Method for preparing single crystal and directional column crystal composite crystal blade

Abstract

The invention relates to a single crystal and directional column crystal composite crystal blade and a preparation method thereof, belongs to the field of precision casting, and solves the problems of single and uncontrollable orientation of a single crystal part, uncontrollable secondary orientation of the single crystal part, uncontrollable secondary orientation of the single crystal part and uncontrollable secondary orientation of the single crystal part in the single crystal and directional column crystal composite blade obtained by the existing preparation method. The crystal orientation, the grain boundary direction and the grain width change greatly. The preparation method of the single crystal and directional column crystal composite crystal blade comprises the following steps: S1, preparing a composite seed crystal; s2, preparing a mold shell; s3, placing the composite seed crystal in a seed crystal cavity of the mold shell; through directional solidification, the single crystal and directional column crystal composite crystal blade is prepared. According to the method, the orientation of the single crystal part in the single crystal and oriented column crystal composite blade can be regulated and controlled and is not limited to [001] oriented grains, secondary orientation is effectively controlled, and the crystal orientation, the grain boundary direction and the grain width in the composite blade can be more accurately controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of precision casting, and in particular to a single crystal and oriented columnar crystal composite crystal blade and a preparation method thereof. Background Art

[0002] Single crystal blades perform well under high temperature and high load conditions and are suitable for high-performance applications such as aircraft engines, but their manufacturing cost and complexity are high. Under the premise of ensuring engine performance, the cost can be significantly reduced by using single crystal structure in key parts of the blade and directional columnar crystal structure in other parts, that is, using single crystal and directional columnar crystal composite blades.

[0003] The existing method for preparing single crystal and oriented columnar crystal composite blades mainly adopts directional solidification technology, such as Figure 1 As shown, the alloy melt is directly poured into the mold shell, and the mold shell is quickly pulled out, so that the alloy grows into oriented columnar crystals in an epitaxial manner, and single crystals are grown in a spiral crystal selection manner; however, the existing method encounters the following problems in the process of preparing single crystal and oriented columnar crystal composite blades: for example, only

[001] oriented grains can be grown in the single crystal and the secondary orientation is uncontrollable, and the crystal orientation, grain boundary direction and grain width in the composite blade vary greatly, affecting the blade performance, and even lateral grain boundaries appear, resulting in the scrapping of the blade, making it difficult to improve the preparation qualification rate of single crystal and columnar crystal composite crystal blades, such as the qualification rate is less than 40%. Summary of the invention

[0004] In view of the above analysis, the present invention aims to provide a single crystal and oriented columnar crystal composite crystal blade and a preparation method thereof, so as to solve at least one of the following problems existing in the single crystal and oriented columnar crystal composite blade obtained by the existing preparation method: (1) the orientation of the single crystal part is single and cannot be adjusted; (2) the secondary orientation of the single crystal part is uncontrollable and affects the blade performance; (3) the crystal orientation, grain boundary direction and grain width vary greatly and affect the blade performance.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The present invention provides a method for preparing a single crystal and oriented columnar crystal composite crystal blade, comprising the following steps:

[0007] S1. preparing a composite seed crystal; comprising:

[0008] Prefabricate single crystal seed crystals and oriented columnar crystal seed crystals, requiring that the single crystal seed crystals and oriented columnar crystal seed crystals are respectively consistent with the single crystal part and oriented columnar crystal part in the composite crystal blade in terms of crystal orientation, grain boundary direction and grain width;

[0009] Connecting the prefabricated single crystal seed crystal and the oriented columnar crystal seed crystal in a preset arrangement to obtain a composite seed crystal;

[0010] S2, prepare the mold shell;

[0011] The mold shell includes: a blade cavity, a seed crystal cavity located at the bottom of the blade cavity, and a runner located at the top of the blade cavity; A2≥A1, and A1>L max ;

[0012] Among them, A1 represents the lateral dimension of the blade cavity, A2 represents the lateral dimension of the seed crystal cavity, and L max Represents the maximum value of the lateral dimensions of a continuous portion of a single crystal seed crystal and a continuous portion of an oriented columnar crystal seed crystal in a composite seed crystal; the lateral dimension is the blade width direction in a plane perpendicular to the growth direction of the seed crystal, i.e., the straight line direction from the leading edge to the trailing edge of the blade;

[0013] S3. placing the composite seed crystal in the seed crystal cavity of the mold shell; and preparing a single crystal and oriented columnar crystal composite crystal blade through directional solidification.

[0014] Furthermore, in step S2, after the mold shell is prepared, a high temperature resistant coating is coated on the inner surface of the mold shell so that the roughness of the inner surface of the mold shell Ra is less than or equal to 0.2 μm.

[0015] Furthermore, in step S3, the gap δ between the composite seed crystal and the seed crystal cavity is ensured to be ≤0.1 mm.

[0016] Further, in step S3, the main steps of directional solidification include: placing the mold shell containing the composite seed crystal in a heater, and when the mold shell is heated to a preset temperature T S Finally, the molten metal is poured into the blade cavity from the runner on the mold shell, and then the mold shell is pulled out and separated from the heater;

[0017] The speed of the pulling process is controlled at 3-8 mm / min; and / or the distance between the composite seed crystal and the heater is controlled within 80 mm.

[0018] Furthermore, the speed of the pulling process is specifically controlled in the following manner:

[0019] (1) The pulling speed of the directional solidification section of the composite seed crystal is 3-5 mm / min;

[0020] (2) The pulling speed of the directional solidification section of the blade is 5-7 mm / min;

[0021] (4) The pulling speed of the directional solidification section of the edge plate is 3-5 mm / min;

[0022] (4) The pulling speed of the directional solidification section of the tenon is 6-8 mm / min.

[0023] Furthermore, during the drawing process, the mold shell is placed on a cooling chassis, and the cooling rate of the cooling chassis is controlled at 30-70°C / min.

[0024] Furthermore, the preset temperature T S Satisfaction: T S =T m +(150~250)℃,T m is the alloy melting point of the composite crystal blade; and / or,

[0025] Pour the molten metal into the blade cavity from the runner on the mold shell, keep it warm for 0.5-5.0 minutes, and then start pulling.

[0026] Further, step S1 specifically includes the following steps:

[0027] S11. Seed crystal material selection: The mother material of the seed crystal should be selected from the same material as the composite crystal blade alloy, or a material with a melting point 0 to 20°C higher than the composite crystal blade mother alloy and the same crystal structure;

[0028] S12, according to the design requirements of the crystal orientation, grain boundary direction and grain width of the single crystal part and the oriented columnar crystal part in the composite crystal blade to be prepared, adopt a directional solidification method to prepare a plate-shaped single crystal seed crystal and a oriented columnar crystal seed crystal with a thickness of 3-8 mm respectively;

[0029] S13. According to the size requirements of the composite crystal blade to be prepared, the required plate-shaped single crystal seed crystal and the oriented columnar crystal seed crystal are spliced ​​to form a composite seed crystal.

[0030] Further, in S13, the middle portion of the composite seed crystal is a directional columnar crystal seed crystal region, and both sides are single crystal seed crystal regions, and the single crystal seed crystal regions are used for epitaxially growing the inlet and outlet edges of the composite crystal blades.

[0031] The present invention also provides a single crystal and oriented columnar crystal composite crystal blade, which is obtained by the preparation method as described above. The crystal orientation of the single crystal region in the single crystal and oriented columnar crystal composite crystal blade can be selected but not limited to the

[001] direction, and the secondary orientation is controllable.

[0032] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0033] (1) Different from the existing method of directional solidification combined with spiral crystal selection, the present invention proposes a new process route; that is, directional solidification combined with the "seed crystal method" is used to prepare single crystal and directional columnar crystal composite blades. Specifically, based on the seed crystal method, a composite seed crystal having the same crystal orientation, grain boundary direction and grain width as the single crystal and directional columnar crystal composite crystal blade to be prepared is pre-placed in the seed crystal cavity of the mold shell, and the alloy melt is epitaxially grown on the unmelted interface of the composite seed crystal by the method of directional solidification to form a single crystal and directional columnar crystal composite crystal blade. The single crystal and directional columnar crystal composite crystal blade has basically the same crystal orientation, grain boundary direction and grain width as the composite seed crystal. Therefore, by using the preparation method of the present invention, composite seed crystals with different crystal orientations, grain boundary directions and grain widths can be selected according to needs, and single crystal and oriented columnar crystal composite crystal blades with different crystal orientations, grain boundary directions and grain widths can be prepared, so that the orientation of the single crystal part in the composite blade can be adjusted as needed and is no longer limited to

[001] oriented grains, thereby effectively solving the problems of the single crystal part in the composite crystal blade obtained by the existing method having a single orientation (only

[001] oriented grains can be grown) and being unable to be adjusted, thereby better meeting different application scenarios.

[0034] (2) The present invention uses a composite seed crystal with specific crystal orientation and other parameters, that is, a composite seed crystal with the same crystal orientation, grain boundary direction and grain width as the single crystal and oriented columnar crystal composite crystal blade to be prepared. Compared with the existing spiral crystal selection method, the present invention can not only control the main orientation of the single crystal part, but also effectively control its secondary orientation, thereby effectively solving the problem of uncontrollable secondary orientation of the single crystal part in the composite crystal blade obtained by the existing method, thereby improving the performance of the blade.

[0035] (3) The present invention pre-places a composite seed crystal having the same crystal orientation, grain boundary direction and grain width as the single crystal and oriented columnar crystal composite crystal blade to be prepared in the seed crystal cavity of the mold shell, and controls the lateral dimension A2 of the seed crystal cavity to be greater than or equal to the lateral dimension A1 of the blade cavity and A1>L max , L maxIt represents the maximum value of the lateral dimensions of a continuous part of a single crystal seed crystal and a continuous part of an oriented columnar crystal seed crystal in the composite seed crystal (which means that the tissue that can grow into the blade cavity contains both single crystals and oriented columnar crystals), to ensure that the single crystal part and oriented columnar crystal part in the composite crystallization blade formed by the composite seed crystal growing upward and completely filling the blade cavity have basically the same crystal orientation, grain boundary direction and grain width as the single crystal seed crystal and oriented columnar crystal seed crystal in the composite seed crystal, so as to achieve the required microscopic crystallization structure of the composite crystallization blade, and then more accurately control the crystal orientation, grain boundary direction and grain width in the composite blade. This method ensures that the microstructure of the blade is more uniform and consistent, effectively solves the problem of large variations in crystal orientation, grain boundary direction and grain width in the composite crystallization blade obtained by the existing method, thereby improving the performance of the blade.

[0036] (4) The preparation method provided by the present invention can achieve the use of single crystal structure in the key parts of the blade, while other parts use oriented columnar crystal structure. Compared with single crystal blades, the composite crystal blades obtained by the preparation method of the present invention can greatly reduce the cost while ensuring that the performance requirements of the blade are met, and have important engineering application value and economic benefits.

[0037] (5) In some preferred embodiments, by controlling some key parameters in the preparation and directional solidification process of the composite seed crystal (such as the roughness of the inner surface of the mold shell, the gap between the composite seed crystal and the seed crystal cavity, the pulling speed, the mold shell cooling rate, the seed crystal thickness, etc.), it is beneficial to more effectively inhibit the formation of impurity defects during the directional solidification process, and better ensure that the crystal orientation, grain boundary direction and grain width in the composite crystal blade obtained based on the seed crystal method are basically consistent with the corresponding parameters in the composite seed crystal.

[0038] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0040] Figure 1 It is a schematic diagram of the process of the preparation method for forming a single crystal and oriented columnar crystal composite blade in the prior art;

[0041] Figure 2 A schematic structural diagram of a mold shell used in the preparation method provided in an embodiment of the present invention;

[0042] Figure 3 A schematic diagram of a process of a preparation method provided by an embodiment of the present invention;

[0043] Figure 4 A schematic diagram of a composite seed crystal A in the preparation method provided in an embodiment of the present invention;

[0044] Figure 5 A schematic structural diagram of a mold shell (including a composite seed crystal A) used in the preparation method provided in an embodiment of the present invention;

[0045] Reference numerals:

[0046] 100-mold shell; 11-blade cavity; 12-seed crystal cavity; 13-runner; A-composite seed crystal; B-composite crystallization blade of single crystal and oriented columnar crystal. DETAILED DESCRIPTION

[0047] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0048] The seed crystal method is a crystal growth method that guides the growth of the crystal by introducing a seed crystal with a specific crystal orientation into the growth environment. In the field of high-temperature alloys, the seed crystal method is used to produce single crystal blades with a specific crystal orientation. Although the seed crystal method has been used in the manufacture of single crystal blades and can control the crystal orientation of single crystal blades, there is very limited research on the production of single crystal and oriented columnar crystal composite blades. In particular, no specific preparation method has been reported in detail, making this field almost blank in academic and industrial applications.

[0049] In the face of the above problems of the single crystal and oriented columnar crystal composite blades obtained by the existing methods, the inventors, through in-depth research and analysis, proposed an innovative idea: to learn from the advantages of the seed crystal method in the precise control of crystal orientation in the manufacture of single crystal blades, and explore its application in replacing the existing preparation methods to develop a new technical path for preparing single crystal and oriented columnar crystal composite blades. In order to achieve this goal, the inventors conducted in-depth research on the preparation of seed crystals, the optimization of directional solidification process, the control of solidification defects, etc., and achieved innovative research results.

[0050] Based on this, the present invention provides a method for preparing a single crystal and oriented columnar crystal composite crystal blade, comprising the following steps:

[0051] S1. preparing a composite seed crystal; comprising:

[0052] Prefabricate single crystal seed crystals and oriented columnar crystal seed crystals, requiring that the single crystal seed crystals and oriented columnar crystal seed crystals are respectively consistent with the single crystal part and oriented columnar crystal part in the composite crystal blade in terms of crystal orientation, grain boundary direction and grain width;

[0053] Connecting the prefabricated single crystal seed crystal and the oriented columnar crystal seed crystal in a preset arrangement to obtain a composite seed crystal;

[0054] S2, prepare the mold shell;

[0055] The mold shell 100 includes: a blade cavity 11, a seed crystal cavity 12 located at the bottom of the blade cavity 11, and a runner 13 located at the top of the blade cavity 11; A2 ≥ A1, and A1>L max ;

[0056] Wherein, A1 represents the transverse dimension of the blade cavity 11, A2 represents the transverse dimension of the seed crystal cavity 12, and L max Represents the maximum value of the lateral dimensions of a continuous portion of a single crystal seed crystal and a continuous portion of an oriented columnar crystal seed crystal in a composite seed crystal; the lateral dimension is the blade width direction in a plane perpendicular to the growth direction of the seed crystal, i.e., the straight line direction from the leading edge to the trailing edge of the blade;

[0057] S3, placing the composite seed crystal in the seed crystal cavity 12 of the mold shell; and preparing a single crystal and oriented columnar crystal composite crystal blade through directional solidification.

[0058] See also Figure 2 The lateral dimension is the blade width direction, i.e., the Y direction, in the XY plane perpendicular to the seed crystal growth direction, i.e., the Z direction, that is, the straight line direction from the leading edge to the trailing edge of the blade.

[0059] Compared with the prior art, the present invention proposes a different process route; that is, directional solidification combined with the "seed crystal method" is used to prepare single crystal and directional columnar crystal composite blades. Specifically, based on the seed crystal method, a composite seed crystal having the same crystal orientation, grain boundary direction and grain width as the single crystal and directional columnar crystal composite crystal blade to be prepared is pre-placed in the seed crystal cavity of the mold shell, and the alloy melt is epitaxially grown on the unmelted interface of the composite seed crystal by the method of directional solidification to form a single crystal and directional columnar crystal composite crystal blade, and the single crystal and directional columnar crystal composite crystal blade has basically the same crystal orientation, grain boundary direction and grain width as the composite seed crystal. Therefore, by using the preparation method of the present invention, composite seed crystals with different crystal orientations, grain boundary directions and grain widths can be selected according to needs, and single crystal and oriented columnar crystal composite crystal blades with different crystal orientations, grain boundary directions and grain widths can be prepared, so that the orientation of the single crystal part in the composite blade can be adjusted as needed and is no longer limited to

[001] oriented grains, thereby effectively solving the problems of the single crystal part in the composite crystal blade obtained by the existing method having a single orientation (only

[001] oriented grains can be grown) and being unable to be adjusted, thereby better meeting different application scenarios.

[0060] Compared with the prior art, the present invention uses a composite seed crystal with specific crystal orientation and other parameters, that is, a composite seed crystal with the same crystal orientation, grain boundary direction and grain width as the single crystal and oriented columnar crystal composite crystal blade to be prepared. Compared with the existing spiral crystal selection method, it can not only control the main orientation of the single crystal part, but also effectively control or reduce the secondary orientation, so as to effectively solve the problem of uncontrollable secondary orientation of the single crystal part in the composite crystal blade obtained by the existing method, thereby improving the performance of the blade.

[0061] It can be understood that "secondary orientation" usually refers to the X and Y directions perpendicular to the Z direction of the principal stress axis, which are secondary orientations in addition to the main orientation (for example, the Z direction of the principal stress axis of the blade is

[001] orientation) during the growth of the single crystal. According to the requirements of the service conditions of the blade, the secondary orientation of the blade also needs to be controlled to improve the performance of the blade. When the secondary orientation is a random orientation, if an orientation with lower strength performance occurs, it will lead to a decrease in blade performance and even cause blade failure in some cases.

[0062] Compared with the prior art, the present invention pre-places a composite seed crystal having the same crystal orientation, grain boundary direction and grain width as the single crystal and oriented columnar crystal composite crystal blade to be prepared in the seed crystal cavity of the mold shell, and controls the lateral dimension A2 of the seed crystal cavity to be greater than or equal to the lateral dimension A1 of the blade cavity and A1>L max , L maxIt represents the maximum value of the lateral dimensions of a continuous part of a single crystal seed crystal and a continuous part of an oriented columnar crystal seed crystal in the composite seed crystal (which means that the tissue that can grow into the blade cavity contains both single crystals and oriented columnar crystals), so as to ensure that the single crystal part and oriented columnar crystal part in the composite crystallization blade formed by the epitaxial growth of the composite seed crystal and completely filling the blade cavity have basically the same crystal orientation, grain boundary direction and grain width as the single crystal seed crystal and oriented columnar crystal seed crystal in the composite seed crystal, so as to achieve the required microscopic crystallization structure of the composite crystallization blade.

[0063] The existing methods are affected by the difference in size and growth rate between single crystals and oriented columns and the temperature field during the actual growth process, resulting in large changes in crystal orientation, grain boundary direction and grain width, which will affect the overall performance of the blade. The present invention uses composite seed crystals and grows through a directional solidification process, which can more accurately control the crystal orientation, grain boundary direction and grain width in the composite crystallization blade. This method ensures that the microstructure of the blade is more uniform and effectively solves the problem of large changes in crystal orientation, grain boundary direction and grain width, thereby significantly improving the performance and preparation qualification rate of the blade. For example, under specific design requirements, the preparation method provided by the present invention can further improve the qualification rate of the existing method by more than 30%.

[0064] In addition, the preparation method provided by the present invention can achieve the use of single crystal structure in the key parts of the blade, while other parts use oriented columnar crystal structure. Compared with single crystal blades, the composite crystal blades obtained by the preparation method of the present invention greatly reduce the cost while ensuring that the performance requirements of the blade are met, and have important engineering application value and economic benefits.

[0065] For example, the preparation method provided by the present invention is described, see Figure 2-Figure 5 A method for preparing a single crystal and oriented columnar crystal composite crystal blade is based on a seed crystal method. A composite seed crystal A having the same crystal orientation, grain boundary direction and grain width as the single crystal and oriented columnar crystal composite crystal blade to be prepared is pre-placed in a seed crystal cavity 12 of a mold shell 100. Through a directional solidification method, an alloy melt is epitaxially grown on an unmelted interface of the composite seed crystal A to form a single crystal and oriented columnar crystal composite crystal blade B. After corrosion observation and measurement, the single crystal and oriented columnar crystal composite crystal blade has basically the same crystal orientation, grain boundary direction and grain width as the composite seed crystal.

[0066] Preferably, in step S2, after the mold shell 100 is prepared, a high temperature resistant coating is coated on the inner surface of the mold shell 100 so that the roughness of the inner surface of the mold shell 100 is Ra≤0.2μm. Exemplarily, the high temperature resistant coating may be selected but is not limited to zirconium oxide type coating. By controlling the roughness of the inner surface of the mold shell to be reduced to 0.2μm or below, it is helpful to reduce the formation of impurities in the remelting zone above the unmelted interface of the composite seed crystal, thereby optimizing the crystal structure, better controlling and ensuring the crystal orientation, grain boundary direction and grain width of the single crystal part and the oriented columnar crystal part in the obtained composite crystal blade are consistent with the prefabricated composite seed crystal, and it is also helpful to control or reduce the secondary orientation of the single crystal part in the obtained composite crystal blade.

[0067] Preferably, in step S3, the composite seed crystal is placed in the seed crystal cavity 12 of the mold shell, and the gap δ between the composite seed crystal and the seed crystal cavity 12 is ensured to be ≤0.1 mm. According to the principle of the seed crystal method, the upper part of the seed crystal melts first during the heating and heat preservation process. If the gap is large, the alloy liquid that has melted the seed crystal flows into the gap and solidifies into miscellaneous crystals under the cooling action of the mold shell; by controlling the gap between the mold shell and the composite seed crystal to be 0.1 mm or less, the molten alloy liquid can avoid downward reflux under the constraint of surface tension, thereby reducing the formation of such miscellaneous crystals, better ensuring that the crystal orientation, grain boundary direction and grain width of the single crystal part and the oriented columnar crystal part in the obtained composite crystal blade are consistent with the prefabricated composite seed crystal, and it is also beneficial to reduce and control the secondary orientation of the single crystal part in the obtained composite crystal blade.

[0068] Specifically, in step S3, the main steps of the directional solidification include: placing the mold shell 100 containing the composite seed crystal in a heater, and heating the mold shell 100 to a preset temperature T S Finally, the molten metal is poured into the blade cavity 11 through the runner 13 on the mold shell 100, and then the mold shell 100 is pulled out and separated from the heater.

[0069] It should be noted that as the entire mold shell 100 is pulled out and separated from the heater, the metal grains grow in the mold shell in the opposite direction of the heat flow. First, a part of the composite seed crystal A melts, and as the mold shell descends, the melted part begins to solidify and grows into the blade cavity 11 in the form of a composite crystal of a single crystal and a directional columnar crystal, and finally a single crystal and directional columnar crystal composite crystal blade B having substantially the same crystal orientation, grain boundary direction and grain width as the composite seed crystal is obtained.

[0070] Preferably, the speed of the pulling process is controlled at 3-8 mm / min.

[0071] Preferably, the distance between the composite seed crystal and the heater is controlled within 80 mm.

[0072] It should be noted that controlling the pulling speed and the distance between the composite seed crystal and the heater plays an important role in improving the quality of directional solidification blades, controlling crystal orientation (including secondary orientation of the single crystal part), grain boundary direction, grain width, and reducing impurity crystals. By setting the pulling speed at 3-8mm / min, the primary dendrite spacing of the composite seed crystal can be controlled to ≤250μm, which is beneficial to promote the preferential growth of grains and reduce the formation of impurity crystals. By controlling the distance between the composite seed crystal and the heater to within 80mm (≤80mm), it is beneficial to control the solid-liquid interface during crystal growth and maintain the required temperature gradient to ensure the uniformity and quality of crystal growth, thereby better controlling the crystal orientation (including secondary orientation of the single crystal part), grain boundary direction, grain width, and reducing impurity crystals.

[0073] In a preferred embodiment, the speed of the pulling process is specifically controlled in the following manner:

[0074] (1) The pulling speed of the directional solidification section of the composite seed crystal is 3-5 mm / min;

[0075] (2) The pulling speed of the directional solidification section of the blade is 5-7 mm / min;

[0076] (3) The pulling speed of the directional solidification section of the edge plate is 3-5 mm / min;

[0077] (4) The pulling speed of the directional solidification section of the tenon is 6-8 mm / min;

[0078] It can be understood that during the directional solidification process, as the pulling action proceeds, the solidification front will gradually advance along the length direction of the blade. Specifically, the solidification process will sequentially go through the following key areas: the directional solidification section of the composite seed crystal, the directional solidification section of the blade body, the directional solidification section of the edge plate, and the directional solidification section of the tenon.

[0079] The use of the above-mentioned preferred multi-step pulling speed can obtain a uniform temperature field, which is beneficial to optimizing the grain structure. It can better control the crystal orientation and grain boundary direction of the resulting composite crystallization blade, and can effectively ensure the grain width of the resulting composite crystallization blade, while achieving controllable secondary orientation of the single crystal structure, thereby obtaining high-quality and excellent performance blade castings. Specifically, by reasonably regulating the pulling speed at different parts, the temperature distribution of the entire blade can be better controlled to ensure a uniform temperature gradient during the solidification process, thereby reducing the risk of thermal stress and thermal cracks. By precisely controlling the pulling speed at different solidification stages, the grains can be guided to grow in the desired direction, which is beneficial to controlling the crystal orientation, grain boundary direction and grain width, and ensuring the uniformity of the microstructure of the resulting composite crystallization blade.

[0080] In some embodiments, during the pulling process, the mold shell 100 is placed on a cooling base, and the cooling rate of the cooling base is controlled at 30-70°C / min. During the directional solidification process, by accurately controlling the cooling rate at the bottom of the composite seed crystal, the growth direction and growth rate of the single crystal and the directional columnar crystal can be better controlled, which is important for obtaining a composite crystal blade with a specific crystal orientation and grain boundary direction. An appropriate cooling rate helps to form a uniform microstructure to obtain a composite crystal blade with a specific grain width. If the cooling rate is too fast or too slow, it may cause uneven grain growth, thereby affecting the performance of the blade.

[0081] Preferably, before directional solidification, the mold shell 100 is heated to a preset temperature T S ; The preset temperature T S Satisfaction: T S =T m +(150~250)℃,T m is the alloy melting point of the composite crystal blade. By preheating the mold to a suitable temperature, the initial temperature of each part in the mold shell can be ensured to be consistent, which helps to form a uniform temperature gradient in the subsequent directional solidification process, thereby promoting the growth of grains in the desired direction, reducing crystal orientation deviation, improving the accuracy of controlling crystal orientation, grain boundary direction and grain width, and reducing thermal stress caused by excessive temperature difference when pouring liquid metal, thereby reducing defects such as thermal cracks and improving the qualified rate of blades.

[0082] In a preferred embodiment, before directional solidification, the molten metal is poured into the blade cavity 11 through the runner 13 on the mold shell 100, kept warm for 0.5-5.0 minutes, and then the pulling is started. Preferably, the heat preservation is 1-2 minutes. By keeping warm for a certain period of time, it can be ensured that the initial temperature of each part in the mold shell is consistent, which helps to form a uniform temperature gradient in the subsequent directional solidification process, thereby promoting the growth of grains in the desired direction and reducing the crystal orientation deviation. The heat preservation process helps to reduce the defects that are easy to occur in composite crystal blades during directional solidification, such as shrinkage, impurities, freckles, small-angle grain boundaries, etc., thereby improving the yield and achieving the optimal balance between cost and efficiency.

[0083] In some preferred embodiments, step S1 specifically includes the following steps:

[0084] S11. Seed crystal material selection: The mother material of the seed crystal should be selected from the same material as the composite crystal blade alloy, or a material with a melting point 0 to 20°C higher than the composite crystal blade mother alloy and the same crystal structure;

[0085] S12, according to the design requirements of the crystal orientation, grain boundary direction and grain width of the single crystal part and the oriented columnar crystal part in the composite crystal blade to be prepared, adopt a directional solidification method to prepare a plate-shaped single crystal seed crystal and a oriented columnar crystal seed crystal with a thickness of 3-8 mm respectively;

[0086] S13. According to the size requirements of the composite crystal blade to be prepared, the required plate-shaped single crystal seed crystal and the oriented columnar crystal seed crystal are spliced ​​to form a composite seed crystal.

[0087] For example, in step S11, according to the composite crystal blade alloy material, the parent material of the single crystal seed crystal includes but is not limited to a nickel-based single crystal high temperature alloy, such as DD6 single crystal high temperature alloy (which can be found according to GB / T 14992-2005). The parent material of the directional columnar crystal seed crystal includes but is not limited to a nickel-based directional solidified columnar crystal, such as IC10, DZ406 (which can be found according to HB 7762-2016).

[0088] In one embodiment, the alloy chemical composition of the composite crystal blade includes, by mass percentage: C: 0.02-0.15%, Cr: 5.0-12.0%, Co: 6.5-8.5%, W: 5-7%, Al: 5-9%, B: 0.001-0.005%, Re: 0-3%, and the remainder is Ni and unavoidable impurities.

[0089] It should be noted that in step S12, it is very important to control the thickness of the single crystal seed crystal and the directional columnar crystal seed crystal to 3-8 mm. If the seed crystal is too thin, excessive remelting is likely to occur during the directional solidification process, resulting in complete melting of the seed crystal and failure to guide the growth of the crystal; by controlling the thickness of the seed crystal within the range of 3-8 mm, it can be ensured that the seed crystal will not be completely melted when the molten metal is poured, thereby maintaining its structural integrity, effectively inheriting the crystal characteristics of the seed crystal, and guiding the growth of the crystal. If the seed crystal is too thick, it cannot be effectively remelted, resulting in the easy formation of miscellaneous crystals or other defects between the seed crystal and the newly solidified crystal. Appropriate seed crystal thickness can ensure that during the directional solidification process, the seed crystal is partially melted to form a remelting zone, thereby promoting the epitaxial growth of the melt on the unmelted seed crystal in the desired direction, reducing the grain orientation deviation, and improving the accuracy of the control of the crystal orientation, grain boundary direction and grain width, thereby improving the performance and qualified rate of the resulting composite crystal blade.

[0090] Preferably, in step S12, the pulling speed of the single crystal seed crystal prepared by directional solidification is controlled at 4-6 mm / min. The pulling speed of the directional columnar crystal seed crystal prepared by directional solidification is controlled at 5-7 mm / min.

[0091] It is understood that the length L and width W of the plate-shaped single crystal seed crystal and the oriented columnar crystal seed crystal can be cut and processed according to actual needs. In some embodiments, the oriented columnar crystal seed crystal is prepared into a plate-shaped shape of 20 to 120 mm long, 15 to 30 mm wide, and 3 to 8 mm thick; the single crystal seed crystal is prepared into a plate-shaped shape of 5 to 25 mm long, 15 to 30 mm wide, and 3 to 8 mm thick.

[0092] Exemplarily, the composite crystal blade is a turbine rotor blade. Considering that the blade will be affected by complex thermal strain and mechanical strain during service, the leading edge (i.e., the air intake edge) and the trailing edge (i.e., the exhaust edge) of the blade are areas where fatigue cracks that extend along the XY plane are prone to initiate. By controlling the crystal orientation of the single crystal grains in this area in the XY plane, the initiation of fatigue cracks that extend in this plane can be effectively suppressed, thereby improving the fatigue performance of the blade. Based on the above considerations, the leading edge (air intake edge) and the trailing edge (exhaust edge) of the blade should adopt a single crystal structure to meet the service performance of the blade, while the remaining parts can use a relatively low-cost oriented columnar crystal structure to better control costs.

[0093] In one embodiment, in step S13, the middle of the composite seed crystal is a directional columnar crystal seed crystal region, and both sides are single crystal seed crystal regions, and the single crystal seed crystal regions are used for epitaxially growing the inlet and outlet edges of the composite crystal blades.

[0094] The preparation method provided by the present invention can achieve the use of single crystal structure in key parts of the blade (such as the leading edge and trailing edge of the blade, that is, the intake side and the exhaust side), while other parts use oriented columnar crystal structure. Compared with single crystal blades, the composite crystal blades obtained by the preparation method of the present invention greatly reduce the cost while ensuring that the performance requirements of the blade are met, and have important engineering application value and economic benefits.

[0095] In some embodiments, in step S13, the required plate-shaped single crystal seed crystal and oriented columnar crystal seed crystal are spliced ​​in a manner including but not limited to spot welding and gluing; preferably, the spot welding point or the gluing position is set at the bottom of the seed crystal, that is, away from the lower end of the remelting zone, and also close to the end of the crystallizer, where the seed crystal will not melt and will not contact the alloy liquid. Preferably, before splicing, the thickness surface of the single crystal seed crystal and the oriented columnar crystal seed crystal is processed to a surface roughness Ra≤1.6μm, and a clamp is used to clamp and fix the single crystal seed crystal and the oriented columnar crystal seed crystal to be spliced ​​during assembly to ensure that the gap η at the splicing is ≤0.01mm. For example, the thickness surface of the single crystal seed crystal and the oriented columnar crystal seed crystal is polished with sandpaper of 800 mesh or above.

[0096] In some embodiments, in step S2, the preparation of the mold shell specifically includes the following steps: after the blade wax mold is pressed, the composite seed crystal is installed at the bottom of the wax mold. The bottom of the wax mold is a specific extension area designed for the wax mold, which is used to place the seed crystal; the shape and size of this extension area need to be precisely matched with the composite seed crystal to ensure that the seed crystal can smoothly guide the crystal growth during the directional solidification process. Then, a refractory material is coated on the surface of the wax mold to form a prefabricated mold shell, which is dewaxed and calcined to form a mold shell 100 for casting.

[0097] The present invention also provides a single crystal and oriented columnar crystal composite crystal blade, which is obtained by the preparation method of the single crystal and oriented columnar crystal composite crystal blade as described above. The crystal orientation of the single crystal region in the single crystal and oriented columnar crystal composite crystal blade can be selected but not limited to the

[001] direction, and the secondary orientation is controllable.

[0098] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0099] Example 1

[0100] This embodiment provides a method for preparing a single crystal and oriented columnar crystal composite crystal blade, comprising the following steps:

[0101] S1, preparing a composite seed crystal, specifically comprising the following steps:

[0102] S11. Selection of seed crystal: Based on the alloy composition of the composite crystal blade to be prepared, select a material with the same alloy composition as the blade as the mother material of the seed crystal. The mother material of the seed crystal has the same melting point as the mother alloy of the composite crystal blade.

[0103] Specifically, the mother alloy of the composite crystal blade to be prepared is IC10 nickel-based high-temperature alloy (which can be found according to HB 7762-2016), and the melting point of the blade alloy is 1330-1380°C.

[0104] S12, based on the seed crystal base material selected in S11, according to the design requirements of the crystal orientation, grain boundary direction and grain width of the single crystal part and the oriented columnar crystal part in the composite crystal blade to be prepared, a directional solidification method is adopted, and a pulling speed of 6 mm / min is used to prepare a plate-shaped oriented columnar crystal seed crystal with a length of 100 mm, a width of 25 mm, and a thickness of 8 mm, and a plate-shaped single crystal seed crystal with a length of 25 mm, a width of 25 mm, and a thickness of 8 mm;

[0105] Specifically, the microstructure design requirements of composite crystal blades include: the grain boundary direction is parallel to the Z axis, the width of the oriented columnar crystal is 5±3mm, and the width of the columnar crystal area is 20±5mm; the deviation of the Z-axis crystal orientation of the single crystal grain from the

[001] orientation is no more than 15°, the deviation of the X-axis crystal orientation from the

[100] orientation is no more than 15°, and the width of the single crystal grain (along the Y direction) is 10±3mm.

[0106] According to the design requirements of the blade, the Z-axis crystal orientation of the prepared single crystal seed crystal deviates from the

[001] orientation by 6°, the X-axis crystal orientation deviates from the

[100] orientation by 8°, and the grain width is 10 mm; the grain width of the prepared oriented columnar crystal seed crystal is 5 mm, and the grain boundary direction is parallel to the Z axis.

[0107] S13. According to the size requirements of the composite crystal blade to be prepared, cut the single crystal seed crystal and oriented columnar crystal seed crystal of the required size, and use 1000 mesh sandpaper to grind the thickness surface of the cut single crystal seed crystal and oriented columnar crystal seed crystal to a surface roughness Ra ≤ 1.6μm. Use a clamp to clamp and fix the polished single crystal seed crystal and oriented columnar crystal seed crystal, and use spot welding to splice their thickness surfaces together along the bottom of the seed crystal to form a composite seed crystal A (see Figure 4 , the blue on both sides are single crystal seed crystal areas, and the green in the middle is oriented columnar crystal seed crystal area), H=8mm, W=20mm, L1=L3=15mm, L2=20mm.

[0108] S2, prepare the mold shell;

[0109] See also Figure 2 and Figure 5 The mold shell 100 includes: a blade cavity 11, a seed crystal cavity 12 located at the bottom of the blade cavity 11, and a runner 13 located at the upper part of the blade cavity 11; the transverse dimension A2 of the seed crystal cavity 12 is 50 mm, and the transverse dimension A1 of the blade cavity 11 is 40 mm; a zirconium oxide coating is applied on the inner surface of the mold shell 100, so that the roughness Ra of the inner surface of the mold shell 100 is ≤ 0.2 μm;

[0110] S3, placing the composite seed crystal A in the seed crystal cavity 12 of the mold shell 100, see Figure 5 ; Place the mold shell 100 containing the composite seed crystal A on the crystallizer of the vacuum induction melting furnace, which is a device that uses electromagnetic induction heating to melt metal under vacuum conditions, and includes a heater and a cooling system to ensure that the distance between the composite seed crystal and the heater is controlled at 70 mm; when the mold shell 100 is heated to a preset temperature T S=1560℃, pour the molten metal at 1560℃ into the blade cavity 11 through the runner 13 on the mold shell 100, keep it warm for 1 minute, and then pull the mold shell 100 downward. As the mold shell descends and leaves the heater, the metal grains grow in the mold shell in the opposite direction of the heat flow. First, a part of the composite seed crystal A melts, and as the mold shell descends, the melted part begins to solidify and grows to the blade cavity 11 in the form of single crystal and oriented columnar crystal composite crystallization, and finally obtains a single crystal and oriented columnar crystal composite crystal blade B with basically the same crystal orientation, grain boundary direction and grain width as the composite seed crystal A;

[0111] Specifically, the speed of the downward pulling process is controlled in the following manner:

[0112] (1) The pulling speed of the directional solidification section of the composite seed crystal is 4 mm / min;

[0113] (3) The pulling speed of the directional solidification section of the blade is 6 mm / min;

[0114] (3) The pulling speed of the directional solidification section of the edge plate is 4 mm / min;

[0115] (4) The pulling speed of the directional solidification section of the tenon is 7 mm / min;

[0116] Specifically, during the drawing process, the mold shell 100 is located on the crystallizer of the vacuum melting furnace and is equipped with a cooling bottom plate, and its cooling rate is controlled at 50°C / min. During the drawing process, the vacuum melting furnace provides external insulation for the portion of the mold shell 100 that is still in the heater, wherein the insulation temperature of the directional solidification section for forming the blade body is set to 1530°C, and the insulation temperature of the directional solidification section for forming the edge plate and the tenon is set to 1550°C.

[0117] After observation and measurement after corrosion, the grain boundary direction of the single crystal and oriented columnar crystal composite crystal blades is parallel to the Z axis, the grain width of the oriented columnar crystal part is 5mm±1mm, the width of the columnar crystal area is 20mm±3mm, the Z-axis crystal orientation of the single crystal part deviates from the

[001] orientation by 6.5°, the X-axis crystal orientation deviates from the

[100] orientation by 9°, and the grain width of the single crystal part is 10mm±1mm.

[0118] Example 2

[0119] The difference between this embodiment and embodiment 1 is that in step S12, the microstructure design requirements of the composite crystal blade include: the grain boundary direction is parallel to the Z axis, the width of the oriented columnar crystal grain is 8±3mm, the deviation of the Z-axis crystal orientation of the single crystal grain from the

[011] orientation is no more than 15°, the deviation of the X-axis crystal orientation from the

[100] orientation is no more than 15°, and the width of the single crystal grain is 10±3mm. According to the design requirements of the blade, the deviation of the Z-axis crystal orientation of the prepared single crystal seed crystal from the

[011] orientation is 13±1°, the deviation of the X-axis crystal orientation from the

[100] orientation is 8±1°, and the width of the single crystal grain is 10mm; the grain width of the prepared oriented columnar crystal grain is 8mm, and the grain boundary direction is parallel to the Z axis. The remaining steps and parameters are similar to those in embodiment 1.

[0120] After observation and measurement after corrosion, the grain boundary direction of the single crystal and oriented columnar crystal composite crystal blade is parallel to the Z axis, the grain width of the oriented columnar crystal part is 8mm±1mm, and the width of the columnar crystal area is 20mm±2mm; the deviation of the Z-axis crystal orientation of the single crystal part from the

[011] orientation is 12.5°, the deviation of the X-axis crystal orientation from the

[100] orientation is 7°, and the grain width of the single crystal part is 10mm±1mm.

[0121] The results of the above-mentioned Examples 1-2 verify that based on the method provided by the present invention, a single crystal and oriented columnar crystal composite crystal blade that meets the specific crystal orientation, grain boundary direction and grain width design requirements can be prepared, and the crystal orientation, grain boundary direction and grain width of the single crystal part and the oriented columnar crystal part in the obtained composite crystal blade are basically consistent with the expected design requirements, and the secondary orientation of the single crystal part is controllable. In addition, Example 2 can illustrate that the crystal orientation of the single crystal part of the composite crystal blade obtained by the preparation method provided by the present invention is not limited to the

[001] direction. Compared with the existing preparation method, the present invention significantly improves the performance and preparation qualification rate of the single crystal and oriented columnar crystal composite crystal blade, greatly reduces the cost, and has important engineering application value and economic benefits.

[0122] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a single crystal and oriented columnar crystal composite crystal blade, characterized in that: The following steps are involved: S1. preparing a composite seed crystal; comprising: Prefabricate single crystal seed crystals and oriented columnar crystal seed crystals, requiring that the single crystal seed crystals and oriented columnar crystal seed crystals are respectively consistent with the single crystal part and oriented columnar crystal part in the composite crystal blade in terms of crystal orientation, grain boundary direction and grain width; Connecting the prefabricated single crystal seed crystal and the oriented columnar crystal seed crystal in a preset arrangement to obtain a composite seed crystal; S2, prepare the mold shell; The mold shell (100) comprises: a blade cavity (11), a seed crystal cavity (12) located at the bottom of the blade cavity (11), and a runner (13) located at the top of the blade cavity (11); A2≥A1, and A1>L max ; Wherein, A1 represents the transverse dimension of the blade cavity (11), A2 represents the transverse dimension of the seed crystal cavity (12), and L max Represents the maximum value of the lateral dimensions of a continuous portion of a single crystal seed crystal and a continuous portion of an oriented columnar crystal seed crystal in a composite seed crystal; the lateral dimension is the blade width direction in a plane perpendicular to the growth direction of the seed crystal, i.e., the straight line direction from the leading edge to the trailing edge of the blade; S3, placing the composite seed crystal in the seed crystal cavity (12) of the mold shell; and preparing a single crystal and oriented columnar crystal composite crystal blade through directional solidification.

2. The preparation method according to claim 1, characterized in that: In step S2, after the mold shell (100) is prepared, a high temperature resistant coating is coated on the inner surface of the mold shell (100) so that the roughness Ra of the inner surface of the mold shell (100) is less than or equal to 0.2 μm.

3. The preparation method according to claim 1, characterized in that: In step S3, the gap δ between the composite seed crystal and the seed crystal cavity (12) is ensured to be ≤0.1 mm.

4. The preparation method according to claim 1, characterized in that: In step S3, the main steps of the directional solidification include: placing the mold shell (100) containing the composite seed crystal in a heater, and heating the mold shell (100) to a preset temperature T S Afterwards, the molten metal is poured into the blade cavity (11) through the runner (13) on the mold shell (100), and then the mold shell (100) is pulled out and separated from the heater; Wherein, the speed of the pulling process is controlled at 3-8 mm / min; and / or, the distance between the composite seed crystal and the heater is controlled within 80 mm.

5. The preparation method according to claim 4, characterized in that: The speed of the pulling process is specifically controlled in the following manner: (1) The pulling speed of the directional solidification section of the composite seed crystal is 3-5 mm / min; (2) The pulling speed of the directional solidification section of the blade is 5-7 mm / min; (3) The pulling speed of the directional solidification section of the edge plate is 3-5 mm / min; (4) The pulling speed of the directional solidification section of the tenon is 6-8 mm / min.

6. The preparation method according to claim 4, characterized in that: During the drawing process, the mold shell (100) is placed on a cooling bottom plate, and the cooling rate of the cooling bottom plate is controlled at 30-70°C / min.

7. The preparation method according to claim 4, characterized in that: The preset temperature T S Satisfaction: T S =T m +(150~250)℃,T m is the alloy melting point of the composite crystal blade; and / or, The molten metal is poured into the blade cavity (11) from the runner (13) on the mold shell (100), kept warm for 0.5-5.0 minutes, and then the pulling is started.

8. The preparation method according to claim 1, characterized in that: Step S1 specifically includes the following steps: S11. Seed crystal material selection: The mother material of the seed crystal should be selected from the same material as the composite crystal blade alloy; or a material with a melting point 0 to 20°C higher than the composite crystal blade mother alloy and the same crystal structure; S12, according to the design requirements of the crystal orientation, grain boundary direction and grain width of the single crystal part and the oriented columnar crystal part in the composite crystal blade to be prepared, adopt a directional solidification method to prepare a plate-shaped single crystal seed crystal and a oriented columnar crystal seed crystal with a thickness of 3-8 mm respectively; S13. According to the size requirements of the composite crystal blade to be prepared, the required plate-shaped single crystal seed crystal and the oriented columnar crystal seed crystal are spliced ​​to form a composite seed crystal.

9. The preparation method according to claim 8, characterized in that: In S13, the middle of the composite seed crystal is a directional columnar crystal seed crystal region, and both sides are single crystal seed crystal regions, and the single crystal seed crystal regions are used for epitaxially growing the inlet and outlet edges of the composite crystal blade.

10. A single crystal and oriented columnar crystal composite crystal blade, characterized in that: The preparation method according to any one of claims 1 to 9 is adopted, and the crystal orientation of the single crystal region in the single crystal and oriented columnar crystal composite crystal blade can be selected but not limited to the [001] direction, and the secondary orientation is controllable.

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