JPH0642318A - Titanium alloy valve having solid solution layer of oxygen or nitrogen on shaft part surface - Google Patents

Abstract

PURPOSE:To provide a valve of generating no looseness by wearing without causing seizure of a shaft part and a valve guide by forming a titanium- contained layer, having specific hardness and layer thickness with solid solution of oxygen or nitrogen or oxygen and nitrogen, in a shaft part surface of applying seizure preventing treatment. CONSTITUTION:Surface treatment of a titanium alloy (Ti-6Al-4V)-made valve 1 is performed by heating a shaft part 2 for 10min at 900 deg.C in the atmosphere with propane gas as fuel, to form an oxide layer of lmum thickness and a hardened layer of 2mum thickness (lmum or more 20mum or less) having hardness of Vickers Hv>=600 or more by oxygen solid solution, in a surface of the shaft part 2. In this titanium alloy valve, wearing of the shaft part is executed by a valve tester, to obtain 1mum after 40 hours and also no change from after 40 hours even after 200 hours. This result is equivalent to a Tufftride method. In this way, seizure of the shaft part and valve guide and looseness by wearing are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shaft portion of a titanium alloy valve used for engines of automobiles and other vehicles.

[0002]

2. Description of the Related Art Conventionally, as a seizure prevention treatment for the shaft surface of a titanium alloy valve used for engines of automobiles and other vehicles, for example, JP-A-62-256956.
Japanese Patent Application Laid-Open No. 61-81
The nitriding treatment disclosed in Japanese Patent Laid-Open No. 505 or the ion nitriding treatment disclosed in Japanese Patent Laid-Open No. 61-234210, and the hard chrome plating or Ni-P disclosed in Japanese Patent Laid-Open No. 01-96407. There are known technical means such as plating and molybdenum spraying disclosed in JP-A-62-41908.

Although this molybdenum spraying has a proven record as a seizure preventing treatment for the shaft surface of a titanium alloy valve of a competitive automobile engine, it has a problem of high cost. Further, in the anti-seizure treatment for applying hard chrome plating or Ni-P plating, it is essentially difficult to secure plating adhesion because of the oxide film which is inevitably present on the surface of the titanium alloy. Efforts have been made to roughen the surface by blasting, remove the oxide film by hydrofluoric acid pickling, and improve plating adhesion by heat diffusion after plating, but they are not perfect.

On the other hand, the oxidation or nitriding treatment is a simple process in which the titanium alloy is heated in the atmosphere, and has attracted more attention than before because it is excellent in adhesion due to the diffusion treatment. However, for example, seizure may occur even if the shaft portion of the titanium alloy valve is subjected to an oxidation treatment at 770 ° C. for 10 minutes, which is a constituent feature of the invention disclosed in Japanese Patent Laid-Open No. 62-256956, and 790
Even if oxidation treatment is performed at 5 ° C. for 5 hours, the oxide scale peels off, causing problems such as “rattle”. Even if this oxide film is removed in advance, if the hardened layer, which is a titanium alloy layer in which the oxide layer is in solid solution, is too thick, it will peel off and the surface roughness will increase, resulting in wear with the valve guide. Will increase.

Further, in the TiN ion plating, which is a constituent feature of the invention disclosed in Japanese Patent Laid-Open No. 61-81505, the TiN layer is peeled off even if it is a layer having a relatively good adhesiveness of 2 to 3 μm. I have something to do. Also, in the nitriding treatment which is a constituent factor of this prior art, when the treatment is performed at 850 ° C. which is a general nitriding treatment condition for 16 hours, the wear of the valve guide is increased and the shaft surface of the titanium alloy valve is burned. The proper range for the sticking prevention treatment was not always clear.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems in the prior art and to provide a titanium alloy valve having excellent seizure resistance.

[0007]

In order to achieve the above object, the present invention provides (1) oxygen or nitrogen having a Vickers hardness of Hv ≧ 600 on the surface of a shaft portion which has been subjected to a seizure prevention treatment. A titanium alloy valve having a solid solution layer of oxygen or nitrogen on the surface of a shaft, the titanium alloy valve having a titanium alloy layer having a thickness of 1 μm or more and 20 μm or less in which oxygen and nitrogen are dissolved, and (2) a base material When the Vickers hardness of is mHv, the amount (mass%) of oxygen and nitrogen in oxygen or nitrogen or a titanium alloy in which oxygen and nitrogen are solid-dissolved, which has a Vickers hardness of 600Hv, has the following values: (1) A titanium alloy valve having a solid solution layer of oxygen or nitrogen on the shaft surface.

[Equation 2]

The present invention will be described in detail below. As a result of repeated research to solve the problems in the prior art, the inventor has found that in the oxidation or nitriding treatment of a titanium alloy, Vickers hardness Hv in which oxygen or nitrogen is dissolved in the titanium alloy
It has been found that the thickness of the hardened layer having a hardness of ≧ 600 is important, and the seizure prevention of the shaft surface of the titanium alloy valve can be achieved by setting the thickness of the hardened layer within an appropriate range. The oxidation behavior of titanium and titanium alloys differs greatly from that of general iron alloys in the following points. That is,
In addition to forming a brittle multi-layered oxide layer, oxygen diffuses into titanium and titanium alloys to form a solid solution, forming a hardened layer. The hardened layer has a characteristic that the surface is hard and becomes softer toward the inside. The nitriding layer has the same characteristics, but the nitride layer is dense because the upper layer is the TiN layer and the lower layer is the Ti ₂ N layer. Nitrogen also diffuses and forms a solid solution in titanium and titanium alloys to form a hardened layer, but its formation rate is slower than that of oxygen.

In the present invention, the titanium alloy valve material is Ti-3Al-2.5V, Ti-6Al-4V, T.
An α + β type titanium alloy such as i-6Al-2Sn-4Zr-2Mo-0.1Si is suitable. When these materials are used, the formation of oxide layers or nitrides is relatively small, and the solid solution layer of oxygen or nitrogen, which is a requirement of the present invention, has relatively good adhesion. Further, pure titanium Gr3, pure titanium Gr4, Ti-8Al-1Mo-1V, Ti-5Al.
-2.5Sn, Ti-5.8Al-4Sn-3.5Zr
-0.5Mo-1Nb-0.35Si-0.06C (I
The α-type and near-α-type titanium alloys such as MI834) have a slightly poorer adhesion than the α + β-type titanium alloys when a solid solution layer of oxygen or nitrogen, which is an important requirement in the present invention, is formed thicker. Of course, it can be used in the present invention. Furthermore, in a β-type titanium alloy represented by Ti-15V-3Cr-3Sn-3Al, an oxide layer is relatively formed during the oxidation treatment and the surface is liable to be rough, but a solid solution layer of oxygen or nitrogen is formed. Since it tends to be formed in an island shape on the surface, it has excellent adhesion and can be used in the present invention.

In the present invention, the hardness of the surface of the shaft portion of the titanium or titanium alloy valve is defined as Vickers hardness Hv ≧ 600 because it is a titanium solid solution of oxygen or nitrogen or a solid solution of oxygen and nitrogen. Even if there is, Hv: 50
It is based on the finding obtained by the inventor that the one having a hardness of less than about 0 has a poor anti-seizure effect, and the one having a hardness of Vickers hardness Hv ≧ 600 exhibits a remarkable anti-seizure effect. It is known that the seizure phenomenon locally becomes a high temperature of 800 ° C to 1000 ° C. Further, the titanium alloy has a low thermal conductivity and is likely to reach a higher temperature than the iron alloy. The present inventor
If it is less than 0 Hv, the high temperature strength will decrease significantly, but 600
It has been found that at Hv and above, the decrease in high temperature strength is much smaller, and as a result, seizure is less likely to occur. Furthermore, when the Vickers hardness of the titanium alloy base material is mHv, 6
Oxygen and nitrogen contents in titanium alloys with 00Hv (ma
ss%) is

[Equation 3] I found that it is good to say. The above are the values found from the experimental results. In the case of mixing oxygen and nitrogen,
Normally, the amount of nitrogen is small, so nitrogen can be obtained by taking it into the base metal hardness. Further, the impurity oxygen and nitrogen taken into the base metal hardness are not included in the above oxygen amount and nitrogen amount.

Next, the thickness of the titanium alloy layer in which oxygen or nitrogen or oxygen and nitrogen is solid-dissolved is 1 μm or more and 20 μm.
The following is defined as a thickness less than 1 μm is insufficient for initial wear, and seizure may occur on the surface of the shaft of the titanium alloy valve, while a thickness over 20 μm may cause seizure. This is because the hardened layer comes off. Oxygen and nitrogen have a significantly higher hardening ability for titanium alloys than other elements, and can be easily solid-dissolved. Further, oxygen has a large diffusion coefficient in the titanium alloy as compared with nitrogen, and is suitable for carrying out the present invention.

Incidentally, referring to the oxide layer and the nitride layer which are inevitably formed during the oxidation and nitridation of the titanium alloy valve, the oxide layer is effective in preventing seizure, but is worn during sliding. If it is left thick as it is easy, it causes large dimensional change and causes “rattle”. However, if the thickness is about 5 μm or less, there is no problem even if it is left. The nitride layer is also effective in preventing seizure, but when the surface is rough (the roughness is high), it is highly aggressive to the mating material and causes “rattle”. The nitride layer having a low surface roughness is obtained by smoothing the surface of the titanium alloy and then forming the nitride layer to a thickness of 3 μm or less in a low temperature region of 850 ° C. or less.

[0013]

Example A valve 1 made of Ti-6Al-4V (titanium alloy) shown in FIG. 1 was prepared. The shaft diameter of the valve is 6.6.
mmφ. The surface was finished to 1.5 Rz or less. The surface treatment was performed by heating the shaft portion 2 shown in FIG. 1 at 900 ° C. for 10 seconds in the atmosphere using propane gas as a fuel. The surface of the shaft portion was composed of an oxide layer with a thickness of 1 μm and a hardened layer with a thickness of 2 μm having a Vickers hardness Hv ≧ 600 or more due to oxygen solid solution. This was confirmed by polishing the cross section of the sample obliquely and measuring it with a micro Vickers hardness meter 25 gf. Also, in the 600 Hv portion, the oxygen amount is 2.4.
It contained mass%. The hardness of the base material is 300 Hv,
Since 0.2 mass% of oxygen has oxygen, 2.2 mass% of oxygen is added. The amount of oxygen was measured by a secondary ion mass spectrometer.

The evaluation of the obtained titanium alloy valve is shown in FIG.
It carried out by the valve testing machine shown in. That is, push the valve spring 10 that compresses 3 mm with a weight of 24 kg.
Push the end of the valve shaft with the rod 20 to 3-10.5
The valve was moved up and down with a stroke of mm. The center of the push rod was applied at a position offset by 2.5 mm from the center of the valve shaft, and the valve shaft was pushed up to twist it up and down 3000 times / minute. The valve was rotated at 10 times / minute. The valve guide was made of pearlite cast iron (FC25 equivalent) which is in practical use. When the spring compression amount was 3 mm, the length from the valve guide to the stem end was 30 mm. The clearance between the valve diameter and the valve guide inner diameter was 40 to 50 μm.

Test result: Shaft wear after 40 hours was 1
.mu.m, the oxide layer was worn, and the wear of the shaft portion after 200 hours was the same as that after 40 hours. This is the current valve (shaft: tuftride processing)
Was equivalent to.

Examples of the present invention are shown in Tables 1 to 4. Table 5
A comparative example is shown in FIG. The test results were evaluated by the wear state after 40 hours. The one according to the invention shows good results. As a heat source for the heat treatment, propane, electricity, high frequency induction heating, laser beam, plasma or the like can be used. Here, when removing the oxide layer,
The valve shaft diameter was finished in consideration of the reduction in shaft diameter due to removal. Further, the average values of oxygen amount and nitrogen amount (excluding the content of the base material) in the 600 Hv portion are the values shown in Table 6. The error is
+0.2, -0.3 for oxygen and +0 for nitrogen.
A variation in the range of 03, -0.1 was recognized.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Table 4]

[0021]

[Table 5]

[0022]

[Table 6]

[0023]

According to the present invention, it is possible to provide a titanium alloy valve free from "rattle" due to seizure of the shaft portion and valve guide and abrasion of the shaft portion or valve guide, which has been a problem in the past. , Has a great effect on the industry.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a titanium alloy valve of the present invention.

FIG. 2 is a diagram showing an outline of a valve testing machine applied to an example of the present invention and a comparative example.

[Explanation of symbols]

 1 Valve 2 Shaft 10 Valve guide and valve spring 20 Push rod

Claims (2)

[Claims] 1. A shaft surface that has been subjected to a seizure prevention treatment,
Vickers hardness Hv ≧ 600, oxygen or nitrogen or a solid solution of oxygen and nitrogen with a thickness of 1 μm or more,
A titanium alloy valve having a solid solution layer of oxygen or nitrogen on the surface of a shaft portion, which has a titanium alloy layer of 20 μm or less. 2. When the base material has a Vickers hardness of mHv, the amount of oxygen and nitrogen (mass%) in oxygen or nitrogen or a titanium alloy in which oxygen and nitrogen are solid-dissolved, which has a Vickers hardness of 600Hv, is as follows. The titanium alloy valve having a solid solution layer of oxygen or nitrogen on the surface of the shaft portion according to claim 1. [Equation 1]