JP7747415B2 - Processing method - Google Patents

Description

This disclosure relates to a processing method.

A technique is known in which alloy steel is coated with aluminum, and then the aluminum coating is heated to oxidize it, thereby forming an alumina layer (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 8-193258

This disclosure provides a technology that can form an aluminum oxide layer with low surface roughness on the surface of a substrate.

A processing method according to one aspect of the present disclosure includes the steps of preparing a substrate, forming an aluminum film on a surface of the substrate, heat-treating the substrate at a first temperature to diffuse and infiltrate the aluminum into the substrate, and heat-treating the substrate into which the aluminum has diffused and infiltrated at a second temperature higher than the first temperature to form an aluminum oxide layer, wherein the substrate is formed from a metal or alloy that does not contain aluminum .

According to the present disclosure, an aluminum oxide layer with low surface roughness can be formed on the surface of a substrate.

1 is a flowchart illustrating an example of a processing method according to an embodiment. Diagram showing the results of composition analysis Diagram showing the results of composition analysis Diagram showing the results of composition analysis Surface roughness measurement results Surface roughness measurement results Corrosion resistance evaluation results Corrosion resistance evaluation results Corrosion resistance evaluation results Corrosion resistance evaluation results

Non-limiting exemplary embodiments of the present disclosure will now be described with reference to the accompanying drawings. In all of the accompanying drawings, the same or corresponding reference numerals will be used to designate the same or corresponding members or components, and redundant descriptions will be omitted.

[Processing method]
An example of a processing method according to an embodiment will be described with reference to Fig. 1. The processing method according to the embodiment includes forming an aluminum oxide layer on the surface of a substrate by carrying out a substrate preparation step S1, a film formation step S2, a first heat treatment step S3, and a second heat treatment step S4 in this order. Each step will be described below.

(Base material preparation step S1)
The substrate preparation step S1 is a step of preparing a substrate to be processed. For example, a metal not containing aluminum (Al) (hereinafter referred to as a "non-Al metal") or an alloy not containing Al (hereinafter referred to as a "non-Al alloy") can be used as the substrate. Examples of non-Al metals include general structural rolled steel (SS material). Examples of non-Al alloys include stainless steels such as SUS304, SUS316, and SUS316L, and nickel-based alloys such as NCF600. Alternatively, a metal containing Al or an alloy containing Al may be used as the substrate. However, from the viewpoints of low material costs and low processing costs, it is preferable to use a substrate formed from a non-Al metal or a non-Al alloy.

(Film forming process S2)
The film-forming step S2 is a step of forming an aluminum film on the surface of the substrate. The aluminum film can be formed by physical vapor deposition (PVD) such as sputtering, vapor deposition, or ion plating. When forming an aluminum film on the surface of the substrate by PVD, a mask such as a metal mask can be used to selectively form the aluminum film only on required areas of the substrate. The thickness of the aluminum film formed on the surface of the substrate in the film-forming step S2 may be, for example, 1 μm to 2 μm.

(First heat treatment step S3)
The first heat treatment step S3 is a step of heat treating the substrate at a first temperature T1 to diffuse and penetrate the aluminum film formed on the surface of the substrate into the substrate. The first heat treatment step S3 is performed in an oxygen-containing atmosphere, for example, an air atmosphere. The first temperature T1 is determined depending on the type of substrate. The first temperature T1 may be equal to or higher than the temperature at which aluminum diffuses and penetrates into the substrate. The first temperature T1 is preferably lower than the alloying temperature between the metal elements contained in the substrate and aluminum. This makes it possible to suppress surface roughening of the substrate due to alloying between the metal elements contained in the substrate and aluminum. The first temperature T1 is, for example, 500°C or higher and 700°C or lower.

(Second heat treatment step S4)
The second heat treatment step S4 is a step of forming an aluminum oxide layer by heat treating the aluminum-diffused and infiltrated substrate at a second temperature T2. The second heat treatment step S4 is performed in an oxygen-containing atmosphere, for example, an air atmosphere. The second temperature T2 is determined depending on the type of substrate. The second temperature T2 is a temperature higher than the first temperature T1. The second temperature T2 is, for example, 750°C or higher and 1000°C or lower.

According to the treatment method of the embodiment described above, an aluminum film is formed on the surface of a substrate, and then the substrate is heat-treated at a first temperature T1 to diffuse and penetrate the aluminum into the substrate. The substrate with the aluminum diffused and penetrated is then heat-treated at a second temperature T2 that is higher than the first temperature T1 to form an aluminum oxide layer. This allows the temperature at which the aluminum diffuses and penetrates into the substrate to be lowered. As a result, alloying between the metal elements contained in the substrate and the aluminum is suppressed, allowing an aluminum oxide layer with low surface roughness to be formed on the surface of the substrate.

[Example]
Example 1
In Example 1, an experiment was conducted to confirm that an aluminum oxide layer was formed on the surface of a substrate by treating the substrate using the treatment method of the embodiment. In Example 1, SUS316L and NCF600 were used as the substrates. In Example 1, a 1.6 μm aluminum film was formed on the surface of the substrate by sputtering in the film-forming step S2. In Example 1, in the first heat treatment step S3, the substrate was heat-treated in an air atmosphere at 560° C. for 3 hours. In Example 1, in the second heat treatment step S4, the substrate was heat-treated in an air atmosphere at 850° C. for 1 hour. In Example 1, after the substrate was treated using the treatment method of the embodiment, the atomic concentration near the surface of the treated substrate was measured by X-ray photoelectron spectroscopy (XPS).

Figure 2 shows the results of measuring the aluminum (Al) atomic concentration, oxygen (O) atomic concentration, and iron (Fe) atomic concentration by XPS after performing the film formation step S2 and first heat treatment step S3 of the processing method of the embodiment on SUS316L. In Figure 2, the horizontal axis represents the depth [nm] from the surface of the substrate, and the vertical axis represents the atomic concentration [at%]. In Figure 2, the solid line represents the Al atomic concentration, the dashed line represents the O atomic concentration, and the dotted line represents the Fe atomic concentration.

As shown in Figure 2, the Al atomic concentration is approximately uniform from the surface of the substrate to a depth of 1000 nm, and is approximately 30 at% to 40 at%. On the other hand, the O atomic concentration decreases from approximately 65 at% to approximately 10 at% from the surface of the substrate to a depth of 1000 nm. Furthermore, the Fe atomic concentration increases from 0 at% to approximately 35 at% from the surface of the substrate to a depth of 1000 nm. These results demonstrate that aluminum diffuses and penetrates into SUS316L by performing the film-forming step S2 and the first heat treatment step S3 in this order in the processing method of the embodiment.

Figure 3 shows the results of measuring the aluminum (Al) atomic concentration, oxygen (O) atomic concentration, and iron (Fe) atomic concentration by XPS after performing the film formation process S2, first heat treatment process S3, and second heat treatment process S4 of the embodiment's processing method on SUS316L. In Figure 3, the horizontal axis represents the depth [nm] from the surface of the substrate, and the vertical axis represents the atomic concentration [at%]. In Figure 3, the solid line represents the Al atomic concentration, the dashed line represents the O atomic concentration, and the dotted line represents the Fe atomic concentration.

As shown in Figure 3, the Al atomic concentration is approximately uniform from the surface of the substrate to a depth of 400 nm, and is found to be approximately 35 at%. Furthermore, the O atomic concentration is approximately uniform from the surface of the substrate to a depth of 400 nm, and is found to be approximately 65 at%. Furthermore, the Fe atomic concentration is approximately 0 at% from the surface of the substrate to a depth of 400 nm. These results indicate that an aluminum oxide layer is formed from the surface of the substrate to a depth of 400 nm.

Figure 4 shows the results of measuring the aluminum (Al) atomic concentration, oxygen (O) atomic concentration, and nickel (Ni) atomic concentration by XPS after NCF600 was subjected to the film formation process S2, first heat treatment process S3, and second heat treatment process S4 in the processing method of the embodiment. In Figure 4, the horizontal axis represents the depth [nm] from the surface of the substrate, and the vertical axis represents the atomic concentration [at%]. In Figure 4, the solid line represents the Al atomic concentration, the dashed line represents the O atomic concentration, and the dotted line represents the Ni atomic concentration.

As shown in Figure 4, the Al atomic concentration is approximately uniform from the surface of the substrate to a depth of 200 nm, and is found to be approximately 35 at%. Furthermore, the O atomic concentration is approximately uniform from the surface of the substrate to a depth of 200 nm, and is found to be approximately 65 at%. Furthermore, the Ni atomic concentration is approximately 0 at% from the surface of the substrate to a depth of 200 nm. These results indicate that an aluminum oxide layer is formed from the surface of the substrate to a depth of 200 nm.

Example 2
In Example 2, an experiment was conducted to confirm that treating a substrate using the treatment method of the embodiment results in the formation of an aluminum oxide layer with low surface roughness on the surface of the substrate. In Example 2, the substrate was treated using the treatment method of the embodiment, and then the surface roughness of the substrate was measured using a laser microscope. In Example 2, SUS316L and NCF600 were used as the substrates. In Example 2, a 1.6 μm aluminum film was formed on the surface of the substrate by sputtering in the film-forming step S2. In Example 2, in the first heat treatment step S3, the substrate was heat-treated in an air atmosphere at 560°C for 3 hours. In Example 2, in the second heat treatment step S4, the substrate was heat-treated in an air atmosphere at 850°C for 1 hour. For comparison, an aluminum oxide layer was formed on the surface of the substrate by calorizing instead of the treatment method of the embodiment, and then the surface roughness of the substrate was measured using a laser microscope.

Figure 5 shows the results of measuring the surface roughness of a substrate made of SUS316L. In Figure 5, the bar graphs show the rate of change in the measured values of the substrate surface after treatment relative to the measured values of the substrate surface before treatment. In Figure 5, the bar graph labeled "After first heat treatment" shows the results when the substrate was subjected to the film-forming step S2 and the first heat treatment step S3 of the processing method of the embodiment. Furthermore, the bar graph labeled "After second heat treatment" shows the results when the substrate was subjected to the film-forming step S2, the first heat treatment step S3, and the second heat treatment step S4 of the processing method of the embodiment. Furthermore, the bar graph labeled "After calorizing treatment" shows the results when the substrate was subjected to calorizing treatment. Furthermore, in Figure 5, "Ra" and "Ry" are the arithmetic mean roughness and maximum height roughness, respectively, as defined in JIS B0601:2013, and "S" is the surface area of the substrate surface.

As shown in Figure 5, it can be seen that the maximum height roughness Ry is smaller "after the second heat treatment" than "after the calorizing treatment." These results demonstrate that when SUS316L is used as the substrate, treating the substrate using the treatment method of the embodiment makes it possible to form an aluminum oxide layer with less surface roughness on the surface of the substrate than when treating the substrate using the calorizing treatment.

Figure 6 shows the results of measuring the surface roughness of a substrate when NCF600 was used as the substrate. In Figure 6, the bar graph shows the rate of change in the measured value of the substrate surface after treatment relative to the measured value of the substrate surface before treatment. In Figure 6, the bar graph labeled "After first heat treatment" shows the results when the substrate was subjected to the film-forming step S2 and the first heat treatment step S3 of the processing method of the embodiment. Furthermore, the bar graph labeled "After second heat treatment" shows the results when the substrate was subjected to the film-forming step S2, the first heat treatment step S3, and the second heat treatment step S4 of the processing method of the embodiment. Furthermore, the bar graph labeled "After calorizing treatment" shows the results when the substrate was subjected to calorizing treatment. Furthermore, in Figure 6, "Ra" and "Ry" are the arithmetic mean roughness and maximum height roughness, respectively, as defined in JIS B0601:2013, and "S" is the surface area of the substrate surface.

As shown in Figure 6, the arithmetic mean roughness Ra and maximum height roughness Ry are smaller "after the second heat treatment" than "after the calorizing treatment." These results demonstrate that even when NCF600 is used as the substrate, treating the substrate using the treatment method of the embodiment makes it possible to form an aluminum oxide layer with less surface roughness on the surface of the substrate than when treating the substrate using the calorizing treatment.

Example 3
In Example 3, an experiment was conducted to confirm that treating a substrate using the treatment method of the embodiment results in the formation of an aluminum oxide layer on the substrate surface that is highly corrosion-resistant against corrosive gases. In Example 3, an aluminum oxide layer was formed on the substrate surface using the treatment method of the embodiment, and then the substrate was exposed to _ClF3 gas, a corrosive gas. Furthermore, elemental analysis of the substrate surface before and after exposure to _ClF3 gas was performed using energy dispersive X-ray spectroscopy (EDX). In Example 3, SUS316L and NCF600 were used as the substrates. In the film-forming step S2, a 1.6 μm aluminum film was formed on the substrate surface by sputtering. In Example 3, in the first heat treatment step S3, the substrate was heat-treated in an air atmosphere at 560°C for 3 hours. In Example 3, in the second heat treatment step S4, the substrate was heat-treated in an air atmosphere at 850°C for 1 hour. In Example 3, when exposing the substrate to _ClF3 gas, the substrate was placed in a chamber, the temperature in the chamber was adjusted to 400°C, the pressure was adjusted to 3 kPa, and _ClF3 gas was supplied into the chamber at a flow rate of 100 sccm, and the chamber was maintained for 5 hours. Also, for comparison, an aluminum oxide layer was formed on the surface of the substrate by calorizing treatment instead of the treatment method of the embodiment, and then the substrate was exposed to _ClF3 gas, and elemental analysis of the substrate surface before and after exposure to _ClF3 gas was performed by EDX.

7 and 8 show the results of elemental analysis when SUS316L was used as the substrate. Fig. 7 shows the results when an aluminum oxide layer was formed on the surface of the substrate using the treatment method of the embodiment, and Fig. 8 shows the results when an aluminum oxide layer was formed on the surface of the substrate by calorizing treatment. In Figs. 7 and 8, the bar graphs show the composition ratio [weight (wt) %] of the substrate. In Figs. 7 and 8, the bar graphs labeled "Before Exposure" show the composition ratio before the substrate was exposed to _ClF3 gas, and the bar graphs labeled "After Exposure" show the composition ratio after the substrate was exposed to _ClF3 gas.

As shown in Figure 7, when an aluminum oxide layer is formed on the surface of a substrate using the processing method of the embodiment, the F concentration, which was 0 wt% before exposure, increases to 6.58 wt% after exposure. Also, as shown in Figure 8, when an aluminum oxide layer is formed on the surface of a substrate using a calorizing treatment, the F concentration, which was 0 wt% before exposure, increases to 10.03 wt% after exposure. That is, when an aluminum oxide layer is formed on the surface of a substrate using the processing method of the embodiment, the F concentration after exposure to _ClF3 gas is lower than when an aluminum oxide layer is formed on the surface of a substrate using a calorizing treatment. These results demonstrate that when using SUS316L as a substrate, the processing method of the embodiment can form an aluminum oxide layer on the surface of the substrate that is more corrosion-resistant to _ClF3 gas than when using a calorizing treatment.

9 and 10 show the results of elemental analysis when NCF600 was used as the substrate. FIG. 9 shows the results when an aluminum oxide layer was formed on the surface of the substrate using the processing method of the embodiment, and FIG. 10 shows the results when an aluminum oxide layer was formed on the surface of the substrate using a calorizing treatment. In FIGS. 9 and 10, the bar graphs show the composition ratio [weight (wt) %] of the substrate. In FIGS. 9 and 10, the bar graphs labeled "Before Exposure" show the composition ratio before the substrate was exposed to _ClF3 gas, and the bar graphs labeled "After Exposure" show the composition ratio after the substrate was exposed to _ClF3 gas.

As shown in Figure 9, when an aluminum oxide layer is formed on the surface of a substrate using the processing method of the embodiment, the F concentration, which was 0 wt% before exposure, increases to 2.64 wt% after exposure. Also, as shown in Figure 10, when an aluminum oxide layer is formed on the surface of a substrate using a calorizing treatment, the F concentration, which was 0 wt% before exposure, increases to 3.68 wt% after exposure. That is, when an aluminum oxide layer is formed on the surface of a substrate using the processing method of the embodiment, the F concentration after exposure to _ClF3 gas is lower than when an aluminum oxide layer is formed on the surface of a substrate using a calorizing treatment. These results demonstrate that even when NCF600 is used as the substrate, the processing method of the embodiment can form an aluminum oxide layer on the surface of the substrate that is more corrosion-resistant to _ClF3 gas than when a calorizing treatment is used.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

In the above embodiment, the first heat treatment step S3 and the second heat treatment step S4 are performed in an atmosphere containing oxygen, but the present disclosure is not limited to this. For example, at least one of the first heat treatment step S3 and the second heat treatment step S4 may be performed in a reducing atmosphere. Examples of reducing atmospheres include an atmosphere containing a reducing gas such as hydrogen gas and an inert gas such as argon gas.

S1 Base material preparation process S2 Film forming process S3 First heat treatment process S4 Second heat treatment process

Claims (5)

providing a substrate;
forming an aluminum film on the surface of the substrate;
heat treating the substrate at a first temperature to diffuse the aluminum into the substrate;
forming an aluminum oxide layer by heat treating the substrate into which the aluminum has been diffused and infiltrated at a second temperature higher than the first temperature;
and
The substrate is formed of an aluminum-free metal or an aluminum-free alloy.
Processing method. the diffusing and penetrating step and the forming step of the aluminum oxide layer are performed in an oxygen-containing atmosphere;
The processing method according to claim 1 . The oxygen-containing atmosphere is an air atmosphere.
The processing method according to claim 2 . The substrate is stainless steel or a nickel-based alloy.
The method according to any one of claims 1 to 3. The aluminum is deposited on the surface of the substrate by physical vapor deposition.
5. The method according to claim 1.