JPH06101063A - Manufacture of titanium alloy member - Google Patents

Abstract

PURPOSE:To provide a method to manufacture a member made of titanium or titanium alloy wherein shrinkage cavity within the cast body is diminished, the hardening treatment of the surface of the cast body can be executed, and the strength of the surface hardened layer is high. CONSTITUTION:This manufacturing method consists of the casting process to pour molten titanium or titanium alloy into a die and to form a cast body 1, the coating process to form coating layers 2, 3 composed of the coating material having the composition mainly consisting of the metallic element to form a compound with titanium on the surface of the cast body 1, and the HIP process to crush the shrinkage cavity existing within the cast body 1 by exerting the hot isostatic pressing of the cast body 1 where the coating layers 2, 3 are formed and to form the melting diffusion layer on the surface of the cast body 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has excellent strength by molding a cast body using titanium or a titanium alloy, eliminating shrinkage cavities inside the cast body, and hardening the surface of the cast body. The present invention relates to a manufacturing method for obtaining a molded article.

[0002]

2. Description of the Related Art In recent years, attempts have been actively made to reduce the weight of valve gears for automobile engines by molding them with titanium or titanium alloy. This kind of titanium (alloy)
The manufactured component is usually formed by a casting method in which a molten metal is poured into a mold, but it is unavoidable that shrinkage cavities are generated inside the cast body during the cooling process or the solidification process of the molten metal to reduce the strength. For this reason, a method such as hot isostatic pressing (hereinafter, abbreviated as HIP) of the obtained cast body to eliminate shrinkage cavities inside is adopted.

By the way, since some of the shrinkage cavities in the cast body are opened on the surface of the cast body, it is impossible to carry out the HIP treatment as it is. Further, since titanium (alloy) itself is not good in corrosion resistance and wear resistance, it is necessary to perform some kind of surface hardening treatment when it is used as the valve train component.

In order to satisfy these conditions, the following manufacturing method has hitherto been adopted. A cast body is formed by a casting method. The shrinkage cavities opening on the surface of the cast body are closed by encapsulating (canning) the cast body in a metal can or by spraying a metal such as Ti or a Ti alloy of the same material on the surface of the cast body. Since the sprayed layer is porous, it is necessary to increase the film thickness. HIP treatment is applied to the cast body. The metal can or sprayed layer is removed from the cast body after pressing. A surface hardening treatment is performed by a method such as forming a nitride layer on the surface of the cast body or depositing an alloy having high wear resistance.

[0005]

However, in the above-mentioned surface hardening method by nitriding, the very surface layer part of titanium (alloy) is used.
Only (for example, about several μm from the surface) can be cured, and wear resistance is insufficient as a valve train component for an automobile engine. In addition, the surface hardening method by depositing metal has a problem in that strength is uncertain because it is difficult to improve the bondability with the metal to be deposited due to the characteristics of titanium.

Further, in the above conventional manufacturing method, HIP is used.
Since the process and the surface hardening treatment process are separately provided, there are disadvantages that the number of the whole process is large and the productivity is low.

As a surface hardening method for titanium (alloy) materials other than the above, titanium (alloy) and metals such as Ni and Co or these metals are proposed as disclosed in Japanese Patent Laid-Open No. 50-28443. A method is also known in which, after coating the alloy, a gas nitriding treatment and a hardening treatment are performed. However, the thickness of the cured layer obtained by this method is as thin as several tens of μm, and it is difficult to obtain satisfactory strength.

The present invention has been made in view of the above circumstances and is capable of eliminating shrinkage cavities inside a cast body and hardening the surface of the cast body, and the surface hardened layer to be obtained has high strength, titanium or It is an object to provide a method for manufacturing a titanium alloy member.

[0009]

Next, the method for manufacturing a titanium or titanium alloy member according to the present invention will be specifically described in the order of steps.

(Casting Step) In the method of the present invention, first, a molten metal of titanium or a titanium alloy is poured into a mold to form a cast body. As the titanium alloy, Ti-6Al-
4V alloy, Ti-13V-11Cr-3Al alloy, Ti
Examples of the alloy include -5Al-2Cr-Fe alloy and Ti-5Al-3Mn alloy, but titanium alloys other than these may be used. The casting method adopted may be a vacuum casting method which has been conventionally used, and the conditions therefor may be the same as the conventional one.

(Coating step) Next, on the surface of the obtained cast body, a coating layer made of a coating material whose main composition is a metal element that forms an eutectic alloy or an intermetallic compound with titanium is formed. To do. As the metal element, Ni, Cr, F
e, Cu, Mo, W, Zr, V, Al, Co, C, B,
N etc. are mentioned. The coating material may further include a substance which forms a compound with titanium such as a carbide, a nitride or a boride. The following substances can be exemplified as specific coating materials.

(A) Ni-based metal: pure Ni, Ni-7C
r-3B-4Si-3Fe alloy, Ni-15Cr-3B
Alloy, Ni-25Cr alloy, Ni-0.5C-3Si-
10Cr-2.5Fe-2B-0.1Co alloy (trade name:
Colmonoy No. 4), Ni-0.65C-12Cr-4.
25Fe-4.0Si-2.5B alloy (trade name: Colmonoy No5), Ni-1.5C-27Cr-8W-1.6F
e-1.55B-0.5Co alloy (Colmonoy No84),
50Ni-32Mo-15Cr-3Si alloy, trade name:
Triballoy 700), BN which is Ni solder of JIS standard
i-2.

(B) Ti-based alloy (titanium brazing material) containing the above metal elements: Ti-48Zr-4Be, Ti-30
V-4Be, Ti-33Cr, Ti-13V-11Cr
-3Al, Cu-25Ti-25Zr. However, the present invention is not limited to the above substances (a) and (b),
Other substances can be used as long as they contain the metal element.

Ceramic particles may be dispersed in the coating material, in which case the abrasion resistance of the final product can be improved. Examples of usable ceramic particles include TiC,
Examples include WC, B ₄ C, CBN, TiN, Si ₃ N ₄ , sialon, and SiC, but are not limited thereto. Whiskers may be used as the ceramic particles, for example. The amount of ceramic particles added is 10
Approximately 50 vol% is suitable. If it is less than 10 vol%, the effect of addition is small, and if it is more than 50 vol%, the formation of the melt diffusion layer is hindered.

Means for forming the coating layer on the surface of the cast body include a method in which a foil made of the coating material is bonded onto the cast body by a method such as pressure bonding, adhesion or spot welding, and a powder of the coating material is heated. After applying a coating material mixed with a removable binder (for example, cellulosic) to the cast body, or after coating the cast body with the binder and sprinkling the coating material powder, the cast body is further coated with 200-300.
Examples include a method of removing the binder by heating to about ℃, a method of coating the coating material on the cast body by an electrolytic plating method or an electroless plating method, and the like.

According to these coating methods, a coating layer having a thickness of several mm can be easily formed. If the layer thickness that can be formed by one time is thin, it may be repeated several times. Also,
A coating method other than the above-mentioned coating method can be adopted as long as a coating layer having a similar thickness can be formed.

(HIP step) Next, the cast body having the coating layer formed thereon is subjected to HIP treatment to crush the shrinkage cavities present in the cast body and form a melt diffusion layer on the surface of the cast body. To do so, first, the cast body with the coating layer formed thereon was treated with 1 × 10 ⁻⁴ t
While degassing in a high vacuum below orr, seal in a heat-resistant container,
This container is set in the HIP device.

The HIP condition cannot be generally stated because it depends on the material of the cast body and the coating layer, but the heating temperature is
When the eutectic point temperature of the main component of the material forming the cast body and the main component of the coating material is T (° C), T-20 to T + 10
It is desirable to set in the range of 0 (° C). T-20
If the temperature is lower than ℃, the melt diffusion reaction will be insufficient, while at T + 100 ℃
If it is higher, the melt diffusion reaction proceeds too much, and in any case, a good melt diffusion layer cannot be formed. A specific example of the heating temperature during HIP is 8 when the material of the cast body is Ti.
Around 90 ℃, 1000 ℃ in the case of Ti-6Al-4V
The front and back are suitable.

The pressure during HIP varies depending on the material of the cast body and the degree of shrinkage cavity formation, but is 300 to 1000 kg.
It is preferably about f / cm ² , particularly 300 to 500 kgf / cm ² . If it is less than 300 kgf / cm ² , it is difficult to eliminate shrinkage cavities, and it is not necessary to make the pressure higher than 1000 kgf / cm ² .

As the pressurizing / heating method at the time of HIP, a method of simultaneously applying pressurizing and heating, a method of preceding pressurizing,
Although any method that precedes heating is possible, the method that precedes heating is particularly suitable for the present invention.

That is, by heating the cast body under the condition that a liquid phase is produced at the interface between the coating layer and the cast body while suppressing the pressing pressure to 10% or less of the required molding pressure in the initial stage of HIP (normal pressure may be used). After the liquid phase is filled in the shrinkage cavities opened on the surface of the cast body, the press pressure is increased to a predetermined molding pressure to crush the shrinkage cavities present in the cast body. In this way, if the method of heating first is adopted, the liquid phase is filled in the shrinkage cavities opening on the surface of the cast body to close the shrinkage cavities, and then the internal shrinkage cavities are crushed. Can be effectively performed. HI
If the pressing pressure at the initial stage of P is higher than 10% of the required molding pressure, the above effect cannot be obtained.

HIP processing for a predetermined time (tens of minutes to tens of hours)
By continuing, the elements forming the coating layer and the elements forming the cast body mutually diffuse, and a molten diffusion layer is formed after cooling.

For example, when a Ni-based alloy is used as the coating material, eutectic alloying of Ni and Ti occurs due to melt diffusion, and an intermetallic compound such as Ti ₂ Ni is produced.
The coating material is C, Si, B, N, Zr, Nb, Cr.
When an element such as the above is included, a binary or ternary eutectic alloy of these elements and Ti or an intermetallic compound is generated, and C is carbide, Si is silicide, B is boride, and N is N. Nitride, Zr, Nb, and Cr each generate an intermetallic compound and contribute to hardening. By these reactions, a melt diffusion layer having a hardness higher than that of the coating material is formed.

Incidentally, only the inner peripheral portion of the coating layer may be melt-diffused, or the entire coating layer may be melt-diffused. Further, although a liquid phase also appears in the melt diffusion layer due to heating, since the method of the present invention uses HIP to apply pressure,
There is no risk of shrinkage cavities in the process of transition of the liquid phase to the solid phase.

FIG. 1 is a photograph of a structure in which a cross section of a general example of a melt diffusion layer obtained by the method of the present invention is magnified 150 times. The melt diffusion layer is made of Ni-25Cr as a coating material.
It is formed by using an alloy and Ti as a cast body, and is composed of an erosion layer and a hardened layer. The hardened layer is formed of a surface layer and a mixed layer, and the eroded layer is formed of a joining layer and a number of anchor portions, respectively. Has been done. The surface layer side of the anchor portion is integrally continuous with the bonding layer, the bonding layer is integrally continuous with the mixed layer, and the mixed layer is continuously continuous with the surface layer.

More specifically, the surface layer is made of Ti ₂
It is a layer in which an intermetallic compound having a composition of Ni is deposited and hardened. The mixed layer and the bonding layer are made of Ti, Ni and Cr, respectively.
And the mixed layer contains a precipitate containing more Ni and Cr than the bonding layer. The anchor portion is formed by biting into the surface of a titanium material in a columnar shape, and contains Ti as a main component, and a small amount of Ni and a small amount of Cr.
Is included.

The reason why the anchor part is generated is considered as follows. When Ni in the coating material and Ti in the cast form a binary alloy, the melting temperature drops, so that a melting zone is formed at the interface between the titanium material and the coating material. Then, at the boundary between the melting zone and the titanium material, a part (nucleus) in which the melting point is partially lowered is formed in an island shape, and the titanium material begins to melt selectively from these nuclei in the depth direction of the titanium material. The part spreads in a column. Then, these molten portions remain as columnar anchor portions during cooling.

According to the structure as shown in FIG. 1, since the hard intermetallic compound having the composition of Ti ₂ Ni is formed over the entire area of the melt diffusion layer, the hardness of the whole is increased. In particular,
A large amount of Ti ₂ Ni intermetallic compound is generated in the surface layer, and the hardness becomes maximum. It is considered that this is because the Ti content and the Ni content are about 2: 1 in the surface portion of the melt diffusion layer. Further, since the anchor portion digs into the titanium material, due to the anchor effect, the joining force between the titanium material and the melt diffusion layer is particularly high, and the cured portion does not peel off even if some plastic working is applied. Further, since the melt diffusion layer has a sufficient thickness of a fraction of a few mm to a few mm, cutting and plastic working are also possible.

[0029]

EXAMPLES Next, the effects of the present invention will be demonstrated with reference to examples. Using Ti-6Al-4V alloy as a raw material, an automobile engine valve 1 as shown in FIG. 2 was produced by a vacuum casting method. Casting temperature is 1800 ℃, vacuum degree during casting is 8
It was set to × 10 ^-4 torr. The size of the cast body 1 is 10
0 mm, outer diameter of valve stem 1B is 8 mm, outer diameter of valve body 1A is 3
It is 1 mm. The density ratio immediately after casting was 99.9%.

As shown in FIG. 2, coating layers 2 and 3 made of a coating material were formed on the outer peripheral surface of the valve rod portion 1B and the outer peripheral upper edge of the valve body portion 1A, respectively. As the coating material, Cu-
A powder of 25Ti-25Zr (particle size # 5000) was used. As the method for forming the coating layer, first, methylcellulose was sprayed as a binder on the above-mentioned site of the cast body 1, and the coating material powder was sprinkled on the coated surface. Application of binder,
The application of the coating material powder was repeated three times. Furthermore, the casting was vacuum heated to 250 ° C. to remove the binder, and the coating amount was 0.08 g / cm ² (0.01 m as a dense coating thickness.
(corresponding to m) was formed.

Next, the cast body 1 having the coating layers 2 and 3 formed thereon.
Was sealed in a container made of SUS304 in a vacuum of 1 × 10 ⁻⁵ torr and applied to a HIP device. The HIP conditions were such that heating was preceded in order to make the packed container sufficiently soft, and heating was performed at 950 ° C. and pressure was maintained for 1 hour.

The density ratio of the obtained molded product was 100%. The surface hardness of the melt diffusion layer was Hv680, whereas the hardness of the exposed surface of the substrate was Hv270, and the melt diffusion layer showed high hardness. Cross-sectional photographs of the melt diffusion layer at the upper end of the valve stem portion 1B are shown in FIG. 3 (× 500) and FIG.
5 (× 500) and FIG. 6 (× 10) are cross-sectional photographs of the melt diffusion layer in the central portion of the valve stem portion 1B.
00).

As is clear from each photograph, the structure was the same as that described with reference to FIG. 1 at all the sites, and the melt diffusion layer exhibited high bonding strength. The thickness of the melt diffusion layer is 0.136 mm at the upper end and 0.119 mm at the center.
It was mm.

Although the present invention has been applied to the manufacture of engine valves in the above embodiments, the present invention is not limited to this, and other members requiring wear resistance, such as valves, are used. It is also applicable to retainers, transmission gears, differential gears, disc brakes, rocker arms, bearings, sliding parts of various pumps, turbine blades, blade edges of ice skates, golf club heads, and the like.

[0035]

In the method for producing a titanium or titanium alloy member according to the present invention, the melt diffusion layer is formed on the surface of the casting by forming the coating layer on the surface of the casting and performing HIP. The melt diffusion layer formed by this method includes a large number of anchor portions that bite into the bulk region of the cast body, a joining layer formed on the bulk region continuously to these anchor portions, and formed on the joining layer. Since it has a hardened hardened layer, the surface hardness of the product is significantly improved by this melt diffusion layer, and the bonding strength of the melt diffusion layer to the cast body is high. Therefore, the strength of the product can be significantly improved as compared with the case where the cast body is simply HIP-treated.

Further, by forming the coating layer on the surface of the cast body, the coating material reacts with the surface of the cast body at the same time as HIP, and a hard and dense melt diffusion layer is formed. It is not necessary to provide it separately and productivity can be improved.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing an example of a melt diffusion layer obtained by a method for producing a titanium or titanium alloy member according to the present invention.

FIG. 2 is a front view showing a state in which a coating layer is formed on an engine valve as an embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional photograph of a molten diffusion layer of the engine valve.

FIG. 4 is an enlarged photograph of a cross section of a molten diffusion layer of the engine valve.

FIG. 5 is an enlarged cross-sectional photograph of a molten diffusion layer of the engine valve.

FIG. 6 is an enlarged cross-sectional photograph of a molten diffusion layer of the engine valve.

[Explanation of symbols]

 1 Engine valve (cast body) 2,3 Coating layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroo Ozeki 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Materials Corporation Mechatronics & Production System Development Center (72) Satoshi Kano 1 Kitabukuro-cho, Omiya-shi, Saitama 297-chome Mitsubishi Materials Corporation Mechatronics / Production System Development Center

Claims (11)

[Claims] 1. A casting process in which a molten metal of titanium or a titanium alloy is poured into a mold to form a cast body, and a metal element which forms a compound with titanium on the surface of the cast body is a main composition. A coating step of forming a coating layer made of a coating material, and by hot isostatic pressing of the cast body on which the coating layer is formed, the shrinkage cavities present in the cast body are crushed, and melt diffusion occurs on the surface of the cast body. A HIP step of forming a layer,
A method of manufacturing a titanium or titanium alloy member, comprising: 2. The metal element forming a compound with titanium is Ni, Cr, Fe, Cu, Mo, W, Zr,
1 or 2 selected from V, Al, Co, C, B, N
The method for producing a titanium or titanium alloy member according to claim 1, wherein the above metal elements are used. 3. The method for producing a titanium or titanium alloy member according to claim 1, wherein the coating material is a Ni—Cr alloy. 4. The method for producing a titanium or titanium alloy member according to claim 1, wherein the coating material is a Ti-based alloy. 5. The method for producing a titanium or titanium alloy member according to claim 1, 2, 3 or 4, wherein the coating material contains ceramic particles. 6. The titanium according to claim 1, wherein the coating layer is formed by fixing a foil made of the coating material on the surface of the casting during the coating step. Alternatively, a method for manufacturing a titanium alloy member. 7. In the coating step, the powder of the coating material is fixed on the surface of the cast body through a binder that can be removed by heating, and then the cast body is heated to remove the binder, thereby coating the coating material. A method for producing a titanium or titanium alloy member according to claim 1, 2, 3, 4 or 5, wherein a coating layer made of is formed. 8. The titanium or titanium alloy according to claim 1, 2, 3, 4 or 5, wherein in the coating step, the coating material is plated on the surface of the cast body to form a coating layer. Method of manufacturing member. 9. In the HIP step, in the initial stage, the cast body is heated under the condition that a liquid phase is generated at the interface between the coating layer and the cast body while suppressing the pressing pressure to 10% or less of the required molding pressure. By filling the liquid phase in the shrinkage cavity opening on the surface of the cast body, the press pressure is increased to a predetermined molding pressure to crush the shrinkage cavity existing in the cast body and melt the melt on the surface of the cast body. 9. A diffusion layer is formed to form a diffusion layer.
A method for producing the titanium or titanium alloy member as described above. 10. The heating temperature in the HIP step is T-30 to T + 100, where T (° C.) is the eutectic point temperature of the main component of the material forming the casting and the main component of the coating material.
The temperature is set in the range of (° C).
2. A method for producing a titanium or titanium alloy member according to 2, 3, 4, 5, 6, 7, 8 or 9. 11. The pressing pressure in the HIP process is
It is set in the range of 300 to 1000 kgf / cm ² , and it is set in the range of 1, 2, 3, 4, 5, 6, 7, 8,
9. The method for producing a titanium or titanium alloy member according to 9 or 10.