JP3388965B2 - TiAl intermetallic compound based alloy - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for use in turbine blades of turbochargers, turbine wheels of small turbochargers, turbine blades of industrial gas turbines and jet engines, and the like. The present invention relates to a TiAl-based intermetallic compound-based alloy having excellent heat resistance and resonance resistance. [0002] In recent years, an alloy containing a main phase of an intermetallic compound TiAl (hereinafter referred to as a TiAl-based alloy) has been attracting attention as a new metal-based material. The greatest feature is its light weight and high strength, and therefore, structural parts for aerospace or rotating parts are considered as applicable parts. When considering a large-sized rotating component, for example, a rotor of an industrial steam turbine, the production technology for producing a large-sized TiAl-based alloy member without defects, that is, the melting, forging and heat-treating technology of the large-sized member is still not available at present. At present, the use of TiAl-based alloys is considered to be small rotating parts, such as turbine blades of turbochargers and gas turbines, or turbine wheels of small turbochargers, because they are not developed. [0003] Conventionally, these parts are 500 ° C.
(Metal temperature, the same applies below)
A 12Cr heat-resistant steel typified by F steel is used, and a superalloy is used in a higher temperature range. At 750 ° C. or higher, there is no material that uses only a superalloy. Therefore, even if the material cost of parts increases, it is unavoidable to guarantee performance.
In the range of 0 to 750 ° C., in terms of material properties, the superalloy is overspecified, and it has been desired to use a less expensive material having less heat resistance than a superalloy. [0004] TiAl-based alloys are less expensive than superalloys and have heat resistance up to about 750 ° C comparable to superalloys, so that they are practically used as blades used at 500 to 750 ° C. Has been expected. Also, in this case, as a secondary effect, the blade weight is 1
/ 2, the centrifugal stress applied to the disk is also reduced to 1/2, and the heat resistance of the disk is lower.
Inexpensive materials can be used, which leads to further cost reduction. In general, when considering materials applied to high-temperature rotating parts such as blades, high-temperature tensile strength, fatigue strength,
General material characteristics such as creep strength, oxidation resistance, and room temperature ductility are required, but in addition, characteristics unique to rotating parts, that is, resonance resistance are required. That is, a certain excitation force acts on these components during use, and there is a possibility that resonance occurs. When the resonance occurs, noise is generated, and at the same time, even the fatigue failure occurs. It is difficult to prevent this dangerous resonance only by design means, and since pursuing this would cause other adverse effects, it is common to think that the material itself has a vibration damping ability. is there. For this purpose, the material requires a damping capacity, that is, a large internal friction. [0006] In recent years, TiAl-based alloys have been actively studied all over the world, and various material properties have been improved. As a result, at the temperature of 500 to 750 ° C., the high-temperature specific strength and the specific creep strength are equal to or higher than that of the superalloy, and the oxidation resistance is inferior to that of the superalloy. It is on a level with almost no problem. Also, the fatigue strength is high and is at a level higher than that of superalloys. Further, the room-temperature ductility is about 2%, which is a state where practically no problem occurs. That is, it can be said that most of the material properties of the TiAl-based alloy have been improved to a level having sufficient performance to cover the temperature range of 500 to 750 ° C. [0007] However, TiAl-based alloys still have one problem, which has not led to practical use. The problem is that the resonance resistance is low as described above, that is, the internal friction is small (1/10 of 12Cr heat-resistant steel and superalloy).
Degree). In other words, in the prior art, TiA
Almost all necessary material properties have been improved in order to put the l-base alloy into practical use in small rotating parts such as blades at about 500 to 750 ° C, but only internal friction is small and resonance resistance is satisfactory. It could not be said that it had not yet been commercialized. In view of the above technical level, the present invention has good material properties such as high-temperature strong specific strength at about 500 to 750 ° C., and has a problem of the prior art. An object of the present invention is to provide a TiAl-based alloy having improved resonance. [0009] The present inventor has proposed a prior art T.
It has been found that the addition of an appropriate amount of Ni is effective for improving internal friction, which was an insufficient property of an iAl-based alloy. Further, in rotating parts such as turbine blades used at 500 to 750 ° C., various necessary material properties are improved in a well-balanced manner, and the light weight, which is the greatest advantage of TiAl-based alloys, is not impaired. It has been found that it is effective to add appropriate amounts of Nb, W, and Mn in order not to cause a rise in cost. The present invention has been made on the basis of these results. Al concentration: 45 to 48 atomic%, Ni concentration: 0.5 to 2 atomic%, Nb concentration: 1 to 3 atomic%, W concentration: 0.2 to 1 This is a TiAl-based intermetallic compound-based alloy excellent in heat resistance and resonance resistance, characterized in that it contains at.% And Mn concentration: 1 to 2 at.% And the balance is made of Ti. (Operation) The operation of each component in the TiAl-based alloy according to the present invention and the reason for the limitation will be described below. (1) Al: Al is a main constituent element of the present alloy. If the concentration is less than 45 atomic%, the ratio of the α ₂ phase in the lamellar structure becomes too large, and the room-temperature ductility decreases. On the other hand, if it exceeds 48 atomic%, α ₂
Undesirably, the proportion of the phase becomes too small and the high-temperature strength decreases. (2) Ni: an additional component for increasing internal friction. If the addition amount is less than 0.5 atomic%, no addition effect is observed. On the other hand, when the content exceeds 2 atomic%, a harmful phase such as a Laves phase is formed, and the ductility at room temperature is undesirably reduced. (3) Nb: Nb is an additive component for improving oxidation resistance. When the addition amount is less than 1 atomic%, no addition effect is observed. On the other hand, if it exceeds 3 atomic%, the specific gravity increases, and Nb is an expensive element, which leads to an increase in material cost, which is not desirable. (4) W: an additive component for improving high-temperature strength. When the addition amount is less than 0.2 atomic%, no addition effect is observed. On the other hand, if it exceeds 1 atomic%, the specific gravity increases, and W is an expensive element, which leads to an increase in material cost, which is not desirable. (5) Mn: an additive component for improving the room-temperature ductility. When the addition amount is less than 1 atomic%, no addition effect is observed. On the other hand, if it exceeds 2 atomic%, the oxidation resistance is lowered, which is not desirable. Embodiments of the present invention will be described below. 99.8% pure sponge Ti and 99.9% pure A
Ingots having the composition shown in Table 1 were produced by high-frequency skull melting using 1, Ni, Nb, W, and Mn as raw materials. Next, for homogenization, 1000 ° C
After a heat treatment of 10 hours, a tensile test piece having a parallel part diameter of 5 mm and a gauge length of 22 mm by machining was used.
mm × 20 mm × 2 mm oxidation test piece and 3 mm × 4 m
An mx 40 mm test piece for measuring internal friction was collected. The room temperature ductility was evaluated by elongation in a tensile test at room temperature, and the high temperature strength was evaluated by tensile strength in a tensile test at 750 ° C. The initial strain rate in the tensile test is 3.8 × 10 ⁻⁴ / s at both temperatures. Oxidation resistance is 75
The evaluation was performed by increasing the amount of oxidation when held at 0 ° C. for 500 hours. The internal friction was measured at room temperature. The test results are also shown in Table 1. Example 1 shows the results when the Al concentration is below the range of the present invention. Although the strength at 750 ° C., the internal friction, and the increase in oxidation were good, the room temperature elongation was poor at 0.7%.
Examples 2 and 3 are alloys of the present invention, which have an elongation at room temperature of at least 2.1%, a strength at 750 ° C. of at least 50 kgf / mm ² , an internal friction (Q ⁻¹ ) of at least 1.1 × 10 ⁻³ , and oxidation. 2.3m increase
g / cm ² or less, all properties were good. Example 4 is the result when the Al concentration is higher than the range of the present invention. Although room temperature elongation, internal friction and oxidation weight increase are good, 750
The strength at 4 ° C. was 42.7 kgf / mm ² , which was poor. Example 5 shows the results when the Ni concentration is below the range of the present invention. Although the room temperature elongation, the strength at 750 ° C. and the oxidation weight increase are good, the internal friction (Q ⁻¹ ) is 5.23 × 10 5
^-4 was bad. Examples 6 and 7 are alloys of the present invention, and have a room temperature elongation of 1.8% or more and a strength at 750 ° C. of 48 kgf /
mm ² or more, internal friction (Q ^-1 ) is 1.1 × 10 ^-3 or more,
The oxidation weight gain was 2.2 mg / cm ² or less, and all properties were good. Example 8 shows the results when the Ni concentration is higher than the range of the present invention. Although the strength at 750 ° C., the internal friction, and the increase in oxidation were good, the room temperature elongation was poor at 0.6%. Example 9 is the result when the Nb concentration is below the range of the present invention. The room temperature elongation, the strength at 750 ° C., and the internal friction were good, but the oxidation weight gain was poor at 4.1 mg / cm ² . Examples 10 and 11 are alloys of the present invention, the elongation at room temperature is 1.7% or more, and the strength at 750 ° C. is 47 kgf / mm.
² or more, the internal friction (Q ^-1 ) was 1.0 × 10 ⁻³ or more, and the oxidation weight gain was 2.6 mg / cm ² or less, and all the properties were good. Example 12 shows the results when the Nb concentration is higher than the range of the present invention. The room temperature elongation, the strength at 750 ° C., the internal friction, and the oxidation weight increase are equivalent to those of the alloy of the present invention. However N
Since b has a large specific gravity and is an expensive element, it can be said that it is inferior to the alloy of the present invention in view of an increase in specific gravity and material cost. Example 13 is the result when the W concentration is below the range of the present invention. Although the room temperature elongation, internal friction and oxidation weight increase are good, the strength at 750 ° C. is 44.4 kgf / mm ^2.
And was bad. Examples 14 and 15 are alloys of the present invention,
Room temperature elongation is 1.9% or more, strength at 750 ° C is 49 kgf
/ Mm ² or more, the internal friction (Q ⁻¹ ) was 1.1 × 10 ⁻³ or more, and the weight gain by oxidation was 2.3 mg / cm ² or less, and all the characteristics were good. Example 16 is the result when the W concentration is higher than the range of the present invention. The room temperature elongation, the strength at 750 ° C., the internal friction, and the oxidation weight increase are equivalent to those of the alloy of the present invention. However, W has a large specific gravity and is an expensive element, so it can be said that W is inferior to the alloy of the present invention in view of an increase in specific gravity and material cost. Example 17 shows the results when the Mn concentration is below the range of the present invention. Although the strength at 750 ° C., the internal friction, and the increase in oxidation were good, the room temperature elongation was poor at 1.0%. Examples 18 and 19 are alloys of the present invention, which have an elongation at room temperature of 1.8% or more, a strength at 750 ° C. of 49 kgf / mm ² or more, an internal friction (Q ⁻¹ ) of 1.1 × 10 ⁻³ or more, and The increase was 2.4 mg / cm ² or less, and all properties were good. Example 20 is the result when the Mn concentration is higher than the range of the present invention. The room temperature elongation, the strength at 750 ° C., and the internal friction were good, but the weight gain on oxidation was poor at 3.2 mg / cm ² . [Table 1] As described above in detail, according to the present invention, a turbine blade of a supercharger, a turbine wheel of a small turbocharger, a turbine blade of an industrial gas turbine and a jet engine, and the like have a temperature of 500 to 750 ° C. And a TiAl-based intermetallic compound-based alloy having excellent heat resistance and resonance resistance suitable for components used in the range described above.

Claims (1)

(57) [Claims 1] Al concentration: 45 to 48 atomic%, Ni concentration: 0.5 to 2 atomic%, Nb concentration: 1 to 3 atomic%, W concentration: 0.2 to A heat- and resonance-resistant TiAl-based intermetallic compound-based alloy containing 1 at% and Mn concentration: 1 to 2 at%, with the balance being Ti.