KR101890642B1 - Method for preparing Ti-Al-Nb-V alloy improved fracture toughness and creep properties - Google Patents

Abstract

(A) heat-treating a Ti-Al-Nb-V alloy having an Al content of 42% or less at a temperature of 1250 to 1350 캜 for 30 to 240 minutes; And (b) cooling the Ti-Al-Nb-V alloy heat-treated in the step (a) at a cooling rate of 1 to 20 ° C / min. ≪ / RTI >
According to the method for producing a Ti-Al-Nb-V alloy according to the present invention, a beta-gamma Ti-Al-Nb-V alloy containing aluminum at an atomic ratio of 42% or less is heat- Cooling step or cooling step by introducing different cooling rate for each section of phase transformation. The formation of a two-phase lamellar structure of α ₂ -phase and γ-phase on the alloy by the cooling-solidification heat treatment method improves fracture toughness and creep resistance Ti-Al-Nb-V alloy can be produced.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a Ti-Al-Nb-V alloy having improved fracture toughness and creep resistance,

The present invention relates to a Ti-Al-Nb-V alloy having a fracture toughness and creep resistance improved by heat treatment and cooling treatment at a specific temperature, or a heat treatment and a step cooling treatment, Nb-V based alloys.

Titanium-aluminum alloy (TiAl alloy) is superior in high temperature strength, oxidation resistance, creep characteristics, etc. and has a smaller specific gravity than conventional titanium alloy, and is used in manufacturing low pressure turbine blades of aircraft engines or turbine wheels of supercharging engines Ti-based alloys or Ni-based superalloys as a promising material.

However, since the TiAl alloy has low ductility at room temperature, it is difficult to process and it is difficult to manufacture a sound alloy because of high activity of Ti at the time of dissolution.

Lamellar structure of, preparing a TiAl alloy by precision casting, or by the addition of certain elements of the third to the TiAl alloy α ₂ phase and the image on the γ 2 in the alloy structure (α ₂ + γ) In order to solve the above problems Various studies have been conducted to improve the ductility. The TiAl alloy having a lamellar structure as described above has improved properties such as fracture toughness, fatigue strength and creep resistance, and provides properties useful for practical use as a lightweight high-temperature material .

However, in the past, studies on improving the fracture toughness and creep resistance of a Beta-Gamma alloy having an Al content of 42% or less have hardly been conducted, and therefore, research is needed.

Korean Patent No. 10-1614124 (Published on 2014.04.21) Korean Patent Laid-Open No. 10-2015-0020760 (published on 2015.02.27) Korean Patent Laid-Open No. 10-2009-0063173 (Published on June 17, 2009)

SUMMARY OF THE INVENTION The present invention has been conceived to solve the problems of the prior art as described above, and it is an object of the present invention to provide a quaternary beta-gamma TiAl alloy having an Al content of 42% or less by heat- And a method of manufacturing a Ti-Al-Nb-V alloy having improved fracture toughness and creep resistance by forming a lamellar structure.

(A) heat-treating the Ti-Al-Nb-V alloy having an Al content of 42% or less at a temperature of 1250 to 1350 ° C for 30 to 240 minutes; And (b) cooling the Ti-Al-Nb-V alloy heat-treated in the step (a) at a cooling rate of 1 to 20 ° C / min. ≪ / RTI >

The Ti-Al-Nb-V alloy contains Nb at an atomic ratio (atomic%) of 6% and Ti-42Al-Nb containing V at an atomic ratio (at.%) Of 6 to 8% 6Nb-V based alloy.

In the step (b), the Ti-Al-Nb-V alloy heat-treated in the step (a) is first cooled at a rate of 3 ° C / min until the temperature reaches 1245 ° C, -Al-Nb-V based alloy at a cooling rate of 18 DEG C / min.

In the step (b), the Ti-Al-Nb-V alloy heat-treated in the step (a) is cooled at a cooling rate of 15 ° C / min.

Also, the present invention provides a Ti-Al-Nb-V alloy, which is produced by the above-described method and has a lamellar structure of? ₂ phase and? Phase of? ₂ +? Lamellar structure.

According to the method for producing a Ti-Al-Nb-V alloy according to the present invention, a beta-gamma Ti-Al-Nb-V alloy containing aluminum at an atomic ratio of 42% or less is heat- Cooling step or cooling step by introducing different cooling rates for each phase section. By forming a structure of α _2- phase and γ-phase two-phase lamellar structure in the alloy through the cooling-solidification heat treatment method, fracture toughness and creep resistance An improved Ti-Al-Nb-V alloy can be produced.

The method for producing a Ti-Al-Nb-V alloy according to the present invention as described above can be applied to improve properties of various TiAl alloys having a low content of Al.

1 is an actual image of an ingot of a Ti-42Al-6Nb-7V alloy manufactured by the method according to the embodiment.
Figure 2 shows the results of differential scanning calorimetry (DSC) of a Ti-42Al-6Nb-7V alloy prepared by the method according to the example.
FIG. 3 is an SEM image of the microstructure of the Ti-42Al-6Nb-7V alloy prepared by the method according to the embodiment and the XRD pattern analysis result.
4 is a state diagram of an alloy having a similar composition of a Ti-42Al-6Nb-7V alloy prepared by the method according to an embodiment.
FIG. 5 is a schematic view showing conditions of a heat treatment and a cooling treatment for three kinds of alloys prepared by the method according to the embodiment. FIG.
6 is a SEM image of a surface of an alloy after three kinds of alloys prepared by the method according to the embodiment were subjected to a heat treatment and a cooling treatment by three methods.

The present invention provides a technique for improving the fracture toughness and creep resistance by heat-treating a quaternary beta-gamma Ti-Al-Nb-V alloy having an Al content of 42% .

For this purpose, in the present invention, a Ti-Al-Nb-V alloy is subjected to a heat treatment and a cooling treatment at a specific temperature to remove the beta phase in the texture of the alloy and form a double lamellar structure on the alpha (alpha ₂ ) And a Ti-Al-Nb-V alloy having improved fracture toughness and creep resistance.

Hereinafter, the present invention will be described in detail.

(A) heat-treating a Ti-Al-Nb-V alloy having an Al content of 42% or less at a temperature of 1250 to 1350 캜 for 30 to 240 minutes; And (b) cooling the Ti-Al-Nb-V alloy heat-treated in the step (a) at a cooling rate of 1 to 20 ° C / min. ≪ / RTI >

The step (a) is a step of heat-treating the Ti-Al-Nb-V alloy at a temperature (Tα) of 1245 ° C. or more to induce α-zone recrystallization of the Ti-Al- And the Ti-Al-Nb-V alloy may be an ingot of a Ti-Al-Nb-V alloy manufactured by a casting or forging method.

The Ti-Al-Nb-V alloy includes Nb at an atomic ratio of 3 to 9 at.%, Has high oxidation resistance of the alloy, has a ductility including V at an atomic ratio of 6 to 8 at.%, The Al alloy is formed at an atomic ratio of 42 at.% Or less and the strength is high, but an alloy structure of a structure in which?,? And? Phases are mixed is formed, so that the alloy itself has insufficient ductility and oxidation resistance.

Wherein the Ti-Al-Nb-V alloy contains Al at an atomic ratio of 42 at.%, Contains Nb at an atomic ratio of 6 at.% And contains V at an atomic ratio of 6 to 8 at. A Ti-42Al-6Nb-6V alloy, a Ti-42Al-6Nb-7V alloy, and a Ti-42Al-6Nb-8V alloy.

In this step, the Ti-Al-Nb-V alloy is subjected to heat treatment at a specific temperature range to induce crystal growth in the alloy to induce recrystallization of the? -Interlayer. Therefore, a weak? The Ti-Al-Nb-V alloy having a structure in which the? ₂ phase (Ti ₃ Al) and the? Phase (TiAl) are finely dispersed can be produced.

For this, in this step, the Ti-Al-Nb-V alloy is heat-treated at a temperature of 1250 to 1350 ° C. for 30 minutes to 240 minutes at a temperature (Tα) to induce α-zone recrystallization, The alloy structure is homogenized to induce a discontinuous precipitation process in the alloy structure and the recrystallization is induced in a step to be described later, whereby the alloy of the α ₂ and γ phase double lamella structure (α ₂ + γ) And heat treatment may preferably be performed at 1300 ° C.

In the step (b), the Ti-Al-Nb-V alloy is heat-treated at a cooling rate of 1 to 20 ° C / min. Ti-Al-Nb-V alloy having improved fracture toughness and creep resistance by forming a double lamellar structure on alpha (alpha ₂ ) and gamma (gamma) by recrystallizing the precipitate formed by discontinuous precipitation process Can be formed.

In this step, Ti-Al-Nb-V alloys were prepared by applying Ti-Al-Nb-V alloys with α- ₂ and γ-phase dual lamellar structures, And the Ti-Al-Nb-V alloy has a phase transformation path of? -? +? +? -? +??.

At a temperature of 1245 ℃ and α using the phase transformation from α phase transformation path as γ by adjusting the cooling rate for each region at a temperature of 1157 ℃ that phase transformation to α ₂ formed of the double lamellar structure on the α ₂ and γ-Ti Al- Nb-V alloy can be produced.

For example, a Ti-42Al-6Nb-6V alloy containing Al at an atomic ratio of 42%, containing Nb at an atomic ratio of 6 at.% And containing V at an atomic ratio of 6 to 8% In the case of the 42Al-6Nb-7V alloy and the Ti-42Al-6Nb-8V alloy, the three kinds of alloys heat-treated as described above are heated at a rate of 2 to 5 ° C / min A Ti-42Al-6Nb-6V alloy in which the α ₂ + γ lamellar structure is uniformly formed by constituting the alloy to be first cooled at a rate of 15 ° C./min and then cooled to room temperature at a cooling rate of 15 to 20 ° C./min, Ti-42Al-6Nb-7V alloy and Ti-42Al-6Nb-8V alloy.

If the Ti-42Al-6Nb-6V alloy, Ti-42Al-6Nb-7V alloy and Ti-42Al-6Nb-8V alloy are heated to 2 to 5 ° C / min There is a problem in that there is not enough time and there is a problem that an α + β lamellar structure which is not a lamellar structure of α ₂ + γ is formed, and that the same as the first cooling treatment There is a problem that the recrystallized grains are coarsened and formation of the lamellar structure is difficult.

Preferably, 3 ℃ / minute treatment primary cooling at a cooling rate, and, 18 ℃ / min was treated secondary cooling at a cooling rate of α ₂ + γ is a lamellar structure formed sufficiently fracture toughness and the creep resistance is improved up to Ti -42Al-6Nb-6V alloy, Ti-42Al-6Nb-7V alloy and Ti-42Al-6Nb-8V alloy.

As another example, a Ti-42Al-6Nb-6V alloy containing Al at an atomic ratio of 42%, containing Nb at an atomic ratio of 6 at.% And containing V at an atomic ratio of 6 to 8%, Ti -42Al-6Nb-7V in the case of alloys and Ti-42Al-6Nb-8V alloy, to configure each one of the three alloys heat treated as described above to cool at a cooling rate of 10 to 20 ℃ / min α + γ ₂ lamellar Ti-42Al-6Nb-6V alloy, Ti-42Al-6Nb-7V alloy and Ti-42Al-6Nb-8V alloy can be produced, respectively, and more preferably, cooled at a cooling rate of 15 ° C / .

According to the method for producing a Ti-Al-Nb-V alloy according to the present invention, a beta-gamma Ti-Al-Nb-V alloy containing aluminum at an atomic ratio of 42% A step of cooling by heating and cooling at a specific cooling rate, or by introducing different cooling rates for each phase section. By forming a two-phase lamellar structure of? ₂ phase and? Phase of the alloy through the cooling-solidification heat treatment method, fracture toughness and creep resistance The improved Ti-Al-Nb-V alloy can be produced.

The method of producing a Ti-Al-Nb-V alloy according to the present invention as described above can improve the physical properties of various TiAl alloys having a low content of Al produced by casting or forging. .

Also, the present invention provides a Ti-Al-Nb-V alloy, which is produced by the above-described method and has a lamellar structure of? ₂ phase and? Phase of? ₂ +? Lamellar structure.

The Ti-Al-Nb-V alloy has a high strength including Al at an atomic ratio of 42 at.% Or less. The Ti-Al-Nb-V alloy has a hexagonal structure and has an α ₂ phase of Ti ₃ Al and TiAl of a tetragonal structure. Phase two-phase lamellar structure distributed in a finely dispersed manner is formed to exhibit improved fracture toughness and creep resistance.

Hereinafter, the present invention will be described in more detail with reference to examples.

The embodiments presented are only a concrete example of the present invention and are not intended to limit the scope of the present invention.

<Examples>

(Ti, Al, Nb, and V) for the production of an alloy containing 42 atomic percent of aluminum, 6 atomic percent of niobium atomic ratio, 6 to 8 atomic percent of iron, and the balance titanium ) for charging the copper pocket (Φ100 mm) were weighed according to the atomic ratio, and plasma arc melting apparatus (plasma arc melting, using a PAM) vacuum (5 × 10 ^- at ³ Torr) to melt the plasma arc, each raw material , Ingots of Ti-42Al-6Nb-6V alloy, Ti-42Al-6Nb-7V alloy and Ti-42Al-6Nb-8V alloy of thickness 10 mm were respectively prepared.

The ingot of the Ti-42Al-6Nb-7V alloy having a thickness of 10 mm was photographed and shown in FIG.

The ingots of the Ti-42Al-6Nb-7V alloy were subjected to differential scanning calorimetry (DSC) analysis using a DSC 404C instrument from Netzsch, Is shown in Fig. The calorimetric analysis was performed by measuring the change in the heat flow during heating and cooling at a rate of 10 ° C / min from 600 ° C to 1450 ° C in an argon gas atmosphere, and a DSC heating curve as shown in Fig. 2 was obtained.

The crystallization temperatures (1140 ° C, 1180 ° C, 1230 ° C, 1300 ° C and 1400 ° C) were determined based on the peak point of the ingot specimen in the DSC heating curve as shown in Fig.

As described above, in order to determine the phase transformation path using the crystallization temperature determined based on the peak point of the ingot specimen, the ingot specimen of the Ti-42Al-6Nb-7V alloy was subjected to the solution heat treatment by the quenching temperature, The experiment was carried out with temperature.

X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analysis were conducted after the temperature-dependent quenching experiment to analyze the compositional change of the ingot specimen by the heat treatment and the cooling treatment as described above. ), And the results are shown in Fig.

As shown in Fig. 3, it was confirmed that the microstructure and the XRD pattern of the ingot specimen coincided with each other in three phases (β + α + γ) when the crystallization temperature was 1180 ° C. and 1230 ° C. Phase is light gray, gamma phase is dark gray). Β ₀ + γ ₂ for 1300 ° C., β + α 1300 ° for 1400 ° C., β phase for 1400 ° C., and reference phase diagram for the similar composition shown in FIG. 4 And the phase transformation path of the ingot specimen of Ti-42Al-6Nb-7V alloy was predicted to be β + γ → β + α + γ → β + α → β.

The above-mentioned three kinds of alloys were subjected to the heat treatment and cooling treatment by using the results of the temperature-dependent quenching experiments. The conditions were divided into three methods as shown below (see the schematic diagram of FIG. 5).

Method 1: The alloy is heated at 1300 캜, which is higher than the Tα temperature (1245 캜), maintained for about 1 hour, heat-treated, cooled to 1245 캜 at a rate of 3 캜 / min and then quenched (AC) Ti-42Al-6Nb-6V alloy, Ti-42Al-6Nb-7V alloy and Ti-42Al-6Nb-8V alloy were heat treated and cooled, respectively.

Method 2: Ti-42Al-6Nb-6V alloy, Ti-42Al-6Nb (Ti) alloy was obtained by heating the alloy at 1300 ° C for about 1 hour and then heat- -7V alloy and Ti-42Al-6Nb-8V alloy were heat-treated and cooled, respectively.

Method 3: The alloy was heated at 1300 ° C for approximately 1 hour, heat-treated, cooled to 1245 ° C at a rate of 3 ° C / minute, cooled and cooled to room temperature at a cooling rate of 18 ° C / ), Ti-42Al-6Nb-6V alloy, Ti-42Al-6Nb-7V alloy and Ti-42Al-6Nb-8V alloy were heat treated and cooled, respectively.

After three kinds of heat treatment and cooling treatments for the three kinds of alloys as described above were performed, the surface of the obtained alloy was photographed and shown in FIG.

As shown in FIG. 6, the Ti-42Al-6Nb-6V alloy, (b) Ti-42Al-6Nb-7V alloy and (c) Ti-42Al- Was too fast and no phase transformation from α → γ or α → α ₂ occurred. Thus, it was confirmed that a lamellar structure of α + β, which is not a structure of α ₂ + γ lamellar structure, was generated.

In the case of Ti-42Al-6Nb-6V alloy, (e) Ti-42Al-6Nb-7V alloy and (f) Ti-42Al- In the case of the Ti-42Al-6Nb-6V alloy and the Ti-42Al-6Nb-8V alloy, it was confirmed that the α ₂ + γ lamellar structure was formed only partially in the 7V alloy, α ₂ + γ lamellar structure was formed.

In the case of Ti-42Al-6Nb-6V alloy, (h) Ti-42Al-6Nb-7V alloy and (i) Ti-42Al- for 7V alloy almost α ₂ + γ was confirmed that the lamellar structure is formed, the Ti-42Al-6Nb-6V alloy and Ti-42Al-6Nb-8V alloy was confirmed that the formation of α ₂ + γ lamellar structure.

As a result, optimum heat treatment and cooling conditions of Ti-42Al-6Nb-6V alloy, Ti-42Al-6Nb-7V alloy and Ti-42Al-6Nb-8V alloy were obtained.

The Vickers hardness of the Ti-42Al-6Nb-6V alloy, (e) Ti-42Al-6Nb-7V alloy and (f) Ti-42Al-6Nb-8V alloy prepared in the methods .

As a result, the Vickers hardness of the Ti-42Al-6Nb-7V alloy formed by the method (2) and having a partially lamellar structure was 400 Hv, whereas the Ti-42Al-6Nb-6V alloy having the complete lamellar structure had Vickers hardness of 440 Hv And the Vickers hardness of the Ti-42Al-6Nb-8V alloy was confirmed to be 430 Hv or more. In addition, the Vickers hardness of the Ti-42Al-6Nb-7V alloy (near α ₂ + γ lamellar) produced by the method ③ and having the lamellar structure is about 420 Hv, whereas the complete lamellar structure (α ₂ + γ lamellar) The Vickers hardness of the Ti-42Al-6Nb-6V alloy was 430 Hv or more, and the Vickers hardness of the Ti-42Al-6Nb-8V alloy was approximately 440 Hv.

As a result of the above-mentioned results, it has been found that a Ti-Al-Nb-V alloy having improved fracture toughness and creep resistance can be produced by forming a lamellar structure in an alloy structure by heat treatment and cooling treatment according to the present invention I can confirm that I can do it.

Claims (5)

(a) a Ti-42Al-6Nb-8V alloy containing 42 at.% aluminum, 6 at.% niobium, 8 at.% vanadium and the balance titanium at a temperature of 1250 to 1350 DEG C for 30 to 240 minutes Heat treating; And
(b) The Ti-42Al-6Nb-8V alloy heat-treated in the step (a) is first cooled at a rate of 2 to 5 ° C / min until the temperature reaches 1245 ° C, / Min to a room temperature at a cooling rate of 5 to 10 minutes / minute. delete The method according to claim 1,
In the step (b), the Ti-42Al-6Nb-8V alloy heat-treated in the step (a) is first cooled at a rate of 3 ° C / min until the temperature reaches 1245 ° C, Wherein the 6Nb-8V alloy is secondarily cooled to room temperature at a cooling rate of 18 DEG C / min. delete A Ti-Al-Nb-V alloy characterized in that a lamellar structure (? ₂ +? Lamellar structure) of? ₂ phase and? Phase is formed by the method described in claims 1 or 3.

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