Intermetallic TiAl-Ti3Al composite materials

Abstract

 A TiAl-Ti₃Al composite material having improved mechanical strength and ductility in which Al is contained in the range of 33 to 35% by weight percentage, the balance is substantially Ti, and TiAl-intermetallic compound contains Ti₃Al-intermetallic compound in the range of 10 to 35% by volume percentage.

Description

[0001] This invention relares to a TiAl -Ti₃Al composite material for use as a raw material of parts required to have excellent heat resistance and toughness, for example, parts to move rotationally such as a gas turbine, a turbine blade of a jet engine and a turbocharger rotor, and parts to move reciprocationally such as a engine valve, a piston and a valve rocker arm.

[0002] Heretofore, in various parts to move rotationally or reciprocationally mentioned above, Ni based heat-­resisting alloys have been used for the turbine blade, the rotor and so on, heat-resisting steels have been used for the engine valve, casting aluminum alloys have been used for the piston, and cast irons have been often used for tha valve rocket arm.

[0003] Meanwhile, titanium and titanium alloys (for example, Ti -6Al -4V) are used as lightweight materials superior in strength in the field of aircraft industry, furthermore, TiAl -intermetallic compound based materials have attracted the attention as lightweight materials having improved heat resistance.

[0004] Said TiAl -intermetallic compound based materilas are light and excellent in heat resistance, however they do not get to the stage of practical application even now because of the poor toughness (ductility) at room temperature.

[0005] Accordingly, the addition of the third element and the dispersion of Ti₃Al - intermetallic compound into TiAl -intermetallic compound were attempted in order to improve the ductility of the TiAl -intermetallic compound based materials at room temperature.

[0006] For example, in Japanese Patent Disclosure No.56-41344, Ti-Al alloy having duplex phase structure is disclosed and it is described that the main phase is γ-­phase (TiAl) and globular α₂-phase (Ti₃Al) is contained a little in said γ-phase.

[0007] And in Japanese Patent Disclosure No.61-41740, an intermetallic compound TiAl -based heat resisting alloy is disclosed, which is added with Mn into TiAl -­intermetallic compound based alloy.

[0008] However, concerning the duplex Ti-Al alloy dispersed with Ti₃Al - intermetallic compound in TiAl -­intermetallic compound, in said Japanese Patent Disclosure No.56-41344, there is only description that the main phase is γ -phase (TiAl ) and the γ -phase contains a little and globular α₂-phase (Ti₃Al), but the optimum amount of Ti₃Al - intermetallic compound in TiAl -intermetallic compound does not become clear. Therefore, there is a problem in that the sufficient clarification is not yet given about the improvement of the ductility at room temperature by dispersing Ti₃Al - intermetallic compound.

[0009] The present invention is made in view of the above mentioned problem of the prior art, it is an object to provide TiAl -Ti₃Al composite material have improved ductility at room temperature by utilizing the excellent light and heat-resisting characteristics of TiAl -­intermetallic compound, furthermore by using Ti₃Al intermetallic compound.

[0010] Inventors have found out that the ductility is improved remarkably and the elongation of alloy at room temparature gets to 1.5% or more in case of containing Ti₃Al -intermetallic compound in a specified range in TiAl - intermetallic compound as a result of investgating the amount of Ti₃Al -intermetallic compound and the strength in datail by X-ray diffraction and the tensile test about ingots melted so as to contain aluminum in the renge of 33 to 35 wt% in titanium.

[0011] That is,the TiAl -Ti₃Al composite material according to this invention has the construction that Al is contained in the range of 33 to 35% by weight percentage, the balance is substantially Ti, and TiAl -­intermetallic compound contains 10 to 35% of Ti₃Al -­intermetallic compound by volume percentage. And the TiAl -Ti₃A composite material according to one of the preferred aspects of this invention has the construction that Al is contained not less than 33% and less than 34% by weight percentage, the balance is substantially Ti, and TiAl -intermetallic compound contains 15 to 35 % of Ti₃Al -intermetallic compound by volume percentage. It is characterized by adopting such the construction of TiAl -Ti₃Al composite material as a means for solving the aforementioned problem.

[0012] In the TiAl -Ti₃Al composite material according to this invention, Al is contained in the range of 33 to 35% by weight percentage, the balance is substanially Ti, and TiAl -intermetallic compound contains 15 to 35% of Ti₃Al -intermetallic compound by volume percentage. Tensile ductility of TiAl -intermetallic compound becomes higest when Ti₃Al -intermetallic compound is contained in the range of 10 to 35%, preferably 15 to 35% by volume percentage in TiAl -intermetallic compound at a state in which Ti₃ Al-intermetallic compound is distributed finely into lamellar form. And it has been found that it is nesessary to contain Al in the range of 33 to 35%, preferably not less than 33% and less than 34% by weight percentage in order to contain Ti₃Al - intermetallic compound in the range of 10 to 35%, preferably 15 to 35% by volume percentage and to precipitate it finely into lamellar form. Furthermore, it has also become clear that the most suitable condition is obtained in case of containing 33.5% of Al . And, when Al content is less than 33% by weight percentage, the amount of Ti₃Al-­intermetallic compound increases and tensile ductility deteriotates, and when Al content exceeds 35% by weight percentage , it is undesirable because the amount of Ti₃Al-intermetallic compound decreases conversely. Therefore, Al content is difined in the range of 33 to 35% by weight percentage so that Ti₃Al-intermetallic compound in the range of 10 to 35% by volume percentage in order to obtain excellent tensile ductility.

[0013] Said Ti₃Al-intermetallic compound in TiAl -inter metallic compound is variable by not only the composition but also by heat treatment at the time of manufacturing. Namely, if TiAl -intermetallic compound solidified in non-equilibrium state at the time of manufacturing is maintained at high temperature more than 1100°C for a long time, Ti₃Al -intermatallic compound dissolves in TiAl -intermetallic compound, the amount of Ti₃Al-­inetrmetallic compound decreases, and Ti₃Al-­intermetallic compound coheres and becomes gross, so that the deterioration of ductility is induced. Accordingly, it is undesirable to perform the heat treatment for a long time at high tempetature in excess of 1100°C. In the case of the heat treatment at 1150°C, for example, it has been found that it is desirable not to exceed 8 hours or so.

[0014] In order to obtain the fine lamellar phase of Ti₃Al -intermetallic compiund in the range of 10 to 35% by volume percentage in TiAl -intermetallic compound, it is possible to obtain by casting. And it is also possible to obtain it by powder metallurgy, which is method of proceccing the sintered mixture of TiAl -intermetallic compound powder and Ti₃Al -intermetallic compound powder.

[0015] The TiAl -Ti₃Al composite material according to this invention contains 33 to 35% of Al by weight percengtage an the blance is substantially Ti, wherein TiAl -­intermetallic compound contains 10 to 35% of Ti₃Al-­intermetallic compound by volume percentage, so Ti₃Al-­intermetallic compound is dispersed in proper quantity in TiAl -intermetallic compound. Consequent, said Ti₃Al -intermetallic compound dispersed in proper quantuty in TiAl -intermetallic compound produces effect that toughness (especially ductility ) of TiAl -intermetallic compound light and excellent in heat resistance is remarkably improved.

EXAMPLE

[0016] Using sponge titanium and high purity granulated aluminum as raw materials, Ti-Al alloys having chemical composition shown in Table 1 as Nos.1 to 10 were melted in an atmosphere of Ar using a plasma skull crucible furnace, and then casted into ingots of approximatelly 5 kg in weight.

[0017] Nextly, tensile test specimens were cut from respective ingots, and 0.2% proof stress, tensile strength, elongation and reduction of area were measured by tensile test without heat treatment (as cast) excepting alloy No.9. And the amount of Ti₃Al-­intermetallic compound in TiAl - intermetallic compound was investigated by X-ray diffraction. The specimen of alloy No.9 having the same chemical composition as that of alloy No.3 was subjected to heat treatment at 1150°C for 24 hours and then air cooling with the intention of reducing the amount of Ti₃Al - intermetallic compound.

[0018] These results are also shown in Table 1.

[0019] As is apparent from the results shown in Table 1, in example alloys Nos.1 to 5 according to the TiAl -Ti₃Al composite material of this invention in which Al is contained in the range of 33 to 35% by weight percentage and Ti₃Al intermetallic compound is contained in TiAl-­intermetallic compound in the range of 10 to 35% by volume percentage, it is evident that the mechanical strength is high and the elongation is more than 1.5%, and so, it has been recognized that they are excellent in toughness. And since the mechanical strength has a tendency to drop in the alloy Nos. 4 and 5 containing Al more than 34% by weight percentage, in this regard it is more preferable to define Al content as less than 34% by weight percentage. And the mechanical strength and the the elongation have a tendency to drop in the alloy No.5 containing Ti₃Al - intermetallic compound less than 15% by volume percentage in TiAl - intermetallic compound, in this regard it has been found that it is more preferable to define the lower limit of the amount of Ti₃Al -­intermetallic compound in TiAl -intermetallic compound as 15% by volume percentage.

[0020] On the contrary, comparative alloy No.6 short of Al content, which is less than 33% by weight percentage, is remarkably inferior in the ductility due to Ti₃Al -­intermetallic compound contained in excess. Comparative alloy No.7 in excess of Al contant, which is more than 35% by weight percentage, is considerably inferior in the ductility similarly to above due to the lack of Ti₃Al -­intermetallic compound. And it has been found that comparative alloy No.8 containing Al more than that of alloy No.7 is more inferior in the mechanical strength and the ductility because Ti₃Al -intermetallic compound decreases furthermore.

[0021] In comparative alloy No.9 containing Al in proper quantity and subjected to heat treatment at high temperature over a long time, it is impossible to obtain the elongation more than 1.5% because Ti₃Al-intermetallic compound decreases by the heat treatment at high temperature over a long time. Furthermore, in comparative alloy No.10 containing V as the third element, it is impossible to obtain the elongation more than 1.5% due to Al content exceeding 35% by weught percentage nevertheless the mechanical strength is comparatively high.

[0022] As described above, the TiAl -Ti₃Al composite material according to this invention contains 33 to 35% of Al by weight percentage and the balance is substantially Ti, wherein TiAl -intermetallic compound contains 10 to 35% of Ti₃Al - intermetallic compound by volume percentage, therefore, it is lightweight and excellent in heat resistance, more over excellent in the mechanical strength and the elongation. And it is a composite material suitable for a raw material of ratational parts required to have heat resistance and toughness such as a turbine blade and a turbocharger rotor, therefore, an excellent effect is obtained that it contributes to the improvement of responsibility by the reduction of the weight. Furthermore, it is a composite material suitable for a raw material of reciprocational parts such a engine valve, a position, and a valve rocker arm, accordingly another excellent effect is obtained that it contributes to speeding of the engine by the reduction of inertial mass.

Claims

1. A TiAl -Ti₃Al composite material containing 33 to 35% of Al by weight percentage and the balance being substantially Ti, wherein TiAl -intermetallic compound contains 10 to 35% of Ti₃Al -intermetallic compound by volume percentage.

2. A TiAl -Ti₃Al composite material containing not less than 33% and less than 34% of Al by weight percentage and the blance being substantially Ti, wherein TiAl -intermetallic compound contains 10 to 35% of Ti₃Al -intermetallic compound by volume percentaqge.

3. A TiAl -Ti₃Al composite material containing 33 to 35% of A by weight percentage and the balance being substantially Ti, wherein TiAl -intermetallic compound contains 15 to 35% of TiAl -intermetallic compound by volume percentage.

4. A TiAl -Ti₃Al composite material containing not less than 33% and less than 34% of Al by weight percentage and the balance being substantially Ti, wherein TiAl -­intermetallic compound contains 15 to 35% of Ti₃Al -­intermetallic compound by volume percentage.

5. A TiAl -Ti₃Al composite material containing 33.5% of Al by weight percengtage and the balance being substantially Ti, wherein TiAl -intermetallic compound contains 15 to 35% of Ti₃Al -intermetallic compound by volume percentage.