A purification and recycling method for DD5 single-crystal cast high-temperature alloy return materials

Abstract

This invention discloses a purification and recycling method for recycled DD5 single-crystal cast high-temperature alloy. The invention utilizes a high-energy beam bombardment process under high vacuum to create molten droplets that undergo thorough deoxidation and denitrification reactions at the gas-liquid interface, achieving ultra-low content control of gaseous elements. Furthermore, an electron beam droplet melting process creates a unique flow field and electromagnetic field in the molten pool, promoting the migration of high-density inclusions generated during the casting process (such as hafnium and rhenium) to the surface of the molten pool, which are then carried into the recycled material. This invention solves the problems of high refractory element content in DD5 alloys, the difficulty of purification and recycling using traditional smelting methods, and the inability to achieve deep removal of gaseous elements such as oxygen and nitrogen, as well as high-density oxide inclusions. It facilitates the same-level recycling of recycled single-crystal cast high-temperature alloys, reducing the waste of my country's strategic metal resources.

Description

Technical Field

[0001] This invention relates to the field of alloy metallurgy technology, specifically to a method for purifying and recycling DD5 single-crystal cast high-temperature alloy return materials. Background Technology

[0002] Nickel-based single-crystal superalloys are the main materials for turbine blades in various aero-engines and gas turbines. Single-crystal blades possess excellent high-temperature mechanical properties, can serve for extended periods in extremely harsh environments, and can withstand alternating stresses at high temperatures. With the increasing demands on the efficiency of aero-engines and gas turbines due to socio-economic development, the high-temperature load-bearing capacity of materials used in hot-end components has become particularly important. DD5, as a second-generation single-crystal superalloy, possesses stable high-temperature mechanical properties, good oxidation resistance, and resistance to hot corrosion, and has achieved engineering applications with steadily increasing annual demand. High-melting-point precious metal elements are added to single-crystal superalloys, especially DD5 single-crystal alloys with added Re and Hf, which cost over 2 million RMB per ton. However, the material utilization rate of single-crystal cast superalloy parts is typically only 10-20%, resulting in high casting costs and a large amount of recycled material. Because single-crystal castings use a directional solidification process with pouring temperatures exceeding 1500℃, the long contact time between the melt and the mold shell leads to the accumulation of impurities and inclusions, which are present in the recycled material. Single-crystal alloys operate at higher temperatures than equiaxed alloys and require higher purity. Therefore, recycled materials must undergo more stringent purification processes before they can be considered for recycling. Some recycled materials are downgraded or used to extract alloying elements such as Ni, resulting in a serious waste of strategic metal resources such as Re, Hf, W, Mo, and Ta, and a significant increase in manufacturing costs.

[0003] DD5 single-crystal cast superalloy contains Re and Hf, which interact strongly with impurity elements during smelting and casting. During remelting using traditional induction melting, the crucible, ladle, riser, and other components in contact with the furnace body easily undergo interfacial reactions with these reactive elements, introducing new inclusions and making purification and recovery difficult. Furthermore, DD5 alloy has a high content of refractory elements, making induction melting ineffective in removing these inclusions. Vacuum arc melting further reduces the content of reactive elements such as Re and Hf, but also results in significant macroscopic segregation in the alloy ingot. Electron beam melting technology, with its high vacuum and high energy density, is mainly used for smelting refractory metals and alloys, and its purification rate is significantly higher than other vacuum melting equipment. Currently, electron beam cold hearth melting technology is widely used for melting multi-component alloys such as titanium alloys, but there is no research on using electron beam melting technology for the purification of recycled materials from single-crystal cast superalloys. How to achieve the purification and recycling of single-crystal solidified casting high-temperature alloy return materials, so that the purity of the returned alloy reaches the level of reuse, remains a challenge in the development and reuse of single-crystal alloy return materials. Summary of the Invention

[0004] To address the aforementioned technical problems in DD5 single-crystal cast superalloys, such as the accumulation of impurities and high-density inclusions in the recycled material, leading to high levels of gaseous elements and high-density oxide inclusions, poor removal of refractory inclusions by induction melting, and severe burn-off and easy macroscopic segregation of reactive elements like Re and Hf by vacuum arc melting, making purification and recovery difficult, this invention provides a purification and recovery method for DD5 single-crystal cast superalloy recycled material. This invention utilizes the high-energy beam bombardment under high vacuum to create molten droplets that undergo thorough deoxidation and denitrification reactions at the gas-liquid interface, achieving ultra-low content control of gaseous elements. Furthermore, the electron beam droplet melting process creates a unique flow field and electromagnetic field in the molten pool, promoting the migration of high-density inclusions such as hafnium and rhenium, which are generated during casting and introduced into the recycled material, to the surface of the molten pool. This invention provides a purification and recycling method for DD5 single-crystal superalloy return material. Its advantages lie in solving the problems of high refractory element content in DD5 alloy, difficulty in purification and recycling using traditional smelting methods, and inability to achieve deep removal of gaseous elements such as oxygen and nitrogen, as well as high-density oxide inclusions. By using electron beam drop melting technology to achieve continuous smelting and purification, the stirring effect of the flow field formed in the molten pool and the rapid cooling effect of the water-cooled copper crucible avoid the generation of macroscopic segregation, thus enabling the purification and recycling of return material. This method facilitates the same-level recycling of single-crystal superalloy return material and reduces the waste of my country's strategic metal resources.

[0005] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0006] A purification and recycling method for DD5 single-crystal cast superalloy return material employs electron beam droplet melting technology. Molten droplets formed by high-energy beam bombardment under high vacuum undergo thorough deoxidation and denitrification reactions at the gas-liquid interface, achieving ultra-low content control of gaseous elements. The electron beam droplet melting process creates a unique flow field and electromagnetic field in the molten pool, promoting the migration of high-density inclusions to the surface of the molten pool. This solves the problem of difficult purification and recycling of DD5 single-crystal superalloy return material using traditional smelting methods. The method includes the following steps:

[0007] S1. Vacuum induction remelting is performed on the returned material of DD5 single crystal casting high-temperature alloy to obtain a raw material bar with suitable size for electron beam melting.

[0008] S2. Place the raw material rod for electron beam melting into the feeding system of the electron beam melting equipment, fix the bottom ingot into the ingot lifting system and adjust it to the bottom of the water-cooled copper crucible, and turn on the electron beam melting equipment for preheating and vacuuming.

[0009] S3. After the vacuum levels in the melting chamber and electron gun chamber reach the required levels, the electron gun is turned on. The electron beam melting power and beam size are adjusted before melting. The high-energy beam bombards the surface of the raw material rod. After the raw material melts, it forms molten droplets. The droplets undergo deoxidation and denitrification reactions in a high vacuum and superheat environment. They are then dropped into a water-cooled copper crucible and, combined with the beam, form a stirring effect, causing high-density oxide inclusions to float to the surface of the molten pool. At the same time, the ingot lifting system is operated to slowly pull out the ingot that has been rapidly solidified in the water-cooled copper crucible at a certain melting speed. This state is maintained and melting continues until all the raw material rods are melted. The electron beam melting power is gradually reduced to zero.

[0010] S4. After the furnace body cools down, the electron beam ingot is removed, and the last solidified impurity-rich area is cut off to obtain the ultrapure DD5 single crystal alloy return material recycled ingot.

[0011] Further, in step S2, the inner diameter D of the water-cooled copper crucible is 90 ~ 200 mm; in step S3, the electron beam melting power P is 30 ~ 70 kW; and the melting speed V of the ingot is 50 ~ 80 cm. 3 / min, and D, P, and V satisfy the following relationship: Because using different crucible inner diameters alters the heat radiation area during melting, and different melting speeds change the cooling loss, the matching of melting power and crucible inner diameter affects the intensity of the flow field and electromagnetic field in the molten pool. To ensure that the DD5 single-crystal superalloy return material achieves deep removal of elements such as oxygen and nitrogen during electron beam melting and promotes the flotation of high-density oxide inclusions, these three parameters are defined by formulas. Research has found that when... At that time, the loss of reactive elements increased significantly; when During this process, the deoxidation and denitrification reactions are not fully carried out, resulting in a high content of impurity elements in the electron beam ingot. Furthermore, the stirring effect of the flow field and electromagnetic field in the molten pool is not obvious, causing some high-density inclusions to not float to the surface of the molten pool. After the lower part of the molten pool gradually solidifies, the inclusions remain inside the electron beam ingot.

[0012] Furthermore, the diameter of the raw material rod used for electron beam melting is in the range of 80 to 150 mm.

[0013] Furthermore, in step S3, the diameter of the electron beam spot is in the range of 40 to 60% of the inner diameter of the water-cooled copper crucible.

[0014] Furthermore, in step S2, the electron beam melting equipment is turned on for preheating and vacuuming, so that the vacuum degree of the melting chamber is less than 2×10⁻⁶. -2 Pa, electron gun chamber vacuum degree less than 8×10 -3 Pa, turn on the electron gun to begin melting.

[0015] Furthermore, in step S2, the inner diameter of the water-cooled copper crucible is not less than the diameter of the raw material rod used for electron beam melting.

[0016] Furthermore, in step S2, the bottom ingot fixed to the ingot lifting system is obtained by machining a single-crystal casting high-temperature master alloy of the same grade.

[0017] Furthermore, in step S4, the thickness of the impurity-rich region at the top of the electron beam melting ingot is 20-30 mm.

[0018] The embodiments of the present invention have the following advantages:

[0019] The present invention provides a purification and recycling method for DD5 single-crystal cast high-temperature alloy return material. It innovatively applies electron beam drop dissolution technology to the purification smelting and recycling of single-crystal cast high-temperature alloy return material, which solves the problems of high refractory element content in DD5 alloy, difficulty in purification and recycling by traditional smelting methods, and inability to achieve deep removal of gaseous elements such as oxygen and nitrogen and high-density oxide inclusions. It can achieve efficient and continuous purification smelting, achieve ultra-low content control of impurity elements and high-density inclusions, and make the purity of the return material reach the level of new material. This invention utilizes high-energy beam bombardment under high vacuum to create molten droplets that undergo thorough deoxidation and denitrification reactions at the gas-liquid interface, achieving ultra-low content control of gaseous elements. Electron beam droplet melting technology creates a unique flow field and electromagnetic field in the molten pool, promoting the migration of high-density inclusions generated during casting (such as hafnium and rhenium) to the surface of the molten pool. This invention employs electron beam droplet melting technology for continuous melting and purification. The stirring effect of the flow field in the molten pool and the rapid cooling effect of the water-cooled copper crucible prevent macroscopic segregation. By controlling process parameters such as melting speed and melting power, the invention ensures thorough removal of impurities and inclusions while avoiding the burn-off of active main elements, achieving the purified recycling of single-crystal alloy return materials. This promotes the same-level recycling of single-crystal alloy return materials and reduces the waste of my country's strategic metal resources. Attached Figure Description

[0020] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0021] Figure 1 A photograph of molten droplets during the electron beam melting process of DD5 single-crystal cast high-temperature alloy return material provided in an embodiment of the present invention. Detailed Implementation

[0022] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] This embodiment provides a method for purifying and recycling DD5 single-crystal cast high-temperature alloy return materials:

[0025] (1) Vacuum induction remelting was performed on the riser and gating of DD5 single crystal casting high temperature alloy to obtain a raw material bar with a diameter of 80 (mm) for electron beam melting;

[0026] (2) Place the raw material rod for electron beam melting into the feeding system of the electron beam melting equipment, use induction melting of DD5 master alloy to process the bottom ingot, use a water-cooled copper crucible with an inner diameter of 100 (mm), and turn on the electron beam melting equipment for preheating and vacuuming.

[0027] (3) The vacuum degree of the melting chamber reaches 1.5×10 -2 (Pa), the vacuum degree of the electron gun chamber reaches 7.4×10. -3 (Pa), turn on the electron gun, adjust the electron beam melting power to 31 (kW), adjust the beam diameter to 60 (mm), and begin melting. Simultaneously, operate the ingot lifting system to move the ingot at an 80 (cm) angle. 3 The raw material bar is pulled out at a melting speed of ( / min) and continuously melted until it is completely melted, and the melting power is gradually reduced to zero.

[0028] (4) After the furnace body is cooled, the ingot is taken out and the impurity enrichment area with a thickness of 20 (mm) on the top is cut off to obtain the electron beam purified and regenerated ingot of DD5 single crystal high temperature alloy return material.

[0029] This invention forms a high-energy electron beam by bombarding a returning material bar. Figure 1 As shown in the diagram, impurity elements in the molten droplets can undergo sufficient degassing and decomposition reactions at the gas-liquid interface, achieving ultra-low content control of impurity elements such as oxygen and nitrogen. The electron beam regenerated ingot of DD5 single-crystal high-temperature alloy recycled material provided in this embodiment exhibits a 65% reduction in oxygen content and a 53% reduction in nitrogen content compared to before smelting, with a Re element burn-off rate of 0.8%, achieving a deep removal effect of impurity elements.

[0030] Example 2

[0031] This embodiment provides a method for purifying and recycling DD5 single-crystal cast high-temperature alloy return materials:

[0032] (1) Vacuum induction remelting was carried out on the waste blades of DD5 single crystal alloy casting to obtain a raw material rod with a diameter of 150 (mm) for electron beam melting;

[0033] (2) Place the raw material rod for electron beam melting into the feeding system of the electron beam melting equipment, use vacuum induction melting to process the DD5 master alloy ingot, use a water-cooled copper crucible with an inner diameter of 180 (mm), and turn on the electron beam melting equipment for preheating and vacuuming.

[0034] (3) The vacuum degree of the melting chamber reaches 1.2×10 -2 (Pa), the vacuum degree of the electron gun chamber reaches 7.8×10. -3 (Pa), turn on the electron gun, adjust the electron beam melting power to 60 (kW), adjust the beam diameter to 80 (mm), and begin melting. Simultaneously, operate the ingot lifting system to move the ingot at a height of 78 (cm). 3 The melting speed is pulled out at a rate of / min, and the feeding system is operated to continuously melt until all the raw material bars are melted, and the melting power is gradually reduced to zero.

[0035] (4) After the furnace body is cooled, the ingot is taken out and the impurity enrichment area with a thickness of 30 (mm) on the top is cut off to obtain the electron beam regenerated ingot of DD5 single crystal high temperature alloy return material.

[0036] The electron beam regenerated ingot of DD5 single crystal high-temperature alloy return material provided in this embodiment has a 78% reduction in oxygen content and a 62% reduction in nitrogen content compared to before smelting, and a Re element burn-off rate of no more than 1.6%. This achieves ultra-low content control of inclusions in single crystal cast high-temperature alloy return material while avoiding excessive Re element burn-off.

[0037] Example 3

[0038] This embodiment provides a method for purifying and recycling DD5 single-crystal cast high-temperature alloy return materials:

[0039] (1) Vacuum induction remelting was carried out on the waste blades cast from DD5 single crystal alloy to obtain two raw material rods with a diameter of 120 (mm) for electron beam melting;

[0040] (2) Place the raw material rod for electron beam melting into the feeding system of the electron beam melting equipment, process the bottom ingot by electroslag remelting DD5 master alloy, use a water-cooled copper crucible with an inner diameter of 150 (mm), and turn on the electron beam melting equipment for preheating and vacuuming.

[0041] (3) The vacuum degree of the melting chamber reaches 9.5×10 -3(Pa), the vacuum degree of the electron gun chamber reaches 6.5×10. -3 (Pa), turn on the electron gun, adjust the electron beam melting power to 45 (kW), adjust the beam diameter to 80 (mm), and begin melting. Simultaneously, operate the ingot lifting system to move the ingot at a height of 60 (cm). 3 The melting speed is pulled out at a rate of / min, and the feeding system is operated to continuously melt until all the raw material bars are melted, and the melting power is gradually reduced to zero.

[0042] (4) After the furnace body is cooled, the ingot is taken out and the impurity enrichment area with a thickness of 25 (mm) on the top is cut off to obtain the electron beam regenerated ingot of DD5 single crystal high temperature alloy return material.

[0043] The electron beam regenerated ingot of DD5 single crystal high-temperature alloy provided in this embodiment reduces the inclusion content in the ingot to 0.23 (cm³). 2 / kg), the Re element burn-off rate does not exceed 1.0%, and the measured Re content in the upper, middle and lower parts of the electron beam casting ingot are 2.95wt%, 2.94wt% and 2.97wt%, respectively. The Re element is relatively uniformly distributed inside the casting ingot, with a composition deviation of no more than 2%, and no macroscopic segregation phenomenon is observed. This achieves ultra-low content control of inclusions in the return material of single crystal casting high temperature alloy while keeping the Re element within the chemical composition requirements of DD5 alloy.

[0044] Comparative Example 1

[0045] The purification and recycling method for DD5 single-crystal cast high-temperature alloy recycled material provided in this comparative example:

[0046] (1) Vacuum induction remelting was carried out on the waste blades of DD5 single crystal alloy casting to obtain a raw material rod with a diameter of 80 (mm) for electron beam melting;

[0047] (2) Place the raw material rod for electron beam melting into the feeding system of the electron beam melting equipment, use vacuum induction melting to process the DD5 master alloy ingot, use a water-cooled copper crucible with an inner diameter of 100 (mm), and turn on the electron beam melting equipment for preheating and vacuuming.

[0048] (3) The vacuum degree of the melting chamber reaches 1.8×10 -2 (Pa), the vacuum degree of the electron gun chamber reaches 7.0×10⁻⁶. -3 (Pa), turn on the electron gun, adjust the electron beam melting power to 24 (kW), adjust the beam diameter to 50 (mm), and begin melting. Simultaneously, operate the ingot lifting system to move the ingot at 80 (cm)... 3 The melting speed is pulled out at a rate of / min, and the feeding system is operated to continuously melt until all the raw material bars are melted, and the melting power is gradually reduced to zero.

[0049] (4) After the furnace body is cooled, the ingot is taken out and the impurity enrichment area with a thickness of 25 (mm) on the top is cut off to obtain the electron beam regenerated ingot of DD5 single crystal high temperature alloy return material.

[0050] The electron beam regenerated ingot of DD5 single crystal superalloy provided in this comparative example has an inclusion content of 0.81 (cm³). 2 / kg), the oxygen content in the ingot decreased by only 22% and the nitrogen content decreased by only 14% compared with that before smelting. There are still many oxide inclusions inside the ingot, which does not achieve the goal of controlling the ultra-low content of inclusions in the return material of DD5 single crystal casting high temperature alloy.

[0051] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method of purifying and reclaiming DD5 single crystal cast superalloy returns, characterized by, The method comprises the following steps: S1, vacuum induction remelting the DD5 single crystal cast high-temperature alloy return material to obtain an electron beam melting raw material rod with a proper size; S2, placing the electron beam melting raw material rod in the feeding system of the electron beam melting equipment, fixing the bottom ingot to the ingot lifting system and adjusting it to the bottom of the water-cooled copper crucible, and starting the electron beam melting equipment for preheating and vacuumizing; S3, after the vacuum degree of the melting chamber and the electron gun chamber reaches the requirement, opening the electron gun, adjusting the electron beam melting power and the beam spot size, and then melting, the surface of the raw material rod is bombarded by a high-energy beam spot, the raw material melts to form a molten droplet, the droplet fully performs deoxidation and denitrification reactions in a high-vacuum and high-heat environment, the droplet is dropped into the water-cooled copper crucible to form a stirring effect combined with the beam current, which promotes the high-density oxide inclusions to float to the surface of the molten pool, at the same time, the ingot lifting system is operated to slowly pull out the ingot rapidly solidified by the water-cooled copper crucible at a certain melting speed, and the state is kept for continuous melting until the raw material rod is completely melted, and the electron beam melting power is gradually reduced to zero; S4, after the furnace body is cooled, the electron beam ingot is taken out, the impurity-rich area of the last solidification is cut off, and a super-pure DD5 single crystal alloy return material regeneration ingot is obtained. In step S2, the water-cooled copper crucible has an inner diameter D = 90 ~ 200 mm, in step S3, the electron beam melting power P = 30 ~ 70 kW, and the melting speed V = 50 ~ 80 cm / min of the ingot, and D, P and V satisfy the following relationship: 3 .​ 2. The method of claim 1, wherein the DD5 single crystal cast superalloy return material is purified. In step S1, the diameter of the electron beam melting raw material rod is in the range of 80-150 mm.

3. The method of claim 1, wherein the DD5 single crystal cast superalloy return material is purified. In step S3, the diameter of the electron beam spot is in the range of 40-60% of the inner diameter of the water-cooled copper crucible.

4. The method of claim 1, wherein the DD5 single crystal cast superalloy return material is purified. In step S2, the electron beam melting equipment is started to preheat and vacuumize, so that the vacuum degree of the melting chamber is less than 2×10 -2 Pa, the vacuum degree of the electron gun chamber is less than 8×10 -3 Pa, and the electron gun is opened to start melting.

5. The method of claim 1, wherein the DD5 single crystal cast superalloy return material is purified. In step S2, the inner diameter of the water-cooled copper crucible is not less than the diameter of the electron beam melting raw material rod.

6. The method of claim 1, wherein the DD5 single crystal cast superalloy return material is purified. In step S2, the bottom ingot fixed to the ingot lifting system is obtained by machining the same brand single crystal cast high-temperature master alloy.

7. The method of claim 1, wherein the DD5 single crystal cast superalloy return material is purified. In step S4, the thickness of the impurity-rich area of the top of the electron beam melting ingot is cut off to be 20-30 mm.

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