JPH02163403A - Engine valve made of titanium alloy and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an engine valve made of titanium alloy having abrasion resistance by padding-welding mixed powder in which pure Ti and/or titanium alloy powder is mixed with tungsten carbide and/or chromium carbide powder on a face surface and a shaft end part in order to form a MoS2 layer, etc., all over the surface except an umbrella part. CONSTITUTION:After an engine valve made of titanium alloy is monobloc formed by hot forging, mixed powder in which pure Ti within the grain size range from 60 to 250 mesh and in the shape of a polygon and/or titanium alloy powder are/is mixed with tungsten carbide and/or chromium carbide powder and if necessary, mixed powder which is mixed with pure metal powder is padding-welded on the face surface and the shaft end part of the above engine valve in order to form a padded part generated by crystallization and/or precipitation of titanium carbide on a beta titanium phase. After that, surface hardening treatment is given in order to form either one of a titanium nitride layer, a titanium carbide layer, a plated layer, a MoS2 layer or a titanium oxide layer all over the surface except an umbrella part. A valve manufactured by this method is remarkably excellent in abrasion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a titanium alloy engine valve having excellent wear resistance and a method for manufacturing the same.

(Conventional technology) In recent years, automobile manufacturers have been considering the use of titanium alloys in engine valve systems to reduce weight in order to increase engine power, but titanium alloys do not have sufficient wear resistance. isn't it. Therefore, it is necessary to apply anti-wear treatment to the sliding parts, and the areas that require anti-wear treatment for engine valves made of titanium alloy are the valve face,
These are the shaft part and the shaft end.

Therefore, the wear-resistant hardfacing treatment for titanium alloys is as follows: ■ Melting the surface layer of titanium and titanium alloy base material by high-energy irradiation, as described in JP-A No. 62-56561; A method of hardening the surface by mixing metal carbide powders such as TiC and 10, metal nitride powders such as TtN, and metal powders such as Fe, St, and Mo into this molten pool, ■ JP-A-61-231151 As described in the publication, metal oxide powders such as Ti1t, tic and II are applied to the surface of titanium and titanium alloy base materials.
Metal carbide powders such as c, metal nitride powders such as TiN, metal boride powders such as TiBz, and Fe,
After attaching metal powder such as AI to the surface, a high-energy beam is irradiated to the powder attachment part to fuse and integrate the titanium and titanium alloy base material and the attached powder on the base material surface. There is a method of hardening the surface portion, and these methods are being considered for use on the face surface and shaft end of titanium alloy engine valves.

Further, as wear-resistant treatments for the shaft portion, Mo spraying and carburizing treatment as disclosed in Japanese Patent Application Laid-open No. 61-291959 have been carried out for engine valves.

(Problem to be Solved by the Invention) However, even if the hardfacing of the face surface and shaft end of a titanium alloy engine valve is carried out by methods 0 and 0 described above, the powder used is metal oxide powder. In the case of metal carbide powder, metal nitride powder, and metal boride powder, the surface hardness of the base material increases to about 700-1000 in Vickers hardness (Hv), making it very hard.
On the contrary, it often becomes brittle and cracks occur in the cured part during use and during the curing process, or bubbles are generated during the curing process, making it impossible to form a sound cured part.

Furthermore, in wear resistance tests with current iron-based sheet materials, most of the hard powders showed insufficient improvement in wear resistance.

Further, when the powder was a metal powder, the surface hardness of the base material increased only by about Hv300 to 380, which was not sufficient in terms of improving wear resistance.

Next, when Mo spraying is used as a wear-resistant treatment for the shaft part, the cost is high and it is difficult to apply to mass-produced engine valves.Also, when Tic is generated on the surface layer by carburizing treatment, the surface layer becomes brittle. , fatigue strength may deteriorate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a titanium alloy engine valve and a method for manufacturing the same, which can solve the conventional problems as described above.

(Means for Solving the Problems) From the above-mentioned viewpoint, the present inventors have developed a titanium alloy engine valve face and shaft end that has excellent wear resistance and that does not cause cracks or bubbles during hardening treatment. As a result of various studies to form a hardfacing layer that does not cause defects or cracks during use, we have applied the well-known PTA method and TIG method to the face surface and shaft end surface of the valve. Furthermore, when forming a hardfacing layer using a laser beam method, an electron beam method, etc., known materials such as pure Ti, α-type Ti alloy, (α+β)-type Ti alloy, and β-type are used as the hardfacing powder. Ti alloy powder is made into a polygonal shape by, for example, a titanium hydride pulverization method without using an atomized method, and the particle size range is adjusted to 60 to 250 mesh.The Ti alloy powder is used as a base powder, and a mixed powder is prepared. Wear resistance is improved by making the overlay part have a structure in which titanium carbide is precipitated in the β-titanium phase. - When a mixture of one or more of tungsten carbide and chromium carbide is used, it improves the wettability to the base material and improves wear resistance. It has good melt penetration properties, and as a result, there are no defects such as cracks or bubbles during overlay processing, and of course there is no cracking during use, and the product is compatible with current sheet materials in terms of wear resistance. We have found that it is possible to form a face surface and a built-up portion on the shaft end of a valve that has properties at low cost.

Furthermore, as a wear-resistant treatment for the entire shaft part, it is sufficient to form a titanium carbonitride film or a plating phase, a Mo52 layer, and a titanium oxide layer by PVD or gas nitriding to provide wear resistance to the valve guide. It was found to be compatible.

The present invention has been made based on the above findings.

That is, the first aspect of the present invention is to apply tungsten carbide and/or pure Ti and/or titanium alloy powder, which has a particle size range of 60 to 250 mesh and has a polygonal shape, to the face surface of an integrally molded titanium alloy engine valve. Alternatively, a titanium alloy engine valve is obtained by overlaying a mixed powder of chromium carbide powder and, if necessary, pure metal powder, and depositing titanium carbide in the β titanium phase.

The second aspect of the present invention is that after integrally molding a titanium alloy engine valve by hot forging, pure Ti and/or titanium in a polygonal shape with a grain size ranging from 60 to 250 mesh is applied to the face surface of the engine valve. Overlay welding a mixed powder of alloy powder, tungsten carbide and/or chromium carbide powder, and pure metal powder as necessary, to form an overlay part in which titanium carbide is precipitated in the β titanium phase. This is a method for manufacturing a titanium alloy engine valve.

The third aspect of the present invention is that the titanium alloy engine valve of the first aspect has a titanium nitride layer, a titanium carbide layer, a plating layer, a MoS2 layer, a titanium oxide layer, etc. This is a titanium alloy engine valve formed with one of the following layers:

A fourth aspect of the present invention is to form a built-up portion made of titanium carbide precipitated in the β-titanium phase on the face surface of the engine valve according to the second aspect, and then apply titanium nitride to the entire surface except for the cap portion. This is a method for manufacturing a titanium alloy engine valve, the gist of which is to perform a surface hardening treatment to form any one of a titanium alloy layer, a titanium carbide layer, a plating layer, a MoS layer, and a titanium oxide layer.

Further, the fifth aspect of the present invention is to apply carbonized pure Ti and/or titanium alloy powder, which has a particle size in the range of 60 to 250 mesh and has a polygonal shape, to the face surface and shaft end of the integrally molded titanium alloy engine valve. Weld a mixed powder of tungsten and/or chromium carbide powder, and pure metal powder as necessary, to precipitate titanium carbide in the β-titanium phase, and then apply a titanium nitride layer to the entire surface except for the cap. This is a titanium alloy engine valve having one of a titanium carbide layer, a plating layer, a MoS2 layer, and a titanium oxide layer.

The sixth aspect of the present invention is to integrally mold a titanium alloy engine valve by hot forging, and then apply pure Ti having a grain size in the range of 60 to 250 mesh and a polygonal shape to the face surface and shaft end of the engine valve. and/or titanium alloy powder, tungsten carbide and/or chromium carbide powder, and if necessary pure metal powder mixed powder is overlaid welded, and titanium carbide is precipitated in the β titanium phase. is formed, and then surface hardening treatment is performed to form any one of a titanium nitride layer, a titanium carbide layer, a plating layer, a MoS layer, and a titanium oxide layer on the entire surface except for the umbrella portion. This is a method for manufacturing a titanium alloy engine valve.

(Function) Titanium alloys used for engine valves include (α+β) type Ti-based (7) Ti-6AI-4V alloy and Near α type Tt-based TiTi-6AI-2Sn-4.
Although there is Zr-2, the titanium alloy used in the present invention is not particularly specified as long as it is a Ti alloy with a strength of about 100 kg/mm''.

In the present invention, the Ti alloy is manufactured as a single piece by hot forging because this method is the cheapest. Then, the Ti alloy valve manufactured by this hot forging is subjected to cutting to remove scale and size, and hardfacing welding is performed.

1) Regarding the valve face surface and shaft end The reason for limiting the particle size range, shape, and type of mixed powder in the hardfacing powder of the present invention as described above will be explained.

(a) If there is a coarse powder that exceeds the particle size range and shape of 60 mesh, it may become undissolved in the hardfacing part, reducing the ability to fuse with the base material and preventing a healthy hardfacing layer. There may be cases where it becomes difficult to form.

On the other hand, if there is a fine powder with a mesh size of less than 250, the fluidity of the added powder decreases and clogging occurs in the powder supply equipment, making it impossible to smoothly supply the powder to the molten pool. Therefore, in the present invention, the particle size range of the titanium alloy powder is set to 60 to 250 mesh.

PREP uses polygonal titanium alloy powder.
Compared to spherical powders manufactured by methods such as tungsten carbide, chromium carbide, and pure metal powders, it has better solubility and dispersion homogenization in the molten pool during hardfacing, and is compatible with powders such as tungsten carbide, chromium carbide, and pure metal powders. This is because it has good uniform mixing properties and it is easy to obtain a uniform mixed powder. By the way, the main steps of the method for producing the above polygonal powder are as follows:
It is preferable to produce by a titanium hydride pulverization method consisting of Ti alloy ingot → hydrogenation → crushing → leaching, drying → sieving → hydrogenated Ti alloy powder → dehydrogenation → crushing → sieving → Ti alloy powder.

Note that the amount of oxygen contained in the titanium alloy powder is not particularly limited, but is preferably 0.2 to 0.5 wtχ. Oxygen has the function of improving wettability and melt penetration into the base material, improving hardness, and preventing plastic deformation during repeated collisions with the valve seat. Therefore, within this range, the hardness of the built-up portion will be approximately 370 to 550 Hv, thereby preventing plastic deformation upon collision with the valve seat.

Although it is preferable that the amount of oxygen contained in the titanium alloy powder is 0.2 to 0.5 wtχ, if it is less than this range, TiO□iO□ may be used to adjust the amount of oxygen contained.

To produce high-oxygen Ti alloy powder, it may be necessary to create a special high-oxygen Ti alloy ingot.
This is because the cost can be reduced by adjusting the amount of titanium oxide such as TiO□.

(b) Type of mixed powder Tungsten carbide and/or chromium carbide powder is used as the mixed powder.

The reason for using the above-mentioned mixed powder is to conduct overlay by mixing various hard powders and investigate the wear resistance of the overlay part to iron-based materials. This is because, for example, the wear resistance of the built-up part that was built up by mixing Cr3C1 was extremely good. lol,
C,, Cr5Cz partially or completely dissolves in the matrix, making the matrix β-phase Ti, and the dissolved C becomes T
It reacts with i to form TiC. It is considered that this β-phase Ti, undissolved WzCs Cr3C1, and Tic have wear resistance. In addition, with other hard powders, the matrix does not turn into the β phase, so it is considered that the wear resistance does not improve.

Pure metal powders such as Mo5Sn, Zr, and Ni, which are added as necessary, may be used to adjust the hardness.

The mixing ratio is not particularly limited, but for example, in the case of 14IC, it is 10wt% or more, and in the case of Cr3C, it is 3tnt%.
If the ratio is less than this, the desired anti-wear effect will be insufficient. The upper limit is 80-t% or less for W and C, Cr3
In the case of C2, it is 30wt% or less. If this ratio is exceeded, cracks will occur in the built-up portion or the toughness will deteriorate. Also-
Similar to the mixing ratio, the particle size of 2C, Cr3C, etc. is not particularly limited, but may be fine particles of, for example, 60 mesh or less.

Note that when tVtC mixed powder is used, undissolved particles h and c may remain in the built-up portion, but there is no particular problem with wear resistance. In addition, if the built-up part is aged in a temperature range of 350 to 550°C, the alpha titanium phase will precipitate, which will further improve the wear-resistant compatibility with the valve seat surface, etc., but this is not done due to cost considerations. do it.

Next, we will take measures to prevent wear of the entire shaft, but detailed wear-resistant treatments include treatments such as PVD and gas nitriding to generate titanium carbonitride, Cr plating, N1-P plating, and Mo5z coating. Baking and treatments that generate oxide scale are effective.

Although Cr plating and N1-P plating are difficult to adhere to Ti, it is possible to do so by using the method disclosed in, for example, Japanese Patent Application Laid-Open No. 110793/1983.

In addition, in order to generate oxide scale, 65
Processing is performed by heating at 0 to 750°C for 30 minutes and then cooling in air. In this case, titanium oxide has sufficient wear resistance.

After this, final finishing cutting (valve face, etc.) is performed to produce the valve product.

(Example 1) It was made into a polygonal shape by the titanium hydride crushing method, and
Prepare a Tj alloy powder adjusted to a particle size range of 0 to 200 mesh and each having the composition shown in Table 1 below, and TtO, powder, LC, and Cr5Ct powder each having a particle size range of 100 to 350 mesh, Using these powders, addi- tive powders ■ to ■ used in the present invention with the mixing ratios shown in Table 1 are prepared, and then, using these additive powders ■ to ■ used in the present invention, diameter 100mmX
On the surface of the base material made of a Tf alloy material with a composition of Ti-6A14v in the order of height 40, P
Plasma torch 1 using TA method or plasma torch method
Speed: 500m/min, current: 150A, voltage = 3
5■, plasma Ar gas amount: 3 J2 /min,
Shield Ar gas amount = 15! /mjn, powder supply amount from nozzle 2: 6cc/min, carrier Ar gas M
: Overlay welding was performed on the surface of the base material 3 under the conditions of 21 /min to form the overlay hardened layer 4.

The hardness of the Ti-6AI-4V base material at this time was Hv330.

For the purpose of comparison, conventional methods using the same plasma torch method and using only hard powder as additive powder ■～■
and the conventional method [phase] in which only oxygen is blown without using additive powder.Furthermore, in order to increase the hardness of the overlay part with Ti alloy powder, overlay ■ and @ using powder mixed only with TiO2, and other methods Overlay mixed with hard ceramic powder＠〜［
phase] was carried out.

Next, wear test pieces 5 with a diameter of 10 mm and a length of 40 mm were cut out from the base material 3 subjected to the surface hardening treatment and the base material 3 before these treatments, and the wear test pieces 5 were subjected to a wear test with their surfaces polished. Served.

In the wear test, as shown in a schematic perspective view in FIG. Using a pin-on-disk method that rotates the disk 7 while applying the force, load: 2 kg, sliding speed: 62.8 m/min, and sliding distance: 2.5 XIO' m.

The test was conducted under the following conditions: mating material: HT60 high-tensile steel, lubricant: none, and the weight loss of the wear test piece 5 after the test was measured. These measurement results are shown in Table 1 below.

Table 1 shows the hardness Hv of the hardened layer and also shows the observation results of the hardened layer.

As shown in Table 1, W2C and Cr are added powders.
The hardfacing layer formed using Ti alloy powder mixed with 3C2 powder (additional powders ■ to ■ used in the present invention) is made of Ti alloy powder.
As is clear from the hardness comparison with the alloy base material, the surface hardness has increased significantly.

Furthermore, the wear loss is extremely small, and the wear resistance is improved. Moreover, the hardened build-up layer is in good condition with no cracks or bubbles.

On the other hand, in the case of the hardened layer formed by the conventional method ■~[phase], although the hardness of the hardened layer increases in all cases, cracks and bubbles occur, making it impossible to put it to practical use. be.

Furthermore, in the overlay method (■@), the hardness of the hardened layer is high and no bubbles are generated, but no significant improvement in wear resistance is observed. Furthermore, as shown in overlay methods ① to ＠, it was found that simply mixing hard ceramics did not improve the wear resistance, but only WtC or CrzCz improved the wear resistance.

In addition, when the amount of oxygen in the Ti alloy powder is 0.2% or less, I/4. C
.

When Cr and C were not mixed, the hardness of the built-up portion was low, and it was observed that the sliding portion of the wear test piece was plastically deformed.

(Example 2) Ti-6A made into polygonal shape by titanium hydride crushing method
I-4V powder, 100-250 mesh CrzCz
10-t% of Ti-6Al-4V powder was mixed with 8% of Ti-6Al-4V powder.
250-350 for particle size range of 0-250 mesh
When a comparative additive powder was prepared with a mesh weight ratio of 15% and a particle size range of 80 to 350 mesh, which is outside the range of the present invention, using a PTA powder feeding device, a feeding test was conducted using a PTA powder feeding device. supply was not possible.

In this case, it is possible to supply powder with a flowability of preferably 150g or less in 35 seconds with a PTA powder feeder without variation when measured in accordance with JIS Z 2502, and the flowability of the comparative additive powder mentioned above was 150g for 45-55 seconds.

In addition, instead of the particle size range of 250 to 350 meshes mentioned above, a particle size range of 40 to 80 meshes is used, and the ratio of this to the particle size range of 80 to 250 meshes is set to 20%, and the particle size range is adjusted to the original size. When build-up welding was carried out under the same conditions as in the above-mentioned example except that a comparative additive powder prepared to have a mesh size of 40 to 250 mesh outside the invention range was used, undissolved powder was present in the hard build-up layer.

(Example 3) Except for making the shape spherical by the PREP method, the particles had a particle size range of 80 to 250 mesh within the scope of the present invention.
Comparison T with a composition of t-6AI-4V-0.4χ0□
Although 50tm tX of 6C powder having a particle size range of 60 to 250 mesh was mixed with the i alloy powder, a homogeneous mixed powder could not be obtained.

(Example 4) After forming an umbrella part by hot forging from a Ti-6AI-4V hot-rolled wire rod with a diameter of 1 tm, 40 wt% L was added to Ti-641-4V on the face surface of a machined engine valve.
111 L of meat was welded using PTA using a powder mixed with C and according to the conditions shown in Table 2 below.

The shaft end was also overlaid under the same conditions as in Table 2 except that the torch speed was changed to Ox/min.

Next, after finish cutting the face surface and shaft end,
PVD treatment under the conditions shown in the table; ■ gas nitriding treatment under the conditions shown in Table 4; and ■ flow order shown in Figure 3.
That is, after washing in a mixed acid of nitric acid and hydrogen fluoride (A), washing with water, surface treatment (B) under the conditions shown in Table 5 below, followed by electrolytic Ni plating (C) under the conditions shown in Table 6. Cr plating treatment by performing electrolytic Cr plating CD) under the conditions shown in Table 7;
In place of R plating, N1-P electroless plating is performed under the conditions shown in Table 8 below, and in addition, oxidation scale treatment (heating in the air) ), and also■ MoS, after application, 500
'CX MoS and baking were performed by heating for 3 hours.

Table 2 Table 5 Table 3 Table 6 Table 4 Table 4 The engine valves subjected to the above treatment were set in a valve train, and an engine test using gasoline fuel was conducted.

The test conditions were: engine speed 1000-5000r;
p, m, The test time was 200 hours, and the wear state of the face, shaft, and shaft end was observed after the test.

For comparison, engine tests were also conducted on engine valves manufactured only by PVD treatment without overlay.

All of the engine valves of the present invention manufactured by the method of the present invention showed good wear resistance with almost no wear on the face, shaft, and shaft end even after a 200-hour engine test. However, the face and shaft end were worn out and the engine stopped after 10 hours.

This revealed the excellent wear resistance of the present invention.

(Effects of the Invention) As mentioned above, the valve of the present invention manufactured by the method of the present invention has extremely excellent wear resistance, so it can be used as an engine valve for mass-produced cars that require no maintenance for a long time. can.

Furthermore, this hardfacing method can also be applied to sliding parts of other mechanical parts.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing the plasma torch method, FIG. 2 is a schematic perspective view showing the wear test mode, and FIG. 3 is a flow diagram of the Cr plating process used in the method of the present invention. (2) is a plasma torch, 2 is a nozzle, 3 is a base material, 4 is a hardened overlay layer, 5 is an abrasion test piece, 6 is a hardened part, and 7 is a disk. Figure 31 Figure 3 1999

Claims (6)

[Claims] (1) Pure Ti and/or titanium alloy powder with a particle size range of 60 to 250 mesh and polygonal shape, tungsten carbide and/or chromium carbide powder, and A titanium alloy engine valve characterized in that titanium carbide is precipitated in the β titanium phase by welding a mixed powder mixed with pure metal powder as necessary. (2) After integrally molding a titanium alloy engine valve by hot forging, 6
Pure Ti and/or titanium alloy powder with a particle size range of 0 to 250 mesh and polygonal shape is overlaid with a mixed powder made by mixing tungsten carbide and/or chromium carbide powder, and pure metal powder as necessary. A method for manufacturing a titanium alloy engine valve, which comprises forming a built-up portion in which titanium carbide is precipitated in a β-titanium phase. (3) Any one of a titanium nitride layer, a titanium carbide layer, a plating layer, a MoS_2 layer, and a titanium oxide layer is formed on the entire surface of the titanium alloy engine valve according to claim 1 except for the umbrella portion. A titanium alloy engine valve that is characterized by: (4) After forming a built-up part in which titanium carbide is precipitated in the β-titanium phase on the face surface of the engine valve by the method according to claim 2, a titanium nitride layer, a titanium nitride layer, and a titanium A method for manufacturing a titanium alloy engine valve, characterized by performing a surface hardening treatment to form any one of a carbide layer, a plating layer, a MoS_2 layer, and a titanium oxide layer. (5) Pure Ti and/or titanium alloy powder with a particle size range of 60 to 250 mesh and polygonal shape is applied to the face surface and shaft end of the integrally molded titanium alloy engine valve. A mixed powder of chromium powder and, if necessary, pure metal powder is welded overlay to precipitate titanium carbide in the β-titanium phase, and then a titanium nitride layer, a titanium carbide layer, and plating are applied to the entire surface except for the cap. An engine valve made of a titanium alloy, characterized in that any one of a layer, a MoS_2 layer, and a titanium oxide layer is formed. (6) After integrally molding a titanium alloy engine valve by hot forging, the face surface and shaft end of the engine valve are made of pure Ti and/or titanium in a polygonal shape with a grain size in the range of 60 to 250 mesh. A mixed powder made by mixing tungsten carbide and/or chromium carbide powder, and pure metal powder as necessary, is applied to the alloy powder by overlay welding to form a built-up part in which titanium carbide is precipitated in the β titanium phase, After that, a titanium nitride layer, a titanium carbide layer,
A method for manufacturing a titanium alloy engine valve, characterized by performing a surface hardening treatment to form any one of a plating layer, a MoS_2 layer, and a titanium oxide layer.