JP4690900B2 - Parts for internal combustion engines or marine and transportation equipment equipped with the same - Google Patents

Description

  The present invention relates to components for internal combustion engines and components for marine use. The invention also relates to a transport device comprising such a part.

  Many motorcycles expose an internal combustion engine and use the appearance of the motorcycle for the design of the motorcycle. In such a motorcycle, the exhaust pipe for leading the exhaust gas from the internal combustion engine also plays an important role in the design. Even when the internal combustion engine is covered with a cowl or the like, the exhaust pipe is rarely completely covered with a cowl or a protector, and at least a part of the exhaust pipe appears on the exterior, and a part of the design of the motorcycle is displayed. Often configured.

  FIG. 10 shows an example of a sports type motorcycle. A motorcycle 200 shown in FIG. 10 includes a V-type engine 201 and an exhaust pipe 202 for guiding exhaust gas. The exhaust pipe 202 is led from each of the two cylinders of the V-type engine 201 and assembled into one, and is extended to the rear wheel side so as to eject exhaust gas from the rear part of the vehicle body. In the present specification, the “exhaust pipe” refers to the entire part constituting the flow path for guiding the exhaust gas from the internal combustion engine, and includes the part constituting the silencer 202a.

  Generally, in order to efficiently exhaust the exhaust gas generated in the internal combustion engine 201, the exhaust pipe 202 needs to have a predetermined thickness. Moreover, in the part which comprises the silencer 202a, in order to accommodate the structure for silence, a diameter becomes large. For this reason, the ratio of the exhaust pipe to the overall appearance of the motorcycle is large, and the influence of the shape and color of the exhaust pipe on the design of the entire motorcycle is great.

  For these reasons, the shape and color of the exhaust pipe are important factors in determining the design of the entire motorcycle. For this reason, the exhaust pipe is smoothly bent to create a strong and powerful impression, and the exhaust pipe surface is finished with a glossy metallic color to emphasize contrast with other components. It has been broken. Alternatively, the surface of the exhaust pipe is finished with a color similar to that of the other constituent parts so as to be integrated with the surrounding structure.

  For example, stainless steel (SUS) is used as the material of the exhaust pipe. Stainless steel is an iron alloy containing chromium and is excellent in corrosion resistance because a chromium oxide film is formed on the surface.

  However, since the exhaust gas passing through the exhaust pipe is directly led from the internal combustion engine, the temperature is high. For this reason, the exhaust pipe becomes hot due to the passage of the exhaust gas, and even the surface of the exhaust pipe made of stainless steel is changed to reddish brown or deteriorates.

  Thus, even if stainless steel is used as the material of the exhaust pipe, the corrosion resistance is not always sufficient. If reddish discoloration or deterioration occurs on the surface of the exhaust pipe with metallic luster, the appearance of the design of the entire motorcycle is impaired. In particular, in recent years, the performance of internal combustion engines has improved, and the temperature of exhaust gas has risen, and such problems are likely to occur.

  As a technique for improving the corrosion resistance of the exhaust pipe, there is a method of electrolytic polishing the surface of the exhaust pipe formed of stainless steel. When such an electrolytic polishing method is performed, the metal is dissolved out as ions from the surface of the exhaust pipe, and the convex portions are preferentially dissolved, so that the surface of the exhaust pipe is smoothed and gloss is increased. In addition, iron preferentially dissolves over chromium, resulting in a high chromium concentration on the surface of the exhaust pipe. Therefore, the corrosion resistance is improved.

  As a technique for increasing the chromium concentration on the surface of the exhaust pipe, a technique of directly injecting chromium into the surface of the exhaust pipe or diffusing and infiltrating it can be considered.

The inventor of the present application has proposed that a silicon oxide film is formed on the surface of the exhaust pipe to prevent discoloration of the exhaust pipe (Patent Document 1). As disclosed in Patent Document 1, by forming a silicon oxide film with a thickness of 0.05 μm or more on the surface of the exhaust pipe using a sol-gel method, discoloration hardly occurs even when heated to about 400 ° C. An exhaust pipe can be obtained.
JP 2002-332838 A

  However, as a result of studies by the inventor of the present application, it was difficult to sufficiently improve the corrosion resistance even when the electrolytic polishing method was used. Moreover, since the electropolishing method is a wet method, waste water treatment is required. Furthermore, since a large amount of hexavalent chromium ions are eluted from the surface of stainless steel, it must be treated to satisfy the emission standards, and it also has a negative impact on the work environment, requiring closed wastewater. Become. In addition, since the hexavalent chromium ions in the wastewater have a higher concentration than when plating with hexavalent chromium, the burden of wastewater treatment is large.

  In addition, the method of directly injecting chromium into the surface of the exhaust pipe or diffusing and infiltrating it requires a large-scale device, which increases the manufacturing cost.

  Furthermore, in the exhaust pipe obtained by the technique disclosed in Patent Document 1, it has been found that the surface discoloration suddenly occurs when exposed to a temperature exceeding 400 ° C. For this reason, even if the exhaust pipe disclosed in Patent Document 1 is used for a high-performance internal combustion engine in which the temperature of the exhaust gas tends to be high, discoloration and deterioration may not be sufficiently prevented.

  High corrosion resistance is required not only for internal combustion engine parts such as the exhaust pipe described above but also for marine parts exposed to seawater (for example, handrails, fishing gear hinges, cleats for fixing ropes, etc.). However, it is still difficult to sufficiently improve the corrosion resistance of marine parts even when the above-described method is used.

  This invention is made | formed in view of the said problem, The objective is to improve the corrosion resistance of the components for internal combustion engines and the components for marine simply and greatly.

  An internal combustion engine or marine component according to the present invention includes a component main body formed of a metal material containing at least chromium, and a ceramic film that covers the outside of the component main body, the component main body having a chromium concentration higher than that inside. The above object is achieved by having a high surface layer.

  In a preferred embodiment, the thickness of the surface layer of the component body is 10 nm or more.

  In a preferred embodiment, the ceramic film has a back layer in contact with the surface layer of the component body and having a higher chromium concentration than the inside of the component body.

  In a preferred embodiment, the thickness of the back layer of the ceramic film is 10 nm or more.

  Alternatively, an internal combustion engine or marine component according to the present invention includes a component main body formed of a metal material containing at least chromium, and a ceramic film that covers the outside of the component main body, and the component of the ceramic film It has a chromium-rich layer that includes a part on the main body side and a part on the ceramic film side of the component main body, and has a higher chromium concentration than the inside of the component main body, thereby achieving the above object.

  In a preferred embodiment, the chromium rich layer has a thickness of 10 nm or more.

  In a preferred embodiment, the ceramic film has a thickness of 10 nm to 150 nm.

  In a preferred embodiment, the thickness of the ceramic film is 20 nm or more and 50 nm or less.

  In a preferred embodiment, the ceramic film includes silicon and / or aluminum.

  In a preferred embodiment, the ceramic film is an oxide film or a nitrided oxide film, and an oxygen concentration in the ceramic film is 30% by mass or more and 70% by mass or less.

  In a preferred embodiment, the oxygen concentration in the ceramic film is 30% by mass or more and 50% by mass or less.

  In a preferred embodiment, the ceramic film has a content of a metal element mainly contained on the surface of the component body of 0.5% by mass or less.

  In a preferred embodiment, the ceramic film is a film formed by physical vapor deposition.

  In a preferred embodiment, the metal material is stainless steel.

  In a preferred embodiment, the component according to the invention is an exhaust pipe for an internal combustion engine.

  The transportation device according to the present invention includes the parts having the above-described configuration, and thereby the above-described object is achieved.

  An internal combustion engine component (or marine component) according to the present invention includes a component main body formed of a metal material containing at least chromium, and a ceramic film covering the outside of the component main body. According to the present invention, since the component body has a surface layer having a higher chromium concentration than the inside, a chromium oxide film that contributes most to corrosion resistance is stably generated. Moreover, since the ceramic film with high acid resistance covers the outside of the component main body, the chromium oxide film is not easily broken. Therefore, the component according to the present invention is excellent in corrosion resistance. In addition, since the component according to the present invention does not require a large-scale apparatus or special waste water treatment for manufacturing, according to the present invention, the corrosion resistance of the component can be easily improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the exhaust pipe will be described as an example. However, the present invention is not limited to this, and is widely used for parts for internal combustion engines, such as exhaust pipe covers, intake system parts, and engine cover parts. The present invention is also used for marine components such as handrails, hinges, and cleats. The marine component refers to a component that can be used as a component of a moving body that navigates a water area containing salt, or a component mounted on such a moving object, and that is exposed to a liquid or gas containing salt. .

  FIG. 1 shows a motorcycle 100 using an exhaust pipe for an internal combustion engine (hereinafter also simply referred to as an exhaust pipe) according to the present invention. The motorcycle 100 includes an internal combustion engine 1 and an exhaust pipe 2 connected to the internal combustion engine 1.

  The exhaust pipe 2 is provided to exhaust exhaust gas generated in the internal combustion engine 1 from the rear of the vehicle body. The exhaust pipe 2 includes a part 2a that constitutes an exhaust path that is bent so as to guide exhaust gas discharged from the front of the internal combustion engine 1 to the rear, and a silencer 2b. The exhaust pipe 2 may be integrally configured by one component, or may be configured by joining a plurality of components.

  In the present embodiment, the entire exhaust pipe 2 is exposed so as to appear in the appearance of the motorcycle 100, and constitutes a part of the design of the entire motorcycle 100. As will be described in detail below, when the entire exhaust pipe 2 is exposed, discoloration of the exhaust pipe 2 does not occur over a long period of time, and the effect of the present invention that maintains the appearance of a new car appears remarkably. However, as long as at least a part of the exhaust pipe 2 appears on the exterior, a part of the exhaust pipe 2 may be covered with a cowl or a protector depending on the design of the motorcycle. Further, the shape of the motorcycle is not limited to that shown in FIG. 1. For example, the exhaust pipe according to the present invention may be adopted in a motorcycle having the structure shown in FIG. 10.

  FIG. 2 is a cross-sectional view showing a part of the exhaust pipe 2 (part 2 a constituting the exhaust path). The exhaust pipe 2 includes a metal pipe (exhaust pipe main body) 5 that surrounds a passage 6 through which exhaust gas passes, and a ceramic film 10 that covers the outside of the metal pipe 5. In other words, exhaust gas flows inside the metal tube 5, and the ceramic film 10 is provided outside the metal tube 5.

  The metal tube 5 is made of a metal material containing at least chromium. For example, stainless steel (SUS) is used as the metal material containing chromium. The metal tube 5 only needs to surround the passage 6, and may adopt a double tube structure including an inner tube that directly surrounds the passage 6 and an outer tube that is held so as to surround the outer side of the inner tube. Good. However, the effect of using the present invention is higher in the single tube structure that directly surrounds the passage 6 because the outside of the metal tube 5 tends to be hot.

  The ceramic film 10 is made of an amorphous material that is dense and hardly oxidizes or decomposes even at high temperatures. Specifically, the ceramic film 10 includes silicon (Si), titanium (Ti), aluminum (Al), zirconium (Zr), molybdenum (Mo), niobium (Nb), tungsten (W), vanadium (V), and the like. And at least one selected from oxides, nitrides, nitride oxides or borides of the above elements. These materials do not necessarily contain elements in a stoichiometric ratio.

  “Ceramics” in the present specification refers to solid materials such as metal or non-metal oxides, nitrides, nitride oxides, etc., and only those formed by a technique including a firing process that has been used frequently in the past. Of course, it also includes those formed by physical vapor deposition such as sputtering, as will be described in detail later.

  The exhaust pipe 2 in the present embodiment is characterized by the distribution of chromium concentration in the thickness direction (depth direction). Specifically, as shown in an enlarged cross-sectional structure of the exhaust pipe 2 in FIG. 2, the metal pipe 5 has a surface layer 5 a having a higher chromium concentration than the inside 5 b of the metal pipe 5. . The ceramic film 10 has a back surface layer 10 a that is in contact with the surface layer 5 a of the metal tube 5 and has a higher chromium concentration than the inside of the metal tube 5.

  That is, the exhaust pipe 2 has a chromium-rich layer including a part of the metal pipe 5 on the ceramic film 10 side (namely, the surface layer 5a) and a part of the ceramic film 10 on the metal pipe 5 side (namely, the back surface layer 10a). ing. “Chromium-rich” in the present specification means that the chromium concentration is higher than the inside of the component main body (here, the inside 5b of the metal tube 5), and means that the chromium concentration is necessarily the highest in the layer. Not to do.

  In the exhaust pipe 2 according to the present invention, since the metal pipe 5 has the surface layer 5a having a higher chromium concentration than the inside 5b, a chromium oxide film that contributes most to the corrosion resistance is stably generated. Further, since the ceramic film 10 having high acid resistance covers the outside of the metal tube 5, the chromium oxide film is hardly broken. Therefore, the exhaust pipe 2 according to the present invention is excellent in corrosion resistance. Moreover, since the exhaust pipe 2 according to the present invention does not require a large-scale device or special waste water treatment for manufacturing as described later, according to the present invention, the corrosion resistance of the exhaust pipe 2 can be easily improved. it can.

  As described above, the corrosion resistance can be improved by at least the metal tube 5 having the chromium-rich surface layer 5a. Furthermore, when the ceramic film 10 has the chromium-rich back surface layer 10a as in the present embodiment, the chromium oxide film is more stably generated, so that the corrosion resistance is further improved.

  In order to ensure sufficient corrosion resistance, the thickness of the surface layer 5a of the metal tube 5 is preferably 10 nm or more, and more preferably 20 nm or more. Further, the thickness of the back surface layer 10a of the ceramic film 10 is preferably 10 nm or more, and more preferably 20 nm or more. The total thickness of the chromium rich layer including the surface layer 5a of the metal tube 5 and the back surface layer 10a of the ceramic film 10 is preferably 10 nm or more, and more preferably 20 nm or more.

  Similarly, from the viewpoint of corrosion resistance, the average concentration of chromium in the surface layer 5a of the metal tube 5 is preferably 1.5 times or more higher than the average concentration of chromium in the inside 5b of the metal tube 5, and more than 2 times higher. It is more preferable. Moreover, the average concentration of chromium in the back surface layer 10a of the ceramic film 10 is preferably 1.5 times or more, more preferably 2 times or more higher than the average concentration of chromium in the interior 5b of the metal tube 5.

  The ceramic film 10 that covers the outside of the metal tube 5 has a metal element content (excluding chromium) that is mainly included in the surface of the metal tube 5 (typically included in a ratio of 50% or more) except 0.5%. It is preferable to be less than mass%. Hereinafter, the reason will be described.

  The inventor of the present application examined in detail the cause of the discoloration and deterioration of the exhaust pipe surface not sufficiently prevented with the silicon oxide film formed by the sol-gel method disclosed in Patent Document 1. As a result, the silicon oxide film formed by the sol-gel method contains a metal element mainly contained on the surface of the exhaust pipe. When this metal is oxidized at a high temperature, the exhaust pipe is discolored or the surface is deteriorated. It was found that it occurred.

  Further, in the sol-gel method, since the organic compound bonded to silicon is vaporized and decomposed during firing, fine voids are generated in the obtained silicon oxide film, and the gas barrier property is lowered. Conceivable. For this reason, when the exhaust pipe is exposed to a high temperature, the metal on the surface of the exhaust pipe diffuses into the silicon oxide film and combines with external oxygen to oxidize, or oxygen penetrates the silicon oxide film and passes through It is thought to cause metal oxidation. When metal is contained in the silicon oxide film or fine voids are formed in the silicon oxide film in this way, iron in the metal constituting the exhaust pipe is reddish oxide on the surface. It will deposit and damage the appearance of the exhaust pipe.

  According to the study of the present inventor, when the main component elements (excluding chromium) on the surface of the metal tube 5 are contained in the ceramic film 10 in an amount of more than 0.5% by mass, the surface of the ceramic film 10 is caused by high heat. It was found that this metal element is oxidized and the surface of the exhaust pipe may be discolored. Further, there is a possibility that the oxidation proceeds from the oxidized metal to the inside of the metal tube 5. On the other hand, when the content of the main component elements (excluding chromium) on the surface of the metal tube 5 is 0.5% by mass or less, discoloration and oxidation due to high heat are prevented. Considering the appearance of the exhaust pipe 2 when the metal contained in the ceramic film 10 is oxidized, the content of the main component elements on the surface of the metal pipe 5 is more preferably 0.4% by mass or less, and 0.3% by mass. More preferably, it is% or less.

  The content of the main component elements (excluding chromium) on the surface of the metal tube 5 may locally vary in the ceramic film 10, but at least 0.5 mass in the central portion in the thickness direction of the ceramic film 10. % Or less is preferable. Further, the content ratio of the main component elements on the surface of the metal tube 5 is 10% of the thickness near the inner surface (on the metal tube 5 side) and near the outer surface of the ceramic film 10 (each of the thickness of the entire ceramic film 10). It is preferable that it is 0.5 mass% or less in the part (namely, the part equivalent to 80% of the whole ceramic film 10) except the part which has).

  In order to reduce the content of main component elements (excluding chromium) on the surface of the metal tube 5 to 0.5% by mass or less, the main component on the surface of the metal tube 5 is formed when the ceramic film 10 is formed outside the metal tube 5. It is preferable to use a method in which elements (excluding chromium) hardly diffuse into the ceramic film 10. The inventor of the present application has conducted various studies, and as a result, when a physical vapor deposition method such as a sputtering method or an ion plating method is used to form the ceramic film 10, the main component elements (excluding chromium) on the surface of the metal tube 5 are ceramic films. 10 was found to be difficult to diffuse. Moreover, since the ceramic film formed by the physical vapor deposition method is dense, it has been found that even at a temperature of about 500 ° C., it has a high gas barrier property and can prevent the surface of the metal tube 5 from being oxidized.

  When the sputtering method is used, a DC sputtering apparatus, an RF sputtering apparatus, a magnetron sputtering apparatus, an ion beam sputtering apparatus, or the like can be used. When these methods are used, the surface of the metal tube 5 can be etched by causing plasma particles to collide with the surface of the metal tube 5 on which the ceramic film 10 is deposited. By utilizing this, the natural oxide film formed on the surface of the metal tube 5 can be removed, and the adhesion between the ceramic film 10 and the metal tube 5 can be improved. That is, it is preferable that a metal element oxide film mainly contained on the surface of the metal tube 5 is not substantially formed between the ceramic film 10 and the metal tube 5. Even when the ceramic film 10 is formed by a deposition method that does not use plasma, the natural oxide film formed on the surface of the metal tube 5 is removed before the ceramic film 10 is formed by a physical or chemical method. It is preferable to keep it.

  The ceramic film 10 formed by physical vapor deposition such as sputtering is basically an amorphous film and remains amorphous even when heated to a high temperature by the operation of the internal combustion engine. The amorphous film here refers to a film that does not have a long-period structure as observed as a diffraction peak by X-ray diffraction. Depending on the formation conditions, a part of the film may crystallize when heated, but there is practically no problem with gas barrier properties.

  Furthermore, when the inventor forms the ceramic film 10 by using physical vapor deposition, diffusion of the main component element (iron in stainless steel) to the ceramic film 10 on the surface of the metal tube 5 is prevented. The inventors discovered a phenomenon that the chromium concentration near the surface of the tube 5 and the back surface of the ceramic film 10 increases. Although the mechanism of this specific phenomenon is not clear, by forming the ceramic film 10 using physical vapor deposition, a chromium-rich surface layer 5a is formed on the metal tube 5, or the ceramic film 10 is chromium-rich. The back surface layer 10a can be formed.

  The ceramic film 10 is preferably a film containing silicon and / or aluminum, that is, a silicon film, an aluminum film, or a composite film (silicon / aluminum film) of silicon and aluminum. For example, a titanium-based ceramic film such as a titanium nitride film is less likely to have a stoichiometric composition and has a poor oxygen barrier property because the film itself is sparse. In addition, the stoichiometric composition is unlikely to occur, and a metal-bonded portion is generated, so that oxidation of the film itself proceeds or oxygen is transferred to the inside. In contrast, a silicon-based ceramic film is covalently bonded with a compound of a nonmetallic element, and the film itself can be formed densely. In addition, since aluminum is an element located at the boundary between a metal element and a non-metal element, an aluminum-based ceramic film can be densely formed as well as a silicon-based ceramic film. Therefore, the silicon-based, aluminum-based, and silicon / aluminum-based ceramic film 10 is excellent in oxygen barrier properties.

  The thickness of the ceramic film 10 is preferably 5 nm or more and 150 nm or less, and more preferably 20 nm or more and 50 nm or less. If the thickness is less than 5 nm, sufficient high-temperature oxidation resistance, high-temperature discoloration resistance, and corrosion resistance may not be ensured. On the other hand, if the thickness exceeds 150 nm, the film formation time becomes too long and the productivity is lowered, the interference color becomes too dark and the color is not suitable for the merchandise, the surface layer 5a of the metal tube 5 or the ceramics. The diffusion of chromium to the back surface layer 10a of the film 10 may be suppressed.

  Further, the inventor of the present application examined in detail the preferable conditions for increasing the chromium concentration in the vicinity of the surface of the metal tube 5 and in the vicinity of the back surface of the ceramic film 10. As a result, the ceramic film 10 is an oxide film or a nitride oxide film, and the oxygen concentration in these films is preferably 30% by mass to 70% by mass, and more preferably 30% by mass to 50% by mass. Has been experimentally confirmed to be more preferable. The results of this experiment will be described later.

  The oxygen concentration in the ceramic film 10 can be adjusted by changing the film forming conditions of the ceramic film 10. For example, when the ceramic film 10 is formed using a sputtering method, the oxygen concentration in the ceramic film 10 can be adjusted by changing the composition of the gas introduced into the chamber of the sputtering apparatus. Table 1 shows an example of the relationship between the gas composition (volume ratio) and the concentrations of silicon, oxygen, and nitrogen in the ceramic film 10 when silicon is used as a target and the silicon-based ceramic film 10 is formed. Show.

  From Table 1, it can be seen that the oxygen concentration in the ceramic film 10 varies depending on the composition of the atmospheric gas. It can also be seen that if the type of gas that is a component of the atmospheric gas is the same, the higher the concentration of oxygen gas, the higher the oxygen concentration in the formed film. Therefore, the oxygen concentration in the ceramic film 10 can be set to a desired value by appropriately setting the composition of the atmospheric gas.

  Next, a method for manufacturing the exhaust pipe 2 will be described. In the following description, an example in which the ceramic film 10 is formed by a sputtering method will be described.

  First, the metal tube 5 which is a component main body is prepared. As the material of the metal tube 5, a metal material such as stainless steel containing at least chromium (however, the main component is not chromium) is used.

  Next, the prepared metal tube 5 is introduced into the chamber of the sputtering apparatus. An example of the sputtering apparatus is shown in FIGS. 3 (a) and 3 (b). FIG. 3A is a side cross-sectional view schematically showing the sputtering apparatus 20, and FIG. 3B is an upper cross-sectional view schematically showing the sputtering apparatus 20.

  The sputtering apparatus 20 includes a plurality of holders 24 in the chamber 21 that suspend and hold the metal tube 5. Each holder 24 revolves in the chamber 21 while rotating around the rotation shaft 23. The inner diameter φ1 of the chamber 21 is, for example, 1200 mm, and an effective region where a film can be formed is, for example, a cylindrical shape having a diameter φ2 of 1080 mm and a height of 1800 mm.

  A plurality of targets 22 are provided outside the track on which the holder 24 rotates. When a silicon film is formed as the ceramic film 10, a silicon target 22 is used.

  By using the sputtering apparatus 20 having the above-described structure, the ceramic film 10 having a uniform thickness can be formed on the entire outside of the metal tube 5 having a three-dimensional shape. Moreover, many metal tubes 5 can be processed in one batch.

  The metal tube 5 is placed in the holder 24, and the inside of the chamber 21 is evacuated using a pump (not shown). When the degree of vacuum in the chamber 21 reaches a predetermined value, argon is introduced into the chamber 21 and discharge is started. While rotating and revolving the holder 24, a bias voltage is applied so that plasma particles generated by discharge collide with the metal tube 5, and the surface of the metal tube 5 is etched by reverse sputtering. The reverse sputtering is preferably performed until the natural oxide film formed on the surface of the metal tube 5 is completely removed. The thickness of the natural oxide film is generally in the range of 2 nm to 3 nm. By removing the natural oxide film, the adhesion between the metal tube 5 and the ceramic film 10 can be enhanced.

  After removing the natural oxide film, argon and oxygen are introduced into the chamber 21 and discharge is started. A bias voltage is applied so that the plasma particles collide with the target, and deposition of the ceramic film 10 is started. In the case of this embodiment, the silicon particles jumping out of the target react with oxygen plasma and are deposited on the surface of the metal tube 5 as a silicon oxide film. The deposition time is determined according to the target film thickness of the ceramic film to be generated, taking into account conditions such as the number of targets, the pressure during reaction, and the bias voltage. The formed ceramic film 10 includes some silicon nitride in addition to silicon oxide. The exhaust pipe 2 is obtained by performing sputtering for a predetermined time to form the ceramic film 10 having a predetermined thickness outside the metal pipe 5.

  The ceramic film 10 formed as described above contains only 0.5% by mass or less of the metal element mainly contained on the surface of the metal tube 5, and the main component element on the surface of the metal tube 5 is substantially contained. It can be said that it is not included. Therefore, the exhaust pipe 2 is not discolored or the surface is not deteriorated when the metal element is oxidized at a high temperature. Therefore, the exhaust pipe 2 is not discolored by high-temperature exhaust gas, and an excellent appearance can be maintained. Since the ceramic film 10 formed by the sputtering method is dense, it has a high barrier property, and external oxygen reaches the metal tube 5 or iron contained in the metal tube 5 is oxidized and deposited on the surface. Can be effectively prevented.

  Further, when the ceramic film 10 is formed as described above, diffusion of the main component element (iron in stainless steel) to the ceramic film 10 on the surface of the metal tube 5 is prevented, while the metal tube 5 is diffused by heating. The chromium concentration in the vicinity of the front surface and in the vicinity of the back surface of the ceramic film 10 increases. That is, in the step of forming the ceramic film 10, the chromium-rich surface layer 5 a is formed near the surface of the metal tube 5, and the chromium-rich back layer 10 a is formed near the back surface of the ceramic film 10. Therefore, the chromium-rich layer can be formed without performing an electropolishing method on the surface of the metal tube 5, directly injecting chromium, or diffusing and penetrating. Therefore, the corrosion resistance of the exhaust pipe 2 can be easily improved without requiring a specially large apparatus or special drainage treatment.

  In addition, it is preferable that the surface of the metal tube 5 has a larger surface roughness than the thickness of the ceramic film 10 as shown in FIG. Specifically, the average roughness Ra of the surface of the metal tube 5 is preferably 0.4 μm or more. When the average roughness is less than 0.4 μm, when visible light is reflected on the surface of the metal tube 5, diffracted light is strengthened when the optical path difference between wavefronts reflected from adjacent grooves is an integral multiple of the wavelength. As a result, the appearance of the exhaust pipe 2 may be impaired. In addition, when the average roughness is reduced and the surface of the metal tube 5 is smooth, the adhesion of the ceramic film 10 may be reduced. There is no particular upper limit to the value of the average roughness Ra on the surface of the metal tube 5, but if the average roughness Ra on the surface of the metal tube 5 is 3.2 μm or more, the light reflectivity is reduced and the merchantability and aesthetics are impaired. It is not preferable.

(Example)
First, the distribution of elements in the depth direction in the exhaust pipe according to the present invention was examined. As an example, a metal tube made of SUS304 was prepared, and a silicon oxide (SiO ₂ ) film was formed on the surface of the metal tube by a sputtering method. Specifically, first, a metal tube polished by No. 800 buff was placed in a chamber of a reactive magnetron sputtering apparatus, and evacuation was performed until a vacuum degree of 3 × 10 ^{−2 to −4} Pa was reached. Next, argon gas was introduced into the chamber at a flow rate of 25 sccm, and while maintaining a pressure of 4 × 10 ⁻¹ Pa, 500 V, 4 A (2.0 kW) power was applied, and reverse sputtering was performed for 1 minute to obtain metal. The natural oxide film on the tube surface was removed. Then, using silicon as a target, power of 2.5 KW was applied while maintaining a pressure of 3 × 10 ⁻¹ Pa in 5-20 volume% argon + 80-95 volume% oxygen atmosphere or 100 volume% oxygen atmosphere. Then, sputtering was performed for 1 minute to form a silicon oxide film having a thickness of 20 nm on the surface of the metal tube.

  In addition, as a comparative example, a metal tube formed of SUS304 was prepared, and a silicon oxide film having a thickness of 170 nm was formed as a ceramic film by a sol-gel method (Comparative Example 1). Furthermore, as another comparative example, an electropolishing method was performed without forming a ceramic film on the surface of a metal tube made of SUS304 (Comparative Example 2).

  The exhaust pipe of the example and the exhaust pipes of Comparative Examples 1 and 2 were heated at 500 ° C. for 4 to 8 hours in an air atmosphere furnace, and then air-cooled. Then, when the silicon oxide film of the exhaust pipe of the example was analyzed with a thin film X-ray diffractometer, it was confirmed to be amorphous. The element distribution in the depth direction of the exhaust pipe of the example and the exhaust pipes of comparative examples 1 and 2 was measured using a GDS method (glow discharge emission spectroscopy).

  FIG. 5A shows an element distribution in the depth direction of the exhaust pipe of the example. As can be seen from FIG. 5 (a), in the exhaust pipe of the example, the chromium concentration near the surface of the metal tube is higher than the chromium concentration inside the metal tube, and a chromium-rich surface layer is formed on the metal tube. Has been. Specifically, the chromium concentration inside the metal tube is about 18% by mass, whereas the chromium concentration in the surface layer exceeds 18% by mass and reaches nearly 30% by mass at a high place. Further, the chromium concentration in the vicinity of the back surface of the ceramic film is also higher than that in the metal tube, and a chromium-rich back layer is formed on the ceramic film. Thus, in the exhaust pipe of the embodiment, a chromium rich layer including a part of the metal pipe and a part of the ceramic film is formed.

  FIG. 5B shows an enlarged portion corresponding to the vicinity of the exhaust pipe surface in FIG. As can be seen from FIG. 5B, in the exhaust pipe of the example, the silicon oxide film, which is a ceramic film, hardly contains iron, which is the main component element on the surface of the metal pipe. Specifically, the elemental concentration of iron in the silicon oxide film is 0.5 mass% or less as shown in FIG.

  FIG. 6A shows the element distribution in the depth direction of the exhaust pipe of Comparative Example 1. FIG. As can be seen from FIG. 6A, in the exhaust pipe of Comparative Example 1, the chromium concentration near the surface of the metal tube is almost the same as the chromium concentration inside the metal tube, and the chromium tube has a chromium-rich surface layer. Not formed. Further, the chromium concentration in the vicinity of the back surface of the ceramic film is almost the same as the chromium concentration in the metal tube, and no chromium-rich back layer is formed on the ceramic film. Thus, in the exhaust pipe of Comparative Example 1, a chromium rich layer having a higher chromium concentration than the inside of the metal pipe was not formed.

  FIG. 6B shows an enlarged portion corresponding to the vicinity of the exhaust pipe surface in FIG. As can be seen from FIG. 6B, in the exhaust pipe of the comparative example, the silicon oxide film formed by the sol-gel method contains a large amount of iron which is the main component metal on the surface of the metal pipe. Specifically, the elemental concentration of chromium in the silicon oxide film exceeds 30% by mass.

  FIG. 7 shows the element distribution in the depth direction of the exhaust pipe of Comparative Example 2. As can be seen from FIG. 7, in the exhaust pipe of Comparative Example 2, the chromium concentration in the vicinity of the surface of the metal tube is slightly higher than that in the metal tube due to electrolytic polishing, but the implementation shown in FIG. Not as high as the exhaust pipe in the example. Specifically, the chromium concentration inside the metal tube is about 18% by mass, whereas the chromium concentration in the vicinity of the surface is about 25% by mass at the highest.

  When the salt water spray test was performed for 96 hours on the exhaust pipe of the example and the exhaust pipes of comparative example 1 and comparative example 2, red rust was generated on the surfaces of the exhaust pipes of comparative example 1 and comparative example 2. In contrast, no red rust occurred on the surface of the exhaust pipe of the example.

  In the exhaust pipe of the example, red rust did not occur because (1) a chromium-rich layer was formed so as to include a part of the metal pipe and a part of the ceramic film, and (2) the metal pipe was covered. This is because the ceramic layer is formed as described above, and (3) the ceramic film does not substantially contain iron as the main component of the surface of the metal tube.

  On the other hand, red rust was generated in the exhaust pipe of Comparative Example 1 because the chromium oxide film was not stably formed because the chromium-rich layer was not formed near the surface of the metal pipe or the back surface of the ceramic film. is there. In addition, the ceramic film contains a large amount of iron, which is the main component of the surface of the metal tube, and this iron is also oxidized.

  In addition, red rust was generated in the exhaust pipe of Comparative Example 2 because the chromium concentration in the vicinity of the surface of the metal tube cannot be sufficiently increased only by the electrolytic polishing method, and a ceramic film covering the surface of the metal tube is formed. Is due to not being. Further, in the exhaust pipe of Comparative Example 2, when heated, iron diffuses on the surface and the appearance is deteriorated, and the corrosion resistance is also lowered thereby.

  Next, the result of verifying the relationship between the chromium concentration in the chromium-rich layer and the oxygen concentration in the ceramic film will be described. As a result of detailed verification by the inventors of the present application, in order to increase the chromium concentration in the vicinity of the surface of the metal tube 5 and in the vicinity of the back surface of the ceramic film 10, the oxygen concentration in the ceramic film is set to 30% by mass or more and 70% by mass or less. It was found that the content is preferably 30% by mass or more and 50% by mass or less. A part of the verification result is shown in FIGS.

  FIG. 8 shows the element distribution in the depth direction of the exhaust pipe when a ceramic film having an oxygen concentration of about 30% is formed by sputtering. As shown in FIG. 8, the chromium concentration is rapidly increased in a portion corresponding to the vicinity of the front surface of the metal tube or the back surface of the ceramic film, and a high-concentration chromium-rich layer is formed.

  FIG. 9 shows the element distribution in the depth direction of the exhaust pipe when a ceramic film having an oxygen concentration of about 80% is formed by sputtering. As shown in FIG. 9, the chromium concentration is not so high in the portion corresponding to the vicinity of the surface of the metal tube or the vicinity of the back surface of the ceramic film.

  According to the present invention, it is possible to easily and greatly improve the corrosion resistance of a component formed from a metal material. The present invention is suitably used for parts for internal combustion engines that are exposed to high temperatures and parts for marine that are exposed to seawater. The component according to the present invention can be widely used in various transportation equipment such as a ship and an airplane, as well as a vehicle such as a motorcycle and an all-weather four-wheel vehicle.

1 is a side view of a motorcycle in which an exhaust pipe for an internal combustion engine according to the present invention is used. It is sectional drawing of the exhaust pipe in suitable embodiment of this invention. (A) And (b) is a figure which shows typically the sputtering device used for manufacture of an exhaust pipe, (a) is a sectional side view, (b) is an upper sectional view. It is a schematic diagram which shows the structure of the surface vicinity of an exhaust pipe. (A) And (b) is a graph which shows element distribution in the depth direction of the exhaust pipe of the Example of this invention. (A) And (b) is a graph which shows element distribution in the depth direction of the exhaust pipe of the comparative example 1. FIG. 10 is a graph showing an element distribution in a depth direction of an exhaust pipe of Comparative Example 2. It is a graph which shows element distribution of the depth direction of an exhaust pipe when a ceramic film | membrane with an oxygen concentration in a film | membrane of about 30% is formed using sputtering method. It is a graph which shows element distribution of the depth direction of an exhaust pipe when the ceramics film | membrane whose oxygen concentration in a film | membrane is about 80% is formed using sputtering method. 1 is a side view showing the appearance of a motorcycle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust pipe 5 Metal pipe 5a Metal pipe surface layer 5b Inside metal pipe 6 Passage 10 Ceramic film 10a Back surface layer of ceramic film 20 Sputtering device 21 Chamber 22 Target 23 Shaft 24 Holder 100 Motorcycle

Claims (15)

A component body formed of a metal material containing at least chromium;
A ceramic film covering the outside of the component main body,
The component body has a surface layer with a higher chromium concentration than the inside ,
The metal material is stainless steel, and is a component for an internal combustion engine or marine.   The component according to claim 1, wherein a thickness of the surface layer of the component main body is 10 nm or more.   The component according to claim 1, wherein the ceramic film has a back surface layer that is in contact with a surface layer of the component body and has a higher chromium concentration than the inside of the component body.   The component according to claim 3, wherein a thickness of the back surface layer of the ceramic film is 10 nm or more. A component body formed of a metal material containing at least chromium;
A ceramic film covering the outside of the component body, and a component for an internal combustion engine or marine comprising:
Including a part of the ceramic body side of the ceramic body and a part of the ceramic body side of the ceramic body, and a chromium-rich layer having a higher chromium concentration than the interior of the ceramic body .
The metal material is stainless steel, and is a component for an internal combustion engine or marine.   The component according to claim 5, wherein the chromium-rich layer has a thickness of 10 nm or more.   The component according to claim 1, wherein the ceramic film has a thickness of 10 nm to 150 nm.   The component according to claim 1, wherein the ceramic film has a thickness of 20 nm to 50 nm.   The component according to claim 1, wherein the ceramic film contains silicon and / or aluminum.   The component according to claim 1, wherein the ceramic film is an oxide film or a nitride oxide film, and an oxygen concentration in the ceramic film is 30% by mass or more and 70% by mass or less.   The component according to claim 10, wherein an oxygen concentration in the ceramic film is 30% by mass or more and 50% by mass or less.   The component according to any one of claims 1 to 11, wherein the ceramic film has a content of a metal element mainly contained on a surface of the component main body of 0.5% by mass or less.   The component according to claim 1, wherein the ceramic film is a film formed by physical vapor deposition. Component according to any of claims 1 to 13 is an exhaust pipe for an internal combustion engine. Transport device with a component according to any of claims 1 to 14.

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