KR101387551B1 - High strength titanium alloy with excellent oxidation resistance and formability and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a high-strength titanium alloy excellent in oxidation resistance and formability, and a method for manufacturing the same. Specifically, 4.0 to 8.0 wt% Al, 2.0 to 6.0 wt% Fe, 0.05 to 0.25 wt% Si, and 0.001 to 0.5 Provided is a high-strength titanium alloy having excellent oxidation resistance and formability, including B by weight, and balance Ti, and a method of manufacturing the same. In the titanium alloy according to the present invention, in the conventional Ti-6Al-4V alloy, vanadium (V) is a β-stabilizing element stronger than vanadium, and inexpensive iron (Fe) is used as an alloying element, and the manufacturing cost is low, and a small amount of boron ( By adding B) and silicon (Si), the crystal grains are refined, the strength is excellent at room temperature, and the elongation is excellent at high temperatures, but the strength is low, and the moldability is excellent, and the oxidation resistance is excellent at high temperatures.

Description

High strength titanium alloy with excellent oxidation resistance and formability and method for manufacturing the same

The present invention relates to a high strength titanium alloy excellent in oxidation resistance and formability and a method for producing the same.

Titanium alloys have been applied to various industries such as aerospace, marine, sports, medical, etc. due to their high specific strength, excellent corrosion resistance and biocompatibility. Pure titanium transforms the α phase having a dense hexagonal structure at room temperature into an β phase having a body-centered cubic structure due to isomorphism at 882 ° C. When alloying elements are added to pure titanium, there exists a region where α and β phases coexist in a specific temperature section, and in some cases, the region extends to room temperature. As such, titanium alloys are generally classified into α alloys, β alloys, and α + β alloys at room temperature. The most widely used alloy is α + β alloy, which has a basic composition based on Ti-Al, which stabilizes the α phase and has a solid solution strengthening effect, and includes molybdenum (Mo), iron (Fe), and vanadium (V). And β-phase stabilizing elements such as chromium (Cr) and neutral elements such as zirconium (Zr) and tin (Sn). The most representative alloy of α + β alloy is Ti-6Al-4V, which accounts for more than 60% of the total titanium alloy usage because of excellent hot workability, weldability, and various mechanical properties obtained by heat treatment.

However, since the development of titanium alloys has been mainly made for aerospace purposes, alloy elements have been selected based on physical properties rather than prices, and have been made of alloy systems that are expensive and not easy to supply. In particular, vanadium (V), which is used for Ti-6Al-4V, is an expensive element and has harmful toxicity to humans. Therefore, there are many constraints on the special use of this alloy. Therefore, efforts have been made to develop low-cost new alloys by replacing vanadium (V), which is a representative β-phase stabilizing element, with other β-phase stabilizing elements which are inexpensive and relatively harmless to the human body. As a result, Ti-5Al-2.5 Although alloys such as Fe and Ti-6Al-0.1Si have been developed, various problems such as the tendency of the mechanical properties at room temperature and high temperature tend to be somewhat insufficient as the content of iron (Fe), which is a β-stabilizing element, are not optimized. have.

Conventionally, patent document 1 relates to the heat resistant titanium alloy material excellent in high temperature corrosion resistance and oxidation resistance, and its manufacturing method. In detail, a surface layer having a multilayer structure of an inner layer of β, γ, and Laves phases of a Ti-Al-Cr alloy and an outer layer of Al-Ti-Cr alloy is formed on the surface of the heat-resistant Ti alloy base material. It is an alloy containing the Al concentration of 50 atomic% or more of an outer layer, and there exists an effect which has heat resistance excellent in high temperature corrosion resistance and oxidation resistance.

In addition, Patent Document 2 relates to a method for producing a (α + β) titanium alloy with improved mechanical properties and dynamic fracture characteristics, in detail, the (α + β) titanium alloy by aging treatment at 400-600 ℃ α ₂ The (α + β) titanium alloy having improved mechanical properties and dynamic fracture characteristics, including the step of depositing a (Ti ₃ Al) phase inside the α phase and quenching the (α + β) titanium alloy obtained in the step. It provides a manufacturing method. The present invention is based on Ti-6Al-4V-based alloys, and has a problem of containing expensive and harmful vanadium.

Accordingly, the present inventors are interested in research on a titanium alloy having low manufacturing cost and excellent oxidation resistance, mechanical properties, and moldability, and the Ti-Al-Fe-Si-B type titanium alloy of the present invention By using vanadium (V) of the conventional Ti-6Al-4V alloy, which is a β-stabilizing element that is stronger than vanadium and inexpensive iron (Fe), as an alloying element, the manufacturing cost is economical, and a small amount of silicon (Si) or silicon (Si)- By adding boron (B), the grains are refined, the room temperature strength is excellent, the elongation is excellent at high temperature, but the strength is low, the strength is low, the moldability is excellent, and the effect of having excellent oxidation resistance at high temperature is confirmed. Was completed.

Patent Document 1: Republic of Korea Patent Publication No. 10-2004-0101267 Patent Document 2: Republic of Korea Patent Publication No. 10-2004-0044840

The object of the present invention is to

It is to provide a high strength titanium alloy excellent in formability.

It is also an object of the present invention to provide a method for producing a high strength titanium alloy having excellent oxidation resistance and formability.

In order to achieve the above object,

The present invention provides a titanium alloy comprising 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si and the balance Ti.

The present invention also provides a titanium alloy comprising 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si, 0.001-0.5 wt% B and balance Ti.

Furthermore, the present invention comprises the steps of dissolving 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si and the balance Ti to produce an alloy ingot (step 1); It provides a method of producing a titanium alloy comprising a; and hot working the ingot (step 2).

In addition, the present invention is to prepare an alloy ingot by dissolving 4.0 to 8.0% by weight of Al, 2.0 to 6.0% by weight of Fe, 0.05 to 0.25% by weight of Si, 0.001 to 0.5% by weight of B and the balance Ti (step One); It provides a method of producing a titanium alloy comprising a; and hot working the ingot (step 2).

Titanium alloy according to the present invention is economical manufacturing cost by using vanadium (V) of the conventional Ti-6Al-4V alloy is a β-stabilization element stronger than vanadium and inexpensive iron (Fe) as an alloying element, and a small amount of silicon (Si ) Or by adding silicon (Si) -boron (B), the grains are refined, the room temperature strength is excellent, the elongation is excellent at high temperature, but the strength is low, the moldability is excellent and the oxidation resistance is excellent at high temperature. There is.

1 is a photograph showing the macrostructure and microstructure of the alloy ingot: (a) Example 1; (b) Example 2; (c) Example 3,
Figure 2 is a graph showing the DSC measurement results for measuring the beta transformation temperature of the alloy: (a) Example 2, (b) Example 3, (c) Example 4,
Figure 3 is a photograph showing the specimen shape before and after the 700 ° C high temperature tensile test: (a) the specimen before the test, (b) Comparative Example 1, (c) Example 2, (d) Example 4,
Figure 4 is a graph showing the results of thermogravimetric analysis for comparing the high temperature oxidation characteristics of the alloy: (a) Comparative Example 1, (b) Example 2, (c) Example 3, (d) Example 4.

Hereinafter, the present invention will be described in detail.

The present invention provides a titanium alloy comprising 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si and the balance Ti.

The present invention also provides a titanium alloy comprising 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si, 0.001-0.5 wt% B and balance Ti.

The role of the metals forming the alloy is as follows.

1) Aluminum (Al)

Aluminum is an element that solidifies and strengthens the α phase of the alloy. As the aluminum content increases, the strength increases due to the solid solution of aluminum to the titanium (Ti) matrix. In addition, aluminum is lighter than titanium and serves to reduce the density of the alloy to achieve high specific strength.

In the titanium alloy of the present invention, the content of aluminum is preferably 4.0 to 8.0% by weight. When the content of aluminum is less than 4.0% by weight, there is a problem in that the effect of reducing the density is not large and the strength is lowered. When the content of aluminum is more than 8.0% by weight, Ti ₃ Al is formed to rapidly decrease the ductility of titanium. In the titanium alloy of the present invention, more preferably, 5.0-7.0 wt% or 4.0-6.0 wt% aluminum can be used.

2) Fe

Iron plays a role in stabilizing the β phase. Iron is an inexpensive yet powerful β-phase stabilizing element whose Mo equivalent is about 3.8 times that of vanadium, and in the case of adding iron instead of vanadium in the Ti-6Al-4V alloy, the basic physical properties of the alloy are greatly improved.

In the titanium alloy of the present invention, the iron content is preferably 2.0 to 6.0% by weight. If the iron content is less than 2.0% by weight, there is a problem that the β phase cannot be sufficiently stabilized at room temperature. If the iron content is more than 6.0% by weight, the strength is increased while the creep strength is lowered. In the titanium alloy of the present invention, more preferably, 3.0 to 5.0% by weight or 2.0 to 4.0% by weight of iron can be used.

3) silicon (Si)

Silicon compensates for the deterioration of high temperature properties caused by the iron alloy element and at the same time, it is dissolved in the titanium base or precipitated as fine particles to serve to improve the tensile strength at room temperature.

In the titanium alloy of the present invention, the content of silicon is preferably 0.05-0.25% by weight. If the silicon content is less than 0.05% by weight, there is a problem in that it is not possible to sufficiently compensate for the deterioration of high temperature properties caused by the iron alloy element. If the silicon content is more than 0.25% by weight, coarse titanium silicide is formed to form crystal grains. There is a problem of suppressing miniaturization. In the titanium alloy of the present invention, more preferably 0.05 to 0.15 wt% or 0.1 to 0.25 wt% silicon can be used.

4) Boron (B)

Boron serves to improve the mechanical strength, formability and oxidation resistance of titanium alloys.

In the titanium alloy of the present invention, the content of boron is preferably 0.001-0.5% by weight. If the content of boron is less than 0.001% by weight, there is a problem that the mechanical strength, moldability and oxidation resistance can not be improved. If the content of boron is more than 0.5% by weight, the strength is increased, but there is a problem that the elongation is lowered. In the titanium alloy of the present invention, more preferably, 0.005-0.5 wt% of boron can be used.

The Ti-Al-Fe-Si alloy according to the present invention preferably comprises 5.0-7.0 wt% Al, 3.0-5.0 wt% Fe, 0.05-0.15 wt% Si and the balance Ti.

In addition, the Ti-Al-Fe-Si alloy according to the present invention preferably comprises 4.0 to 6.0% by weight of Al, 2.0 to 4.0% by weight of Fe, 0.1 to 0.25% by weight of Si and the balance Ti.

The Ti-Al-Fe-Si-B alloy according to the present invention is 5.0-7.0 wt% Al, 3.0-5.0 wt% Fe, 0.05-0.15 wt% Si, 0.005-0.5 wt% B and the balance Ti It is preferable to include.

In addition, the Ti-Al-Fe-Si-B alloy according to the present invention is 4.0 to 6.0% by weight of Al, 2.0 to 4.0% by weight of Fe, 0.1 to 0.25% by weight of Si, 0.005 to 0.5% by weight of B and It is preferable to include the balance Ti.

Furthermore, the present invention provides a titanium alloy consisting of 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si, balance Ti and inevitable impurities.

The present invention also provides a titanium alloy consisting of 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si, 0.001-0.5 wt% B, balance Ti and inevitable impurities.

Referring to Experimental Example 1, the macrostructures and microstructures of the ingots of the titanium alloy according to the present invention were observed, and the Ti-6Al-4Fe-0.1Si alloy ingots had an initial beta grain of 500-700 μm in size. Compared with the Ti-6Al-4Fe-0.1Si-0.01B alloy, the initial beta (prior-β) grain size was reduced to about 200 μm, and the Ti-6Al-4Fe-0.1Si-0.05B alloy was about fine. It can be seen that the grains became finer at about 70 μm. In addition, the size of acicular alpha (a) in the grains was also found to gradually become fine with the addition of boron. From this, it can be seen that the Ti-Al-Fe-Si-B alloy of the present invention has a significant grain refinement by addition of boron.

Referring to Experimental Example 2, the Ti-Al-Fe-Si-B alloy according to the present invention has a beta transformation temperature in the range of 935-940 ℃, it was shown that the beta transformation temperature increases with the addition of boron. From this, the beta transformation temperature of the Ti-Al-Fe-Si-B alloy of the present invention is about 50 ° C lower than the beta transformation temperature of commercial Ti-6Al-4V alloy, thereby lowering the process temperature for crushing the casting structure of the ingot. It can be seen that there are advantages.

Referring to Experiment 3, the Ti-Al-Fe-Si alloy and Ti-Al-Fe-Si-B alloy according to the present invention were about 150 ° C. than 850 ° C., which is the superplasticity of the commercial Ti-6Al-4V alloy. It can be seen that at low temperatures of 700 ° C., superplasticity can be expressed. In addition, the room temperature strength was higher than that of the Ti-6Al-4V alloy, but the strength at the molding temperature of 700 ° C was found to be lower. From this, it can be seen that the Ti-Al-Fe-Si alloy and the Ti-Al-Fe-Si-B alloy of the present invention have excellent moldability compared to the Ti-6Al-4V alloy.

Referring to Experimental Example 4, when the Ti-Al-Fe-Si-B alloy according to the present invention was subjected to a high temperature treatment in an air atmosphere and to a high temperature treatment in an air atmosphere, compared to a commercial Ti-6Al-4V alloy, The change in weight per unit area was smaller, and the higher the boron content, the smaller the change in weight per unit area over time. From this, it can be seen that the Ti-Al-Fe-Si-B alloy of the present invention has excellent high temperature oxidation resistance compared to the Ti-6Al-4V alloy, and the higher the boron content, the better the high temperature oxidation resistance.

Furthermore, the present invention comprises the steps of dissolving 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si and the balance Ti to produce an alloy ingot (step 1); It provides a method of producing a titanium alloy comprising a; and hot working the ingot (step 2).

In addition, the present invention is to prepare an alloy ingot by dissolving 4.0 to 8.0% by weight of Al, 2.0 to 6.0% by weight of Fe, 0.05 to 0.25% by weight of Si, 0.001 to 0.5% by weight of B and the balance Ti (step One); It provides a method of producing a titanium alloy comprising a; and hot working the ingot (step 2).

Hereinafter, the above-described manufacturing method will be described in detail step by step.

First, in the method for producing a titanium alloy of the present invention, the step 1 is 4.0 to 8.0 wt% Al, 2.0 to 6.0 wt% Fe, 0.05 to 0.25 wt% Si and the balance Ti, or 4.0 to 8.0 wt% Al, 2.0-6.0% by weight of Fe, 0.05-0.25% by weight of Si, 0.001-0.5% by weight of B and the balance Ti is further dissolved to prepare an alloy ingot.

Specifically, the content of aluminum in the step 1 is preferably 4.0 to 8.0% by weight. When the content of aluminum is less than 4.0% by weight, there is a problem in that the effect of reducing the density is not large and the strength is lowered. When the content of aluminum is more than 8.0% by weight, Ti ₃ Al is formed and the ductility of titanium is sharply reduced.

In addition, the iron content in step 1 is preferably 2.0 to 6.0% by weight. If the iron content is less than 2.0% by weight, there is a problem that the β phase cannot be sufficiently stabilized at room temperature. If the iron content is more than 6.0% by weight, the strength is increased while the creep strength is lowered.

Furthermore, the content of silicon in step 1 is preferably 0.05-0.25% by weight. If the silicon content is less than 0.05% by weight, there is a problem in that it is not possible to sufficiently compensate for the deterioration of high temperature properties caused by the iron alloy element. If the silicon content is more than 0.25% by weight, coarse titanium silicide is formed to form crystal grains. There is a problem of suppressing miniaturization

In addition, the content of boron in step 1 is preferably 0.001-0.5% by weight. If the content of boron is less than 0.001% by weight, there is a problem that the mechanical strength, moldability and oxidation resistance can not be improved. If the content of boron is more than 0.5% by weight, the strength is increased, but there is a problem that the elongation is lowered.

Furthermore, the dissolution of step 1 may be dissolved by adding silicon and boron after melting by adjusting the weight ratio of titanium, aluminum and iron. At this time, the dissolution method that can be used to dissolve the titanium alloy may be one selected from the group consisting of electrode electrode vacuum dissolution method (VAR), electron beam dissolution method, plasma arc dissolution method, non-consumer arc dissolution method, induction skull dissolution method. It is more preferable to use an induction skull dissolution method. Induction skull dissolving method is to replace the crucible with water cooling in the conventional induction melting to avoid the problem of melt contamination by the crucible. In induction melting, the electromagnetic force acts on the molten metal in the center direction, so there is little opportunity for the molten metal to come into direct contact with the water-cooled crucible. Because you can't. The molten alloy is poured into a mold made of graphite to produce an ingot. In the method for producing a titanium alloy of the present invention, the dissolution of step 1 may be carried out under the condition of 10-20 kW and 4-9 kHz using an induction skull melting furnace.

Next, in the method for producing a titanium alloy of the present invention, step 2 is a step of hot working the ingot prepared in step 1. Hot working is carried out by forging over two stages. Hot working is a processing performed at a temperature higher than the recrystallization temperature (T _β ), when the hot processing is performed has the effect of improving the mechanical properties and workability. α + β-type titanium alloy can have a variety of microstructures according to the processing heat treatment process, the mechanical properties and workability of the alloy can be changed accordingly. In particular, the mechanical properties vary depending on the phase fraction formed by the processing heat treatment process, the shape and size of the alpha grains, the distribution and the texture of the aggregates.

Specifically, the hot working of the step 2 is preferably carried out by forging over two times, the first forging is performed at 1000-1100 ℃ and then water-cooled, the second forging after performing at 800-900 ℃ Air cooling is preferred.

The first forging is a process for crushing the cast structure at the same time as the homogenization treatment of the titanium alloy ingot prepared in step 1, giving a large deformation in the beta transformation temperature range of the titanium alloy produced in 1000-1100 ℃, It breaks down the coarser beta grains and induces dynamic recrystallization, thereby minimizing beta grains. If the primary forging temperature is less than 1000 ℃ there is a problem that the cracking occurs with a high processing pressure, if more than 1100 ℃ there is a problem that can lead to significant grain growth. After the hot working at this temperature to form a fine Widmanstatten structure through water cooling, it is easy to generate an alpha phase of the equiaxed crystal in the second forging process.

In addition, the second forging is a process of hot forging in the α + β region in order to change the needle-like alpha phase into a fine globular structure to improve the formability, it is preferable to perform air cooling after performing at 800-900 ℃. If the secondary forging temperature is less than 800 ℃, there is a problem that a high molding pressure is required to cause cracks on the material surface, and if the second forging temperature is higher than 900 ℃, processing in the beta phase region due to the heat of processing, resulting in α + β mixed phase There is a problem that is not formed.

In addition, the present invention provides a Ti-Al-Fe-Si alloy and a Ti-Al-Fe-Si-B alloy produced by the above production methods. The titanium alloy produced by the above production methods of the present invention By using vanadium (V) of the conventional Ti-6Al-4V alloy, which is a β-stabilizing element that is stronger than vanadium and inexpensive iron (Fe), as an alloying element, the manufacturing cost is economical, and a small amount of silicon (Si) or silicon (Si)- By adding boron (B), the crystal grains are refined, the room temperature strength is excellent, the elongation is excellent at high temperatures, the moldability is excellent, and there is an effect of having excellent oxidation resistance at high temperatures.

Hereinafter, the present invention will be described in more detail with reference to the following Examples and Experimental Examples.

However, the following examples and experimental examples are intended to illustrate the contents of the present invention, but the scope of the invention is not limited by the examples and the experimental examples.

< Example  1> Ti -6 Al -4 Fe -0.1 Si  Manufacture of alloys

Step 1. Melt the metal forming alloy Ingot  Steps to manufacture

6% by weight of aluminum, 4% by weight of iron, 0.1% by weight of silicon and 90% by weight of titanium were added to the induction skull melting furnace and dissolved at the conditions of 15 kW and 6 kHz. At this time, the skull formed in the water-cooled crucible used was made of a Ti-Al-Fe alloy. The molten alloy was injected into a mold made of cylindrical graphite having a diameter of 50 mm and a length of 150 mm to prepare a Ti-6Al-4Fe-0.1Si alloy ingot.

Step 2. Hot working  Steps to Perform

The ingot produced in step 1 was subjected to forging for two times using a hydraulic press. The first forging was performed at 1050 ° C., followed by water cooling. The second forging was performed at 880 ° C., followed by air cooling to prepare a Ti-6Al-4Fe-0.1Si alloy having an α + β mixed structure.

< Example  2> Ti -6 Al -4 Fe -0.1 Si Preparation of -0.01B Alloy

Exgot 1 was prepared in step 1 of Example 1 using 6 wt% aluminum, 4 wt% iron, 0.1 wt% silicon, 0.01 wt% boron and 89.99 wt% titanium of titanium. A Ti-6Al-4Fe-0.1Si-0.01B alloy was prepared in the same manner as in Example 1.

< Example  3> Ti -6 Al -4 Fe -0.1 Si Preparation of -0.05B Alloy

Except that ingot 1 was prepared in step 1 of Example 1 using 6 weight percent aluminum, 4 weight percent iron, 0.1 weight percent silicon, 0.05 weight percent boron and 89.95 weight percent titanium of titanium. In the same manner as in Example 1, a Ti-6Al-4Fe-0.1Si-0.05B alloy was prepared.

< Example  4> Ti -6 Al -4 Fe -0.1 Si Preparation of -0.1B Alloy

Exgot was prepared in step 1 of Example 1 using 6 wt% aluminum, 4 wt% iron, 0.1 wt% silicon, 0.1 wt% boron and 89.9 wt% titanium of titanium. In the same manner as in Example 1, Ti-6Al-4Fe-0.1Si-0.1B alloy was prepared.

< Comparative Example  1> Ti -6 Al Preparation of -4V Alloy

A Ti-6Al-4V alloy was prepared in the same manner as in Example 1, except that ingot was manufactured using 6 wt% of aluminum, 4 wt% of vanadium, and 90 wt% of titanium in Step 1 of Example 1. Prepared.

< Experimental Example  1> Observation of Macro and Microstructures

In order to observe the refined grains of the titanium alloy according to the present invention, the macrostructure and microstructure were observed for the alloy ingots of Examples 1 to 3, and the results are shown in FIG. 1.

As a result, as shown in FIG. 1, the boron of Example 2 was reduced in the case of the Ti-6Al-4Fe-0.1Si alloy ingot of Example 1 to which boron was not added, as compared with the initial beta grains of 500-700 μm. The initial beta (prior-β) grain size was reduced to about 200 μm in the case of 0.01 wt% of the alloy added, and the finer grain was made to about 70 μm in the case of the alloy of 0.05 wt% of Example 3 It can be seen that. In addition, the size of acicular alpha (a) in the grains was also found to gradually become fine with the addition of boron. From this, it can be seen that the Ti-Al-Fe-Si-B alloy of the present invention has a significant grain refinement by addition of boron.

< Experimental Example  2> Measurement of beta transformation temperature

In order to measure the beta transformation temperature of the titanium alloy according to the present invention, differential scanning calorimetry (DSC) thermal analysis was performed on the alloys of Examples 2 to 4 using a DSC 404C model of Netzsch, and the results are shown in FIG. Indicated.

As a result, as shown in FIG. 1, the beta transformation temperature of the alloy of Example 2-4 which added 0.01-0.1 wt.% Of boron to Ti-6Al-4Fe-0.1Si alloy was in the range of 935-940 degreeC. It was found that the beta transformation temperature increased with increasing boron content. Since the beta transformation temperature of the Ti-Al-Fe-Si-B alloy of the present invention is about 50 lower than the beta transformation temperature of commercial Ti-6Al-4V alloy, it is possible to lower the process temperature for breaking the cast structure of the ingot. It can be seen that there are advantages.

< Experimental Example  3> Analysis of mechanical properties

In order to determine the yield strength, tensile strength and elongation of the titanium alloy according to the present invention, the tensile test and the superplasticity test were performed on the alloys of Examples 1, 2, 4 and Comparative Example 1, and the results are shown in Table 1. It was. The hot forged alloys of Examples 1, 2, 4 and Comparative Example 1 were made of a sheet of final 2 mm thickness through a rolling pass two to three times at 880 ° C., and at 30 ° C. at 704 ° C. to remove internal residual stress. Mechanical properties were analyzed using a plate prepared by annealing heat treatment for minutes. Tensile tests were performed using sub-size specimens using an Instron tester (INSTRON 8801 model), and the superplasticity test was carried out at 700 ° C., about 150 ° C. lower than the superplasticization temperature of Ti-6Al-4V alloy. It was.

division
Room temperature 700 ℃ Yield strength
(MPa) Maximum tensile strength
(MPa) Maximum tensile strength
(MPa) Elongation
(%) Comparative Example 1 1028 1093 136 400 Example 1 1040 1167 79 840 Example 2 1187 1242 59 1240 Example 4 1239 1289 60 1180

As a result, as shown in Table 1, the titanium alloys of Examples 1, 2 and 4 according to the present invention were about 150 ° C. lower than 850 ° C., which is the superplasticity of the commercial Ti-6Al-4V alloy of Comparative Example 1, 700 ° C. Superplasticity is expressed at a temperature of ℃, it can be seen that the elongation is better than the commercial Ti-6Al-4V alloy of Comparative Example 1. In addition, the room temperature strength was higher than that of the Ti-6Al-4V alloy of Comparative Example 1, but the strength at the molding temperature of 700 ℃ was found to be lower. From this, the Ti-Al-Fe-Si alloy and Ti-Al-Fe-Si-B alloy of the present invention have superior room temperature strength compared to the Ti-6Al-4V alloy, and the molding is lower than that of the Ti-6Al-4V alloy. It can be seen that it is possible in temperature and has excellent moldability in terms of economy.

< Experimental Example  4> high temperature Oxidation resistance  A rating

In order to investigate the improved high temperature oxidation resistance of the titanium alloy according to the present invention, thermogravimetric analysis was performed on the alloys of Examples 2 to 4 and Comparative Example 1, and the results are shown in Table 2 and FIG. 3. Thermogravimetric analysis was carried out in the atmosphere of 700 ℃ or 800 ℃ using a thermogravimetric analyzer (model: SETARAM) to indicate the degree of oxidation as the weight change per unit area over time.

division 700 ℃ 800 ° C Comparative Example 1 (mg / cm ² ) 3.170 14.99 Example 2 (mg / cm ² ) 0.913 7.748 Example 3 (mg / cm ² ) 0.910 6.650 Example 4 (mg / cm ² ) 0.949 5.411

As a result, as shown in Table 2 and Figure 3, in the case of the Ti-Al-Fe-Si-B alloy of Examples 2-4 of the present invention as the oxidation proceeds at 700 ℃, the weight change is 0.913, 0.919 and Compared to 0.949 mg / cm ² , the commercial Ti-6Al-4V alloy of Comparative Example 1 was found to increase significantly to 3.170 mg / cm ² . In addition, the Ti-Al-Fe-Si-B alloy of Examples 2-4 at 800 ° C. showed excellent high temperature oxidation resistance of 7.748, 6.650 and 5.411 mg / cm ² , whereas the commercial Ti of Comparative Example 1 The -6Al-4V alloy has a weight change of 14.99 mg / cm ^{2, which} is about 3 times higher than that of Example 4, indicating that the oxidation resistance is significantly decreased. In addition, the higher the boron content at 800 ℃ showed a smaller weight change per unit area over time.

It can be seen that the Ti-Al-Fe-Si-B alloy of the present invention has excellent high temperature oxidation resistance compared to the Ti-6Al-4V alloy, and the higher the boron content, the better the high temperature oxidation resistance.

On the other hand, in all experimental temperature ranges of these alloys, these curves show a parabolic behavior at the beginning, which is rapidly oxidized due to the direct exposure of the specimen surface to high temperatures. This is because it prevents oxidation by disturbing the diffusion path of various ions. The curves that initially exhibited parabolic behavior show linear oxidation behavior over time. This suggests that the increase in the diffusion rate of material ions at high temperature affects the oxidation more than the protective ability of the oxide film which served as a barrier to the diffusion path. Rapid oxidation at 800 ℃ causes the oxide film to crack due to the increase of internal residual stress and thermal stress as the oxide film grows over time, and the gap between the oxide layer and the base material makes it easier to diffuse oxygen. I think it is because of the loss.

Claims (16)

A titanium alloy comprising 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si, 0.001-0.5 wt% B, balance Ti, and unavoidable impurities.
The method of claim 1,
The titanium alloy is characterized in that the titanium alloy consisting of 5.0 to 7.0% by weight of Al, 3.0 to 5.0% by weight of Fe, 0.05 to 0.15% by weight of Si, 0.001 to 0.5% by weight of B, balance Ti, and unavoidable impurities. .
The method of claim 1,
The titanium alloy is characterized in that the titanium alloy consisting of 4.0 to 6.0% by weight of Al, 2.0 to 4.0% by weight of Fe, 0.1 to 0.25% by weight of Si, 0.001 to 0.5% by weight of B, the balance Ti, and unavoidable impurities. .
delete delete delete The method of claim 1,
The titanium alloy is titanium alloy, characterized in that the size of the initial beta grains of the titanium alloy ingot 70-200 ㎛.
The method of claim 1,
The titanium alloy is a titanium alloy, characterized in that the beta transformation temperature is 935-940 ℃.
The method of claim 1,
The titanium alloy is characterized in that the superplasticity is expressed at 700-850 ℃ titanium alloy.
delete delete delete Preparing an alloy ingot by dissolving 4.0-8.0 wt% Al, 2.0-6.0 wt% Fe, 0.05-0.25 wt% Si, 0.001-0.5 wt% B and the balance Ti (step 1); And
Hot working the ingot (step 2); Method of producing a titanium alloy comprising a.
14. The method of claim 13,
Dissolution of step 1 is a method of producing a titanium alloy, characterized in that carried out under the conditions of 10-20 kW and 4-8 kHz using an induction skull melting furnace.
14. The method of claim 13,
The hot working of step 2 is carried out by forging over two times,
The first forging is water-cooled after performing at 1000-1100 ℃, the second forging is a method for producing a titanium alloy, characterized in that the air-cooled after performing at 800-900 ℃.
Titanium alloy produced by the manufacturing method of claim 13.

Images