NICKEL-COBALT ALLOY

Abstract

A NiCo alloy includes 30 to 65 wt % Ni, >0 to max. 10 wt % Fe, >12 to <35 wt % Co, 13 to 23 wt % Cr, 1 to 6 wt % Mo, 4 to 6 wt % Nb+Ta, >0 to <3 wt % Al, >0 to <2 wt % Ti, >0 to max. 0.1 wt % C, >0 to max. 0.03 wt % P, >0 to max. 0.01 wt % Mg, >0 to max. 0.02 wt % B, >0 to max. 0.1 wt % Zr, which fulfils the following requirements and criteria: a) 900 C.< solvus temperature<1030 C. with 3 at %<Al+Ti (at %)<5.6 at % and 11.5 at %<Co<35 at %; b) stable microstructure after 500 h of ageing annealing at 800 C. with a ratio Al/Ti>5 (on the basis of the contents in at %).

Claims

1. A component of an aircraft turbine comprising an NiCo alloy with 30 to 65 wt % Ni, >0 to max. 10 wt % Fe, >12 to <35 wt % Co, 13 to 23 wt % Cr, 1 to 6 wt % Mo, 4 to 6 wt % Nb+Ta, >0 to <3 wt % Al, >0 to <2 wt % Ti, >0 to max. 0.1 wt % C, >0 to max. 0.03 wt % P, >0 to max. 0.01 wt % Mg, >0 to max. 0.02 wt % B, >0 to max. 0.1 wt % Zr, 0 to 0.5 wt % Cu, 0 to 0.015 wt % S, 0 to 1.0 wt % Mn, 0 to 1.0 wt % Si, 0 to 0.01 wt % Ca, 0 to 0.03 wt % N, 0 to 0.02 wt % 0, 0 to 4 wt % V, and 0 to 4 wt % W, wherein the alloy satisfies the requirements and criteria listed below: a) 900 C.-solvus temperature1030 C. at 3 at %Al+Ti (at %)5.6 at % as well as 11.5 at %Co35 at %; b) stable microstructure after 500 h of aging annealing at 800 C. and an Al/Ti ratio5 (on the basis of the contents in at %).

2. The component according to claim 1, wherein the alloy satisfies the requirement 945 C.-solvus temperature1000 C..

3. The component according to claim 1, wherein the alloy has T (-) 80 K and Al+Ti4.7 at % as well as Co contents11.5 at % and 35 at %.

4. The component according to claim 1, wherein the alloy has a temperature interval between -solvus and -solvus temperatures equal to or greater than 140 K and a Co content 15 at % and 35 at %.

5. The component according to claim 1, wherein the alloy has a Ti content of 0.8 at %.

6. The component according to claim 1, wherein the alloy has a Ti content of 0.65 at %.

7. The component according to claim 1, wherein the alloy has a content of 4.7Nb+Ta5.7 wt %.

8. The component according to claim 1, wherein the alloy has contents of Ti, Al and Co in accordance with the following limit values: 0.05 at %Ti0.5 at %, 3.6 at %Al4.6 at %, 15 at %Co32 at %.

9. The component according to claim 1, wherein the component comprises a rotating turbine disk.

10. The component according to claim 1, wherein the component comprises a stationary turbine component.

11. An NiCo alloy with 30 to 65 wt % Ni, >0 to max. 10 wt % Fe, >12 to <35 wt % Co, 13 to 23 wt % Cr, 1 to 6 wt % Mo, 4 to 6 wt % Nb+Ta, >0 to <3 wt % Al, >0 to <2 wt % Ti, >0 to max. 0.1 wt % C, >0 to max. 0.03 wt % P, >0 to max. 0.01 wt % Mg, >0 to max. 0.02 wt % B, >0 to max. 0.1 wt % Zr, 0 to 0.5 wt % Cu, 0 to 0.015 wt % S, 0 to 1.0 wt % Mn, 0 to 1.0 wt % Si, 0 to 0.01 wt % Ca, 0 to 0.03 wt % N, 0 to 0.02 wt % 0, 0 to 4 wt % V, and 0 to 4 wt % W, wherein the alloy satisfies the requirements and criteria listed below: a) 900 C.-solvus temperature1030 C. at 3 at %Al+Ti (at %)5.6 at % as well as 11.5 at %Co35 at %; b) stable microstructure after 500 h of aging annealing at 800 C. and an Al/Ti ratio5 (on the basis of the contents in at %).

12. Use of the alloy according to claim 11, in engine construction, in furnace construction, in boiler construction, in power-plant construction.

13. Use of the alloy according to claim 11, as a structural part in oil and gas extraction engineering.

14. Use of the alloy according to claim 11, as a structural part in stationary gas and steam turbines.

15. Use of the alloy according to claim 11, as a weld filler material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

[0037] In the drawings,

[0038] FIG. 1 shows -Solvus temperatures of the test alloys versus the sum of the Al+Ti contents (atomic %) of the chemical compositions.

[0039] FIG. 2 shows -Solvus temperatures of the test alloys versus the sum of the Al+Ti contents (at %) of the chemical compositions with the restricted temperature range between 945 C. and 1000 C.

[0040] FIG. 3 shows occurrence of the -phase versus the plots of the contents of Co and Ti of the test alloys.

[0041] FIG. 4 shows the difference between -solvus and -solvus temperature of the test alloys versus the sum of the Al+Ti contents (at %). Open squares: Co<11.5 at %, open diamonds: 11.5 at %Co18 at %, closed diamonds: Co>18 at %.

[0042] FIGS. 5A-5J show exemplary SEM photographs for test alloys L4, V10, V15, V16 and V17 after aging annealing for 500 h at 800 C.

[0043] FIG. 6 shows A 780 variants in comparison with Alloy 718 (tension test: Rp 0.2)

[0044] FIG. 7 shows A 780 variants in comparison with Alloy 718 (tension test: Rm)

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] The properties of the inventive alloy are discussed hereinafter:

[0046] Numerous laboratory heats with different chemical compositions were produced by means of a laboratory vacuum arc furnace.

[0047] Each heat was cast into a heavy-duty cylindrical copper chill mold with a diameter of 13 mm. During smelting, three bars with a length of approximately 80 mm were produced. All alloys were homogenized after smelting. The entire process took place in the vacuum furnace and consisted of 2 stages: 1140 C./6 h+1175 C./20 h. This was followed by quenching in an argon atmosphere. Hot forming for the smelted alloys was carried out using a rotary swaging machine. The bars had a diameter of 13 mm at the beginning and were reduced in diameter by four rotary swaging operations of one millimeter each to obtain the final diameter of 9 mm.

[0048] Table 1 discloses the chemical composition of Alloy 718 corresponding to the prior art as specified by the valid AMS 5662 standard, while Table 2 presents the mechanical properties of that alloy.

[0049] Table 3 discloses the chemical composition of Waspaloy corresponding to the prior art as specified by the valid AMS 5662 standard, while Table 4 presents the mechanical properties of that alloy.

[0050] The inventive chemical compositions of the laboratory heats are listed in Table 5. At the bottom, the known alloys A718, A718 Plus and Waspaloy are also included as reference materials. In addition to the reference materials, the test alloys are identified with the letters V and L plus 2 numerals each. The chemical compositions of these test alloys include variations in the contents of the elements Ti, Al, Co and Nb.

[0051] When the contents of the elements Ti, Al and Co as well as the sum of Al+Ti and the Al/Ti ratio of the contents of the elements are expressed in atomic percent, very good technological properties are obtained in selected ranges for the -solvus temperature, the difference between -solvus and -solvus temperatures, the absence of primary delta phase and absence of the -phase, the microstructural stability at 800 C. after aging annealing tests for 500 h and the mechanical hardness HV after a standard heat treatment comprising solution annealing and three-stage precipitation-hardening annealing for A718 (980 C./1 h+720 C./8 h+620 C./8 h, see the AMS 5662 standard).

[0052] Table 6a lists the contents in atomic percent of the elements Al, Ti and Co as well as the sum of the Al+Ti contents (in atomic percent) and the Al/Ti ratios for the test alloys and the 3 reference materials of Table 5.

[0053] Furthermore, Table 6b contains the calculated solvus temperatures of the -phase and of the -phase as well as the temperature difference T (-) calculated therefrom between the -solvus and -solvus temperatures. Table 6b also indicates the mechanical hardness values 10 HV determined for the test alloys (after three-stage precipitation-hardening heat treatment of 980 C./1 h+720 C./8 h+620 C./8 h in accordance with the AMS 5662 standard for A718). Moreover, Table 6b indicates remarks on the occurrence of the -phase (calculated or observed).

[0054] The criteria for selection of the inventive alloy are explained and exemplary test alloys are indicated in the following descriptions.

[0055] For reasons of strength and microstructural stability, the -solvus temperature of the inventive alloy should be 50 K higher than that of alloy A718, which has a -solvus temperature of approximately 850 C. On the other hand, the -solvus temperature of the inventive alloy should be lower than or equal to 1030 C. This 1030 C. corresponds approximately to the -solvus temperature of Waspaloy. A higher -solvus temperature would influence the hot formability very negatively since, in the forging process, for example, -precipitates already lead to extensive precipitation hardening of the surface of the forged piece if the surface temperatures of the forged piece are slightly below the -solvus temperature, and this in turn may lead to considerable disruptions of the surface of the forged piece during further forming by forging.

[0056] Thus the requirement 900 C.-solvus T1030 C. should be satisfied.

[0057] In FIG. 1, the -solvus temperature of the test alloys is plotted against the sum of the Al+Ti contents (at %) of their chemical compositions.

[0058] From FIG. 1 it is evident that the requirement 900 C.-solvus T1030 C. is satisfied by the restriction 3 at %Al+Ti (at %)5.6 at %. The test alloys V12, V13, V14, V15, V16, V17, V20, V21, V22, L04, L07, L09, L15, L16, L17 and L18 are exemplary alloys for this range.

[0059] For even better hot formability, the -solvus temperature of the inventive alloy should be <1000 C., and for microstructural stability at even higher temperature it should be >945 C. The test alloys V14, V16, V17, V20, V21, V22 L04, L15, L16, L17 and L18 are exemplary alloys for this range. The temperature range bounded between 945 C. and 1000 C. is evident from FIG. 2.

[0060] The Co content of the test alloys influences the -solvus and -solvus temperatures and thus AT (-). The Co content of the inventive alloy is not permitted to be too high, to ensure that no primary -phase develops. This restricts the Co content to <35 at %. Exemplary alloys in which primary -phase develops are the test alloys L12 and L13, both of which have a Co content of approximately 50 at %.

[0061] FIG. 3, in which the occurrence of the -phase is marked on the plots of the Co and Ti contents of the test alloys, shows that the Ti content of the inventive alloy must be limited to 0.8 at % in alloys with Co contents greater than 16 at %, in order to prevent the development of a stable -phase. Exemplary alloys with Ti0.8 at % are the test alloys V12, V13, V14, V15, V16, V17, V21 and V22. Preferred alloys have a Ti content of 0.65 at %. These are the exemplary test alloys V16, V17, V21 and V22.

[0062] During the forging process, minor proportions of -phase are consumed for grain refining of the microstructure. In other words, forging in the last forging heats is carried out starting from a temperature slightly below the -solvus temperature, in order to produce a very fine-grained microstructure of the respective forged piece. On the other hand, in order to make it possible to work with a sufficiently broad window of forging temperatures, the -solvus temperature cannot be permitted to be too high, and it must lie well below the -solvus temperature of the inventive alloys. For the window of forging temperature to be sufficiently broad, it must be 80 K. Therefore the difference T (-) between -solvus temperature and -solvus temperature must be 80 K.

[0063] From FIG. 4, it can be seen that T (-) is 80 K when the sum of the Al+Ti contents is 4.7 at % and the Co content is 11.5 at %. Even greater temperature intervals of 140 K between -solvus temperature and -solvus temperature are possible if at the same time the Co content of the alloy is 15 at %.

[0064] A further criterion results from the requirement that states that the microstructure of the inventive alloy should be stable at an aging temperature of 800 C. (after 500 h). This criterion is satisfied by the inventive alloys that have an Al/Ti ratio of 5.0. Exemplary alloys for this condition are the test alloys V13, V15, V16, V17, V21 and V22.

[0065] Table 7 lists exemplary test alloys for the requirement of the Al/Ti ratio of the inventive alloy.

[0066] FIGS. 5A-5J show exemplary SEM photographs for the test alloys L4, V10, V15, V16 and V17 after aging annealing for 500 h at 800 C.

TABLE-US-00005 TABLE 1 Chemical composition of Alloy 718 in accordance with the AMS 5662 standard Element Weight per cent C max. 0.08 Mn max. 0.35 P max. 0.015 S max. 0.015 Si max. 0.35 Cr 17-21% Ni 50-55% Fe Rest Mo 2.8-3.3% Nb 4.75-5.5% Ti 0.65-1.15% Al 0.2-0.8% Al + Ti 0.85-1.95% Co max. 1% B max. 0.006% Cu max. 0.3% Pb max. 0.0005% Se max. 0.0003% Bi max. 0.00003%

TABLE-US-00006 TABLE 2 Mechanical properties of Alloy 718 in accordance with the AMS 5662 standard Requirements in accordance Mechanical properties Test conditions with AMS 5662 Offset yield strength Rp0.2 20 C. 1034 MPa Tensile strength Rm 20 C. 1276 MPa Elongation A5 20 C. 12% Hardness HB 20 C. 331 HB Offset yield strength Rp0.2 650 C. 862 MPa Tensile strength Rm 650 C. 1000 MPa Elongation A5 650 C. 12% Reduction of area at break Z 650 C. 15% Stress rupture test Time to break 650 C. 23 h Elongation A5 Load 725 MPa 4%

TABLE-US-00007 TABLE 3 Chemical composition of Waspaloy in accordance with the AMS 5704 standard Element Weight per cent C 0.02-0.10% Mn max. 0.1% P max. 0.015% S max. 0.015% Si max. 0.15% Cr 18-21% Fe max. 2% Mo 3.5-5.0% Nb Ti 2.75-3.25% Al 1.2-1.6% Co 12-15% Ni Rest B 0.003-0.01% Cu max. 0.1% Zr 0.02-0.08% Pb max. 0.0005% Bi max. 0.00003% Se max. 0.0003% Ag max. 0.0005%

TABLE-US-00008 TABLE 4 Mechanical properties of Waspaloy in accordance with the AMS 5704 standard Requirements in accordance Mechanical properties Test conditions with AMS 5662 Offset yield strength Rp0.2 20 C. 827 MPa Tensile strength Rm 20 C. 1207 MPa Elongation A5 20 C. 15% Hardness HB 20 C. 341 HB and 401 HB Offset yield strength Rp0.2 538 C. 724 MPa Tensile strength Rm 538 C. 1069 MPa Elongation A5 538 C. 15% Reduction of area at break Z 538 C. 18% Stress rupture test Time to break 732 C. 23 h Elongation A5 Load 552 MPa 5% Stress rupture test Time to break 816 C. 23 h Elongation A5 Load 293 MPa 5%

TABLE-US-00009 TABLE 5 Chemical compositions (in weight percent) of the test alloys (actual analysis). The C content of all alloys is approximately 0.025 wt %. If necessary, the respective alloy may contain the following elements as residual elements: Cu, S, Mn, Si, Ca, N, O. Depending on application, W up to 4 wt % and/or V up to 4 wt % may also be present in the respective alloy. The alloys A718Plus and Waspaloy respectively contain 1 wt % W. Alloy Ni Fe Cr Mo Ti Al Nb + Ta Co V05 Rest 0.05 18.17 2.96 2.00 1.96 5.50 17.03 V07 Rest 0.06 18.40 2.96 2.01 1.97 5.45 29.95 V10 Rest 0.05 18.48 3.03 1.11 2.04 5.38 17.03 V11 Rest 0.06 18.50 3.05 1.11 2.03 5.39 30.04 V12 Rest 0.05 18.40 2.97 0.50 1.23 5.53 17.04 V13 Rest 0.04 18.41 2.99 0.49 1.97 5.50 16.98 V14 Rest 0.04 18.43 2.99 0.49 1.60 5.52 17.01 V15 Rest 0.04 18.50 2.96 0.50 2.33 5.45 17.05 V16 Rest 0.05 18.25 2.98 0.17 1.90 5.51 17.25 V17 Rest 0.05 18.48 2.96 0.17 1.90 5.40 24.98 V20 Rest 0.05 18.70 2.99 0.52 2.04 5.60 30.10 V21 Rest 0.04 18.70 2.96 0.20 2.04 5.58 25.06 V22 Rest 0.04 18.70 2.96 0.20 2.04 5.40 30.10 L03 Rest 0.18 18.20 2.90 0.75 0.63 5.49 16.98 L04 Rest 0.04 18.45 3.06 1.09 1.24 5.46 17.05 L06 Rest 0.21 18.40 2.91 0.73 0.64 5.49 30.00 L07 Rest 0.38 18.32 2.93 1.07 0.92 5.49 17.04 L09 Rest 0.46 18.40 2.94 1.46 1.23 5.60 16.90 L12 Rest 0.34 18.50 2.90 0.72 0.61 5.36 49.76 L13 Rest 0.45 18.32 2.90 1.48 0.69 5.59 49.88 L15 Rest 0.03 18.47 3.03 1.09 1.25 5.38 13.99 L16 Rest 0.03 18.46 3.02 1.64 0.92 5.40 12.00 L17 Rest 0.04 18.42 3.04 1.12 1.23 5.41 25.14 L18 Rest 0.05 18.49 3.04 1.11 1.24 5.38 30.01 A718 Rest 17.06 18.71 2.93 0.99 0.48 5.32 0.02 A718Plus Rest 10.00 18.00 2.75 0.70 1.45 5.45 9.00 Waspaloy Rest 0.20 19.5 4.25 3.00 1.30 0 13.5

TABLE-US-00010 TABLE 6a Element contents in atomic percent or ratios of element contents of the test alloys Alloy at % Al/Ti Al + Ti Ti Al Co V05 1.74 6.58 2.40 4.18 16.65 V07 1.73 6.62 2.42 4.20 29.27 V10 3.28 5.69 1.33 4.36 16.65 V11 3.24 5.68 1.34 4.34 29.40 V12 4.36 3.27 0.61 2.66 16.85 V13 7.15 4.81 0.59 4.22 16.65 V14 5.83 4.03 0.59 3.44 16.75 V15 8.28 5.57 0.60 4.97 16.64 V16 20.35 4.27 0.20 4.07 16.94 V17 20.35 4.27 0.20 4.07 24.52 V20 20.00 4.64 0.62 4.02 29.58 V21 18.10 4.61 0.24 4.37 24.49 V22 18.17 4.60 0.24 4.36 29.48 L03 1.49 2.29 0.92 1.37 16.94 L04 2.02 3.99 1.32 2.67 16.83 L06 1.55 2.30 0.90 1.40 29.93 L07 1.53 3.31 1.31 2.00 16.96 L09 1.49 4.44 1.78 2.66 16.75 L12 1.51 2.21 0.88 1.33 49.73 L13 0.83 3.33 1.82 1.51 49.83 L15 2.04 4.01 1.32 2.69 13.80 L16 0.99 3.99 2.00 1.99 11.87 L17 1.95 4.01 1.36 2.65 24.83 L18 1.98 4.02 1.35 2.67 29.63 A718 0.86 2.55 1.37 1.18 0.02 A718Plus 3.66 4.43 0.95 3.48 9.00 Waspaloy 0.77 6.3 3.56 2.74 13.5

TABLE-US-00011 TABLE 6b Solvus temperatures of the -phase and of the - phase, difference T ( ) of the solvus temperatures of the - and -phases, hardness 10 HV (after precipitation-hardening heat treatment 980 C./1 h + 720 C./8 h + 620 C./8 h in accordance with the AMS 5662 standard for A718) and remarks on the -phase for the test alloys. Remarks on the T -phase -solv. -solv. ( ) Hardness (calculated or Alloy T ( C.) T ( C.) (K) 10 HV observed) V05 1080 1077 3 506 Large amounts of -phase V07 1157 1037 120 539 -Phase V10 1090 1050 40 491 No -phase V11 1180 1037 143 486 -Phase stable from 1127 C. V12 1097 917 180 415 No -phase V13 1087 1027 60 426 No -phase V14 1097 967 130 417 No -phase V15 1077 1027 50 470 No -phase V16 1097 997 100 442 No -phase V17 1152 957 195 448 No -phase V20 1162 950 212 446 Small amounts of -phase; if necessary after aging at 800 C. V21 1127 952 175 455 No -phase V22 1177 952 225 No -phase L03 1117 887 230 396 -Phase stable from 937 C. L04 1100 977 123 410 Small amounts of -phase, stable from 950 C. to 910 C. L06 1200 700 500 473 -Phase stable from 1050 C. L07 1100 900 200 442 -Phase stable from 1050 C. L09 1100 950 150 488 -Phase more stable than L12 1250 none 530 -Phase primary, -phase primary, Laves phase L13 1240 none 503 -Phase primary, -phase primary, Laves phase L15 1077 977 100 423 -Phase stable L16 1070 977 93 450 -Phase stable L17 1152 952 200 464 -Phase stable from 1097 C. L18 1157 977 180 452 -Phase stable from 1047 C. A718 1027 847 180 441 No -phase A718Plus 1027 976 51 -Phase Nb.sub.3Al.sub.0.5Nb.sub.0.5 Waspaloy 1035 No -phase, no -phase

TABLE-US-00012 TABLE 7 Exemplary test alloys for the requirement of the Al/Ti ratios for inventive alloys. Microstructural stability after Alloy Al/Ti 500 h at 800 C. Notes L04 2.02 Not satisfied Exemplary alloy that does not satisfy the requirement V13 7.15 Satisfied Exemplary alloy that V15 8.28 satisfies the requirement, but at a relatively high -solvus temperature V16 20.35 Satisfied Exemplary alloys that V17 20.35 Satisfied satisfy the requirement

TABLE-US-00013 TABLE 8 Mechanical test values for A780 in comparison with A718 tested on upsetting-test specimens (solution-annealed + precipitation-hardened) Hot tension test at Hot tension test at Hot tension test at Tension test at 20 C. 650 C. 700 C. 750 C. 20 20 650 700 750 750 20 C. 20 C. C. C. 650 C. 650 C. 650 C. C. 700 C. 700 C. 700 C. C. 750 C. 750 C. C. C. Rp0.2 Rm A5 Z Rp0.2 Rm A5 Z Rp0.2 Rm A5 Z Rp0.2 Rm A5 Z Batch (MPa) (MPa) (%) (%) (MPa) (MPa) (%) (%) (MPa) (MPa) (%) (%) (MPa) (MPa) (%) (%) 25 1179 1495 24 32 1046 1388 12 15 1000 1245 11 13 908 1075 15 13 26 1191 1521 26 37 1015 1292 12 17 984 1203 10 10 910 1057 6 8 27 1222 1556 23 38 1055 1363 11 14 1032 1255 8 9 943 1109 11 12 A718 1262 1494 16 29 1031 1231 23 59 958 1100 25 72 729 865 34 87 (420159)

[0067] By way of further description of the subject matter of the invention, FIGS. 6 and 7 are considered in conjunction with Table 8.

[0068] FIGS. 6 and 7 show diagrams containing data on strength tests at 20 C., 650 C., 700 C. and 750 C. on the new alloy (VDM Alloy 780 Premium), in this case batches 25, 26 and 27, in comparison with Alloy 718 (batch 420159) belonging to the prior art. From the diagrams it is evident that A 780, even when subjected to higher test parameters in hot tension tests, achieves higher Rp 0.2 strength values (measured on upsetting-test specimens in the precipitation-hardened condition) than A 718.

[0069] Furthermore, it was observed that, in the creep and stress rupture test at 700 C., A 780 also achieves the desired mechanical properties of creep elongation much smaller than 0.2% as well as much longer times to failure of >23 h in the stress rupture testunder otherwise identical test conditions where these properties are achieved by A 718 only at test temperatures up to 650 C.

[0070] Table 8 shows the batches 25 to 27 indicated in FIGS. 6 and 7 in comparison with A 718. Here it is evident that especially the tensile strength Rm of A 780 batches 25 to 27 achieves higher values than A 718 at higher temperatures (700 C. and 750 C.) in the hot tension tests.