KR20170122083A - Precipitation hardening titanium alloy with high strength and high ductility and method of manufacturing the same - Google Patents

Abstract

Disclosed are a precipitation hardening titanium alloy with high strength and high ductility and a method of manufacturing the same. According to the present invention, the method of manufacturing the precipitation hardening titanium alloy with high strength and high ductility comprises the following processes of: homogenizing a titanium alloy base material containing Al and Fe at over transformation temperature; cooling the titanium alloy base material in a first temperature area under the transformation temperature for a compound in TiFe metal in the first temperature area to be extracted on an interface of -phase and -phase; and increasing fraction of the -phase by raising a temperature in a second temperature area higher than the first temperature area.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength and high ductility titanium alloy,

TECHNICAL FIELD The present invention relates to a titanium alloy manufacturing technique, and more particularly, to a precipitation hardening type high strength and high ductility titanium alloy and a manufacturing method thereof.

In the titanium industry, studies are underway to develop new alloys utilizing titanium scrap or low-cost elements to lower the price of titanium or titanium alloys.

When titanium scrap is utilized, the mechanical properties and workability of the scrap may be deteriorated due to impurities such as oxygen, carbon, nitrogen and hydrogen contained in the scrap. Particularly in titanium, oxygen is a very important alloying element. When the amount is more than 1,000 ppm, the brittleness increases, and the elongation and toughness are adversely affected.

Recently, a high-strength titanium alloy (Patent Document 1) has been developed which has excellent oxidation resistance and moldability. Here, instead of expensive vanadium (V), high-strength characteristics are obtained while lowering the? Transformation temperature by using iron (Fe) .

However, Ti-Al-Fe alloys have problems in that the TiFe intermetallic compound precipitates during the heat treatment process, particularly when aging at a specific temperature for a long time, deteriorates the mechanical properties.

Patent Document 1: Korean Patent No. 10-1387551 (Announcement of Apr. 24, 2014)

An object of the present invention is to provide a Ti-Al-Fe-based alloy which is produced by producing an alloy having mechanical strength equal to or higher than that of a commercial Ti-6Al-4V alloy by using scrap having a high oxygen content and iron as a low- And a method for producing a titanium alloy having excellent physical properties by controlling the precipitation of an intermetallic compound of TiFe that occurs in a molding process.

The present invention also provides a precipitation hardening type high strength and high ductility titanium alloy.

In order to accomplish the above object, a method of manufacturing a titanium alloy according to the present invention includes a homogenization step, a TiFe intermetallic compound interface precipitation step, and a β phase fraction increasing step.

In the homogenization step, a titanium alloy base material containing Al and Fe is homogenized at a beta transformation temperature or higher.

In the TiFe intermetallic compound interface precipitation step, the homogenized product is cooled to a first temperature range below the? Transformation temperature, and the TiFe intermetallic compound is precipitated at the? -Phase and? -Phase interface in the first temperature range.

In the β phase fraction increasing step, the result of precipitation of the TiFe intermetallic compound is increased to a second temperature region higher than the first temperature region to increase the β phase fraction.

At this time, at least a part of the TiFe intermetallic compound precipitated at the interface between the? -Phase and the? -Phase can be precipitated into the? -Phase in the? Phase fraction increasing step in the TiFe intermetallic compound interface precipitation step.

On the other hand, the titanium alloy base material may include 3.0 to 5.0% of Al, 2.0 to 4.0% of Fe, and 0.3 to 0.5% of O, with the balance being Ti and unavoidable impurities. In this case, the first temperature range may be 500 to 700 ° C, and the second temperature range may be 750 to 850 ° C.

Further, the alloy base material can be manufactured by a solution treatment of a semi-finished titanium alloy containing Al and Fe, refining the crystal grains, and hot rolling in the? +? Region. In addition, the semi-finished alloy may be manufactured from a titanium alloy scrap.

In order to achieve the above object, the titanium alloy according to an embodiment of the present invention includes 3.0 to 5.0% of Al, 2.0 to 4.0% of Fe, and 0.3 to 0.5% of O, Wherein the number of TiFe intermetallic compounds precipitated in the? Phase is larger than the number of TiFe intermetallic compounds precipitated in the? Phase.

At this time, the volume fraction of the beta phase may be larger than the volume fraction of the alpha phase.

The titanium alloy may have a tensile strength of 1090 to 1140 MPa, a yield strength of 950 to 1010 MPa, and an elongation of 18 to 20%.

The titanium alloy manufacturing method according to the present invention controls the precipitation of the TiFe intermetallic compound generated in the forming process of the Ti-Al-Fe alloy by using the? Phase fraction increasing. As a result, mechanical property can be improved by allowing the TiFe intermetallic compound to precipitate in the? Phase through? Phase fraction increase.

As a result, the titanium alloy according to the present invention can exhibit mechanical strength equal to or higher than that of a commercially available Ti-6Al-4V alloy, while being manufactured using scrap having a high oxygen content and iron as a low-cost element as alloying elements.

Fig. 1 shows the coarse TiFe precipitate shape and diffraction pattern analysis results formed on the? /? Interface of the titanium alloy.
FIG. 2 is a schematic view showing improvement in mechanical properties of a titanium alloy having an α-phase and a β-phase using TiFe precipitation control.
FIG. 3 is a schematic view illustrating a method of manufacturing a titanium alloy using TiFe precipitation by increasing a? Phase fraction according to the present invention.
Fig. 4 shows the tensile test results at room temperature for the specimens 1 to 4, which are Ti-Al-Fe-O based titanium alloys prepared by the method according to the present invention.
FIG. 5 shows the tensile test results at room temperature for a specimen 5, which is a Ti-Al-Fe-based titanium alloy manufactured by the method according to the comparative example.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a precipitation hardening type high strength and high ductility titanium alloy according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 shows the coarse TiFe precipitate shape and diffraction pattern analysis results formed on the? /? Interface of the titanium alloy.

When the annealing is performed at a temperature of about 700 ° C or less, a Ti-Al-Fe-O based alloy has a spherical TiFe intermetallic compound precipitate phase of about B2 nm Can be seen.

When such a TiFe intermetallic compound precipitation phase is formed at the interface between the α-phase and the β-phase of the titanium alloy, there is a high possibility of interface fracture.

The inventors of the present invention have conducted extensive studies on inducing TiFe intermetallic compound to precipitate into the? Base in order to suppress the possibility of interfacial destruction as described above.

FIG. 2 is a schematic view showing improvement in mechanical properties of a titanium alloy having an α-phase and a β-phase using TiFe precipitation control.

As shown in the example of FIG. 2, when the volume fraction of the β phase is increased, a part of the TiFe intermetallic compound formed at the interfaces between the α-phase and the β-phase is induced to precipitate into the β-phase. Thus, the amount of the TiFe intermetallic compound precipitated at the interface between the? -Phase and the? -Phase can be reduced. As a result, strength and ductility can be improved.

A method of manufacturing a titanium alloy according to the present invention using the above principle is as follows.

FIG. 3 is a schematic view of a method for manufacturing a titanium alloy using TiFe precipitation by controlling the? Phase fraction according to the present invention.

The method of producing a titanium alloy according to the present invention includes a homogenization step, a TiFe intermetallic compound interface precipitation step and a? Phase fraction increasing step.

First, in the homogenization step, an alloy base material containing 3.0 to 5.0% of Al, 2.0 to 4.0% of Fe and 0.3 to 0.5% of O and the balance of Ti and unavoidable impurities is homogenized at a β transformation temperature or more do. More specifically, the homogenization can be performed at a temperature of about 1000 캜 or higher, more preferably 1000 to 1100 캜.

For example, a semi-product alloy such as ingot, billet and the like having the above alloy composition is subjected to solution treatment at about 1050 DEG C, and the crystal grains are finely refined by a method such as crushing, . ≪ / RTI > In addition, the semi-finished alloy may be made from titanium alloy scrap.

Hereinafter, components included in the alloy base material for producing the titanium alloy according to the present invention will be described.

Al: 3.0 to 5.0 wt%

In titanium alloys, Al is added to improve oxidation resistance and creep characteristics. However, excessive addition of Al is a factor for reducing ductility and moldability of the titanium alloy. In the case of a commercially available Ti-6Al-4V alloy, about 6 wt% of Al is contained, but in this case, the moldability may be adversely affected. In order to improve the molding performance, the content of Al is reduced to 3.0 to 5.0% by weight in the present invention. When the Al content is less than 3.0% by weight, it is difficult to secure sufficient oxidation resistance and creep characteristics. On the other hand, when the content of Al exceeds 5% by weight, it may be difficult to achieve an elongation of 18% or more.

Fe: 2.0 to 4.0 wt%

In the present invention, Fe is added in an amount of 2.0 to 4.0% by weight in order to lower the? Transformation temperature, which determines an important forming temperature in a titanium alloy, using iron (Fe) which is inexpensive instead of expensive vanadium (V) as an alloy element.

O: 0.3 to 0.5 wt%

In addition, in the present invention, the alloy base material can utilize titanium scrap as described above. In the case of titanium scrap, the content of oxygen (O) is inevitably high, and when the deoxidation process for lowering the oxygen content is accompanied, the cost of the titanium alloy is increased accordingly. Therefore, in the present invention, Was set in the range of 0.3 to 0.5 wt%. However, when the oxygen content exceeds 0.5% by weight, it is difficult to ensure elongation and toughness of the titanium alloy to be produced because the brittleness is greatly increased.

Next, in the TiFe intermetallic compound interface precipitation step, the homogenized product is cooled to a first temperature region below the &bgr; transformation temperature, and then maintained in the first temperature region for a certain period of time. As a result, the TiFe intermetallic compound precipitates at the interface between the alpha phase and the beta phase, as shown in the example shown in Fig.

Since the TiFe intermetallic compound precipitated at the interface between the α-phase and the β-phase increases the possibility of interfacial breakage, it is desirable to lower the possibility of interfacial breakage. Accordingly, in the present invention, by increasing the β- The amount of the TiFe intermetallic compound precipitated at the interface between the TiFe layer and the TiFe layer was reduced.

Next, in the β phase fraction increasing step, the result of precipitation of the TiFe intermetallic compound is increased to a second temperature region higher than the first temperature region to increase the β phase fraction. The higher the temperature, the larger the β phase fraction increasing effect can be, and the longer the time in the second temperature range, the larger the β phase fraction increasing effect can be. However, the second temperature range is lower than the? Transformation temperature.

As a result of the increase of the? Phase fraction, at least a part of the TiFe intermetallic compound precipitated at the? -Phase and? -Phase interface can be precipitated into? Phase as shown in FIG. As a result, as a result, the TiFe precipitated phase can be uniformly distributed in each of the? -Phase and the? -Phase.

In this case, the first temperature range may be 500 to 700 ° C, and the second temperature range may be 750 to 850 ° C. What is important is the second temperature region. When the lower limit of the second temperature region is less than 700 占 폚, there is almost no? Phase increase effect. However, when the second temperature region is set to 750 캜, a sufficient and reproducible? -Phase increase effect can be obtained. That is, the difference between the first temperature region and the second temperature region must be at least 50 ° C or more, the driving force of the interfacial diffusion can be increased. On the other hand, when the upper limit of the second temperature range exceeds 850 占 폚, the? -Phase fraction fraction becomes too small to exhibit undesired property deterioration.

The titanium alloy produced by the above process contains 3.0 to 5.0% of Al, 2.0 to 4.0% of Fe, and 0.3 to 0.5% of O, and has a microstructure including alpha -phase and beta -phase .

The titanium alloy according to the present invention is characterized in that the TiFe intermetallic compound precipitate is controlled by the β phase increase as described above, whereby the number of TiFe intermetallic compounds precipitated in the β phase is reduced to the TiFe intermetallic phase It is characterized by more than the number of compounds.

Further, the titanium alloy according to the present invention may have a volume fraction of the beta phase larger than a volume fraction of the alpha phase. The volume fraction of the β phase can be adjusted according to the temperature and time at which the β phase fraction increasing step is carried out. That is, the higher the temperature at which the β-phase fraction increase is performed or the longer the β-phase fraction increase is performed, the greater the β-phase volume fraction can be.

The titanium alloy according to the present invention may exhibit a tensile strength of 1090 to 1140 MPa, a yield strength of 950 to 1010 MPa and an elongation of 18 to 20% in terms of mechanical properties.

The titanium alloy manufacturing method according to the present invention controls the precipitation of the TiFe intermetallic compound generated in the forming process of the Ti-Al-Fe alloy by using the? Phase fraction increasing. As a result, mechanical property can be improved by allowing the TiFe intermetallic compound to precipitate in the? Phase through? Phase fraction increase.

As a result, the titanium alloy according to the present invention can exhibit mechanical strength equal to or higher than that of a commercially available Ti-6Al-4V alloy, while being manufactured using scrap having a high oxygen content and iron as a low-cost element as alloying elements.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense. The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Preparation of Titanium Alloy Specimens

Using an induction scull melting furnace which is easy to produce an alloy of homogeneous composition, it was made into an ingot shape comprising the alloy composition shown in Table 1 and the remaining Ti and inevitable impurities.

[Table 1] (unit:% by weight)

Psalm 1 ~ 4 (Illustrated)

The ingot was subjected to a solution treatment at 1,050 ° C, followed by an ingot crushing process for grain refinement, followed by hot rolling in the α + β region of the alloy to produce a plate having a final thickness of 3 mm. After homogenization and processing at about 1050 占 폚, which is not less than the? Transformation temperature of the alloy, annealing treatment was performed at 600 占 폚 for two hours, that is, a TiFe intermetallic compound was precipitated at the interface between? And? Phases, Heat treatment for 1 hour, that is, increase of fraction of β phase was performed.

Sample 5 (comparative example)

In the case of specimen 5, after the solution treatment at 1,050 ° C, the ingot was crushed for grain refinement, and then hot rolling was performed in the β region of the alloy to produce a plate having a final thickness of 3 mm. After homogenization and processing at about 1050 占 폚, which is the? Transformation temperature of the alloy, the alloy was annealed at 704 占 폚 for 1.5 hours and aged at 600 占 폚 for 10 hours.

2. Mechanical Properties of Titanium Alloy Specimens

Fig. 4 shows the tensile test results at room temperature for the specimens 1 to 4, which are Ti-Al-Fe-O based titanium alloys prepared by the method according to the present invention. Each specimen was subjected to a room temperature tensile test twice.

Referring to FIG. 4, it can be seen that the produced titanium alloy exhibits a tensile strength of 1090 to 1140 MPa, a yield strength of 950 to 1010 MPa, and an elongation of 18 to 20%.

The mechanical strength of this alloy showed a difference of about 40 MPa depending on the contents of aluminum and iron. However, overall, the Ti-Al-Fe-O based titanium alloy according to the present invention has a higher value than the strength of commercial Ti-6Al-4V alloy.

In addition, the titanium alloys according to the present invention exhibited a particularly high elongation, even with a high oxygen content, than the 10-15% elongation of the commercial Ti-6Al-4V alloy.

FIG. 5 shows the tensile test results at room temperature for a specimen 5, which is a Ti-Al-Fe-based titanium alloy manufactured by the method according to the comparative example.

5, the tensile strength of specimen 5 is about 1,200 MPa, but the elongation is only about 11%, which is relatively low as compared with specimens 1 to 4. The poor ductility of specimen 5 can be attributed to the precipitation of a large amount of TiFe phase at the α / β interface after the aging treatment.

3. α-phase and β-phase fraction changes

For the specimens 1 to 4, the TiFe precipitation fraction after annealing at 600 ° C for 1.5 hours was calculated using the TTTI3 database from Thermocalc, and the stable TiFe phase fraction in each specimen was calculated and shown in Table 2.

In the case of specimen 6, the composition of specimen 5 is the same as that of specimen 5, and the manufacturing process of specimens 1 to 4 including annealing at 600 ° C for 1.5 hours and heat treatment at 800 ° C for 1 hour was applied.

[Table 2]

Referring to Table 2, it can be seen that the larger the content of Fe is, the larger the TiFe precipitation fraction is. When annealing is performed at 600 ° C for 1.5 hours, TiFe will exist on the interface between the alpha phase and the beta phase with relatively low interfacial energy. When this is heat-treated at 800 ° C. for 1 hour, as shown in Table 2, the β-phase fraction increases, and the interface between α-phase and β-phase shifts. Depending on the movement of the interfaces between the? -Phase and the? -Phase, precipitates existing on the? -Phase and? -Phase interface can be finely distributed in the? -Phase base in which the mechanical properties can be improved as a result.

Considering the result of the test piece 6, the manufacturing method according to the present invention is characterized in that, in addition to the alloy composition including 3.0 to 5.0% of Al, 2.0 to 4.0% of Fe, and 0.3 to 0.5% of O, And other titanium alloys including Fe.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

Claims (9)

(a) homogenizing a titanium alloy base material containing Al and Fe at a temperature not lower than the? transformation temperature;
(b) cooling the homogenized product to a first temperature region below the &bgr; transformation temperature, and precipitating a TiFe intermetallic compound at an interface between the [alpha] phase and the [beta] phase in the first temperature region; And
(c) raising the result of precipitation of the TiFe intermetallic compound to a second temperature region higher than the first temperature region to increase the fraction of the? phase.
The method according to claim 1,
Wherein at least a part of the TiFe intermetallic compound precipitated at the interface between the? -Phase and the? -Phase is precipitated into the? -Phase in the step (c).
The method according to claim 1,
Wherein the titanium alloy base material comprises 3.0 to 5.0% of Al, 2.0 to 4.0% of Fe, and 0.3 to 0.5% of O, and the balance of Ti and unavoidable impurities, in weight percent .
The method of claim 3,
Wherein the first temperature range is 500 to 700 ° C, and the second temperature range is 750 to 850 ° C.
The method according to claim 1,
Wherein the titanium alloy base material is produced by a solution treatment of a semi-finished product titanium alloy containing Al and Fe, followed by refining the crystal grains and then hot rolling in the? +? Region.
6. The method of claim 5,
Wherein the semi-finished alloy is manufactured from a titanium alloy scrap.
The steel sheet according to any one of claims 1 to 3, further comprising: 3.0 to 5.0% of Al, 2.0 to 4.0% of Fe and 0.3 to 0.5% of O, with the balance being Ti and unavoidable impurities,
And the number of TiFe intermetallic compounds precipitated in the? Phase is larger than the number of TiFe intermetallic compounds precipitated in the? Phase.
8. The method of claim 7,
Wherein the volume fraction of the? Phase is greater than the volume fraction of the? Phase.
8. The method of claim 7,
Wherein the titanium alloy exhibits a tensile strength of 1090 to 1140 MPa, a yield strength of 950 to 1010 MPa, and an elongation of 18 to 20%.

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