KR101963428B1 - Titanium alloy and fabrication method of titanium alloy - Google Patents

Abstract

The present invention relates to a titanium alloy and a method for manufacturing the same. According to an embodiment of the present invention, the titanium alloy comprises: 4.0-5.5 wt% of aluminum (AI); 2.0-3.0 wt% of iron (Fe); 0.08-0.41 wt% of oxygen (O); and the remainder consisting of Ti and unavoidable impurities.

Description

TECHNICAL FIELD [0001] The present invention relates to a titanium alloy and a titanium alloy,

The present invention relates to a titanium alloy and a method for producing the titanium alloy.

Titanium is a lightweight metal with a specific gravity of about 4.0 g / cm ³ and is known to be a new material with excellent strength and corrosion resistance. Despite the excellent properties of titanium, the reason why titanium is not used for general purposes is that it is expensive compared with general structural materials. In order to lower the price of titanium, researches on the development of titanium alloy and improvement of process have been actively carried out in recent years using scrap, low-cost element, or intrusion-type element control such as oxygen or nitrogen.

The biggest problem in the recycling of titanium scrap is that the impurities such as oxygen and nitrogen contained in scrap are influenced greatly by the influx of metal impurities. Oxygen has a high solubility in titanium bases of up to about 33 at%, which is a reference to the classification of industrial pure (CP). Oxygen contained in titanium is a solid solution strengthening alloy element that strengthens the lattice without significantly affecting corrosion resistance. However, when the oxygen concentration is excessive, the impact resistance is drastically reduced by suppressing twin strain at low temperature, so that the soft-brittle transition temperature . ≪ / RTI >

In titanium alloys, oxygen is a strong α-phase stabilizing element, and increasing oxygen content affects mechanical properties such as elongation, toughness and long-term high temperature stability. For this reason, in titanium alloys, it is necessary to develop heat treatment technology along with proper process condition setting according to oxygen concentration.

In addition, since the titanium alloy can control physical properties through microstructure control, it is necessary to set appropriate processing conditions and heat treatment conditions. In general, the two-phase α + β titanium changes the mechanical properties of the alloy depending on the shape of α-phase and β-phase and the fraction of each phase. Such microstructure control is determined according to processing conditions such as forging or rolling at a specific temperature, heat treatment conditions and the like. When the size of the product is large in the actual heat treatment process of titanium, the temperature change varies depending on the region. Especially, in the case of the titanium alloy containing iron (Fe) or oxygen, various phase changes occur according to the cooling rate change. And development of heat treatment process technology for controlling mechanical properties are needed.

U.S. Patent No. 6,632,396

It is an object of the present invention to provide a titanium alloy with controlled microstructure and excellent mechanical properties.

It is another object of the present invention to provide a method of manufacturing a titanium alloy having controlled microstructure and excellent mechanical properties.

The titanium alloy according to the embodiment of the present invention is characterized by comprising 4.0 to 5.5% by weight of aluminum (Al), 2.0 to 3.0% by weight of iron (Fe), 0.08 to 0.41% by weight of oxygen (O), the balance Ti and unavoidable impurities do.

Also, the titanium alloy may have a beta transformation temperature of 980 to 1050 ° C.

A method of producing a titanium alloy according to another embodiment of the present invention comprises: 4.0 to 5.5% by weight of aluminum (Al), 2.0 to 3.0% by weight of iron (Fe), 0.08 to 0.41% by weight of oxygen (O), the balance Ti and unavoidable impurities Preparing an ingot containing the ingot; Hot working the ingot; Solubilizing the ingot that has undergone the hot working; And cooling at a cooling rate of 0.05 to 100 캜 / s after the solution heat treatment.

Also, the cooling rate in the cooling step after the solution heat treatment may be 0.2 to 1.0 DEG C / s.

Further, the step of hot working the ingot may include a plurality of hot working steps.

Also, the first hot working may be performed at a temperature of? Transformation temperature (T _? ) + 50 占 폚? Transformation temperature (T _? ) + 150 占 폚 of the titanium alloy.

Also, the second hot working may be performed at a temperature of? Transformation temperature (T _? ) -150 deg. C to? Transformation temperature (T _? ) -50 deg. C of the titanium alloy.

The titanium alloy according to the present invention can provide a titanium alloy with controlled microstructure according to the content of oxygen concentration and having excellent mechanical properties.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing each step of a method for producing a titanium alloy according to another embodiment of the present invention. FIG.
Fig. 2 is a continuous DSC-TAG graph of the titanium alloy according to Example 1, Example 2, and Example 3. Fig.
Fig. 3 shows hardness values according to the cooling rates of the titanium alloy according to Examples 1, 2 and 3. Fig.
Fig. 4 shows the? -? Phase transformation temperature according to the change of the cooling rate after the solution treatment of the titanium alloy prepared in Example 1. Fig.
5 is a graph showing a change in microstructure according to a change in cooling rate after the solution treatment of the titanium alloy prepared in Example 1. Fig.
Fig. 6 shows a state of continuous cooling according to a change in cooling rate after the solution treatment of the titanium alloy prepared in Example 1. Fig.
Fig. 7 shows a state of continuous cooling according to a change in cooling rate after the solution treatment of the titanium alloy prepared in Example 2. Fig.
Fig. 8 shows a state of continuous cooling according to a change in cooling rate after the solution treatment of the titanium alloy prepared in Example 3. Fig.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. Accordingly, the shapes and sizes of the elements in the drawings may be exaggerated for clarity of description, and the elements denoted by the same reference numerals in the drawings are the same elements. In the drawings, like reference numerals are used throughout the drawings. In addition, "including" an element throughout the specification does not exclude other elements unless specifically stated to the contrary.

Titanium alloy

The titanium alloy according to the embodiment of the present invention is characterized by comprising 4.0 to 5.5% by weight of aluminum (Al), 2.0 to 3.0% by weight of iron (Fe), 0.08 to 0.41% by weight of oxygen (O), the balance Ti and unavoidable impurities do.

Hereinafter, components of the titanium alloy according to the present invention and a range of components thereof will be described.

Aluminum (Al): 4.0 to 5.5 weight%

Aluminum is added to enhance the alpha phase solubility of the titanium. Aluminum is an element which solidifies and strengthens the alpha phase of the titanium alloy. As the content of aluminum increases, the strength increases by the employment of aluminum in the titanium (Ti) base. In addition, aluminum is lighter than titanium and plays a role in reducing the density of the alloy to achieve high specific strength, improving creep strength and increasing the modulus of elasticity. When the content of aluminum is less than 4.0 wt%, the effect of decreasing the density is not significant and the strength is lowered. When the aluminum content is more than 5.5 wt%, Ti ₃ Al is matched to form a regular lattice Ti ₃ Al intermetallic compound, It has been reported that the material is weakened by the slip band in the middle and causes spalling phenomenon during cooling at high temperature. Therefore, the aluminum content is limited to 5.5% by weight or less.

Iron (Fe): 2.0 to 3.0 weight%

Iron plays a role in stabilizing the titanium beta phase.

When the content of iron is less than 2.0% by weight, there is a problem that the? Phase can not be sufficiently stabilized at room temperature. When the content of iron exceeds 3.0% by weight, strength is increased while creep strength is lowered.

Iron is the cheapest among the alloying elements and does not form an intermetallic compound in the titanium matrix even after the heat treatment, exhibits solid solution strengthening effect and exhibits property that is not inferior to vanadium (V). In addition, it exhibits β stabilization effect three times higher than vanadium, and has the advantage of significantly lowering the molding temperature by increasing the α / β phase boundary at the same mass percentage.

Oxygen (O): 0.08 to 0.41 weight%

In titanium alloys, oxygen plays a role in stabilizing the strong alpha phase. The increase in oxygen content affects mechanical properties such as elongation, toughness and long-term high temperature stability.

If the content of oxygen exceeds 0.41% by weight, the brittleness may be increased and the workability may be deteriorated. This is because as the oxygen content increases, the sleep mode changes from a prismatic slip to a finer planar slip and changes from a uniform slip to a non-uniform slip. It is also known that oxygen exhibits enhanced solubility as it segregates to dislocation, but increases in brittleness when the concentration is excessive. If the content of oxygen is less than 0.08%, the strength of the titanium alloy may be deteriorated. Therefore, in the titanium alloy, the oxygen content may preferably be 0.08 to 0.41% by weight.

The titanium alloy according to the embodiment of the present invention is titanium (Ti) except for the above components. However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are self-evident to those of ordinary skill in the art of manufacturing, and therefore, not all thereof are specifically referred to herein.

The titanium alloy may have a beta transformation temperature of 980 to 1050 캜.

The beta transformation temperature of pure titanium is 882 ° C. The beta transformation temperature can be changed according to the oxygen content of the titanium alloy. When the oxygen content of the titanium alloy according to the embodiment of the present invention is changed from 0.08 to 0.41 wt%, the beta transformation temperature may vary from 980 to 1050 캜.

Manufacturing method of titanium alloy

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing each step of a method for producing a titanium alloy according to another embodiment of the present invention. FIG.

Referring to FIG. 1, a method for manufacturing a titanium alloy according to another embodiment of the present invention includes 4.0 to 5.5 wt% of aluminum, 2.0 to 3.0 wt% of iron, 0.08 to 0.41 wt% of oxygen, Preparing an ingot containing the remainder Ti and unavoidable impurities (step 1); Hot working the ingot (step 2); A step (3) of solubilizing the ingot subjected to the hot working; And cooling the solution at a cooling rate of 0.2-1.0 DEG C / s after the solution heat treatment (step 4).

Hereinafter, a method of manufacturing a titanium alloy according to another embodiment of the present invention will be described.

In the method for producing a titanium alloy according to another embodiment of the present invention, step 1 is a step of preparing a titanium alloy containing 4.0 to 5.5 wt% of aluminum (Al), 2.0 to 3.0 wt% of iron (Fe), 0.08 to 0.41 wt% Ti and unavoidable impurities.

In the step of preparing the ingot of step 1, a mixture containing 4.0 to 5.5% by weight of aluminum (Al), 2.0 to 3.0% by weight of iron (Fe), 0.08 to 0.41% by weight of oxygen (O), the balance Ti and unavoidable impurities A method selected from the group consisting of a vacuum melting method (VAR), an electron beam melting method, a plasma arc melting method, a non-consuming electrode arc melting method, and an inductive scull melting method may be used and more preferably an induction scull melting method is used . The induction skull melting method has been changed from the conventional induction melting to the crucible by water cooling, and the problem of molten metal contamination by the crucible can be avoided. In induction melting, there is little opportunity for the molten metal to directly contact the water-cooling crucible due to the action of a force in the center direction on the molten metal by the electromagnetic force. Even if the molten metal contacts the crucible, the crucible is immediately cooled, I can not do it. The molten alloy is poured into a mold made of graphite to make an ingot. In the method for producing the titanium alloy of the present invention, the dissolution of the step 1 may be performed under the conditions of 10 - 20 kW and 4 - 9 kHz using an induction scull melting furnace.

The aluminum content in step 1 is preferably 4.0 to 5.5 wt%.

When the content of aluminum is less than 4.0 wt%, the effect of decreasing the density is not significant and the strength is lowered. When the aluminum content is more than 5.5 wt%, Ti ₃ Al is matched to form a regular lattice Ti ₃ Al intermetallic compound, It has been reported that the material is weakened by the slip band in the middle and causes spalling phenomenon during cooling at high temperature. Therefore, the aluminum content is limited to 5.5% by weight or less.

The iron content in step 1 is preferably 2.0 to 3.0 wt%.

When the content of iron is less than 2.0% by weight, there is a problem that the? Phase can not be sufficiently stabilized at room temperature. When the content of iron exceeds 3.0% by weight, strength is increased while creep strength is lowered.

The oxygen content in step 1 is preferably 0.08 to 0.41 wt%.

If the content of oxygen exceeds 0.41% by weight, the brittleness may be increased and the workability may be deteriorated. This is because as the oxygen content increases, the sleep mode changes from a prismatic slip to a fine planar slip and changes from a uniform slip to a non-uniform slip. It is also known that oxygen exhibits enhanced solubility as it segregates to dislocation, but increases in brittleness when the concentration is excessive. If the content of oxygen is less than 0.08%, the strength of the titanium alloy may be deteriorated. Therefore, in the titanium alloy, the oxygen content may preferably be 0.08 to 0.41% by weight.

Further, in the method of manufacturing a titanium alloy according to another embodiment of the present invention, the titanium alloy is titanium (Ti) except for the above components. However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are self-evident to those of ordinary skill in the art of manufacturing, and therefore, not all thereof are specifically referred to herein.

In the method for producing a titanium alloy according to another embodiment of the present invention, Step 2 is a step of hot working the ingot of Step 1 above.

The hot working is a working which is carried out at a temperature higher than the recrystallization temperature, and when the hot working is performed, the mechanical properties and the workability are improved. The α + β type titanium alloy can have various microstructures according to the processing heat treatment process, and thus the mechanical properties and processability of the alloy can be changed. Particularly, the mechanical properties vary depending on the phase fraction formed by the processing heat treatment process, the shape and size of the? Grains, the distribution, and the texture.

In step 2, a plurality of steps of hot working may be performed, for example, a first hot working performed in a first temperature range, and a second hot working performed in a second temperature range. In the step of performing the hot working, the working strain of the ingot may not be particularly limited.

Specifically, the first hot working is performed at a temperature of + β transformation temperature (T _β ) + 50 ° C. to β transformation temperature (T _β ) + 150 ° C. of the titanium alloy, and the second hot working is performed by heating the titanium alloy it may be preferable to perform air cooling after performing at a temperature of? transformation temperature (T _? ) -150 deg. C to? transformation temperature (T _? ) -50 deg.

The first hot working is a step for crushing the casting structure simultaneously with the homogenizing treatment of the titanium alloy ingot manufactured in Step 1 and gives a large deformation at a temperature exceeding the beta transformation temperature region of the produced titanium alloy, The former beta crystal grains are crushed to induce dynamic recrystallization, thereby finerizing the beta crystal grains. When the primary hot working temperature is lower than the? Transformation temperature (T _? ) + 50 占 폚, there is a problem that cracks occur together with a high working pressure, and when? Transformation temperature (T _? ) + 150 占 폚 causes significant crystal growth There is a problem. It is easy to form a minute bead-only texture through water-cooling after hot working at the above-mentioned temperature, and to produce an equiaxed α-phase in the second forging process described below.

The secondary hot working is preferably carried out below the beta phase transition temperature of the titanium alloy. This is to perform hot forging in the? +? Region to secondarily planarize the plate-like? -Phase. Second there is a problem that can result in cracks on the material surface and requires a high molding pressure during the molding in the hot working during β transformation temperature (T _β) less than -150 ℃, β transformation temperature (T _β) formed from greater than -50 ℃ , There is a problem that the processed mixture is processed in the? -Phase region due to the heat of processing and the? +? Mixed phase is not formed.

When performing the hot working, it may further include applying an antioxidant material to the surface of the ingot manufactured in the previous step.

The antioxidant is not particularly limited. For example, water and a glass lubricant (delta-graze) may be mixed at a ratio of 2: 1 and thinly coated on the ingot surface.

In the method for producing a titanium alloy according to another embodiment of the present invention, step 3 is a step of solubilizing the ingot subjected to the hot working.

The temperature at which the solution treatment is performed may be preferably performed at a temperature exceeding the beta transformation temperature of the titanium alloy according to the embodiment of the present invention. The solution treatment may be performed at the specified temperature for 30 minutes to 2 hours, and may be cooled at the designated cooling rate in the subsequent step.

In the method of manufacturing a titanium alloy according to another embodiment of the present invention, step 4 is a step of cooling at a cooling rate of 0.05 to 100.0 DEG C / s after the solution heat treatment.

In the method of manufacturing a titanium alloy according to another embodiment of the present invention, an image formed inside the titanium alloy may be changed by a change of a cooling rate according to an oxygen content of the titanium alloy, and physical properties such as hardness and toughness Can vary.

If the heat treatment temperature is less than 0.05 ° C / s, there may be a problem that the cooling time is long due to the cooling rate, and when the heat treatment temperature exceeds 100 ° C / s, it is difficult to control the phase formed inside the titanium alloy .

The cooling rate after the solution heat treatment in step 4 may be 0.05 to 1.0 DEG C / s.

The hardness value of the titanium alloy having passed the cooling rate section may increase due to the precipitation strengthening effect of the intermetallic compound in the above temperature range.

Example

Example 1

The raw materials used for the alloying were Grade 1, 2 Titanium, 10 mm x 20 mm x 0.5 mm strips, 8-12 mm aluminum with 99.9% purity, 99.99% purity with 1 to 4 mm size, purity 99.9% Of titanium dioxide (TiO ₂ ) of 1 to 4 mm in size was used.

A mixture was prepared by adjusting the amount of the titanium dioxide (TiO ₂ ), and the mixture was dissolved to prepare a ingot having the following composition.

The alloy was prepared by the plasma arc melting (PAM) method and the primary buttoning ingot was prepared by dissolving it in the conditions of 6000 Hz, 100 A, and 300 V through the induction scull melting method (ISM) .

The cast alloy was machined into a cylinder of 40x60 mm and subjected to hot forging to crush the cast structure. In order to prevent oxidation of the specimen surface during hot forging, water and a glass lubricant (delta-graze) were mixed at a ratio of 2: 1 and thinly coated on the surface of the ingot. The ingot breakdown forging was carried out by using a 150 ton hydraulic press with the temperature of the forging block being set at 200 ° C and dividing into 1 and 2 pieces. For the first forging, hold for 1 hour in a temperature range 50 ° C higher than the β transformation temperature of each alloy, and then set up to a compression rate of 25%. The specimens were rotated at 90 ° for forging at a compression ratio of 50% And then water-cooled. After that, the second forging is maintained for 1 hour in the α + β region, which is 50 ° C lower than the β transformation temperature, and then the specimen is rotated at 90 ° in the same manner as the first forging. Ti-5Al-2.5Fe-0.40O.

Example 2

The procedure of Example 1 was repeated except that the amount of the TiO ₂ strips was controlled so that the composition of the final alloy was Ti-5Al-2.5Fe-0.20O at the time of preparation of the mixture of Example 1, .

Example 3

The procedure of Example 1 was repeated except that the amount of TiO ₂ strip was adjusted so that the composition of the final alloy was Ti-5Al-2.5Fe-0.08O at the time of preparation of the mixture of Example 1, .

The compositions of the titanium alloys prepared in Examples 1, 2 and 3 are shown in Table 1 below.

Al Fe C H O N Ti Example 1 4.95 2.53 0.014 0.006 0.41 0.004 Remainder Example 2 4.93 2.54 0.015 0.010 0.21 0.009 Remainder Example 3 5.10 2.58 0.016 0.005 00.076 0.004 Remainder

Example 4

Example 1 was prepared in the same manner as in Example 1 except that the amount of aluminum was controlled so that the composition of the final alloy was Ti-4Al-2.5Fe-0.084O.

Experimental Example 1

Beta transformation temperature measurement

Simultaneous thermogravimetric analysis and simultaneous DSC-TGA (SDT), TA Instrument, Q-600) were used to measure the β transformation temperature of Ti-5Al-2.5Fe alloy with oxygen content. In order to prevent oxidation, argon (Ar) gas with a purity of 99.999% was injected at a rate of 100 ml / min from room temperature to 1200 ° C at a rate of 5 ° C / min. β transformation temperature was measured, and it is shown in FIG.

Fig. 2 is a continuous DSC-TAG graph of the titanium alloy according to Example 1, Example 2, and Example 3. Fig.

In FIG. 2, the? -Phase conversion temperature measured using SDT is represented by the maximum value (dx / dy = 0) of the inflection point at which the phase transformation is completed. It was confirmed that the? Phase transformation temperature was decreased by 68 占 폚 at 1045 占 폚 for the titanium alloy prepared by Example 1, 1014 占 폚 for the titanium alloy prepared by Example 2, and 977 占 폚 for the titanium alloy prepared by Example 3 Similar to the previous calculation results.

Through the above experiment, it can be seen that oxygen acts as an α phase stabilizing element by raising the temperature of the Ti - β transformation temperature.

Experimental Example 2

Hardness measurement

In order to examine the change of the mechanical properties according to the cooling rate after the solution treatment step of the titanium alloy according to the embodiment of the present invention, the hardness was measured at 500 g for 10 seconds through a micro-Vickers hardness tester (Future-Tech, FM-700) And the results are shown in FIG.

Fig. 3 shows hardness values according to the cooling rates of the titanium alloy according to Examples 1, 2 and 3. Fig.

Referring to FIG. 3, the hardness at a cooling rate of 100 ° C / s shows a hardness of 455 HV in the titanium alloy prepared in Example 1, 436HV in the titanium alloy prepared in Example 2, The prepared titanium alloy showed excellent hardness at high oxygen content of 360 HV.

The hardness of each alloy was found to be 377 HV in the titanium alloy prepared in Example 1, 339 HV in the titanium alloy prepared in Example 2, and in Example 3 The prepared titanium alloy showed a tendency to decrease to 299 HV.

On the other hand, all alloys showed an increase in hardness at a cooling rate of 0.05 ° C / s. In the case of general phase change behavior, coarse grain formation shows a decrease in strength, but the alloys used in this study can form precipitation phases such as TiFe or Ti ₃ Al in a certain temperature range. The formation of such a precipitate phase causes an increase in the strength of the titanium alloy.

The highest hardness value in the titanium alloy prepared by Example 1 and the above result can be considered to be due to the fact that oxygen acts as a strong alpha phase stabilizing element in the titanium alloy and strengthens the alpha phase.

Experimental Example  3

Yield strength measurement

Table 2 below shows the tensile properties of Ti-4Al-2.5Fe and Ti-5Al-2.5Fe alloys containing about 0.36% oxygen prepared by Example 1 and Example 4. These two alloys are water - cooled after forging at a temperature above the beta transformation temperature and air - cooled after cooling in the α + β region. Both alloys showed equal or better strength than the similar heat treatment conditions of the Ti-6Al-4V alloy, which is a commercial alloy, and the elongation was remarkably excellent.

Yield strength
(YS, MPa) Maximum tensile strength
(UTS, MPa) Elong. (%) Example 1
Ti-5Al-2.5Fe 1028 1138 20.5 Example 2
Ti-4Al-2.5Fe 971 1095 18

The tensile test specimens of the material were manufactured in accordance with ASTM E-8 standard and the tensile test was carried out using a universal material testing machine (model INSTRON 5585H) at a crosshead speed of 10 ^-3 mm / s. Elongation was measured using an extensometer with a 25 mm gage length of INSTRON.

Experimental Example 4

Continuous cooling Phase change  Experiment

For the phase change test with continuous cooling, the thermal expansion coefficient measurement device Theta (Dilatronic-Ⅲ) was used. In order to uniformly induce the initial structure, each of the specimens of the titanium alloy prepared in Examples 1 to 3 was maintained in the region of? Transformation temperature of 50 or more for 1 hour, and then cooled to homogeneity. Each alloy was made into a specimen of? . The cooling rate for dilatometer testing was cooled at a cooling rate of 100 ° C / s to 0.05 ° C / s in the region between water cooling, air cooling and low cooling. 3.0 x 10 ^- was raised in a vacuum atmosphere of ⁴ Torr to 15 ℃ / s rate in the β transformation temperature + 50 target temperature, then held for 30 minutes at the target temperature 100, 50, 20, 4.2, 1, 0.2, 0.05 ℃ / s < / RTI > at a purity of 99.999%.

Continuous cooling of the titanium alloy prepared according to Example 1 Phase change  Experiment

Fig. 4 shows the? -? Phase transformation temperature according to the change of the cooling rate after the solution treatment of the titanium alloy prepared in Example 1. Fig.

From the cooling rate of 50 ° C / s, the titanium alloy prepared according to Example 1 having the highest oxygen content showed a somewhat higher value than that of the prior two alloys at the beginning and completion temperatures of 846 ° C and 710 ° C.

Referring to FIG. 5, the titanium alloy prepared by Example 1 has a grain boundary? Observed at a cooling rate of 50 占 폚 / s. As a result of observation of the microstructure of the intergranular α formation in FIG. 5, it can be seen that the formation of intergranular α started at a rapid cooling rate with increasing oxygen content.

This is because oxygen functions as a strong α-phase stabilizing element and the α-phase nucleation rate formed at β-crystal grains becomes faster as α-phase stabilization degree is increased, so that grain boundary α formation at a rapid cooling rate becomes possible. In addition, the internal needle-shaped structure forms a group having a directionality, and as it grows, it exhibits bead-stamper structure. Since the driving force for microstructure formation increases by cooling from a higher temperature, internal tissue growth is promoted.

The titanium alloy according to the embodiment of the present invention exhibits a general behavior in which the hardness value of the material decreases as the cooling rate is slowed down after the solution treatment. However, as the cooling rate slows down below 0.2 ° C / s, the hardness value increases. This behavior can be an effect of precipitation strengthening by intermetallic compounds such as TiFe and Ti ₃ Al.

Continuous cooling of the titanium alloy prepared according to Example 2 Phase change  Experiment

The? -? Phase transformation temperature was measured in accordance with the change of the cooling rate after the solution treatment of the titanium alloy prepared in Example 2 in the same manner as in Example 1 above.

The titanium alloy prepared according to Example 2 starts to form alpha phase at 732 DEG C at a cooling rate of 100 DEG C / s and is completed at 683 DEG C, and alpha phase formation from 758 DEG C at a cooling rate of 50 DEG C / And is completed at 665 ° C.

At a cooling rate of 20 占 폚 / s, the? Phase start temperature greatly increases to 862 占 폚. It can be seen that the α phase start temperature is lower than the cooling rate of 4.2 ° C./s of the titanium alloy prepared in Example 1. In the case of the titanium alloy prepared in Example 2, a grain boundary? Formed along? Crystal grains can be formed at a cooling rate of 20 占 폚 / s.

Continuous cooling of the titanium alloy prepared according to Example 3 Phase change  Experiment

The? -? Phase transformation temperature was measured in accordance with the change of the cooling rate after the solution treatment of the titanium alloy prepared in Example 3 in the same manner as in Example 1 above.

The titanium alloy prepared according to Example 3 starts to form alpha phase at 802 ° C at a cooling rate of 100 ° C / s, which is the fastest cooling rate, and is completed at 705 ° C. When the cooling rate is 20 ° C / Image formation starts.

The titanium alloy prepared according to Example 3 may be a martensitic transformation region that forms a fine needle-shaped? 'Phase by quenching-free diffusion at a rapid cooling rate of 20 ° C / s or more. In a titanium alloy, this martensitic transformation can be accomplished for a short time at a somewhat lower temperature below the? Transformation temperature.

At a cooling rate of 4.2 캜 / s, the start of α phase formation at 841 ° C. is shown and completed at 612 ° C. The α phase formation start temperature increased with the cooling rate at 20 ° C / s. As the cooling rate slowed, the α phase formation start temperature tended to increase near β transformation temperature (T _β = 980 ° C).

After the cooling rate of 4.2 캜 / s, the temperature of completion of the phase transformation was found to be in the vicinity of 607 캜 to 604 캜.

Table 3 shows the phase initiation and termination temperatures of the phase transition from? Phase to? Phase according to the cooling rate after the solution treatment of the titanium alloy prepared in Examples 1 to 3 confirmed in the above experiment.

Cooling
Condition
(° C / s)
Transformation temperature (캜) Example 1 Example 2 Example 3 start End start End start End 100 802 705 732 683 802 710 50 793 630 758 665 846 710 20 787 622 862 658 861 722 4.2 841 612 882 655 924 624 One 958 604 968 626 1018 628 0.2 977 607 1002 620 1037 615 0.05 978 604 1016 610 - -

6, Fig. 7, and Fig. 8, and the results are shown in Table 3 and Fig. 5, and the cooling rate after the solution treatment of the titanium alloy prepared in Example 1, Example 2, Respectively.

Fig. 6 shows a state of continuous cooling according to a change in cooling rate after the solution treatment of the titanium alloy prepared in Example 1. Fig.

Fig. 7 shows a state of continuous cooling according to a change in cooling rate after the solution treatment of the titanium alloy prepared in Example 2. Fig.

Fig. 8 shows a state of continuous cooling according to a change in cooling rate after the solution treatment of the titanium alloy prepared in Example 3. Fig.

Referring to FIGS. 6, 7 and 8, the area forming each phase with the increase of the oxygen content showed a shift toward the left side of the continuous cooling transformation degree. As the nucleation rate increases, the α 'phase region is narrowed to the α _GB + α _w + β region due to grain boundary α formation at a rapid cooling rate, and as the internal structure grows from the formation of grain boundary α, Tissue formation and growth were promoted.

The present invention is not limited to the above-described embodiment and the accompanying drawings, but is intended to be limited by the appended claims. It will be apparent to 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. something to do.

Claims (7)

delete delete Preparing an ingot comprising 4.0 to 5.5 wt% of aluminum (Al), 2.0 to 3.0 wt% of iron (Fe), 0.08 to 0.41 wt% of oxygen (O), the balance titanium (Ti) and unavoidable impurities;
Subjecting the ingot to primary heat treatment at a temperature of? Transformation temperature (T _? ) + 50 ° C to? Transformation temperature (T _? ) + 150 ° C;
A second hot working step at a temperature of? Transformation temperature (T _? ) -150 deg. C to? Transformation temperature (T _? ) -50 deg. C after the first hot working;
Treating the ingot subjected to the hot working at a temperature exceeding the beta transformation temperature of the titanium alloy; And
And cooling the solution at a cooling rate of 0.05 to 100.0 ° C after the solution heat treatment.
The method of claim 3,
Wherein the cooling rate in the cooling step after the solution heat treatment is 0.05 to 1.0 DEG C / s.
delete delete delete

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