JPH0361743B2 - - Google Patents

Description

[Detailed description of the invention]

purpose of invention

[Industrial application field]

The present invention relates to the improvement of Ti-Al alloys, particularly alloys containing the intermetallic compound TiAl as a main constituent phase.

[Prior art]

For example, components that rotate or reciprocate, such as turbine blades and engine valves, are becoming increasingly lightweight in response to demands for higher performance, ie, higher response and higher output. Therefore,
For the heat-resistant materials used in these parts, not just strength but specific strength (strength/density) is important, and efforts are being made to improve it. Under these circumstances, Ti--Al alloys, particularly those containing the intermetallic compound TiAl as a main constituent phase, are attracting attention. TiAl can withstand temperature (stress 28.1Kg
The temperature at which creep rupture life corresponds to 1000 hours at f/mm ² ) is 800℃, and the commonly used Ti alloy (Ti-6Al
-4V) at 550℃, and the specific gravity is 3.8, which is higher than that of ceramics (gi ₃ N ₄ ) than 4.5 of Ti alloy.
3.2, it has workability not found in ceramics, and its specific strength exceeds that of Ni superalloy (Inconel 713C). However, Ti-Al alloys containing TiAl as the main constituent phase have the disadvantage that they have lower ductility than Ti alloys and Ni-based superalloys, and are difficult to plastically work.
Therefore, efforts have been made to improve the ductility (for example, JP-A-56-4344 discloses the addition of an appropriate amount of V), but this has not yet been put to practical use.

[Problems to be solved by the invention]

The present invention is based on the intention of proposing a solution to one of the above-mentioned problems, and its purpose is to use an intermetallic compound TiAl as the main constituent phase.
The object of the present invention is to provide a lightweight heat-resistant alloy that is easy to plastically work by increasing the ductility of a Ti-Al alloy. Composition of aftermath

[Means to solve the problem]

The Ti-Al heat-resistant alloy for ingot material with improved ductility of the present invention has Al: 32 to 38% and B: 0.005% to
Contains 0.20%, the balance is unavoidable impurities and
It has a composition consisting of Ti. Preferably, for the above alloy components, C:
Significant amounts of one or more of the following: 0.2% or less, O: 0.3% or less, N0.3% or less, but O + N: 0.4%
It is added and contained as follows. As a means of manufacturing desired components from the Ti-Al alloy of the present invention, not only casting but also forging can be employed.

[Effect]

The reason for selecting the above-mentioned composition in the Ti-Al alloy of the present invention is as follows. Al: 32-38% The stoichiometric composition that gives the intermetallic compound Ti-Al (for γ) is Ti-36% Al, and the reason why TiAl exists as a single phase in the Ti-Al binary alloy is because
Al: ranges from 34 to 42%. However, Al
If it exceeds 38%, the ductility decreases and defeats the purpose, so this is set as the upper limit. On the other hand, 34%
When the composition becomes Ti-rich with less Al, Ti ₃ Al
( _α2 phase) is formed, and this compound helps improve ductility in small amounts. Since Ti ₃ Al itself is brittle, embrittlement will occur if the amount is large, so 32%
was chosen as the lower limit. B: 0.005 to 0.20% B strengthens the grain boundaries of the TiAl compound, increases ductility, and refines crystal grains, contributing to improved strength. This effect can be obtained by adding as little as 0.005%. On the other hand, if the amount is too large, brittle borides are formed and ductility is reduced, so an upper limit of 0.20% was set. C: 0.20% or less C forms carbide TiC with Ti and increases the strength of the alloy. The effect gradually becomes saturated and a large amount of
Since TiC causes embrittlement, the upper limit was set at 0.2%. O: 0.3% or less, N: 0.3% or less, however, O+N: 0.4% or less. Both O and N are dissolved in TiAl to strengthen it.
However, when the amount of solid solution exceeds the above limit, ductility decreases. [Example] A Ti-Al alloy having the composition shown in the table was melted. Melting was carried out in an Ar gas atmosphere using a plasma arc as a heat source and a skull furnace equipped with a water-cooled copper crucible. Nos. 1 to 5 are examples of the first invention, Nos. 6 to 8 are examples of the second invention, and Nos. 9 to 11 are examples according to known techniques cited for comparison. . Cut out a test piece from an alloy ingot,
A tensile test was conducted at 900°C. The results are also shown in the table. Thereby, it is clear that the alloys of the present invention have improved ductility. Alloy No. 2 was subjected to 30% or 50% upsetting at 1150°C. Even with an upset amount of 50%, no cracks were observed on the surface of the test piece.

【table】

[Table] Effects of the invention The present invention has high heat resistance and specific strength.
The ductility of Ti-Al alloys has been increased, making plastic working easier. Therefore, various rotating or reciprocating mechanical parts, such as blades of aircraft jet engines and industrial gas turbines, intake and exhaust valves of motorcycle or automobile engines, rocker arms,
Conrods, turbo wheels, etc. can be manufactured easily. The ease of plastic working also significantly reduces the reliability problems of products caused by difficult working.

Claims (1)

[Scope of Claims] 1. A Ti for ingot lumber containing 0.005 to 0.20% of B in addition to 32 to 38% of Al, with the remainder being substantially Ti.
-Al-based heat-resistant alloy. 2 Contains B: 0.005 to 0.2% in addition to Al: 32 to 38%, further C: 0.2% or less, O: 0.3% or less,
A Ti-Al system for melt-molded materials containing one or more N: 0.3% or less by adding a significant amount, but O + N: 0.4% or less, and the remainder substantially consisting of Ti. Heat resistant alloy.