CN115446291A - A Method for Evaluating the Tendency of Stray Crystal Formation in Single Crystal Superalloys - Google Patents

Abstract

The present invention provides a method for evaluating the formation tendency of single crystal superalloy miscellaneous crystals, which designs an initial sample with multiple edge plate platforms, and prepares a single crystal superalloy sample according to the method of precision investment casting , to evaluate the formation tendency of single crystal superalloy miscellaneous crystals according to the number of edge plate platforms where miscellaneous crystals are generated on the sample, or evaluate the influence of directional solidification process parameters on the formation tendency of single crystal superalloy miscellaneous crystals. The evaluation method provided in this application can evaluate the formation tendency of miscellaneous crystals after the as-cast sample is obtained after pouring, without heat treatment and other detection means, the method is simple, fast and efficient, and saves time and cost.

Description

A Method for Evaluating the Tendency of Stray Crystal Formation in Single Crystal Superalloys

technical field

The invention relates to the technical field of single crystal superalloys, in particular to a method for evaluating the formation tendency of single crystal superalloys.

Background technique

The working environment of the aero-engine is very harsh. As one of the core hot-end components of the aero-engine, the working blade of the turbine works under extremely harsh conditions such as high temperature, high stress, and gas corrosion. Due to the elimination of the grain boundary perpendicular to the principal stress axis, the single crystal superalloy can significantly improve the temperature bearing capacity at high temperature. Therefore, it has become the material of choice for high-performance aeroengine turbine blades.

With the continuous improvement of the thrust-to-weight ratio of advanced aero-engines, the temperature in front of the turbine continues to increase, and the requirements for the temperature-bearing capacity of single crystal superalloys continue to increase. The structure is becoming more and more complex. These factors aggravate the instability of the temperature field, solute field and temperature gradient field during the directional solidification of single crystal turbine blades. The above changes all make the formation tendency of crystal defects such as miscellaneous crystals in single crystal turbine blades continue to increase.

As a kind of crystallization defect, miscellaneous crystals destroy the single crystal integrity of single crystal turbine blades, significantly reduce the performance of single crystal turbine blades, reduce the pass rate of single crystal turbine blades, and improve the quality of single crystal turbine blades. Therefore, it is of great significance to carry out research on the formation tendency of single crystal superalloy miscellaneous crystals and develop a directional solidification process with less tendency to produce miscellaneous crystals.

At present, the research on miscellaneous crystals in single crystal superalloys mainly focuses on the formation mechanism of miscellaneous crystals and the method of eliminating miscellaneous crystals. There are few studies on the evaluation of the formation tendency of miscellaneous crystals and the influence of directional solidification process parameters on the formation of miscellaneous crystals. It is very necessary to scientifically and effectively evaluate the formation tendency of single crystal superalloys. In the paper "Study and Comparison of Supercooling Ability and Single Crystal Castability of Several Nickel-based Superalloys", Ma Dexin and others tested the solidification behavior of several single crystal superalloys in ceramic shells, and obtained various conclusions. The liquidus temperature T _L , the critical nucleation temperature T _N and the critical nucleation undercooling degree ΔT _N = T _L -T _N of the alloy, and the ability of the single crystal superalloy to resist the formation of miscellaneous crystals can be judged by the supercooling ability of the alloy , it is considered that the lower the supercooling ability of the alloy, the weaker its ability to resist the formation of stray crystals. This method requires accurate measurement of the liquidus temperature and critical nucleation temperature of the alloy. The liquidus temperature and critical nucleation temperature of the alloy are related to the cooling rate during the test. This method is complex in operation and low in efficiency. The cost is high, and it is difficult to evaluate the influence of directional solidification process parameters on the formation of single crystal superalloy miscellaneous crystals.

In patent CN102706920A, Zhang Xiaoli et al. designed mold A with different edge plate platform lengths and mold B with different edge plate platform heights, and cast single crystal castings A and B of various alloys according to these two molds; by analyzing castings A and The length and height of the edge plate platform formed by the miscellaneous crystals in B quantitatively evaluate the ability of the alloy to form miscellaneous crystals; the smaller the minimum edge plate platform length formed by the miscellaneous crystals or the higher the maximum edge plate platform height formed by the miscellaneous crystals, it indicates the miscellaneous crystals of the alloy The stronger the tendency to form. Although this patent is to evaluate the formation tendency of single crystal superalloy miscellaneous crystals, the patent is only used to evaluate the formation of single crystal superalloy miscellaneous crystals by using the minimum edge plate platform length and maximum edge plate platform height. However, it cannot be used to study the effect of directional solidification process parameters on the formation tendency of single crystal superalloys.

Contents of the invention

The technical problem solved by the present invention is to provide a method for evaluating the formation tendency of single crystal superalloy miscellaneous crystals. The method provided by the application can be used to evaluate the formation tendency of single crystal superalloy miscellaneous crystals, and can also evaluate the effect of directional solidification process parameters on single crystal superalloys. The influence of the formation tendency of stray crystals in crystal superalloys.

In view of this, the present application provides a method for evaluating the formation tendency of single crystal superalloy stray crystals, comprising the following steps:

A) design an initial sample with a plurality of edge plate platforms, and the edge plate platforms are symmetrically distributed on both sides of the initial sample along the direction of directional solidification;

B) Using the method of precision investment casting, under the directional solidification process parameters, preparing single crystal superalloy samples with different components according to the initial sample;

C) counting the number of edge plate platforms that generate miscellaneous crystals on the single crystal superalloy sample, and evaluating the tendency of single crystal superalloy miscellaneous crystal formation according to the number of edge plate platforms that generate miscellaneous crystals;

or B') using the precision investment casting method to prepare single crystal superalloy samples according to the initial sample under different directional solidification process parameters;

C') counting the number of edge plate platforms that generate miscellaneous crystals on the single crystal superalloy sample, and evaluating the influence of directional solidification process parameters on the tendency of miscellaneous crystal formation according to the number of edge plate platforms that generate miscellaneous crystals.

Preferably, the number of the edge plate platforms is 3-5 pairs.

Preferably, the length L ₁ of the edge plate platform is 10-20 mm, the width W is 6-15 mm, and the thickness H ₁ is 2-5 mm; the distance H ₂ between the adjacent edge plate platforms is 30-60 mm.

Preferably, the width L2 of the main body of the initial sample is _15-35 mm.

Preferably, in step B), the directional solidification process parameters in the precision investment casting method are: the temperature of the upper heater is 1500°C-1600°C, the temperature of the lower heater is 1500°C-1600°C, and the pouring temperature is 1500°C ～1600℃, the drawing speed is 1.0mm/min～7.0mm/min.

Preferably, in step B'), the directional solidification process parameters in the precision investment casting method are as follows: the temperature of the upper heater is controlled at 1500°C to 1600°C, the temperature of the lower heater is controlled at 1500°C to 1600°C, and the pouring temperature The temperature is controlled at 1500°C to 1600°C, and the drawing speed is 1.0mm/min to 7.0mm/min.

This application provides a method for evaluating the formation tendency of single-crystal superalloy miscellaneous crystals. It designs an initial sample with multiple edge plate platforms, and prepares a single-crystal superalloy sample according to the method of precision investment casting , using the number of edge plate platforms that produce miscellaneous crystals on the sample to evaluate the formation tendency of single crystal superalloy miscellaneous crystals, or evaluate the influence of directional solidification process parameters on the formation tendency of single crystal superalloy miscellaneous crystals; After the as-cast sample is obtained, the evaluation of miscellaneous crystal formation tendency can be carried out without heat treatment and other detection means. The method is simple, fast and efficient, and saves time and cost.

Description of drawings

Fig. 1 is the positive triaxial survey of the multi-edge plate platform structure symmetrical sample designed by the present invention;

Fig. 2 is the left view and relevant dimensions of the multi-edge plate platform structure symmetrical sample designed by the present invention;

Fig. 3 is the front view and related dimensions of the symmetrical sample of the multi-edge plate platform structure designed by the present invention.

detailed description

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than limiting the claims of the present invention.

In view of the mechanism of miscellaneous crystal formation caused by supercooled nucleation at the corners of the edge plate during the directional solidification of single crystal superalloys, this application designed an initial sample with multiple edge plates, and prepared a single crystal high temperature alloy by directional solidification pouring. Alloy preparation, and then count the number of edge plates that produce miscellaneous crystals in the prepared single crystal superalloy samples, so as to evaluate the influence of different single crystal superalloy miscellaneous crystal formation tendency or directional solidification parameters on the miscellaneous crystal formation tendency. Specifically, the embodiment of the present invention discloses a method for evaluating the tendency to form miscellaneous crystals, including the following steps:

A) design an initial sample with a plurality of edge plate platforms, and the edge plate platforms are symmetrically distributed on both sides of the initial sample along the direction of directional solidification;

B) Using the method of precision investment casting, under the directional solidification process parameters, preparing single crystal superalloy samples with different components according to the initial sample;

C) counting the number of edge plate platforms that generate miscellaneous crystals on the single crystal superalloy sample, and evaluating the tendency of single crystal superalloy miscellaneous crystal formation according to the number of edge plate platforms that generate miscellaneous crystals;

or B') using the precision investment casting method to prepare single crystal superalloy samples according to the initial sample under different directional solidification process parameters;

C') counting the number of edge plate platforms that generate miscellaneous crystals on the single crystal superalloy sample, and evaluating the influence of directional solidification process parameters on the tendency of miscellaneous crystal formation according to the number of edge plate platforms that generate miscellaneous crystals.

In the method for evaluating the formation tendency of miscellaneous crystals provided by the present application, an initial sample with multiple edge plate platforms is firstly designed, as shown in Figure 1, Figure 2 and Figure 3, where 1 is the seed crystal and 2 is the primer. Crystal end, 3 are edge plate platforms, and 4 are blade bodies. In the present application, the number of the edge plate platforms is 3 to 5 pairs, that is, there are 3 to 5 edge plate platforms evenly distributed along the direction of directional solidification on each side of the initial sample. In the present application, the length L1 _of the edge plate platform is 10-20 mm, the width W is 6-15 mm, and the thickness H1 is _2-5 mm; the distance _H2 between the adjacent edge plate platforms is 30-60 mm, The width L2 of the main part of the mold is _15-35mm ; more specifically, the length L1 _of the edge plate platform is 12-18mm, the width W is 8-12mm, and the thickness H1 is 3-4mm _; The distance H ₂ of the adjacent edge plate platform is 40-50 mm, and the width L ₂ of the main part of the initial sample is 20-30 mm. The analysis of the formation of stray crystals in the actual turbine blade preparation process and the research results of the formation mechanism of single crystal superalloys show that the length and thickness of the edge plate platform of the sample have an important impact on the formation of stray crystals. The longer the plate length and the smaller the thickness, the easier it is to form miscellaneous crystals. The initial sample size (the length and thickness of the edge plate platform, the distance between the edge plate platforms, etc.) designed in the present invention is designed according to the actual blade size, while considering the influence of actual process conditions. If the size of the edge plate is not within the scope of this application, under the given process parameters, the edge plate may all form miscellaneous crystals (the edge plate is too long, too thin) or no miscellaneous crystals are formed at all (the edge plate is too short, too thin) thick) the tendency of single crystal superalloys to form stray crystals cannot be evaluated.

In the actual operation process of the present application, the mold design and processing are carried out according to the size of the initial sample, the wax film is pressed using the mold, the precision investment casting method is used to prepare the mold shell, and then poured in a directional solidification furnace, that is, the same Single crystal superalloy specimens with consistent initial specimen dimensions.

When investigating the tendency of different single crystal superalloys to form stray crystals, single crystal superalloys with different compositions can be prepared, and single crystal superalloy samples with different compositions can be prepared according to the above method, and the impurities produced on different single crystal superalloy samples can be counted. According to the number of edge plate platforms that produce stray crystals, the tendency of single crystal superalloys to form stray crystals can be evaluated, and thus it can be obtained which composition of single crystal superalloys is more likely to form stray crystals.

When investigating the influence of directional solidification parameters on the formation tendency of stray crystals, the composition of the single crystal superalloy is fixed, changing the directional solidification parameters, and counting the number of edge plate platforms that produce stray crystals on the prepared single crystal superalloy samples, according to The number of edge plate platforms that generate miscellaneous crystals can evaluate the tendency of miscellaneous crystal formation under different directional solidification parameters, thereby obtaining the influence of directional solidification parameters on the tendency of miscellaneous crystal formation.

In the present application, during the directional solidification process, the temperature of the upper heater is 1500°C-1600°C, the temperature of the lower heater is 1500°C-1600°C, the pouring temperature is 1500°C-1600°C, and the pulling speed is controlled at 1mm /min～7.0mm/min.

After the single crystal superalloy sample is obtained, chemical etching is first carried out to clearly show the miscellaneous crystals on the sample, so as to facilitate the counting of the number of edge plate platforms on the sample where miscellaneous crystals are generated. The greater the number of edge plate platforms that produce stray crystals on the sample, the greater the tendency of the single crystal superalloy to produce stray crystals or the greater the tendency of the single crystal superalloy to produce stray crystals under the directional solidification process parameters, vice versa.

According to the mechanism of miscellaneous crystal formation caused by the supercooling nucleation of the side plate platform, the present invention designs a symmetrical sample with multiple side plate platforms, and evaluates the formation of miscellaneous crystals by using the number of side plate platforms that produce miscellaneous crystals The tendency of or the effect of directional solidification process parameters on the formation tendency of single crystal superalloys. The mold designed by the present invention has simple structure, low preparation cost, convenient implementation method and easy operation. Single crystal superalloy castings prepared by investment casting method can be evaluated after chemical corrosion. Eliminate the influence of random crystal formation on the formation of stray crystals, and ensure the accuracy of the evaluation of the tendency of stray crystals in single crystal superalloys. In addition, this method can also be used to study the influence of directional solidification process parameters on the formation of stray crystals in single crystal superalloys. The influence of properties is used to optimize the preparation process of single crystal superalloy castings, which can further improve the pass rate of single crystal superalloy castings.

In order to further understand the present invention, the method for evaluating the tendency to form miscellaneous crystals provided by the present invention will be described in detail below in conjunction with examples, and the scope of protection of the present invention is not limited by the following examples.

Example 1

Using the method for evaluating the formation tendency of single crystal superalloy miscellaneous crystals of the present invention to evaluate the tendency of single crystal superalloy DD6 and single crystal superalloy DD9 to form miscellaneous crystals:

First, the sample mold design is carried out. The design sample size is: the length L1 _of the edge plate platform is 15mm, the width W is 10mm, the thickness H1 is 3mm, the distance _H2 between the edge plate platforms is 40mm, and the width _of the main part of the sample is L ₂ is 25mm, and there are 4 edge plate platforms on each side;

Use the designed mold to press 12 wax models, engrave the number 01-12 on the wax models, connect the 6 wax models with the pouring system to form a module with a chassis of 200mm, after coating, strengthening, dewaxing, and roasting Then prepare the mold shell; use a vacuum induction directional solidification furnace to cast a single crystal superalloy sample, the temperature of the upper heater is 1510°C, the temperature of the lower heater is 1520°C, the pouring temperature is controlled at 1520°C, and the pulling speed is 3mm/min ;

After cleaning the surface shell of the sample obtained above, the impurities on the sample were clearly revealed after chemical corrosion; the total number of edge plate platforms with mixed crystals on each of the 6 samples of the two alloys was counted, and the results are shown in the table 1 shown;

Table 1 adopts the method of the present invention to prepare the single crystal superalloy sample to produce the edge plate platform number statistical result of miscellaneous crystal

It can be seen from Table 1 that under the given same process conditions, 6 DD9 alloy samples have a total of 48 edge plate platforms, and 21 edge plate platforms have produced miscellaneous crystals, and 6 DD6 alloy samples have a total of 48 edge plate platforms. Miscellaneous crystals were produced on 29 edge plate platforms, indicating that the tendency of DD6 alloy to form miscellaneous crystals is greater than that of DD9 alloy, indicating that this method can effectively evaluate the formation tendency of miscellaneous crystals of different single crystal superalloys.

Example 2

The method for evaluating the formation tendency of single crystal superalloy miscellaneous crystals of the present invention is used to study the influence of the pulling rate during directional solidification on the formation tendency of DD9 alloy miscellaneous crystals:

First, the sample mold design is carried out. The design sample size is: the length L1 _of the edge plate platform is 15mm, the width W is 10mm, the thickness H1 is 3mm, the distance _H2 between the edge plate platforms is 40mm, and the width _of the main part of the sample is L ₂ is 25mm, and there are 4 edge plate platforms on each side;

Use the designed mold to press 18 wax models, engrave the number 01-18 on the wax models, connect the 6 wax models with the pouring system to form a module with a chassis of 200mm, after coating, strengthening, dewaxing and roasting Then get the shell. The samples were poured in a vacuum induction directional solidification furnace. The temperature of the upper heater was controlled at 1510°C, the temperature of the lower heater was controlled at 1530°C, and the pouring temperature was controlled at 1530°C. The pulling rates of the three groups of samples were 2.0mm/min, 4.0mm/min, 6.0mm/min;

After cleaning the surface shell of the sample obtained above, after chemical corrosion, the miscellaneous crystal defects on the sample clearly appeared; the number of edge plate platforms with miscellaneous crystals on the three groups of samples was counted, and the results are shown in Table 2;

Table 2 Statistical results of the number of edge plate platforms with mixed crystals in single crystal superalloy samples at different pulling rates

It can be seen from the table that as the pulling rate increases from 2mm/min to 4mm/min and 6mm/min, the number of edge plate platforms on the sample that generate mixed crystals increases from 11 to 29 and 37, indicating that the increase The pumping rate promotes the formation of stray crystals in the third generation single crystal superalloy.

The results of the above two examples show that the method for evaluating the formation tendency of miscellaneous crystals provided by the present invention can effectively evaluate the tendency of single crystal superalloys to form miscellaneous crystals, and can also be applied to research on the effect of directional solidification process parameters on single crystal superalloys. The influence of casting miscellaneous crystal formation tendency. The designed mold structure is simple, the realization process is convenient, the evaluation efficiency is improved, resources are saved, and the cost is reduced. Crystal formation control studies.

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (6)

1. A method for evaluating the formation tendency of single crystal superalloy miscellaneous crystals, comprising the following steps: A) design an initial sample with a plurality of edge plate platforms, and the edge plate platforms are symmetrically distributed on both sides of the initial sample along the direction of directional solidification; B) Using the method of precision investment casting, under the directional solidification process parameters, preparing single crystal superalloy samples with different components according to the initial sample; C) counting the number of edge plate platforms that generate miscellaneous crystals on the single crystal superalloy sample, and evaluating the tendency of single crystal superalloy miscellaneous crystal formation according to the number of edge plate platforms that generate miscellaneous crystals; or B') using the precision investment casting method to prepare single crystal superalloy samples according to the initial sample under different directional solidification process parameters; C') counting the number of edge plate platforms that generate miscellaneous crystals on the single crystal superalloy sample, and evaluating the influence of directional solidification process parameters on the tendency of miscellaneous crystal formation according to the number of edge plate platforms that generate miscellaneous crystals. 2. The method according to claim 1, characterized in that, the number of said edge plate platforms is 3-5 pairs. 3. The method according to claim ₁ , wherein the length L1 of the edge plate platform is 10-20 mm, the width W is 6-15 mm, and the thickness H1 is _2-5 mm; the adjacent edge plate The distance H ₂ of the platform is 30-60 mm. 4. The method according to claim 1 or ₃ , characterized in that the width L2 of the main part of the initial sample is 15-35 mm. 5. The method according to claim 1, characterized in that, in step B), the directional solidification process parameters in the precision investment casting method are: the temperature of the upper heater is 1500°C to 1600°C, and the temperature of the lower heater is The temperature is 1500℃～1600℃, the pouring temperature is 1500℃～1600℃, and the drawing speed is 1.0mm/min～7.0mm/min. 6. The method according to claim 1, characterized in that, in step B'), the directional solidification process parameters in the precision investment casting method are as follows: the temperature of the upper heater is controlled at 1500°C to 1600°C, and the lower heating The temperature of the device is controlled at 1500°C to 1600°C, the pouring temperature is controlled at 1500°C to 1600°C, and the drawing speed is 1.0mm/min to 7.0mm/min.

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