KR20150020760A - Ti-Al alloys with superior creep resistance - Google Patents

Abstract

The present invention relates to a titanium (Ti)-aluminum (Al) alloy with excellent creep resistance which includes 51-55 wt% of Ti, 30-32 wt% of Al, 12.9-15.4 wt% of Nb, 0.0005-0.003 wt% of B, and inevitable impurities. The titanium (Ti)-aluminum (Al) alloy with excellent creep resistance has a lamellar structure formed of two phases of α-TiAl and γ-Ti_3Al, improves thermal resistance and creep resistance, has numerical stability by suppressing the expansion of alloy caused by phase transformation because the phase transformation is not generated during heating and cooling, and can be applied to a turbine wheel of a turbo charger by being lightweight.

Description

Ti-Al alloys with superior creep resistance < RTI ID = 0.0 > (Ti) < / RTI &

The present invention relates to a titanium (Ti) -aluminum (Al) alloy excellent in creep resistance, and more particularly, to a titanium-aluminum (Al) alloy having a lamellar structure, (Ti) -Aluminum (Al) alloy having an excellent creep resistance by adding an element capable of further improving the creep resistance.

Since the 1980s, turbochargers have been rapidly installed in general diesel vehicles, as energy conservation and environmental issues have focused attention on improving fuel efficiency and power output of automotive diesel engines. The turbo charger converts the energy discharged from the internal combustion engine exhaust gas into the rotational energy of the turbine and increases the charging efficiency of the mixed gas coming into the intake system. Therefore, the combustion efficiency and the output of the automotive engine are increased.

In addition, there has been an attempt to install a turbocharger in a gasoline engine as one of the methods for achieving the same performance although the size of the engine is reduced as the automobile becomes smaller and lighter.

However, the turbocharger, which has been mainly used for diesel engines, required heat resistance of about 800 ° C. However, gasoline engines required heat resistance of about 1000 ° C.

In order to overcome the above problem, the turbine wheel of the conventional turbocharger is mainly made of a high heat resistant nickel (Ni) alloy containing nickel (Ni). To improve the responsiveness of the turbocharger, titanium ) -Aluminum (Al) -based alloys are also partially applied.

The high heat-resistant nickel (Ni) alloy has high heat resistance, but has a density of 7.7 to 8.0 g / cm ^{3, which} is similar to the density of general steel. Therefore, when the high-heat-resistant nickel (Ni) alloy is applied to a turbine wheel of a turbocharger, there is a problem that a turbo lag is generated which lowers the operational response of the turbine wheel.

On the other hand, the titanium (Ti) -aluminum (Al) alloy has a high melting point and low density, is lightweight and excellent in heat resistance, and thus is considered to be the most promising material to replace the super heat resistant nickel have. Since the density is in the range of 3.7 to 4.0 g / cm ³ and is about half of the nickel (Ni) alloy, it has the advantage of being able to rotate at a high speed. However, due to its alloy characteristics, parts such as turbine wheels of turbochargers There is a problem that the creep resistance and the like are insufficient at a high temperature as compared with the nickel (Ni) alloy, so that the operating life is short.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art described above, and it is an object of the present invention to provide a method of manufacturing a titanium-aluminum (Al) alloy by forming a lamellar structure in a base structure of a titanium (Ti) Heat resistance and creep resistance at high temperatures.

In order to achieve the above-mentioned object, a titanium-aluminum (Al) alloy excellent in creep resistance is composed of 51 to 55% of Ti, 30 to 32% of Al, 12.9 to 15.4% of Nb, : 0.0005 to 0.003%, and other unavoidable impurities.

At this time, it is preferable that the alloy further contains 0.05 to 0.14% of C and 0.11 to 0.27% of Si.

Further, it is preferable that the alloy further contains 0.53 to 0.74% of Cr and 0.12 to 0.26% of V.

In addition, it is preferable that the alloy further contains 0.15 to 0.25% of Ni.

In addition, it is preferable that the alloy further contains 0.05 to 0.14% Fe and 0.05 to 0.11% S.

Here, it is preferable that the alloy has a lamellar structure composed of two phases of? -TiAl and? -Ti ₃ Al.

At this time, it is preferable to cast a turbine wheel of a turbocharger using the alloy.

Effects of the present invention having the configuration as mentioned above, titanium (Ti) and aluminum (Al) is α-TiAl and γ-Ti ₃ 2 on the lamellar structure composed of Al (lamellar structure) configuration, heat resistance and creep of the alloy by Temperature characteristics such as resistance can be improved and phase transformation does not occur during heating and cooling, so that the expansion of the alloy due to the phase transformation can be suppressed and the numerical stability can be secured.

Further, the present invention has an advantage that the response of the turbo charger can be improved because the density is half the density of the Ni-based cast alloy applied to the turbine wheel of the conventional turbocharger.

1 is a graph comparing the creep times of Examples and Comparative Examples at 800 ° C / 60 MPa.
2 is a graph comparing the creep times of Examples and Comparative Examples at 900 ° C / 60 MPa.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Hereinafter, the present invention will be described in detail with reference to tables and drawings.

The present invention relates to a titanium (Ti) -aluminum (Al) alloy excellent in creep resistance.

More specifically, α-TiAl and titanium (Ti) to form a lamellar structure (lamellar structure) tissue base (base) made of a second phase of the γ-Ti ₃ Al - aluminum (Al) alloys have high temperature creep (creep) resistance and heat resistance (C), silicon (Si), chromium (Cr), vanadium (V), nickel (Ni), and the like ), Iron (Fe), sulfur (S), and the like.

More specifically, titanium (Ti) and aluminum-titanium (Ti) consisting of (Al), such as aluminum (Al) base structure of alloys have a microstructure consisting of two merchant lamellar structure of the α-TiAl and γ-Ti ₃ Al Therefore, it is an alloy excellent in heat stability and little in phase transformation due to temperature change and excellent in dimensional stability.

Herein, niobium (Nb) and boron (B) are added to the titanium (Ti) -aluminum (Al) alloy to further refine the layered structure to improve the creep resistance at high temperature strength, toughness and high temperature of the alloy.

Further, carbon (C) and silicon (Si) are further added to the alloy to stabilize the matrix structure to improve the creep resistance at high temperatures. Further, chromium (Cr) and vanadium (V) (Fe) and sulfur (S) can be prevented from being added to the steel sheet, and it is possible to improve the creep resistance at high temperature by addition of nickel (Ni) And the workability of the alloy can be secured.

In this case, the amount of titanium (Ti) is 51 to 55%, aluminum (Al) is 30 to 32%, niobium (Nb) is 12.9 to 15.4%, boron (B) is 0.0005 to 0.003% (Ni), 0.15 to 0.25% of vanadium (V), 0.15 to 0.25% of vanadium (V), 0.15 to 0.25% of chromium (Cr) Fe) of 0.05 to 0.14% and sulfur (S) of 0.05 to 0.11%.

Hereinafter, the function of each component contained in the present invention and the reason for its content will be specifically confirmed.

1. Components and content of the present invention

1.1. Titanium (Ti) and aluminum (Al)

The titanium (Ti) and aluminum (Al), titanium (Ti) as a main component - the base structure of aluminum (Al) alloy is composed of a lamellar structure composed of a two-phase of α-TiAl and γ-Ti ₃ Al, the alloy Temperature characteristics such as high temperature strength and high temperature toughness can be improved, so that creep resistance and heat resistance at high temperature can be maximized.

At this time, the titanium (Ti) is preferably 51 to 55% by weight based on the weight of the entire alloy. At this time, when the amount of titanium (Ti) is less than 51%, the α-TiAl structure is relatively increased and the balance of the whole layer structure is broken, so that creep resistance and heat resistance at high temperature can be reduced. On the other hand, when the content of titanium (Ti) exceeds 55%, the structure of γ-Ti ₃ Al is relatively increased and the balance of the whole layer structure is broken, so that creep resistance and heat resistance at high temperature can be reduced.

The aluminum (Al) is preferably 30 to 32% by weight based on the weight of the entire alloy. At this time, when the aluminum (Al) is less than 30%, the γ-Ti ₃ Al structure increases relatively as in the case where the titanium (Ti) exceeds 55%, and the balance of the whole layer structure is broken, Resistance and heat resistance can be reduced. On the other hand, when the aluminum (Al) content exceeds 32%, the α-TiAl structure is relatively increased and the balance of the whole layer structure is broken as in the case where the titanium (Ti) content is less than 51%, so that the creep resistance and heat resistance Etc. can be reduced.

1.2. Niobium (Nb) and boron (B)

The niobium improves the oxidation resistance and the like of the titanium (Ti) -aluminum (Al) alloy and further reduces the layer-to-layer spacing of? -TiAl and? -Ti ₃ Al. It is an element added to improve creep resistance at high temperature of aluminum (Al) alloy.

At this time, the niobium (Nb) is preferably 12.9 to 15.4% by weight based on the weight of the entire alloy. At this time, when the niobium (Nb) is less than 12.9%, it is difficult to expect sufficient creep resistance of the titanium (Ti) -aluminum (Al) alloy. On the other hand, when the niobium (Nb) exceeds 15.4% The creep resistance is saturated and the economical efficiency may be lowered.

The boron (B) is an element which suppresses the growth of macroparticular structure and forms a microstratified structure, and the boron (B) is added in an amount of 0.0005 to 0.003% by weight, . If the amount of boron (B) is less than 0.0005%, it is difficult to sufficiently suppress the growth of the layered structure. On the other hand, when the amount of boron (B) exceeds 0.003%, excess boron carbide is formed in the grain boundary, .

1.3. Carbon (C) and silicon (Si)

The carbon (C) improves the castability of a titanium (Ti) -aluminum (Al) alloy and forms a stable carbide at high temperatures by combining with chromium (Cr) and vanadium (V) And improve the heat resistance.

At this time, the carbon (C) is preferably 0.05 to 0.14% by weight based on the weight of the entire alloy. If the amount of carbon (C) is less than 0.05%, sufficient carbide is formed, whereas when the amount of carbon (C) is more than 0.14%, coarse carbide is formed to cause high temperature strength deterioration and brittleness of the alloy It can be active.

The silicon (Si) improves the fluidity of the molten titanium (Ti) -aluminum (Al) alloy so that the elements contained in the alloy can be uniformly distributed. By stabilizing the layered structure, (Ti) -Aluminum (Al) alloy.

At this time, it is preferable that the silicon (Si) is 0.11 to 0.27% by weight with respect to the weight of the total alloy, and when the silicon (Si) is less than 0.11%, the sufficient amount of the titanium (Ti) It is difficult to expect creep resistance. On the other hand, when the silicon (Si) content exceeds 0.27%, the creep resistance to be improved is saturated and the economical efficiency may be lowered.

1.4. Chromium (Cr) and vanadium (V)

The chromium (Cr) binds with carbon (C) to form a stable carbide at a high temperature, thereby improving the creep resistance of the titanium (Ti) -Aluminum (Al) alloy at high temperature and increasing the oxidation resistance of the alloy.

At this time, it is preferable that the chromium (Cr) is 0.53 to 0.75% by weight based on the weight of the entire alloy. When the chromium (Cr) is less than 0.53%, sufficient creep resistance and oxidation resistance are difficult to expect, When the chromium (Cr) is more than 0.75%, coarse carbide is generated in the grain boundary, and intergranular fracture may occur.

The vanadium (V) bonds with carbon (C) to form a stable carbide at a high temperature. Since the vanadium (V) participates in the growth of the layered structure to finely form the layered structure, the titanium (Ti) Which improves creep resistance.

In this case, the vanadium (V) is preferably 0.12 to 0.26% based on the weight of the entire alloy. When the vanadium (V) is less than 0.12%, it is difficult to expect sufficient creep resistance. If it is more than 0.26%, the creep resistance to be improved is saturated and the economical efficiency may be lowered.

1.5 Nickel (Ni)

The nickel (Ni) is an element for preventing brittleness by improving toughness of a titanium (Ti) -aluminum (Al) alloy. The nickel (Ni) And it is preferably 0.15 to 0.25%. If the nickel (Ni) content is less than 0.15%, it may be difficult to improve the toughness of the alloy sufficiently. On the other hand, when the nickel content exceeds 0.25%, the strength of the alloy may be rapidly lowered at room temperature.

1.6. Iron (Fe) and sulfur (S)

The iron (Fe) and sulfur (S) are added to the titanium (Ti) -Aluminum (Al) alloy in small amounts to improve workability such as machinability of the alloy and facilitate mass production.

The iron (Fe) and sulfur (S) are preferably 0.05 to 0.14% by weight based on the weight of the entire alloy. When the iron (Fe) and sulfur (S) are each less than 0.05%, it is difficult to obtain sufficient workability. On the other hand, when the iron (Fe) and sulfur (S) - High temperature strength of aluminum (Al) alloy may be lowered.

2. Usage

The titanium (Ti) -aluminum (Al) alloy having excellent creep resistance according to the present invention is preferably applied to a region where excellent physical properties such as creep resistance are required under harsh conditions. Particularly, a turbocharger turbocharger of a turbocharger.

3. Manufacturing Method

A titanium (Ti) -aluminum (Al) alloy having excellent creep resistance according to the present invention can be suitably manufactured by those skilled in the art with reference to known technologies. The alloy according to the present invention can be used to produce a turbine wheel of a turbocharger wheel and the like are preferably cast.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not construed as being limited by these embodiments.

In order to confirm the superior creep resistance at high temperature of the titanium-aluminum alloy having excellent creep resistance according to the present invention, a test piece containing the same contents as shown in Table 1 was manufactured, and then the creep life at 900 ° C / And the creep life is measured in Table 2 below.

division unit Chemical composition Ti Al Nb Si V Cr Fe Ni S C B Example 1 wt% 53.1 31.2 14.3 0.19 0.21 0.62 0.05 0.21 0.06 0.06 0.0015 Comparative Example 1 wt% 53.8 30.5 14.2 0.21 0.21 0.63 0.06 0.22 0.07 0.06 - Comparative Example 2 wt% 53.2 30.8 14.5 0.19 0.22 0.64 0.06 0.21 0.08 0.07 0.0035 Comparative Example 3 wt% 53.8 31.9 12.8 0.23 0.19 0.65 0.07 0.19 0.07 0.08 0.0016 Comparative Example 4 wt% 51.8 31.3 15.5 0.21 0.17 0.63 0.06 0.19 0.08 0.07 0.0020 Comparative Example 5 wt% 53.9 30.2 14.5 0.10 0.22 0.62 0.07 0.20 0.07 0.08 0.0015 Comparative Example 6 wt% 53.4 30.7 14.3 0.28 0.22 0.65 0.09 0.18 0.07 0.08 0.0025 Comparative Example 7 wt% 52.6 31.5 14.6 0.21 0.11 0.61 0.05 0.21 0.06 0.07 0.0017 Comparative Example 8 wt% 53.3 31.0 14.2 0.18 0.27 0.62 0.09 0.21 0.07 0.07 0.0017 Comparative Example 9 wt% 53.4 31.2 14.1 0.19 0.18 0.52 0.06 0.23 0.08 0.07 0.0016 Comparative Example 10 wt% 52.9 30.9 14.6 0.20 0.19 0.75 0.07 0.20 0.06 0.08 0.0026 Comparative Example 11 wt% 52.1 31.8 14.7 0.20 0.19 0.66 - 0.18 0.06 0.07 0.0018 Comparative Example 12 wt% 52.4 31.5 14.5 0.20 0.21 0.63 0.15 0.20 0.09 0.08 0.0019 Comparative Example 13 wt% 53.3 30.9 14.5 0.19 0.21 0.65 0.07 0.09 0.07 0.06 0.0021 Comparative Example 14 wt% 52.6 31.2 14.6 0.22 0.21 0.66 0.08 0.28 0.06 0.09 0.0026 Comparative Example 15 wt% 53.6 30.7 14.3 0.21 0.20 0.63 0.07 0.21 - 0.08 0.0019 Comparative Example 16 wt% 53.0 30.9 14.6 0.19 0.19 0.69 0.06 0.20 0.12 0.06 0.0028 Comparative Example 17 wt% 53.6 30.6 14.3 0.20 0.22 0.67 0.08 0.21 0.07 - 0.0015 Comparative Example 18 wt% 53.1 31.0 14.4 0.19 0.18 0.61 0.06 0.19 0.08 0.15 0.0016

Table 1 is a table for comparing the contents of the test pieces for constituting components for measuring the creep resistance at 800 캜 / 60 MPa and 900 캜 / 60 MPa of the examples and the comparative examples. Based on the above table, .

division Creep Life (hours) Condition 800 DEG C / 60 MPa 900 DEG C / 60 MPa Example 1 7534 625 Comparative Example 1 4139 343 Comparative Example 2 3769 213 Comparative Example 3 5541 391 Comparative Example 4 5553 395 Comparative Example 5 5762 413 Comparative Example 6 5877 421 Comparative Example 7 6323 474 Comparative Example 8 6337 475 Comparative Example 9 5987 443 Comparative Example 10 5548 419 Comparative Example 11 6825 556 Comparative Example 12 6592 526 Comparative Example 13 6714 511 Comparative Example 14 6699 497 Comparative Example 15 6995 598 Comparative Example 16 6494 546 Comparative Example 17 4966 375 Comparative Example 18 4671 341

Table 2 compares the creep times at 800 ° C / 60 MPa for the test pieces composed of the constituents shown in Table 1. The creep resistance test conditions were ASTM E139 'Standard Test Methods for Conducting Creep, Creep-Rupture, and Stress The time was measured until the specimens broke at 800 ° C / 60 MPa and 900 ° C / 60 MPa according to 'Rupture Tests of Metallic Materials'.

The data of the table are shown graphically for easy comparison of the test results summarized in the above table. FIG. 1 is a graph comparing the creep times of Examples and Comparative Examples at 800 ° C./60 MPa, and FIG. 2 is a graph comparing creep times of Examples and Comparative Examples at 900 ° C./60 MPa.

As a result of the test, the time required for the test piece to break, that is, the creep time, was the longest in all of the Examples and Comparative Examples. This result means that the fracture of the test piece is suppressed in the example compared to the comparative example, so that it can be judged that the creep of the embodiment is suppressed.

More specifically, it was found through comparison examples 1 to 4 that the creep time was short when the content of niobium (Nb) and boron (B) deviated from the present invention. This indicates that the creep resistance of the comparative example Which means it is inferior to the embodiment.

It was also found from the comparison examples 15 to 18 that the creep time was short when the content of carbon (C) and silicon (Si) deviated from the present invention. This indicates that the creep resistance of the comparative example It means that it is inferior.

Further, it was found through comparison examples 7 to 10 that the creep time was short when the content of chromium (Cr) and vanadium (V) deviated from the present invention. This indicates that the creep resistance of the comparative example It means inferiority.

Further, it was found through Comparative Example 13 and Comparative Example 14 that when the content of nickel (Ni) deviated from the present invention, the creep time was short, which means that the creep resistance of the comparative example is inferior to that of the embodiment .

It was also found that when the contents of iron (Fe) and sulfur (S) deviated from the present invention through Comparative Example 11, Comparative Example 12, Comparative Example 15 and Comparative Example 16, the creep time was short, Which means that the exemplary creep resistance is inferior to the example.

Accordingly, it was confirmed that the titanium-aluminum alloy according to the present invention and the content thereof are superior in creep resistance at a high temperature to the conventional comparative example.

Although the present invention has been described in connection with the specific embodiments of the present invention, it is to be understood that the present invention is not limited thereto. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Various modifications and variations are possible.

Claims (7)

Titanium (Ti) -aluminum (Al) alloy characterized by comprising, by weight%, 51 to 55% of Ti, 30 to 32% of Al, 12.9 to 15.4% of Nb, 0.0005 to 0.003% of B and other unavoidable impurities. Alloy.
The method according to claim 1,
Wherein the alloy further comprises 0.05 to 0.14% of C and 0.11 to 0.27% of Si.
The method according to claim 1,
Wherein the alloy further comprises 0.53 to 0.74% of Cr and 0.12 to 0.26% of V.
The method according to claim 1,
Wherein the alloy further comprises 0.15 to 0.25% Ni. ≪ RTI ID = 0.0 > 15. < / RTI >
The method according to claim 1,
Wherein the alloy further comprises 0.05% to 0.14% Fe and 0.05% to 0.11% S (Al).
The method according to claim 1,
Wherein the alloy has a lamellar structure consisting of two phases of? -TiAl and? -Ti ₃ Al.
A turbine wheel of a turbocharger cast using the alloy of any one of claims 1 to 6.

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