JPH05171218A - Production of sintered titanium alloy member having hollow part - Google Patents

Abstract

PURPOSE:To improve the dimensional accuracy of a sintered titanium alloy member having a hollow part. CONSTITUTION:A large round bar-shaped jig 21 and a small round bar-shaped jig 22 are inserted respectively into hollow large-journal parts 11 and hollow small-journal parts 12 of a green compact molding 1. These jigs 21, 22 consist of a material having the higher coefft. of linear expansion than the coefft. of linear expansion of a titanium alloy and is hardly reactable with the titanium alloy at a sintering temp. The inside surfaces of the large-journal parts 11 and small-journal parts 12 are adhered to the outside surfaces of the jigs 21, 22 by the linear expansion of the jigs 21, 22 and the shrinkage of the green compact molding 1, by which the inside surface shapes of the large-journal parts 11 and small-journal parts 12 are corrected along the outside surface shapes of the jigs. Clearances are made between the jigs 21, 22 and the respective journal parts 11, 12 by a difference in the coefft. of linear expansion after cooling down to room temp., by which the jigs 21, 22 are easily removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered titanium alloy member having a hollow portion.

[0002]

2. Description of the Related Art Titanium alloy has a low specific gravity and also has higher specific strength and specific toughness as compared with high strength materials such as super strong steel and high strength aluminum alloy. For this reason, titanium alloys are widely used for structural parts in which weight reduction and high strength are essential, such as structural parts for aircraft, space equipment, racing cars, and the like.

This titanium alloy has a high material cost and has a poor material yield because of its difficult workability. For these reasons, it has been difficult to apply titanium alloys to parts for mass-produced vehicles, but recent advances in powder metallurgy technology, specifically improvement of sintering technology, CIP molding, and HIP The above problems are being solved by the practical application of new molding techniques such as processing.

The powder metallurgy method is roughly classified into an alloy powder method and an elemental powder mixing method.
This is a method of directly solidifying by IP treatment or the like, and the latter is a method of mixing pure titanium powder and strengthening mother alloy powder, molding and sintering. Comparing the two, the raw powder mixing method is extremely low in both raw material powder and manufacturing process,
A significant cost reduction can be expected.

[0005]

When a sintered titanium alloy member is manufactured by the above-mentioned raw powder mixing method, when a green compact molded from raw material powder is sintered, it is accompanied by densification due to sintering. Dimensional shrinkage of about 10% occurs. Further, since the sintering is usually performed at a high temperature of about 1300 ° C., the powder compact tends to warp due to its own weight. Particularly, a member having a hollow portion is likely to be deformed in shape during sintering. In addition, when manufacturing connecting rods made of titanium alloy,
It is necessary to precisely process the inner surface shape and inner diameter of the hollow portion. For this reason, it is indispensable to improve the dimensional accuracy of the hollow portion by machining after sintering, and the cost is increased.

The present invention has been made in view of the above circumstances, and when manufacturing a sintered titanium alloy member having a hollow portion by an elementary powder mixing method, the dimensional accuracy of the hollow portion is improved in the as-sintered state. An object of the present invention is to provide a sintering method that can be performed.

[0007]

A method for producing a sintered titanium alloy member having a hollow portion according to the present invention has an outer surface shape smaller than an inner surface shape of the hollow portion of a titanium alloy powder compact having a hollow portion. And a step of inserting a jig made of a material having a linear expansion coefficient larger than that of the titanium alloy and at least the outer surface of which is difficult to react with the titanium alloy at the sintering temperature into the hollow portion of the powder compact. The powder compact formed by inserting a jig into the hollow is heated to a sintering temperature, and the inner surface of the hollow of the compact is closely adhered to the outer surface of the jig. And a step of cooling the jig and the sintered body and withdrawing the jig from the hollow portion of the sintered body.

[0008]

According to the method for producing a sintered titanium alloy member having a hollow portion of the present invention, a jig having an outer surface shape smaller than the inner surface shape of the hollow portion is inserted into the hollow portion of the powder compact, and these are predetermined. It is performed by heating and holding at the sintering temperature. As schematically illustrated in FIG. 4, the relationship between the inner diameter of the hollow portion and the outer shape of the jig before and after sintering, both the green compact and the jig are thermally expanded during the heating process of heating to the sintering temperature. .. During the sintering process in which the powder compact is held at the sintering temperature for a predetermined time, the powder compact shrinks, and the hollow part of the powder compact also shrinks. Therefore, during the sintering, the inner surface of the hollow portion comes into close contact with the outer surface of the jig, and the inner surface shape of the hollow portion is corrected along the outer surface shape of the jig. Further, since the outer surface of the jig is made of a material that does not easily react with the titanium alloy at the sintering temperature, even a highly active titanium alloy does not have the disadvantage of reacting with the jig during the sintering. In this way, the shrinkage due to sintering of the powder compact can be used to correct the inner surface shape of the hollow part with the outer surface shape of the jig while sintering the powder compact, so that the dimensional accuracy of the inner surface of the hollow part can be improved. It is possible to improve.

In the cooling process of cooling from the sintering temperature to room temperature after the above-mentioned sintering, both the sintered body and the jig thermally contract, but the jig is made of a material having a larger linear expansion coefficient than the titanium alloy. Therefore, it shrinks more than the sintered body made of titanium alloy. As a result, a gap is formed between the inner surface of the hollow portion of the sintered body and the outer surface of the jig, and the jig can be easily extracted from the hollow portion.

[0010]

EXAMPLES Examples in which the present invention is applied to the production of a titanium alloy connecting rod will be described below. (Example 1) Pure titanium powder (-100 mesh, average particle size 70 µm) and Al-40V alloy powder (-100 mesh, average particle size 1) with Ti-6Al-4V as the target composition.
0 μm). A plurality of connecting rod-shaped powder compacts 1 were molded from this mixture by CIP molding at a pressure of 4 ton / cm ² . The green compact 1 has a hollow large journal portion 11 and a hollow large journal portion 12 at both ends thereof. The green compact 1 is generally larger than the actual part size of the connecting rod in consideration of shrinkage due to sintering.

A large round bar jig 21 having an outer diameter slightly smaller than the actual part size of the inner diameter of the large journal part of the connecting rod, and a small round bar jig 22 having an outer diameter slightly smaller than the actual part size of the inner diameter of the small journal part. Prepared.
The large round bar jig 21 and the small round bar jig 22 are made of zirconia (ZrO ₂ , linear expansion coefficient: about 10.5 × 10 ⁻⁶ / ° C.).
It has a larger linear expansion coefficient than titanium alloy (Ti-6Al-4V alloy, linear expansion coefficient: about 9 × 10 ⁻⁶ / ° C.),
Moreover, it is difficult to react with the titanium alloy even at high temperatures (1200 to 1300 ° C.).

The large round bar jig 21 and the small round bar jig 22 are connected to the large journal portion 11 and the small journal portion 12 of the powder compact 1.
Inserted into each. Since the green compact 1 is formed larger than the actual part size as described above, the space between the large journal portion 11 and the large round bar jig 21 and between the small journal portion 12 and the small round bar jig 22 is increased. There are gaps between them.

In order to maintain the large round bar jig 21 and the small round bar jig 22 in parallel and to set the axial distance to a predetermined value, a pair of both ends of the large round bar jig 21 inserted into the large journal portion 11 is formed. While being horizontally fixed to the lower part of the holding table 3, the both ends of the small round rod-shaped jig 22 inserted into the small journal portion 12 were horizontally mounted above the pair of holding tables 3. In addition, through holes 31 are formed in the lower portions of the pair of holding bases 3 at the same height position.
Both ends of the large round bar-shaped jig 21 are inserted and fitted in 1. Further, the U-shaped grooves 32 having the same depth are provided on the upper portions of the pair of holding bases 3, respectively.
Is formed in the U-shaped groove 32.
Two end portions of 2 are arranged. At this time, the small round bar jig 22 and the bottom of the U-shaped groove 32 are not in contact with each other. That is, the depth of the U-shaped groove 32 depends on the size of the large round bar-shaped jig 21 and the small round bar-shaped jig 22 when the small round bar-shaped jig 22 is supported on the bottom of the U-shaped groove 32 due to the contraction of the powder compact 1. Is set to be equal to the actual part dimension of the distance between the axes of the connecting rods. Therefore, since the powder compact 1 is formed larger than the actual part size as described above, the small round bar jig 22 and the bottom of the U-shaped groove 32 are not in contact with each other.

The thus set product was inserted into a vacuum furnace and vacuum-sintered for 4 hours under the conditions of 10 ^-5 torr and 1300 ° C. Since the green compact 1 shrinks during this sintering process, the inner peripheral surfaces of the large journal portion 11 and the small journal portion 12 are in close contact with the outer peripheral surfaces of the large round bar jig 21 and the small round bar jig 22, respectively. , Each journal section 11, 1
A roundness of 2 is corrected.

After the completion of sintering, when cooled to room temperature, the axial distance between the large journal portion 11 and the small journal portion 12 is shortened due to the contraction of the powder compact 1, and it is laid horizontally above the pair of holding bases 3. The small round bar jig 22 thus abutted and held on the bottom of the U-shaped groove 31. That is, the large journal portion 11 and the small journal portion are held by the large round rod-shaped jig 21 and the small round rod-shaped jig 22 which are held in parallel by the pair of holding bases 3 with a distance equal to the actual part dimension of the axial distance of the connecting rod. It was possible to sinter by correcting the axial distance and parallelism of the part 12 correctly. Further, depending on the difference in linear expansion coefficient between the titanium alloy and zirconia, there are gaps between the large journal portion 11 and the large round bar jig 21, and between the small journal portion 12 and the small round bar jig 22, respectively. The large round bar-shaped jig 21 and the small round bar-shaped jig 22 could be easily removed. The roundnesses of the large journal section 11 and the small journal section 12 were also extremely good. (Embodiment 2) In Embodiment 2, the flatness and parallelism of both end surfaces (thrust surfaces) of the large journal portion 11 and the small journal portion 12 of the connecting rod are improved.

As in Example 1, pure titanium powder and A
From a mixture with 1-40V alloy powder by CIP molding,
A plurality of connecting rod-shaped powder compacts 1 each having a hollow large journal portion 11 and a hollow large journal portion 12 at both ends thereof were formed. As shown in FIGS. 2 and 3,
Zirconia spacer 4 and large round bar jig 2
1. A small round bar jig 22 was prepared. The outer diameter of the large round bar jig 21 is set to be slightly smaller than the actual part size of the inner diameter of the large journal portion of the connecting rod, and the outer diameter of the small round bar jig 22 is set to be slightly smaller than the actual part size of the inner diameter of the small journal portion. ..

The spacer 4 includes a lower spacer portion 41 having a ring-shaped protrusion 41a corresponding to the end face of the large journal portion 11, a central recess 41b and a guide hole 41c, and a ring-shaped protrusion corresponding to the end face of the lower journal portion 12. The upper spacer portion 42 has a portion 42a, a central recess 42b, and a guide rod 42c. The guide rod 42b of the upper spacer portion 42 is slidably held in the guide hole 41b of the lower spacer portion 41. When the upper end surface 41d of the lower spacer portion 41 abuts on the lower end surface 42d of the upper spacer portion 42, the large round bar jig 21 held in the central recess 41b.
And the distance between the small round bar jig 22 held in the central recess 42b is set to be equal to the actual part dimension of the axial distance of the connecting rod. Further, the inner diameter of the central recess 41b of the lower spacer portion 41 is substantially equal to the outer diameter of the large round bar jig 21, and the central recess 42 of the upper spacer portion 42 is formed.
The inner diameter of b is set to be substantially equal to the outer diameter of the small round bar jig 22.

The large round bar-shaped jig 21 and the small round bar-shaped jig 22 are attached to the large journal portion 11 and the small journal portion 12 of the powder compact 1.
Inserted into each. Since the green compact 1 is formed larger than the actual part size as described above, the space between the large journal portion 11 and the large round bar jig 21 and between the small journal portion 12 and the small round bar jig 22 is increased. There are gaps between them.

Then, both ends of the large round rod-shaped jig 21 inserted into the large journal portion 11 are inserted into the central concave portions 41b of the adjacent lower spacer portions 41, and both ends of the small round rod-shaped jig 22 inserted into the small journal portion 12 are inserted. It was inserted into the central recess 42b of each adjacent upper spacer portion 42. In this way, the three green compacts 1 were set so as to be sandwiched by the four spacers 4, respectively. At this time, between both ends of the large round bar jig 21 and the bottom of the central recess 41b of each lower spacer section 41, and between both ends of the small round bar jig 22 and the bottom of the central recess 42b of each upper spacer section 42. There are gaps in each.

The thus set product was inserted into a vacuum furnace, and vacuum sintering was carried out for 4 hours under conditions of 10 ^-5 torr and 1300 ° C. while applying a load of 1 kg from the spacers 4 on both outer sides. In this sintering process, the green compact 1
Contract, the inner peripheral surfaces of the large journal portion 11 and the small journal portion 12 are in close contact with the outer peripheral surfaces of the large round rod-shaped jig 21 and the small round rod-shaped jig 22, respectively.
The roundness of is corrected. Further, both end surfaces of the large journal portion 11 and the small journal portion 12 are respectively attached to the lower spacer portion 4
The ring-shaped protrusion 41a of No. 1 and the ring-shaped protrusion 42a of the upper spacer 42 are brought into close contact with each other, and their parallelism and flatness are corrected. At this time, the amount of compression of the large journal portion 11 between the ring-shaped protrusions 41a is regulated by contacting both ends of the large round bar jig 21 with the bottoms of the ring-shaped protrusions 41a. In addition, the compression amount of the small journal portion 12 between the ring-shaped protrusions 42a is also the same as that of the small round bar jig 2.
Both ends of 2 are regulated by abutting on the bottom of each ring-shaped protrusion 42a.

After the sintering, when cooled to room temperature, the axial distance between the large journal portion 11 and the small journal portion 12 is contracted due to the shrinkage of the powder compact 1, and the upper spacer portion 42 slides downwards. The lower end surface 42d of the slide portion 42 was held in contact with the upper end surface 41d of the lower slide portion 41. That is, the large journal portion 11 and the small journal portion are held by the large round rod-shaped jig 21 and the small round rod-shaped jig 22 which are held in parallel with the spacers 4 adjacent to each other with a distance equal to the actual part dimension of the axial distance of the connecting rod. It was possible to correct the inter-axis distance and parallelism of 12 correctly and sinter. Also,
Depending on the difference in linear expansion coefficient between titanium alloy and zirconia,
There are gaps between the large journal portion 11 and the large round rod jig 21, and between the small journal portion 12 and the small round rod jig 22, respectively. It could be pulled out easily. The roundnesses of the large journal section 11 and the small journal section 12 were also extremely good. Furthermore, the flatness and parallelism of both end surfaces of the large journal portion 11 and the small journal portion 12 were also extremely good.

In the first and second embodiments, the large round bar-shaped
As the tool 21 and the small round bar jig 22, those made of zirconia
Was used, the coefficient of linear expansion was larger than that of titanium alloy, and
CaO, a material that does not easily react with titanium alloys at the sintering temperature
(Coefficient of linear expansion: about 13 × 10 ^-6/ ° C), MgO (linear expansion
Coefficient: About 13.5 × 10^-6/ ° C) etc.
You may stay. In addition, as the above jig, stainless steel etc.
It is made of a material with a larger linear expansion coefficient than titanium alloy.
Only the outer surface of ZrO₂At the sintering temperature such as
Use a material that is hard to react with gold
You can also

In the first and second embodiments described above, an example of the hollow portion formed by the through hole like the journal portion of the connecting rod is shown, but the shape of the hollow portion is not limited to this, and is, for example, hemispherical. It may be a hollow portion formed by a recessed portion that is hollowed.

[0024]

As described in detail above, the method for producing a sintered titanium alloy member having a hollow portion according to the present invention is made of a material having a linear expansion coefficient larger than that of a titanium alloy, and at least the outer surface of the material has a sintering temperature at a sintering temperature. By performing the sintering with the jig made of a material that does not easily react with the titanium alloy inserted in the hollow part, the inner surface of the hollow part is corrected with the outer surface of the jig and then the sintering is performed. From this, the jig can be easily removed, and the dimensional accuracy of the inner peripheral surface of the hollow portion can be improved. Therefore, it is not necessary to perform machining after sintering to improve the dimensional accuracy, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a method for manufacturing a sintered titanium alloy having a hollow portion according to a first embodiment.

FIG. 2 is a cross-sectional view illustrating a method of manufacturing a sintered titanium alloy having a hollow portion according to a second embodiment.

FIG. 3 is a front view of a spacer used in Example 2.

FIG. 4 is a diagram schematically illustrating a relationship between an inner diameter of a hollow portion and an outer shape of a jig before and after sintering.

[Explanation of symbols]

Reference numeral 1 is a powder compact, 11 is a large journal portion, 12 is a small journal portion, 21 is a large round bar jig, and 22 is a small round bar jig.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Taku Saito Nagakute-cho, Aichi-gun, Aichi Prefecture 1-41 Yokomichi, Yokochi Central Research Institute Co., Ltd. (72) Inventor Tadahiko Furuta, Nagakute-cho, Aichi-gun 41, Yokoyokomichi Toyota Central Research Institute Co., Ltd.

Claims (1)

[Claims] 1. A titanium alloy powder compact having a hollow portion is made of a material having an outer surface shape smaller than the inner surface shape of the hollow portion and having a linear expansion coefficient larger than that of the titanium alloy, and at least the outer surface thereof is burnt. A step of inserting a jig made of a material that does not easily react with the titanium alloy at the binding temperature into the hollow part of the powder compact, and heating the powder compact with the jig inserted into the hollow part to the sintering temperature. Then, while the inner surface of the hollow portion of the powder compact is closely attached to the outer surface of the jig, the step of sintering the powder compact to obtain a sintered body, and the jig and the sintered body A method for producing a sintered titanium alloy member having a hollow portion, which comprises cooling and removing the jig from the hollow portion of the sintered body.