JPH0765134B2 - Single crystal Ni-based super heat resistant alloy - Google Patents

Description

TECHNICAL FIELD The present invention relates to a single crystal Ni-base superalloy having excellent creep rupture strength and creep rupture ductility, which is mainly used for gas turbine engine blades.

[Conventional technology]

In general, metal fracture at high temperature occurs at grain boundaries,
The creep rupture strength at high temperatures is significantly improved by making the turbine blade a single crystal structure without grain boundaries and performing appropriate heat treatment. Based on this concept, United Technology Corporation, Alloy 444 (described in US Patent No. 4,116,723), Alloy 454 (described in US Patent No. 4,209,348), Alloy 203E (described in US Patent No. 4,222,794), Air Research Inc. , NASAIR100, Ni-based super heat-resistant alloys for single crystals such as CMSX-2 (described in JP-A-57-89451), CMSX-3 (described in JP-A-59-190342), Canon Canon Skeggon. Was developed.

[Problems to be solved by the invention]

The above-mentioned single crystal alloy has far superior creep rupture strength as compared with conventional polycrystalline alloys, but it is still not sufficient in terms of component balance, microstructure control and the like. For example NASA
It has been found that IR100 precipitates harmful phases such as α-W phase and μ phase and reduces creep rupture strength. α-
In order to prevent the precipitation of harmful phases such as W phase, it is necessary to reduce the amount of W, Mo, Ta, etc. added, but since these are alloy strengthening elements, the creep rupture strength decreases if the amount is added more than necessary.

Regarding the individual addition amount of such alloying elements and the component balance among the alloying elements, the present inventors have made detailed studies to improve the creep rupture strength, and as a result,
Cr4-10%, Al4-6.5%, W4-10%, Ta4-9%, Mo1.5-
6%, balance Ni and impurities, and 1 / 2W + 1 / 2Ta + M
o = 9.5 to 13.5%, a single crystal alloy,
They have found that they have excellent creep rupture strength and are structurally stable, and achieved the purpose. The applicant has already applied for a patent for the above alloy in Japanese Patent Application No. 60-258078.

By the way, in order to improve the reliability of the turbine blade, not only creep rupture strength but also creep rupture ductility is required to be large.

While it has been found that the alloys have excellent creep rupture strength, they do not always have satisfactory properties in terms of creep rupture elongation.

The present inventors have conducted further studies on the above alloys in order to meet the above demands, that is, the object of the present invention is to provide a single crystal Ni-based superheat-resistant alloy having excellent creep rupture strength and creep rupture ductility. Especially.

[Means for solving problems]

The present invention, by weight% Cr4 ~ 10%, Al4 ~ 6.5%, W4 ~ 10
%, Ta4-9%, Mo3-6%, Co12% or less, balance Ni and impurities, and 1 / 2W + 1 / 2Ta + Mo = 9.5-13.5%, a single crystal Ni-base super heat-resistant alloy. .

The reasons for limiting the components of the alloy of the present invention will be described below.

Cr has the effect of improving the oxidation resistance and corrosion resistance of the alloy, but excessive addition thereof causes harmful precipitation phases such as the σ phase and reduces the creep rupture strength, so the content is limited to 4-10%.

Al is the main element that forms an intermetallic compound called the γ'phase that precipitates and strengthens the Ni-base superalloy. The basic composition of the γ'phase is represented by Ni ₃ Al, but it is further strengthened by solid solution of Ti, Ta, W, Mo, etc. other than Al. The action of these elements will be described later. A single crystal alloy usually contains a large amount of γ'phase of 50% or more in volume ratio, but at the end of solidification there is a coarse γ'phase called a eutectic γ'phase.
Called phase. ) In order to form a solid solution, the solution treatment is performed at a high temperature. The γ'phase solid-solved by the solution treatment strengthens the alloy by uniformly and finely precipitating during aging treatment during cooling and thereafter. If Al is less than 4%, the amount of γ'phase produced is not sufficient, and if it exceeds 6.5%, too much γ'phase is produced.
Creep rupture strength decreases because the eutectic γ'phase cannot be completely dissolved by solution treatment. Therefore Al is 4 ~
Limited to 6.5%.

W is an element that forms a solid solution in the γ phase and γ'phase and strengthens both phases, and at least 4% is necessary. However, excessive addition causes precipitation of a phase called α-W phase, which rather decreases the creep rupture strength. Therefore, W is limited to 4 to 10%.

Ta mainly forms a solid solution in the γ'phase to strengthen the γ'phase and also increases the amount of the γ'phase. Therefore, Ta must be at least 4%, but if it is added excessively, it becomes difficult to form a solid solution in the eutectic γ'phase, and the morphology of the γ'phase also changes, which lowers the creep rupture strength. Therefore, Ta is 4-9%
Limited to

Mo is mainly solid-dissolved in the γ phase and strengthens the γ phase, so it is preferably 3% or more. However, excessive addition causes the α-Mo phase and decreases the creep rupture strength, so the content should be 3 to 6%. limit.

Since the three elements of W, Ta and Mo described above have different strengthening effects, it is important to add the three elements together. In the present invention, the total amount of addition of these three elements is 1/2 W
It is specified by the amount of + 1 / 2Ta + Mo. The reason why W and Ta are respectively halved here is that the present invention is carried out in atomic% rather than weight%. When 1 / 2W + 1 / 2Ta + Mo is lower than 9.5%, the solid solution strengthening of both γ and γ'phases is not enough, 13.5%
When it is more, harmful phases such as α- (W, Mo) are precipitated. Even if 1 / 2W + 1 / 2Ta + Mo is 13.5% or less, α- (W, Mo) phase may precipitate if the addition amount of each element is out of the specified range. This is observed, for example, when the added amount of W is very high and Ta and Mo are not added or the added amount is low, it is not possible to add three elements at a certain amount together with α- (W, Mo). Is also important for preventing the precipitation of and stabilizing the structure.

In the above-mentioned NASAIR100 alloy, the precipitation of α-W phase is seen, but this is because W is considerably high at 10.5%, and the CMSX-2 alloy which improved this lowers W and replaces Ta with Ta. By increasing the amount, the precipitation of α-W is suppressed, but the solid solution strengthening with W, Ta and Mo is not yet sufficient. In the alloy of the present invention, among the three elements of W, Ta, and Mo, the addition amount of Mo in particular is made higher than that of the conventional alloy, and the individual and total addition amount of each element is regulated. This is the maximum solid solution strengthening of the γ and γ'phases within the range where no harmful phase is produced.

The gist of the present invention is to find that creep rupture elongation is improved by adding Co. It is considered that this is because the addition of Co reduces the stacking fault energy of the alloy. However, excessive addition of Co deteriorates the oxidation resistance of the alloy, so Co is specified as 12% or less.

Note that Ti is often added to conventional single crystal alloys. Ti dissolves in the γ'phase and is useful for forming the γ'phase and strengthening the solid solution, but it is easy to form the eutectic γ'phase and lowers the melting point of the alloy, so it is necessary to raise the solution treatment temperature sufficiently. However, it is difficult to form a solid solution with the eutectic γ ′ phase. Therefore, Ti was not added to the alloy of the present invention.

As with other single crystal alloys, C,
Since B, Zr, etc. lower the initial melting temperature of the alloy, it is necessary to suppress them to the impurity level.

〔Example〕

Table 1 shows the chemical composition of the samples used to compare the properties of the alloy of the present invention, the comparative alloy and the conventional alloy, and the temperature of 1050.
The rupture time and the creep rupture elongation in the results of the creep rupture test performed at ℃ and stress of 15.0 kgf / mm ² are shown. The sample used for the creep rupture test was cast into a single crystal,
The following heat treatment was performed. That is, all of the alloys of the present invention and the comparative alloys were heat-treated at 1310 to 1345 ° C. for 4 hours and then air cooled, further heated at 1080 ° C. for 5 hours and then air cooled, and further heated at 870 ° C. for 20 hours and then air cooled. Conventional alloy NASAIR10
0 is a heat treatment of heating at 1320 ° C. for 4 hours and then air cooling, further heating at 980 ° C. for 5 hours and then air cooling, further heating at 870 ° C. for 20 hours and then air cooling, and CMSX-2 heating at 1316 ° C. for 4 hours and then air cooling. After heating at 980 ° C. for 5 hours, air cooling was performed, and further heating at 870 ° C. for 20 hours and air cooling were performed.

The comparative alloys shown in Table 1 are the alloys described in Japanese Patent Application No. 60-258078, and are alloys having a composition very close to the alloys of the present invention except Co. It can be seen that the creep rupture time of the comparative alloy is significantly longer than that of the conventional alloy. On the other hand, the alloy of the present invention exhibits excellent values in both creep rupture time and creep rupture elongation as compared with the conventional alloy.

[Effects of the Invention] As described above, the alloy of the present invention has excellent creep rupture strength and sufficient creep rupture ductility as compared with existing alloys, and therefore, it greatly contributes to the improvement of its efficiency when used for gas turbine blades. .

Claims (1)

[Claims] 1. Cr4-10%, Al4-6.5%, W4-1 in weight%
0%, Ta4-9%, Mo3-6%, Co12% or less, balance Ni and impurities, and 1 / 2W + 1 / 2Ta + Mo = 9.5-13.5%
A single-crystal Ni-based superheat-resistant alloy characterized by: