JP6978995B2 - Method of surface modification of base material and method of manufacturing fluid equipment - Google Patents

Description

The present invention relates to a method for surface modification of a base material, a fluid device, and a powder.

Stainless steel with excellent corrosion resistance is used in various fields such as semiconductor manufacturing equipment, automobiles, and building interior / exterior materials. However, the usage environment of the stainless steel base material has been diversified, and there have been cases where the required corrosion resistance cannot be satisfied only by the corrosion resistance of the stainless steel material. Therefore, conventionally, the surface of a stainless steel base material has been modified by using a laser. For example, Patent Document 1 discloses a method of forming a clad layer having a large amount of chromium on the surface of a base material by applying a metal powder composed of Cr, Ni, and Mo to the surface of the base material and firing it by laser irradiation. Has been done.

Japanese Patent No. 2819635

However, the above technique has the following problems. That is, the method for modifying the surface of a base material described in Patent Document 1 strengthens an oxide film (passivation film) by increasing the amount of chromium on the surface of the base material. However, this oxide film may be broken when it comes into contact with a highly corrosive fluid such as chlorine-based or silane-based.

For example, in semiconductor manufacturing equipment, chlorine-based and silane-based highly corrosive fluids flow into fluid equipment such as pipes and valves. When the flow path surface of a fluid device is modified by the method described in Patent Document 1, pitting corrosion or corrosion may occur when the modified flow path surface comes into contact with a highly corrosive fluid. Further, for example, in the ALD process in the semiconductor manufacturing process, the corrosive fluid is vaporized under atmospheric pressure conditions and heated to 200 ° C. or higher. Generally, in stainless steel, even if the oxide film is destroyed, the oxide film is repaired by the contact of Cr with oxygen, and the corrosion resistance is maintained. However, the oxide film lacked stability at high temperatures, and the destroyed oxide film could not be repaired, resulting in pitting corrosion and corrosion.

Here, SUS316L and Hastelloy (registered trademark) have excellent corrosion resistance. Therefore, it is considered that if the base material is constructed using SUS316L or Hastelloy, the corrosion resistance can be improved without performing the method described in Patent Document 1. However, SUS316L and Hastelloy are expensive and have poor workability. Therefore, for example, it is not appropriate in terms of cost and processing to form a complicated shape such as a flow path surface of a fluid device with SUS316L or Hastelloy.

Further, the surface modified by the method described in Patent Document 1 has measures against cracking, but has not taken measures against wear. Therefore, for example, when a clad layer is formed on the surface of a plunger of a fluid device used for controlling a highly corrosive fluid by the method described in Patent Document 1, the clad layer is destroyed by wear and corrodes the base material. It was exposed to the sexual atmosphere and could corrode the plunger.

The present invention has been made to solve the above problems, and is a method for modifying the surface of a base material, which can achieve both high corrosion resistance and wear resistance on the surface of the base material, a fluid device, and a powder. The purpose is to provide.

(1) One aspect of the method for modifying the surface of a base material of the present invention is a film forming step of forming a film made of a powder containing Ni, Cr, Mo and B on the surface of a base material made of stainless steel. By irradiating the film with a laser beam, the film and a part of the base material are melted and solidified to form a densified modified layer, which comprises a modification step of the powder. The components are Cr: 20 to 25% by mass, Mo: 24 to 29% by mass, B: 1 to 2% by mass, and Ni: the balance.

In the surface modification method of the base material having the above configuration, the film formed on the surface of the base material has many pores and has low adhesion to the base material. A part of the base material is melted and rapidly cooled and solidified. As a result, the vicinity of the surface of the base material is alloyed with a film made of powder containing Ni, Cr, Mo and B, and a densified modified layer is formed on the surface. The base material on which the modified layer is formed in this way has improved corrosion resistance and abrasion resistance as compared with the base material on which only the film is formed and the base material itself.

Although the mechanism by which the surface modification method of the substrate of the present invention can improve the corrosion resistance and the wear resistance is not clear, it is considered as follows.

The modified layer contains stainless steel and membrane components as the powder and substrate are mixed as they melt. Cr and Mo combine with oxygen to form an oxide film on the surface of the modified layer and prevent corrosion. Further, Ni has a property of improving corrosion resistance. On the other hand, B has a property of improving hardness, but has a property of easily causing pitting corrosion and corrosion in combination with an acid. Therefore, it is considered inappropriate to add B to the modified layer for improving the corrosion resistance.

However, the inventor has confirmed from experiments that the corrosion resistance of the surface of the base material can be made better than that of Hastelloy or SUS316L according to the surface modification method of the present invention. It is considered that this is because B is covered with the oxide film formed by Cr and Mo and does not precipitate on the surface of the base material, so that pitting corrosion and corrosion are less likely to occur. Further, according to the surface modification method of the present invention, the abrasion resistance of the surface of the substrate is determined by the hot isostatic pressing method of the substrate on which neither the film nor the modified layer is formed or the powder forming the film. The inventor has confirmed from experiments that it can be made better than the sintered body by (Hot Isostatic Pressing, hereinafter abbreviated as "HIP"). It is considered that this is because B cures the modified layer. Therefore, according to the surface modification method of the present invention, a film composed of powder containing Cr, Mo, B, and Ni is formed on the surface of the base material, and the film is irradiated with laser light to form a modified layer. Therefore, it is considered that both high corrosion resistance and wear resistance of only the surface of the base material can be realized.

(2) In the surface modification method of the base material according to (1), the larger the power density of the laser beam used in the modification step, the thicker the modification layer, and the modification. The larger the component ratio of the stainless steel contained in the layer and the smaller the power density of the laser beam used in the reforming step, the thinner the modified layer becomes and the more it is contained in the modified layer. It is preferable that the component ratios of Ni and Mo are large, and that the modified layer and the base material have the same Cr component ratio.

Here, "to the same degree" means that, for example, the difference in the component ratio of Cr between the modified layer and the base material is within ± 10% by mass.

For example, when stainless steel comes into contact with a halogen-based element such as chlorine, the oxide film is broken and pitting corrosion tends to occur easily. Therefore, in the above configuration, when the modified layer is in contact with a halogen-based element such as chlorine, the power density is increased to form the modified layer. When the power density is high, the amount of melting of the base material increases, and the ratio of the metal component contained in the film contained in the modified layer decreases. Therefore, a modified layer having a large component ratio of stainless steel is formed thickly on the surface of the base material. In a substrate having a thick modified layer, halogen-based elements destroy the modified layer, making it difficult for the substrate to come into contact with the substrate, and pitting corrosion and corrosion are suppressed. On the other hand, when the modified layer comes into contact with a highly corrosive fluid that does not contain halogen-based elements, the power density is reduced to form the modified layer. When the power density is low, the amount of melt of the base material is reduced, and the ratio of the metal component contained in the film to the modified layer is increased. Therefore, a modified layer having a large Ni and Mo component ratio is formed thinly on the surface of the base material. Ni and Mo have the property of strengthening the oxide film. Therefore, it is possible to improve the corrosion resistance even with a thin modified layer. Therefore, according to the surface modification method of the substrate having the above configuration, if the power density is adjusted according to the type of the fluid in contact with the modified layer, the modified layer having properties suitable for the fluid is applied to the surface of the substrate. It can be formed and the corrosion resistance can be improved.

(3) In the method for modifying the surface of a substrate according to (1) or (2), it is preferable that the laser beam irradiates the substrate with a power density that can be modified.

Here, the "modifiable power density" means, for example, a power density capable of modifying stainless steel, and more specifically, 3 × 10 ⁴ W / cm ² or more and 7 × 10 ⁴ W / cm ² or less. The power density of.

According to the above configuration, it is possible to suppress the reflection of the laser beam on the film, improve the thermal efficiency when performing the reforming step, and it is easy to adjust the thickness and characteristics of the reformed layer.

Another aspect of the method for modifying the surface of a substrate according to the present invention is (4) a substrate made of stainless steel having a fluid contact portion in contact with a highly corrosive fluid, and the surface of the fluid contact portion. In a film forming step of forming a film composed of a powder containing Ni, Cr, Mo and B, and by irradiating the film with laser light, the film and a part of the fluid contact portion are melted. Having a reforming step of solidifying to form a densified reformed layer, the components of the powder are Cr: 20 to 25% by mass, Mo: 24 to 29% by mass, B: 1 to 2 mass. %, Ni: It is preferable that it is the balance.

(5) One aspect of the fluid device according to the present invention is a fluid contact portion made of stainless steel and in contact with a highly corrosive fluid, and a modified layer formed by alloying on the surface of the fluid contact portion. The modified layer is characterized by containing an alloy composed of Cr, Mo, B, and Ni, and an alloy produced by melting the stainless steel.

(6) One aspect of the powder according to the present invention is a film forming step of forming a film on the surface of a base material made of stainless steel, and one of the film and the base material by irradiating the film with laser light. It is used as a material for the film in a method of surface modification of a base material having a modification step of melting and solidifying the portion to form a densified modified layer, Cr: 20 to 25. It is a powder characterized by mass%, Mo: 24-29 mass%, B: 1-2 mass%, Ni: the balance.

According to the present invention, it is possible to realize a method for modifying the surface of a base material, a fluid device, and a powder, which can achieve both high corrosion resistance and wear resistance on the surface of the base material.

It is a figure explaining the procedure of the surface modification method of the base material which concerns on embodiment of this invention, and shows the film formation process. It is a figure explaining the procedure of the surface modification method of a base material, and shows the modification process. It is a figure explaining the procedure of the surface modification method of a base material, and shows the modification process. It is a table which shows the composition of the test material. It is a figure which shows the cross-sectional observation result. It is a figure which shows the cross-sectional observation result. It is a graph which compares the pitting corrosion potential measurement result. It is a graph which compares the anodic polarization curves. It is a table which shows the EPMA qualitative analysis result. Sample No. It is a graph which shows the X-ray diffraction evaluation result of E. Sample No. It is a graph which shows the X-ray diffraction evaluation result of 2. Sample No. It is a figure which shows the cross-sectional observation result of 2. It is a table which compares the depth of the wear mark. It is a graph which compares the width of the wear mark.

Hereinafter, the method for modifying the surface of the base material, the fluid device, and the embodiment of the powder according to the present invention will be described with reference to the drawings.

(Method of surface modification of base material)
1 to 3 are views illustrating a procedure of a surface modification method for a base material according to an embodiment of the present invention. In the figure, reference numeral 1 is a base material, reference numeral 1a is a surface of the base material 1, reference numeral 2 is a powder, reference numeral 3 is a film, and reference numeral 4 is a modified layer.

<Membrane formation process>
In the surface modification method of the base material 1, as shown in FIG. 1, a film 3 made of powder 2 containing Ni, Cr, Mo and B is formed on the surface 1a of the base material 1 made of stainless steel.

The base material 1 is preferably stainless steel, which forms a dense oxide film (passivation film), has excellent corrosion resistance, and has good workability. For example, the base material 1 may be a stainless steel containing Cr and Ni, and may be an austenitic stainless steel.

The component of the powder 2 is preferably Cr of 20% by mass or more and 25% by mass or less. This is because if Cr is less than 20% by mass, the modified layer 4 described later cannot form an oxide film having a sufficient thickness, and if Cr is more than 25% by mass, the cost is high. Further, Mo is preferably 24% by mass or more and 29% by mass or less. This is because if Mo is less than 24% by mass, the oxide film formed on the surface of the modified layer 4 cannot be sufficiently strengthened, and if it is more than 29% by mass, the cost becomes high. B is preferably 1 to 2% by mass. This is because if B is less than 1% by mass, sufficient hardness cannot be obtained, and if it is more than 2% by mass, B is deposited on the surface of the modified layer 4 and the corrosion resistance is lowered. The rest should be Ni. This is because Ni can improve the corrosion resistance. Further, the powder 2 has a particle size of 20 μm or less. This is because if the particle size of the powder 2 is larger than 20 μm, the powder 2 is not sufficiently melted when irradiated with the laser beam, and the composition components cannot be dispersed and mixed in the base material 1.

The surface 1a of the base material 1 is covered with the film 3 made of the powder 2. The film 3 may be formed by spraying the powder 2 onto the surface 1a of the base material 1. Further, the film 3 may be formed by applying a powder 2 dispersed in a solution to the surface 1a of the base material 1 and drying the film 3. Further, the film 3 may be formed by spraying the powder 2 onto the surface 1a of the base material 1.

Here, the average film thickness of the film 3 may be appropriately set depending on the intended use and usage environment of the base material, but is preferably 10 μm or more and 40 μm or less, for example. This is because when the average film thickness of the film 3 is less than 10 μm, the components of the film 3 are not sufficiently contained in the modified layer 4, and the modification of the surface 1a of the substrate 1 is insufficient. On the other hand, when the average film thickness of the film 3 is larger than 40 μm, rapid heating / cooling by the laser beam 5 becomes insufficient, and it is difficult to form a dense and hard modified layer 4.

<Modification process>
After that, as shown by the arrow D in the drawings of FIGS. 2 and 3, the film 3 and a part of the base material 1 are melted and solidified by irradiating the film 3 with the laser beam 5, and the film 3 is densified. The layer 4 is formed.

As shown in FIG. 2, the laser beam 5 is irradiated in a straight line in parallel at a predetermined pitch P. The single irradiation line is set to a distance longer than the width of the surface 1a. The predetermined pitch P is set to a value smaller than the spot diameter of the laser beam 5. For example, when the spot diameter is 0.6 mm, the predetermined pitch P is set to 0.2 mm. The laser beam 5 is irradiated so that the later irradiation line overlaps with the earlier irradiation line. Therefore, the laser beam 5 evenly irradiates the film 3.

As shown in FIG. 3, the laser beam 5 irradiates the film 3 with a power density capable of transferring heat from the film 3 to a part of the substrate 1. The laser beam 5 may irradiate the film 3 with a power density that can be modified with respect to the substrate 1. This is to suppress the reflection of the laser beam 5 on the film 3 to increase the thermal efficiency, and to adjust the power density so that the thickness and characteristics of the modified layer 4 can be adjusted.

For example, when the material of the base material 1 is an austenitic stainless steel such as SUS304, the laser wavelength is preferably 0.5 μm or more and 2.0 μm or less. Further, for example, when the material of the base material 1 is an austenitic stainless steel such as SUS304, the power density of the laser beam 5 is preferably 3 × 10 ⁴ W / cm ² or more and 7 × 10 ⁴ W / cm ² or less. ..

In the base material 1, behind the laser light 5, the film 3 melted by the heat of the laser light 5 and a part of the base material 1 are mixed and rapidly solidified. As a result, the modified layer 4 containing an alloy composed of Cr, Mo, B, and Ni, and an alloy produced by melting stainless steel has a substantially uniform thickness on the surface 1a of the base material 1. Formed by.

The thickness and characteristics of the modified layer 4 are adjusted by the power density of the laser beam 5. For example, when the film 3 is irradiated with the laser beam 5 at the second power density (power density: 3.5 × 10 ⁴ W / cm ^{2) where the laser output is 100 W, the laser is used to form the second modified layer.} The amount of melting of the base material 1 compared to the case where the film 3 is irradiated with the laser beam 5 at the first power density (power density is 7 × 10 ⁴ W / cm ^{2) with an output of 200 W to form the first modified layer.} Is reduced, and the second modified layer is formed thinner than the first modified layer.

Further, since the first modified layer has a larger amount of melted base material 1 in the modifying step than the second modified layer, the component ratio of stainless steel is larger than that of the second modified layer. On the other hand, since the amount of the base material 1 melted in the reforming step of the second modified layer is smaller than that of the first modified layer, Mo contained in the powder 2 constituting the film 3 is compared with the first modified layer. ， Ni component ratio increases.

Therefore, if the power density of the laser beam 5 is adjusted to be small, the modified layer 4 having a large component ratio of Mo and Ni can be formed thinly. On the other hand, if the power density of the laser beam 5 is increased, the modified layer 4 having a large component ratio of stainless steel can be formed thickly. Cr and Ni combine with oxygen to form an oxide film and improve corrosion resistance. Mo combines with oxygen to form an oxide film and improves corrosion resistance. B improves the hardness. As described above, each modifying element has its own characteristics. Therefore, the characteristics of the modified layer 4 can be adjusted by changing the component ratio of the modified layer 4 only by adjusting the power density.

<Effect>
In the surface modification method of the base material of the present embodiment described above, the surface 1a of the base material 1 has better corrosion resistance than the base material 1 because the modified layer 4 contains Cr, Ni and Mo. At the same time, the modified layer 4 is hardened by B to improve wear resistance. Therefore, according to the surface modification method of the base material and the base material 1 of the present embodiment, it is possible to realize both high corrosion resistance and wear resistance of only the surface 1a.

<Others>
The surface modification method of the base material of this embodiment is applied to, for example, a fluid device used in the semiconductor industry. Fluid equipment is, for example, a pipe, a valve, a flow rate controller, a measuring instrument, etc., and the inner peripheral surface of the pipe, the flow path surface of the valve / fluid controller, the surface of the valve body / plunger of the valve, etc. This is an example of a fluid contact part.

For example, when manufacturing an electromagnetic fluid control valve used in the ALD process, an austenitic stainless steel such as SUS304 is used to form a flow path block. Austenitic stainless steel has good workability and can easily process input ports, input flow paths, valve chambers, valve seats, valve holes, output flow paths, output ports, and the like. Further, since austenitic stainless steel has a large distribution amount, a flow path block can be formed at low cost. The flow path surface of the flow path block formed in a predetermined shape has corrosion resistance due to the oxide film, and a modified layer is further formed by using the surface modification method of the above-mentioned base material. Therefore, even when the fluid control valve controls a gas having high corrosiveness at a high temperature of 200 ° C. or higher, the oxide film is stable and pitting corrosion and corrosion are unlikely to occur on the flow path surface. As a result, the fluid control valve can prevent or suppress the generation of fine particles and can meet the corrosion resistance requirement from the semiconductor industry.

Further, in the fluid control valve, a plunger having a desired shape is formed of austenitic stainless steel, and a modified layer is formed on the surface of the plunger by using the surface modification method of the base material. When the fluid control valve airtightly partitions the valve chamber by the diaphragm and the plunger is arranged on the back chamber side of the diaphragm, the plunger does not corrode even if the highly corrosive gas permeates the diaphragm. In addition, the plunger is less likely to wear due to the modified layer. Therefore, the durability of the fluid control valve is improved.

Next, the effect obtained by the present invention will be clarified by an example.

(About test materials)
FIG. 4 is a table showing the configuration of the test material. In the column of "presence / absence" in the "film" of the table, "yes" was entered when the film forming step was carried out, and "no" was entered when the film forming step was not carried out. In the "presence / absence" column of the "modified layer" in the table, "yes" was entered when the reforming step was carried out, and "no" was entered when the reforming step was not carried out. As a comparative example, the test materials shown in Sample Nos. A to E of FIG. 4 were prepared, and as an example in which the present invention was carried out, Sample No. 4 of FIG. 4 was prepared. The test materials shown in 1 to 3 were prepared.

Here, the "Ni-based corrosion-resistant alloy powder" in the table is a product of Sanyo Special Steel Co., Ltd. The Ni-based corrosion resistant alloy powder is a raw material powder produced by the gas atomizing method. The composition of the Ni-based corrosion-resistant alloy powder is Cr: 22% by mass, Mo: 26% by mass, B: 1.4% by mass, and Ni: the balance.

Sample No. A is made of SUS304, and neither a film nor a modified layer is formed. Sample No. B is composed of SUS316L, and neither a film nor a modified layer is formed. Sample No. C is a sintered body of Ni-based corrosion-resistant alloy powder made of HIP. Sample No. D consists only of Hastelloy. Sample No. E is a film having a film thickness of 30 μm formed by spraying a Ni-based corrosion-resistant alloy powder on the surface of a base material made of SUS304.

Sample No. 1-No. In No. 3, a film having a film thickness of 30 μm was formed by spraying a Ni-based corrosion-resistant alloy powder on the surface of a material made of SUS304, and then a modified layer was formed by changing the laser irradiation conditions. Sample No. The laser irradiation conditions of 1 are power density: 3.5 × 10 ⁴ W / cm ² (laser output: 100 W, scanning speed 50 mm / s, scanning pitch: 0.2 mm, spot diameter: diameter 0.6 mm, N2 gas purge flow rate. : 15 L / min). Sample No. ^{The laser irradiation condition of No. 2} is a power density of 7 × 10 ⁴ W / cm 2 (the same laser irradiation condition as that of the sample No. 1 except for the laser output: 200 W). Sample No. The laser irradiation condition of No. 3 is a power density of 1.1 × 10 ⁴ W / cm ² (the same laser irradiation condition as that of sample No. 1 except for the laser output: 300 W).

(Observation of cross section of base material)
Sample No. 2 and sample No. A test piece of a predetermined size was collected from No. 1, and the cross section of the modified layer was observed using a microscope. Sample No. The cross-sectional observation result of No. 2 is shown in FIG. Sample No. The cross-sectional observation result of No. 1 is shown in FIG.

As shown in FIG. 5, the sample No. The average thickness W1 of the modified layer 4X of No. 2 was about 100 μm. On the other hand, as shown in FIG. 6, the sample No. The average thickness W2 of the modified layer 4Y of No. 1 was about 50 μm. This is because the higher the power density, the deeper the substrate melts from the surface in contact with the film. Therefore, as the power density is increased, the thickness W of the modified layer 4 can be increased. That is, the thickness W of the modified layer 4 can be adjusted by adjusting the power density.

(Measurement of pitting potential)
The pitting potential was measured in accordance with JIS G0577, the pitting potential was investigated, and the corrosion resistance to chlorine was investigated.

<Test piece>
Sample No. A to E and sample No. 1-No. A test piece having a length of 25 mm, a width of 25 mm, and a thickness of 2 mm was collected from the surface layer of the test material shown in No. 2, and a test piece coated with a silicon coating material was prepared, leaving a ^{wetted area of 1 cm 2.}

<Test method>
The test piece was immersed in a 3.5% (mass fraction) sodium chloride aqueous solution, the potential was swept at a rate of 20 mV / min with a potentiostat, and the measurement was completed when the current flowed to 0.5 mA. ..

<Evaluation of pitting potential>
FIG. 7 is a graph comparing the results of pitting corrosion potential measurement. The vertical axis shows the current density (mA / cm ² ), and the horizontal axis shows the potential (V). The current density rises sharply when pitting corrosion occurs on the test piece. Therefore, it can be considered that the higher the pitting potential when the current density rises sharply, the more difficult it is for pitting corrosion and the higher the corrosion resistance.

As shown in P1 of the graph X4, the sample No. In No. 2, pitting corrosion occurred at about 1.08 V. As shown in P2 of the graph X3, the sample No. In No. 1, pitting corrosion occurred at about 0.95 V. On the other hand, as shown in P3 of the graph X1, the sample No. In A, pitting corrosion occurred at about 0.4 V. As shown in P4 of the graph X5, the sample No. For E, pitting corrosion occurred at about -0.1 V.

From this, it was found that simply forming a film of the Ni-based corrosion-resistant alloy powder on the base material of SUS304 is more likely to be pitted and the corrosion resistance is lower than that of the base material alone. However, it was found that when the film formed on the surface of the base material of SUS304 is irradiated with a laser to form a modified layer, it is less likely to be pitted and the corrosion resistance is improved as compared with the case of using only the base material.

Then, sample No. 1 and sample No. 1 and sample No. Reference numeral 2 is a sample No. 2 shown in graph X7 in the figure. D and the sample No. shown in graph X2 in the figure. B and the sample No. shown in graph X6 in the figure. Pitting corrosion occurs at a higher potential than C.

From this, SUS304 constituting the base material has lower corrosion resistance than the sintered body of Hastelloy, SUS316L, or Ni-based corrosion-resistant alloy powder by HIP, but the powder containing Cr-Mo-B-Ni is sprayed on the surface of the base material. When a film is formed and the modified layer is formed by irradiating the film with a laser, the surface of the base material has superior corrosion resistance to the sintered body of Hastelloy, SUS316L, or Ni-based corrosion-resistant alloy powder made of HIP. It turned out. That is, the sample No. 1 and sample No. According to the surface modification method of the base material applied to No. 2, it was clarified that only the surface of the base material can have higher corrosion resistance than Hastelloy, SUS316L and Ni-based corrosion resistant alloy powder having high corrosion resistance.

Here, it is generally said that the oxide film of stainless steel such as SUS304 is broken when it comes into contact with a halogen-based element such as chlorine. However, the sample No. 2 is the sample No. Pitting corrosion resistance is superior to 1. From this, it was found that the higher the power density is, the more the modified layer can be formed, which is less likely to be pitted even when in contact with halogen-based elements. It is considered that this is because the larger the laser output, the better the film and the base material are mixed to form a dense and thick modified layer, and the local corrosion is less likely to occur.

(Measurement of anode polarization curve)
The anodic polarization curve was measured in accordance with JIS G0579, and the corrosion resistance to acid was investigated.

<Test piece>
Sample No. A to E and sample No. Test pieces having a length of 25 mm, a width of 25 mm, and a thickness of 2 mm or 8 mm were collected from the surface layers of the test materials 1 to 3, and a test piece coated with a silicon coating material was prepared, leaving a ^{wetted area of 1 cm 2.}

<Test method>
The test piece was immersed in a 5% (mass fraction) sulfuric acid aqueous solution, polarized with a potentiostat at a rate of 60 mV / min from -1 V to 1.5 V, and anodic polarization measurement was performed.

<Anode polarization curve evaluation>
FIG. 8 is a graph comparing the anodic polarization curves. The vertical axis shows the current density (mA / cm ² ), and the horizontal axis shows the potential (V). The current density shown in the anodic polarization curve directly represents the amount of metal elution at the measurement point. Therefore, it is considered that the lower the current density is, the better the corrosion resistance is when the polarization is advanced to the anode side (high potential side) from the natural potential.

Sample No. The anodic polarization curve X13 of No. 1 and the sample No. The anodic polarization curve X14 of No. 2 and the sample No. The anodic polarization curve X18 of No. 3 is the sample No. Compared with the anodic polarization curve X11 of A, the current density in the potential range of 0 V or more and 1 V or less is reduced from about half to about one-third. In addition, sample No. The anodic polarization curve X15 of E is the sample No. Compared with the anodic polarization curve X11 of A, the current density is larger at a potential of 0.2 V or higher.

From this, it was found that the surface of SUS304 on which the film of Ni-based corrosion-resistant alloy powder was formed was more soluble in acid and inferior in corrosion resistance as compared with the surface of SUS304 alone. However, it has been clarified that when a film of Ni-based corrosion-resistant alloy powder is irradiated with a laser to form a modified layer on the surface of SUS304, it becomes less soluble in acid and the corrosion resistance to acid is improved as compared with the surface of SUS304 alone. ..

Sample No. The anodic polarization curve X13 of No. 1 and the sample No. The anodic polarization curve X17 of D has a similarly small current density in the potential range of 0 V or more and 1 V or less. Therefore, it was found that when a film of Ni-based corrosion-resistant alloy powder is irradiated with laser light at a laser output of 100 W to form a modified layer on the surface of SUS304, the corrosion resistance to acid can be made to the same level as Hastelloy.

On the other hand, sample No. The anodic polarization curve X14 of No. 2 and the sample No. The anodic polarization curve X18 of 3 draws a similar locus. Sample No. 2 and Sample No. 2 in the potential range of 0 V or more and 1 V or less. Reference numeral 3 is sample No. The current density is higher than 1. Therefore, it can be seen that the corrosion resistance to acid cannot be improved even if the laser output is increased. That is, it can be seen that the thinner the modified layer, the better the corrosion resistance to acid.

(Surface elemental analysis)
The component ratio (mass%) of Fe, Ni, Cr, and Mo contained in the modified cross section was analyzed by EPMA (electron probe microanalyzer) qualitative analysis.

FIG. 9 is a table showing the results of EPMA qualitative analysis. Sample No. having a modified layer. 1 and sample No. No. 2 is a sample No. 2 having neither a film nor a modified layer. In both A, the sample No. in which only the film was formed. The component ratio is also different from E. Therefore, it can be seen that the surface of the base material is modified by the modified layer.

Sample No. Fe in E is the sample No. It is as small as about 1/100 of Fe in A. From this, it can be seen that the film only covers the surface of the base material and is hardly mixed with the base material. On the other hand, sample No. 1 and sample No. Fe in 2 is the sample No. It is about 30% to 75% of Fe in A. As a result, the sample No. 1 and sample No. In No. 2, it can be seen that the film and the base material are melted and mixed to be alloyed by irradiating the film with a laser.

Cr is the sample No. A and sample No. E and sample No. 1 and sample No. It doesn't change much with 2. That is, even if the Ni-based corrosion-resistant alloy powder and SUS304 are mixed by laser irradiation, the Cr component ratio does not change much. It is considered that this is because the Ni-based corrosion-resistant alloy powder contains Cr of the same level as SUS304 constituting the base material.

Ni is the sample No. Sample No. rather than A. D and sample No. 1 and sample No. 2 is more. It is considered that this is because the Ni-based corrosion-resistant alloy powder has a higher Ni component ratio than SUS304.

Mo is an element not found in SUS304 and is added by Ni-based corrosion resistant alloy powder. Sample No. 1 and sample No. In No. 2, the film and the base material are mixed to form a modified layer by irradiating the film with a laser. The component ratio of Mo is smaller than that of E. Sample No. 2 is the sample No. Compared with 1, the amount of melted base material is increased, so the component ratio of Mo is small.

From the above, in the modified layer, Mo and Ni contained in the film are mixed with SUS304 constituting the base material and superimposed on Cr to form an oxide film. Therefore, as shown in FIGS. 7 and 8, the base material having the modified layer has higher corrosion resistance than the base material having neither the film nor the modified layer formed on the surface and the base material having only the film formed. Is expected to have.

Here, when the modified layer is formed by laser irradiation, if the power density is increased, the Fe component ratio is increased and the Ni and Mo component ratios are decreased. On the other hand, when the power density is reduced, the component ratios of Ni and Mo contained in the film are increased, and the component ratio of Fe is decreased. Therefore, by adjusting the power density, the component ratios of Fe, Mo, and Ni in the modified layer can be changed, and the characteristics of the modified layer can be adjusted.

(Crystal structure on the surface of the substrate)
The crystal structure on the surface of the substrate was investigated by performing X-ray diffraction evaluation and cross-sectional observation using a microscope.

<X-ray analysis evaluation>
FIG. 10 shows the sample No. It is a graph which shows the X-ray diffraction evaluation result of E. FIG. 11 shows the sample No. It is a graph which shows the X-ray diffraction evaluation result of 2. The vertical axis represents the "X-ray irradiation angle" and the horizontal axis represents the "detection intensity".

Solids include "crystals" in which atoms are regularly arranged and "amorphous" in which atoms are randomly arranged. When X-ray diffraction is performed, the crystalline component shows a peak, and the amorphous component shows a broad halo pattern.

As shown in FIG. 10, the sample No. E indicates a halo pattern shown in M1 in the figure and a peak shown in M2 in the figure. On the other hand, as shown in FIG. 11, the sample No. No. 2 shows a peak as shown in M3 in the figure, but does not show a halo pattern. Therefore, the sample No. 2 is the sample No. Compared to E, it can be seen that the elements on the surface of the base material are arranged regularly and are denser.

<Cross-section observation using a microscope>
FIG. 12 shows the sample No. It is a figure which shows the cross-sectional observation result of 2. The film 3 contains many pores inside, and has a gap between the film 3 and the surface 1a of the base material 1. On the other hand, the modified layer 4 does not contain any vacancies inside and is densified. The modified layer 4 is formed by alloying with the base material 1, and there is no gap between the modified layer 4 and the base material 1. Therefore, the modified layer has denser crystals than the film and is firmly bonded to the substrate.

<Summary>
As shown in FIG. 9, the sample No. E is the sample No. 1 and sample No. The component ratio of Ni and Mo is larger than 2. However, as shown in FIGS. 7 and 8, the sample No. E is the sample No. 1 and sample No. Corrosion resistance is lower than 2. This is because, as shown in FIGS. 10, 11, and 12, the membrane has more pores than the modified layer, and there is a gap between the film and the substrate, so that pitting corrosion and crevice corrosion are likely to occur. it is conceivable that.

(Abrasion resistance evaluation)
Abrasion resistance was investigated using a ball-on-disk type tester.

<Test piece>
Sample No. B, sample No. C, sample No. 1. Sample No. From the surface of No. 2, a test piece was taken with dimensions of 25 mm in length, 25 mm in width, and 2 mm or 8 mm in thickness. The surface of the test piece was polished with # 600 water-resistant abrasive paper until the surface roughness was Ra: 0.05 μm.

<Test method>
In the test, an alumina ball having a diameter of 10 mm was pressed against the test material and slid back and forth. The loads were 4.9N and 0.98N. The sliding speed was 10 mm / s. The sliding distance was set to 300 times (6 m) for 10 mm reciprocation.

<Evaluation method>
The wear resistance was evaluated by profiling the wear marks formed on the sliding portion of the test piece after the test. FIG. 13 is a table comparing the depths of wear marks. FIG. 14 is a graph comparing the widths of wear marks.

<Abrasion resistance evaluation>
As shown in FIG. 13, when the load is 0.98 N, the sample No. 1 and sample No. 2 is the sample No. B and sample No. The depth of wear marks is shallower than C. Then, as shown in FIG. 14, when the load is 0.98N, the sample No. 1 and sample No. 2 and sample No. B and sample No. In C, the width of the wear mark is about the same.

Further, as shown in FIG. 13, the sample No. 1 is the sample No. The depth of wear marks is shallower than 2. That is, the sample No. 1 is the sample No. The thickness of the modified layer is thinner than that of 2, but the wear resistance is superior. It is considered that the thinner the modified layer, the smaller the component ratio of SUS304 and the larger the component ratio of wear-resistant B.

On the other hand, as shown in FIG. 13, when the load is 4.9 N, the sample No. 1 and sample No. 2 is the sample No. The depth of wear marks was 15% to 20% shallower than that of B. Sample No. C is the sample No. The depth of the wear marks was more than twice as deep as that of B.

As shown in FIG. 14, when the load is 4.9 N, the sample No. 1 and sample No. 2 is the sample No. The width of the wear mark can be reduced to about 70% with respect to B, and the sample No. The width of the wear mark can be reduced to about 50% with respect to C. In addition, sample No. C is the sample No. The width of the wear mark is about 180% with respect to B.

From the above, it can be seen that the HIP sintered body of the Ni-based corrosion-resistant alloy powder is easily worn even though it is harder than SUS316L. However, it was found that when a film of Ni-based corrosion-resistant alloy powder was formed on the surface of the base material and the film was irradiated with a laser to form a modified layer, the wear resistance of the base material was better than that of SUS316L.

Here, B is considered to be a factor that lowers the corrosion resistance, and tends not to be added to the member that requires the corrosion resistance. However, although the modified layer contains B, as shown in FIGS. 7 and 8, the corrosion resistance is improved as compared with the substrate made of SUS304. It is considered that this is because B is contained in the modified layer so as not to be deposited on the surface of the modified layer by the oxide film (passivation film) formed by Cr, Ni, and Mo contained in the modified layer.

The inventors of the sample No. As a result of X-ray diffraction evaluation of the elements precipitated on the surface of the modified material, it was confirmed that B was not deposited on the surface of the modified layer.

As shown in FIGS. 13 and 14, the sample No. 2 is the sample No. The modified layer is formed thicker than No. 1, but the wear resistance is the same as that of the sample No. 1. It is about the same as 1. Therefore, it was clarified that even if B is contained in the Ni-based corrosion-resistant alloy powder in a small ratio of 1.4% by mass, the substrate is cured of the modified layer and the wear resistance is improved. ..

(summary)
Therefore, a powder composed of 20 to 25% by mass Cr-24 to 29% by mass Mo-1 to 2% by mass B-residue Ni is sprayed onto a base material made of stainless steel to form a film, and a laser is formed on the film. When a modified layer is formed by irradiating light to locally rapidly heat a part of the film and the base material to melt it and then rapidly cooling it, high corrosion resistance and wear resistance of only the surface of the base material can be achieved. It can be realized at the same time.

Its corrosion resistance is superior to Hastelloy and SUS316L. Therefore, austenitic stainless steel with good workability and low cost is formed into a desired shape, and for example, the surface modification method of the base material of the above-mentioned form is applied to a liquid contact portion in contact with a chlorine-based or acid-based highly corrosive fluid. By modifying the surface, only the liquid contact portion can be made highly corrosion-resistant and wear-resistant. In this case, since it is only necessary to form a film using powder such as Ni-based corrosion-resistant alloy powder only at the liquid contact portion, the amount of powder used can be suppressed, and high corrosion resistance and wear resistance can be realized at low cost. be able to.

The present invention is not limited to the above embodiment. For example, the surface modification method for a base material can be applied not only to fluid equipment used in the semiconductor manufacturing industry, but also to members used in the steel industry, the automobile industry, the aviation / space industry, the energy industry, and the like.

1 Base material 1a Surface 2 Powder 3 Membrane 4 Modified layer

Claims (4)

A film forming step of forming a film made of powder containing Ni, Cr, Mo and B on the surface of a base material made of stainless steel,
By irradiating the film with laser light at a power density that can be modified , the film and a part of the substrate are melted and solidified to form a densified modified layer. Having a reforming step to form,
The components of the powder are
Cr: 20 to 25% by mass
Mo: 24-29% by mass
B: 1-2% by mass
Ni: Being the rest,
By adjusting the power density, the component ratio of the modified layer is changed to adjust the characteristics of the modified layer.
A method for modifying the surface of a base material. In the method for modifying the surface of a base material according to claim 1,
The larger the power density of the laser beam used in the reforming step, the thicker the modified layer becomes , and the larger the component ratio of the stainless steel contained in the modified layer.
Before Kiaratame electrolyte layer and the base material, it component ratio of Cr is comparable,
A method for modifying the surface of a base material. In the method for modifying the surface of a base material according to claim 1,
The smaller the power density of the laser beam used in the reforming step, the thinner the thickness of the modified layer and the larger the component ratio of Ni and Mo contained in the modified layer.
The modified layer and the base material have the same Cr component ratio.
A method for modifying the surface of a base material. Made of stainless steel, a method for producing a fluid device that have a fluid contact portion in contact with the highly corrosive fluids,
A film forming step of forming a film made of a powder containing Ni, Cr, Mo, and B on the surface of the fluid contact portion, and a film forming step.
By irradiating the film with laser light at a power density that can be modified , the film and a part of the fluid contact portion are melted and solidified, and the modified layer is densified. To have a reforming process, which forms
The components of the powder are
Cr: 20 to 25% by mass
Mo: 24-29% by mass
B: 1-2% by mass
Ni: Being the rest,
By adjusting the power density, the component ratio of the modified layer is changed to adjust the characteristics of the modified layer.
A method for manufacturing a fluid device.

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