JP2737487B2 - Method for producing titanium alloy for high-density powder sintering - 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 titanium alloy for high-density powder sintering having excellent mechanical properties.

[0002]

2. Description of the Related Art Titanium alloys are lightweight, have high strength, and are excellent in corrosion resistance, so that they are expected to be widely applied to industrial parts and consumer parts. In particular, it is being studied to apply such properties to automotive parts. However, in the method of manufacturing from ingot material by machining or cold working, although excellent in mechanical properties can be obtained, titanium is a difficult-to-work material, so there is a drawback that working is difficult and cost is high. In order to avoid such a drawback, application of powder metallurgy technology in which a titanium alloy raw powder is mixed, formed into a predetermined shape, and then fired in a vacuum to obtain a sintered body has been attempted.
However, when the powder metallurgy technique is used, there is a problem that the mechanical properties of the product, particularly ductility and fatigue strength, are lower than that of the ingot material, because pores remain in the product.

[0003] In order to eliminate pores and increase the density after sintering, it has been attempted to perform HIP (hot isostatic pressing) after sintering (JESmugeresky et al. Powder).
Metallugy, 1981 and Hagiwara et al., Iron and Steel, 1986 (or Japanese Patent Publication No. 1-29864). If the HIP process is performed, the density certainly increases, and a powder sintered material having almost the same characteristics as the melted and forged material can be obtained. In particular, the ductility (elongation and drawing) is improved, but the manufacturing unit price becomes extremely high. .

As another method, there is a method in which sintering is carried out at a temperature at which a liquid phase appears (Yoshiharu Matsuyama et al.
Gakkai, Showa 47, Nikkan Kogyo Shimbun, 110 pages and
143-151) . This is to cause a liquid phase to partially appear and fill the voids with the liquid phase. However, this method has the disadvantage that the heterogeneous phase formed by solidification of the partially liquid phase is generally brittle, and the resulting product is also brittle. That is,
Although the density can be increased, the mechanical properties are deteriorated. In addition, there is a disadvantage that the relationship between the sintering temperature and the mechanical properties is delicate, and the properties change greatly with a slight temperature change.

Further, in the case of manufacturing a powdered sintered titanium alloy by powder metallurgy, there is a problem that the productivity is low due to the sintering step, in addition to the problem that pores remain in the product. . That is, since Ti is a high melting point metal, the temperature for sintering is high and the time is long. Therefore, it is desired that sintering at a low temperature and a short time be possible, but this cannot be achieved by the above two methods. In particular, in the case of the latter method, since firing is performed at a high temperature at which a liquid phase is generated, it is essentially impossible to satisfy such requirements. As described above, a technique for obtaining a dense and small-sized powdery sintered body at low cost and high productivity has not yet been established.
The present invention has been made in view of such circumstances,
It is an object of the present invention to provide a method for producing a high-density powder sintered titanium alloy which can be inexpensively and highly productively densified.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention comprises one or more elements selected from the group consisting of Fe, Ni, and Co;
And the content of these, the 0.5 ≦ 0.5Fe + Ni + 0.6Co ≦ 4 satisfies the condition of (% by weight), high density powder sintering for titanium alloy balance of Ti and unavoidable impurities, less than 1200 ° C. Baked
99.5% by sintering with sintering time of 193 minutes or less
A method for producing a titanium alloy for high-density powder sintering, characterized by having the above density is provided.

[0007] Also, in this composition, 10% or less of Al, 20% or less of Mo, 15% or less of Nb, 15%
Ta below, V below 25%, Ag below 10%, 5%
B below, 5% or less Be, 15% or less Cr, 5% or less Cu, 15% or less Mn, 5% or less Pb, 5% or less Pd, 5% or less Si, 10% or less One or more selected from W, Sn of 15% or less, Zr of 10% or less, and O of 1% or less, in the case of two or more, further contains 30% or less in total. It may be.

The inventors of the present invention have conducted various studies from the viewpoint of the alloy composition in order to obtain a compact and low-voided powder sintered body with good productivity. That is, a composition that can be densely sintered in a short time at a low temperature without performing a treatment such as HIP was studied. To perform dense sintering at low temperature and short time, a high sintering rate is required. For this purpose, the diffusion rate in Ti is high, and it acts as an alloy element for Ti, and its mechanical properties It was concluded that it is sufficient to add an appropriate amount of an element that does not adversely affect water.

As a result of investigating elements having a high diffusion rate in βTi, it was found that Fe, Ni, and Co corresponded to such elements. That is, the diffusion rate (diffusion coefficient) of these elements is 10 ^{−11 at} 950 ° C. Order (m
^Two Sec- ¹ ), which is the self-diffusion rate of Ti, 10
^-13 100 times greater than Further, these elements contribute to an increase in strength. The present invention has been made based on such knowledge, and is characterized by adding an appropriate amount of Fe, Ni, and Co to Ti. Next, the reasons for limiting the composition will be described.

A study by Majima et al. (Powder and Powder Metallurgy, 19
According to 87), there is a possibility that densification may progress up to the vicinity of the composition that does not enter the solid-liquid coexistence region in the binary system diagram of Fe, Ni, Co and Ti. Further, from these binary phase diagrams, the composition in which solid-liquid coexistence appears at 1200 ° C. is 1 Fe
5%, 7% for Ni, and 11% for Co.
However, when these amounts are large, ductility (toughness) is reduced. Therefore, when these are added alone, the upper limit is F
e 8%, Ni 4%, Co 6.67%. Also,
If these amounts are too small, the effect of densification cannot be obtained.
Therefore, the lower limit when these are added alone is Fe1
%, Ni 0.5%, and Co 0.83%. However, since they have the same effect, they need to be defined in total. Therefore, their contents are defined so as to satisfy the following equation. 0.5 ≦ 0.5Fe + Ni +
0.6Co ≦ 4 (% by weight)

Further, Al, Mo, Nb, Ta, V, A
g, B, Be, Cr, Cu, Mn, Pb, Pd, Si,
W, Sn, Zr, O, and the like are used as additive elements in the ingot material and do not hinder the sinterability intended in the present invention, so that they can be added in appropriate amounts in the same concept as ordinary ingot materials. Al and O are α-stabilizing elements, and when contained in the above-mentioned range, form a solid solution with Ti to significantly increase the strength. Mo, Nb, Ta, and V are β-stabilizing elements and are completely dissolved in Ti. By containing these in the above range, the strength increases.

Ag, B, Be, Cr, Cu, Mn, P
B, Pd, Si, and W are β-stabilizing elements, and cause an eutectoid reaction with Ti. Incorporation of these in the above range also increases the strength. Sn and Zn are neutral elements, and form a solid solution uniformly in the α phase and the β phase, and improve not only static strength but also creep strength.

The titanium alloy for powder sintering of the present invention defined as described above is manufactured by mixing titanium powder and a pre-alloyed alloy powder, and molding and sintering the mixed powder. Is preferred. By adopting this method, uniformity is improved and densification can be promoted. As such a method, Japanese Patent Publication No. 2-501
No. 72 is disclosed. this is,

(A) A pre-alloy composed of two or more metals, having a mean particle size of 0.5 to 20 μm by using a pulverizer capable of giving high energy to alloy-forming particles that can be alloyed with titanium. Crushed into

(B) This and average particle size of 40 to 177 μm
To form a powder mixture in which the weight ratio of the titanium-based metal particles is 70 to 95% and the balance is the alloy-forming particles. The main point is that the green compact is formed into a green compact having a density of 80 to 90%, and (d) the green compact is sintered at a temperature lower than a temperature at which a liquid phase is generated.

By using this method, the theoretical density of 9
A titanium alloy sintered body having a density of 9.0 to 99.8% can be obtained, and a density much higher than 94.5 to 96.5% of a titanium alloy prepared by simply mixing elementary powders can be obtained. It becomes possible. The mechanical properties are almost the same as those of the smelted / forged titanium alloy. In the case of a titanium alloy having a conventionally used composition, sintering can be performed at a sintering temperature of 1260 ° C. for 4 hours by using this method. It becomes possible.

[0017]

Embodiments of the present invention will be described below. (Example 1)

The raw material powder was blended so as to obtain a titanium alloy having the composition shown in Tables 1 and 2. Composition numbers 1 to 19 in Table 1 are examples within the scope of the present invention, and composition numbers 20 to 27 in Table 2 are comparative examples out of the range. In Tables 1 and 2, EQ1 is 0.5Fe + Ni + 0.6
Represents Co.

In Tables 1 and 2, a single element powder having an average particle diameter of about 2 μm was used as a raw material to which any one of Fe, Ni and Co was added alone. For alloy systems containing two or more elements as alloying elements, master alloy powders corresponding to the respective compositions were produced.

In this case, the master alloy powder was manufactured as follows. First, master alloys of each composition were melted in an argon atmosphere arc melting furnace, solidified, coarsely ground to −100 mesh, and placed in an attritor with about 10 kg of steel balls having a diameter of about 3 mm and 2 liters of freon for about 60 minutes. Crushed. Thereafter, the pulverized powder was taken out of the attritor and dried. As a result of measuring the particle size of the master alloy powder particles manufactured in this manner with a laser micron sizer, the average particle size was 3 to 5 μm.

The single element powder, master alloy powder and pure titanium powder of -100 mesh (average particle size of about 75 μm) were mixed by a V blender so as to have the compositions shown in Table 1. Then, the mixed powder thus produced was filled in a steel mold, and the pressure was 5.0 tonf / cm ^2.
To form a compact of 4 × 4 × 15 (mm). The density of the green compact was about 85% of the theoretical value.

The green compacts of the respective compositions thus formed were set in a thermal expansion tester, the inside of which was evacuated to the order of 10 ^-5 Torr, and then heated to 1250 ° C. at a rate of 10 ° C./min. Table 1 shows the temperature at which the density of the sintered body of each composition sintered by this heating was 99%. When sintering to 99%, the test piece shrinks by almost 5%, and the point at which the test piece shrinks by 0.75 mm (5% of the original length of 15 mm) was defined as the density of 99%. As shown in Table 1, within the range of the present invention, it was confirmed that a density of 99% can be obtained at a low temperature of less than 1200 ° C.

FIG. 1 shows the relationship between the value of 0.5Fe + Ni + 0.6Co and the temperature at which the density reaches 99%. As is clear from this figure, 0.5Fe + Ni +
It can be seen that the temperature decreases as the value of 0.6Co increases. And such an effect is 0.5F
It is understood that the value of e + Ni + 0.6Co becomes significant when the value is 0.5% or more. Table 1 also shows the amounts of single additions of Fe, Ni, and Co, but it can be seen that each of the elements exhibits substantially equivalent effects. Composition Nos. 17 to 19 were obtained by adding Al and V as other alloy elements, but it was confirmed that the sinterability was not adversely affected even if they were included.

On the other hand, 0.5Fe + Ni + 0.6
Composition No. 20 of Comparative Example in which the value of Co is less than 0.5%,
In the case of 24, 26, and 27, as shown in Table 2, the temperature at which the density became 99% suddenly shifted to the high temperature side and changed to 1200 ° C.
Temperature. Among them, composition number 2
At 0 and 24, the final density did not reach 99%. (Example 2)

[0025] create a green compact of Example 1 4 by mixing powder of each composition in a similar procedure as × 4 × 15 (mm), and set the thermal expansion tester therein 10 ^-5 Torr Order Then, the temperature was raised to 1150 ° C. at a rate of 10 ° C./min and kept at that temperature for 4 hours. From the amount of shrinkage of the test piece during this time,
The time required for the density to reach 99.5% of the theoretical density was determined. Table 1 shows the values. When sintering to 99.5%, the test piece shrinks by about 5.2%.
The point at which the test piece contracted 0.78 mm (5.2% of the original length of 15 mm) was defined as a density of 99.5%. As shown in Table 1, within the range of the present invention, 99.
It was confirmed that a density of 5% was obtained.

FIG. 2 shows the relationship between the value of 0.5Fe + Ni + 0.6Co and the time required for the density to reach 99.5%. As is apparent from this figure, 0.5Fe + N
It can be seen that as the value of i + 0.6Co increases, the time required for the density to reach 99.5% at 1150 ° C. decreases. In addition, such an effect is obtained by 0.5F
It is understood that the value of e + Ni + 0.6Co becomes significant when the value is 0.5% or more.

On the other hand, 0.5Fe + Ni + 0.6
Composition No. 20 of Comparative Example in which the value of Co is less than 0.5%,
In the case of 24, 26 and 27, as shown in Table 2, the density did not become 99.5% in 4 hours. (Example 3)

A green compact of 13 × 13 × 69 (mm) was formed from the mixed powder of each composition in the same procedure as in Example 1,
The sintering was performed at 1250 ° C. for 4 hours in a vacuum of the order of 10 ⁻⁵ Torr. Tensile test specimens having a parallel portion diameter of 6.25 mm and a distance between gauge points of 25 mm were prepared from the sintered bodies of each composition thus produced, and a tensile test was performed at room temperature. Table 1,
2 also shows the values of tensile strength and breaking elongation at that time.
As is evident from Table 1, for compositions within the scope of the present invention,
It was confirmed that both the tensile strength and the elongation at break show sufficient values.

FIG. 3 shows the relationship between the value of 0.5Fe + Ni + 0.6Co and the elongation at break. As apparent from this figure, the elongation at break was 0.5Fe + Ni + 0.6.
It can be seen that there is a tendency for the value to decrease as the value of Co increases, and when this value exceeds 4.0%, the elongation sharply decreases.

That is, as shown in Table 2, 0.5Fe
Composition Nos. 21, 22, 23, and 25 of Comparative Examples in which the value of + Ni + 0.6Co exceeds 4.0% have an extremely low elongation at break of 3% or less, and the value of 0.5Fe + Ni + 0.6Co is 4.0%.
It was confirmed that addition exceeding 0% was not preferable. This is considered to be the result of the excessive addition of Fe, Ni, and Co that promotes the formation of intermetallic compounds and significantly reduces toughness.

It is confirmed that the composition numbers 17 to 19 to which Al and V are added as alloy elements have a high tensile strength. For example, when comparing Alloy Nos. 2 and 17, the tensile strength is 39 kgf / cm ^2. Is also rising. That is, A
It was confirmed that the addition of 1, V increased the strength.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

According to the present invention, there is provided a high-density powder sintered titanium alloy which can be manufactured at a low cost and with high productivity.

[Brief description of the drawings]

FIG. 1: 0.5Fe + Ni + 0.6Co and 99% density
FIG. 4 is a diagram showing a relationship between the temperature and the temperature at which the temperature reaches the threshold.

FIG. 2: 0.5Fe + Ni + 0.6Co and density of 99.
The figure which shows the relationship with the time required to reach 5%.

FIG. 3 is a diagram showing the relationship between 0.5Fe + Ni + 0.6Co and elongation.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yuji Imato 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-62-263940 (JP, A) JP-A-2 -290933 (JP, A) JP-A-51-71206 (JP, A) JP-A-50-51013 (JP, A)

Claims (2)

(57) [Claims] 1. An alloy containing one or more elements selected from the group consisting of Fe, Ni, and Co, and their content is 0.5 ≦ 0.5Fe + Ni + 0.6Co ≦ 4 (weight satisfies the condition of%), high density powder sintering for titanium alloy balance of Ti and inevitable impurities, less than 1200 ° C. baked
99.5% by sintering with sintering time of 193 minutes or less
A method for producing a titanium alloy for high-density powder sintering, characterized by having the above density . 2. In weight%, up to 10% Al, up to 20% Mo, up to 15% Nb, up to 15% Ta, 25
% V, 10% Ag, 5% B, 5% Be, 15% Cr, 5% Cu, 15%
The following Mn, 5% or less Pb, 5% or less Pd, 5% or less Si, 10% or less W, 15% or less Sn, 10%
One or more kinds selected from the following Zr and 1% or less O are further contained in a range of 30% or less in total when two or more kinds are selected. 2. The method for producing a titanium alloy for high-density powder sintering according to 1.