A method of ultrasonic-assisted preparation of single crystal alloys
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NORTHWESTERN POLYTECHNICAL UNIV
- Filing Date
- 2026-03-26
- Publication Date
- 2026-06-26
AI Technical Summary
Traditional directional solidification methods are difficult to control precisely in terms of crystallographic orientation when preparing single-crystal alloys, and the solidification microstructure is limited in scale, resulting in poor performance of high-temperature alloys.
An ultrasonic-assisted directional solidification method is adopted. By applying an ultrasonic field with specific parameters at the key stage of directional solidification, the growth of non-preferred orientation grains is selectively suppressed and the growth of target orientation grains is promoted. Furthermore, by combining the multi-physics field coupling of acoustic field, thermal field and flow field, the solute boundary layer and dendrite spacing at the solidification interface are precisely controlled.
It significantly improves the crystallographic orientation concentration of single-crystal alloys, shortens the preparation time, reduces costs, and enhances the application performance of high-temperature alloys.
Smart Images
Figure CN121896715B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of single-crystal alloy preparation technology, specifically relating to a method for preparing single-crystal alloys with ultrasound assistance. Background Technology
[0002] Single-crystal alloys are widely used in extreme service environments such as aerospace engines and gas turbines. Their performance is highly dependent on the material's microstructure, such as growth orientation and dendrite spacing. Single-crystal alloys are generally prepared through directional solidification methods, and their growth orientation is closely related to... <001> The degree of proximity of preferred orientations directly affects the creep, fatigue, and other properties of alloys. Traditional directional solidification mainly relies on the control of temperature gradients and solidification rates. However, due to the instability of the liquid-solid interface and the competitive growth of grains, uneven micro-orientation distribution is often caused, or additional crystal selection processes may be required, increasing costs and time. Furthermore, in practice, large-scale changes in pumping rate parameters are needed to achieve microstructural transformations such as "flat-cellular-dendritic." Limited by the range of parameter control, the thickness of the microscopic solute diffusion boundary layer is difficult to adjust precisely, resulting in limited precision in controlling the microstructure of columnar crystals and dendrite spacing in single-crystal high-temperature alloys.
[0003] In recent years, physical field-assisted solidification has attracted widespread attention due to its influence on solute transport, interface disturbance, and microstructure evolution. Ultrasonic fields, as a physical field control method, have been widely applied to metal solidification, promoting grain refinement, eliminating porosity, and improving solute segregation. However, the effects of ultrasound on directional solidification interfaces and crystal growth are more complex, and there is limited research on related systems for columnar superalloys. Therefore, there is an urgent need for an experimental system and control method integrating ultrasonic excitation, directional solidification, and acoustic field detection to elucidate the dynamic evolution process under real-time acoustic field monitoring and control conditions, and to achieve precise control over the microstructure of directional solidification superalloys. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing single-crystal alloys with ultrasound assistance.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] This invention provides a method for preparing single-crystal alloys with ultrasound assistance, comprising the following steps:
[0007] Step 1: Melt and hold the alloy raw materials at a certain temperature to obtain an alloy melt;
[0008] Step 2: Perform first-stage directional solidification on the alloy melt until competitive growth is complete;
[0009] Step 3: After the competitive growth is completed, the system undergoes a second stage of directional solidification until stable growth is completed;
[0010] Step 4: After the system has been stabilized and grown, it is subjected to ultrasonic-assisted directional solidification, then stabilized and grown to the target height again, and then quenched to obtain the single crystal alloy.
[0011] Preferably, the melting temperature T 熔化 =T L +150K, the T L This refers to the liquidus temperature corresponding to the alloy raw material;
[0012] The heat preservation time is 40-60 minutes.
[0013] Preferably, the solidification rate V in the first stage of directional solidification 竞争 Satisfying 150μm / s≥V 竞争 ≥50μm / s;
[0014] The growth distance h corresponding to the competitive growth 竞争 ≥2cm.
[0015] Preferably, the solidification rate V in the second stage of directional solidification 稳定 ≤2.6μm / s;
[0016] The growth distance h corresponding to stable growth 稳定 ≥k s (T L -T C ) / (k L G L +ρvL f ), where k s T is the thermal conductivity of the solid phase; C The cold end temperature; k L G is the thermal conductivity of the liquid phase. L ρ is the liquid phase temperature gradient; ρ is the liquid phase density; v is V. 稳定 L f This is the latent heat of solidification.
[0017] Preferably, the solidification rate V of the ultrasound-assisted directional solidification is... 超声 It has the same solidification rate as in the second stage of directional solidification.
[0018] Preferably, the method for determining the ultrasonic frequency of the ultrasonic-assisted directional coagulation includes: determining the resonance frequency of the solid-liquid mixture after the stable growth is completed, which is the ultrasonic frequency;
[0019] The system after stable growth includes unsolidified alloy melt and the solid phase obtained in steps 1 and 2.
[0020] Preferably, the amplitude A of the ultrasound in the ultrasound-assisted directional coagulation satisfies A max ≥A≥Amin A max and A min The value of is determined by the formula A=f(θ)=σ0 / {2πF[ρ / (S 11 -2(S 11 -S 12 -1 / 2S 44 (sin) 2 (θ)-(3 / 4)sin 4 (θ)))] 1 / 2} Calculate, where θ is the grain size and... <001> The orientation difference, σ0 is the high-temperature fatigue damage threshold, ρ is the alloy density, and S 11 S 12 S 44 Let A be the compliance constant of the target alloy, F be the ultrasonic frequency, and f(θ) represent the fatigue fracture stress corresponding to the θ-orientation difference grain, where A max =f(θ=5°), A min= f(θ=15°).
[0021] Preferably, the growth distance h of the ultrasound-assisted directional coagulation 超声 ≥(λ u / λ s ) 3 D / V, where λ s λ is the primary arm spacing during stable dendrite growth. u denoted as the first arm spacing for stable dendrite growth under ultrasound, D as the diffusion coefficient, and V as the solidification rate of ultrasound-assisted directional solidification.
[0022] Preferably, the solidification rate during the second-stage directional solidification is the same as the solidification rate during the second-stage directional solidification.
[0023] Preferably, the quenching conditions include: a quenching speed greater than 2 cm / s, a quenching medium of liquid metal, wherein the liquid metal is a GaInSn alloy, and the temperature of the liquid metal is controlled at 15~25℃ by water cooling.
[0024] Compared with the prior art, the present invention has the following advantages:
[0025] (1) In the competitive growth stage of columnar crystals during directional solidification, this invention selectively suppresses the growth of non-preferred orientation grains by applying an ultrasonic field with specific parameters and utilizing the differentiated responses of grains with different crystallographic orientations to ultrasonic stress, while simultaneously promoting the continuous growth of grains with the target preferred orientation. This mechanism significantly improves the high concentration of crystallographic orientation in the final solidified structure, overcomes the limitations of traditional directional solidification technology in the precise control of crystal orientation, and provides a key technology for preparing high-quality single crystals or highly concentrated columnar crystal materials.
[0026] (2) This invention precisely limits the ultrasonic action to the critical stage of crystal orientation competition screening, rather than throughout the entire solidification process. This staged, point-to-point ultrasonic intervention can efficiently accelerate the elimination process of non-preferred orientation grains, thereby completing crystallographic orientation selection within a relatively short growth distance. This significantly shortens the time and growth length required for crystal orientation selection in traditional methods, significantly improves the efficiency of single crystal preparation, and effectively reduces production costs.
[0027] (3) This invention effectively controls the thickness of the solute boundary layer near the solidification interface by introducing an ultrasonically induced acoustic field and flow field, thereby affecting the stability of the solidification morphology and the evolution law of dendrite spacing. While optimizing orientation, it achieves the microstructure control of cell tip splitting, dendrite initiation, and steady-state dendrite growth, breaking through the limitations of temperature gradient and pulling speed on the structural scale of solidification microstructure in traditional directional solidification conditions. This invention breaks through the limitations of traditional directional solidification on the structural scale of solidification microstructure by multi-physics field coupling of acoustic field, thermal field, and flow field, providing a new technical path for the preparation of high-performance single-crystal high-temperature alloys and comprehensively improving the application performance of metallic materials.
[0028] (4) This invention provides a systematic and scientific method for optimizing ultrasonic parameters. This method integrates theoretical analysis and precise experimental verification of the anisotropy of the elastic modulus of materials, achieving microstructure refinement while maintaining directional growth, and comprehensively controlling the application performance of metallic materials. The method has good operability, repeatability and wide applicability, providing a reliable technical path for controlling the crystal orientation of different alloy systems. Attached Figure Description
[0029] Figure 1 The microstructure of the DZ411 alloy obtained in Example 1 and Comparative Example 1 is shown in the longitudinal section with a growth rate of V = 2 μm / s, where (a) is Comparative Example 1 and (b) is Example 1.
[0030] Figure 2 The image shows the EBSD analysis of the longitudinal section of the DZ411 alloy obtained in Example 1 with a growth rate of V = 2 μm / s.
[0031] Figure 3 This is a comparison of the tensile properties of the DZ411 alloy in Example 1 and Comparative Example 1 at 760°C. Detailed Implementation
[0032] This invention provides a method for preparing single-crystal alloys with ultrasound assistance, comprising the following steps:
[0033] Step 1: Melt and hold the alloy raw materials at a certain temperature to obtain an alloy melt;
[0034] Step 2: Perform first-stage directional solidification on the alloy melt until competitive growth is complete;
[0035] Step 3: After the competitive growth is completed, the system undergoes a second stage of directional solidification until stable growth is completed;
[0036] Step 4: After the system has been stabilized and grown, it is subjected to ultrasonic-assisted directional solidification, then stabilized and grown to the target height again, and then quenched to obtain the single crystal alloy.
[0037] Step 1 of the present invention involves melting and holding the alloy raw materials at a certain temperature to obtain an alloy melt.
[0038] The present invention does not have any special limitation on the type of alloy raw material, and any material well known to those skilled in the art can be used.
[0039] In this invention, the melting temperature T 熔化 =T L +150K, the T L The liquidus temperature is the temperature corresponding to the alloy raw material; the holding time is preferably 40~60min, specifically 40min, 42min, 44min, 46min, 48min, 50min, 52min, 54min, 56min, 58min, and 60min.
[0040] In this invention, the alloy raw material is preferably added in the form of a cylinder, the size of which is preferably Ø9.50±0.05mm; the surface roughness Ra of which is preferably ≤0.8μm.
[0041] In this invention, the directional solidification is preferably carried out in an ultrasonic directional solidification device, which preferably includes a crucible, an ultrasonic transducer, an amplitude transformer, a liquid cooling tank, and temperature and sound field control devices, with the crucible placed on the amplitude transformer.
[0042] In this invention, the directional solidification is preferably carried out under a protective atmosphere, preferably high-purity argon or high-purity nitrogen. This protective atmosphere is used to prevent oxidation of the alloy raw materials at high temperatures.
[0043] In this invention, the preferred specific process of step 1 is as follows: First, the alloy raw material is melted to obtain a uniform ingot; then, the ingot is processed into a cylindrical sample; the surface of the sample needs to be finely machined to ensure its flatness and good fit with subsequent contact parts, with a roughness Ra≤0.8μm; the processed sample is loaded into the crucible in the ultrasonic directional solidification device, and the crucible and the sample inside are correctly placed on the ultrasonic amplitude transformer; then, under a protective atmosphere (to completely remove residual oxygen inside the device, multiple vacuuming and protective atmosphere cycling can be used), the alloy raw material is heated to melting and held at that temperature through a temperature control system, so that the alloy melt is completely melted and reaches a sufficiently homogeneous and stable state of composition and temperature, eliminating the macroscopic and microscopic segregation of the original as-cast structure, and providing a uniform liquid phase for subsequent directional solidification.
[0044] After obtaining the alloy melt, step 2 of the present invention is to perform a first-stage directional solidification of the alloy melt until competitive growth is completed.
[0045] In this invention, the solidification rate V in the first stage of directional solidification 竞争 Satisfying 150μm / s≥V 竞争 ≥50μm / s; the growth distance h corresponding to the competitive growth 竞争 ≥2cm.
[0046] In this invention, after the first stage of directional solidification, it is preferable to perform static heat preservation, and the static heat preservation time is preferably 10 minutes.
[0047] In this invention, the first-stage directional solidification aims to ensure that the system achieves optimal vibration transmission efficiency and ultrasonic effect during subsequent ultrasonic application. The competitive growth in this stage is primarily due to the tendency for impurities to form during the initial pulling process caused by the instantaneous change in supercooling; therefore, it is necessary to ensure that these impurities are eliminated through competitive growth first.
[0048] After the competitive growth is completed, step 3 of the present invention is to perform a second-stage directional solidification of the system after the competitive growth is completed until stable growth is completed.
[0049] In this invention, the solidification rate V in the second stage of directional solidification 稳定 ≤2.6μm / s. In this invention, the growth distance h corresponding to the stable growth is... 稳定 (i.e., the height at which columnar crystals achieve stable directional growth) ≥ k s (T L -T C ) / (k L G L +ρvL f ), where k s T is the thermal conductivity of the solid phase;C The cold end temperature; k L G is the thermal conductivity of the liquid phase. L ρ is the liquid phase temperature gradient; ρ is the liquid phase density; v is V. 稳定 L f This is the latent heat of solidification.
[0050] In this invention, the purpose of performing a second-stage directional solidification is to develop the solidification interface into a stable columnar crystal growth morphology, ensuring that the solidification interface has fully developed into a stable columnar crystal structure before the ultrasonic action is initiated.
[0051] After the stable growth is completed, step 4 of the present invention is to perform ultrasonic-assisted directional solidification on the system after the stable growth is completed, then grow it to the target height again, and then quench it to obtain the single crystal alloy.
[0052] In this invention, the solidification rate V of the ultrasound-assisted directional solidification is... 超声 Solidification rate V in the second stage of directional solidification 稳定 same.
[0053] In this invention, the method for determining the ultrasonic frequency in ultrasonic-assisted directional solidification preferably includes: determining the resonance frequency of the solid-liquid mixture after the stable growth is completed, which is the ultrasonic frequency; the system after the stable growth is completed preferably includes the unsolidified alloy melt and the solid phase obtained in steps 1 and 2. This invention does not impose any special limitations on the process of determining the resonance frequency; any method well-known to those skilled in the art can be used, specifically, confirmation through impedance curves.
[0054] In this invention, the amplitude A of the ultrasound in the ultrasound-assisted directional coagulation preferably satisfies A max ≥A≥A min A max and A min The value of is determined by the formula A=f(θ)=σ0 / {2πF[ρ / (S 11 -2(S 11 -S 12 -1 / 2S 44 (sin) 2 (θ)-(3 / 4)sin 4 (θ)))] 1 / 2} Calculate, where θ is the grain size and... <001> The orientation difference, σ0 is the high-temperature fatigue damage threshold, ρ is the alloy density, and S 11 S 12 S 44 Let A be the compliance constant of the target alloy, F be the ultrasonic frequency, and f(θ) represent the fatigue fracture stress corresponding to the θ-orientation difference grain, where A max =f(θ=5°), A min=f(θ=15°).
[0055] In this invention, the growth distance h of the ultrasound-assisted directional coagulation 超声 ≥(λ u / λ s ) 3 D / V; λ s λ is the primary arm spacing during stable dendrite growth. u The distance between the first arm of dendrites for stable growth under ultrasound is given by D, where D is the diffusion coefficient and V is the solidification rate of ultrasound-assisted directional solidification. 超声 .
[0056] In this invention, the ultrasonic-assisted directional solidification involves applying ultrasonic waves to the leading region of the solid-liquid interface. The introduction of ultrasonic waves utilizes the acoustic flow induced in the melt to disturb and refine the solute boundary layer at the solidification interface, thereby affecting the interface instability mechanism and inducing the solidification morphology to continuously evolve from cellular crystals to stable dendrites.
[0057] In this invention, the solidification rate of the second-stage stable growth and the solidification rate V in the second-stage directional solidification are mentioned. 稳定 The process is the same; specifically, it is preferred to refer to step 3. In this invention, by stabilizing the growth again, the length requirement of the optimized single-crystal structure can be met by controlling the growth distance of the process.
[0058] In this invention, the preferred quenching conditions include: a quenching speed greater than 2 cm / s; a quenching medium of liquid metal, specifically a GaInSn alloy, wherein the GaInSn alloy preferably contains 21.5% In by mass, 10% Sn by mass, and the remainder Ga; and the temperature of the liquid metal is controlled at 15-25°C by water cooling. In this invention, quenching is performed to rapidly solidify the interface, fix its microstructure, and prevent changes in the microstructure during cooling after solidification.
[0059] In this invention, the quenching process preferably includes cooling the system to room temperature.
[0060] Furthermore, the present invention can also achieve precise control of the dendrite primary arm spacing by applying ultrasound; the precise control of the dendrite primary arm spacing is preferably achieved by controlling the amplitude of the ultrasound.
[0061] In this invention, when precise control of the dendrite primary arm spacing is required, the method for determining the value of the amplitude A preferably includes:
[0062] (1) According to the method for preparing single-crystal alloys provided by the present invention, one ultrasonic test without ultrasound and at least two ultrasonic tests with different ultrasonic amplitudes A are performed. After each directional solidification is completed, longitudinal section sampling and metallographic observation are performed on the final alloy sample to obtain the static (i.e., ultrasonic-free) first arm spacing λ at this pumping speed. s and the first arm spacing λ corresponding to different amplitudes A u The value;
[0063] (2) According to the formula λ u =Cλ s A -β By fitting the formula (which describes the quantitative relationship between ultrasonic amplitude and dendrite spacing refinement), the values of the coefficient C and the power coefficient β of the formula are obtained;
[0064] (3) Based on the target value, use A=(λ) u / C / λ s )β is calculated to obtain the result with λ u Corresponding ultrasonic amplitude A u The value of A. max ≥A u ≥A min A=A u ; when A u ≥A max A=A max ; when A u ≤A min A=A min .
[0065] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.
[0066] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0067] Example 1
[0068] Taking the nickel-based superalloy DZ411 as an example, ultrasonic-assisted directional solidification was performed;
[0069] Step 1: The smelted DZ411 alloy is processed into a cylindrical sample with a diameter of Ø9.50mm and a length of 120mm, and the surface is ground to Ra≤0.8μm; it is loaded into a high-purity alumina crucible and placed inside an ultrasonic directional solidification device, ensuring that the bottom of the crucible is in close contact with the ultrasonic amplitude transformer.
[0070] Evacuate the device to 1×10⁻⁶ -3 Pa, then high-purity argon gas is introduced to 50 kPa, and this process is repeated 3 times;
[0071] Start the heating system and heat the DZ411 alloy to 150K above the liquidus temperature, i.e., 1600℃; hold at this temperature for 50 minutes to allow the alloy to melt completely and reach a homogeneous state.
[0072] Step 2: Activate the motion system, using V 竞争 The first stage of directional solidification was carried out at a speed of 100 μm / s to a height of h. 竞争 =30mm, then turn off the motion system and keep warm for 10 minutes;
[0073] Step 3: After the heat preservation is completed, use V 稳定 The second stage of directional solidification was carried out at a speed of 2 μm / s, and the stable growth height was h. 稳定 =5mm;
[0074] Step 4: While maintaining V 稳定 With the amplitude A = 2 μm / s constant, the ultrasonic vibration system is turned on, and ultrasonic waves with a frequency F = 30 kHz and an amplitude A = 2 μm are applied to the solid-liquid interface. The growth distance h of ultrasonic-assisted directional solidification is... 超声 =8mm;
[0075] Turn off ultrasound, maintain V 稳定 Under the condition that the growth rate remains constant at 2 μm / s, the sample continues to grow stably for 17 mm to the target height. The heating system is then turned off, and the sample is subjected to rapid liquid quenching. The quenching speed is 5 cm / s, the quenching medium is a GaInSn alloy (In is 21.5 wt%, Sn is 10 wt%, and the remainder is Ga), and the temperature of the liquid metal is controlled at 20 °C by water cooling.
[0076] After the device has cooled down, remove the solidified DZ411 alloy bar.
[0077] Comparative Example 1
[0078] Directional solidification was performed as in Example 1, wherein no ultrasonic assistance was applied in step 4, i.e., the material was directly grown to the target height at a rate of V=2μm / s.
[0079] Performance testing
[0080] like Figure 1 As shown in (a), the longitudinal section of the DZ411 alloy obtained in Comparative Example 1 with a growth rate of V=2μm / s shows that its solidification morphology is mainly coarse cellular crystals with an average size of 170μm.
[0081] like Figure 1As shown in (b), using the ultrasonic-assisted method of the present invention, the longitudinal section of the DZ411 alloy with a growth rate of V=2μm / s under ultrasonic action with an applied amplitude A=2μm shows that its solidification morphology changes from cellular crystals to fine stable dendrites, the dendrite primary arm spacing is significantly refined to 33μm, and the distribution is uniform.
[0082] like Figure 2 As shown in the figure, the longitudinal section EBSD analysis diagram of the DZ411 alloy with a growth rate of V=2μm / s obtained in Example 1 shows that the crystal orientation difference along the temperature gradient direction decreased from 40° to 15°, which was significantly optimized, and most grains showed a highly concentrated preferred orientation.
[0083] Figure 3 Table 1 shows a comparison of the tensile properties of the DZ411 alloy in Example 1 and Comparative Example 1 at 760°C;
[0084] Table 1. Comparison of tensile properties of DZ411 alloy at 760°C in Example 1 and Comparative Example 1
[0085]
[0086] like Figure 3 As shown in Table 1, the tensile properties test results of the DZ411 alloy in Example 1 and Comparative Example 1 at 760℃ show that its tensile strength and elongation also exhibit significant improvements. This demonstrates that the present invention, through precise control of the solidification structure, can comprehensively improve the mechanical properties of high-temperature alloys at different service temperatures.
[0087] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.
Claims
1. A method for ultrasonic-assisted preparation of single-crystal alloys, characterized in that, Includes the following steps: Step 1: Melt and hold the alloy raw materials at a certain temperature to obtain an alloy melt; Step 2: Perform first-stage directional solidification on the alloy melt until competitive growth is complete; The solidification rate V in the first stage of directional solidification 竞争 Satisfying 150μm / s≥V 竞争 ≥50μm / s; the growth distance h corresponding to the competitive growth 竞争 ≥2cm; Step 3: After the competitive growth is complete, the system undergoes a second stage of directional solidification until stable growth is achieved; the solidification rate V during the second stage of directional solidification... 稳定 ≤2.6μm / s; the growth distance h corresponding to the stable growth 稳定 ≥k s (T L -T C ) / (k L G L +ρvL f ), where k s T is the thermal conductivity of the solid phase; L T represents the liquidus temperature corresponding to the alloy raw material. C The cold end temperature; k L G is the thermal conductivity of the liquid phase. L ρ is the liquid phase temperature gradient; ρ is the liquid phase density; v is V. 稳定 L f Latent heat of solidification; Step 4: After the system has been stabilized and grown, it is subjected to ultrasonic-assisted directional solidification, then stabilized and grown to the target height again, and then quenched to obtain the single crystal alloy; the method for determining the ultrasonic frequency of the ultrasonic-assisted directional solidification includes: determining the resonance frequency of the solid-liquid mixture system after the stable growth is completed, which is the ultrasonic frequency. The amplitude of the ultrasound in the ultrasound-assisted directional coagulation is 2 μm; The growth distance h of the ultrasound-assisted directional coagulation 超声 It is 8mm.
2. The method according to claim 1, characterized in that, The melting temperature T 熔化 =T L +150K, the T L This refers to the liquidus temperature corresponding to the alloy raw material; The heat preservation time is 40-60 minutes.
3. The method according to claim 1, characterized in that, The solidification rate V of the ultrasound-assisted directional coagulation 超声 It has the same solidification rate as in the second stage of directional solidification.
4. The method according to claim 1, characterized in that, The solid-liquid mixture system after the stable growth is completed includes the unsolidified alloy melt and the solid phase obtained in steps 1 and 2.
5. The method according to claim 1, characterized in that, The solidification rate during the re-stabilized growth is the same as the solidification rate during the second-stage directional solidification.
6. The method according to claim 1, characterized in that, The quenching conditions include: a quenching speed greater than 2 cm / s, a quenching medium of liquid metal, wherein the liquid metal is a GaInSn alloy, and the temperature of the liquid metal is controlled at 15~25℃ by water cooling.