JP3113144B2 - Method for producing high density sintered titanium alloy - Google Patents

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 by a powder metallurgy method, and more particularly, to a method of using a raw titanium powder and a powder for adding an alloy element as raw material powders. The present invention relates to the production of a sintered titanium alloy by a method.

[0002]

2. Description of the Related Art Titanium and titanium alloys have excellent corrosion resistance and are lightweight and high-strength, and have been widely used mainly in the chemical industry, space and aircraft industries where these characteristics are strongly required. However, this material is expensive, and its workability and machinability in hot and cold are extremely poor. Therefore, the total cost including the processing cost up to the final product is extremely high, and automobile Active application to consumer goods, including the first, has been avoided.

[0003] Various applications of powder metallurgy which do not necessarily require hot and cold working or cutting work have been studied. In particular, the "raw powder unmixing method" in which titanium powder and alloy element addition powder are mixed, compacted, and sintered at 1000 to 1350 ° C. for 1 hour or more under vacuum or an inert atmosphere, Since the soft and good-formability titanium powder occupies the majority, products with a shape closer to the final shape can be directly manufactured, and since alloying is performed at the same time as sintering, the manufacturing cost is relatively low. Has the advantage of becoming

In the unmixed powder method, inexpensive "Hunter sponge fine", which is produced as a by-product when titanium is produced by a sodium reduction method called "Hunter method", has been frequently used. Then, there are almost no manufacturers producing titanium by the Hunter method, and the Hunter method sponge fine can no longer be used as a raw material powder.

As one of the alternative titanium powders, there can be mentioned hydrodehydrogenated titanium powders. This hydrodehydrogenated powder is a powder obtained by absorbing hydrogen into a smelted titanium material to form brittle titanium hydride, pulverizing the powder into powder, and finally performing dehydrogenation annealing in a vacuum or an inert atmosphere. It is. However, this hydrodehydrogenated titanium powder is almost twice as expensive as the Hunter sponge fine, and has the disadvantage of increasing the production cost of the final sintered titanium alloy product. In particular, in the step of dehydrogenating the pulverized titanium hydride powder, in order to dehydrogenate to a hydrogen concentration of 0.01% by weight or less, it depends on the degree of vacuum and the evacuation capacity, but at 600 to 800 ° C. for several tens of hours. Dehydrogenation annealing is necessary, and at this time, the powder that has been pulverized is pseudo-sintered and a powder of a desired particle size cannot be obtained, or the powder adheres to a container in which the powder is inserted, and the yield is significantly reduced. However, these have resulted in a significant increase in the price of hydrodehydrogenated titanium powder.

[0006] In addition, the dehydrogenation is insufficient and 0.01%
If more than 1% by weight of hydrogen remains, the dehydrogenation time is shortened according to the residual hydrogen concentration, and pseudo-sintering of the powder and adhesion to the vessel are reduced, but this powder is mixed with the powder for alloying element addition. Then, filling in a container, compacting, and sintering in a vacuum or inert atmosphere, the hydrogen gas discharged into the gap between the powders prevents the gap from shrinking due to the pressure, so that high-density sintering is performed. There was a drawback that the body could not be obtained.
The sintered body having the insufficient density can be densified by subsequently performing HIP (Hot Isostatic Pressing) treatment. However, since the production cost is greatly increased, the cost associated with shortening the dehydrogenation annealing time is required. There was a drawback that the reduction fee would be canceled.

[0007]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and it is an object of the present invention to provide a method for unmixing raw powder using hydrodehydrogenated titanium powder, which comprises a total production from titanium powder production to sintering. It is an object of the present invention to provide a method for producing a sintered titanium alloy having a lower cost and a higher density than before.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies on the compacting behavior and sintering behavior of titanium powder containing a high concentration of hydrogen and the dehydrogenation behavior of the compacted body. Using a titanium powder having a specific hydrogen concentration as a raw material titanium powder, and further adding a step of heating and holding for a specific time in a specific temperature range in the middle of heating to a sintering temperature, the raw powder using the hydrodehydrogenated titanium powder In the unmixed method, it has been found that it is possible to produce a high-density sintered titanium alloy at a lower production cost than before.

That is, according to the present invention, in a raw powder unmixing method using a titanium powder produced by a hydrodehydrogenation method, a titanium powder containing hydrogen at a concentration of 0.02% by weight or more and less than 2% by weight is alloyed. After mixing with the powder for element addition, filling into a container and compacting, heating and holding in a vacuum or an inert gas atmosphere at a temperature range of 600 ° C. or more and less than 800 ° C. for 10 hours or more and less than 30 hours, and subsequently at 1000 ° C. Above 1
It is characterized in that it is heated and held in a temperature range of 350 ° C. or lower for 1 hour or more and sintered.

[0010]

The present invention will be described below in detail. As described in the section of [Background Art], pulverized titanium hydride powder can be used directly as raw material powder.
Dehydrogenation to a hydrogen concentration of 1% by weight or less requires dehydrogenation annealing at 600 to 800 ° C. for several tens of hours, depending on the atmosphere and exhaust capacity. The present invention, by performing a part of the dehydrogenation step in the course of raising the temperature to the sintering temperature, conventionally occurred with long-term dehydrogenation annealing,
This technique aims to avoid disadvantages such as pseudo sintering and adhesion to a container, and as a result, to reduce the total production cost from powder production to sintering.

However, this technique can only be achieved by making the following two technical improvements. First, the hydrogen concentration in the raw titanium powder is 0.02% by weight.
As described above, the content needs to be 2% by weight or less. This is not so much as when dehydrogenating to a hydrogen content of less than 0.02% by weight but is not as great as when dehydrogenating to about 0.01% by weight, but it still requires dehydrogenation annealing on the order of tens of hours. In the meantime, pseudo-sintering and powder adhesion to the container occur, which lowers the powder yield and increases the total manufacturing cost. In addition, when hydrogen is contained in an amount exceeding 2% by weight, Remarkably deteriorates and cracks occur during compacting,
This is because a high-density sintered body cannot be obtained.

Second, after the above-mentioned titanium powder and the alloying element-adding powder are mixed and compacted, sintering (usually heating and holding at 1000 to 1350 ° C. for 1 hour or more) is performed in a vacuum atmosphere or an inert atmosphere. In the course of heating to a temperature of 10 to 10 ° C. in a temperature range of 600 ° C. or more and less than 800 ° C.
It is necessary to perform sintering by heating and holding for at least 30 hours but not more than 30 hours (hereinafter referred to as holding in the middle) and subsequently heating and holding at a temperature range of 1000 ° C. to 1350 ° C. for 1 hour or more. Here, while heating and holding for 10 hours to less than 30 hours in a temperature range of 600 ° C. or more and less than 800 ° C., hydrogen is discharged from the green compact and dehydrogenation is completed.
At this time, the heating and holding temperature must be not less than 600 ° C. and not more than 800 ° C. The reason for this is that the dehydrogenation rate is slow at a temperature lower than 600 ° C., and the dehydrogenation requires a great deal of time, so that the total production cost is rather high. Is sintered to form closed voids and hydrogen is discharged therefrom, so that shrinkage of the voids is inhibited during subsequent sintering at 1000 to 1350 ° C., and a high-density sintered body cannot be obtained.
Also, the heating and holding for 10 hours or more and less than 30 hours is because if the heating and holding are not performed for 10 hours or more, the hydrogen remains in the green compact and the hydrogen discharged into the voids during the subsequent sintering process Hampers the shrinkage of the voids, fails to produce a high-density sintered body, and even a compacted titanium powder compact containing about 2% by weight of hydrogen, which is the maximum hydrogen content in the titanium powder in the present invention, is 30 hours. Dehydrogenation is completed by about
This is because holding more than this is wasteful in terms of energy.

The intermediate holding is not necessarily performed at a constant temperature. For example, the heating rate at the time of heating to the sintering temperature is controlled, and the time required to exceed 600 ° C. and reach 800 ° C. is 10 hours. The time may be set to be less than 30 hours.

[0014]

The present invention will be described in more detail with reference to the following examples. The powder used was a titanium powder in which the residual hydrogen concentration was controlled by changing the dehydrogenation time as shown in Table 1 and a powder for alloying element addition having a composition of 60Al40V, and 90: 6 by weight ratio of Ti: Al: V. : 4 (i.e., a composition of Ti-6Al-4V), filled into a urethane rubber container, and subjected to CIP (cold isostatic pressing) at a pressure of 450 MPa. A compact test piece having a diameter of about 20 mm and a length of 150 mm was produced by compacting. The average particle size of the powder used was 10 μm or more and 45 μm or less for both the titanium and alloy element addition powders.
0 μm.

Using these compacts, Test 1 and Test 2 described below were performed. [Test 1] The green compact was subjected to vacuum sintering at 1250 ° C. for 2 hours, which is a usual sintering condition, and the density was measured. As shown in Table 1, heating to the sintering temperature was performed. On the way, a process of holding at various temperatures for various times was performed (hereinafter, referred to as intermediate holding). The rate of temperature rise before and after the holding is about 10 ° C /
Minutes (10 minutes per 100 ° C.), which was extremely short as compared with the holding time, and was ignored without considering the intermediate holding time shown in Table 1. In addition, the sintering density was represented by a relative value (%) when the ingot material of the same composition was set to 1.

[0016]

[Table 1]

In Table 1, test number 1 is 0.0
This is a case where a titanium powder containing 1% of hydrogen was used and no intermediate holding was performed, which is an example corresponding to a conventional method.
Although the sintering density is as high as 99.5%, the dehydrogenation process of titanium powder production requires as much as 50 hours, during which time the powder may be pseudo-sintered or adhere to the container. Therefore, only a yield of 75% is obtained. Therefore, the total manufacturing cost is high. Test No. 2 was a case where titanium powder containing 0.015% by weight of hydrogen was used as a raw material titanium powder and directly sintered as in Test No. 1, and the sintered density was 97.8%. Only low values were obtained. This is because the powder containing hydrogen remaining in an amount exceeding 0.01% by weight was used, and the hydrogen gas discharged into the gaps between the powders prevented the reduction of the gaps due to the pressure. Even if the same powder is used, a high sintering density of 99.0% or more can be obtained when the intermediate powder is held as shown in Test No. 3. However, the dehydrogenation step in the production of titanium powder requires 45 hours, and the yield is as low as 78% due to pseudo sintering and powder adhesion to the container during that time. The total manufacturing cost up to the conclusion was high.

According to the test results, a titanium powder containing 0.2% by weight or more of hydrogen was used, and the temperature was raised to 600 to 800 ° C. in the course of raising the temperature to the sintering temperature for 10 hours or more.
Examples of the present invention held for less than 0 hours (Test Nos. 4, 6,
7, 8, 11, and 12) all provide a high powder production yield of 90% or more and a high sintering density of 99.0% or more. The total time is also up to 54 hours, which is not a large increase as compared with the conventional example (test number 1). That is,
Both low total manufacturing costs and high sintering densities have been achieved. This uses a titanium powder with a moderate hydrogen content,
This is because sufficient holding properties and sufficient dehydrogenation during the holding during the holding were achieved because the holding was performed in the middle of an appropriate temperature and time.

On the other hand, Test Nos. 5, 9, 10, and 14, which are comparative examples of the present invention, did not provide a sufficient sintered density. The reason is as follows. In Test No. 5, since the halfway holding time was below the range of the present invention, the dehydrogenation during the halfway holding was insufficient and hydrogen remained in the compact, and the hydrogen discharged into the voids during the subsequent sintering process Prevented the shrinkage of the voids, and a high-density sintered body could not be obtained. In Test No. 9, since the intermediate holding temperature was lower than the lower limit of the present invention, hydrogen was retained even though the dehydrogenation rate was slow and the intermediate holding was performed for 45 hours, and a high sintered density was not obtained. . In this sample, if the intermediate holding time is further increased, a high sintering density may be obtained.However, the total dehydrogenation time has already been as large as 73 hours. It makes no sense because the total manufacturing cost is rather high. In Test No. 10, since the holding temperature in the middle was equal to or higher than the upper limit of the present invention, some of the powders were sintered to form closed voids, and hydrogen was discharged there. , And a high-density sintered body could not be obtained.

Further, in Test No. 14, since the hydrogen concentration in the titanium powder used was equal to or higher than the upper limit of the present invention, countless fine cracks were generated during the CIP molding. I couldn't get my body.

In Test No. 13, a high-density sintered body was obtained, but in Test No. 12 in which powders of the same hydrogen concentration were used and were held for a short period of time at the same temperature, the same degree was obtained. The sintered density is obtained, and it is held during the extra time, which is wasteful in energy.

[Test 2] In Test 2, instead of holding a green compact formed using titanium powder containing 0.5% by weight of hydrogen at a constant temperature as in Test 1, As shown in FIG. 2, by changing the heating rate, 6
It was held halfway in a temperature range of 00 to 800 ° C., and then subjected to vacuum sintering at 1250 ° C. × 2 hours, which is a usual sintering condition, to measure the density.

As shown in Table 2, from 600 ° C. to 800 ° C.
Test number 16 held for 10 hours or more and less than 30 hours during
In Nos. 17 and 17, a high sintered density of 99.0% or more was obtained. A high sintering density was also obtained in Test No. 18 held for 33 hours in this temperature range, but since the results were similar to those of Test No. 17 having a shorter holding time, extra holding was performed. This is wasteful in terms of energy. In Test No. 15, since the holding time was shorter than the lower limit of the present invention, dehydrogenation was insufficient and a high sintering density was not obtained.

[0024]

[Table 2]

[0025]

As described above, by applying the present invention, the total production cost from titanium powder production to sintering in the raw powder unmixed method using the hydrodehydrogenated titanium powder is lower than in the past. It is also possible to produce a titanium alloy at a low cost and with a high density.

Continued on the front page (72) Inventor Masao Yamamiya 2-6-3 Otemachi, Chiyoda-ku, Tokyo Nippon Steel Corporation (72) Inventor Wataru Kagohashi 3-3-5 Chigasaki, Chigasaki City, Kanagawa Prefecture Kuni Higashi Within Titanium Co., Ltd. (72) Inventor Eiichi Fukasawa 3-3-5 Chigasaki, Chigasaki-shi, Kanagawa Prefecture In-House Titanium Co., Ltd. In-company (58) Field surveyed (Int.Cl. ⁷ , DB name) B22F 3/10 C22C 1/04

Claims (1)

(57) [Claims] 1. An unmixed powder method using titanium powder produced by a hydrodehydrogenation method, wherein a titanium powder containing hydrogen at a concentration of 0.02% by weight or more and less than 2% by weight is added to an alloy element adding powder. , Mixed into a container and then compacted,
600 ° C or higher and 800 ° C in a vacuum or inert atmosphere
Heating and holding in a temperature range of less than 10 hours to less than 30 hours,
Subsequently, the temperature range from 1000 ° C to 1350 ° C
A method for producing a high-density sintered titanium alloy, comprising heating and holding for at least an hour and sintering.