The same applies when another precipitation hardening type alloy is used as the discharge electrode.

It is an optical microscope photograph which shows the cross section of the film containing the Ni-based alloy which is the 1st film formed by the discharge surface treatment based on Embodiment 1 of this invention. FIG. 2 is a distribution diagram of carbon extending from the surface of the coating (first coating) containing the Ni-based alloy in FIG. 1 to the inside of the coating. It is a characteristic view which shows the relationship between the processing time of the ion etching which concerns on the 2nd Embodiment of this invention, and the carbon content of the surface of the 1st film of the Ni-based alloy obtained by the discharge surface treatment. When the ion etching according to the second embodiment of the present invention is performed with an input power of 500, 1000, or 1500 W, the ion etching processing time and the carbon amount on the surface of the first film of the Ni-based alloy It is a characteristic view which shows a relationship. When the ion etching according to the second embodiment of the present invention is performed with the etching atmosphere being Ar, Kr, or Xe, the ion etching treatment time and the amount of carbon on the surface of the first film of the Ni-based alloy It is a characteristic view which shows a relationship. It is the figure which showed the conditions of the heat processing which concerns on the 2nd Embodiment of this invention. It is a figure which shows the result of 0.2% yield strength measurement which concerns on the 2nd Embodiment of this invention. It is a characteristic view which shows the relationship between the tensile strength in 600 degreeC of the 2nd film by the 2nd Embodiment of this invention, the carbon content of the surface of a 1st film, and the processing time of an ion etching process. The figure which compares and compares the 2nd film which concerns on the 2nd Embodiment of this invention, and the film obtained by carrying out similarly to this Embodiment except not performing an annealing process in 600 degreeC. It is. It is a characteristic view which shows the relationship between the density of the discharge electrode which concerns on the 3rd Embodiment of this invention, the tensile strength of the film in 600 degreeC of a 2nd film, and the carbon content in a film.

Explanation of symbols

  1 1st film, 2 material to be treated.

Claims (5)

  In processing oil, a voltage is applied between a discharge electrode formed using a precipitation hardening type alloy material and the material to be processed to generate a discharge, and a first film is formed on the surface of the material to be processed A discharge surface treatment step to perform, a carbon removal step to remove carbon on the surface of the first coating, and a heat treatment to obtain a second coating by performing precipitation hardening after annealing the first coating from which the carbon has been removed A surface treatment method comprising the steps.   2. The surface treatment method according to claim 1, wherein the precipitation hardening type alloy material is a Ni-based alloy material containing Cr or Fe. The surface treatment method according to claim 1 or 2, wherein the density of the discharge electrode is 3.0 to 5.0 g / cm ³ .   The surface treatment method according to claim 1, wherein the carbon removing step is performed by ion etching.   The surface treatment method according to claim 4, wherein ion etching is performed using a rare gas for 4 minutes or more.

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