CN107747120B

CN107747120B - Method for controlling dendrite spacing in growth process of Ni-based single crystal high-temperature alloy

Info

Publication number: CN107747120B
Application number: CN201710992617.XA
Authority: CN
Inventors: 孟祥斌; 李金国; 刘纪德; 张朝威; 王猛; 赵乃仁; 王志辉; 金涛; 孙晓峰
Original assignee: Institute of Metal Research of CAS
Current assignee: Institute of Metal Research of CAS
Priority date: 2017-10-23
Filing date: 2017-10-23
Publication date: 2020-11-03
Anticipated expiration: 2037-10-23
Also published as: CN107747120A

Abstract

The invention discloses a method for controlling dendrite spacing in the growth process of a Ni-based single crystal high-temperature alloy, and belongs to the technical field of single crystal high-temperature alloys. The method aims at the Ni-based single crystal high-temperature alloy, and achieves the purpose of controlling the dendritic crystal spacing by adjusting the growth path of the dendritic crystal in the directional solidification process. When the dendritic crystal of the Ni-based single crystal casting is coarsened, the dendritic crystal spacing can be adjusted by changing the growth mode of the single crystal casting. The invention achieves the purpose of controlling the dendrite spacing by adjusting the growth path of the dendrite, and lays a foundation for preparing a single crystal structural member with variable cross-section characteristics in the future.

Description

Method for controlling dendrite spacing in growth process of Ni-based single crystal high-temperature alloy

Technical Field

The invention relates to the technical field of single crystal high-temperature alloys, in particular to a method for controlling dendrite spacing in the growth process of a Ni-based single crystal high-temperature alloy.

Background

In order to meet the requirement of advanced aeroengine turbine blades on temperature resistance, the monocrystal high-temperature alloy with a high-temperature weak structure of a grain boundary is eliminated, and the monocrystal high-temperature alloy is gradually the preferred material for preparing the advanced aeroengine turbine blades due to the excellent high-temperature performance. The design structure and the manufacturing quality of the single crystal superalloy turbine blade directly influence the temperature bearing capacity and the overall performance of the aircraft engine. Throughout the development process of advanced aero-engines, the upsizing of the size and the structural complication of single crystal superalloy turbine blades have become an effective means and a necessary trend to continue to improve the overall performance of the critical hot-end components of aero-engines. However, with the large size and complicated structure of the single crystal blade, the dendrite is easy to be coarse in the growth process of the single crystal, which causes the problems of the performance fluctuation of the single crystal blade, the service life shortening and the like. Firstly, the novel single crystal blade has a complex structure, the blade body has a thin wall and a changeable cross section, which causes a complex single crystal growth path and a large growth rate difference, and easily causes thick dendrites and reduced blade performance. Secondly, the large-scale of novel single crystal blade size causes the dendritic crystal growth path to lengthen in the directional solidification process, especially in the single crystal growth later stage at the distal end of the water-cooling disc, because the temperature gradient in the dendritic crystal growth direction sharply reduces, causes dendritic crystal coarsening more easily, leads to the blade to scrap. Therefore, it is very important to optimize the single crystal growth mode, adjust the dendrite growth path, and control the dendrite spacing.

Disclosure of Invention

The invention aims to provide a method for controlling dendrite spacing in the growth process of a Ni-based single crystal high-temperature alloy, which solves the problem of dendrite coarsening caused by the change of a dendrite growth path in the directional solidification process of the single crystal high-temperature alloy by controlling the dendrite spacing.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for controlling dendrite spacing in the growth process of Ni-based single crystal high-temperature alloy is provided, which aims at the Ni-based single crystal high-temperature alloy and realizes the control of dendrite spacing by adjusting the growth path of dendrite in the directional solidification process of the Ni-based single crystal high-temperature alloy.

In the directional solidification process, when a rod-shaped specimen having a fixed cross-sectional size is grown, the dendrite spacing increases as the cross-sectional size of the specimen increases.

In the directional solidification process, when a specimen with a variable cross section is grown, the dendrite spacing when the cross-sectional dimension of the specimen increases in an abrupt manner is larger than the dendrite spacing when the cross-sectional dimension of the specimen increases in a continuous manner.

The section diameter of the sample is phi 8-16 mm.

Aiming at the characteristics of complex structure and variable shape of the nickel-based single crystal casting, a reasonable single crystal growth mode is adopted, the growth path of dendrites is adjusted, and the dendrite spacing can be effectively controlled. However, the unreasonable single crystal growth method can cause the dendrite spacing to be significantly coarsened.

The invention has the following advantages and beneficial effects:

1. according to the invention, by researching the response relation between the geometric dimension of the Ni-based single crystal high-temperature alloy sample and the dendrite spacing, the transverse width of the test bar is increased, the dendrite spacing is obviously increased, and the dendrite coarsening is determined under the condition that the directional solidification process is not changed; and in the widening process of the test bar, the sectional size of the test sample is continuously increased, so that the coarsening of the dendrite can be effectively controlled.

2. The Ni-based single crystal casting has a complex structure and a variable shape, and the situation of thick dendritic crystals is easy to occur. Particularly, in the later stage of directional solidification, as the distance between a solid-liquid interface and a water cooling disc is increased, the temperature gradient and the cooling rate are obviously reduced, the dendritic crystal is obviously coarsened, and the dendritic crystal spacing of the single crystal casting is fluctuated. The method adopts an optimized growth mode of the single crystal casting and adjusts the growth path of the dendritic crystal to achieve the purpose of controlling the dendritic crystal spacing, thereby laying a foundation for preparing the single crystal structural member with the variable cross-section characteristic in the future.

Drawings

FIG. 1 is a schematic view of test bars of different sizes.

FIG. 2 shows the dendrite morphology of test bars with different sizes.

FIG. 3 shows the dendrite spacing of single crystal test bars of different sizes.

FIG. 4 is a schematic view of a blade simulator with different growth modes.

FIG. 5 shows the dendrite morphology of different growth mode blade simulations.

Detailed Description

The invention is described in detail below with reference to the accompanying drawings and examples. In the following examples, nickel-based single crystal superalloy test rods (grades: SRR99, AM3, DD5, DD98) of different sizes were prepared by a conventional directional solidification process, and a corresponding control method was proposed by studying the relationship between the dendrite growth path and the dendrite spacing.

As shown in FIG. 1, to study the effect of dendrite path on dendrite spacing, a set of test bars with different geometries were designed. The module mainly includes: a crystal selector, a transition section and a sample.

In order to quantify the specimen size, in fig. 1, several major dimensions of the specimen are labeled, including mainly the geometric and structural features of the specimen. Specific sample dimensions are detailed in table 1.

TABLE 1 geometric dimensions of the samples

(Note: the expanded means that the cross-sectional size (diameter) of the sample increases in a continuous manner, gradually increases from narrow to wide, and the continuous means that the size of the sample changes continuously; the abrupt change means that the cross-sectional size (diameter) of the sample increases in an abrupt manner, and the abrupt change means that the cross-sectional size of the sample 4 increases suddenly from 8mm to 12mm, then increases suddenly to 16mm, and no transition process occurs when the cross-sectional size increases.)

As shown in FIG. 4, in order to study the influence of the dendrite growth mode on the dendrite spacing of the blade, a group of simulators with typical blade structures such as tenons, flanges and blade bodies are designed.

Example 1:

as shown in FIG. 2, under the condition of the constant directional solidification process, the dendrite growth path is different according to the size of the sample, so that the dendrite spacing in the single crystal test bar is also different. As shown in FIG. 3, when the dendrite is grown in sample 1 having a size of φ 8, the dendrite is fine and dense, and the dendrite spacing is about 246 μm; when dendrites were grown in sample 2 having a size of phi 16, the dendrites were significantly coarsened with a dendrite spacing of about 297 μm; when dendrites grow in sample 3 with a size of phi 8-16 continuously expanding, the morphology of the dendrites is similar to that in sample 3, and the dendrite spacing is about 287 mu m; when dendrites were grown in sample 4, which had a size of phi 8-16, abrupt expansion, the dendrites were much coarser with a dendrite spacing of about 330 μm. When the size of the sample is within the range of phi 8-16mm, the dendrite spacing increases along with the increase of the size of the sample; the magnitude of the increase in dendrite spacing due to the sudden increase in specimen size is greater than the continuous increase in specimen size. Therefore, the aim of controlling the dendrite spacing can be achieved by changing the growth path of the dendrite.

Example 2:

according to the difference of dendrite spacing of dendrites in different growth paths in the embodiment 1, the growth mode of single crystal in the simulated blade is adjusted from tenon up to tenon down, as shown in FIG. 4. There is also a significant difference in dendrite spacing in the leaves due to the different growth patterns. FIG. 5 shows the dendrite morphology of different growth mode blade simulations. In the blade simulation piece with the tenon growing mode, dendritic crystals are finer and compact, and the dendrite spacing is about 280 mu m; in the blade simulation piece of the lower growth mode, the dendrites are coarse, and the dendrite spacing is about 300 μm. Therefore, the aim of controlling the dendrite spacing can be achieved by changing the growth mode of the blade simulation piece.

Claims

1. A method for controlling dendrite spacing in the growth process of a Ni-based single crystal superalloy is characterized by comprising the following steps: the method aims at the Ni-based single crystal high-temperature alloy, and realizes the control of dendrite spacing by adjusting the growth path of dendrite in the directional solidification process of the Ni-based single crystal high-temperature alloy;

in the directional solidification process, when a sample with a variable cross section is grown, the dendritic crystal spacing when the cross section size of the sample is increased in an abrupt mode is larger than the dendritic crystal spacing when the cross section size of the sample is increased in a continuous mode;

the diameter of the section of the sample is phi 8-16 mm;

in the growth process of the Ni-based single crystal high-temperature alloy, the growth mode of a single crystal casting is changed, so that the growth path of dendrites is adjusted, and the control of dendrite spacing is realized.