Ni-based heat-resistant alloy

Abstract

The present invention relates to a Ni-based heat-resistant alloy including Ir: 5.0 mass % or more and 50.0 mass % or less, Al: 1.0 mass % or more and 8.0 mass % or less, W: 5.0 mass % or more and 25.0 mass % or less, and balance Ni, having an L1.sub.2-structured γ′ phase present in the matrix, and including at least one of Zr: 0.01 mass % or more and 3.0 mass % or less and Hf: 0.01 mass % or more and 3.0 mass % or less. This Ni-based heat-resistant alloy has improved toughness over a conventional Ni-based heat-resistant alloy based on a Ni—Ir—Al—W-based alloy, and is also excellent in ambient-temperature strength.

Claims

1. A polycrystalline Ni-based heat-resistant alloy comprising Ir: 5.0 mass % or more and 50.0 mass % or less, Al: 1.0 mass % or more and 8.0 mass % or less, W: 5.0 mass % or more and 25.0 mass % or less, and balance Ni, having an L12-structured γ′ phase present in the matrix, and including at least one of Zr: 0.8 mass % or more and 2.0 mass % or less and Hf: 1.0 mass % or more and 2.0 mass % or less.

2. The polycrystalline Ni-based heat-resistant alloy according to claim 1, further comprising C: 0.001 mass % or more and 0.5 mass % or less.

3. The polycrystalline Ni-based heat-resistant alloy according to claim 1, comprising 1.2 mass % or more and 2.0 mass % or less of Zr.

4. The polycrystalline Ni-based heat-resistant alloy according to claim 1, comprising 1.2 mass % or more and 2.0 mass % or less of Hf.

5. The polycrystalline Ni-based heat-resistant alloy according to claim 1, comprising 1.0 mass % or more and 2.0 mass % or less of Zr and 1.0 mass % or more and 2.0 mass % or less of Hf.

6. The polycrystalline Ni-based heat-resistant alloy according to claim 1, comprising at least one addition element selected from the following: B: 0.001 mass % or more and 0.1 mass % or less Co: 5.0 mass % or more and 20.0 mass % or less Cr: 1.0 mass % or more and 25.0 mass % or less Ta: 1.0 mass % or more and 10.0 mass % or less Nb: 1.0 mass % or more and 5.0 mass % or less Ti: 1.0 mass % or more and 5.0 mass % or less V: 1.0 mass % or more and 5.0 mass % or less Mo: 1.0 mass % or more and 5.0 mass % or less.

7. The polycrystalline Ni-based heat-resistant alloy according to claim 6, comprising 1.0 mass % or more and 2.0 mass % or less of Zr and 1.0 mass % or more and 2.0 mass % or less of Hf.

8. The polycrystalline Ni-based heat-resistant alloy according to claim 6, further comprising C: 0.001 mass % or more and 0.5 mass % or less.

9. The polycrystalline Ni-based heat-resistant alloy according to claim 8, comprising 1.2 mass % or more and 2.0 mass % or less of Zr.

10. The polycrystalline Ni-based heat-resistant alloy according to claim 8, comprising 1.0 mass % or more and 2.0 mass % or less of Zr and 1.0 mass % or more and 2.0 mass % or less of Hf.

Description

DESCRIPTION OF EMBODIMENTS

(1) Hereinafter, preferred embodiments of the present invention will be described.

(2) First Embodiment: In this embodiment, with respect to the Ni—Ir—Al—W alloy, which is the basic composition of the Ni-based heat-resistant alloy of the present invention, the effect of the addition of Zr and Hf was examined. Alloys with addition of 2.0 mass % Ru and 3.0 mass % Re were produced. Specifically, a Ni—Ir—Al—W alloy (Ir: 25.0 mass %, Al: 4.38 mass %, W: 14.33 mass %, and balance Ni) and a Ni-based heat-resistant alloy obtained by adding 1.2 mass % of Zr and Hf to this alloy were produced, and their mechanical properties were evaluated. In addition, a Ni-based heat-resistant alloy obtained by adding an addition element such as Co to a Ni—Ir—Al—W alloy was also produced and evaluated.

(3) In the production of a Ni-based heat-resistant alloy, in a melting/casting step, molten metals of various compositions were ingoted by arc melting in an inert gas atmosphere, and cast in a mold and cooled/solidified in air. Each alloy ingot produced in the melting/casting step was subjected to a homogenizing heat treatment under conditions of 1,300° C. for 4 hours, and, after heating for a predetermined period of time, air-cooled. The ingot was then subjected to an aging heat treatment under conditions of a temperature of 800° C. and a retention time of 24 hours, and, after heating for a predetermined period of time, annealed to give an ingot 7 mm in diameter, and a test piece was produced therefrom. The test pieces of various compositions thus obtained were evaluated and examined as follows.

(4) [Measurement of γ′ Phase Dissolution Temperature]

(5) Each test piece was subjected to scanning differential calorimetry (DSC) to measure the γ′ phase dissolution temperature (solvus temperature). The measurement conditions were such that the measurement temperature range was up to 1,600° C., and the temperature rise rate was 10° C./min. Then, from the endothermic peak position appearing as a result of the decomposition/dissolution of the γ′ phase, the γ′ phase dissolution temperature was measured.

(6) [Strength Evaluation]

(7) Each test piece was subjected to a Vickers test (load: 500 gf, pressing time: 15 seconds) to measure the hardness. The hardness measurement was performed at ambient temperature (room temperature: 25° C.) and a high temperature (900° C.).

(8) [Toughness Evaluation]

(9) Each test piece was subjected to a hot bending test to evaluate the toughness (ductility) of the alloy. In this test, the test piece was subjected to a bending test in a high-temperature atmosphere of 900° C. under varying loads to prepare a load-displacement diagram, and the amount of displacement at material break was measured.

(10) The compositions of the produced alloys and the various evaluation results in this embodiment are shown in Table 1.

(11) TABLE-US-00001 TABLE 1 Alloy composition (mass %) No. Ni Ir Al W Co Cr Ta C B Zr Example A1 Balance 25.00 4.38 14.33 — — — — — 1.20 A2 25.00 4.38 14.33 7.64 6.10 4.68 — — A3 25.00 4.38 14.33 7.64 6.10 4.68 0.11 — A4 25.00 4.38 14.33 — — 4.68 — — B1 25.00 4.38 14.33 — — — — — — B2 25.00 4.38 14.33 7.64 6.10 4.68 — — B3 25.00 4.38 14.33 7.64 6.10 4.68 0.11 — B4 25.00 4.38 14.33 — — 4.68 — — Conventional C1 25.00 4.38 14.33 — — — — — — Example Alloy γ′ Phase composition dissolution Hardness (Hv) (mass %) temperature Ambient Amount of No. Hf (° C.) temperature 900° C. displacement Example A1 — 1328 358 264 1.23 A2 1364 377 279 1.01 A3 1391 396 301 0.88 A4 1261 418 314 0.71 B1 1.20 1460 353 176 1.18 B2 1411 405 221 0.83 B3 1421 373 276 0.78 B4 1483 441 334 0.55 Conventional C1 — 344 228 0.25 Example

(12) Based on Table 1, the properties of the Ni-based heat-resistant alloys in this embodiment will be examined below. As compared with the conventional example (C1), which is a Ni—Ir—Al—W alloy serving as the basic composition of the Ni-based heat-resistant alloy of the present invention, it can be confirmed that in the alloys produced by adding Zr and Hf to the Ni-based heat-resistant alloy, the amount of displacement in the bending test at 900° C. significantly increased, and the toughness in a high temperature range was significantly improved (No. A1, No. B1). In addition, these alloys have increased hardness at ambient temperature. Therefore, it was confirmed that in a Ni—Ir—Al—W alloy of the basic composition containing no addition elements such as Co, the addition of Zr or Hf can achieve improvement in toughness in a high temperature range and enhancement in ambient-temperature strength.

(13) However, a Ni—Ir—Al—W alloy of the basic composition originally has low hardness. Therefore, the addition of Zr or Hf reduces the hardness at high temperatures. This tendency is particularly seen in the alloy No. B1 with Hf addition. Thus, addition elements (Co, Cr, Ta, C, etc.) are added to raise the level of the strength properties of the alloy, and Zr or Hf is then added; as a result, a Ni-based heat-resistant alloy having further improved strength at high temperatures can be obtained (No. A2 to No. A4, No. B2 to No. B4). Incidentally, it was also confirmed that even when these addition elements are added, the precipitation of the γ′ phase can be developed, and also there are no problems with its high-temperature stability (dissolution temperature).

(14) Second Embodiment: Alloys were prepared with reference to the results of the first embodiment. That is, the amount of Zr and Hf added was fixed to 1.2 mass %, while the concentration of Ir of the base Ni-based alloy was changed within a range of 5.0 mass % to 35 mass %. The alloy production process was basically the same as in the first embodiment, and alloy ingots after melting/casting were subjected to a homogenizing treatment and then to an aging heat treatment to cause the precipitation of the γ′ phase. However, according to the Ir concentration, the temperature of the aging heat treatment was adjusted to 1,200° C. to 1,400° C., and the temperature of the homogenizing treatment to 700° C. to 900° C. Then, after the processing of test pieces, the same evaluation test as in the first embodiment was performed. The results are shown in Table 2.

(15) TABLE-US-00002 TABLE 2 Alloy composition (mass %) No. Ni Ir Al W Co Cr Ta C B Zr Example A5 Balance 5.00 4.77 14.13 9.06 7.19 5.56 0.14 0.01 1.20 A6 10.00 4.60 13.62 8.74 6.94 5.36 0.13 0.01 A7 25.00 4.38 14.33 7.64 6.10 4.68 0.11 0.01 A8 35.00 3.75 11.08 7.11 5.64 4.36 0.11 0.01 B5 5.00 4.77 14.13 9.06 7.19 5.56 0.14 0.01 — B6 10.00 4.60 13.62 8.74 6.94 5.36 0.13 0.01 B7 25.00 4.38 14.33 7.64 6.10 4.68 0.11 0.01 B8 35.00 3.75 11.08 7.11 5.64 4.36 0.11 0.01 Conventional C1 25.00 4.38 14.33 — — — — — — Example Alloy γ′ Phase composition dissolution Hardness (Hv) (mass %) temperature Ambient Amount of No. Hf (° C.) temperature 900° C. displacement Example A5 — 1243 514 285 0.50 A6 1258 543 340 0.51 A7 1256 618 395 0.49 A8 1306 612 413 0.48 B5 1.20 1243 468 263 0.79 B6 1248 506 313 0.66 B7 1252 486 363 0.52 B8 1338 549 384 0.62 Conventional C1 — 344 228 0.25 Example

(16) From Table 2, it was confirmed that even when the amount of Ir added to Ni-based heat-resistant alloys with addition of Zr and Hf is set in a wide range, the γ′ phase is stable, and these alloys have suitable high-temperature strength and toughness.

(17) Third Embodiment: attention was here focused on the Ni—Ir—Al—W alloys No. A7 and No. B7 (the amount of Ir added: 25 mass %), which were excellent in hardness and compressive strength at both ambient temperature and a high temperature, and also had excellent toughness, in the second embodiment. In this embodiment, the amounts of Zr and Hf added were changed in this alloy system to produce Ni-based heat-resistant alloys, and their properties were evaluated. The alloy production process and the evaluation method are basically the same as in the first embodiment. The evaluation results are shown in Table 3.

(18) TABLE-US-00003 TABLE 3 Alloy composition (mass %) No. Ni Ir Al W Co Cr Ta C B Zr Example A9 Balance 25.00 4.38 14.33 7.64 6.10 4.68 0.11 0.01 2.00 A10 1.50 A7 1.20 A11 0.80 A12 0.01 B9 — B10 — B7 — B11 — B12 — AB1 0.90 AB2 0.60 AB3 0.30 Comparative X1 4.00 Example X2  0.005 Y1 — Y2 — Conventional C2 — Example Alloy γ′ Phase composition dissolution Hardness (Hv) (mass %) temperature Ambient Amount of No. Hf (° C.) temperature 900° C. displacement Example A9 — 1216 673 360 0.88 A10 — 1208 585 368 0.79 A7 — 1256 618 395 0.66 A11 — 1270 610 376 0.58 A12 — 1251 504 356 0.51 B9 2.00 1249 588 367 0.59 B10 1.50 1297 622 365 0.56 B7 1.20 1252 486 363 0.52 B11 0.80 1277 576 380 0.47 B12 0.01 1302 588 397 0.44 AB1 0.30 1271 653 381 0.53 AB2 0.60 1264 627 355 0.46 AB3 0.90 1243 630 352 0.43 Comparative X1 — 1155 630 311 2.21 Example X2 — 1260 565 362 0.32 Y1 4.00 1221 640 301 1.41 Y2  0.005 1257 593 358 0.33 Conventional C2 — 1253 482 399 0.23 Example

(19) It is noted from Table 3, as a result of the proper addition of Zr and Hf, at least one of the hardness and compressive strength at ambient temperature was enhanced in Ni—Ir—Al—W alloys over the alloy of a conventional example having no addition (No. C2). Then, it can also be confirmed that the amount of displacement in a hot bending test also increased, and the toughness in a high temperature range was significantly improved. The addition of one of Zr and Hf is effective, and the addition of both is also effective.

(20) Meanwhile, in the case where the amounts of Zr and Hf added are too small, the effects of these addition elements are weak, and the margin of improvement in toughness (the amount of bending displacement) is small (No. X2, No. Y2). In addition, when the amounts of Zr and Hf added are too large, the high-temperature strength significantly decreases, showing the minimum valve (No. X1, No. Y1). In particular, excessive addition of Zr also tends to decrease the dissolution temperature of the γ′ phase, and may affect the stability of the γ′ phase. Therefore, it was confirmed that the effects of Zr and Hf are exhibited only when their amounts added are controlled.

INDUSTRIAL APPLICABILITY

(21) The present invention is a Ni-based heat-resistant alloy capable of stably exhibiting high-temperature strength. The present invention is suitable for members of gas turbines, airplane engines, chemical plants, automotive engines such as turbocharger rotors, high-temperature furnaces, and the like. In addition, as a particularly useful application, a tool for friction stir welding (FSW) is mentioned. The Ni-based heat-resistant alloy of the present invention has improved high-temperature strength and toughness, and is unlikely to break or snap during use as an FSW tool. In addition, the Ni-based heat-resistant alloy has improved ambient-temperature strength, and is also applicable to FSW of high-hardness ferrous materials and metal materials such as titanium alloys, nickel-based alloys, and zirconium-based alloys.