CN112746183B - Method for synchronously removing high-density impurities and low-density impurities in high-temperature alloy - Google Patents
Method for synchronously removing high-density impurities and low-density impurities in high-temperature alloy Download PDFInfo
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Abstract
The invention provides a method for synchronously removing high-density impurities and low-density impurities in a high-temperature alloy, which comprises the following steps: s1, preprocessing a high-temperature alloy raw material; and S2, removing low-density and high-density inclusions in the high-temperature alloy by electron beam refining to obtain the DD406 high-temperature alloy cast ingot with low density and low high-density inclusion content. The invention adopts the electron beam refining technology to synchronously remove low-density and high-density inclusions in the high-temperature alloy. The method comprises the steps of dissolving and removing small-size low-density and high-density inclusions in a melt by increasing melt overheating in a high vacuum refining process, decomposing and removing large-size low-density inclusions on the surface of the melt in situ under the bombardment action of high-energy electron beams, and capturing and removing large-size high-density inclusions under the adsorption action of a solidified shell at the bottom of an ingot, so that the low-density and high-density inclusions in the alloy are completely removed, and a high-purity high-temperature alloy ingot blank is obtained through casting.
Description
Technical Field
The invention relates to a method for synchronously removing high-density impurities and low-density impurities in a high-temperature alloy.
Background
A large amount of alloying elements can be added in the preparation process of the high-temperature alloy, so that the high-temperature alloy has good service performance, and with the continuous improvement of the use requirement of the alloy, some noble metal elements such as Ta, Hf, Re and the like are gradually added into the high-temperature alloy, particularly into the oriented and single-crystal high-temperature alloy. Active elements in the high-temperature alloy, such as Al, Ti and the like, are easy to combine with O, N in the melt to form low-density inclusions with extremely high stability, such as Al2O3And TiN, etc. On the other hand, certain noble alloying elements (e.g., Hf, etc.) are highly reactive with crucibles, shells, and other refractories during smelting to form fine, high density inclusions, such as HfO2And the like. TheseThe low-density and high-density inclusions seriously affect the normal-temperature and high-temperature mechanical properties of the alloy, particularly the low-cycle fatigue property, and therefore need to be strictly controlled.
At present, the method of filtering and promoting the floating of inclusions in a molten pool or adsorbing the inclusions floating to the surface of a melt by adopting foamed ceramics is a main way for removing the inclusions in the smelting process. From Stokes law of the motion of the inclusions, when the sizes of the inclusions are smaller, the floating or sedimentation speed of the inclusions is slower, the removal of the inclusions by a mode of promoting floating or sedimentation becomes more difficult, and the ceramic filtration has a better effect only on the large-size inclusions. The existing method can successfully remove the low-Perilla inclusions with the grain size of more than 10 mu m in the high-temperature alloy, and has very limited removal effect on the inclusions with small grain size (<10 mu m). In addition, high-density inclusions in the high-temperature alloy have a large specific gravity relative to an alloy melt, and floating conditions are difficult to create in the smelting process, so that the traditional inclusion removal method is difficult to realize deep removal of the high-density inclusions in the high-temperature alloy.
The electron beam refining technology is a technological process for bombarding the surface of a material by using an electron beam with high energy density to melt the material and refine the material, and is widely applied to the fields of refining refractory metals and alloys, preparing high-purity special steel and ultra-clean steel, refining and purifying titanium and titanium alloys and the like. The electron beam has extremely high energy density, controllable beam current, adjustable beam spot and high automation degree, and can generate local ultrahigh temperature after the electron beam with high energy density acts on the melt>3000K) Combined with high vacuum (5X 10)-3Pa) and the characteristic of large temperature gradient in the melt, can create the conditions for removing the impurities in situ.
Disclosure of Invention
According to the proposed current existing means, the low-fringed inclusions with the grain size of more than 10 mu m in the high-temperature alloy can be successfully removed, but the removal effect on the inclusions with small grain size (<10 mu m) is very limited; in addition, high-density inclusions in the high-temperature alloy have a larger specific gravity relative to an alloy melt, and floating conditions are difficult to create in the smelting process, so that the technical problem that the traditional inclusion removing method is difficult to realize deep removal of the high-density inclusions in the high-temperature alloy is solved, and the method for synchronously removing the high-density inclusions and the low-density inclusions in the high-temperature alloy is provided. The invention mainly adopts an electron beam refining technology to synchronously remove low-density and high-density inclusions in the high-temperature alloy. The method comprises the steps of dissolving and removing small-size low-density and high-density inclusions in a melt by increasing melt overheating in a high vacuum refining process, decomposing and removing large-size low-density inclusions on the surface of the melt in situ under the bombardment action of high-energy electron beams, and capturing and removing large-size high-density inclusions under the adsorption action of a solidified shell at the bottom of an ingot, so that the low-density and high-density inclusions in the alloy are completely removed, and a high-purity high-temperature alloy ingot blank is obtained through casting.
The technical means adopted by the invention are as follows:
a method for synchronously removing high-density impurities and low-density impurities in a high-temperature alloy comprises the following steps:
s1, pretreatment of the high-temperature alloy raw material:
s11, the raw material is DD406 alloy containing different types of inclusions;
s12, processing the raw materials to a proper size, wherein the raw materials can be placed into a water-cooled copper crucible for refining;
s13, polishing the processed raw material, and removing ceramic adhesion, an oxidation layer, processing traces and the like on the surface to ensure that the alloy has no external pollutants;
s14, cleaning and drying the polished raw materials for later use;
s2, removing low-density and high-density inclusions in the high-temperature alloy by electron beam refining:
s21, cleaning the water-cooled copper crucible for electron beam refining and solidification: polishing, wiping with alcohol and drying to ensure that the water-cooled copper crucible is clean and pollution-free;
s22, cleaning pollutants on the furnace body and the furnace wall of the electron beam melting furnace, and avoiding the introduction of foreign impurities in the refining process;
s23, placing the pretreated raw material in a water-cooled copper crucible for refining, and closing a furnace door of the electron beam melting furnace after the raw material is determined to be ready and the furnace body is cleaned;
s24, opening the electron beam refining equipment, pumping the electron beam melting furnace and the electron gun body to a target vacuum state, and preheating the equipment after reaching the target vacuum degree;
s25, starting high pressure after preheating is finished, slowly increasing the beam current of the electron gun on the left side to 600mA after the high pressure is stabilized, and uniformly scanning and melting the raw materials in the water-cooled copper crucible for refining;
s26, after the raw materials are completely melted, refining the raw materials for 10 min;
s27, carrying out melt overheating treatment on the refined raw material;
s28, after the melt is subjected to overheating treatment, enriching large-size low-density inclusions in a final solidification region on the surface of the cast ingot;
s29, performing high-temperature pyrolysis on the large-size low-density inclusion in the final solidification region until the inclusion is completely decomposed, and fully settling the large-size high-density inclusion to the bottom of the melt so as to be captured by a solidified shell;
s210, after refining is finished, instantly adjusting the beam current of the electron gun on the left side to 0mA, and simultaneously starting a melting crucible dumping mechanism to enable the refined melt to flow into a water-cooled copper crucible for solidification, wherein a skull in the water-cooled copper crucible for melting is reserved in an original crucible;
s211, uniformly scanning the high-temperature alloy melt in the water-cooled copper crucible for solidification through the right-side electron gun, so that the surface of the melt in the water-cooled copper crucible for solidification is uniform;
s212, closing the high pressure of the electron gun, increasing the beam current of the two electron guns to 60-120 mA to enable the high pressure value to be 0, and then closing the electron gun to enable the cast ingot to be fully solidified and cooled in a water-cooled copper crucible for solidification;
s213, taking out the DD406 alloy ingot after electron beam refining to obtain the DD406 high-temperature alloy ingot with low density and high density and extremely low inclusion content.
Further, the specific steps of step S14 are as follows:
and ultrasonically cleaning the polished DD406 alloy raw material by using deionized water and alcohol respectively, cleaning for three times by using the deionized water and the ultrasonic, placing the alloy into a drying box after cleaning, and drying at 30 ℃ for electron beam refining.
Further, the specific steps of step S26 are as follows:
after the alloy is completely melted, refining the alloy for 10min in an electron beam annular scanning mode, wherein the beam spot radius is kept at 20-25 mm, so that volatile gas impurities (O, N and the like) in the high-temperature alloy melt are fully removed, and meanwhile, large-size high-density inclusions gradually settle to the bottom of a molten pool and are captured by a skull.
Further, the specific steps of step S27 are as follows:
increasing the beam current of the electron beam on the left side to 800mA, and carrying out melt overheating treatment on the DD406 alloy for 20min, so that small-size low-density and high-density inclusions and ordered atomic groups in the DD406 alloy are fully dissolved.
Further, the specific steps of step S28 are as follows:
after the melt is subjected to overheating treatment, the beam current size is reduced to 500mA, electron beam refining parameters are controlled, the beam spot of the electron beam is enabled to move slowly from left to right, the beam current size is gradually reduced in a slow beam current reduction mode in the moving process of the beam spot, the radius of the beam spot is shrunk, the beam current size and the beam spot size are 0 at the same time when the beam spot moves to the edge area on the right side of the ingot, and enrichment of large-size low-density inclusions in the final solidification area on the surface of the ingot is achieved.
Further, the specific steps of step S29 are as follows:
adjusting the beam spot radius of the left electron gun to 5mm, gradually increasing the beam current to 600mA, and performing high-temperature pyrolysis on large-size low-density inclusions in a final solidification region by using an electron beam with high energy density; and adjusting the beam spot radius to 25mm after the inclusions are completely decomposed, and continuously refining the DD406 alloy in the water-cooled copper crucible by using an annular scanning path for 10min, so that the large-size high-density inclusions are fully settled to the bottom of the melt and then captured by a skull.
Further, the specific steps of step S211 are as follows:
increasing the beam current of the right electron gun to 500-600 mA, adjusting the radius of the beam spot to 25mm, uniformly scanning the alloy melt in the water-cooled copper crucible for solidification in an annular path to ensure that the surface of the melt in the water-cooled copper crucible for solidification is uniform, and then reducing the beam current of the right electron gun to 0 mA.
Compared with the prior art, the invention has the following advantages:
1. the invention provides a method for synchronously removing high-density inclusions and low-density inclusions in a high-temperature alloy, which innovatively provides that low-density inclusions and high-density inclusions in the high-temperature alloy are synchronously removed by adopting an electron beam refining technology, in-situ dissolution and removal of small-size low-density inclusions and high-density inclusions in a melt are realized by utilizing a local large overheating environment in an electron beam refining process, in-situ decomposition and removal of large-size low-density inclusions on the surface are realized by utilizing a high-energy electron beam bombardment effect, and capture and removal of large-size high-density inclusions are realized by utilizing a capture effect of a condensing shell at the bottom of the melt, so that the aim of comprehensively removing the low-density inclusions and the high-density inclusions in the high-temperature alloy is fulfilled.
2. The method for synchronously removing the high-density impurities and the low-density impurities in the high-temperature alloy provided by the invention creatively provides the method for synchronously removing the low-density impurities and the high-density impurities in the high-temperature alloy by adopting an electron beam refining technology. The method comprises the steps of dissolving and removing small-size low-density and high-density inclusions in a melt by increasing melt overheating in a high vacuum refining process, decomposing and removing large-size low-density inclusions on the surface of the melt in situ under the bombardment action of high-energy electron beams, and capturing and removing large-size high-density inclusions under the adsorption action of a solidified shell at the bottom of an ingot, so that the low-density and high-density inclusions in the alloy are completely removed, and a high-purity high-temperature alloy ingot blank is obtained through casting.
3. According to the method for synchronously removing the high-density inclusions and the low-density inclusions in the high-temperature alloy, on the basis of fully removing volatile impurities in the process of refining the high-temperature alloy by using the electron beams, the small-size low-density and high-density inclusions in the melt are dissolved and removed by increasing the overheating of the melt in the process of refining the high-temperature alloy by using the high-temperature high-vacuum electron beams, the in-situ decomposition and removal of the large-size low-density inclusions on the surface are realized by the direct bombardment of the electron beams, the capture and removal of the large-size high-density inclusions in the melt are realized by the adsorption action of a skull at the bottom of an ingot on the large-size inclusions which are settled below a molten pool, and then a high-purity high-temperature alloy ingot is obtained by casting. The sizes and the number of the low-density and high-density inclusions in the high-temperature alloy ingot obtained by the method are obviously reduced, so that the purpose of comprehensively removing the inclusions in the high-temperature alloy is achieved, and a new way is provided for effectively removing the high-temperature alloy inclusions.
In conclusion, the technical scheme of the invention can solve the problem that the existing means can successfully remove the low-density periwinkle inclusion with the particle size of more than 10 mu m in the high-temperature alloy, but has very limited removal effect on the inclusion with smaller particle size (less than 10 mu m); in addition, high-density inclusions in the high-temperature alloy have a large specific gravity relative to an alloy melt, and floating conditions are difficult to create in the smelting process, so that the traditional inclusion removing method has the problem that the deep removal of the high-density inclusions in the high-temperature alloy is difficult to realize.
Based on the reasons, the method can be widely popularized in the fields of removing high-density and low-density inclusions in the high-temperature alloy and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic view of electron beam melting for removing small-sized inclusions.
FIG. 2 is a schematic view showing the decomposition of large-sized low-density inclusions on the surface according to the present invention.
FIG. 3 is a schematic view of the casting process after electron beam refining according to the present invention.
FIG. 4 is a graph showing the Reynolds number of the relative motion between high-density inclusions and the fluid and the size of the inclusions according to the present invention.
FIG. 5 is a graph showing the relationship between the moving rate of high-density inclusions and the particle size of inclusions according to the present invention.
In the figure: 1. an oil diffusion pump; 2. a valve; 3. a mechanical pump; 4. local overheating areas of the melt; 5. an alloy melt; 6. condensing a shell layer; 7. water-cooling the copper crucible; 8. a melting crucible dumping mechanism; 9. cooling water; 10. an electron gun; 11. an electron beam; 12. a roots pump; 13. a large-size low-density inclusion enrichment area on the surface of the melt.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate. Any specific values in all examples shown and discussed herein are to be construed as exemplary only and not as limiting. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.
As shown in the figure, the invention provides a method for synchronously removing high-density impurities and low-density impurities in a high-temperature alloy, which comprises the following steps:
pretreatment of high-temperature alloy raw materials
1. Taking the DD406 alloy as an example, the DD406 alloy raw material containing different types of inclusions is processed to an appropriate size so as to be put into a water-cooled copper refining crucible.
2. And polishing the processed DD406 alloy to remove ceramic adhesion, oxide layer, processing trace and the like on the surface, so that the alloy has no external pollutants.
3. And ultrasonically cleaning the polished DD406 alloy raw material by using deionized water and alcohol respectively, cleaning for three times by using the deionized water and the ultrasonic, placing the alloy into a drying box after cleaning, and drying at 30 ℃ for electron beam refining.
Secondly, electron beam refining is carried out to remove low-density and high-density inclusions in the high-temperature alloy
1. The water-cooled copper crucible for electron beam refining and solidification is cleaned (polished, wiped by alcohol and dried) to ensure that the crucible is clean and pollution-free.
2. Cleaning the furnace body and the furnace wall of the electron beam melting furnace, and avoiding the introduction of foreign impurities in the refining process.
3. The pretreated DD406 alloy raw material is placed in a water-cooled copper crucible for refining, the preparation is determined, and the furnace door is closed after the furnace body is cleaned.
4. And opening electron beam refining equipment, pumping the furnace body and the gun body to a target vacuum state, starting the electron guns on the left side and the right side after the target vacuum degree is reached, and preheating the equipment.
5. Starting high pressure after preheating is finished, slowly increasing the beam current of the electron gun on the left side to 600mA after the high pressure is stabilized, and uniformly scanning and melting the DD406 alloy raw material in the water-cooled copper crucible.
6. After the alloy is completely melted, refining the alloy for 10min in an electron beam annular scanning mode, wherein the beam spot radius is kept at 20-25 mm, so that volatile gas impurities (O, N and the like) in the high-temperature alloy melt are fully removed, and meanwhile, large-size high-density inclusions gradually settle to the bottom of a molten pool and are captured by a skull.
7. The beam current on the left side is increased to 800mA, and the DD406 alloy is subjected to melt overheating for 20min, so that small-size low-density and high-density inclusions and ordered atomic groups in the alloy are fully dissolved (figure 1).
8. After the melt is subjected to overheating treatment, the beam current size is reduced to 500mA, electron beam refining parameters are controlled, the beam spot of the electron beam is enabled to move slowly from left to right, the beam current size is gradually reduced in a slow beam current reduction mode in the moving process of the beam spot, the radius of the beam spot is shrunk, the beam current size and the beam spot size are 0 at the same time when the beam spot moves to the edge area on the right side of the ingot, and enrichment of large-size low-density inclusions in the final solidification area on the surface of the ingot is achieved.
9. The radius of the beam spot of the electron gun on the left side is adjusted to 5mm, the beam current is gradually increased to 600mA, and the electron beam with high energy density is utilized to carry out high-temperature pyrolysis on the large-size low-density inclusion in the final solidification region (figure 2). And adjusting the beam spot radius to 25mm after the inclusions are completely decomposed, and continuously refining the DD406 alloy in the water-cooled copper crucible by using an annular scanning path for 10min, so that the large-size high-density inclusions are fully settled to the bottom of the melt and then captured by a skull.
10. After refining, the beam current of the electron gun on the left side is instantly adjusted to 0mA, and meanwhile, the pouring mechanism of the melting crucible is started, so that the refined melt flows into the water-cooled copper crucible for solidification, and a solidified shell in the water-cooled copper crucible for melting is remained in the original crucible (figure 3).
11. Increasing the beam current of the right electron gun to 500-600 mA, adjusting the radius of the beam spot to 25mm, uniformly scanning the alloy melt in the water-cooled copper crucible for solidification in an annular path to ensure that the surface of the melt in the water-cooled copper crucible for solidification is uniform, and then reducing the beam current of the right electron gun to 0 mA.
12. And (3) closing the high pressure of the electron gun, increasing the beam current of the two electron guns to 60-120 mA to enable the high pressure value to be 0, and then closing the electron gun to enable the cast ingot to be fully solidified and cooled in the water-cooled copper crucible for solidification.
13. And taking out the DD406 alloy ingot refined by the electron beam so as to obtain the DD406 high-temperature alloy ingot with low density and high density and extremely low inclusion content.
Fig. 1 is a schematic view showing the removal of small-sized inclusions by electron beam super-thermal dissolution according to the present invention, fig. 2 is a schematic view showing the decomposition of large-sized low-density inclusions on the surface according to the present invention, and fig. 3 is a schematic view showing the casting process after electron beam refining according to the present invention. The invention adopts the equipment shown in figures 1-3 to remove high-density inclusions and low-density inclusions in the high-temperature alloy. The electron gun 10 is fixed at two side corners of the top of the electron beam melting furnace, the water-cooled copper crucible for melting 7 (namely, the water-cooled copper crucible for refining) is placed in the electron beam melting furnace through the melting crucible dumping mechanism 8, the water-cooled copper crucible for solidification 7 is placed at the bottom of the electron beam melting furnace, and cooling water 9 is introduced. The DD406 alloy raw material is placed in a water-cooled copper crucible 7 for melting and is in the scanning range of an electron beam 11. The oil diffusion pump 1 is adjacent to the mechanical pump 3, and the communication relationship between the oil diffusion pump 1 and the mechanical pump is controlled by a valve 2; the roots pump 12 is adjacent to the furnace body mechanical pump 3, and the two are connected together. The alloy melt 5 is a molten metal raw material in a water-cooled copper crucible 7 and forms a local overheating zone 4 of the melt after melting. After the melt is subjected to overheating treatment, electron beam refining parameters are controlled to form a large-size low-density inclusion enrichment area 13 on the surface of the melt. The melt refined in the water-cooled copper crucible for melting 7 flows into the water-cooled copper crucible for solidification 7, and the skull layer 6 in the water-cooled copper crucible for melting is retained in the original crucible.
On the basis of fully removing volatile impurities in the process of refining the high-temperature alloy by using the electron beams, the method realizes the dissolution removal of small-size low-density and high-density impurities in the melt by increasing the overheating of the melt in the process of refining the high-temperature high-vacuum electron beams, realizes the in-situ decomposition removal of large-size low-density impurities on the surface by the direct bombardment of the electron beams, realizes the capture removal of the large-size high-density impurities in the melt by the adsorption action of a skull at the bottom of an ingot on the large-size impurities settled below a molten pool, and further obtains a high-purity high-temperature alloy ingot by casting. The sizes and the number of the low-density and high-density inclusions in the high-temperature alloy ingot obtained by the method are obviously reduced, so that the purpose of comprehensively removing the inclusions in the high-temperature alloy is achieved, and a new way is provided for effectively removing the high-temperature alloy inclusions.
The mechanism for capturing the high-density inclusion skull is as follows:
HfO compared to the alloy melt2The inclusions have a higher density, and in the melting phase, the high-density inclusions gradually sink to the bottom of the melt under the action of gravity, and the inclusions in the raw material have sufficient time to settle before the end of the refining phase, assuming that the inclusions are uniform spherical particles with a diameter dpThe force was analyzed as follows:
the gravity borne by the inclusions is FgComprises the following steps:
in the formula, ρpThe density of inclusions and g is the acceleration of gravity.
Buoyancy of inclusions in the melt Fb：
Wherein rho is the density of the alloy melt.
The inclusions are subjected to the resultant force of gravity and buoyancy:
density of inclusions ρpGreater than the rho of the alloy melt, so that the inclusions move downwards and gradually sink to the bottom of the molten pool, and the resistance F suffered by the inclusions in the process of sinkingrComprises the following steps:
in the formula, CDIs a coefficient of drag (drag), ApIs the projected area of the particle in the direction of the fluid, and u is the relative velocity of the fluid and the solid.
The comprehensive stress F of the inclusion particles is as follows:
F＝Fg-Fb-Fr (5)
according to newton's second law, the resultant force F in the above formula can be represented by the following formula, where a is the acceleration:
F＝ma (6)
at the moment when the inclusion begins to rise, its initial velocity u is zero and the resistance F is setrZero, so the acceleration is at a maximum; the resistance of the inclusions increases with increasing speed u during the ascent, and the acceleration a correspondingly decreases, when the speed reaches a critical value utWhen the force is zero, the acceleration of the impurities is zero, and the speed u of the impurities is zerotNo longer changed.
Because the specific surface area of the small particles is large, the resistance of the impurities in the particles in the extremely short time of rising of the particles is close to balance with the net gravity (namely gravity minus buoyancy) borne by the particles, and the accelerated rising of the impurities is usually negligible for the whole rising process. When a is 0, u is utAs can be seen from the formula (3-6),
coefficient of resistance CDReynolds number Re which is the relative motion between the inclusions and the fluidtFunction of Reynolds number RetIs defined as:
in the formula, μ is the viscosity Pa · s of the fluid.
Assuming that the inclusions are spherical particles having a maximum particle diameter of 100 μm, the precipitation behavior of the inclusions is in Ret<1 hour obeys Stokes' law, coefficient of resistance CDComprises the following steps:
the final velocity of the rise of the inclusions can be calculated by the formula (7-9):
reynolds number Re of the movement of inclusions in the melttCalculated from equations (8) and (10):
where ρ isgAnd ρ are the density of the high density inclusions and the alloy melt, respectively. With HfO2For example, the high density inclusion density was 9680kg/m3The density of the alloy melt is 8500kg/m3The viscosity mu range of the nickel-based alloy is about 0.005-0.01 Pa.s, and the gravity acceleration is 9.8m/s2Therefore, the Reynolds number Re of the relative motion of the inclusions and the fluid under different viscosities can be calculatedtThe relationship with the size of inclusions is shown in FIG. 4. ByFIG. 4 shows the Reynolds number Re of the relative motion between the inclusions and the fluid at different viscositiestAre all less than 1, and therefore the sedimentation process of high density inclusions obeys Stokes law. The relationship between the rate of inclusion settling and the inclusion particle size was calculated for different melt viscosities, as shown in fig. 5.
As can be seen from fig. 5, the lower the melt viscosity, the larger the size of the inclusions, and the faster the sedimentation rate. For example, when the melt viscosity is 0.007Pa.s and the size of the inclusions is 40 μm, the sedimentation rate is 1.47X 10-4m.s-1. During electron beam refining, high density inclusions can be sufficiently settled in the melt, 40 μm of high density inclusions move in the melt for a distance of 88.2mm when the refining time is 10min, and the distance of the settlement of the inclusions increases as the refining time increases. When the depth of the molten pool is less than the sediment distance of the inclusions, the inclusions can be captured by the skull layer at the bottom of the molten pool and then retained in the skull layer. After full sedimentation, high-density inclusions in the alloy are enriched in the solidified shell layer, and the high-purity alloy cast ingot can be obtained by pouring the residual alloy melt into a solidification crucible.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (7)
1. A method for synchronously removing high-density inclusions and low-density inclusions in a high-temperature alloy is characterized in that in-situ dissolution and removal of small-size low-density and high-density inclusions in a melt are realized by using a local large superheated environment in an electron beam refining process, in-situ decomposition and removal of large-size low-density inclusions on the surface are realized by using a high-energy electron beam bombardment effect, and capture and removal of large-size high-density inclusions are realized by using a capture effect of a condensation shell at the bottom of the melt, so that low-density inclusions and high-density inclusions in the high-temperature alloy are completely removed;
the method comprises the following steps:
s1, pretreatment of the high-temperature alloy raw material:
s11, the raw material is DD406 alloy containing different types of inclusions;
s12, processing the raw materials to a proper size, wherein the raw materials can be placed into a water-cooled copper crucible for refining;
s13, polishing the processed raw material, and removing ceramic adhesion, an oxidation layer, processing traces and the like on the surface to ensure that the alloy has no external pollutants;
s14, cleaning and drying the polished raw materials for later use;
s2, removing low-density and high-density inclusions in the high-temperature alloy by electron beam refining:
s21, cleaning the water-cooled copper crucible for electron beam refining and solidification: polishing, wiping with alcohol and drying to ensure that the water-cooled copper crucible is clean and pollution-free;
s22, cleaning pollutants on the furnace body and the furnace wall of the electron beam melting furnace, and avoiding the introduction of foreign impurities in the refining process;
s23, placing the pretreated raw material in a water-cooled copper crucible for refining, and closing a furnace door of the electron beam melting furnace after the raw material is determined to be ready and the furnace body is cleaned;
s24, opening the electron beam refining equipment, pumping the electron beam melting furnace and the electron gun body to a target vacuum state, and preheating the equipment after reaching the target vacuum degree;
s25, starting high pressure after preheating is finished, slowly increasing the beam current of the electron gun on the left side to 600mA after the high pressure is stabilized, and uniformly scanning and melting the raw materials in the water-cooled copper crucible for refining;
s26, after the raw materials are completely melted, refining the raw materials for 10 min;
s27, carrying out melt overheating treatment on the refined raw material;
s28, after the melt is subjected to overheating treatment, enriching large-size low-density inclusions in a final solidification region on the surface of the cast ingot;
s29, performing high-temperature pyrolysis on the large-size low-density inclusion in the final solidification region until the inclusion is completely decomposed, and fully settling the large-size high-density inclusion to the bottom of the melt so as to be captured by a solidified shell;
s210, after refining is finished, instantly adjusting the beam current of the electron gun on the left side to 0mA, and simultaneously starting a melting crucible dumping mechanism to enable the refined melt to flow into a water-cooled copper crucible for solidification, wherein a skull in the water-cooled copper crucible for melting is reserved in an original crucible;
s211, uniformly scanning the high-temperature alloy melt in the water-cooled copper crucible for solidification through the right-side electron gun, so that the surface of the melt in the water-cooled copper crucible for solidification is uniform;
s212, closing the high pressure of the electron gun, increasing the beam current of the two electron guns to 60-120 mA to enable the high pressure value to be 0, and then closing the electron gun to enable the cast ingot to be fully solidified and cooled in a water-cooled copper crucible for solidification;
s213, taking out the DD406 alloy ingot after electron beam refining to obtain the DD406 high-temperature alloy ingot with low density and high density and extremely low inclusion content.
2. The method for synchronously removing the high-density inclusions and the low-density inclusions in the high-temperature alloy according to claim 1, wherein the specific steps of the step S14 are as follows:
and ultrasonically cleaning the polished DD406 alloy raw material by using deionized water and alcohol respectively, cleaning for three times by using the deionized water and the ultrasonic, placing the alloy into a drying box after cleaning, and drying at 30 ℃ for electron beam refining.
3. The method for synchronously removing the high-density inclusions and the low-density inclusions in the high-temperature alloy according to claim 1, wherein the specific steps of the step S26 are as follows:
after the alloy is completely melted, refining the alloy for 10min in an electron beam annular scanning mode, wherein the beam spot radius is kept at 20-25 mm, so that volatile gas impurities (O, N and the like) in the high-temperature alloy melt are fully removed, and meanwhile, large-size high-density inclusions gradually settle to the bottom of a molten pool and are captured by a skull.
4. The method for synchronously removing the high-density inclusions and the low-density inclusions in the high-temperature alloy according to claim 1, wherein the specific steps of the step S27 are as follows:
increasing the beam current of the electron beam on the left side to 800mA, and carrying out melt overheating treatment on the DD406 alloy for 20min, so that small-size low-density and high-density inclusions and ordered atomic groups in the DD406 alloy are fully dissolved.
5. The method for synchronously removing the high-density inclusions and the low-density inclusions in the high-temperature alloy according to claim 1, wherein the specific steps of the step S28 are as follows:
after the melt is subjected to overheating treatment, the beam current size is reduced to 500mA, electron beam refining parameters are controlled, the beam spot of the electron beam is enabled to move slowly from left to right, the beam current size is gradually reduced in a slow beam current reduction mode in the moving process of the beam spot, the radius of the beam spot is shrunk, the beam current size and the beam spot size are 0 at the same time when the beam spot moves to the edge area on the right side of the ingot, and enrichment of large-size low-density inclusions in the final solidification area on the surface of the ingot is achieved.
6. The method for synchronously removing the high-density inclusions and the low-density inclusions in the high-temperature alloy according to claim 1, wherein the specific steps of the step S29 are as follows:
adjusting the beam spot radius of the left electron gun to 5mm, gradually increasing the beam current to 600mA, and performing high-temperature pyrolysis on large-size low-density inclusions in a final solidification region by using an electron beam with high energy density; and adjusting the beam spot radius to 25mm after the inclusions are completely decomposed, and continuously refining the DD406 alloy in the water-cooled copper crucible by using an annular scanning path for 10min, so that the large-size high-density inclusions are fully settled to the bottom of the melt and then captured by a skull.
7. The method for synchronously removing the high-density inclusions and the low-density inclusions in the high-temperature alloy according to claim 1, wherein the specific steps of the step S211 are as follows:
increasing the beam current of the right electron gun to 500-600 mA, adjusting the radius of the beam spot to 25mm, uniformly scanning the alloy melt in the water-cooled copper crucible for solidification in an annular path to ensure that the surface of the melt in the water-cooled copper crucible for solidification is uniform, and then reducing the beam current of the right electron gun to 0 mA.
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