JP4641284B2 - Titanium parts for internal combustion engines - Google Patents

Description

  The present invention relates to a titanium component formed of titanium or a titanium alloy, and more particularly to a titanium component for an internal combustion engine that is exposed to combustion gas of the internal combustion engine.

  In recent years, titanium and titanium alloys (collectively referred to as “titanium materials”) have been used as materials for engine parts in order to increase engine output and weight.

  Titanium material is light and has high strength, but has poor wear resistance. Therefore, oxidation treatment may be applied to titanium parts that require high wear resistance. When the oxidation treatment is performed, a hard titanium oxide film is formed on the surface of the titanium component, so that the wear resistance is improved. However, since titanium oxide is brittle, the fatigue strength and impact strength of a titanium component on which a titanium oxide film is formed are reduced. Although the fatigue strength and impact strength can be improved to some extent by forming the parts thick, in this case, the weight increases and the significance of using the titanium material is diminished.

  Titanium parts that do not require high wear resistance do not need to be oxidized. However, even when such titanium parts are used at high temperatures, the surface must be As a result, the fatigue strength and impact strength are reduced.

As a technique for solving the above-described problem, Patent Document 1 discloses a method in which aluminum powder is adhered to the surface of a titanium bulb or a titanium connecting rod by firing. Patent Document 2 discloses a method of performing nitriding in advance on a titanium component using a nitriding chamber. According to these methods, the aluminum film or titanium nitride film formed on the surface of the titanium component functions as an oxygen barrier layer that inhibits oxygen from reaching the base titanium material. Therefore, oxidation of the titanium material is suppressed, and fatigue strength and impact strength are improved. In addition, by forming the above-described oxygen barrier layer on a predetermined part of the titanium part and then subjecting the entire titanium part to an oxidation treatment, while ensuring the fatigue strength of the part where the oxygen barrier layer is formed, the other part ( The wear resistance of the portion where titanium oxide is formed by oxidation treatment can be improved.
Japanese Patent No. 3151713 JP 2004-115907 A

  However, the methods disclosed in Patent Documents 1 and 2 cannot obtain a sufficient antioxidant effect for the following reasons.

  When an aluminum film is used as an oxygen barrier layer, a brittle intermetallic compound (between the metal between aluminum and titanium) is used between the aluminum film and the titanium material layer located inside it during oxidation treatment or use at high temperatures. Compound) layer is formed. For this reason, cracks are generated inside the intermetallic compound layer due to stress during engine operation, and the aluminum film as the oxygen barrier layer may fall off. Therefore, a stable antioxidant effect may not be obtained. Moreover, since the film formed by firing the powder becomes a porous layer, it cannot function suitably as a gas barrier layer.

  Further, since titanium nitride is very hard and brittle, a slight crack may be generated in the titanium nitride film due to stress. Therefore, even when the titanium nitride film is used as an oxygen barrier layer, a stable antioxidant effect may not be obtained.

  Furthermore, since the aluminum film and titanium nitride film formed as described above are not dense in the first place, the oxygen barrier property is not so high. Therefore, when exposed to highly oxidizing gas such as engine combustion gas, the gas passes through these films and reaches the titanium material, and the titanium material is oxidized. Therefore, the formed titanium oxide layer is cracked by subsequent use, and the crack often progresses inside the part.

  The present invention has been made in view of the above problems, and an object thereof is to improve the fatigue strength and impact strength of titanium parts exposed to combustion gas of an internal combustion engine.

  A titanium component for an internal combustion engine according to the first aspect of the present invention is a titanium component for an internal combustion engine that is formed of titanium or a titanium alloy and is exposed to the combustion gas of the internal combustion engine, and has a ceramic layer formed on the surface. The ceramic layer has a thickness of more than 10 nm and not more than 750 nm, and contains silicon or aluminum.

  In a preferred embodiment, the ceramic layer has a thickness of 20 nm to 500 nm.

  In a preferred embodiment, the ceramic layer has a thickness of 50 nm or more and 250 nm or less.

  In a preferred embodiment, the ceramic layer has a titanium content of 0.5 wt% or less.

  A titanium component for an internal combustion engine according to a second aspect of the present invention is a titanium component made of titanium or a titanium alloy and exposed to the combustion gas of the internal combustion engine, and has a ceramic layer formed on the surface. The ceramic layer contains silicon or aluminum and has a titanium content of 0.5 wt% or less.

In a preferred embodiment, the number of granular deposits having a particle diameter of 1 μm or more present on the surface of the ceramic layer is 80 / mm ² or less.

  In a preferred embodiment, the ceramic layer includes silicon oxide, nitride, or nitride oxide.

  In a preferred embodiment, the ceramic layer includes aluminum oxide, nitride, or nitride oxide.

  In a preferred embodiment, the titanium component for an internal combustion engine according to the present invention has a titanium layer or a titanium alloy layer inside the ceramic layer, and between the ceramic layer and the titanium layer or the titanium alloy layer, A titanium oxide layer having a thickness of 1 μm or less is included.

  In a preferred embodiment, the ceramic layer is selectively formed on a part of the surface.

  In a preferred embodiment, the titanium component for an internal combustion engine according to the present invention includes a titanium oxide layer having a thickness of 10 μm or more on another part of the surface.

  In a preferred embodiment, the titanium component for an internal combustion engine according to the present invention is a valve constituting a combustion chamber of the internal combustion engine.

  In a preferred embodiment, the titanium component for an internal combustion engine according to the present invention is an exhaust valve that opens and closes an exhaust port.

  In a preferred embodiment, the titanium component for an internal combustion engine according to the present invention is a valve, and includes a stem portion and a face portion, and a neck portion connecting the stem portion and the face portion. The ceramic layer is formed on the surface.

  In a preferred embodiment, the stem portion has a cotter portion that engages with a valve cotter, and the ceramic layer is also formed on a surface of the cotter portion.

  In a preferred embodiment, the titanium component for an internal combustion engine according to the present invention is a valve, and includes a stem portion having a cotter portion engaged with the valve cotter, and the ceramic layer is formed on a surface of the cotter portion. .

  In a preferred embodiment, the ceramic layer is a deposited film formed by a deposition method.

  In a preferred embodiment, the ceramic layer is a deposited film formed by a sputtering method.

  A titanium component for an internal combustion engine according to a third aspect of the present invention is a titanium component made of titanium or a titanium alloy and exposed to the combustion gas of the internal combustion engine, and has a ceramic layer formed on the surface. The ceramic layer has a thickness of more than 10 nm and 750 nm or less, and the titanium content is 0.5 wt% or less.

A titanium component for an internal combustion engine according to a fourth aspect of the present invention is a titanium component made of titanium or a titanium alloy and exposed to the combustion gas of the internal combustion engine, and has a ceramic layer formed on the surface. The ceramic layer contains silicon or aluminum, and the number of granular deposits having a particle diameter of 1 μm or more present on the surface of the ceramic layer is 80 / mm ² or less.

  The internal combustion engine by this invention is equipped with the titanium component for internal combustion engines which has the said structure.

  A transportation device according to the present invention includes an internal combustion engine having the above-described configuration.

  A titanium valve for an internal combustion engine according to the present invention is a titanium valve for an internal combustion engine formed of titanium or a titanium alloy, and has a ceramic layer selectively formed on a part of the surface, and the ceramic layer has a thickness of 10 nm. More than 750 nm and contains silicon or aluminum.

  In a preferred embodiment, a titanium valve for an internal combustion engine according to the present invention includes a stem portion that slides in a valve guide, a face portion that contacts a valve seat, and a neck portion that connects the stem portion and the face portion. And the ceramic layer is formed on the surface of the neck portion.

  In a preferred embodiment, the stem portion has a cotter portion that engages with a valve cotter, and the ceramic layer is also formed on a surface of the cotter portion.

  In a preferred embodiment, the titanium valve for an internal combustion engine according to the present invention includes a stem portion that slides in a valve guide, and the stem portion includes a cotter portion that engages with a valve cotter, and the surface of the cotter portion. The ceramic layer is formed.

  A method for manufacturing a titanium component for an internal combustion engine according to the present invention is a method for manufacturing a titanium component for an internal combustion engine that is exposed to combustion gas of the internal combustion engine, the step of preparing a titanium component formed from titanium or a titanium alloy, Depositing a ceramic layer having a thickness of more than 10 nm and not more than 750 nm on the surface of the titanium component by vapor deposition.

  In a preferred embodiment, the ceramic layer includes silicon or aluminum.

  In a preferred embodiment, the ceramic layer has a titanium content of 0.5 wt% or less.

  In a preferred embodiment, the step of depositing the ceramic layer is performed by a sputtering method.

  In a preferred embodiment, in the step of depositing the ceramic layer, the ceramic layer is selectively deposited on a part of the surface of the titanium component.

  In a preferred embodiment, the method for manufacturing a titanium component for an internal combustion engine according to the present invention includes a titanium oxide layer having a thickness of 10 μm or more on the other part of the surface of the titanium component after the step of depositing the ceramic layer. Is further included.

  The titanium component according to the first aspect of the present invention has a ceramic layer formed on the surface. Since this ceramic layer contains silicon or aluminum, it can be formed densely and has a high oxygen barrier property. Further, since this ceramic layer has a thickness of more than 10 nm and not more than 750 nm, the oxygen barrier property is insufficient when it is too thin, and cracks are hardly generated when it is too thick. Therefore, a high antioxidant effect can be obtained even when used for a long time at high temperature, and high fatigue strength and impact strength are realized.

  Since the ceramic layer formed on the surface of the titanium component according to the second aspect of the present invention contains silicon or aluminum, it can be formed densely and has a high oxygen barrier property. Further, this ceramic layer has a titanium content of 0.5 wt% or less and substantially does not contain titanium, so that the titanium of the base material is prevented from being oxidized through the titanium in the ceramic layer. . Therefore, a high antioxidant effect can be obtained even when used for a long time at high temperature, and high fatigue strength and impact strength are realized.

  Since the ceramic layer formed on the surface of the titanium component according to the third aspect of the present invention has a thickness of more than 10 nm and not more than 750 nm, the oxygen barrier property is insufficient or too thick by being too thin. Almost no cracking occurs. Further, this ceramic layer has a titanium content of 0.5 wt% or less and substantially does not contain titanium, so that the titanium of the base material is prevented from being oxidized through the titanium in the ceramic layer. . Therefore, a high antioxidant effect can be obtained even when used for a long time at high temperature, and high fatigue strength and impact strength are realized.

Since the ceramic layer formed on the surface of the titanium component according to the fourth aspect of the present invention contains silicon or aluminum, it can be formed densely and has a high oxygen barrier property. Further, the number of granular deposits having a particle diameter of 1 μm or more present on the surface of the ceramic layer is 80 pieces / mm ² or less. That is, there is almost no coarse granular deposit on the surface of the ceramic layer. Therefore, the denseness of the film is high, and a sufficient antioxidant effect can be obtained even with a film thickness of several tens nm to several hundreds nm.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification, parts formed from titanium or a titanium alloy are collectively referred to as “titanium parts”. Since the titanium component according to the present invention is excellent in fatigue strength and impact strength, it is suitably used as a component for an internal combustion engine exposed to combustion gas. Hereinafter, the present invention will be described with a titanium valve as an example of a titanium component.

  FIG. 1 shows a titanium valve 10 in the present embodiment. The titanium valve 10 is made of a titanium material, that is, titanium or a titanium alloy. In this specification, the titanium alloy includes titanium as a main component, and contains 0.5 wt% of at least one of Al, V, Fe, Mo, Cr, Zr, Sn, and C (preferably at least Al). This refers to an alloy added with 10.0 wt% or less.

  The titanium valve 10 includes a rod-shaped stem portion 1 and an umbrella-shaped umbrella portion 2. The umbrella part 2 includes a frustoconical face part 3 that contacts the valve seat, and a neck part 4 that connects the stem part 1 and the face part 3.

  The end 5 of the stem portion 1 opposite to the umbrella portion 2 is called a stem end. In the vicinity of the stem end 5 of the stem portion 1, a recess (called a cotter portion) 6 that engages with the valve cotter is provided.

  FIG. 2 shows a state in which the titanium valve 10 is attached to the exhaust port 31 of the engine. As shown in FIG. 2, an exhaust port 31 is formed so as to extend from the lower part of the cylinder head 30 toward the side part.

  A valve guide 32 is provided in a hole formed in the cylinder head 30, and the stem portion 1 of the titanium valve 10 is inserted into the valve guide 32. The titanium valve 10 is biased so as to be lifted upward by a valve spring 33.

  The valve spring 33 is held by a spring seat 34 and a retainer 35. The retainer 35 is locked to the stem portion 1 of the titanium valve 10 by a valve cotter 36 that engages with the cotter portion 6 of the titanium valve 10.

  A cam 37 is rotatably provided above the titanium valve 10. As the cam 37 rotates, the convex portion (large diameter portion) of the cam pushes down the valve lifter 43, and the valve spring 33 pushes up the titanium valve 10. As a result, the titanium valve 10 moves up and down, and the exhaust port 31 is opened and closed.

  When the titanium valve 10 moves up and down, the stem portion 1 slides in the valve guide 32. Further, when the titanium valve 10 returns to the uppermost position, the face portion 3 comes into contact with (collides with) the valve seat 38, and thereby the exhaust port 31 is closed. At this time, if there is a single contact of the titanium bulb 10 or the like, a strong impact force is applied to the neck portion 4 and a bending stress is also generated. This repetition may lead to bending fatigue failure. Further, when the titanium valve 10 moves up and down, a load is applied to the stem end 5 located on the cam 37 side. Since the force applied to the titanium valve 10 increases as the rotational speed of the engine increases, the impact force on the titanium valve 10 increases in a high-rotation engine used in a motorcycle or the like.

  As described above, when the exhaust port 31 is opened and closed, the stem portion 1, the face portion 3, and the stem end 5 of the titanium valve 10 are in contact with other members, so that excellent wear resistance is required. Therefore, it is preferable to form a titanium oxide layer on the surface of these parts by performing an oxidation treatment. In order to obtain sufficiently high wear resistance, the thickness of the titanium oxide layer is preferably 10 μm or more.

  On the other hand, the neck portion 4 and the cotter portion 6 of the titanium valve 10 are required to have high fatigue strength and impact strength because stress due to the seating of the titanium valve 10 occurs. A ceramic layer as described later is formed as an oxygen barrier layer on the surfaces of the neck portion 4 and the cotter portion 6 of the titanium valve 10 in the present embodiment, and thereby, the fatigue strength and impact strength of these portions are reduced. It becomes possible to make it high enough. Hereinafter, the ceramic layer in the present embodiment will be described more specifically.

  In the titanium valve 10 in the present embodiment, as shown in FIG. 3, the ceramic layer 7 is formed on the neck portion 4, the cotter portion 6, and the surface in the vicinity of the cotter portion 6 (the hatched portion in FIG. 3). Is formed.

  Specifically, the ceramic layer 7 is a ceramic film containing silicon or aluminum. The ceramic layer 7 is made of, for example, silicon oxide, nitride, or nitride oxide, or aluminum oxide, nitride, or nitride oxide.

  A titanium-based ceramic film such as a titanium nitride film formed by the technique disclosed in Patent Document 2 is less likely to have a stoichiometric composition, and the film itself is sparse, resulting in poor oxygen barrier properties. ing. 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 ceramic layer 7 in this embodiment is excellent in oxygen barrier property. Therefore, even if the entire titanium valve 10 is oxidized to form a titanium oxide layer on the surfaces of the stem portion 1, the face portion 3 and the stem end 5, the neck portion 4 and the cotter portion 6 are sufficiently oxidized. Can be suppressed. Further, oxidation of the neck portion 4 and the cotter portion 6 when exposed to the combustion gas during engine operation can be sufficiently suppressed. Therefore, the titanium valve 10 in this embodiment is excellent in fatigue strength and impact strength. In addition, since sufficient fatigue strength and impact strength can be obtained, it is not necessary to make a design change that is disadvantageous for weight reduction, such as an increase in wall thickness.

  In general, nitrides are denser than oxides and have excellent gas barrier properties. For this reason, from the viewpoint of the antioxidant effect, the ceramic layer 7 is preferably a silicon nitride oxide film, more preferably a silicon nitride film, rather than a silicon oxide film. Similarly, the ceramic layer 7 is preferably an aluminum nitride oxide film, more preferably an aluminum nitride film, rather than an aluminum oxide film.

  In addition, a silicon-based ceramic film is preferably used from the viewpoint of the denseness of the film, and an aluminum-based ceramic film is preferably used from the viewpoint that an inexpensive target can be used. Aluminum is more suitable for sputtering because it has higher conductivity and is easier to use for sputtering than silicon and has a lower evaporation temperature. In addition, aluminum nitride has a thermal conductivity about 10 times that of aluminum oxide and is resistant to thermal shock. Therefore, it is preferable to use an aluminum nitride film for an engine operated at a high load.

  If the ceramic layer 7 is too thin, the gas barrier property may be insufficient. If the ceramic layer 7 is too thick, cracks may be generated due to thermal expansion at high temperatures. As will be described later, the inventors of the present invention have studied, and in order to more reliably prevent the occurrence of cracks while ensuring sufficient gas barrier properties, the thickness of the ceramic layer 7 is more than 10 nm and less than 750 nm. It was found that the thickness was preferably 20 nm or more and 500 μm or less, and more preferably 50 nm or more and 250 nm or less.

  Strictly speaking, it is not possible to completely prevent the titanium material from being oxidized even at the portion where the ceramic layer 7 is formed on the surface. However, by providing the ceramic layer 7 as in this embodiment, the thickness of the titanium oxide layer formed between the ceramic layer 7 and the titanium material layer (titanium layer or titanium alloy layer) is 1 μm or less. It is possible to sufficiently suppress the decrease in fatigue strength and impact strength due to the thick titanium oxide layer.

  Moreover, it is preferable that the ceramic layer 7 does not contain much titanium. Specifically, the titanium content of the ceramic layer 7 is preferably 0.5 wt% or less. If the ceramic layer 7 contains titanium, the titanium in the ceramic layer 7 is combined with oxygen and oxidized, and further oxygen may be passed to the base material side titanium which is the same element and oxidized. . Such oxidation can be sufficiently suppressed by setting the titanium content of the ceramic layer 7 to 0.5 wt% or less (that is, making the ceramic layer 7 substantially not contain titanium). Note that the titanium-based ceramic film hardly contains a stoichiometric composition as described above, and therefore contains a large amount of unreacted titanium. For this reason, the base material is likely to be oxidized as described above.

  In the present embodiment, the ceramic layer 7 is formed on both the neck portion 4 and the cotter portion 6, but may be formed only on one of the neck portion 4 and the cotter portion 6 as necessary. It is also preferable to form the ceramic layer 7 on the surface of the umbrella part 2 on the combustion chamber side. As shown in FIG. 4, a crack 9 may occur from the surface 8 on the combustion chamber side of the umbrella portion 2 due to an impact when the titanium valve 10 is seated on the valve seat 38. By forming the ceramic layer 7 on the surface 8 on the combustion chamber side, the impact strength of the surface 8 on the combustion chamber side can be improved, and the occurrence of cracks 9 can be suppressed.

  Next, a method for manufacturing the titanium valve 10 will be described.

  First, a titanium valve 10 on which the ceramic layer 7 is not formed is prepared. As a material of the titanium valve 10, pure titanium or a titanium alloy can be used. The titanium bulb 10 before the ceramic layer 7 is formed can be formed by various known methods.

  Next, a ceramic layer 7 having a predetermined thickness is deposited on the surface of the titanium bulb 10. At this time, the ceramic layer 7 is selectively deposited on a part of the surface of the titanium bulb 10, more specifically, on the surface near the neck portion 4, the cotter portion 6, and the cotter portion 6. As described above, the thickness of the ceramic layer 7 is preferably more than 10 nm, more preferably 20 nm or more, and further preferably 50 nm or more from the viewpoint of gas barrier properties. The thickness of the ceramic layer 7 is preferably 750 nm or less, more preferably 500 nm or less, and further preferably 250 nm or less from the viewpoint of suppressing the occurrence of cracks due to thermal expansion.

  As already described, since it is preferable that the ceramic layer 7 does not contain much titanium, the ceramic layer 7 is a method in which titanium in the titanium valve 10 body diffuses into the ceramic layer 7 and is not contained in the layer. Is preferably formed. Specifically, the ceramic layer 7 is preferably formed by a vapor deposition method. That is, the ceramic layer 7 is preferably a vapor deposition film formed by a vapor deposition method. In this specification, “evaporation method” refers to a CVD (chemical vapor deposition) method and a physical vapor deposition method in which a material to be deposited is deposited in a gaseous state (preferably under vacuum). As the vapor deposition method, it is more preferable to use a physical vapor deposition method such as a sputtering method or an ion plating method. In particular, since the film formed by the sputtering method has high density, the ceramic layer 7 is more preferably formed by the sputtering method.

  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 titanium bulb 10 can be etched (that is, reverse sputtering) by causing plasma particles to collide with the surface of the titanium bulb 10 on which the ceramic layer 7 is deposited. By utilizing this, the natural oxide film formed on the surface of the titanium bulb 10 can be removed, and the adhesion between the ceramic layer 7 and the titanium bulb 10 body can be improved.

  Even when the ceramic layer 7 is formed using a deposition method that does not use plasma, the natural oxide film formed on the surface of the titanium bulb 10 is formed by a physical or chemical method. It is preferred to remove it before.

  Further, when using the sputtering method, the ceramic layer 7 can be selectively deposited on a part of the surface of the titanium bulb 10 by performing masking with a jig or a shield, for example.

  Thereafter, a titanium oxide layer having a predetermined thickness is formed on another part of the surface of the titanium bulb 10, specifically, the stem portion 1, the face portion 3, and the stem end 5. From the viewpoint of realizing sufficient wear resistance, the thickness of the titanium oxide layer is preferably 10 μm or more. This oxidation treatment step is performed, for example, by holding the titanium bulb 10 at a high temperature (for example, about 650 ° C. to 850 ° C.) in the atmosphere. At this time, in the portion where the ceramic layer 7 is formed on the surface, the ceramic layer 7 functions as an oxygen barrier layer, thereby suppressing the formation of the titanium oxide layer.

  In the following, the results of various tests performed by actually making a prototype of the titanium valve 10 in the present embodiment will be described.

First, a titanium valve 10 formed of a titanium alloy having a composition of Ti-6Al-4V was placed in a chamber of a sputter deposition apparatus, and evacuation was performed until the degree of vacuum reached 3 × 10 ⁻⁴ Pa.

  Next, argon was introduced into the chamber at a flow rate of 25 sccm and a pressure of 0.4 Pa was maintained, while a power of 500 V × 4 A (2.0 kW) was applied and reverse sputtering was performed for 1.5 minutes. The natural oxide film on the surface was removed.

  Subsequently, using silicon as a target, while keeping the pressure at 0.2 Pa in an atmosphere of argon and oxygen (or argon and nitrogen), a power of 700 V × 7 A (4.9 kW) was applied and sputtering was performed for 1 minute. A ceramic layer 7 was formed by depositing a 25 nm thick silicon oxide film (or silicon nitride film) on the surface of the titanium bulb 10.

  When the titanium bulb 10 having the ceramic layer 7 formed as described above is heated and held at 700 ° C. for 24 hours in the atmosphere, it is formed between the surface of the titanium bulb 10 body (that is, a layer of titanium material) and the ceramic layer 7. The thickness of the formed titanium oxide film was 0.5 μm or less (that is, it was hardly formed), and it was confirmed that the formation of the titanium oxide film was suppressed.

  Next, a plurality of titanium valves having different thicknesses of ceramic layers (here, silicon nitride films) were manufactured by changing the sputtering time, and their antioxidant effects were evaluated. The results are shown in Table 1 below. In Table 1, “◎” indicates that the antioxidant effect is very high, and “◯” indicates that the antioxidant effect is high. “Δ” indicates that the antioxidant effect is practically sufficient, and “x” indicates that the antioxidant effect is insufficient.

  As shown in Table 1, when the thickness of the ceramic layer 7 was 10 nm, the antioxidant effect was insufficient. This is because the gas barrier property is not sufficient because the thickness of the film itself is small. Therefore, from the viewpoint of gas barrier properties, the thickness of the ceramic layer 7 is preferably more than 10 nm, more preferably 20 nm or more, and further preferably 50 nm or more.

  Further, as shown in Table 1, when the thickness of the ceramic layer 7 was 2 μm or 1 μm, the antioxidant effect was insufficient. This is because cracks occurred in the film due to thermal expansion at a high temperature. On the other hand, when the thickness of the ceramic layer 7 was 750 nm or less, cracks due to thermal stress were not generated, and a sufficient antioxidant effect was obtained. However, when the thickness of the ceramic layer 7 is 750 nm, cracks due to external stress or impact load may occur depending on the use environment. If the thickness of the ceramic layer 7 is 500 nm or less, the occurrence of such cracks can be suppressed, and if it is 250 nm or less, it can be more reliably suppressed. Therefore, from the viewpoint of avoiding the occurrence of cracks due to thermal expansion, the thickness of the ceramic layer 7 is preferably 750 nm or less, more preferably 500 nm or less, and even more preferably 250 nm or less.

  Subsequently, the titanium valve 10 in which the ceramic layer 7 is selectively formed on a part of the surface is subjected to an oxidation treatment, and both the portion where the ceramic layer 7 is formed and the portion where the ceramic layer 7 is not formed, Cross-sectional observation was performed using an optical microscope and a scanning electron microscope.

  5A and 5B show a cross section of a portion where the ceramic layer 7 is formed. 5A and 5B are an optical micrograph and a scanning electron micrograph of a cross section taken along line 5-5 'in FIG. 5C, respectively.

  FIG. 5A shows that a very thin titanium oxide layer of 1 μm or less is formed on the outermost surface of the titanium bulb 10. FIG. 5B shows that a very thin titanium oxide layer of about 0.5 μm is formed on the outermost surface of the titanium bulb 10.

  6A and 6B show a cross section of a portion where the ceramic layer 7 is not formed. 6A and 6B are an optical micrograph and a scanning electron micrograph of a cross section taken along line 6-6 'in FIG. 6C, respectively.

  From FIG. 6A, it can be seen that a thick titanium oxide of about 6 μm is formed on the outermost surface of the titanium bulb 10. Further, FIG. 6B shows that a thick titanium oxide of about 5.6 μm is formed on the outermost surface of the titanium bulb 10.

  Thus, there is a significant difference in the thickness of the titanium oxide layer formed by the oxidation treatment between the portion where the ceramic layer 7 is formed on the surface and the portion where the ceramic layer 7 is not formed. The excellent antioxidant effect of layer 7 was confirmed.

  Subsequently, the present inventor conducted the following verification in order to quantitatively estimate the influence of the thickness of the titanium oxide layer on the fatigue strength.

  Since the titanium oxide layer formed on the surface of the titanium component is very brittle, it can be regarded as a crack generated on the surface of the titanium component. Therefore, assuming that the thickness of the titanium oxide layer is the depth of the crack, it can be considered that the stress intensity factor KI at the bottom of the crack is a factor determining the fatigue strength. The stress intensity factor KI is a parameter indicating the strength of the stress field at the bottom of the crack. The stress intensity factor KI is expressed by the following equation, for example.

KI = 1.12 × σ × √ (π · a)
In the above equation, σ is the acting stress, and a is the crack depth. From the above equation, it can be seen that the stress intensity factor KI is proportional to the square root of the crack depth a. This leads to the inference that the stress intensity factor KI is proportional to the square root of the thickness of the titanium oxide layer. Therefore, the actual fatigue strength was measured by changing the oxidation treatment conditions to change the thickness of the titanium oxide layer. The relationship between the thickness of the titanium oxide layer and the fatigue strength is shown in Table 2 below. FIG. 7 is a graph showing the relationship between the square root of the thickness of the titanium oxide layer and the fatigue strength.

  From Table 2 and FIG. 7, a good proportional relationship is found between the square root of the thickness of the titanium oxide layer and the fatigue strength. From this result, it can be seen that the thickness of the titanium oxide layer determines the fatigue strength of the titanium component.

  From the proportional relationship shown in FIG. 7, when a titanium oxide layer having a thickness of 10 μm or more is formed in order to improve wear resistance, the fatigue strength can be estimated to be 470 MPa or less. On the other hand, when the thickness of the titanium oxide layer is 1 μm or less by forming the ceramic layer 7, the fatigue strength can be estimated to be 600 MPa or more. Thus, it can be seen that the fatigue strength can be improved by 22% or more by forming the ceramic layer 7.

  For example, as shown in FIG. 5B, the fatigue strength is about 518 MPa when the thickness of the titanium oxide layer is about 5.6 μm as shown in FIG. When the thickness of the titanium oxide layer is about 0.5 μm, the fatigue strength is about 637 MPa, which is improved by about 23%.

  Subsequently, the results of a comparative examination of the antioxidant effect of a silicon nitride oxide (SiON) film formed by sputtering and a titanium carbonitride (TiCN) film formed by ion plating will be described. Table 3 shows the presence or absence of cracks after the heating test at 700 ° C. for 1 hour with respect to the titanium bulb 10 having a silicon nitride oxide film formed on the surface as the ceramic layer 7 and the increase in weight due to oxidation. Show. Table 4 shows similar data for a titanium valve having a titanium carbonitride film formed on the surface.

  As can be seen from the comparison between Table 3 and Table 4, when the silicon nitride oxide film is formed, the amount of increase in weight due to oxidation is significantly smaller than when the titanium carbonitride film is formed. Thus, the silicon nitride oxide film has a significantly higher antioxidation effect than the titanium carbonitride film. Also, from Table 3, the film thickness is preferably 750 nm or less from the viewpoint of suppressing the occurrence of cracks, more preferably 500 nm or less, and more preferably 250 nm or less considering the length of the film formation time. It turns out that it is preferable. From the viewpoint of oxygen barrier properties, it can be seen that the film thickness preferably exceeds 10 nm, more preferably 20 nm or more, and even more preferably 50 nm or more.

  As described above, the titanium carbonitride film is not a silicon-based or aluminum-based ceramic film, and contains titanium, so that the antioxidant effect is low, but the results shown in Tables 3 and 4 are the results. The difference is also attributed to the film formation method. The inventor of the present application has conducted a detailed study on the method of forming the ceramic film, and found that it is easier to form a dense ceramic film by using the sputtering method than by using the ion plating method.

  8A, 8B, and 8C, a silicon nitride oxide (SiON) film formed by a sputtering method, a titanium carbonitride nitride (TiCN) film and a titanium aluminum nitride film formed by an ion plating method ( A micrograph of the surface of the (TiAlN) film is shown.

  As shown in FIGS. 8B and 8C, many coarse granular deposits are observed on the surfaces of the titanium carbonitride film and the titanium aluminum nitride film formed by the ion plating method. If the particles deposited in this way are coarse, the denseness of the film will be low. Even if the film thickness is 1 μm or more, there is a granular deposit larger than the film thickness, so the film tends to be porous. Therefore, it is difficult to realize a sufficient oxygen barrier property.

  On the other hand, coarse granular deposits are not observed on the surface of the silicon nitride oxide film formed by sputtering as shown in FIG. Since the deposited particles are very fine (for example, the particle size is less than 1 nm), the film has high density and a sufficient oxygen barrier property is easily realized. Therefore, a sufficient antioxidant effect can be obtained even with a film thickness of several tens nm to several hundreds nm.

Further, the number of coarse granular deposits on the surface of the ceramic layer 7 can be used as a parameter for evaluating the denseness of the film. In order to realize sufficient oxygen barrier properties, the amount of granular deposits having a particle diameter of 1 μm or more present on the surface of the ceramic layer 7 is preferably 80 pieces / mm ² or less. FIG. 9 shows the cumulative particle size distribution of granular deposits existing on the surface of a silicon nitride oxide film formed by sputtering and a titanium carbonitride film and a titanium aluminum nitride film formed by ion plating. . The particle size and number of the granular deposits are, for example, as shown in FIGS. 10 (a), (b) and (c) in the micrographs shown in FIGS. After image processing (specifically binarization), analysis can be performed using predetermined software (for example, Analysis Five manufactured by Olympus Corporation).

As shown in FIG. 9, the amount of granular deposits having a particle size of 1 μm or more exceeds 200 / mm ² on the surface of the film formed by ion plating, whereas the nitridation oxidation formed by sputtering is used. On the surface of the silicon film, there is almost no granular deposit having a particle size of 1 μm or more, and the amount thereof is 50 pieces / mm ² or less. Note that although a silicon nitride oxide film is described here, similar results were obtained for an aluminum nitride oxide (AlON) film formed by a sputtering method.

  The titanium valve 10 in this embodiment is widely used in various engines for motor vehicles and machines. As described above, the titanium valve 10 in the present embodiment is excellent in fatigue strength and impact strength, and thus is particularly suitable for an engine that is operated at a high speed. FIG. 11 shows an example of the engine 100 including the titanium valve 10.

  The engine 100 includes a cylinder 20 as shown in FIG. A piston 21 is provided in the cylinder 20 so as to reciprocate up and down. A cylinder head 30 is provided on the cylinder 20.

  An exhaust port 31 is formed so as to extend from one side of the cylinder head 30 to the lower center. An intake port 39 is formed so as to extend from the other side portion of the cylinder head 30 toward the center lower portion.

  An exhaust valve 41 and an intake valve 42 are provided at the lower end opening of the exhaust port 31 and the lower end opening of the intake port 39, respectively. The exhaust valve 41 and the intake valve 42 are urged by a valve spring 33 so as to be lifted obliquely upward. A cam 37 is rotatably provided above the exhaust valve 41 and the intake valve 42. As the cam 37 rotates, the exhaust valve 41 and the intake valve 42 move up and down, whereby the exhaust port 31 and the intake port 39 are opened and closed at predetermined timings, respectively.

  The exhaust chamber 41, the intake valve 42, the cylinder 20, and the cylinder head 30 constitute a combustion chamber 22. The engine 100 includes the titanium valve 10 in the present embodiment as the exhaust valve 41 and the intake valve 42. Therefore, engine 100 is excellent in durability. Although it is not always necessary to use the titanium valve 10 in this embodiment for both the exhaust valve 41 and the intake valve 42, the exhaust valve 41 for opening and closing the exhaust port 31 is always exposed to high-temperature combustion gas. It is preferable to use the titanium valve 10 in this embodiment as at least the exhaust valve 41.

  FIG. 12 shows a motorcycle 200 including the engine 100 shown in FIG. Since the motorcycle 200 includes the engine 100 using the titanium valve 10 in the present embodiment, the motorcycle 200 has suitable performance.

  In the present embodiment, the present invention has been described by taking the engine valve 10 as an example. However, the present invention is not limited to this and is widely used for titanium parts for internal combustion engines that are exposed to the combustion gas of the internal combustion engine. For example, the present invention can be used for a titanium connecting rod, and also for a butterfly valve for controlling the flow rate of exhaust gas outside the combustion chamber.

  Moreover, although this embodiment demonstrated the case where a ceramics layer was selectively formed in a part of surface of a titanium component, this invention is not limited to this. For titanium parts that do not require high wear resistance, a ceramic layer may be formed over the entire surface.

  According to the present invention, it is possible to improve the fatigue strength and impact strength of titanium parts exposed to the combustion gas of an internal combustion engine. The titanium component according to the present invention is suitably used as a component for various internal combustion engines, and the internal combustion engine provided with the titanium component according to the present invention is suitably used for various transportation equipment.

It is a front view showing typically a titanium valve in a suitable embodiment of the present invention. It is a figure which shows the state which attached the titanium valve in suitable embodiment of this invention to the exhaust port of the engine. It is a front view showing typically a titanium valve in a suitable embodiment of the present invention. It is a figure which shows typically a mode that a crack generate | occur | produces when a titanium valve seats on a valve seat. (A)-(c) is a figure which shows the observation result of the titanium valve actually produced as an experiment, (a) And (b) is a cross section (ceramic layer) along the 5-5 'line in (c), respectively. FIG. 2 is an optical micrograph and a scanning electron micrograph of a cross section of a portion where is formed. (A)-(c) is a figure which shows the observation result of the titanium valve actually produced as an experiment, (a) And (b) is the cross section (ceramic layer) along the 6-6 'line in (c), respectively. 2 is an optical micrograph and a scanning electron micrograph of a cross section of a portion where no is formed. It is a graph which shows the relationship between the square root of the thickness (micrometer) of a titanium oxide layer, and fatigue strength (MPa). (A) is a micrograph of the surface of a silicon nitride oxide (SiON) film formed by sputtering, and (b) and (c) are titanium carbonitride (TiCN) films formed by ion plating. 2 is a photomicrograph of the surface of a titanium aluminum nitride (TiAlN) film. It is a graph which shows the integrated particle size distribution of the granular deposit which exists in the surface about the silicon nitride oxide film formed by the sputtering method, and the titanium carbonitride nitride film and titanium aluminum nitride film formed by the ion plating method. (A), (b) and (c) are images obtained by processing the micrographs shown in FIGS. 8 (a), (b) and (c) for analysis. It is sectional drawing which shows typically an example of the engine provided with the titanium valve in suitable embodiment of this invention. FIG. 12 is a cross-sectional view schematically showing a motorcycle including the engine shown in FIG. 11.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stem part 2 Umbrella part 3 Face part 4 Neck part 5 Stem end 6 Cotter part 7 Ceramic layer 8 Umbrella part combustion chamber side surface 10 Titanium valve 20 Cylinder 21 Piston 22 Combustion chamber 30 Cylinder head 31 Exhaust port 32 Valve guide 33 Valve spring 34 Spring seat 35 Retainer 36 Valve cotter 37 Cam 38 Valve seat 39 Intake port 41 Exhaust valve 42 Intake valve 43 Valve lifter 100 Engine 200 Motorcycle

Claims (24)

A titanium component for an internal combustion engine formed from titanium or a titanium alloy and exposed to combustion gas of the internal combustion engine,
Having a ceramic layer formed on the surface,
The ceramic layer has a 10nm beyond following 750nm thickness, and, looking containing silicon or aluminum,
A titanium component for an internal combustion engine, wherein the ceramic layer has a titanium content of 0.5 wt% or less .   2. The titanium component for an internal combustion engine according to claim 1, wherein the ceramic layer has a thickness of 20 nm to 500 nm.   2. The titanium component for an internal combustion engine according to claim 1, wherein the ceramic layer has a thickness of 50 nm to 250 nm. A titanium component for an internal combustion engine formed from titanium or a titanium alloy and exposed to combustion gas of the internal combustion engine,
Having a ceramic layer formed on the surface,
The titanium layer for an internal combustion engine, wherein the ceramic layer contains silicon or aluminum and has a titanium content of 0.5 wt% or less. Said particulate deposits or particle size 1μm on the surface of the ceramic layer, 80 / mm ² or less for internal combustion engines titanium component according to any one of claims 1 to 4. The ceramic layer is an oxide of silicon, an internal combustion engine for a titanium component according to any of claims 1 5 comprising a nitride or oxynitride. The titanium component for an internal combustion engine according to any one of claims 1 to 5 , wherein the ceramic layer includes an oxide, nitride, or nitride oxide of aluminum. Having a titanium layer or a titanium alloy layer inside the ceramic layer,
The titanium component for an internal combustion engine according to any one of claims 1 to 7 , further comprising a titanium oxide layer having a thickness of 1 µm or less between the ceramic layer and the titanium layer or the titanium alloy layer. The titanium component for an internal combustion engine according to any one of claims 1 to 8 , wherein the ceramic layer is selectively formed on a part of the surface. The titanium component for an internal combustion engine according to claim 9 , comprising a titanium oxide layer having a thickness of 10 µm or more on another part of the surface. The titanium component for an internal combustion engine according to any one of claims 1 to 10 , which is a valve constituting a combustion chamber of the internal combustion engine. The titanium component for an internal combustion engine according to claim 11 , which is an exhaust valve for opening and closing an exhaust port. The titanium component for an internal combustion engine according to claim 11 or 12 , wherein the titanium component is a valve.
A stem portion and a face portion; and a neck portion connecting the stem portion and the face portion;
The titanium component for an internal combustion engine according to claim 11 or 12 , wherein the ceramic layer is formed on a surface of the neck portion. The stem portion has a cotter portion that engages with a valve cotter,
The titanium component for an internal combustion engine according to claim 13 , wherein the ceramic layer is also formed on a surface of the cotter portion. The titanium component for an internal combustion engine according to claim 11 or 12 , wherein the titanium component is a valve.
A stem portion having a cotter portion that engages with the valve cotter;
The titanium component for an internal combustion engine according to claim 11 or 12 , wherein the ceramic layer is formed on a surface of the cotter portion. The ceramic layer is an internal combustion engine for a titanium component according to any of claims 1 15 which is a vapor-deposited film formed by vapor deposition. The titanium component for an internal combustion engine according to claim 16 , wherein the ceramic layer is a vapor deposition film formed by a sputtering method. A titanium component for an internal combustion engine formed from titanium or a titanium alloy and exposed to combustion gas of the internal combustion engine,
Having a ceramic layer formed on the surface,
The titanium layer for an internal combustion engine, wherein the ceramic layer has a thickness of more than 10 nm and 750 nm or less, and a titanium content is 0.5 wt% or less. An internal combustion engine comprising the titanium component for an internal combustion engine according to any one of claims 1 to 18 . A transportation device comprising the internal combustion engine according to claim 19 . A titanium valve for an internal combustion engine formed from titanium or a titanium alloy,
Having a ceramic layer selectively formed on part of the surface;
The ceramic layer has a 10nm beyond following 750nm thickness, and, looking containing silicon or aluminum,
A titanium valve for an internal combustion engine, wherein the ceramic layer has a titanium content of 0.5 wt% or less . A stem portion that slides in the valve guide, a face portion that contacts the valve seat, and a neck portion that connects the stem portion and the face portion,
The titanium valve for an internal combustion engine according to claim 21 , wherein the ceramic layer is formed on a surface of the neck portion. The stem portion has a cotter portion that engages with a valve cotter,
The titanium valve for an internal combustion engine according to claim 22 , wherein the ceramic layer is also formed on a surface of the cotter portion. With a stem that slides inside the valve guide,
The stem portion has a cotter portion that engages with a valve cotter,
The titanium valve for an internal combustion engine according to claim 21 , wherein the ceramic layer is formed on a surface of the cotter portion.