KR101963118B1 - Titanium alloy having high strength and high formability using transformation induced plasticity - Google Patents

Abstract

A titanium alloy having a high strength and a high solidity formation using transformational organic firing is disclosed.
The titanium alloy according to the present invention, according to the present invention, And the balance of Ti and unavoidable impurities, wherein the content of Al is 3.5% or more to 5.0% or less, the content of Fe is more than 1.5% to less than 4.5%, the content of Si is 0.3% or less and the content of O is 0.3% Characterized in that the structure comprises an alpha phase, a beta phase and a martensite phase.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a titanium alloy having a high strength and a high-

The present invention relates to a titanium alloy, and more particularly, to a titanium alloy having an alloy composition and a microstructure capable of simultaneously exhibiting high strength and solidity formation by TRIP (Transformation-Induced Plasticity) phenomenon during deformation.

Titanium alloys are higher in strength and corrosion resistance than general carbon steels, stainless steels and special alloy steels, and are the next richest metals in the earth mined metals such as iron, aluminum, and magnesium. Due to the high noble strength of titanium alloy, excellent corrosion resistance and biocompatibility, it is replacing existing materials as structural materials and functional materials with titanium, and it is applied to various industrial fields such as aviation, space, marine, sports, medical .

In recent years, studies have been conducted to achieve weight reduction of products such as automobiles and airplanes using ultra high strength alloys, and alloys using transformation induced plasticity (TRIP) phenomena are being manufactured. The alloy using TRIP can control a cooling rate and a cooling termination temperature in a cooling process after austenite is formed to allow some austenite to remain at room temperature and retain the austenite in martensite And the strength and ductility of the alloy are increased at the same time.

For example, a titanium alloy using a TRIP phenomenon is a β-type alloy containing an expensive element such as Mo, Nb, Zr, Hf and the like. The content of the expensive element is 10 to 30% There is a problem that a manufacturing process is difficult due to a high melting point element.

Therefore, it is necessary to study a low cost titanium alloy having excellent mechanical properties and low manufacturing cost.

As a background art related to the present invention, there is Korean Patent Laid-Open Publication No. 10-2017-0003449 (published on Jan. 1, 2017), which discloses a TiNi-based medical alloy and a manufacturing method thereof.

It is an object of the present invention to provide a low cost titanium alloy having high strength and high formability.

In order to achieve the above object, the titanium alloy according to the present invention comprises And the balance of Ti and unavoidable impurities, wherein the content of Al is 3.5% or more to 5.0% or less, the content of Fe is more than 1.5% to less than 4.5%, the content of Si is 0.3% or less and the content of O is 0.3% Characterized in that the structure comprises an alpha phase, a beta phase and a martensite phase.

The α-phase may be 70% or less by volume.

The alpha phase may be at least 10% by volume.

The titanium alloy may have an elongation of 20 to 35% and a tensile strength of 1000 to 1500 MPa.

The titanium alloy according to the present invention has a transformation induced plasticity (TRIP) phenomenon due to the heat treatment at a specific temperature in a range of contents of Al, Fe, Si, and O which are specific elements, .

In the present invention, the transformation of martensite during deformation occurs from the residual? -Phase after heat treatment, and the work hardening ability is increased, so that moldability and strength are excellent. In addition, by using Fe and Al, which are low-cost elements, the manufacturing cost of the titanium alloy can be reduced.

1 is a graph comparing the work hardenability of a TRIP titanium alloy and a general titanium alloy according to the present invention.
2 is a graph showing the tensile strength according to the elongation in the content range of Fe (1.5% and 4.5%) in the titanium alloy.
3 is a graph showing the tensile strength according to elongation in the content of Fe in the titanium alloy of the present invention.
4 is a graph showing the elongation 인 tensile strength according to the Fe content of the present invention.
5 shows the microstructure (SEM) of the titanium alloy and Fe according to the volume% of the? Phase according to the present invention.
6 schematically shows the microstructure of a titanium alloy according to% strain (tensile strain) according to the present invention.
7 and 8 are graphs showing the tensile curves of the α-phase volume% of the titanium alloy containing 2.0% Fe.
FIG. 9 shows the results of electron backscattered diffraction (EBSD) analysis when the volume% of the α phase of the titanium alloy containing 2.0% Fe is 0%.
FIG. 10 shows electron backscattered diffraction (EBSD) analysis results when the volume percentage of the α phase of the titanium alloy containing 4.0% of Fe (left) and 2.0% of Fe (right) is greater than 0% and less than 70%.
FIG. 11 shows the results of electron backscattered diffraction (EBSD) analysis when the volume percentage of the α phase of the titanium alloy containing 4.0% Fe exceeds 70%.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with 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. Like reference numerals refer to like elements throughout the specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

1 is a graph comparing the work hardenability of a TRIP titanium alloy and a general titanium alloy according to the present invention.

Referring to FIG. 1, a TRIP (Titanium Alloy) alloy according to the present invention has a martensite phase formed from a metastable β phase during deformation, resulting in increased ductility and strength.

The alloy using TRIP can control a cooling rate and a cooling termination temperature in a cooling process after austenite is formed to allow some austenite to remain at room temperature and retain the austenite in martensite And the strength and ductility of the alloy are increased at the same time.

In order for the TRIP phenomenon to take place effectively, it is preferable to have a sufficient? Phase for forming a martensite phase before deformation (tensile test). (TRIP) phenomenon does not occur when the content of the element (ex. Fe) which increases the stabilization of the β phase is large. When the content is small, martensite is formed from the β phase during the heat treatment, TRIP) phenomenon is not enough to occur. Therefore, the composition of the alloy is important at an early stage.

The titanium alloy according to the present invention And the balance of Ti and unavoidable impurities, wherein the content of Al is 3.5% or more to 5.0% or less, the content of Fe is more than 1.5% to less than 4.5%, the content of Si is 0.3% or less and the content of O is 0.3% Characterized in that the structure comprises an alpha phase, a beta phase and a martensite phase.

Al: not less than 3.5% and not more than 5.0%

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 order to strengthen the solid solution, the Al content is preferably 3.5% by weight or more, and when the Al content exceeds 5.0%, the elongation is decreased and the formability is deteriorated.

Fe: more than 1.5% and less than 4.5%

In order to produce a titanium alloy having excellent mechanical properties by the TRIP phenomenon, it is preferable to adjust the Fe content to more than 1.5% and less than 4.5%.

When the content of Fe is 1.5% or less, 100% of martensite or? Phase is formed after the heat treatment, so there is no room for transformation of martensite during deformation. On the contrary, when the content of iron is 4.5% or more, the phase stability of the β phase becomes high, and the transformation of martensite during the transformation is not achieved.

2 to FIG. 4 were 15 to 35%, and the upper volume% was formed in a similar range, followed by a heat treatment and a tensile test.

FIG. 2 is a graph showing the tensile strengths according to the elongation ratios in the content ranges of Fe (1.5% and 4.5%) in the titanium alloy, and FIG. 3 is a graph showing the tensile strengths according to the elongation ratios in the content of Fe in the titanium alloy of the present invention. to be.

In FIGS. 2 to 4, the .alpha. Phase volume% is an equilibrium volume% calculated value of JMatPro-8.0, as follows.

Fig. 2 shows the relationship between 4.5Fe: alpha phase 19%, 1.5Fe: alpha phase 24%

Fig. 3 is a graph showing the results of the experiment. Fig. 3 is a graph showing the relationship between the ratio of 2.0Fe: alpha phase 35%, 2.5Fe: alpha phase 24%, 3.0Fe: alpha phase 25%, 3.5Fe: alpha phase 15%

FIG. 4 shows that 24%, 35%, 24%, 25%, 15%, 18% and 19% of the .alpha. Phase volume from the left (1.5Fe).

Referring to FIG. 2, when the content of Fe is 1.5% and 4.5% in the titanium alloy, the elongation is 15% or less and the TRIP phenomenon does not occur.

On the other hand, in FIG. 3, when the content of Fe in the titanium alloy is 2.0% to 4.0%, the elongation is 20 to 35% and the tensile strength is in the range of 1000 to 1500 MPa. The elongation and tensile strength are the results of the tensile test after heat treatment, and the firing organic transformation (TRIP) occurs during the tensile test.

4 is a graph showing the elongation 인 tensile strength according to the Fe content of the present invention.

When the content of Fe exceeds 1.5% to less than 4.5%, the value of the elongation 인 tensile strength is in the range of 15000 to 43000 MPa ·, particularly when the content of Fe is 2.0% to 4.0% To 43000 MPa.%.

Therefore, it is preferable to adjust the content of Fe in the titanium alloy to more than 1.5% and less than 4.5%.

Si  : Not more than 0.3%, and O: not more than 0.3%

The Si and O are preferably added for solid solution strengthening, and when the content of Si and O is more than 0.3%, the elongation is decreased and the formability is deteriorated.

In the present invention, the volume% of the phase is an important variable for controlling the phase stability of the β phase. Referring to FIG. 5, as the? Phase increases, the Fe element, which is the? Element and the? Element, is diffused into the remaining? Phase, so that the phase stability of the? Phase containing a large amount of iron is increased do. That is, when the volume% of the α phase is increased, the phase transition stability of the β phase may not be caused by the TRIP phenomenon.

Therefore, in the present invention, it is preferable that the? Phase is 70% or less by volume and preferably exceeds 10%.

More specifically, the? -Phase may have a volume percentage of more than 10% to less than 70%, and a total volume percentage of other phases may be more than 30% and less than 90%. The remaining other phases refer to? -Phase, non-planar (martensite phase,? Phase), and the like.

The ω-phase is a phase often generated after the heat treatment, and the ω-phase is very small in size, so it may be difficult to measure the phase fraction.

6 schematically shows the microstructure of a titanium alloy according to% strain (tensile strain) according to the present invention. Fig. 6 shows that martensite is formed during deformation. When the tensile strain is 0%, it is composed only of? -Phase and? -Phase. When the tensile strain is 2%, the microstructure shows linear martensitic transformation Show that it happened. In addition, it shows that the martensite transformation progresses more actively as the tensile strain increases from 5 to 20%, and most of the β phase is transformed into martensite at the time of fracture.

7 and 8 are graphs showing the tensile curves of the α-phase volume% of the titanium alloy containing 2.0% Fe. Referring to FIG. 8, when the volume percentage of the? Phase is more than 0% and not more than 70%, excellent strength and elongation are exhibited without occurrence of fracture, whereas when the volume percentage of the? Phase is out of the range in FIG. 7, Or low strength.

The volume% of the? Phase represents the equilibrium volume% calculated value of JMAtPro-8.

FIG. 9 shows the results of electron backscattered diffraction (EBSD) analysis when the volume% of the α phase of the titanium alloy containing 2.0% Fe is 0%. Referring to FIG. 9, it can be seen that too much martensite is produced, which may degrade the mechanical performance of the titanium alloy. When the volume% of α phase is 0%, water-cooling is carried out above the beta-transus temperature. At this time, most martensite is generated on unstable β phase, and the transformation phase (TRIP) It can be difficult to get up.

FIG. 10 shows electron backscattered diffraction (EBSD) analysis results when the volume percentage of the α phase of the titanium alloy containing 4.0% of Fe (left) and 2.0% of Fe (right) is greater than 0% and less than 70%. Referring to the left photograph (2.4 volume% of the? Phase) in FIG. 10, a transformation of martensite during deformation occurs from the residual? Phase after the heat treatment, showing a titanium alloy of high strength and high ductility. It is also confirmed that an appropriate amount of martensite is produced during cooling according to the heat treatment temperature even before the deformation (tensile test).

Referring to the right photograph of Fig. 10 (volume of the? Phase 54.2%), the generation of? Phase increases the? Phase phase stability together with the? Phase Fe content and suppresses the formation of martensite even after the heat treatment.

FIG. 11 shows the results of electron backscattered diffraction (EBSD) analysis when the volume percentage of the α phase of the titanium alloy containing 4.0% Fe exceeds 70%.

Referring to FIG. 11, it can be confirmed that the phase stability of the β phase becomes too high as the volume percentage of the α phase exceeds 70%, and the transformation of the martensite does not occur during the deformation.

As described above, it can be seen that martensite does not undergo transformation during cooling and a small amount of martensite is produced in the volume percentage and composition range of the? Phase.

In addition, the titanium alloy according to the present invention has a transformation induced plasticity (TRIP) phenomenon due to heat treatment at a specific temperature in a range of contents of Al, Fe, Si and O which are specific elements, % And a tensile strength of 1000 to 1500 MPa.

The elongation and tensile strength are the results of the tensile test after heat treatment, and the firing organic transformation (TRIP) occurs during the tensile test.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It is to be understood that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (4)

And the balance of Ti and unavoidable impurities, the content of Al is 3.5% or more to 5.0% or less, the content of Fe is 2.0% to 4.0%, the content of Si is 0.3% or less, and the content of O is 0.3%
The microstructure includes an alpha phase, a beta phase and a martensite phase,
And the α-phase is 70% or less by volume (excluding 0%).
delete The method according to claim 1,
Wherein the alpha phase is at least 10% by volume.
The method according to claim 1,
Wherein the titanium alloy has an elongation of 20 to 35% and a tensile strength of 1000 to 1500 MPa.

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