A low segregation, low melting point, cellular dendritic Ni-W-Cr seed composition design and structure regulation method

Abstract

The application belongs to the technical field of single crystal superalloy preparation, and discloses a low segregation, low melting point, cell dendritic Ni-W-Cr seed crystal component design and structure regulation method, which is characterized by comprising the following steps: S1, determining alloy components; S2, smelting Ni-20W-20Cr alloy; S3, determining a suitable pulling rate through a step jump increasing rate pulling experiment; and S4, repeatedly using Ni-20W-20Cr heterogeneous seed crystal alloy; the cell dendritic heterogeneous seed crystal alloy liquidus temperature prepared by the application is only 1419.1 DEG C, can be well fused with the parent alloy, the cell dendritic structure has the characteristics that the cell crystal structure is not easy to break, and the secondary orientation can be judged through the dendritic characteristics; through EDS point line analysis, the segregation coefficient of Ni is 0.984, the segregation coefficient of W is 1.189, the segregation coefficient of Cr is 0.857, and the element distribution also meets the characteristics of low segregation; the obtained Ni-20W-20Cr heterogeneous seed crystal can be repeatedly used, effectively improving the utilization rate of the seed crystal and reducing the cost of the seed crystal method.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of single crystal superalloy preparation, and particularly relates to a low-segregation, low-melting-point, cell-branching Ni-W-Cr seed crystal component design and structure regulation method. BACKGROUND

[0002] With the development of advanced aerospace technology, higher requirements are put forward for the temperature resistance and use performance of the hot end components of aerospace engines and the materials used therefor. At present, high-temperature components such as turbine blades usually adopt single crystal superalloys with excellent high-temperature mechanical properties. The highest success rate of single crystal superalloy preparation is the seed crystal method. The seed crystal method is to melt the top end of a pre-placed single crystal as a seed crystal by heating, and then to obtain a single crystal with a desired orientation by casting the alloy liquid at a certain rate. The three-dimensional orientation of the single crystal can be accurately controlled in theory, and the temperature resistance of the nickel-based single crystal superalloy can be fully utilized. The main problem existing in the preparation of single crystal superalloys by the existing seed crystal method is that the thick paste zone has a dendritic structure, and the dendrites are easily broken during the remelting transformation. The broken dendrites will become heterogeneous crystal nucleation points, resulting in the failure of single crystal preparation, and the seed crystal cannot be reused, which greatly increases the use cost of the seed crystal method.

[0003] United States Patent 6740176B2 patent proposes Ni-W or Ni-Ta alloy as a heterogeneous seed crystal for preparing nickel-based single crystal superalloy. It is found in the literature "Toloraiya et al. Advanced method for single crystal casting of turbine blades for gas turbine engines and plants, Metal Science and Heat Treatment 2002" that the success rate of preparing nickel-based single crystal superalloy blades is higher by using the Ni-W low-segregation seed crystal with a cellular structure than by using the Ni-W seed crystal with a dendritic structure. In general, the cellular Ni-W heterogeneous seed crystal can effectively solve the problem of dendrite breakage during the remelting transformation, and solve the problems of non-reusable seed crystal and high cost. However, the melting point of the cellular Ni-W heterogeneous seed crystal is too high, which is above 1500 DEG C. In the casting process, the seed crystal cannot be completely combined with the parent alloy, which cannot guarantee the integrity of the single crystal and the structure is cellular, and the secondary orientation of the dendrites cannot be determined. SUMMARY

[0004] In view of the problems in the above background art, the purpose of the present application is to provide a low-segregation, low-melting-point, cell-branching Ni-W-Cr seed crystal component design and structure regulation method.

[0005] To achieve the above technical purposes, the technical scheme adopted by the present application is as follows:

[0006] A low segregation, low melting point, dendritic Ni-W-Cr seed composition design and structure control method, characterized in that it comprises the following steps:

[0007] S1, determining the alloy composition;

[0008] Based on the Ni-20W binary alloy, the third element required to be added is determined by Pandat thermodynamic software calculation;

[0009] The alloy design principle is: the alloy crystallization melting point is ≤1440℃, the crystallization temperature interval is ≤20℃, and the solidification path is L→L+Fcc→Fcc;

[0010] According to the mass percentage:

[0011] W accounts for 20%, Cr accounts for 12% to 20%, and the rest is Ni;

[0012] Taking the lowest liquid-solid line temperature as the benchmark, the theoretical element ratio of the seed alloy is obtained: Ni accounts for 60%, W accounts for 20%, and Cr accounts for 20%, the liquid-solid line temperature is 1396℃ or 1378℃ respectively, and the crystallization temperature interval is 18℃;

[0013] S2, melting Ni-20W-20Cr alloy;

[0014] S2.1, the alloy raw materials are initially melted by using a non-consumable arc melting furnace;

[0015] In the environment of power 300A-350A until the alloy is completely melted, then turn off the power, until the solution solidifies, use the turnover spoon to turn the button ingot, repeat the melting for 8 times, then rotate the crucible, melt the next group of samples, until 9 alloy ingots are obtained;

[0016] S2.2, using HRS high gradient directional solidification technology in a directional solidification furnace with a maximum capacity of 2 kg for secondary melting;

[0017] S2.2.1, the alloy ingot obtained in step S2.1 is placed into a 2 kg crucible, and the alloy ingot is completely melted under the condition that the crucible power is 7.5kW, to obtain an alloy solution;

[0018] S2.2.2, fix the mold on the water-cooled disc in the directional solidification furnace, pour the alloy solution obtained in step S2.2.1 into the mold shell of the mold, until the mold shell is completely filled, after cooling, take out the mold shell, and obtain the Ni-20W-20Cr master alloy;

[0019] S3, determine the appropriate pulling rate by step jump pulling experiment;

[0020] S3.1, prepare <001> oriented CMSX-2 single crystal test rod deviating from the axial direction by 0-12° by the selection method, for preparing Ni-20W-20Cr heterogeneous single crystal test rod, cut the CMSX-2 single crystal test rod into seed crystal test rod with a diameter size of 6.98mm and a length size of 25mm;

[0021] S3.2, prepare a corundum tube, and sequentially place the CMSX-2 seed crystal test rod and the Ni-20W-20Cr master alloy into the corundum tube in the order of the CMSX-2 seed crystal test rod below and the Ni-20W-20Cr master alloy above;

[0022] S3.3, install the corundum tube containing the CMSX-2 seed crystal test rod and the Ni-20W-20Cr master alloy on the bottom platform of the LMC directional solidification furnace, heat the directional solidification furnace to 1560℃ at a rate of 10℃ / min and keep the temperature, and make the master alloy in the corundum tube melt, after the end of the heat preservation, pull down at a step jump rate of 10μm / s, 15μm / s, 20μm / s and 40μm / s, and pull for 30mm for each distance, after the end of the pulling, take out the corundum tube after the directional solidification furnace cools to 100℃, and obtain the <001> Ni-20W-20Cr heterogeneous single crystal test rod deviating from the axial direction by 0-12°;

[0023] S3.4, grind and observe the alloy rod, and determine by EDS point line analysis, at a pulling rate of 20μm / s, the segregation coefficient of Ni is 0.984, the segregation coefficient of W is 1.189, and the segregation coefficient of Cr is 0.857, and stable cell-branch organization can be obtained, that is, 20μm / s is the most appropriate pulling rate;

[0024] S4, repeat the use of the Ni-20W-20Cr heterogeneous seed crystal alloy;

[0025] S4.1, take another corundum tube, take the CMSX-2 alloy as the master alloy, and sequentially place the obtained Ni-20W-20Cr heterogeneous seed crystal and the CMSX-2 master alloy into the corundum tube in the order of the Ni-20W-20Cr heterogeneous seed crystal below and the CMSX-2 master alloy above;

[0026] S4.2, install the corundum tube containing the seed crystal and the master alloy on the bottom platform of the LMC directional solidification furnace; heat the directional solidification furnace to 1525℃ at a rate of 10℃ / min and keep the temperature, and make the master alloy in the corundum tube melt; after the end of the heat preservation, pull down at a speed of 20μm / s; after the end of the pulling, take out the corundum tube after the directional solidification furnace cools to 100℃, and obtain the first <001> CMSX-2 single crystal test rod deviating from the axial direction by 0-12°;

[0027] S4.3, the recovered Ni-20W-20Cr heterogeneous seed crystal is loaded into a corundum tube, the corundum tube is placed in an LMC directional solidification furnace, and the process of preparing the first CMSX-2 single crystal test rod is repeated to obtain a second CMSX-2 single crystal test rod;

[0028] S4.4, the process of recycling and reusing the Ni-20W-20Cr heterogeneous seed crystal is repeated, and the recycled Ni-20W-20Cr heterogeneous seed crystal is obtained again, and the process of preparing the second CMSX-2 single crystal test rod is repeated to obtain a third CMSX-2 single crystal test rod;

[0029] S4.5, the process of recycling the seed crystal and preparing the CMSX-2 single crystal alloy test rod is cycled until the required number of CMSX-2 single crystal alloy test rods is obtained, and thus the reuse of the Ni-20W-20Cr heterogeneous seed crystal alloy is completed.

[0030] Further limited, in step S2.2.1, the melting power is increased from 4.3Kw to 7.5Kw step by step, the induction heating is performed for 25-35min, and after the alloy is completely melted, the pulling is performed at a rate of 100um / s to ensure the melting effect.

[0031] Further limited, the length of the Ni-20W-20Cr heterogeneous seed crystal cut from the first CMSX-2 single crystal test rod is consistent with the length of the original Ni-20W-20Cr heterogeneous seed crystal, so as to ensure the equivalence of the materials.

[0032] Further limited, in steps S3.3 and S4.2, the holding time is at least 60min to ensure sufficient melting.

[0033] The beneficial effects of the application are as follows:

[0034] The cell dendritic heterogeneous seed crystal alloy prepared by the application has a liquidus temperature of only 1419.1℃, can be well fused with the parent alloy, and has the characteristics that the cell crystal structure is not easy to break, and the secondary orientation can be judged through the dendritic characteristics.

[0035] The application can obtain stable cell dendritic structure at a pulling rate of 20um / s, through EDS point line analysis, the segregation coefficient of Ni is 0.984, the segregation coefficient of W is 1.189, and the segregation coefficient of Cr is 0.857, and the element distribution also meets the characteristics of low segregation, the Ni-20W-20Cr heterogeneous seed crystal obtained by the application can be reused for many times, effectively improves the utilization rate of the seed crystal, and reduces the cost of the seed crystal method. BRIEF DESCRIPTION OF DRAWINGS

[0036] The application can be further illustrated by the non-limiting embodiments shown in the drawings.

[0037] Figure 1 A flowchart of an embodiment of the low segregation, low melting point, cellular dendritic Ni-W-Cr seed composition design and microstructure control method of the present application;

[0038] Figure 2 A Ni-W-Cr phase diagram obtained by Pandat thermodynamic software calculation for an embodiment of the low segregation, low melting point, cellular dendritic Ni-W-Cr seed composition design and microstructure control method of the present application;

[0039] Figure 3 An XRD pattern of a CMSX-2 test bar prepared by the third preparation of the Ni-20W-20Cr heterogeneous seed for an embodiment of the low segregation, low melting point, cellular dendritic Ni-W-Cr seed composition design and microstructure control method of the present application;

[0040] Figure 4 Microstructure patterns of the cross section and longitudinal section of a Ni-20W-20Cr single crystal test bar prepared at a pulling rate of 20 μm / s for an embodiment of the low segregation, low melting point, cellular dendritic Ni-W-Cr seed composition design and microstructure control method of the present application;

[0041] Figure 5 A microstructure pattern of the cross section of a CMSX-2 single crystal test bar prepared by the third preparation of the Ni-20W-20Cr heterogeneous seed for an embodiment of the low segregation, low melting point, cellular dendritic Ni-W-Cr seed composition design and microstructure control method of the present application;

[0042] Figure 6 A longitudinal section microstructure pattern of the seed paste area after the CMSX-2 single crystal test bar is produced by the third seed for an embodiment of the low segregation, low melting point, cellular dendritic Ni-W-Cr seed composition design and microstructure control method of the present application. DETAILED DESCRIPTION

[0043] In order for those skilled in the art to better understand the present application, the technical solutions of the present application are further described below in conjunction with the accompanying drawings and examples.

[0044] As shown in Figures 1-6 A low segregation, low melting point, cellular dendritic Ni-W-Cr seed composition design and microstructure control method of the present application includes the following steps:

[0045] S1, determining the alloy composition;

[0046] Based on the Ni-20W binary alloy, the third element to be added is determined by Pandat thermodynamic software calculation;

[0047] The alloy design principle is that the alloy crystallization melting point is less than or equal to 1440 DEG C, the crystallization temperature interval is less than or equal to 20 DEG C, and the solidification path is L→L+Fcc→Fcc;

[0048] According to the mass percentage, the alloy is composed of 60% of Ni, 20% of W and 20% of Cr.

[0049] W accounts for 20%, Cr accounts for 12% to 20%, and the rest is Ni.

[0050] Based on the lowest liquid-solid phase line temperature, the theoretical element ratio of the seed crystal alloy is obtained as follows: Ni accounts for 60%, W accounts for 20%, and Cr accounts for 20%, and the liquid-solid phase line temperature is 1396 DEG C or 1378 DEG C, and the crystallization temperature interval is 18 DEG C.

[0051] S2, melting Ni-20W-20Cr alloy;

[0052] S2.1, primary melting of the alloy raw material is performed by using a non-consumable arc melting furnace;

[0053] In the power of 300A to 350A environment until the alloy completely melts, then turn off the power, until the solution solidifies, using a turnover spoon to turn the button ingot, repeat the melting 8 times, rotate the crucible, melt the next group of samples, until 9 alloy ingots are obtained;

[0054] S2.2, secondary melting is performed by using HRS high gradient directional solidification technology in a directional solidification furnace with a maximum capacity of 2 kg;

[0055] S2.2.1, the alloy ingot obtained in step S2.1 is placed into a 2 kg crucible, and the alloy ingot is completely melted under the condition that the crucible power is 7.5 kW, to obtain an alloy solution;

[0056] S2.2.2, the mold is fixed on the water-cooled disc in the directional solidification furnace, the alloy solution obtained in step S2.2.1 is poured into the mold shell of the mold, until the mold shell is completely filled, after cooling, the mold shell is taken out, and a Ni-20W-20Cr master alloy is obtained;

[0057] S3, determine the appropriate pulling rate by step jump increasing speed pulling experiment;

[0058] S3.1, prepare a <001> oriented CMSX-2 single crystal test rod deviated from the axial direction by 0 to 12 degrees by selecting crystal method, which is used for preparing a Ni-20W-20Cr heterogeneous single crystal test rod, and the CMSX-2 single crystal test rod is cut into a seed crystal test rod with a diameter size of 6.98 mm and a length size of 25 mm;

[0059] S3.2, prepare a corundum tube, and put the CMSX-2 seed test rod and the Ni-20W-20Cr mother alloy into the corundum tube in the order of the CMSX-2 seed test rod below and the Ni-20W-20Cr mother alloy above;

[0060] S3.3, install the corundum tube containing the CMSX-2 seed test rod and the Ni-20W-20Cr mother alloy on the bottom platform of the LMC directional solidification furnace, and heat the directional solidification furnace to 1560℃ at a rate of 10℃ / min and keep the temperature, so that the mother alloy in the corundum tube is solidified, after the end of the temperature keeping, pull down at a stepwise increasing speed of 10μm / s, 15μm / s, 20μm / s and 40μm / s, and pull for 30mm in each distance, after the end of the pulling, take out the corundum tube after the directional solidification furnace is cooled to 100℃, and obtain a <001>Ni-20W-20Cr heterogeneous single crystal test rod deviating from the axial direction by 0-12°;

[0061] S3.4, observe the alloy rod by grinding and sampling, and determine by EDS point and line analysis, at a pulling speed of 20μm / s, the segregation coefficient of Ni is 0.984, the segregation coefficient of W is 1.189, and the segregation coefficient of Cr is 0.857, and stable cell-branch structure can be obtained, that is, 20μm / s is the most suitable pulling speed;

[0062] S4, repeat the use of the Ni-20W-20Cr heterogeneous seed alloy;

[0063] S4.1, take another corundum tube, use CMSX-2 alloy as the mother alloy, and put the obtained Ni-20W-20Cr heterogeneous seed and the CMSX-2 mother alloy into the corundum tube in the order of the Ni-20W-20Cr heterogeneous seed below and the CMSX-2 mother alloy above;

[0064] S4.2, install the corundum tube containing the seed and the mother alloy on the bottom platform of the LMC directional solidification furnace, heat the directional solidification furnace to 1525℃ at a rate of 10℃ / min and keep the temperature, so that the mother alloy in the corundum tube is solidified, after the end of the temperature keeping, pull down at a speed of 20μm / s, after the end of the pulling, take out the corundum tube after the directional solidification furnace is cooled to 100℃, and obtain a first <001>CMSX-2 single crystal test rod deviating from the axial direction by 0-12°;

[0065] S4.3, put the recycled Ni-20W-20Cr heterogeneous seed into the corundum tube, and put the corundum tube into the LMC directional solidification furnace, repeat the process of preparing the first CMSX-2 single crystal test rod, and obtain a second CMSX-2 single crystal test rod;

[0066] S4.4, repeat the process of recycling and reusing the Ni-20W-20Cr heterogeneous seed crystal, and obtain the recycled Ni-20W-20Cr heterogeneous seed crystal again, repeat the process of preparing the second CMSX-2 single crystal test rod, and obtain the third CMSX-2 single crystal test rod;

[0067] S4.5, recycle the seed crystal--the process of preparing the CMSX-2 single crystal alloy test rod until the required number of CMSX-2 single crystal alloy test rods are obtained, at this time, the repeated use of the Ni-20W-20Cr heterogeneous seed crystal alloy is completed

[0068] In the embodiment, based on the Ni-20W binary alloy, the third element required to be added is determined by Pandat thermodynamic software calculation, and the alloy design principle is: melting point ≤ 1440℃, crystallization temperature interval ΔT ≤ 20℃, and the simplest solidification path is: L→L+Fcc→Fcc, wherein the mass percentage includes W ~ 20%, Cr 12% ~ 20%, and the balance of Ni, the element content of the low segregation, low melting point, cellular dendritic Ni-W-Cr seed crystal of the application is based on the lowest liquid-solid phase line temperature, and the element ratio of the seed crystal alloy is obtained: Ni ~ 60%, W ~ 20%, Cr ~ 20%, the liquid-solid phase line temperature is 1396℃ / 1378℃, and the crystallization temperature interval is 18℃, according to the element ratio of the seed crystal alloy, the alloy raw materials corresponding to different elements are smelted, and the Ni-20W-20Cr seed crystal master alloy is obtained, since Ni, W and Cr are refractory elements, two steps of preparation are required, that is, initial smelting in a non-consumable arc smelting furnace and remelting in a directional solidification furnace, and the seed crystal master alloy is obtained;

[0069] The liquid / solid phase line temperature and the crystallization temperature interval of the Ni-20W-20Cr alloy are measured by using a DSC device, the liquid / solid phase line temperature is 1419.1℃ / 1399.7℃, and the crystallization temperature interval is 19.4℃;

[0070] Firstly, the HRS high gradient directional solidification technology is used in the directional solidification furnace with a maximum capacity of 2 kg to prepare a CMSX-2 single crystal test rod with a diameter of 16 mm and a length of 110 mm for cutting the seed crystal, the single crystal test rod has a <001> orientation deviating from the axial direction by 0-12°; the CMSX-2 single crystal test rod is cut into a short single crystal test rod with a length slightly larger than that of the seed crystal, then the single crystal orientation is measured by using an X-ray single crystal orientation tester, the measurement results are marked on the single crystal sample, a plane is cut by using an electric spark wire cutting machine, the plane is used as the bottom surface, and then the electric spark wire cutting machine is used to cut a seed crystal rod with a diameter of 3.8 mm and a length of 35 mm from the single crystal test rod, the seed crystal rod has a <001> orientation deviating from the axial direction by 0°, and the seed crystal is polished to be smooth by using 1200# sandpaper;

[0071] A corundum tube is used again, and a Ni-20W-20Cr heterogeneous single crystal test rod is prepared with the corundum tube as a container, the inner diameter of the corundum tube is 3.81-4.11 mm, the length is 150 mm, the Ni-20W-20Cr alloy is used as a mother alloy, the obtained CMSX-2 seed crystal and the Ni-20W-20Cr mother alloy are placed in the corundum tube in the order of the seed crystal below and the Ni-20W-20Cr mother alloy above, and the corundum tube containing the CMSX-2 seed crystal and the mother alloy is installed on the bottom platform of the LMC directional solidification furnace;

[0072] The directional solidification furnace is heated at a rate of 10 ℃ / min to 1560 ℃ and kept for 60 min, the mother alloy in the corundum tube is melted, and the seed crystal generates a 1-2 mm paste area, after the end of the heat preservation, the downward pulling is increased at a step rate of 10 μm / s, 15 μm / s, 20 μm / s and 40 μm / s, and each distance is pulled for 30 mm, after the pulling is completed, the corundum tube is taken out after the directional solidification furnace is cooled to 100 ℃, and a <001> Ni-20W-20Cr heterogeneous single crystal test rod deviating from the axial direction by 0-12° is obtained;

[0073] In order to cut the cross-sectional structure of the steady-state or near steady-state growth region, the longitudinal cutting of the Ni-20W-20Cr heterogeneous single crystal test rod prepared in the above step is carried out using an electric spark wire cutting machine, the cold inlaying is carried out after the sample is polished, the aqua regia (HCl:HNO3=3:1) is used for etching, the change in the number of dendrite columns is counted within a constant intercept of 6 mm in the longitudinal section by a microscope, it is found that the length of the non-steady-state section caused by the pulling rate transition is less than 12 mm; then the steady-state cross section is cut at a distance of 15 mm from the pulling rate change interface under each pulling rate, the cold inlaying is carried out after the sample is polished, the aqua regia (HCl:HNO3=3:1) is used for etching, and it is found by microscope observation that the structure presents a cell dendrite state under a pulling rate of 20 μm / s, and therefore the appropriate pulling rate is determined to be 20 μm / s;

[0074] It is determined by EDS point line analysis that under a pulling rate of 20 μm / s, the segregation coefficient of Ni is 0.984, the segregation coefficient of W is 1.189, and the segregation coefficient of Cr is 0.857;

[0075] A Ni-20W-20Cr heterogeneous seed crystal monocrystal test rod with a diameter of 6.98 mm and a length of 83.2 mm having a

[001] orientation deviating from the axial direction by 0-12° is prepared using the LMC directional solidification furnace at a pulling rate of 20 μm / s, the monocrystal test rod is cut into short monocrystal test rods with a length of 25 mm using an electric spark wire cutting machine, and the seed crystal and CMSX-2 mother alloy are polished to be smooth using 1200# sandpaper;

[0076] The specific process of repeatedly using the Ni-20W-20Cr heterogeneous seed crystal alloy is as follows:

[0077] Another corundum tube is taken, and a CMSX-2 monocrystal test rod is prepared using the corundum tube as a container, the corundum tube has an inner diameter of 7.05-7.12 mm and a length of 115 mm, the CMSX-2 alloy is used as a mother alloy, the obtained Ni-20W-20Cr heterogeneous seed crystal and the CMSX-2 mother alloy are placed in the corundum tube in the order of seed crystal below and CMSX-2 mother alloy above, the corundum tube containing the seed crystal and the mother alloy is installed on the bottom table of the LMC directional solidification furnace, the directional solidification furnace is heated to 1525°C at a rate of 10°C / min and is kept for 60 min, the mother alloy in the corundum tube is solidified, after the end of the heat preservation, the crystal is pulled downward at a speed of 20 μm / s, after the end of the crystal pulling, the corundum tube is taken out after the directional solidification furnace is cooled to 100°C, and a first <001> CMSX-2 monocrystal test rod deviating from the axial direction by 0-12° is obtained;

[0078] The first CMSX-2 monocrystal test rod has a diameter of 6.98 mm and a length of 57 mm, and the gap between the first CMSX-2 monocrystal test rod and the corundum tube is 0.07-0.14 mm;

[0079] The length of the Ni-20W-20Cr heterogeneous seed crystal cut from the obtained first CMSX-2 monocrystal test rod is consistent with the length of the original Ni-20W-20Cr heterogeneous seed crystal, the diameter is 6.98 mm, and the length is 25 mm;

[0080] In the preparation, the recycled seed crystal is installed in the corundum tube, the corundum tube is placed in the LMC directional solidification furnace, and the process of preparing the first CMSX-2 monocrystal test rod is repeated to obtain a second CMSX-2 monocrystal test rod;

[0081] The process of recycling and repeatedly using the seed crystal is repeated to obtain recycled seed crystal again, and the process of preparing the second CMSX-2 monocrystal test rod is repeated to obtain a third CMSX-2 monocrystal test rod;

[0082] Cyclically recycling the seed crystals until a desired number of CMSX-2 single crystal alloy test bars are produced;

[0083] At this point, the Ni-20W-20Cr heterogeneous seed alloy is ready for reuse.

[0084] The above examples are only illustrative of the principles of and the efficacies of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A method for designing and controlling the microstructure of low-segregation, low-melting-point, dendritic Ni-W-Cr seed crystals, characterized in that, Includes the following steps: S1. Determine the alloy composition; Based on the Ni-20W binary alloy, the required third element was determined by calculation using Pandat thermodynamic software; The alloy design principle is: the alloy crystallization melting point is ≤1440℃, the crystallization temperature interval is ≤20℃, and the solidification path is L→L+Fcc→Fcc; Calculated as a percentage by mass: W accounts for 20%, Cr accounts for 12% to 20%, and the remainder is Ni; Based on the lowest liquidus-solid temperature, the theoretical elemental composition of the seed crystal alloy is: Ni 60%, W 20%, Cr 20%, with liquidus-solid temperatures of 1396℃ or 1378℃, and a crystallization temperature interval of 18℃. S2, Smelting Ni-20W-20Cr alloy; S2.

1. Use a non-consumable arc furnace for initial melting to perform initial melting of the alloy raw materials; In an environment with a power of 300A to 350A, the alloy is melted completely. Then the power is turned off and the melt is allowed to solidify. The button ingot is then flipped over using a flipping spoon. The melting process is repeated 8 times. The crucible is then rotated to melt the next set of samples until 9 alloy ingots are obtained. S2.2, Secondary melting is carried out using HRS high gradient directional solidification technology in a directional solidification furnace with a maximum dosage of 2 kg; S2.2.1 Place the alloy ingot obtained in step S2.1 into a 2 kg crucible, and melt the alloy ingot completely under the condition of crucible power of 7.5 kW to obtain an alloy solution. S2.2.2 Fix the mold on the water-cooled plate in the directional solidification furnace, pour the alloy solution obtained in step S2.2.1 into the mold shell until the mold shell is completely filled, wait for cooling, remove the mold shell, and obtain Ni-20W-20Cr master alloy. S3. Determine the appropriate pulling speed through a step-by-step speed-increasing pulling experiment; S3.1, Prepare crystals with an axial deviation of 0–12° by selective crystal selection. <001> Oriented CMSX-2 single crystal test rods were used to prepare Ni-20W-20Cr heterogeneous single crystal test rods. The CMSX-2 single crystal test rods were cut into seed crystal test rods with a diameter of 6.98 mm and a length of 25 mm. S3.

2. Prepare a corundum tube and place the CMSX-2 seed crystal test bar and the Ni-20W-20Cr mother alloy into the corundum tube in the order of CMSX-2 seed crystal test bar at the bottom and Ni-20W-20Cr mother alloy at the top. S3.3 The corundum tube containing the CMSX-2 seed crystal test rod and the Ni-20W-20Cr master alloy is installed on the bottom platform of the LMC directional solidification furnace. The furnace is heated to 1560℃ at a rate of 10℃ / min and held at that temperature to melt the master alloy inside the corundum tube. After holding, the tube is pulled downwards at a step-incremental speed of 10μm / s, 15μm / s, 20μm / s, and 40μm / s, with each step being 30mm. After pulling, the corundum tube is removed after the directional solidification furnace cools to 100℃, yielding a deviation of 0–12° from the axial direction. <001> Ni-20W-20Cr heterogeneous single crystal test rod; S3.

4. The alloy rod was ground and observed. EDS point-line analysis was used to determine that at a pulling rate of 20 μm / s, the segregation coefficient of Ni was 0.984, the segregation coefficient of W was 1.189, and the segregation coefficient of Cr was 0.

857. Stable cell branch structure could be obtained, that is, 20 μm / s was determined to be the most suitable pulling rate. S4. Reuse of Ni-20W-20Cr heterogeneous seed crystal alloy; S4.1 Take another corundum tube, using CMSX-2 alloy as the master alloy, and place the obtained Ni-20W-20Cr heterogeneous seed crystal and CMSX-2 master alloy into the corundum tube in the order of Ni-20W-20Cr heterogeneous seed crystal at the bottom and CMSX-2 master alloy at the top. S4.2 The corundum tube containing the seed crystal and the master alloy is installed on the bottom platform of the LMC directional solidification furnace; the directional solidification furnace is heated to 1525°C at a rate of 10°C / min and held at that temperature to melt the master alloy inside the corundum tube; after holding at that temperature, it is pulled downwards at a speed of 20μm / s; after pulling, the corundum tube is removed after the directional solidification furnace cools to 100°C, obtaining the first tube deviating from the axial direction by 0–12°. <001> CMSX-2 single crystal test rod; S4.

3. The recovered Ni-20W-20Cr heterogeneous seed crystal is loaded into the corundum tube, and the corundum tube is placed in the LMC directional solidification furnace. The above process for preparing the first CMSX-2 single crystal test rod is repeated to obtain the second CMSX-2 single crystal test rod. S4.4 Repeat the process of recycling and reusing Ni-20W-20Cr heterogeneous seed crystals to obtain recycled Ni-20W-20Cr heterogeneous seed crystals again, and repeat the process of preparing the second CMSX-2 single crystal test rod to obtain the third CMSX-2 single crystal test rod. S4.5, the process of recycling seed crystals to prepare CMSX-2 single crystal alloy test rods continues until the required number of CMSX-2 single crystal alloy test rods are obtained. This completes the reuse of Ni-20W-20Cr heterogeneous seed crystal alloy.

2. The method for compositional design and microstructure control of low-segregation, low-melting-point, dendritic Ni-W-Cr seed crystals according to claim 1, characterized in that: In step S2.2.1, the melting power is gradually increased from 4.3 kW to 7.5 kW, and induction heating is performed for 25 to 35 minutes. After the alloy is completely melted, it is pulled at a rate of 100 μm / s.

3. The method for compositional design and microstructure control of low-segregation, low-melting-point, dendritic Ni-W-Cr seed crystals according to claim 2, characterized in that: The length of the Ni-20W-20Cr heterogeneous seed crystal cut from the first CMSX-2 single crystal test bar is the same as the length of the original Ni-20W-20Cr heterogeneous seed crystal.

4. The method for compositional design and microstructure control of low-segregation, low-melting-point, dendritic Ni-W-Cr seed crystals according to claim 3, characterized in that: In steps S3.3 and S4.2, the heat preservation time is at least 60 minutes.

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