JPS59581B2 - Silver-added intermetallic compound TiAl-based heat-resistant alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a heat-resistant intermetallic compound TiA1 with improved ductility.
Regarding base alloys.

The titanium-aluminum binary system has an intermetallic compound phase TiAI (hereinafter referred to as TiA
(referred to as l phase) exists.

This TiAl phase has the following characteristics. ■ Light ■ Good oxidation resistance at high temperatures.

■ Strength increases as temperature rises and reaches its maximum at approximately 700°C.

■ Poor ductility.

For this reason, alloys based on the TiAl phase have the potential to become innovative lightweight heat-resistant materials, and numerous studies are being conducted on them.

However, until now, it has not been possible to improve the poor ductility of this type of alloy, and no TiA single-based alloy has been put to practical use. An object of the present invention is to improve the ductility of an intermetallic compound TiAl-based alloy based on a TiAl phase, and to provide a TiAl-based heat-resistant alloy that can be put to practical use.

As a result of research to achieve the above-mentioned object, the present inventors have found that silver or silver is added to an intermetallic compound phase TiAl having a crystal type L1o in which the weight ratio of titanium and aluminum is 66:34 to 40:60. It has been discovered that the ductility of a TiA single-base alloy can be significantly improved by adding an alloy, and the present invention has been completed based on this finding. According to the research of the present inventors, the intermetallic compound phase TiAl whose crystal type is Llo and silver constitute a pseudo-binary system including a peritectic reaction.

As an example, FIG. 1 shows a case where the weight ratio of Ti content to Al content in the TiAl phase is 62.5:37.5.

As can be seen from the phase diagram, in a TiAl-based alloy containing silver, during solidification, the crystal grains of the TiAl phase form a structure surrounded by a primary solid solution of silver, and the grain boundaries between the TiAl phases disappear. This is considered to be the reason why the ductility of the TiA mono-based alloy to which silver is added is improved. The TiA1 phase contains many other elements such as niobium, zirconium, vanadium, chromium, tungsten, and tantalum.

In the present invention, the intermetallic compound phase TiAl is mainly composed of titanium and aluminum, and its crystal structure is Ll.
As long as it is o-type, it also includes those in which other elements such as those mentioned above are dissolved. Silver also forms a solid solution with many elements, such as copper, palladium, cadmium, beryllium, magnesium, manganese, platinum, and zinc. In the present invention, even if elements other than titanium and aluminum are dissolved in solid solution, as long as silver is the main component, it is considered to be a primary solid solution of silver. The relationship between the TiAl phase in which other elements are dissolved and the primary solid solution of silver is also the same as shown in FIG. 1, and the ductility of the TiAl-based alloy can be improved by the mechanism described above. Therefore, the present invention includes the case where the additive to the TiAl-based alloy is a silver alloy. The amount of silver in the alloy necessary for the appearance of a primary solid solution of silver at the grain boundaries of the TiAl phase varies depending on the cooling rate during casting and the composition of the alloy.

The limit at which a primary solid solution of silver does not appear under any conditions is a silver content of 0.5% by weight, preferably 1.0% by weight. On the other hand, the ductility of TiAl-based alloys increases with increasing silver content. However, increasing the amount of silver reduces the lightweight advantage of the TiAl-based alloy. In this sense, the upper limit of the silver content is preferably 50% by weight or less, preferably 40% by weight or less. A TiAl-based alloy whose ductility has been improved by adding silver exhibits the original characteristics of the TiAl phase and becomes a material with excellent high-temperature strength.

Even in the alloy shown as an example, the strength at 500 C or higher is that of Ti-6% A, which is a typical titanium alloy.
I- Surpasses 4%V. Conventionally, titanium alloys have been heated at temperatures between 400°C and 600°C, which would make them unusable in aircraft engines, etc.
℃ temperatures, iron-based alloys have been used. Ti containing silver
Al-based alloys are considered suitable for use at such temperatures. Replacing iron-based alloys with TiAl-based alloys results in weight reduction of aircraft engines. This has the excellent effect of significantly reducing the overall weight of the aircraft and improving its performance. Example Sponge titanium with purity Ci 9.7%, 14t99.9
TiAl made using aluminum with a weight ratio of 9 and silver with a purity of 99.9% to Ag alloy with a weight ratio of 10 (T in TiAl)
A test piece having a size of 3 squares and a height of 6.5 squares was cut out from the sample (i content: 62.5 weight ratio, AI content: 37.5 weight ratio), and a compression test was performed.

The results were as shown in Table 1. In addition, to create the alloy, a predetermined amount of the raw material is weighed, and a diameter of 40 mm is prepared using a press.
A ricket with a height of about 50 mm was made, and this was arc melted using a water-cooled copper crucible, a W electrode, and an argon atmosphere. The breaking strength was determined by dividing the load by the cross-sectional area when a crack occurred in the test piece.

The following values were used as the compression ratio. [(Initial height of test piece) - (Height of test piece when crack occurs))XIOO
÷ (initial height of specimen). For comparison, 1 at 1300℃
A test piece was made from a time-annealed TiAl alloy (Ti content: 58.3% by weight, AI content: 41.7% by weight), and a compression test was conducted in the same manner as described above.

The results were as shown in Table 2. As is clear from the comparison of the results shown in Tables 1 and 2 above, it can be seen that the improvement in ductility due to the addition of silver in the present invention is remarkable.

Furthermore, in TiAl alloys that do not contain silver, the strength of the TiAl phase is not sufficiently exhibited due to the brittleness of the material, and it can be seen that the strength of the TiAl phase of the present invention is also significantly improved.

[Brief explanation of the drawing]

FIG. 1 is an equilibrium diagram of the TiAl-Ag pseudo-binary system.

Claims (1)

[Claims] 1 Titanium and aluminum weight ratio 66:34-40
:60, intermetallic compound phase T whose crystal type is LI_0
A heat-resistant alloy based on the intermetallic compound TiAl, which is based on iAl and has 0.5 to 50% by weight of silver added thereto.