JPH0688153A - Production of sintered titanium alloy - Google Patents

Abstract

PURPOSE:To produce the sintered titanium alloy without executing a stage for a higher density treatment, such as HIP, and without impairing the intrinsic characteristics of the sintered titanium alloy at a low cost by improving the sinterability of the powder. CONSTITUTION:The powder of alloy components is added and mixed to and with the a powder mixture prepd. by compounding TiH2 powder contg. <=25mum grain sizes at 95wt.% with Ti powder contg. a >=45 and <=150mum grain size rang at >=90wt.% in place of the Ti powder in such a manner that the compounding ratio attains >=10wt.% and <75wt.% and such mixture is subjected to molding of a green compact by CIP (cold isotropic press molding method), etc., and the green compact is subjected to vacuum sintering or is sintered in an inert atmosphere at the time of producing the Ti powder by a blank powder mixing method.

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, and more particularly to a method for producing a sintered titanium alloy by an elementary powder mixing method.

[0002]

2. Description of the Related Art The powder metallurgy method is suitable as a manufacturing method for obtaining a product such as a titanium alloy having poor workability, formability, or machinability, since the material can be formed into a shape close to the final shape.

In particular, pure titanium powder and alloying powder are mechanically mixed, pressed into a predetermined shape by pressing or CIP (cold isostatic pressing), and sintered in a vacuum or an inert gas atmosphere. And the alloying heat treatment are performed at the same time, and then the densification treatment such as HIP (hot isostatic pressing) and forging, etc. is performed as needed. Since it occupies the most part, it has good moldability and can manufacture a green compact with a precise shape at room temperature. It is possible to manufacture various alloys with different compositions by changing the mixing ratio of the raw material powders. And so on.

As the titanium powder as a raw material, it is possible to use, as an inexpensive material, so-called sponge fine, which is a powder generated during the production of titanium sponge by the Hunter method. However, since sponge fine contains a large amount of chlorine and chlorine cannot be removed sufficiently in the vacuum heat treatment process, a large amount of pores are generated due to chlorine remaining in the product, and as a result, sintered titanium Degrades the mechanical properties of the alloy. Therefore, the use of sponge fine powder as a raw material in the elementary powder mixing method cannot be said to utilize the excellent properties of titanium alloy. in this way,
One of the properties required for the raw material titanium powder is that the chlorine content is low, and at present, the raw material powder is obtained by crushing a pure titanium ingot.

However, pure titanium has good ductility,
Grinding is difficult with normal mechanical methods. For this reason,
The production of titanium powder is performed by so-called HDH treatment in which titanium is embrittled by performing hydrogenation treatment, crushed to a predetermined particle size, and then dehydrogenation treatment is further performed. This HD
The HDH powder produced by the H treatment has a hydrogen content of 600 to 800 in order to reduce the hydrogen content of the titanium powder to 0.02 wt% or less, which is the hydrogen content of a normal titanium alloy, in the dehydrogenation process.
Long-term vacuum heat treatment at 6 ° C. for 6 to 20 hours is required. For this reason, the fine titanium hydride powder, which was about 10 μm at the time of pulverization, is apt to adhere to the coarse powder and to agglomerate the fine powders, diffuse and bond during the dehydrogenation heat treatment, and become coarse after dehydrogenation. It becomes a fine powder. For this reason, it is very difficult to obtain a fine powder, and even if classification is performed, only a very small amount can be obtained.

Further, since titanium has a very high oxygen solid-solubility, oxygen adsorbed on the surface of the powder diffuses and forms a solid solution in the titanium powder during the heat treatment to increase the amount of oxygen. The fine titanium powder produced from such a titanium hydride powder has a high oxygen content, and therefore the titanium alloy product produced by this powder has a high oxygen content. Increasing the oxygen content in a titanium alloy is not desirable because it lowers mechanical properties, especially ductility and leads to deterioration of fatigue properties.

The HDH titanium powder that is industrially produced and used usually has an average particle size of 1 because of the difficulty of obtaining such a fine powder and the increase in the amount of oxygen due to the refinement of the powder.
The one having a diameter of about 00 μm is often used. Since such a coarse powder is used, only low density products can be obtained under normal sintering conditions, and in order to apply it to members that require fatigue characteristics, it is necessary to sinter at high temperature for a long time. In addition, densification treatment such as HIP and forging is required. Such process conditions are not desirable for the maintenance of the furnace, and an increase in the number of processes leads to an increase in processing cost, which does not always match the current situation where cost reduction is required.

As a method for obtaining a high density sintered body, a liquid phase sintering method in which a low melting point material is added and a part of the material is melted during sintering is also considered. Although this method is effective for increasing the density, coarsening of crystal grains and segregation of low-melting-point components at grain boundaries occur, leading to deterioration of mechanical properties.

Further, as described in JP-A-61-246333, there is a method of mixing titanium powder and alloying powder, adding a coagulant, and then pulverizing by a mechanical method to perform molding and sintering. . This method can certainly improve the sinterability, but when observing the powder obtained by this method in detail, the titanium powder is crushed into a flat plate due to pulverization, and there is a concern that the amount of oxygen increases. .

On the other hand, "Powder Metallurgy Internationa
Magazine ”(issued in 1974) No. 2, as described on page 66, in the case of sintered pure titanium material, titanium hydride powder or a mixed powder of titanium hydride powder and titanium powder is used as the raw material powder, and the dehydrogenation step and the sintering step are performed. There is a way to do it at the same time. In this method, an inexpensive titanium hydride powder that does not undergo a dehydrogenation step can be used, and since one heat treatment step can be omitted, there is an advantage that contamination by oxygen that adversely affects the characteristics of the titanium alloy can be reduced. Further, there is an advantage that the diffusion of titanium is activated by a large amount of dislocations contained in the titanium hydride powder, and the sintering proceeds at a low temperature in a short time as compared with the case where only the titanium powder is used.

However, this method cannot be directly applied to the method for producing a sintered titanium alloy by the elementary powder mixing method. The reason is as described below. First, the titanium alloy contains a large amount of elements other than Ti such as Al, V, Fe and Mo, and these alloy elements interact strongly with hydrogen. Therefore, in the production of a sintered titanium alloy using a raw material powder containing hydrogen, the dehydrogenation heat treatment requires a very long time as compared with the production of sintered pure titanium. At this time, a part of hydrogen is confined as a gas in the pores remaining inside the material as the sintering progresses. The hydrogen gas trapped in the material dissolves into the material again as the temperature rises and the gas pressure increases due to dehydrogenation, and is not discharged to the outside of the material without going through the process of exiting from the material surface. It will take time. At the same time, the pressure of hydrogen gas delays the disappearance of pores inside the material, which hinders the progress of sintering. Further, hydrogen that cannot be completely removed during sintering and remains in the material adversely affects characteristics such as embrittlement of the titanium alloy.

[0012]

DISCLOSURE OF THE INVENTION According to the present invention, when a sintered titanium alloy is produced by the elementary powder mixing method, the sinterability of the powder is improved and the densification treatment step such as HIP is not performed. It is an object of the present invention to provide a method for producing a sintered titanium alloy at a low production cost without impairing the inherent properties of the sintered titanium alloy.

[0013]

Means for Solving the Problems The present invention for achieving the above object comprises (1) a method for producing a sintered titanium alloy by an elemental powder mixing method, wherein 95% by weight or more of powder having a particle diameter of 25 μm or less is used. Fine titanium hydride powder containing, 45μ
Pure titanium powder containing 90% by weight or more of powder having a particle diameter of m or more and 150 μm or less, and the amount of titanium hydride powder is 10 to 7
The alloying powder is mechanically mixed with 5% by weight of the compounded powder, green compacting is performed, and vacuum sintering is performed. (2) Elemental powder mixing method The method for producing a sintered titanium alloy is characterized in that the green compact molding described in the item (1) is performed by using CIP (cold isostatic pressing).

In the present invention, the titanium hydride powder means
This is a powder containing 3.0% by weight or more of hydrogen in titanium, and TiH ₂ occupies most of this powder. The sintered titanium alloy is a titanium alloy composed of Ti, Al, V, Fe, alloy components other than these, and impurities.
i-6Al-4V alloy, Ti-3Al-2.5V alloy,
It is an alloy such as Ti-5Al-2.5V alloy, and refers to an alloy inevitably containing less than 0.7% by weight of Fe, O, C, N, and H impurities in the product.

In producing such a sintered titanium alloy by the elementary powder mixing method, Al, V, Fe and other alloy components are alloy powders such as Al-V master alloy and Al-V master alloy. May be added by mixing,
Metal element powders such as Al powder, V powder, and Fe powder may be added to the respective predetermined components. In Ti, Al, V,
It is also possible to mix an alloy containing one kind or two or more kinds of additive alloy components such as Fe.

[0016]

The present invention will be described in detail below. As a result of repeated research on the production and use of titanium powder, the present inventors have found that when producing a sintered titanium alloy by the elementary powder mixing method, a specific amount of fine titanium hydride powder is contained in the titanium powder as a raw material. It has been found that the mixing improves the sinterability to an extent sufficient to compensate for the delay in sintering due to the generation of hydrogen, and increases the density of the sintered body. In addition to this effect, they have also found that the use of titanium hydride powder significantly reduces the oxygen level of the product. The present invention has been made based on these new findings.

The reason why the density of the sintered body is increased by adding the fine titanium hydride powder is as follows.
First, since the titanium HDH powder is a coarse powder, a coarse space is generated between the powders during powder compaction.
By filling this space with fine titanium hydride powder, the packing density of the powder is increased and the compact density is significantly improved. Secondly, the fine powder greatly increases the specific surface area, which promotes surface diffusion during sintering. Due to these two effects, the density of the sintered body is greatly increased, and by omitting the heat treatment step of dehydrogenation, oxygen adsorbed on the surface of the powder is prevented from diffusing into the inside of the powder, and the fine titanium powder is removed. It is possible to produce products with lower levels of oxygen than when used.

In order to make full use of these effects, titanium hydride powder having a particle size distribution of 25 μm or less should be used.
It is necessary to contain 5% by weight or more. If the content is less than this, a large amount of powder that is too large to fill the space between the powders will be included, and the density of the compact will decrease, leading to a decrease in the density of the sintered body.

The content of titanium hydride powder must be 10% by weight or more and 75% by weight or less. That is, the amount of titanium hydride powder was limited to 10% by weight or more because the amount less than this was not sufficient as an absolute amount for the space between the powders, while the ratio due to the addition of fine powder was The effect of improving the sinterability by increasing the surface area is not sufficient. Therefore, the effect of compensating for the delay of sintering due to the inclusion of hydrogen does not appear, and the increase in the density of the sintered body is hindered. In addition, most of the raw materials use titanium powder that has already undergone the dehydrogenation process, and there is little advantage of cost reduction due to process saving. The upper limit of the compounding amount of titanium hydride powder is set to 75% by weight or less. When the compounding amount is more than this, the moldability is rapidly deteriorated due to the refinement of the powder particle size, and the compact density is insufficient. The reason for this is that the increase of the hydrogen content is more effective than the activation of the surface diffusion in the effect of delaying the sintering due to the increase of the hydrogen gas pressure in the holes in the material, and the effect of the present invention is not sufficient.

Pure titanium HDH powder is 45 μm to 150 μm
It is necessary to include 90% by weight or more in the range of the particle size of m. The reason for this is as follows. First, when a pure titanium powder containing a powder of 45 μm or less in an amount of 10% by weight or more is used, a large increase in the oxygen content is caused, so that the characteristics of the product are significantly reduced. 10% by weight of powder exceeding 150 μm
When the pure titanium powder containing the above is used, the density of the sintered body decreases due to the decrease of the density of the compact. In addition, it is generally said that the surface of the product becomes rougher as the particle size of the powder becomes coarser. Secondary processing and surface treatment are required to use the product made from the coarse powder, so avoiding cost increase. I can't. Further, when the total weight of the powder of less than 45 μm and the powder of more than 150 μm is contained in an amount of 10% by weight or more, the above-mentioned drawbacks of increased oxygen amount and decreased sintered body density are combined.

Further, unlike the method of compression molding in a uniaxial direction such as a die press, the CIP in which the powder is molded according to claim 2 of the present invention can apply a uniform pressure to the material and can be uniform without being dense and dense. Since such a molded body can be obtained, dehydrogenation becomes smooth, which is an advantageous molding method.

[0022]

EXAMPLES The present invention will be described in more detail based on the case where the present invention is applied to various titanium alloys. First, Ti-6
An example is shown when applied to Al-4V (Al: 6% by weight, V: 4% by weight, balance: substantially Ti, containing a small amount of impurities). Table 1 shows the particle size distribution of the TiH ₂ powder. Powder D contains 96% by weight of powder of 25 μm or less, powder E contains almost 100% by weight of powder of 25 μm or less, and both powder D and powder E are claimed in the present invention. It is in. Also, powder F
Contains 10% by weight of more than 25 μm and is used as a comparative material.
iH ₂ powder.

[0023]

[Table 1]

Table 2 shows the particle size distribution of the Ti powder used in this example. The powder A is a titanium powder containing 95% by weight in the range of 45 μm to 150 μm, and has a particle size distribution within the scope of the present invention. Powder B was a raw material powder containing 20% by weight of a powder having a particle size of less than 45 μm, and powder C was a raw material powder containing 15% by weight of a powder having a particle size of more than 150 μm, and each was used as a comparative material of the present invention. The additive alloy components Al and V are
AlV master alloy powders (60% by weight of Al and 40% by weight of V) having an average particle size of 30 μm and a maximum particle size of 45 μm were used and mixed so that the weight ratio of Ti to the master alloy was 9: 1.

[0025]

[Table 2]

In Table 3, green compacts of various titanium powder mixtures are molded, further heated at 20 ° C./min, and sintered at a holding temperature and a holding time of 1150 ° C. for 2 hours for vacuum sintering. The results of measuring the relative density of the ties are shown. The relative density here is a ratio when the density of a sample obtained when an alloy having the same composition is manufactured by a melting method is 100%. Table 3 also shows the result of the tensile test and the fatigue test of the as-sintered test piece and the measurement result of the oxygen content.

In Table 3, test number 1 is HDH-Ti.
This is a case where a powder obtained by mixing powder and 60Al40V mother alloy powder at a ratio of 9: 1 is used as a raw material and corresponds to the conventional method. This mixed powder was molded by CIP at 490 MPa, and 1150
When vacuum sintering is performed at ℃ × 2 hours, the relative density of the obtained sintered body is 85%. The tensile strength is 650 MPa, the elongation is 8%, the fatigue limit is 200 MPa, and the oxygen content is 0.15%.

Test No. 4 is HDH-Ti powder A instead of HDH-Ti powder A used in test No. 1 as the raw material powder.
And TiH ₂ powder D were mixed at a ratio of 5: 5, and a test was conducted using a mixed powder containing titanium hydride powder within the scope of the claims of the present invention. Molded by CIP in the same way as Test No. 490
This is a case where vacuum sintering was performed at 1150 ° C. for 2 hours under MPa. The relative density of the obtained sintered body was 98%,
The improvement of the compact density due to the increase of the powder packing density by the incorporation of fine titanium hydride powder and the effect of promoting the surface diffusion by the increase of the specific surface area are more effective than the effect of inhibiting the sintering due to the generation of hydrogen gas. Therefore, the density of the sintered body is significantly improved as compared with the conventional method. Tensile strength and elongation are also 900MPa, 16
%, Which is significantly higher than the conventional method, and the oxygen content is 0.12% by weight.
And the fatigue strength rises to 450 MPa.

The blended powders were used in which the blending amounts of the titanium hydride powders of the raw material powders of Test Nos. 3 and 5 were set close to the lower limit value and the upper limit value, respectively, within the claims of the present invention.
In these cases, the density and various characteristics are slightly lower than those of Test No. 4, but a marked increase is seen compared to the conventional method,
This is an effect of improving the density of the compact with the increase of the powder packing density by blending the fine titanium hydride powder, and promoting the surface diffusion by increasing the specific surface area.

On the other hand, test number 2 which is a comparative example of the present invention
Then, as shown in Table 3, the ultimate density was 82% under the sintering condition of 1150 ° C. × 2 hours, which was deteriorated together with various characteristics as compared with the conventional method. The reason for this is that since the amount of titanium hydride powder blended is 5% by weight, which is less than the lower limit of the claims of the present invention, the effect of improving the sintered body density due to the incorporation of fine titanium hydride powder does not appear. This is because the sintering delay due to the gas confinement became remarkable. Test No. 6 is 75 which is the upper limit of the compounding amount of the titanium hydride powder in the claims of the present invention.
Since it is more than wt%, the formability is rapidly deteriorated due to the refinement of the powder particle size, the compact density is not sufficient, and the delay effect of sintering due to the increase of hydrogen gas pressure in the holes in the material is superior,
This is because the effect of the present invention becomes insufficient.

Test No. 7 is the same as Test No. 4 of Example, except that only TiH ₂ powder D is finer than TiH ₂ powder E.
It is a result within the scope of the claims of the present invention in which various tests were performed under the same conditions. In this case, since TiH ₂ powder finer than that of Test No. 4 was blended, diffusion was further promoted, the ultimate density was as high as 99%, and both mechanical properties and fatigue strength were improved. However, although a slight increase can be seen due to the increase in the surface, it is within the practical range.

On the other hand, Test No. 8 was conducted by adding TiH ₂ powder D to T
is the result of a comparative example for Test No. 4 and 7 was replaced by iH ₂ powder E. The ultimate density was significantly reduced to 80%, and both mechanical properties and fatigue limit were significantly degraded. This is T
This is because the iH ₂ powder E contains a large amount of powder having a size of 25 μm or more as compared with the claimed range of the present invention, so that the density of the molded body is lowered and the density of the sintered body is lowered.

Test No. 9 shows the particle size of Ti powder as 45 in Table 1.
Changed to powder B containing 10 μ% or more of powder having a particle size of μm or less,
This is a comparative example using a mixture of TiH ₂ powder D in the same ratio as in Test No. 4. The ultimate density of the sintered body is 98%
However, since the amount of fine Ti powder increased, the oxygen content was 0.35% by weight, which was extremely high.
Although the strength is higher than the result of Test No. 4, the ductility and fatigue strength are also extremely deteriorated.

Test No. 10 shows the grain size of Ti powder as 1 in Table 1.
This is a comparative example in which a powder C containing 10% by weight or more of powder of 50 μm or more was mixed and TiH ₂ powder D was blended in the same ratio as in Test No. 4. In this case, the ultimate density of the sintered body is as low as 80%, and the mechanical properties and fatigue properties are greatly deteriorated. This is a result of an increase in the Ti powder containing coarse powder of 150 μm or more, resulting in an increase in voids between the powders, resulting in a decrease in compact density and a decrease in sintered density.

Test No. 11 is the result of vacuum sintering of a sample obtained by using a raw material powder having the same mixing ratio as in Test No. 4 and performing molding by a die press instead of CIP. . In this case, the relative density of 97% is reached, and the effect of the present invention is sufficient. But CI
The reached density is lower than that of test number 4 in which P molding was performed.
The reason for this is that since the die press is compression molding in the uniaxial direction, the density can be varied depending on the position of the molded sample, whereas CIP applies uniform pressure to the material to obtain a homogeneous molded body. Therefore, the CIP-molded sample discharges the hydrogen gas generated during sintering more smoothly to the outside of the material. Although the effects of the present invention can be expected even if the molding is carried out by the die press method as described above, the effects are further enhanced by carrying out the molding by the CIP method.

[0036]

[Table 3]

Table 4 shows the results of the conventional production test of titanium alloys of various components and the test conducted within the scope of the claims of the present invention. Test numbers 12 and 13 are Ti-3A
1-2.5V (Al: 3% by weight, V: 2.5% by weight, balance: substantially Ti, containing a small amount of impurities), respectively, as a result of the conventional test and HDH-Ti powder A And Ti
Of H ₂ powder D 5: was blended at a ratio of 5, the result of the test was carried out in the claims of the present invention, the test numbers 14 and 15, Ti-10V-2Fe-3Al (V: 10 wt%, Fi: 2% by weight, Al: 3% by weight, balance: substantially Ti, containing a small amount of impurities) and the results of the conventional method and Example, and test numbers 16 and 17 are Ti-
15V-3Cr-3Sn-3Al (V: 15% by weight, C
r: 3% by weight, Sn: 3% by weight, Al: 3% by weight, balance: substantially Ti, containing a small amount of impurities).
It is a result of a conventional method and an example. When the present invention is applied to any of the titanium alloys, the density is significantly increased, the mechanical properties and the fatigue properties are improved regardless of the components and the addition amount of the additive alloy, and the effect of the present invention is sufficiently exerted. To do.

[0038]

[Table 4]

[0039]

As described above, by applying the present invention, in producing a sintered titanium alloy by the elementary powder mixing method, the sinterability of the powder is improved and the densification treatment such as HIP is performed. It is possible to perform the manufacturing process at a low manufacturing cost without deteriorating the inherent properties of the sintered titanium alloy without performing the above process.

Claims (2)

[Claims] 1. A method for producing a sintered titanium alloy by an elementary powder mixing method, wherein 95 powders having a particle size of 25 μm or less are used.
Fine titanium hydride powder containing at least 50% by weight and pure titanium powder containing 90% by weight or more of powder having a particle size of 45 μm or more and 150 μm or less are blended so that the amount of titanium hydride powder is from 10 to 75% by weight. A method for producing a sintered titanium alloy, characterized in that alloying powder is mechanically mixed with the powder thus obtained, green compacting is performed, and vacuum sintering is performed. 2. The green compact molding according to claim 1, CIP
A method for producing a sintered titanium alloy, which is performed by (cold isostatic pressing).