JPH059630A - Sintered titanium alloy and production thereof - Google Patents

Abstract

PURPOSE:To produce a low-cost sintered Ti alloy having high strength. CONSTITUTION:This sintered Ti alloy consists of, by mass, 4-8% Al, 2-6% V, 0.15-0.8% O, a prescribed amt. of one or more kinds of elements selected among at least 0.2-5% B, 0.5-3% one or more among Mo, W, Ta, Zr, Nb and Hf, 0.05-2% one or more of the groups Ia, IIa and IIIa elements and 0.05-0.5% one or more kinds of halogen elements and the balance Ti with inevitable substances and has a three-phase structure consisting of d-phase, beta-phase and grains of one or more among at least boride, oxide and halide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, inexpensive sintered titanium alloy and a method for producing the same, more specifically,
The present invention relates to a sintered titanium alloy having a three-phase structure of α phase, β phase and dispersed particles and excellent in strength characteristics, and a method for producing the same.

[0002]

2. Description of the Related Art Titanium alloy has higher specific strength and specific toughness than ultra-high strength steel and high strength aluminum alloy, but the material price is high.
It has been difficult to apply it to mass-produced parts because of the difficulty of melting and casting and the poor yield due to difficult workability.

However, according to the powder metallurgy method, Near Net
It is possible to manufacture Shape parts, and among them, the raw material powder is inexpensive, the material yield is high, and the manufacturing process is simple. It has advantages such as, and can be expected to significantly reduce costs. However, the conventional elemental powder mixing method has a problem in that the mechanical properties of the obtained sintered titanium alloy, particularly fatigue strength, are as low as those of cast materials. Therefore, it is used in large quantities for small items such as nuts, fasteners, filters, dome housings, gyro gimbals and other missile parts where fatigue strength is not a serious problem, but important parts that require fatigue strength. Had the problem that it was not applicable to.

Therefore, in order to solve these problems, recently, a high-purity titanium powder from which impurities are removed as much as possible is used as a raw material,
Moreover, attempts have been actively made to improve fatigue strength by performing HIP treatment and heat treatment after sintering.

For example, the constituent metal element powders are mixed, molded,
Vacuum-sintered sintered titanium alloy is further quenched from the β temperature range below the vacuum sintering temperature to a temperature below room temperature, and thereafter,
"Titanium alloy manufacturing method by elemental powder mixing method" (Japanese Patent Publication No. 1-29864) has been proposed in which residual voids are removed by heating under pressure in the α + β2 phase region of 800 ° C or higher to β transformation temperature. . In this method, the HIP treatment and the heat treatment are successfully combined to strengthen the sintered titanium alloy, so that it is possible to realize a fine homogeneous structure similar to the alloy powder method even though it is the elementary powder mixing method. Fatigue characteristics could be realized.

That is, the alloy powder method and the elemental powder mixing method have quite different structures even if they are α + β alloys produced by the same HIP treatment. Because HI
This is because the tissue state before P treatment differs between the two. In the case of the former alloy powder method, in order to solidify the alloy powder rapidly cooled at the time of powder production as it is at a temperature below the β transition point, HI
Martensite is tempered during P treatment, resulting in fine α + β
Become an organization. On the other hand, in the latter case of the raw powder mixing method, coarse acicular α phase is formed by β / α transformation in the cooling process after sintering, and even if this is HIP-treated at a temperature below the β transition point. The organization hardly changes.

Therefore, in Japanese Examined Patent Publication No. 1-29864, after sintering β
After quenching to make the structure once uniform martensite, HIP treatment is performed. Here, the residual vacancies play an important role. That is, when performing solution treatment in the β range, about 5 vol% of pores remaining in the sintered body completely suppress the β phase grain growth, so the martensite structure obtained by quenching this is obtained. Becomes finer. Therefore,
Subsequent HIP treatment in the α + β two-phase region results in the formation of a fine α-phase having a small aspect ratio similar to the alloy powder. In this Japanese Examined Patent Publication No. 1-29864, a titanium alloy having fatigue properties comparable to those of the alloy powder method is manufactured by using the ultra-low chlorine titanium powder as a raw material and performing the above-mentioned improvement treatment to completely remove the residual pores. can do.

In the production of the high density sintered titanium alloy, a. The alloy forming particles are pulverized by a pulverizer capable of imparting high energy to an average particle size of 0.5 to 20 μm, and b. Titanium-based metal particles having an average particle size of 40 to 177 microns and the crushed alloy-forming particles are mixed, and the weight ratio of titanium-based metal particles is 70 to 95.
%, Forming a powder mixture with the balance comprising the alloy-forming particles, and c. Molding the mixture into a green compact and sintering below the temperature at which the liquid phase forms. Method ”(Japanese Patent Publication No. 2-50172). By this method, the mechanical energy applied at the time of pulverization is accumulated as strain energy in the powder to promote the sintering, and the relative density becomes as high as 99% or more only in the powder molding + sintering process, which is a normal density. It is said that mechanical properties are significantly improved as compared with the method.

In addition, 2 powders having a particle size of 325 mesh or less are used.
Ti or Ti alloy powder containing 5 wt% or more, and particle size 32
"Manufacturing method of high-density Ti sintered alloy" in which a powder obtained by mixing an alloying additive powder having a size of 5 mesh or less in a predetermined amount is processed by a mechanical pulverizing means, and compacted and sintered. -1307
No. 32) is proposed. In this method, a mixture of titanium powder and master alloy powder is subjected to strong working using a device such as a high-energy volmill to finely pulverize the titanium powder and master alloy together, and then these fine powders are mixed. The particles are mechanically combined to increase the size. It is said that a dense sintered body can be obtained by molding and sintering the powder thus produced.

[0010]

However, according to Japanese Patent Publication No. 1-29864, the mechanical properties of sintered titanium alloy can be improved by using HIP treatment and heat treatment together. In such a method, it is necessary to use expensive ultra-low chlorine powder as a raw material, HIP treatment and heat treatment are required after sintering, and a large increase in cost is inevitable. It has a problem that it cannot be applied to mass-produced products.

Further, in Japanese Examined Patent Publication No. 2-50172, since a commonly used master alloy such as Al ₃ V has almost no plastic deformability, strain energy enough to accelerate sintering during pulverization is applied to the inside of the powder. Cannot be stored in. Therefore, the densification achieved by this method is due to a decrease in the average particle size of the mother alloy powder in the crushing process of the mother alloy and merely an increase in the surface energy. However, it is a known fact that such pulverization promotes sintering, and although the fatigue strength obtained by this method is higher than that by the usual method, it is at most 40 kg / mm ² even if the molding pressure is increased. It has a problem that it is less than the above.

Further, in Japanese Patent Laid-Open No. 63-130732, the titanium powder is finely powdered together with the mother alloy powder, but in order to finely powder the highly ductile titanium powder, extremely high energy is applied, It is necessary to strongly deform the titanium powder. Titanium powder that has undergone such strong deformation is significantly work-hardened, so the compressibility of the powder decreases, and a much higher molding pressure is required in order to increase the density of the compact, as compared with the ordinary method. Further, after further pulverization and further intense processing, the particle size increases again, but it is known that such a particle size-increased powder generally has a simple shape and is extremely inferior in moldability. Further, since titanium powder is active, it is unavoidable to take in a large amount of oxygen in the step of pulverizing the titanium powder, and there is a problem that mechanical properties after sintering, particularly ductility, are significantly reduced.

Further, all of these prior arts are directed to known alloy compositions developed for melt forging, and there is no disclosure of alloy compositions utilizing the features of the production method of the elementary powder mixing method. Not not.

Therefore, the inventors of the present invention have earnestly studied to solve the above-mentioned problems of the prior art, and as a result of various systematic experiments, the present invention has been accomplished.

(Object of the Invention) An object of the present invention is to provide a high-strength, inexpensive sintered titanium alloy and a method for producing the same.

The present inventors have focused their attention on the following problems of the prior art. That is, in the powder titanium mixed method sintered titanium alloy, as the essential conditions for strengthening without performing HIP treatment or heat treatment, residual pores are fine as they are as sintered, and slow cooling after sintering. Attention was paid to the fact that the microstructure is refined in the above state, and further, in order to obtain such a sintered body, the optimal combination of the alloy composition and the manufacturing process is indispensable.

Therefore, in order to satisfy the above conditions,
Instead of using the alloy composition developed for ordinary melting and forging as it is as in the prior art, use a raw material powder having an alloy composition suitable for the elementary powder mixing method, and in terms of the manufacturing process, By controlling the shape of the titanium powder and improving the packing density of the powder to a specified value, the residual pores can be made finer. In addition, it has been included in titanium, which has been treated as a troublesome component by the conventional method, which deteriorates the characteristics. The present invention was achieved by focusing on solving problems from an approach from a new perspective different from the conventional ones, such as positively utilizing the impurities and inclusions that are generated as a property improving / improving agent. .

[0018]

[Means for Solving the Problems]

(First invention) The sintered titanium alloy of the first invention is mass%,
Aluminum (Al) 4-8% and vanadium (V) 2
~ 6%, oxygen (O) 0.15 to 0.8%, at least boron (B) 0.2 to 5%, molybdenum (Mo), tungsten (W), tantalum (Ta), zirconium (Z
r), one or more of niobium (Nb) and hafnium (Hf) 0.5 to 3%, one or more of Ia group, IIa and IIIa group elements 0.05 to 2%, one or more of halogen group element 0.05
Contains one or more elements in a predetermined amount selected from ~ 0.5%, the balance consisting of titanium (Ti) and an unavoidable substance,
It is characterized by having a three-phase structure of α phase and β phase and at least one kind of particles of boride, oxide and halide.

(Second invention) A method for producing a sintered titanium alloy according to the second invention comprises mixing titanium powder and a strengthening mother alloy powder,
A method for producing an α + β type sintered titanium alloy by compacting and firing the compact without pressure, wherein the titanium powder is pressurized and rubbed together before the compacting, and the packing density of the raw material powder is It is characterized in that the uniform nucleation site is increased at the time of recrystallization of the titanium powder and / or the transformation from α to β, while maintaining a predetermined value.

[0020]

The mechanism by which the method for producing a sintered titanium alloy according to the first aspect of the invention and the method for producing a sintered titanium alloy according to the second aspect of the invention exhibit excellent effects is not clear yet, but it is considered as follows.

(Operation of the First Invention) In the present sintered titanium alloy, the Al content is 4 to 8 mass%. This Al
Is an element most commonly used as a strengthening element for titanium alloys, and has the roles of solid solution strengthening and α-phase stabilization. If the content is less than 4%, the strengthening effect is insufficient, and if it exceeds 8%, the ductility is extremely reduced.

The V content is 2 to 6 mass%. This V is also an element that is generally used as a strengthening element for titanium alloys and has the effects of solid solution strengthening and β-phase stabilization. When the content is less than 2%, the strengthening effect and β-stabilizing effect are insufficient, and when the content exceeds 6%, the β-stabilizing effect is too strong.

The O content is 0.15 to 0.8 mass%. This O is an element that lowers the ductility of the titanium alloy, and its upper limit value is usually strictly limited to about 0.15%. However, in the case of the elemental powder mixed method sintered titanium alloy,
The reason is not clear, but the ductility-lowering effect is small,
It is an effective element as a strengthening alloy component. The content is
If it is less than 0.15%, the strengthening effect is too small, and if it exceeds 0.8%, the ductility is extremely lowered even in the case of a sintered titanium alloy.

The content of B is 0.2 to 5 mass%.
This B hardly forms a solid solution in the titanium alloy, and therefore most of the B in the sintered body is finely dispersed in the matrix in the form of TiB (provided that even if a small amount of carbon coexists, it is Part may be replaced with TiB ₂ ). The fine TiB particles suppress the growth of β crystal grains during the sintering process and promote the uniform nucleation of the α phase during the cooling process after sintering. Due to these combined effects, the α phase in the sintered body structure becomes equiaxed, and the grain boundary α phase disappears. The content is
If it is less than 0.2%, the amount of TiB deposited is too small, and if it exceeds 5%, the amount of TiB deposited is too large to obtain sufficient ductility.

The content of Mo, W, Ta, Zr, Nb, and Hf is 0.5 to 3 mass% for one or more of them. All of these elements diffuse extremely slowly in the titanium alloy, lower the β transition temperature, and further lower the mobility of the β / α interface. It has the effect of significantly reducing the size. If the total content of at least one of these is less than 0.5%, the above effect is insufficient, and if it exceeds 3%, the homogenization of the components is insufficient in the sintering process, and the β transition temperature Is too low.

The content of the elements of group Ia, group IIa, and group IIIa is 0.05 to 2 mass% for one or more of them. These elements generally have a T bond strength with oxygen or a halogen group element.
Since it is stronger than i, it coexists with oxygen and halogen group elements in the titanium alloy, and most of them exist as oxides or halides. The oxide particles and the halide particles suppress the growth of β crystal grains in the sintering process and promote the uniform nucleation of the α phase in the cooling process after sintering. Due to these combined effects, the α phase in the sintered body structure becomes equiaxed, and the grain boundary α phase disappears. If the total content of one or more of these elements is less than 0.05%, the amount of oxides or halides deposited is too small, and if it exceeds 2%, the oxide particles or halide particles become coarse, and Its distribution is also non-uniform.

The content of one or more halogen group elements is 0.05 to 0.5 mass%. These elements combine with the elements of group Ia, group IIa, and group IIIa in the titanium alloy to form fine halides. The halide is NaCl, MgCl ₂ , CaCl ₂ , YCl ₃ ,
Examples thereof include KCl and BaCl ₂ . If the total content of one or more of these elements is less than 0.05%, the amount of halide precipitation is insufficient, and if it exceeds 0.5%, the halide grains become coarse, and their dispersion is also large. It becomes non-uniform and the ductility decreases.

Sintered titanium alloys containing the above elements are α
It has a three-phase structure of a phase, a β phase, and at least one kind of particles of boride, oxide, and halide. As described above, the three-phase structure eliminates the coarse needle-shaped α phase and the grain boundary α phase, which are one of the factors that reduce the fatigue strength, and has a uniform equiaxed α + β structure. From the above, it is considered that the sintered titanium alloy has high strength.

(Operation of the Second Invention) In the method for producing a sintered titanium alloy of the second invention, when an α + β type sintered titanium alloy is produced by pressureless firing, it comprises titanium powder and mother alloy powder for strengthening. Before molding the mixed powder, the titanium powder is pressed and rubbed to make the packing density of the raw material powder a predetermined value.

As described above, when the titanium powder is pressed and rubbed together, deformation causes the protrusions of the powder particles to be crushed and the surface to be smoothed. As a result, the fluidity of the powder is improved, the voids between the particles of the raw material powder are made fine, and the packing density is improved. When this powder is molded and sintered, the residual pores become extremely isolated and fine.

Further, by the above-mentioned processing, an appropriate strain energy is accumulated in the titanium powder and the number of uniform nucleation sites during sintering and / or transformation from α to β is increased, so that the initial β crystal grain size distribution is obtained. Are uniformed, the crystal grain growth rate in the β region (steady grain growth rate) is significantly reduced, and abnormal grain growth (secondary recrystallization) is suppressed. As a result, the β crystal grain size is unlikely to coarsen even during the long-term sintering process. If the workability of the titanium powder is too large, a lower structure (aggregate of dislocations) is formed, and the initial β crystal grain size distribution is likely to be nonuniform. When such an alloy is heated in the β region, the steady grain growth rate increases and abnormal grain growth easily occurs, resulting in the β crystal grains becoming significantly coarse, and a high-strength sintered body cannot be obtained. .

In addition, in general, a sintered titanium alloy using titanium powder having a high chlorine content may be used even after HIP.
It is known that even if the treatment is performed, coarse pores remain and the fatigue strength cannot be improved. For this reason, it has been conventionally considered that reducing the chlorine content is an essential condition for improving the mechanical properties of the sintered titanium alloy. However, the reason why coarse pores are formed when high chlorine titanium powder is used is
This is because coarse inclusion particles such as NaCl and MgCl ₂ exist instead of chlorine itself. Therefore, even the inexpensive high chlorine titanium powder is uniformly mixed with the titanium powder in the state in which the coarse inclusions are crushed and pulverized by performing the above-mentioned processing as in the present invention. From this, it is possible to remove the coarse residual pores which were considered to be inevitable in the material using the high chlorine titanium powder.

When cooled after sintering, the α phase nucleates from the β phase grain boundaries, but its growth is stopped by the β phase grain boundaries. Therefore, by suppressing the β-grain growth during sintering, it is possible to suppress the formation of coarse needle-shaped crystals as in the conventional case.

As described above, by pressing the titanium powder and rubbing it together, the packing density of the raw material powder is set to a predetermined value and the titanium powder is recrystallized and / or transformed from α to β. It is considered that a uniform nucleation site can be increased, and as a result, a sintered titanium alloy with high density and improved fatigue strength, in which residual pores are isolated and fine and the structure is fine, is obtained.

[0035]

【The invention's effect】

(Effect of First Invention) The sintered titanium alloy of the first invention is a high-strength sintered titanium alloy.

(Effect of the Second Invention) Even if an inexpensive titanium powder containing a large amount of impurities is used as a raw material by the method for producing a sintered titanium alloy according to the second invention, the cost is increased.
It is possible to obtain a titanium alloy having a high strength like an expensive ingot forged material by only sintering without performing P treatment or heat treatment. Therefore, the original cost merit of the sintered alloy can be fully exerted, and it can be applied to mass-produced products such as automobile parts where cost is the highest priority.

[0037]

EXAMPLES Specific examples of the first and second inventions will be described below.

First, the sintered titanium alloy of this example will be described below.

The sintered titanium alloy of the first specific example has a mass% of aluminum (Al) of 4 to 8% and vanadium (V) 2.
.About.6%, boron (B) 0.2 to 5%, and oxygen (O) 0.
It is characterized by containing 15 to 0.5%, the balance consisting of titanium and an unavoidable substance, and having a three-phase structure of α phase, β phase and boride particles.

The sintered titanium alloy of the first example is a high-strength, inexpensive sintered titanium alloy in which the α phase is equiaxed due to the presence of titanium boride particles. Further, when the aspect ratio is 2 or less, a sintered titanium alloy having higher strength can be obtained.

The sintered titanium alloy of the second specific example has a mass% of aluminum (Al) of 4 to 8% and vanadium (V) 2.
.About.6%, boron (B) 0.2 to 5%, and oxygen (O) 0.
15-0.5% and one or more of molybdenum (Mo), tungsten (W), tantalum (Ta), zirconium (Zr), niobium (Nb), hafnium (Hf) 0.5-
3%, and the balance consisting of titanium and unavoidable substances, α
It is characterized by having a three-phase structure of a phase, a β phase, and boride particles.

In the sintered titanium alloy of the second specific example, the α phase is equiaxed by the presence of titanium boride particles, and M
Owing to the presence of one or more substances of o, W, Ta, Zr, Nb, and Hf, the intragranular α phase is remarkably refined, and it is a sintered titanium alloy having higher strength and lower cost.

The sintered titanium alloy of the third specific example contains 4 to 8% by mass of aluminum (Al) and vanadium (V) 2.
.About.6%, oxygen (O) 0.25 to 0.8%, group Ia such as sodium (Na) and potassium (K), magnesium (Mg), calcium (Ca), strontium (S)
r) or the like, and at least one element selected from the group of the group IIIa elements such as scandium (Sc), yttrium (Y), and cerium (Ce), such as scandium (Sc), 0.05 to 2%,
The balance is composed of titanium and an unavoidable substance, and has a three-phase structure of α phase, β phase and oxide particles.

Most of the elements of Group Ia, Group IIa, and Group IIIa exist as oxides because they have a stronger bond with oxygen than Ti. The oxide particles suppress the growth of β-phase crystal grains and serve as a uniform nucleation site during β → α transformation, so that the intra-grain α phase is equiaxed and no grain boundary α phase is generated. Therefore, it is a sintered titanium alloy having higher strength and lower cost.

The sintered titanium alloy of the fourth specific example contains 4 to 8% by mass of aluminum (Al) and vanadium (V) 2.
.About.6%, boron (B) 0.2 to 5%, and oxygen (O) 0.
25 to 0.8% and one or more of molybdenum (Mo), tungsten (W), tantalum (Ta), zirconium (Zr), niobium (Nb), hafnium (Hf) 0.5 to 0.8%
3% and one or more elements of genus Ia, genus IIa, and genus IIIa.
It is characterized in that it has a three-phase structure of α phase, β phase, boride particles and oxide particles, with the balance comprising titanium and unavoidable substances.

In the sintered titanium alloy of the fourth specific example, the presence of fine titanium boron particles and oxide particles suppresses the growth of β-phase crystal grains, and these particles have β → α.
Since it becomes a uniform nucleation site at the time of transformation, the intragranular α phase is made equiaxed, and the grain boundary α phase is not generated. Therefore, it is a sintered titanium alloy having higher strength and lower cost.

The sintered titanium alloy of the fifth specific example contains 4 to 8% by mass of aluminum (Al) and vanadium (V) 2.
.About.6%, oxygen (O) 0.15 to 0.5%, and genus Ia,
Includes at least 0.05 to 2% of Group IIa and Group IIIa elements and at least 0.05 to 0.5% of Group Halogen elements,
The balance is composed of titanium and an unavoidable substance, and has a three-phase structure of α phase, β phase and halide grains.

The sintered titanium alloy of the fifth example is a sintered titanium alloy of higher strength and lower cost.

The sintered titanium alloy of the sixth specific example has a mass% of aluminum (Al) of 4 to 8% and vanadium (V) 2.
~ 6%, oxygen (O) 0.15 to 0.5%, molybdenum (Mo), tungsten (W), tantalum (Ta),
0.5 to 3% of one or more of zirconium (Zr), niobium (Nb), and hafnium (Hf), and Ia group, IIa group,
IIIa group element or more 0.05 to 2%, and halogen group element 1 or more 0.05 to 0.5%, the balance consisting of titanium and inevitable substances, α phase, β phase and halide grains And a three-phase structure of

The sintered titanium alloy of the sixth example is a sintered titanium alloy of higher strength and lower cost.

Here, a specific example of the microstructure of this sintered titanium alloy will be described with reference to FIGS.

FIG. 1 is a diagram schematically showing the structures of the sintered titanium alloys shown in the first concrete example, the third concrete example and the fifth concrete example. These alloys have equiaxed α and β phases,
And at least one kind of fine particles of titanium boride, oxide, and halide.

FIG. 2 is a diagram schematically showing the structures of the sintered titanium alloys shown in the second concrete example, the fourth concrete example and the sixth concrete example. These alloys are used in the first concrete example and the third concrete
Since the sintered titanium alloys shown in the concrete examples and the fifth concrete examples further contain one or more substances of Mo, W, Ta, Zr, Nb, and Hf, the first concrete example and the third concrete example. , The α phase is further miniaturized as compared with the fifth specific example.

FIG. 1 schematically shows the structure of an α + β type titanium alloy prepared by the conventional method. The alloy is composed of a grain boundary α phase along the old β grain boundary and coarse acicular α phase and β phase in the grain.

A preferred specific example of the method for producing a sintered titanium alloy of the second invention will be described.

A preferred method for producing the present sintered titanium alloy is, substantially in mass%, aluminum (Al) 4 to 8%,
Vanadium (V) 2-6% and oxygen (O) 0.15-
0.5%, at least boron (B) 0.2 to 5%, molybdenum (Mo), tungsten (W), tantalum (T
a), one or more of zirconium (Zr), niobium (Nb) and hafnium (Hf) 0.5 to 3%, Group Ia, IIa
Species, containing at least one element of a group IIIa of 0.05 to 2% and at least one element of halogen group of 0.05 to 0.5%, and a balance of titanium (T
i) and a step of preparing a raw material powder composed of titanium powder and a strengthening powder so as to become an unavoidable substance (a raw material powder preparation step), and pressing and rubbing the titanium powder among the raw material powders to prepare a raw material powder. A step (processing step) of increasing the packing density to a predetermined value and increasing the uniform nucleation site during recrystallization of the titanium powder and / or during the transformation from α to β, and a step of mixing the raw material powder ( Raw material powder mixing step) and a step of molding the mixed powder (molding step)
And a step of firing the molded body without pressure (sintering step)
And a method for producing a sintered titanium alloy.

Here, the titanium powder and the reinforcing powder are powders which are raw materials of the sintered titanium alloy. Titanium powder is
It is generally called pure titanium powder and may be of any kind. For example, (a) sponge fine, which is a by-product of sodium reduction sponge titanium,
(B) Hydrogenated and dehydrogenated titanium powder produced by hydrogenating → pulverizing → dehydrogenating magnesium reduction sponge titanium,
(C) Magnesium reduction method Three types of ultra-low chlorine titanium powder, which are produced by once dissolving titanium sponge titanium to remove impurities and then hydrogenating, pulverizing, and dehydrogenating, are typical.

Generally, the strengthening master alloy powder is produced by crushing an ingot produced by plasma melting or arc melting. Therefore, a composition that can be easily crushed is preferable. For example, Al-V and Al-V are used as alloys used for producing typical α + β alloys.
-Fe, Al-Sn-Zr-Mo, Al-V-Sn, A
A basic alloy composition including l-Fe and the like is known. In this specific example, the raw material powder is substantially mass%, aluminum (Al) 4 to 8, vanadium (V) 2 to 6, oxygen (O) 0.15 to 0.5, and at least boron (B). ) 0.
2 to 5, molybdenum (Mo), tungsten (W), tantalum (Ta), zirconium (Zr), niobium (N
b), one or more of hafnium (Hf) 0.5 to 3, Ia
A predetermined amount of one or more elements selected from the group consisting of genus, genus IIa, one or more elements of group IIIa 0.05 to 2 and one or more elements of halogen group 0.05 to 0.5, and the balance titanium (Ti) In order to become an unavoidable substance, a predetermined substance is added, or an alloy is prepared in advance so as to prepare a powder for strengthening by an appropriate method and form. For example, there is a method of producing an alloy having a predetermined composition or adding a necessary substance in the form of boride powder, oxide powder, halide powder, or pure metal powder.

Here, the reason why the preferable composition of the raw material and the limitation of the numerical range are limited will be described below.

The amount of Al added is 4 to 8 mass%. This Al is the most general element as a strengthening element for titanium alloys, and has the roles of solid solution strengthening and α-phase stabilization. If the addition amount is less than 4%, the strengthening effect is insufficient,
If it exceeds 8%, the ductility is extremely reduced.

The amount of V added is 2 to 6 mass%. This V is also an element that is generally used as a strengthening element for titanium alloys and has the effects of solid solution strengthening and β-phase stabilization. If the amount added is less than 2%, the strengthening action and β-stabilizing action are insufficient, and if it exceeds 6%, the β-stabilizing action is too strong.

The amount of O added is 0.15 to 0.8 mass%. This O is an element that lowers the ductility of the titanium alloy, and its upper limit value is usually strictly limited to about 0.15%. However, in the case of the elemental powder mixed method sintered titanium alloy,
The reason is not clear, but the ductility-lowering effect is small,
It is an effective element as a strengthening alloy component. The amount added is
If it is less than 0.15%, the strengthening effect is too small, and if it exceeds 0.8%, the ductility is extremely lowered even in the case of a sintered titanium alloy.

The amount of B added is 0.2 to 5 mass%.
This B hardly forms a solid solution in the titanium alloy, and therefore most of the B in the sintered body is finely dispersed in the matrix in the form of TiB (provided that even if a small amount of carbon coexists, it is Part may be replaced with TiB ₂ ). The fine TiB particles suppress the growth of β crystal grains during the sintering process, and promote the nucleation of the α phase during the cooling process after sintering. Due to these combined effects, the α phase in the sintered body structure becomes equiaxed, and the grain boundary α phase disappears. When the addition amount is 0.
If it is less than 2%, the TiB precipitation amount is too small, and if it exceeds 5%, the TiB precipitation amount is too large, and sufficient ductility cannot be obtained.

The addition amount of Mo, W, Ta, Zr, Nb, and Hf is 0.5 to 3 mass% for one or more of them. All of these elements diffuse extremely slowly in the titanium alloy, lower the β transition temperature, and further lower the mobility of the β / α interface. It has the effect of significantly reducing the size. If the total amount of one or more of these added is less than 0.5%, the above effect is insufficient, and if it exceeds 3%, the homogenization of the components becomes insufficient during the sintering process, and the β transition temperature Is too low.

Group Ia such as sodium (Na) and potassium (K), magnesium (Mg), calcium (C)
a), Group IIa such as strontium (Sr), scandium (Sc), yttrium (Y), cerium (Ce)
The addition amount of the group IIIa element such as 1 or more is 0.
It is 05-2 mass%. Since these elements generally have a stronger binding force with oxygen and halogen group elements than Ti, when they coexist with oxygen or halogen group elements in the titanium alloy, most of them become oxides or halides.
The oxide particles suppress the growth of β crystal grains during the sintering process and promote the nucleation of the α phase during the cooling process after sintering. Due to these combined effects, the α phase in the sintered body structure becomes equiaxed, and the grain boundary α phase disappears. If the total amount of one or more of these elements added is less than 0.05%, the amount of precipitated oxides or halides is too small, and if it exceeds 2%, the oxide particles or halide particles become coarse, and Its distribution is also non-uniform.

The amount of the halogen group element added is 0.05 to 0.5 mass% for one or more of them. These elements have a role of forming fine halides by combining with elements of group Ia, group IIa, and group IIIa in the titanium alloy. The halide grains suppress the growth of β crystal grains during the sintering process and promote the nucleation of the α phase during the cooling process after sintering. Due to these combined effects, the α phase in the sintered body structure becomes equiaxed, and the grain boundary α phase disappears. If the total amount of one or more of these elements added is less than 0.05%, the precipitation amount of the halide is insufficient, and if it exceeds 0.5%, the halide grains become coarse, and their dispersion is also large. It becomes non-uniform and the ductility decreases.

As a preferable raw material powder, a raw material powder composed of titanium powder and a strengthening mother alloy powder is prepared so that the compositions of the first to sixth specific examples of the sintered titanium alloy are practically obtained. By doing so, a more excellent effect can be achieved.

The fatigue strength of a sintered titanium alloy is determined by the amount of residual voids (density), the size of the residual voids, the strength of the alloy itself, the notch susceptibility of the alloy (the likelihood of fatigue cracking). ) Etc. The amount of residual voids is determined by the density of the compact and the sinterability, and the size of the residual voids is determined by the particle size of the raw material powder, the filling property of the powder, and the sinterability. If the particle size of the titanium powder is too large, coarse pores that reduce the fatigue strength tend to be generated, while if the average particle size of the strengthening mother alloy powder is large, the sinterability will decrease and sufficient sintering will occur. Body density cannot be obtained. Therefore, it is preferable that the maximum particle size of the titanium powder is 150 μm or less and the average particle size of the strengthening master alloy powder is 10 μm or less.

Next, in the processing step, the titanium powder is pressed to some extent and the titanium powder is rubbed together.
The filling rate (filling density) of titanium powder is set to a predetermined value. By this step, the projections of the individual particles of titanium powder are crushed and the surface is smoothed. Therefore, the fluidity of the powder is improved, and the desired packing density can be achieved.

The packing density of the powder depends on the particle size distribution and the particle shape of the powder. That is, it is desirable that the particle size distribution be such that there is an appropriate amount of small and medium particles having the optimum particle size to fill the voids of the coarse particles, but even if the particle size distribution is optimum, if the fluidity of the powder is poor, the packing rate of the powder will be low. Does not improve. In the case of sponge fine, the powder has a porous and amorphous shape and has extremely poor fluidity, so the packing density is about 1.5 g / cm ³ . In addition, the hydrogenated / dehydrogenated titanium powder has a square shape because it is a crushed powder, and although it is slightly superior to sponge fine, its fluidity is significantly inferior to ordinary atomized powder. It is about 2.0 g / cm ³ at most. Even if the raw material powder is formed in such a state, the particles hardly move due to the frictional force between the particles and are deformed as they are, so that coarse pores are easily formed in the molded body.
Further, when this molded body is fired, coarse pores are inherited in the sintered body, which easily becomes a starting point of fatigue fracture. Even if the molding pressure is increased to improve the density, it is difficult to make the residual pores in the sintered body fine. In order to improve the fluidity of these powders, it is necessary to change the shape of the powders by the main processing step so that the powders have a packing density of the predetermined value.

In this step, 15% or more, more preferably 30% or more, when sponge fine is used as the titanium powder, based on the titanium powder currently on the market.
When the hydrogenated / dehydrogenated titanium powder or the ultra-low chlorine titanium powder is used, it is preferable to deform the titanium powder by 20% or more so as to improve the packing density.

The packing density is 2.0 g / cm ^{3 to} 3.0 g /
It is preferably cm ³ . When the packing density is within this numerical range, it can have appropriate fluidity and tap density. If the packing density is less than 2.0 g / cm ³ , the coarse pores cannot be completely eliminated, so that the fatigue fracture strength of the sintered body cannot be sufficiently improved, and 3.0 g / cm ³ If it exceeds cm ³ , the powder formability is remarkably reduced, which is not preferable.

When sponge fine is used as the titanium powder, the packing density of the powder is 2.0 g / cm ^{3 to} 2.5.
When the hydrogenated / dehydrogenated titanium powder or the ultra low chlorine titanium powder is used, the packing density of the powder is 2.3 to g / cm ^3.
It is preferable to give processing so that the amount becomes 3.0 g / cm ³ . As a result, the diameter of 50μ, which can be the starting point of fatigue fracture
Coarse vacancies of m or more can be eliminated, and at most 2
It is possible to make independent pores of about 0 μm. Than this,
Mechanical properties, especially ductility and fatigue strength, are significantly improved.

Moreover, by setting the filling rate within the above numerical range, it is possible to prevent the individual pores from coarsening even when the molding pressure is lowered and a large number of pores remain.
In addition, it is preferable that the above-mentioned processing is given only to titanium powder because contamination of the powder can be avoided, but in some cases, even if it is performed on a mixture of titanium powder and strengthening mother alloy powder, high A strong and inexpensive sintered titanium alloy can be obtained.

As a method of giving the above-mentioned processing, there are the following methods. That is, this step is a light processing such as smoothing the protrusions on the powder surface or crushing agglomerated powder such as sponge fine. For example, the raw material powder is placed in a ball mill or an attritor containing steel balls. It is carried out by, for example, a method of charging and stirring for a very short time (1 to 20 min.). By such a treatment, the titanium powder is rubbed against each other, and the projections thereof are pressed and flattened. In addition,
As will be described repeatedly, crushing and refining the titanium powder particles and subjecting the titanium powder to strong working that causes remarkable work hardening must be avoided because the compressibility decreases and the oxygen content also increases.

For mixing the raw material powders in the raw material powder mixing step, a device such as a ball mill or a V-type mixer is used.
Any mixing method may be used.

In the molding step, as a method of molding the raw material powder that has been subjected to the above-mentioned processing, die press molding, CIP
(Cold isostatic press) There are methods such as molding.

In the sintering step, the molded body is fired. Considering the densification of the sintered body, homogenization of the alloy composition, durability of the furnace, economic efficiency, etc., the firing temperature and firing time are 1
The range of 000 to 1350 ° C. and 1 to 20 hours is desirable.
Further, as the firing atmosphere, the titanium alloy is liable to react with the atmosphere gas (oxygen, nitrogen, other reducing gas), so that it should be in a vacuum of 10 ^-3 torr or more or in an inert gas such as argon or helium. Good.

Generally, the structure of α + β type titanium alloy has a mesh-like grain boundary α along the old β grain boundary in the state of being gradually cooled after sintering.
Phase and coarse acicular α phase in old β grains. However, as in the method of this specific example, trace components (boron, oxygen,
(Ia group, IIa group, IIIa group element, halogen group element) are appropriately combined and added, and boride, oxide, or halide particles are finely precipitated in the matrix, and these are β crystal grains in the sintering process. It suppresses the coarsening of Al and facilitates the nucleation of α phase during β → α transformation during cooling. As a result, in the microstructure after cooling, the α phase becomes equiaxed and the grain boundary α phase disappears.

Further, specific transition metal elements (Mo, W, T
a, Zr, Nb, Hf) are extremely slow in diffusion in the titanium alloy, lower the β transition temperature, and further lower the mobility of the β / α interface. It has the effect of significantly refining the phase.

Further, among the alloying elements, oxygen is an element that reduces ductility, and efforts have been made so far to keep it as low as possible. However, in the sintered titanium alloy prepared by the raw powder mixing method, although the reason is not clear, the allowable amount (0.
It is an important alloying element that can be strengthened without lowering the ductility even if it is contained in about 15% or more).

Examples of the present invention will be described below.

First Embodiment 100 mesh high chlorine pure titanium powder (sponge fine; Ti: 99.6%, O: 0.1%, Cl: 0.1%, N
a: 0.08%) is charged into an attritor together with a steel ball,
After processing for 10 minutes, Al-40% V powder having an average particle size of 7 μm was mixed in the ratio of titanium powder: Al-40% V powder = 9: 1 (weight ratio). At this time, the packing density of the Ti powder after the processing was 2.30 g / cm ³ , which was an improvement of 43%.

Then, the mixture was subjected to CIP at a pressure of 4 ton / cm.
^The molded body obtained in Example 2 was sintered in a vacuum of 10 ⁻⁵ torr at 1300 ° C. for 4 hours to obtain a sintered titanium alloy according to this example (Sample No. 1). Incidentally, FIG. 4 shows S showing the particle structure of the titanium powder after the above-mentioned processing treatment.
An EM (scanning electron microscope) photograph (magnification: 500 times) and an optical microscope photograph (magnification: 200 times) showing the metal structure of the produced sintered body are shown in FIG. 5, respectively. As is clear from FIG. 4, it is found that the titanium powder of the present example is subjected to appropriate deformation in the powder due to processing and the irregularities are reduced. Further, as is clear from FIG. 5, in the sintered titanium alloy obtained in this example, the residual pores are made finer and the α phase is equiaxed.

Second Embodiment 100 mesh low chlorine pure titanium powder (hydrogenated / dehydrogenated titanium powder; Ti: 99.8%, O: 0.2%, Cl: 0.
(01%) and 0.2% of Y ₂ O ₃ powder were charged into an attritor together with steel balls, and processed for 10 minutes. Two types of titanium powder were used, one having an average particle size of 60 μm (sample number: 2) and one having an average particle size of 80 μm (sample number: 3). The packing density of the Ti powder after processing at this time was 2.7 g / cm ³ , which was an improvement of 24%. Then, Al-40% V powder having an average particle size of 7 μm was mixed at a ratio (weight ratio) of titanium powder: Al-40% V powder = 9: 1. Then, a sintered titanium alloy according to this example was manufactured by the same forming / sintering method as in the first example (sample numbers: 2 and 3).

Third Embodiment Low chlorine pure titanium powder (average particle size 6
0 .mu.m) and a 0.2% YCl ₃ powder was treated by the same processing as in the first embodiment, this 10% Al-40
% V powder. Then, the mixture was molded and fired in the same manner as in Example 1 to produce a sintered titanium alloy according to this example (Sample No. 4).

Fourth Embodiment Low chlorine pure titanium powder (average particle size 8
0 μm) was processed by the same method as in the first embodiment, to which 0.2% YCl ₃ powder and 10% Al-40 were added.
% V powder. Then, the mixture was molded and fired in the same manner as in Example 1 to produce a sintered titanium alloy according to this example (Sample No. 5).

Fifth Example The same high chlorine pure titanium powder as in the first example was treated in the same manner as in the first example, to which 0.5% TiB ₂ powder and 1% Mo powder were applied. And 10% Al-40% V powder were mixed. Then, the mixture was molded and fired in the same manner as in Example 1 to produce a sintered titanium alloy according to this example (Sample No. 6). An optical micrograph (magnification of 200) showing the metal structure of the produced sintered body is shown in FIG.
Indicates. As is clear from FIG. 6, the sintered titanium alloy obtained in this example has finer residual pores and a significantly finer structure than the sintered titanium alloy of the first example. I understand.

Sixth Embodiment The same low chlorine pure titanium powder as in the second embodiment was treated in the same manner as in the first embodiment, to which 0.2% YCl ₃ powder and 1% W powder were applied. And 10% Al-40% V powder were mixed. Then, the mixture was molded and fired in the same manner as in Example 1 to produce a sintered titanium alloy according to this example (Sample No. 7).

Seventh Example -100 mesh low chlorine pure titanium powder (hydrogenated / dehydrogenated titanium powder; Ti:
99.8%, O: 0.3%, Cl, 0.01%) was treated in the same manner as in the first example, and 10% Al-4 was added thereto.
0% V-2% Ca powder was mixed. After that, the mixture was molded and fired in the same manner as in Example 1 to produce a sintered titanium alloy according to this example (Sample No. 8).

Eighth Example The same high oxygen and low chlorine pure titanium powder as in the seventh example was treated in the same manner as in the first example, and 1% Mo was added thereto.
The powder was mixed with 10% Al-40% V-2% Ca powder. Then, the mixture is molded in the same manner as in the first embodiment,
Firing was performed to produce a sintered titanium alloy according to this example (sample number: 9).

First Comparative Example The same high chlorine pure titanium powder as in the first example was mixed with Al-40% V powder having an average particle size of 40 μm. The mixture was molded and fired in the same manner as in Example 1 without any processing, to produce a comparative sintered body (Sample No. C1). It is to be noted that FIG. 7 is a SEM photograph (magnification: 500 times) showing the particle structure of the titanium powder, and FIG. 8 is an optical micrograph (magnification: 20) showing the metal structure of the produced sintered body.
0 times each). As is clear from FIG. 7, it is found that the titanium powder is highly uneven and that there are many voids between the particles. Further, as is clear from FIG. 8, the residual pores of the comparative sintered body are coarse and the amount thereof is large, and the α phase is coarse acicular crystals.

Second Comparative Example The same high chlorine pure titanium powder as in the first example was mixed with Al-40% V powder having an average particle size of 7 μm. Molding the mixture in the same manner as in the first embodiment, without processing.
Firing was performed to manufacture a comparative sintered body (sample number: C2).

Third Comparative Example The same low chlorine pure titanium powder as in the second example was mixed with Al-40% V powder having an average particle size of 40 μm. The mixture was molded and fired in the same manner as in Example 1 without any processing, to produce a comparative sintered body (Sample No. C3).

Fourth Comparative Example The same low chlorine pure titanium powder as in the second example was mixed with Al-40% V powder having an average particle size of 7 μm. Molding the mixture in the same manner as in the first embodiment, without processing.
Firing was performed to manufacture a comparative sintered body (Sample No. C4).

Fifth Comparative Example The same high chlorine pure titanium powder as in the first example and Al-40% V powder having an average particle size of 7 μm were placed in an attritor together with a steel ball and processed for 60 minutes. went. afterwards,
The mixture was molded and fired in the same manner as in Example 1 to produce a comparative sintered body (Sample No. C5). In addition, in FIG.
S showing the particle structure of the mixed powder after performing the above-mentioned processing
An EM photograph (magnification: 500 times) is shown in FIG. 10, and an optical microscope photograph (magnification: 200 times) showing the metal structure of the produced comparative sintered body is shown in FIG. As is clear from FIG. 9, the powder of this comparative example was processed for too long,
The powder was remarkably strongly processed and the whole powder was flattened, and the packing density of the powder was 1.50 g / cm ^3, which was as low as the raw powder. Further, as is clear from FIG. 10, in the comparative sintered titanium alloy obtained by this comparative example, not only the residual pores became coarse and the density also decreased to 98.0%, but also this comparative example. Is excessively hard-processed to lose the excellent characteristics of the present invention.

Characteristic Evaluation Test of Sintered Body The packing density, structure, tensile strength and fatigue of the sintered bodies obtained by the above-mentioned first to seventh examples and the first to fifth comparative examples. Various properties such as strength were measured. The result is
It shows in FIG. As is clear from FIG. 7, the sintered body of this example is superior in properties such as density, tensile strength, elongation, and fatigue strength to those of the comparative example.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing the structure of a sintered titanium alloy in one specific example of the present invention.

FIG. 2 is an explanatory view schematically showing the structure of another sintered titanium alloy in one specific example of the present invention.

FIG. 3 is an explanatory diagram schematically showing the structure of an α + β type sintered titanium alloy obtained by a conventional method.

FIG. 4 is a SEM photograph showing the particle structure of titanium powder after the processing treatment in the first embodiment of the present invention (magnification:
500 times).

FIG. 5 is an optical micrograph showing the metal structure of the sintered titanium alloy obtained in the first example of the present invention (magnification: 20).
0 times).

FIG. 6 is an optical microscope photograph (magnification: 20) showing the metal structure of the sintered titanium alloy obtained in the fifth example of the present invention.
0 times).

FIG. 7 is an SEM photograph (magnification: 500 times) showing a particle structure of titanium powder in the first comparative example.

FIG. 8 is an optical micrograph (magnification: 200 times) showing a metal structure of a comparative sintered body manufactured in a first comparative example.

FIG. 9 is a SEM photograph (magnification: 500 times) showing a particle structure of a mixed powder after processing in a fifth comparative example.

FIG. 10 is an optical micrograph (magnification: 200 times) showing a metal structure of a comparative sintered body manufactured in a fifth comparative example.

FIG. 11 is a diagram showing performance evaluation test results of the sintered bodies obtained in the first to eighth examples of the present invention and the first to fifth comparative examples.

[Explanation of symbols]

1 ... α phase 2 ... β phase 3 ... Boride particles or oxide particles or halide particles 4 ... Grain boundary α phase 5 ... Intra-grain α phase

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C22F 1/18 H 9157-4K

Claims (2)

[Claims] 1. Aluminum (Al) 4 to 8 in mass%
%, Vanadium (V) 2 to 6%, and oxygen (O) 0.1
5 to 0.8%, at least boron (B) 0.2 to 5%, molybdenum (M
o), tungsten (W), tantalum (Ta), zirconium (Zr), niobium (Nb), hafnium (Hf)
A predetermined amount selected from the group consisting of one or more of 0.5 to 3%, one or more of Ia, IIa and IIIa elements of 0.05 to 2% and one or more of halogen elements of 0.05 to 0.5%. Containing one or more elements, the balance consisting of titanium (Ti) and unavoidable substances, and having a three-phase structure of α phase and β phase and at least one or more particles of boride, oxide and halogen Sintered titanium alloy characterized by. 2. A method for producing an α + β type sintered titanium alloy by mixing and molding titanium powder and strengthening mother alloy powder and firing the molded body without pressure, wherein before the molding. The titanium powder is rubbed while being pressed, and the packing density of the raw material powder is set to a predetermined value and the number of uniform nucleation sites during the recrystallization of the titanium powder and / or the transformation from α to β is increased. A method for producing a sintered titanium alloy, which is characterized.