JPH0841565A - Titanium alloy casting having high strength and high toughness - Google Patents

Abstract

PURPOSE:To improve the structure of a Ti alloy casting and to improve its strength and toughness by incorporating specified small amounts of O2 and Si into a Ti alloy casting having a specified compsn. CONSTITUTION:At the time of producing a castin from a Ti allay contg., by weight, 5 to 12% V, 2 to 5% Al, 0.5 to 8% Mo, and the balance Ti, the one obtd. by furthermore adding and incorporating 0.15 to 0.5% O2 and 0.1 to 0.5% Si into the Ti alloy material as a raw material is used, and the casting is subjected to solution treatment and is successively subjected to aging treatment. In the added Si, its formation into solid solution is promoted by the solution treatment, and furthermore, the addition of oxygen refines and uniformizes the precipitation of coarse alpha phase by the aging treatment to form a structure which fine short fiber-shaped alpha phase is uniformly and densely precipitated into the matrix, by which the Ti alloy casting excellent in both strength and toughness can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Ti alloy casting having a high strength and a high toughness by providing a structure in which α phase is uniformly and densely deposited in the form of fine short fibers in a base material. Is.

[0002]

2. Description of the Related Art Conventionally, various Ti alloy castings have been widely used as structural members for aircraft, automobiles, etc., which generally require strength, toughness, and light weight. In addition, the above various T
Among the i alloy castings, as a Ti alloy casting having particularly high strength, in% by weight (hereinafter,% means% by weight), V: 5
12%, Al: 2-5%, Mo: 0.5
It is known that a Ti alloy casting containing 0.1 to 8%, the balance of which is Ti and unavoidable impurities, and a structure in which coarse growth flaky α-phases are dispersed and distributed in the base material.

[0003]

On the other hand, in recent years, the performance and energy saving of aircrafts and automobiles have been remarkable, and further research and development have been conducted. With this, Ti alloys, which are these structural members, have been developed. Casting is also strongly required to have a complicated shape and a thin wall, but the above conventional high strength T
At present, i alloy castings do not have sufficient strength and toughness to meet these requirements.

[0004]

Therefore, the present inventors have
From the above viewpoint, as a result of focusing on the above conventional high-strength Ti alloy castings and conducting research to further improve the strength and toughness thereof, the above-mentioned conventional high-strength Ti alloy castings show that oxygen as an unavoidable impurity. : 0.1% or less and S
i: 0.01% or less, but in each of them, oxygen: 0.15 to 0.5%, S
i: 0.1 to 0.5%, and is conventionally applied to the above high strength Ti alloy (β transformation point −100 ° C.)
~ (Β transformation point + 20 ° C) ~ (β
When the solution treatment of quenching after heating to a predetermined temperature in the range of (transformation point + 300 ° C.) and the subsequent aging treatment of heating at a predetermined temperature in the range of 550 to 700 ° C. for 1 hour or more are performed, Si containing 0.1 to 0.5% accelerates solid solution in the solution treatment, and oxygen containing 0.15 to 0.5% finely precipitates α phase in the aging treatment. As a result, the fine fibrous α-phases have a uniform and dense structure in the matrix, which results in coarse growth in the matrix. The research results were obtained that the strength and toughness of the cast iron alloy are much higher than those of the conventional high-strength Ti alloy castings having a structure in which the flaky α-phase is dispersed and distributed.

The present invention was made based on the above research results, and V: 5 to 12%,
Ti alloy having a composition containing Al: 2 to 5%, Mo: 0.5 to 8%, and the balance of Ti and unavoidable impurities, and a structure in which coarse growth piece-like α phase is dispersed and distributed in the base material. Oxygen: 0.15 to 0.5% in the casting, with oxygen and Si as alloy components in the whole, respectively.
Si: 0.1 to 0.5% is contained, and by making the above-mentioned structure into a structure in which fine short fibrous α-phases are uniformly and densely deposited in the base material, strength and toughness are further improved. It is characterized by a Ti alloy casting that has been further improved.

Next, the reason why the composition of the Ti alloy casting of the present invention is limited as described above will be explained. (A) V, Al, and Mo It has been already known that these components have the action of improving the strength in the state of coexisting inclusion, and therefore any content of these components V: If it is less than 5%, Al: less than 2%, and Mo: less than 0.5%, the desired high strength cannot be ensured, while V: 12% even if the content of any of these components is V. , A
If the content exceeds 1: 5% and Mo: 8%, the strength tends to decrease, so the contents are V: 5-12%, Al: 2-5%, and Mo: 0.
It is set at 5-8%.

(B) Si The Si component promotes solid solution in the solution treatment,
Although it has a function of suppressing the precipitation of the α phase into a single phase and sufficiently exerting the precipitation promoting effect of the α phase in oxygen in the later aging treatment, if the content is less than 0.1%, The desired effect cannot be obtained on the action, and therefore the desired strength and toughness cannot be improved. On the other hand, when the content exceeds 0.5%, the precipitation of the α phase during the aging treatment is suppressed, Since the desired strength improving effect cannot be obtained, the content thereof is set to 0.1 to 0.5%. Desirably 0.
The content of 1 to 0.3% is preferable.

(C) Oxygen Oxygen is combined with the solution promoting action by Si described above,
The aging treatment has the function of uniformly precipitating the α phase in the form of fine short fibers, but if the content is less than 0.15%, the above function cannot be sufficiently performed, resulting in strength and toughness. However, if the content exceeds 0.5%, the α-phase short fiber shape will collapse and become coarse, and sufficient strength and toughness improvement effects will not be obtained. From the content of 0.15
It was set to 0.5%. Desirably, the content is 0.15 to 0.25%.

[0009]

EXAMPLES Next, the Ti alloy castings of the present invention will be specifically described by way of examples. As a raw material, sponge titanium,
Al-V master alloy pellets, Al-Mo master alloy pellets,
Using TiO ₂ powder and high-purity Si, these raw materials are blended into a predetermined blend composition and press-molded into a briquette,
Use this consumable electrode type vacuum arc melting device to remove this briquette.
Stage melting and casting into an ingot, forging and cutting this ingot to make an electrode shape, melting with a consumable electrode type melting centrifugal casting device, casting in a lost wax precision casting mold, diameter: 12 mm × Length: Round bar with dimensions of 100 mm, cross section: 20 mm × 20 mm, length: 100
A square bar with a size of mm is formed, on which temperature: 720
HI under conditions of ℃, pressure: 1500 atm, time: 120 minutes
After performing P treatment to remove casting defects, in vacuum, 820
After holding at a predetermined temperature in the range of ~ 1100 ° C for 2 hours, Ar
550 to 50% solution treatment by forced cooling by blowing gas
Ti alloy castings 1 to 9 of the present invention and comparative Ti alloy castings 1 having the component compositions shown in Tables 1 and 2 by performing an aging treatment for holding for 10 hours at a predetermined temperature within the range of 700 ° C.
~ 6 were produced respectively.

The comparative Ti alloy castings 1 to 6 have a composition in which the content of oxygen and / or Si in the constituents is out of the range of the present invention. For the purpose of comparison, the heat treatment for the tensile test piece and the three-point bending test piece is the same, except that the temperature is kept in the range of 600 to 750 [deg.] C. for 2 hours in vacuum and then the mixture is allowed to cool. Conventional Ti alloy castings 1 to 3 having the composition shown in Table 2 under the conditions were manufactured. Then, with respect to various Ti alloy castings obtained as a result, the tensile strength was measured using the round bar, and the fracture toughness value was measured using the square bar to evaluate the strength and the toughness. The measurement results are shown in Tables 1 and 2. Further, FIG. 1 shows a photograph of a Ti alloy casting 7 of the present invention, and FIG. 2 shows a photograph of a metal structure of a conventional Ti alloy casting 2 by an electron microscope (magnification: 5000 times).

[0011]

[Table 1]

[0012]

[Table 2]

[0013]

From the results shown in Tables 1 and 2 and FIGS. 1 and 2, the Ti alloy castings 1 to 9 of the present invention show that oxygen and Si
With the inclusion of Al, the fine Ti fiber-like α-phases have a uniformly dense and precipitated structure in the base material, and the conventional Ti alloy castings 1 to 3 have a structure in which coarse growth-piece-like α-phases are dispersed and distributed in the base material. It is clear that it has much higher strength and toughness as compared with the above, while when the content of oxygen and / or Si deviates from the range of the present invention as shown in Comparative Ti alloy castings 1 to 6, the desired high strength is obtained. It is clear that high toughness cannot be obtained. As described above, since the Ti alloy casting of the present invention has high strength and high toughness, when used as a structural member of an aircraft, an automobile, etc., it can sufficiently cope with the complicated shape and weight reduction of the structural member. You can do it.

[Brief description of drawings]

FIG. 1 is an electron micrograph (magnification: 5000 times) of a Ti alloy casting 7 of the present invention, taken by an electron microscope.

FIG. 2 is a metallographic photograph (magnification: 5000 times) of a conventional Ti alloy casting 2 by an electron microscope.

Claims (1)

[Claims] 1. A composition containing, by weight, V: 5 to 12%, Al: 2 to 5%, Mo: 0.5 to 8%, and the balance consisting of Ti and unavoidable impurities, and a coarse base material. In a Ti alloy casting having a structure in which various growth-like α-phases are dispersed and distributed, oxygen and Si as alloy components in the total proportion, respectively, oxygen: 0.15 to 0.5%, Si: 0.1 0.5
%, A Ti alloy casting having high strength and high toughness, characterized in that the above-mentioned structure is a structure in which fine short fibrous α-phases are uniformly and densely precipitated in the base material.