JPS6169937A - Titanium alloy for superplastic working having high specific strength at high temperature - Google Patents

Abstract

PURPOSE:To obtain a Ti alloy for superplastic working having superior specific strength and ductility at high temp. as well as superior superplasticity by adding specified amounts of Al, V, Sn, Zr, Mo, Cr, Fe and O to Ti. CONSTITUTION:This Ti alloy contains, by weight, 6.2-6.8% Al, 1.2-1.6% V, 1.2-1.6% Sn, 0.8-1.2% Zr, 2.7-3.1% Mo, 1.9-2.3% Cr, 1.4-1.8% Fe and 0.10-0.15% O. The alloy has a structure consisting of 30-70% alpha-phase and the balance beta-phase at 850 deg.C, and it has superior specific strength and ductility at high temp. as well as superior superplasticity. A rotor for a compressor or the like can be manufactured without requiring machining by plastically working the alloy, so the yield of starting material is remarkably improved, and the cost of manufacture is considerably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a titanium alloy scale for superplastic working with high high temperature specific strength. More specifically, it contains 30 to 70% α phase at 850C, and the remainder consists of β phase, and has been manufactured at high temperature.
%, and not only was the yield extremely low, but also the workability was extremely poor. To improve this, superplastic working of K and Ti alloys is an effective means. For superplastic working, Ti alloys have a volume ratio of α phase to β phase close to 1:1 at the working temperature. Further, a temperature around 900C is suitable for the superplastic working temperature. At high temperatures higher than 9υOC, coarsening and oxidation of crystal grains tend to occur, resulting in deterioration of superplastic properties. Furthermore, at temperatures lower than 900C, grain boundary climbing becomes difficult to occur, resulting in deterioration of superplastic properties and increased deformation stress, making superplastic processing difficult. Conventional titanium alloys for superplastic working include Ti-6AI-4V alloy and Ti-6A
I-2Sn-4Zr-2Fvlo alloy, Ti-6A
I-2Sn-4Zr-6Mo alloy is known. However, all of these Ti alloys have a drawback of lower strength than the β-type Ti alloy.

Purpose of the Invention The present invention aims to improve the drawbacks of the conventional titanium alloys for ultra-molecular working, and its purpose is to provide a titanium alloy for superplastic working that has excellent superplastic properties, high-temperature specific strength, and ductility. It is in providing alloys.

Structure of the Invention As a result of research to achieve the above object, the present inventors have discovered 850
C contains about 30 to 70% α phase, and the remainder consists of β phase,
We have discovered a titanium alloy for super-heavy processing that has excellent superplastic properties, high-temperature specific strength, and ductility. The present invention was completed based on this knowledge.

The titanium alloy of the present invention has an AI of 6.2 to 6.8% and a V of 6.2 to 6.6 in terms of weight.
%, Sn6.2-6.6%, Zr0.8-6.2%,
Mo 2.7-3.1%, Cr6.9-2.3%, F
Contains e6.4-6.8%, O0.10-0.15%,
The remainder is a super-heavy working titanium alloy with high high-temperature specific strength consisting essentially of Ti.

The effects of the compositional components and the reasons for limiting the composition ratios in the alloy of the present invention are as follows.

AI mainly acts as a solid solution in the α phase to strengthen the α phase. The amount of AI was 6.2% (% indicates weight Ik%).

If Alt is less than 6.8, the α phase strengthening effect will not be sufficiently obtained, and if the amount exceeds 6.8, the α phase amount will increase and sufficient superplastic properties will not be obtained. 2~
It needs to be 6.8%.

(2) acts as a solid solution in the α phase and β phase to strengthen these phases. If Vi- is less than 6.2%, a sufficient strengthening effect cannot be obtained, and if the amount exceeds 6.6%, the amount of α phase decreases and sufficient ultra-m properties cannot be obtained. 6
．． It is necessary that it is 2 to 6.6%.

When Sn and Zr are dissolved in solid solution in the α phase and the β phase at approximately the same ratio, they act to strengthen the n and other phases. If the amount of Sn is less than 6.2%, a sufficient strengthening effect will not be obtained, and the amount will be 6.6%.
If it exceeds 5, the specific gravity will increase and the specific strength will decrease.
nii needs to be 6.2 to 6.6%. Furthermore, if the amount of Zr is less than 0.8%, no strengthening effect will be obtained, and if the amount exceeds 6.2%, the amount of α phase will decrease and sufficient superplastic properties will not be obtained. is 0.8
~6.2% is required.

Mo, Cr, and Fe mainly act as solid solutions in the β phase to strengthen the β phase. If the amount of Mo is less than 2.7%, a sufficient strengthening effect will not be obtained, and if the amount exceeds 3.1%, the specific gravity will increase and the specific strength will decrease, so Mojl is 2.7 to 3.1. % is required. If the amount of Crfk is less than 6.9%, a sufficient strengthening effect cannot be obtained, and if the amount exceeds 2.3%, the amount of α phase decreases and sufficient superplastic properties cannot be obtained, so the amount of Cr is 6.9-2.3%
It is necessary that In addition, if the amount of Pa is less than 6.4%, a sufficient strengthening effect cannot be obtained, and the amount is 1.8%.
If the Fe content exceeds 6.4% to 6.8%, the amount of α phase decreases and sufficient superplastic properties cannot be obtained.

O mainly acts as a solid solution in the α phase to strengthen the α phase. If Oi is less than 0.10%, the reinforcing effect will not be sufficiently obtained, and if the needle exceeds 0.15%, the amount of α phase will increase and sufficient superplastic properties will not be obtained. 0.
It is necessary that the content is 10 to 0.15%.

In a titanium alloy containing each of the above elements in the proportions described above, at 850C, the α phase is 30 to 70, and the remainder is the β phase. The α phase and the β phase mutually inhibit the growth of crystal grains and improve the super-m property. When the α-phase content is less than 30%, the β-phase crystal grains become coarser and more likely to become 2-prone, resulting in deterioration of superplastic properties. Moreover, if the α phase exceeds 70%, the crystal grains of the α phase tend to become coarse, resulting in deterioration of superplastic properties.

The minimum content of each element required to strengthen the α and β phases is:
It is determined by the balance with the content of other elements.

For example, when the Zr content is as high as 5.0 to 7.5%, the minimum AI content is 5.3%, but as in the present invention, when Zrfk is as low as 0.8 to 6.2%, the minimum content of AI is 5.3%. In this case, the AI amount is 6
．． 2% or more is required. Further, the amount of α phase is also determined by the balance of the contents of all alloying elements. The titanium alloy of the present invention has sufficient properties for superplastic working within the content ranges of each of the above-mentioned elements, and has excellent high-temperature specific strength and ductility.

Effects of the Invention As is clear from the comparative examples in the Examples below, the alloy of the present invention has superior superplastic properties compared to conventional titanium alloys for superplastic working, is easy to superplastically work, and has a high temperature ratio. Strength and ductility are also significant. Therefore, the cutting process F, C
L, parts such as compressor rotors can be manufactured at low cost. Further, by using this, it has excellent effects such as making it possible to reduce the weight and increase the efficiency of various gas turbines such as jet engines and power generation equipment.

EXAMPLE A 59d ultra-high-performance test v~ was prepared for comparison with the alloy of the present invention having the composition shown in Table 1 below.

The high-temperature tensile test piece was heat-treated at 850-900 C for 1 hour, then water-cooled, heat-treated again at 500-600 C for 4 hours, air-cooled, and subjected to the test. High temperature tensile test is 300 t:
The strain rate was 3 x 10'S-''.

The superplastic specimen was subjected to the test in the hot-rolled state.

Superplasticity test at 850C, 6.7X in argon atmosphere
The results were as shown in Table 2 and Table ÷ 3 below.

As shown in the results in Table N2, the Ti alloy of the present invention is superior to the existing Ti-6AI-4V, Ti-6AI-2Sn-4Z.
It can be seen that the ductility and specific strength are significantly superior to the r2Mo and TiTi-6AI-2Sn-4Zr-6 alloys. That is, in the Ti alloy of the present invention, an elongation of 9.1% is secured under the condition that the specific strength shows a value of 30.9 Kpf/md/p/atl, whereas the Ti alloy
-6AI-4V and Ti -6AI-2Sn-4Zr-
Such a high specific strength cannot be obtained with the 2Mo alloy.

In addition, in the case of Ti-6AI-2Sn-4Zr-6Mo alloy, the specific strength is 29.9 K9f/rui/11/a
The elongation decreases to 5.2% when increasing to ll.

As this result shows, the titanium alloy of the present invention has a K of 416 to
It has a superplastic elongation of 698% and a maximum deformation stress of 6.3~
2. s xyr7mi, which is sufficiently low, compared to the existing Ti-6
It is significantly superior to the AI-2Sn-4Zr-6Mo alloy.

Patent applicant: Ryu Kawa, Director, Research Institute for Metals, Science and Technology Agency −

Claims (1)

[Claims] In weight%, Al6.2-6.8%, V1.2-1.6%
, Sn1.2-1.6%, Zr0.8-1.2%, Mo
2.7-3.1%, Cr1.9-2.3%, Fe1.4
A titanium alloy for superplastic working with high high-temperature specific strength, containing ~1.8% and 0.10-0.15% of O, and the remainder being substantially Ti.