JP3694341B2 - TiAl intermetallic compound based alloy material with excellent high temperature characteristics and method for producing the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a TiAl intermetallic compound base alloy excellent in high temperature tensile strength and high temperature / room temperature ductility, and a method for producing the same.
[0002]
[Prior art]
TiAl intermetallic compound-based alloy materials are being developed as environmentally resistant structural materials. Since this material has excellent high-temperature strength characteristics, it is expected to be developed as a future high-temperature structural material. This material is attracting attention for its high-temperature strength, which is comparable to the characteristic values of conventional Ni-base and Co-base superalloys. Furthermore, considering that the specific gravity of TiAl intermetallic compound-based alloy material is 3.8 and the specific gravity of these superalloys is close to 10, TiAl intermetallic compound-based alloy material is superior to superalloy at high temperature specific strength. Is. Therefore, it is promising as a next-generation aircraft material that requires light weight.
[0003]
However, the use temperature of alloy-type high-temperature strength materials such as superalloys including TiAl intermetallic compound-based alloy materials is limited to 900 ° C., and no metal-type material having sufficient strength at 900 to 1100 ° C. has ever been available. . Rather, non-metallic materials such as ceramics and C / C (carbon / carbon fiber) are used in a temperature range of 1000 ° C. or higher. However, although these materials have high strength at high temperatures, in most cases, fracture occurs within elastic stress and the ductility is zero. For this reason, considering safety, an alloy material having ductility is desired.
[0004]
As a conventional technique, there is a near net shape casting technique for producing an intermetallic compound sheet. Near net shape thin plate manufacturing technology has made rapid progress in recent years, especially in the case of metal materials, which are being applied to stainless steel and thin plate manufacturing. As a thin plate manufacturing technique, various casting methods have been proposed. Among them, the twin roll method is suitable for manufacturing a continuous thin plate having a uniform thickness.
[0005]
As an application example of the above technique to an intermetallic compound material, a nickel-aluminum intermetallic compound (Ni) whose ductility is improved by adding a small amount of boron.₃Examples of Al) are known. This was reported at an international conference on “Casting of Near Net Shape Products” held in November 1988 (Proceedings of an International Sympo-sium of Near Net Shape Products). 315-333 pages, published by The Metallurgical Society). Moreover, the manufacturing method of a TiAl intermetallic compound thin plate is described in Japanese Patent Application No. 3-501367.
[0006]
Further, as for TiAl intermetallic compound material added with boron, U.S. Pat. No. 4,842,820 which discloses a manufacturing method by plasma melting and isothermal forging, and a U.S. patent which discloses a manufacturing method by mechanical alloying. No. 4,751,048.
[0007]
As for the TiAl intermetallic compound material added with chromium, plasma melting and isothermal forging manufacturing methods are disclosed in US Pat. No. 4,842,819 and US Pat. No. 4,879,092. .
[0008]
[Problems to be solved by the invention]
An object of the present invention is to obtain a TiAl-based intermetallic compound material having improved high-temperature strength characteristics, and to further improve room temperature ductility while maintaining the high-temperature strength characteristics.
[0009]
[Means for Solving the Problems]
  The gist of the present invention is as follows. That is,
  (i) O₂In one or both of the grain boundaries and the grains in the alloy having a concentration of 1000 to 5000 ppm by weight, fine alumina (Al₂O₃) O₂The concentration is 1000 to 5000 ppm by weight, the particle size is 200 to 500 nm and the alloy is dispersed in TiAl composed of Ti 50 to 53 at% and Al 47 to 50 at%.₂A TiAl intermetallic compound-based alloy material having excellent high-temperature strength characteristics, comprising a phase.
  (ii) The TiAl intermetallic compound-based alloy material as described in (i) above, further containing 1 to 3 at% of one or more of Cr, Mn and V.
  (iii) O₂In one or both of the grain boundaries and the grains in the alloy having a concentration of 1000 to 5000 ppm by weight, fine alumina (Al₂O₃) O₂The concentration is 1000 to 5000 ppm by weight, the particle size is 200 to 500 nm, and boride (TiB₂) With a B concentration of 0.1 to 10 at% and a particle size of 500 nm or less, and as an alloy, TiAl is composed of Ti 50 to 53 at% and Al 47 to 50 at%.₂A TiAl intermetallic compound-based alloy material excellent in high-temperature strength and ductility, characterized by comprising a phase.
  (iv) The TiAl intermetallic compound-based alloy material as described in (iii) above, further containing 1-3 at% of one or more of Cr, Mn and V.
[0010]
The present invention is described in detail below.
In addition to the matrix of the conventional TiAl intermetallic compound base alloy, the present inventors added Al having a particle size of 500 nm or less in the matrix.₂O₃It was found that high strength and high strength can be obtained by dispersing fine oxides at intervals of 10 μm or less.
[0011]
In addition, the inventors further added a boride (TiB) to the matrix of the TiAl intermetallic compound base alloy.₂) In a composite dispersion₂O₃It has been found that ductility at room temperature can be further secured while maintaining the high temperature and high strength achieved by dispersing the selenium alone.
In other words, although the normal temperature ductility was improved by miniaturization, the strength decrease due to the promotion of grain boundary sliding expected at the high temperature was not observed, and the high temperature strength could be dramatically improved. is there.
[0012]
Here, the mechanism of the high temperature strength is described.
Generally, the temperature range in which an alloy material exhibits strength is set to a temperature that is 0.6 times the melting point when expressed in terms of the absolute temperature of the material. This is because diffusion becomes dominant at temperatures higher than this, and the material deforms in a viscous manner when the material is sheared with a stress lower than the yield point. That is, creep deformation is mainly used.
[0013]
In the case of TiAl, since the melting point is 1470 ° C. in the binary system, the absolute temperature is 1743K, and 0.6 times that is 1046K. That is, 772 ° C. is considered to be the limit of strength expression. When the temperature is higher than this, grain boundary slip and slip due to dislocation within the grain are activated, and yield stress and strength are reduced. In a TiAl intermetallic compound base alloy that has been subjected to conventional heat treatment or isothermal forging, the strength at 800 ° C. is 180 to 300 MPa, the strength at 1000 ° C. is 80 to 150 MPa, and the strength at 1100 ° C. is 40 MPa or less. It was.
[0014]
On the other hand, like the present invention material, Al₂O₃Fine oxides and TiB₂Yield stress and strength of the matrix subjected to the composite dispersion of are improved. This is considered to be due to the following reasons.
[0015]
First, regarding the grain boundary sliding, the presence of fine oxides on the grain boundary increases the stability of the crystal grains at high temperature, and the grain boundary is pinned to improve the strength. Further, when dislocations in the grains slip, the dislocations accumulate on the fine oxide in the grains, and further movement of dislocations is hindered, and the strength increases. Further, since the growth of dislocations is suppressed in this way, the increase in concentrated dislocation density, which is the driving force for recrystallization, is reduced, so that a decrease in strength due to dynamic recrystallization can be prevented. These mechanisms are Al₂O₃Fine oxides and TiB₂This is explained by the fact that the composite dispersion itself acts as a fine inclusion.
[0016]
Another important mechanism is α, which is the constituent phase of the lamellar structure of TiAl.₂A strengthening mechanism by solid solution of oxygen in the phase is mentioned. This α₂The phase serves as an oxygen getter in TiAl. Γ phase and α in TiAl₂The lamellar structure composed of phases has an interphase spacing, especially the second phase α₂Is about 10 nm finely. For this reason, it was difficult to quantify the oxygen concentration contained in this phase by a normal analysis method. However, the oxygen concentration can be quantified by using a material having a high oxygen concentration of 1.5 wt%, further facilitating oxygen identification, and using an AP-FIM analysis capable of an atomic order area and quantitative analysis as an analysis means. It has become possible. As a result, most oxygen is α₂Absorbed by the phase, α₂It became clear that the oxygen solid solution of the phase was at the 5 atomic% level (R. Uemori, T. Hanamura and H. Morikawa, Sc-ripta Metall. Mater., 26 (1992), 969.).
[0017]
Later, a French researcher made a follow-up with AP-FIM, and the oxygen level at the ppm level could be quantified (A. Huguet and A. Menand, Applied Science, 76/77 (1994), 191.). . According to this, the oxygen solid solubility limit in the γ phase is 300 wt. ppm, most oxygen is α₂Dissolved in the phase, α₂The solid solubility limit in the phase is estimated to be 5 atomic%.
[0018]
From these, Al₂O₃Oxygen other than α₂Exists in the phase, α₂It is thought that the phase is strengthened by solid solution. In Ti alloys, oxygen is generally known as an α-phase stabilizing element.₂Α at high temperature by dissolving in the phase₂It is conceivable that the stability of the phase is increased and it contributes to the high temperature strength. This leads to suppression of dynamic recrystallization.
[0019]
As described above, it is considered that high-temperature strength can be achieved by the synergistic effect of suppression of grain boundary sliding, suppression of intragranular sliding, and suppression of dynamic recrystallization.
[0020]
Next, the fine particle dispersion strengthening mechanism using only these fine oxides in the present invention will be considered using the Ashby equation.
[0021]
First, the parameters are set as follows.
[0022]
R: radius of fine oxide
μ: Elastic constant of γTiAl
l: Distance between average particles of fine oxide
f: Volume fraction of fine oxide
b: Burgers vector of dislocations in γTiAl
M: Poisson's constant
σ: Strength (stress)
τ: Strength (shear stress)
First, considering the volume of fine oxide, the following relational expression is established.
[Expression 1]
This
[Expression 2]
Shear stress can be expressed as:
[Equation 3]
Therefore, the shear stress due to fine oxide dispersion is
[Expression 4]
From now on, the strength (stress) due to fine oxide dispersion is
[Equation 5]
[0023]
Next, each parameter is set to the following numerical value.
M = 3, μ = 5 × 10^TenPa, b = 0.25 nm,
R = 200 nm, f = 0.1% to 10^-3
Substituting this into equation (6) above
[Formula 6]
[0024]
From the above, it can be concluded that the increase in strength due to the contribution of only fine oxide dispersion is at most a level of 4 MPa, according to an approximation from Ashby's logical formula. From this calculation result, it can be said that the reason why the actual high-temperature strength at 1100 ° C. is improved from the conventional 40 MPa level to the 220 MPa level is simply not enough to explain only the dispersion of fine oxides. After all, fine oxide dispersion, α in fine lamella₂This is thought to be due to the solid solution strengthening of oxygen in the phase and the synergistic effect of the consistency between the lamellar and the fine oxide. In consideration of this synergistic effect, the smaller the fine lamella spacing is, and the smaller the fine oxide size matches the fine lamella spacing, the higher the contribution of lamellar interface consistency and the higher high temperature strength. It is estimated that
[0025]
One reason for the increase in strength due to the refinement of the lamella spacing is the experimental result using the TiAlpolysynthetic-twin result by Umagoshi et al. (Y. Umakoshi, T. Nakano and T. Yamane, Mat. Sci. And Eng. , A152 (1992), 81.). In this paper, it is proved that the lamella spacing exhibits a Hall Petch relationship with the intensity.
[0026]
In the present invention, in order to achieve high temperature strength, finely dispersed Al₂O₃Must have a particle size of 500 nm or less. The lower limit is a particle size of 100 nm, preferably 200 nm. The reason is that when the thickness is 100 nm or less, the interaction with dislocations is weak, and the suppression of slip in the grains is insufficient. In addition, when the particle size is 500 nm or more, the particle size is too large, and on the contrary, it acts as a starting point of crack generation, thereby reducing the ductility of the material.
[0027]
  Al having this particle size range₂O₃To getIn alloyThe oxygen concentration is 1000 to 5000 ppm by weight, preferably 1000 to 4000 ppm by weight, and more preferably 1000 to 2500 ppm by weight. The reason is that if the amount is less than 1000 ppm by weight, the amount of oxide is too small to obtain sufficient high-temperature strength, whereas if it exceeds 5000 ppm by weight, Al is not enough.₂O₃This is because the material becomes coarse and acts as a crack generation site, thereby reducing the ductility and toughness of the material.
[0028]
The TiAl intermetallic compound-based alloy material of the present invention may contain 3 atom% or less of one or more of Cr, Mn, and V as additive elements. Cr, Mn, and V refine the structure by adding isothermal forging, and precipitate the β phase at the γ grain boundary. Therefore, Cr, Mn, and V have an effect of improving superplastic performance at high temperature and improving hot ductility.
[0029]
Generally, when the structure is refined, the strength and ductility at normal temperature are improved, but the grain boundary slip is promoted due to the fine grains, and the strength at high temperature is lowered. However, the material of the present invention disperses fine oxides and TiB₂Addition of can improve high temperature ductility and further normal temperature ductility by 2% or more without abruptly decreasing high temperature strength.
[0030]
In order to increase the room temperature ductility of the TiAl intermetallic compound-based alloy material, it is important to make the structure uniform and fine. Conventionally, this has required a process for performing isothermal forging at a low strain rate in a high temperature region near 1200 ° C. In a normal cast structure, for example, a binary system having a composition of Ti: 50 atomic% and Al: 50 atomic%, the crystal grain size of the as-cast structure becomes as large as about 2 mm. Further, the TiAl intermetallic compound base alloy thin plate by direct thin plate casting has a problem that the reduction of about 80% by constant temperature forging necessary for structure control cannot be applied because the plate thickness is as thin as 1.5 mm as cast.
[0031]
In the present invention, uniform fine particles of 20 μm were obtained in the as-cast state. Below, the expression mechanism of this room temperature ductility is demonstrated.
First, alumina fine grains are used as the generation sites of crystal nuclei for crystal grain refinement. However, since it is not easy to grow crystal grains using alumina alone as a core, another precipitation phase that is compounded and precipitated on alumina is used. This precipitation phase is present in a molten state in the melt of the TiAl intermetallic compound base alloy, and it is desirable that the precipitation phase be consistently deposited on the alumina when the TiAl intermetallic compound base alloy is solidified. Along with this precipitation, the constituent elements of the precipitate around the alumina are reduced, so that the latent time of crystal nucleus generation is reduced in the local region around the alumina, and the nucleus generation occurs. If many aluminas are finely dispersed in advance, the generation of crystal nuclei occurs simultaneously in many regions, so that a fine grain structure can be obtained.
[0032]
TiB as a precipitate matching both alumina and the matrix phase γTiAl phase₂The experiment was conducted. As a result, a uniform fine grain structure of 100 μm could be obtained by ordinary high-frequency melting (VIM melting) and normal ingot casting.
[0033]
In order to further refine the structure, it is more effective to combine the effects of supercooling. Rapid cooling can be used for this. TiB₂The crystal grain size could be controlled to 20 μm by performing twin roll direct casting of the TiAl master alloy in which is dispersed. With this fine uniform structure, room temperature tensile ductility of 2.12% could be obtained by twin roll casting + HIP (high temperature isostatic pressing) treatment + 1000 ° C. strain relief annealing.
[0034]
In the present invention, when melting an alloy, the crucible used for high-frequency melting is coated with alumina (AlO) coated with calcia (CaO) powder.₂O₃) Use a crucible to suppress contamination of oxygen and other contaminants from the crucible. This is because calcia is thermodynamically stable as compared with alumina, and alumina reacts with Ti as a raw material and is reduced, whereas calcia hardly reacts with Ti.
[0035]
  In the present invention, the oxygen concentration in the atmosphere is reduced by heating the Ti plate close to 1000 ° C. in the container of the twin-roll casting equipment to getter the oxygen inside the container. At this time, oxygen concentration is in the atmosphere.0.2%Although it is necessary to make it below, it is desirable to lower to 100 ppm or less. When the oxygen concentration in the atmosphere is 100 ppm or less, the oxygen concentration in the cast material can be directly reduced to 0.25 wt% or less by the combined use of the crucible coating. Thereby, the alumina oxide in a matrix can be controlled to an optimal state. Also, the oxygen concentration in the atmosphere is0.2%Even in the following cases, the oxide can be controlled.
[0036]
In the present invention, alumina oxide can be dispersed as fine particles of 500 nm or less. The reason is that during melting of the base material by high frequency melting, the molten metal is always stirred in strong convection caused by high frequency and is frozen as it is by direct casting of twin rolls. The term “freezing” as used herein refers to a state in which the oxide is solidified while maintaining the dispersion of the oxide at a high temperature, whereby the coarsening due to the aggregation of the oxide can be suppressed.
[0037]
In general, alumina oxide tends to agglomerate and become coarse, and when the oxygen concentration is 1.5 wt%, it becomes coarse to a diameter of 50 μm when cast into a normal ingot. Even if it freezes using a twin roll, it will be 2-3 micrometers, but according to this invention, dispersion | distribution of the fine oxide below 500 nm diameter is carried out by the combination of the low oxygen concentration of 0.25 wt% and the twin roll method. Can be achieved.
[0038]
In the present invention, TiB necessary for microstructure refinement₂When the mother alloy is melted by VIM, it is inserted in a state of being wrapped in a Ti foil in the molten metal 2 to 3 minutes before pouring into the mold. This is because TiB is reduced by reducing the staying time in the molten metal.₂The aim is to prevent agglomeration.
[0039]
【Example】
The present invention will be further described below with reference to examples and comparative examples.
[0040]
First, an example of a direct casting sheet manufacturing machine used in the present invention will be described with reference to FIG. In FIG. 1, a tundish 2 for uniformly supplying a molten metal is disposed below a crucible 1 for melting an intermetallic compound, and a hot water reservoir 5 (mold) comprising a cooling drum 3 and a side dam 4 immediately below the tundish 2. These are disposed in the atmosphere adjuster 7. 8 is an inert gas introduction mechanism, and 9 is an exhaust mechanism.
[0041]
Example 1
Aluminum ingot and titanium sponge are blended in a composition of Ti: 50 atomic% and Al: 50 atomic%, and this is alumina (Al) coated with calcia (CaO) powder.₂O₃) Using a crucible, melting was performed by high frequency melting (VIM) to melt a mother alloy. The size of the crucible is 110 (inner diameter) × 125 (outer diameter) × 180 (height) mm. The conditions of high frequency melting were as follows: voltage: 62 V, current: 76 A, power: 10 kW for the first 10 minutes, and voltage: 75 V, current: 80 A, power: 20 kW for the latter 20 minutes.
[0042]
The mother alloy was cut out in a weight range of 2000 to 3500 g, put into the crucible, the container was sealed, vacuumed, and then replaced with an Ar gas atmosphere.
In an Ar atmosphere, in a container of a twin roll casting facility, the Ti plate was heated to near 1000 ° C. to getter the oxygen inside the container, thereby reducing the oxygen concentration in the atmosphere. At this time, the oxygen concentration inside the container of the twin roll casting machine was continuously monitored by an oxygen concentration meter. Although the oxygen concentration before gettering was 1%, it could be reduced to 0.2% or less by gettering. The 1000 ° C. heating of the getter was continued until the production of the twin roll plate was completed.
[0043]
Next, the master alloy was heated and melted in the above Ar atmosphere, adjusted to a temperature of 1600 ° C., and then poured into the hot water reservoir 5 through a tundish having an opening having a width of 4 mm and a length of 95 mm. The cooling drum 3 constituting the hot water reservoir 5 is made of a pair of copper alloys having a diameter of 300 mm and a width of 100 mm, and is internally cooled. The molten metal has a constant drum support force and 10³Rapid solidification was performed at a cooling rate of ° C./sec to produce a continuous plate-shaped slab. At this time, the sheet thickness was unified to 1.5 mm by setting the twin roll interval (1.5 mm), the roll rotation speed (0.44 m / s), and the molten metal temperature (1600 ° C.) during the molten metal pouring.
[0044]
The slab 6 fed out from the cooling drum 3 was inserted into the transport container while being gradually cooled in the atmosphere adjustment container 7 at a cooling rate of 1 ° C./sec.
In the cross-sectional structure in the casting direction of the obtained slab, the solidified structure as cast is only columnar crystals from both surfaces of the slab toward the center, or equiaxed crystals existing in the vicinity of the columnar crystal and the center of the slab It is composed of mixed tissues.
[0045]
  Figure 2 to Figure3As shown in FIG. 4, the microstructure of the slab obtained in the present invention is Al having a diameter of 500 nm or less.₂O₃Is finely dispersed. FIG.Is the crystal structure of alumina in the material with an oxygen concentration of 0.25 wt%.3Is an enlarged view thereof.
[0046]
Example 2
  AluminumNiHigh frequency melting (VIM) of an ingot and sponge titanium using an alumina crucible coated with calcia (CaO) powder was performed, and Cr was added as an additive element to produce a mother alloy of Ti-47Al-3Cr. This was cast in the same manner as in Example 1, that is, twin roll sheet casting, and a slab was obtained by high-temperature isostatic pressing (HIP).
[0047]
Table 1 shows the mechanical properties of the slab thus obtained at a high temperature. The mechanical property test is performed in a test atmosphere vacuum of 5 × 10.^-Fivetorr, strain rate: 7.2 × 10^-Foursec^-1It went on condition of.
[0048]
[Table 1]
  The effect of oxygen concentration on the tensile strength of Ti-47Al-3Cr material at 1000 ° C4Shown in From this result, in this invention, the upper limit of oxygen concentration is 5000 weight ppm, Preferably it is 4000 weight ppm or less.
[0049]
Comparative Examples 1-5
As comparative examples, conventional TiAl alloy materials as shown in Table 2, that is, plasma-melted annealing materials, isothermal forging materials, and commercially available superalloys were taken up.
[0050]
[Table 2]
  Next, the high temperature characteristics of the TiAl intermetallic compound based alloy material of the present invention and the conventional material were compared. Figure5Shows the relationship between specific strength and temperature of both materials. Figure5From these data, it can be said that the material of the present invention has the highest strength as an alloy system in the high temperature specific strength characteristics.
[0051]
According to the present invention, the mechanical properties of the resulting slab or treated sheet are significantly improved. This is mainly because the oxygen concentration in the material is reduced due to the reduction of impurity contamination, so that the optimum amount of oxygen is obtained, and the oxide is finely divided by high-frequency agitation. It is thought that it was frozen.
[0052]
Example 3
  Aluminum base metal and sponge titanium were blended in a composition of Ti: 50 atomic% and Al: 50 atomic%, and this was melted by high frequency melting (VIM) to prepare a master alloy. At that time, TiB equivalent to 1 atomic% at the final molten metal pouring stage₂The powder wrapped in Al foil was added to the molten metal. This allows TiB into the γTiAl matrix.₂The powder was dispersed.
[0053]
Next, before melting, the crucible used for high frequency melting is coated with calcia (CaO) powder alumina (Al₂O₃) A crucible was prepared.
A material obtained by cutting out the mother alloy in a weight range of 2000 to 3500 g was put into the crucible, the container was sealed, vacuumed, and then replaced with an Ar gas atmosphere.
[0054]
In an Ar atmosphere, in a container of a twin roll casting facility, the Ti plate was heated to near 1000 ° C. to getter the oxygen inside the container, thereby reducing the oxygen concentration in the atmosphere. At this time, the oxygen concentration inside the container of the twin roll casting machine was continuously monitored by an oxygen concentration meter. Although the oxygen concentration before gettering was 1%, it could be reduced to 0.2% or less by gettering.
The heating of the getter at 1000 ° C. was continued until the production of the twin roll plate was completed.
[0055]
Next, the mother alloy was heated and melted in an Ar atmosphere, adjusted to a temperature of 1700 ° C., and then poured into the hot water reservoir 5 through a tundish having an opening having a width of 4 mm and a length of 95 mm. The cooling drum 3 constituting the hot water reservoir 5 is made of a pair of the same alloy having a diameter of 300 mm and a width of 100 mm, and is internally cooled. The molten metal has a constant drum support force and 10³Rapid solidification was performed at a cooling rate of ° C./sec to produce a continuous plate-shaped slab. At this time, the sheet thickness was unified to 1.5 mm by setting the twin roll interval (1.5 mm), the roll rotation speed (0.44 m / s), and the molten metal temperature (1600 ° C.) during the molten metal pouring.
[0056]
The slab 6 fed out from the cooling drum 3 was inserted into the transport container while being gradually cooled in the atmosphere adjustment container 7 at a cooling rate of 1 ° C./sec.
Table 3 shows the sample / composition and processing / heat treatment conditions used as examples.
[0057]
[Table 3]
  TiB₂The effect of addition on microstructure refinement was observed. Figure6Is TiB₂Additive-free comparative material (Comparative Example 10), FIG.Is 1 atomic% TiB₂Invention material of addition (Example)3It is an optical microscope metallographic photograph of a plate thickness cross section of ().
[0058]
  Figure6~ Figure7All of these photos are in 5 discs. The left side of the photo(i)： Cross section photo, upper center(ii): Enlarged photo of the plate thickness surface, lower center(iii): Enlarged photo centered on the plate thickness, and upper right(iv):(ii)Enlarged photo of the lower right(v):(iii)It is an enlarged photograph of.
[0059]
  Figure6~ Figure7As you can see, TiB₂The addition of 1 makes the structure remarkably fine, and the addition of 1 atom% results in a 10 μm level. In addition, TiB which does not perform quenching by twin rolls₂With an additive-free 300 ppm acid material (50 atomic% Ti-50 atomic% Al), the crystal grain size becomes as large as 2 mm.
[0060]
  TiB₂The effect of addition on mechanical properties was investigated. TiB₂Additive-free comparative material (Comparative Example 13)TiB ₂ Invention material of 1 atomic% addition (Example)3) Shows the tensile strength at high temperature8And also show ductility9Respectively.
[0061]
  In addition, the present invention material (Example3Table 4 shows the tensile strength characteristics at room temperature and high temperature. TiB as a comparative material₂Table 5 shows the tensile strength characteristics at room temperature and high temperature of the directly cast TiAl material (Comparative Example 13) to which no is added.
[0062]
[Table 4]
[0063]
[Table 5]
[0064]
As can be seen from these results, the material of the present invention is TiB.₂Addition of C increases the high temperature ductility without lowering the high temperature strength, and further improves the normal temperature ductility from 0% to 2.12%.
[0065]
  Next, the high temperature strength characteristics of the TiAl intermetallic compound base alloy materials produced by the method of the present invention and the conventional method were compared. The method of the present invention is a twin roll casting,In alloyOxygen concentration 2500ppm, conventional methods are plasma melting, constant temperature forging,In alloyThe production conditions were such that the oxygen concentration was 500 ppm.
[0066]
  Method of the present invention(Example3) And a conventional method (Comparative Example 7) Ti-50Al-1TiB₂Figure shows the relationship between yield stress and temperature of thin sheet.10Shown in
[0067]
  FIG.As can be seen from the results shown in the above, the TiAl intermetallic compound-based alloy material produced by the method of the present invention is remarkably improved in high temperature strength.. MaIn addition, since the specific gravity of the present invention material is 3.8, which is as low as ceramics, the specific strength is also high.
[0068]
Comparative Examples 6-13
As comparative examples, conventional TiAl alloy materials as shown in Table 3, that is, materials not included in the composition range of the material of the present invention or materials manufactured by methods other than the method of the present invention and commercially available superalloys were taken up.
[0074]
As described above in each example, according to the present invention, the mechanical properties of the obtained slab or treated thin plate are remarkably improved. This is mainly because the oxygen concentration in the material is reduced due to the reduction of impurity contamination, so that the optimum amount of oxygen is obtained, and the oxide is finely divided by high-frequency agitation. It is thought that it was frozen. In addition, by achieving a uniform microstructure by the alumina / boride composite precipitation effect, a ductility of 2.12% at room temperature was obtained while maintaining this high temperature strength.
[0075]
【The invention's effect】
The TiAl intermetallic compound base alloy material produced by the present invention is excellent in high temperature tensile strength and high temperature / room temperature ductility, and should be used for automobile exhaust valves, turbo chargers, turbine blades of jet engines, etc. Can do.
[Brief description of the drawings]
FIG. 1 is a cross-sectional side view showing an outline of a direct casting sheet making machine used for carrying out the present invention.
FIG. 2 is a photograph showing the crystal structure of alumina in an oxygen concentration 0.25 wt% material of the present invention.
FIG. 3 is an enlarged view of the photograph of FIG.
FIG. 4 is a graph showing the relationship between oxygen concentration (ppm) and tensile strength (MPa) at 1000 ° C. for Ti-47Al-3Cr material (atomic%) which is the material of the present invention.
FIG. 5 is a graph comparing the specific strengths of the Ti-47Al-3Cr material, which is the material of the present invention, with pure Ti, a Ti alloy, and a conventional TiAl alloy.
FIG. 6 TiB₂It is a metallographic photograph of the plate | board thickness cross section of an additive-free TiAl intermetallic compound base alloy material.
FIG. 7 1 atomic% TiB₂It is a metallographic photograph of the plate | board thickness cross section of the added TiAl intermetallic compound base alloy material.
FIG. 8 TiB₂It is the graph which showed the tensile strength of the direct casting TiAl intermetallic compound base alloy material when changing addition amount (0 and 1 atomic%).
FIG. 9 TiB₂It is the graph which showed the ductility of the direct casting TiAl intermetallic compound base alloy material when changing addition amount (0 and 1 atomic%).
FIG. 10 shows Ti-50Al-1TiB produced by the method of the present invention (double roll casting, oxygen concentration 2500 ppm) and the conventional method (VIM melting, isothermal forging, oxygen concentration 1000 ppm) and tensile strength.₂It is the graph which compared and showed the yield stress-temperature characteristic about a thin plate.
[Explanation of symbols]
1 crucible
2 Tundish
3 Cooling drum
4 Side Dam
5 Hot water reservoir
6 Slab
7 Atmosphere adjuster
8 Inert gas introduction mechanism
9 Exhaust mechanism

Claims (4)

Fine alumina (Al ₂ O ₃ ) is dispersed at a grain size of 200 to 500 nm at one or both of the grain boundaries and grains in the alloy having an O ₂ concentration of 1000 to 5000 ppm by weight. 53at%, and characterized in that it comprises a alpha ₂ phase in TiAl consisting Al47~50at%, TiAl intermetallic compound-base alloy material having excellent high-temperature strength properties. Fine alumina (Al ₂ O ₃ ) is dispersed at a grain size of 200 to 500 nm in one or both of the grain boundaries and grains in the alloy having an O ₂ concentration of 1000 to 5000 ppm by weight. TiAl metal excellent in high-temperature strength characteristics, characterized by containing 1 to _{2 at} % of Mn and V, and containing α2 phase in TiAl composed of Ti50 to 53 at% and Al47 to 50 at% Intermetallic compound material. Fine alumina (Al ₂ O ₃ ) is dispersed in a grain size of 200 to 500 nm at one or both of the grain boundaries and grains in the alloy having an O ₂ concentration of 1000 to 5000 ppm by weight, and boride (TiB ₂ ) Is dispersed at a B concentration of 0.1 to 10 at% and a particle size of 500 nm or less, and as an alloy, TiAl composed of Ti 50 to 53 at% and Al 47 to 50 at% contains an α ₂ phase. TiAl intermetallic compound based alloy material with excellent strength and ductility. Fine alumina (Al ₂ O ₃ ) is dispersed in a grain size of 200 to 500 nm at one or both of the grain boundaries and grains in the alloy having an O ₂ concentration of 1000 to 5000 ppm by weight, and boride (TiB ₂ ) Is dispersed with a B concentration of 0.1 to 10 at% and a particle size of 500 nm or less, and contains 1 to 3 at% of one or more of Cr, Mn and V as an alloy, and Ti 50 to 53 at% and A TiAl intermetallic compound-based alloy material excellent in high-temperature strength and ductility, characterized by containing α2 phase in TiAl composed of Al 47 to 50 at%.