JPH01298128A - Intermetallic compound ti3al-base lightweight heat-resisting alloy - Google Patents

Abstract

PURPOSE:To improve the cold ductility of the title alloy without impairing the excellent high temp. strength of Ti3Al by adding specific amt. of V to Ti3Al of which specific amt. of Al is incorporated into Ti. CONSTITUTION:The lightweight heat-resisting alloy is constituted of, by weight, 12-16% Al, 3-12% V and the balance Ti. In the Ti alloy, since Ti3Al which does not show the drastical lowering of strength even if the range of high temp. is regulated to the base, it has excellent high temp. strength, and since the two-phase structure of (Ti3Al+beta) can be obtd. by the addition of V, its cold ductility is ensured. In the Ti alloy, at the time of <12% Al content, even if the above two-phase structure is obtd., strength is lowered, and, at the time of >16% Ti3Al single phase is easy to form and cold ductility can not be ensured, and even if the above two-phase structure is obtd., a large amt. of V addition is required to impair its lightweight characteristics. As for the V content, the above two-phase structure can not be obtd. at the time of <3%, and a beta phase is run to excess at the time of >15% to reduce the high temp. strength and to lose the lightweight characteristics.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to parts for space/aircraft engines, gas turbine parts for power generation, etc., which are lightweight, have excellent high-temperature strength, and have good room-temperature ductility. Suitable intermetallic compound Ti
:+Aj! This relates to heat-resistant alloys based on

<Prior art and its problems> Ti-Al! Binary alloys include TizAl, TiA
j! and T i Aj! The existence of three types of intermetallic compounds is known, among which rTi3AlJ is “
It is also called "α2 phase" and has a Dol-type crystal structure, with a stoichiometric composition (Ti -15,8% by weight Aλ).
It forms a wide solid solution range on the 2 side, and transforms into the β phase via the α+β phase at high temperatures. And this Ti3Aj! Intermetallic compounds are lighter than titanium and have higher strength, and in addition to not significantly decreasing their strength up to about 750°C, they also have favorable properties such as good oxidation resistance up to around this temperature. It was something that I had.

Therefore, considering that the upper limit temperature for use of high-temperature titanium alloys currently in practical use is approximately 600°C, Ti3A I
! It has also been speculated that the use of intermetallic compounds can further improve the operating temperature limits of practical titanium alloys, which will further expand the range of applications of titanium alloys to jet engine parts, turbine parts, etc. I was hopeful that I would get it.

However, although Ti*AR has high strength, it has a problem of extremely poor cold ductility, and for this reason, its practical application as an industrial product is currently limited.

For this reason, we aim to put Ti3Al into practical use, and add 11 to 16 at% of Nb (19.5 to 30,000% by weight) to it.
A proposal has also been made to improve the ductility in the room temperature and low temperature range by adding it (US Pat. No. 4,292.077).

This proposal involves adding Nb, which is a β-stabilizing element, to make the alloy structure (TizAj!+β), thereby increasing the Ti
The purpose is to improve the ductility of 38f, and specifically, the chemical composition of the titanium alloy is changed to (Ti - (13-15) wt% Aj
! - (], 9.5 to 30) weight% Nb), of which Nb is composed of 4 atomic% by V.
It is said that it is possible to replace up to

However, the above proposal described in U.S. Pat. No. 4,292,077 contains 19.5 to 30% by weight of Nb.
Because it contains a large amount of Ti3A I, it greatly impairs the attractive feature of Ti3A I, which is its lightness.
Since Nb is an expensive metal, it also has economic problems such as an unavoidable increase in product prices.
In practical terms, this left quite a bit of dissatisfaction.

Therefore, the present invention has a cold ductility of 2% or more and a
This was made for the purpose of providing a lightweight alloy exhibiting a tensile strength of 33 kgf/- or more at °C.

<Means for Solving the Problems> From the above-mentioned viewpoints, the present inventors suppressed the increase in specific gravity and the decrease in high-temperature strength as much as possible to produce Ti3A I! While maintaining the favorable features of lightweight and excellent heat resistance found in
Cheap Ti3Aj that is lightweight and has excellent heat resistance? As a result of research aimed at providing a practical alloy, the following findings were obtained.

That is, as mentioned above, to improve the ductility of Ti,
Although it is effective to disperse a small amount of β phase in the 3Δl matrix, the appearance of this β phase is strictly controlled especially in relation to the amount of He2 added. This can also be achieved by selecting it as the third additive element for 8!, which is relatively inexpensive. When Ti contains (1) and (2) in a specific proportion, the room-temperature ductility is improved without losing the above-mentioned features of the Ti3A e intermetallic compound, and the high-temperature strength and room-temperature strength are sufficiently satisfactory for practical use. They discovered that it is possible to obtain a heat-resistant alloy with low specific gravity that also has good ductility.

The present invention has been made based on the above findings, and includes Ti3A E in a chemical composition containing 12 to 16% by weight of A1 and 3 to 12% by weight of By constructing an alloy based on , it is lightweight and inexpensive, and has excellent heat resistance and room-temperature ductility.

Now, the above titanium alloy according to the present invention has a temperature of 600 to 750°C.
It is possible to maintain sufficient strength even in the above temperature range, because it is based on Ti3J1 which does not show any particular decrease in strength even in the above-mentioned high temperature range.

Furthermore, in the titanium alloy according to the present invention, in order to ensure room-temperature ductility in addition to the above-mentioned heat resistance properties, by adding ■, a small amount of β phase is dispersed in the TizAl matrix. However, if the β-phase is in excess, the high-temperature strength decreases, so the amount of the β-phase must be carefully controlled so as not to cause an undesired decrease in the high-temperature strength. For this purpose, it is important to precisely adjust the chemical composition of the alloy.

In the present invention, the chemical composition of the titanium alloy is numerically limited as described above in order to keep the amount of the β phase within the "optimal range" determined through vigorous exploration. The reason will be explained together with the effects of each component.

<Function> fa) Af When the Af content is less than 12 weight in the alloy according to the present invention, even if a CTiJII+β] two-phase structure is obtained, the amount of TiJl is small and the high-temperature strength of the alloy is significantly reduced. descend. On the other hand, if Af is contained in excess of 16%, it tends to become a Tizz^l single phase structure, making it impossible to ensure sufficient room temperature ductility.
Even if a phase structure can be obtained, in that case a large amount of (2) must be added (20% by weight or more in the case of a furnace cooling material), which impairs the lightweight properties of the alloy. Therefore, I
The V gold content was determined to be 12 to 16% by weight.

(b) V ■If the content is less than 3% by weight, (Ti3Ai!+β]2
Since a Japanese structure cannot be obtained, the room-temperature ductility desired for a practical alloy cannot be secured. On the other hand, if the content of ■ exceeds 15% by weight, the amount of β phase becomes excessive, resulting in a decrease in high-temperature strength and a loss of lightness. be exposed. Therefore, the content of (1) was determined to be 3 to 15% by weight.

Although the titanium alloy according to the present invention requires the addition of V, it is possible to use an inexpensive "Af-V alloy commercially available as an alloy raw material" as a source, which reduces the number of single flats and improves economy. No. 4 of the above-mentioned U.S. Pat.
Needless to say, this is significantly more advantageous than the Nb-containing alloy proposed in No. 292,077.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

<Example> Sponge titanium with a purity of 99.7%, purity 99.99
An ingot (1.2 kg) having a chemical composition as shown in Table 1 was melted by vacuum arc melting using Affi of % by weight and AN master alloy of V-16% by weight as raw materials.

Next, this was hot forged into a round bar with an outer diameter of 1511 m,
Furthermore, annealing was performed at 700°C for 2 hours in a vacuum.

Next, from this round bar annealed material, the outer diameter is 4 mm, and the gauge mark l='
d. A 16 mm round bar tensile test piece was taken and a tensile test was conducted.

The tensile test was carried out at both "room temperature" and "700°C", and the strain rate at this time was 0.000000000000000000000000000000000000000000 until rupture.
The speed was set at 5χ/min.

The results of the above tensile test are also shown in Table 1.

In addition, Table 1 shows T3-15.8% by weight for comparison.
(TiJi! Huatai) The results of a similar test conducted on the material are also listed.

As is clear from the results shown in Table 1, the alloy of the present invention exhibits much better ductility at room temperature than TiJj2 alone, and its strength at 700°C is almost comparable to that of Ti2Al alone. It can be confirmed that this is a lightweight, heat-resistant alloy with excellent practicality.

Furthermore, the results shown in Table 1 clearly show that if the chemical composition of the alloy deviates from the conditions specified in the present invention, well-balanced strength and cold ductility properties cannot be ensured.

<Summary of Effects> As explained above, according to the present invention, it is possible to provide an alloy that is lightweight and has excellent heat resistance and cold ductility at a low cost, and is suitable for use in space/aircraft and power generation gas. It can be expected to improve the performance of equipment related to turbines, etc., resulting in extremely useful effects industrially.

Claims (1)

[Claims] By weight percentage Al: 12-16%, V: 3-12% Ti and inevitable impurities: remainder A lightweight heat-resistant alloy based on Ti_3Al.