Method for manufacturing components made of single crystal (SX) or directionally solidified (DS) nickelbase superalloys

Abstract

The invention relates to a method for manufacturing a component, especially of a gas turbine, made of a single crystal (SX) or directionally solidified (DS) nickelbase superalloy, including a heat treatment and a machining and/or mechanical treatment step. The ductility of the component is improved by doing the machining and/or mechanical treatment step prior to said heat treatment and a solution heat treatment of the component is done prior to the machining/mechanical treatment step.

Claims

1. A method for manufacturing a component comprised of a nickelbase superalloy, the nickelbase superalloy being one of: single crystal (SX) and directionally solidified (DS), the method comprising: heating the component in a first heat treatment to a temperature below a gamma prime solvus temperature of the component, the first heat treatment comprising solution heat treatment; machining at least one portion of the component after the first heat treatment; mechanically treating the component after the first heat treatment; heating the component in a second heat treatment after the machining and after the mechanically treating, the second heat treatment heating the component to a temperature that is below a gamma prime solvus temperature; applying a coating onto at least one portion of the component; performing a third heat treatment on the component after the coating is applied, the third heat treatment comprising at least one of: coating diffusion heat treatment and precipitation heat treatment.

2. The method of claim 1, wherein the component is a component of a gas turbine.

3. The method of claim 1, wherein the third heat treatment comprises both coating diffusion heat treatment and precipitation heat treatment.

4. The method of claim 3, wherein the mechanically treating of the component comprises shot peening of at least one cooling channel defined in the component.

5. The method of claim 3, wherein the component is a gas turbine blade.

6. The method of claim 5, wherein the coating is applied onto an airfoil of the gas turbine blade.

7. The method of claim 6, wherein the second heat treatment is a brazing heat treatment.

8. The method of claim 6, wherein the at least one portion of the component that is machined is a portion of a fir tree of the gas turbine blade.

9. The method of claim 8, wherein the mechanically treating of the component comprises mechanically treating at least one of the fir tree and a cooling channel of the gas turbine blade.

10. The method of claim 8, wherein the third heat treatment heats the component to a temperature below a gamma prime solvus temperature of the component.

11. The method of claim 1, wherein the component is a gas turbine blade and the coating is applied onto an airfoil of the gas turbine blade.

12. The method of claim 1, wherein the machining and the mechanically treating of the component affects a surface of the component and the second heat treatment modifies a microstructure of the surface affected by the machining and the mechanically treating.

13. The method of claim 1, wherein the third heat treatment heats the component to a temperature below a gamma prime solvus temperature of the component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

(2) FIG. 1 shows the rupture strain in a stress-strain diagram;

(3) FIG. 2A shows the uniaxial loading of a component and FIG. 2B shows the corresponding stress-strain diagram;

(4) FIG. 3A shows the multiaxial loading of a component and FIG. 3B shows the corresponding stress-strain diagram with its reduced rupture strain;

(5) FIG. 4 shows the reduction of ductility due to multiaxial stress according to 2 different models;

(6) FIG. 5 shows a central part of a gas turbine blade;

(7) FIG. 6 shows the distribution of the stress ratio r in three different cut planes of the blade according to FIG. 5;

(8) FIG. 7 shows an exemplary manufacturing procedure for a gas turbine component according to the prior art;

(9) FIG. 8 shows a micrograph of a body manufactured according to the prior art procedure of FIG. 7;

(10) FIG. 9 shows in a diagram similar to FIG. 7 an embodiment of the manufacturing method according to the present invention;

(11) FIG. 10 shows a micrograph of a body manufactured according to the procedure of FIG. 9 and

(12) FIG. 11 shows the coarse / microstructure with its cellular recrystallisation of the body according to FIG. 10.

DETAILED DESCRIPTION

(13) The present invention is based on investigations comprising tensile tests of specimens made of a nickelbase superalloy, which have seen different combinations of surface and heat treatments. In particular, it was successfully tried to modify the surface in a way that a subsequent heat treatment results in the formation of a ductile layer. That has been achieved by a heat treatment below the (gamma prime) solvus temperature, resulting in a coarse / (gamma/gamma prime) microstructure (cellular recrystallisation) in the outermost area.

(14) The impact of surface layer modification on tensile ductility has been observed on SX tensile specimens.

(15) FIG. 7 shows a (prior art) reference procedure where a heat treatment T(t) with 3 different heat treatment steps HTS1-3 has been done first on test bars and final machining (machining step S.sub.M) and testing (testing step S.sub.T) of the specimens has been done after heat treatment (specimen Z6 in Table 1).

(16) In contrast, according to FIG. 9, plastic deformation and machining of the final specimen geometry (machining step S.sub.M) has been done before the heat treatment (heat treatment steps HTS1-3) (specimen Z1 in Table 1), but after the solution heat treatment. Thereby, the surface near region, previously affected by plastic deformation and machining (e.g. by cold work hardening, for instance) was modified by the heat treatment.

(17) TABLE-US-00001 TABLE 1 Plastic Yield Tensile Elongation Specimen Deformation strength strength after fracture Z6 (acc. FIG. 7) None 966 MPa 1061 MPa 4.3% Z1 (acc. FIG. 9) 0.26% 948 MPa 1299 MPa 13.1%

(18) According to Table 1, significant higher ductility was achieved due to previous surface treatment (plastic deformation) in specimen Z1 compared to specimen Z6. The modified surface layer 17 of specimen 15 (Z1) just below the surface 16 is shown in FIGS. 10 and 11. For comparison, the un-affected surface area at the surface 16 of specimen 15 (Z6) is shown in FIG. 8.

(19) The effect of increased ductility on SX components has also been observed on other specimens at room temperature T.sub.R as well as at 600 C. even without previous plastic deformation, only due to the specimen machining step S.sub.M.

(20) Table 2 shows the results for 4 different specimen with specimen 1A and 1B having been machined after a heat treatment (HTS1, HTS2, HTS3) procedure according to FIG. 7 while specimen 2A and 2B were machined before a heat treatment HTS1, HTS2, HTS3) procedure according to FIG. 9

(21) TABLE-US-00002 TABLE 2 Testing Tensile Elongation Specimen temperature Yield strength strength after fracture 1A 23 C. 832 MPa 870 MPa 9.1% 1B 600 C. 805 MPa 959 MPa 6.4% 2A 23 C. 805 MPa 864 MPa 20.9% 2B 600 C. 751 MPa 935 MPa 16.3%

(22) Again, significant higher ductility values were achieved in specimens 2A/2B compared to specimen 1A/1B.

(23) A potential heat treatment sequence for increased ductility in the attachment area (fir tree) and/or areas of multiaxiality of a gas turbine blade could be as follows: a) solution heat treatment of the blade at casting house b) machining of fir tree c) mechanical treatment (for example shot peening) of the fir tree and/or inner surfaces of cooling channel d) heat treatment at elevated temperature, but below (gamma prime) solvus temperature (e.g. during brazing heat treatment) e) application of an additional coating for the airfoil; f) coating diffusion heat treatment and precipitation heat treatment.

(24) The characteristics of the present invention are: Turbine parts require a sufficient ductility of the material for carrying structural loads. SX (or DS) materials have typically a low ductility, which is on the limit for turbine blade applications. The SX (or DS) ductility can be improved by changing the sequence of machining and heat treatment.