JPS63125634A - Ti-Al heat-resistant alloy for melted lumber - Google Patents

Abstract

PURPOSE:To obtain a lightweight heat-resisting Ti-Al alloy improved in ductility and facilitated in plastic working, by specifying a composition consisting of Al, B, and Ti. CONSTITUTION:The Ti-Al alloy has a composition consisting of 32-38% Al, 0.005-0.20% B, and the balance essentially Ti and further containing, preferably, 0.2% C and <=0.3% O and/or <=0.3% N in a range satisfying (O+N)<=0.4%. In this alloy, a primary constituent phase is composed of an intermetallic compound TiAl and further, by the addition of additive elements, ductility and strength are improved. The above B has a function of strengthening the grain boundaries of TiAl to improve ductility and also refining crystals to contribute toward the improvement of strength. Moreover, C, N, O, etc., improve the strength of the alloy when added in the amounts within the prescribed ranges, respectively.

Description

[Detailed description of the invention]

purpose of invention

[Industrial Application Field] The present invention relates to the improvement of Ti-A, 11-based alloys, particularly alloys containing the intermetallic compound TiA, 11 as a main constituent phase. [Prior art] Like turbine blades and engine valves,
Components that cover rotation or reciprocating motion are becoming increasingly lightweight in response to demands for higher performance, ie, higher responsiveness and higher output. Therefore, for the heat-resistant materials used in these parts, not only the strength but also the specific strength (strength/density) is important, and efforts are being made to improve it. Under these circumstances, attention has been paid to i-Al alloys, particularly those having intermetallic compounds 1-iA and fl as main constituent phases. TiAl has a withstand temperature (stress of 28.1K
gf/m" (temperature equivalent to 1000 hours of creep rupture ticket life) or 800'C and a commonly used Ti alloy (
-68 and -4,V) exceeds 550°C, and the specific gravity is 3.8, which is closer to 3°2 of ceramics (S13N4) than 4.5 of T1 alloy, and has workability that ceramics lack. In addition, the specific strength is that of Ni-based superalloy (■nc
onel 713C). However, Ti-Al alloys containing TiAfl as a 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 ductility (for example,
No. 6-4344 discloses the addition of an appropriate amount of V), but
It has not yet been put into 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 provide an intermetallic compound Ti All as the main constituent phase. Ti-A,fl
It is necessary to provide a lightweight, heat-resistant alloy that is easy to plastically work by increasing the ductility of the alloy. Composition of the invention

[Means to solve the problem]

Ti-A with improved ductility of the present invention, [! The alloys are △
β: 32-38% plus B: 0.005%-0.20
%, with the remainder consisting of unavoidable impurities and Ti. Preferably, for the above alloy composition, C:O. 2% or less, O: 0.3% or less and/or N: 0
．． Add 3% or less, but 0.4% or less of O and N. As a means of manufacturing desired components from the Ti-Al alloy of the present invention, not only casting but also @-casting can be adopted.

[For use]

The reason for selecting the above component composition in the Ti-AN alloy of the present invention is as follows. A, Il: 32-38% The stoichiometric composition giving the intermetallic compound TiA, IJ (γ phase) is Ti-36%l, and in the Ti-to-ρ binary alloy, Ti A,l) is a single phase. Al is present in the range of 34 to 42%. However, if A and σ exceed 38%, the ductility decreases and is contrary to the purpose, so this is set as the upper limit. On the other hand, Al
When the composition becomes T1-rich with less
(α2 phase) is produced, and if this compound is present in a small amount, it helps improve ductility. Since T i 3 A fJ itself is brittle, embrittlement will occur if the amount is too large, so 32% was selected as the lower limit. B: 0.005 to 0.20% B strengthens the grain boundaries of the TiAβ compound, increases ductility, and refines crystal grains, contributing to improved strength. This effect can be obtained by adding as little as 5% of 01OO. On the other hand, since a large amount leads to the formation of brittle borides and reduces ductility, 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 TiC causes embrittlement, so the upper limit was set at 0°2%. 0: 0.3% or less, N: 0.3% or less, but 0+N:
0.4% or less of both O and N are dissolved in Ti A, Q to strengthen them. However, when the amount of solid solution exceeds the above limit, ductility decreases. [Example] A Ti-AlJ alloy having the composition shown in the table was produced. 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 Nα9 to 11 are examples according to known techniques cited for comparison. A test piece was cut from an alloy ingot and heated to 900'C.
A tensile test was conducted. The results are also shown in the table. Thereby, it is clear that the alloys of the present invention have improved ductility. For N02 alloys, 30% at 1150'C
Or 50% upsetting was performed. Even at an upset amount of 50%, no cracks were observed on the surface of the test piece. -〇- “Effects of the Invention The present invention provides Ti-AJ with high heat resistance and specific strength.
The ductility of the 2-series alloy 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, bolts, turbo wheels, etc. can be easily manufactured. The ease of plastic working also significantly reduces the reliability problems of products caused by difficult working.

Claims (2)

[Claims] (1) Al: 32-38% plus B: 0.005-0
．． Ti-
Al-based alloy. (2) Al: 32-38% plus B: 0.005-0
．． 2%, further C: 0.2% or less, and 0:0.
3% or less and/or N: 0.3% or less, but O
+N: 0.4% or less, and the remainder substantially consists of Ti.