SUBSTRATE-TRIGGERED DIRECTIONAL SOLIDIFICATION PROCESS FOR SINGLE CRYSTAL SUPERALLOY

Abstract

The present invention relates to a substrate-triggered single crystal superalloy directional solidification process, including: (1) preparing a single crystal substrate material having crystallographic characteristics that match crystallographic characteristics of the single crystal superalloy; (2) fabricating a single crystal substrate chilling plate using the obtained single crystal substrate material; and (3) applying the obtained single crystal substrate chilling plate in a directional solidification apparatus, and then preparing a single crystal alloy product by performing superalloy melting and directional solidification. Compared with grain selector method and seeding with grain selector method, in addition to control the crystallographic orientation of the single crystal superalloy precisely, the present invention could reduce the height of block and the whole mold through canceling the spiral grain selector, significantly improve the axial heat dissipation and temperature gradient at the solid-liquid interface, and then reduce the occurrence of freckles and stray grains near platform.

Claims

1. A substrate-triggered single crystal superalloy directional solidification process, comprising: a step (1) preparing a single crystal substrate material having crystallographic characteristics that match crystallographic characteristics of the single crystal superalloy; a step (2) fabricating a single crystal substrate chilling plate using the obtained single crystal substrate material; and a step (3) applying the obtained single crystal substrate chilling plate in a directional solidification apparatus, and then preparing a single crystal alloy product by performing superalloy melting and directional solidification.

2. The substrate-triggered single crystal superalloy directional solidification process according to claim 1, wherein the crystallographic characteristics of the single crystal superalloy and the single crystal substrate material in the step (1) satisfy the following relation: the lattice mismatching degree between a crystal plane of the single crystal substrate material that contacts with a superalloy melt and a crystal plane of the single crystal superalloy is less than or equal to 7.8%.

3. The substrate-triggered single crystal superalloy directional solidification process according to claim 2, wherein a low-index crystal plane is selected as the crystal plane of the single crystal substrate material that contacts with the superalloy melt.

4. The substrate-triggered single crystal superalloy directional solidification process according to claim 1, wherein the single crystal substrate material in the step (1) is prepared through grain selection directional solidification process, and is detected by using the following method: ensuring the macrostructure of the single crystal substrate material is free of stray grains by using a sand blasting treatment and a macrostructure etching treatment; performing an orientation test on the qualified single crystal substrate material by using Laue Diffraction; and cutting the single crystal substrate material by using wire-cutting based on the test result of the Laue Diffractometer to obtain the single crystal substrate material with the expected crystal plane.

5. The substrate-triggered single crystal superalloy directional solidification process according to claim 4, wherein the single crystal substrate material is a single crystal bar with a cylindrical shape.

6. The substrate-triggered single crystal superalloy directional solidification process according to claim 1, wherein the single crystal substrate chilling plate in the step (2) can also be formed by using a complex processing of the single crystal substrate material and pure copper.

7. The substrate-triggered single crystal superalloy directional solidification process according to claim 1, wherein an inner portion of the single crystal substrate chilling plate is disposed with a water-cooling channel with a ring shape, and an outer portion of the single crystal substrate chilling plate is disposed with threads to connect with a pulling rod of the directional solidification apparatus.

8. The substrate-triggered single crystal superalloy directional solidification process according to claim 1, wherein in the step (3), the melting temperature of the superalloy is 1450° C. to 1600° C., the pouring speed of a melt superalloy is 3°/s to 10°/s, and during directional solidification, the heating temperatures for the upper furnace and the lower furnace are 1500° C. to 1600° C. and 1450° C. to 1550° C., respectively, and the pulling rate is 20 μm/s to 100 μm/s.

9. The substrate-triggered single crystal superalloy directional solidification process according to claim 1, wherein the prepared single crystal alloy product is subjected to macrostructure detection and microstructure detection.

10. The substrate-triggered single crystal superalloy directional solidification process according to claim 9, wherein the macroscopic structure detection comprises surface sand blasting and macrostructure etching, the blasting time is 5 min to 10 min, and an etchant depends on the type of the superalloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 are schematic diagrams of grain selection method (a), combination of seeding method and grain selector method (b), and substrate-triggered method (c) of the present invention, respectively;

[0031] FIG. 2 is schematic diagram of the assembled single crystal substrate chilling plate;

[0032] FIG. 3 is the inverse pole diagram of single crystal DD5 alloy triggered by a single crystal DD5 substrate chilling plate; and

[0033] FIG. 4 is a microstructure of the single crystal DD5 alloy triggered by the single crystal DD5 substrate chilling plate.

DESCRIPTION OF THE EMBODIMENTS

[0034] The present invention is described in detail below with reference to the accompanying drawings and the specific embodiments.

EMBODIMENT

[0035] In the present embodiment, DD5 superalloy is used to prepare a certain type of single crystal turbine blade, which is mainly made of the following alloy elements: C (0.040-0.060), Cr (6.75-7.25), Co (7.00-8.00), W (4.75-5.25), Al (6.00-6.40), Ta (6.30-6.70), Mo (1.30-1.70), Hf (0.12-0.18), B (0.003-0.005), Re (2.75-3.25), and the balance nickel.

[0036] The present embodiment particularly includes:

[0037] (1) Prepare single crystal materials for substrate which owns similar crystallographic characteristics as that of DD5 single crystal superalloy.

[0038] In the present embodiment, DD5 superalloy is selected as the single crystal substrate material: (a) Since both the single crystal superalloy and the single crystal substrate material use the alloy DD5, lattices of which perfectly match each other, so as to satisfy that a lattice mismatching degree is smaller than or equal to 7.8%. (b) A crystal face, in contact with a superalloy melt, of the DD5 single crystal substrate material is (001), which is a low-index crystal face of a face-centered cubic crystal and has high interface stability in a high-temperature environment.

[0039] The DD5 single crystal substrate material is prepared through grain selection directional solidification process. The main casting parameters are as follows: the melting temperature is 1480-1550° C. and the pouring speed of the melt molten is 5°/s; the heating temperature for the upper furnace and the lower furnace are 1500-1550° C. and 1450-1500° C., respectively; and the pulling rate during directional solidification is 20 μm/s-50 μm/s. The casting mold for DD5 superalloy is cylindrical. The single crystal bar is subjected to sand blowing and macroscopic etching, and is free of stray grains on macrostructure. Then, the orientation of the single crystal bar is tested by Lauer Diffraction. Finally, the DD5 single crystal bar is wire-cut based on the result of the Laue Diffractometer and a single crystal substrate material with (001) crystal plane is gotten.

[0040] (2) Fabricate a single crystal substrate chilling plate using the obtained DD5 single crystal material.

[0041] In the present embodiment, the single crystal substrate chilling plate is assembled single crystal substrate chilling plate as shown in FIG. 2. The diameter and the height of the DD5 single crystal substrate are 20 mm and 5 mm, respectively. The DD5 single crystal substrate and pure copper are connected through tin soldering.

[0042] (3) Melt and directional solidify the DD5 superalloy in a directional solidification furnace with obtained DD5 single crystal substrate chilling plate. The schematic diagram is shown in FIG. 1(c).

[0043] The main parameters for DD5 superalloy directional solidification are as follows: the melting temperature is 1450-1600° C. and the pouring speed of the melt molten is 5°/s; the heating temperature for the upper furnace and the lower furnace are 1500-1550° C. and 1450-1500° C., respectively; and the pulling rate during directional solidification is 20 μm/s-50 μm/s.

[0044] (4) Obtain a single crystal DD5 superalloy product by directional solidification and detect the macrostructure and microstructure.

[0045] Take out the single crystal blade with mold from the directional solidification furnace, and then knock off the mold with a hammer. Sand blast the single crystal blade for 5 min and macroscopic etching it with the etchant of HCl+H.sub.2O.sub.2 (9:1) for 1-20 min.

[0046] FIG. 3 and FIG. 4 are the inverse pole diagram and the microstructure of the surface from the obtained DD5 single crystal blade which is adjacent to the single crystal substrate chilling plate respectively. It can be seen from the figures that the melt replicates the orientation of the substrate after nucleation and solidification and grows a standard (001) crystal in the substrate-triggered directional solidification.

[0047] The description described above of the embodiments is intended to make it convenient for those of ordinary skill in the art to understand and use the present invention. It will be apparent to those skilled in the art that various modifications may be readily made to these embodiments and the general principles described herein may be applied to other embodiments without making the inventive efforts. Therefore, the present invention is not limited to the embodiments described above, and improvements and modifications made by those skilled in the art in light of the present invention without departing from the scope of the present invention shall all fall within the scope of protection of the present invention.