A method for preparing a complex precision structure piece of molybdenum alloy by using an additive manufacturing technology

Abstract

The application discloses a method for preparing a molybdenum alloy complex precision structural member by using an additive manufacturing technology, and mainly comprises the following steps: Mo powder and TiC powder are weighed according to the mass percentage of Mo 50-70% and TiC 30-50%, 3D printing powder is prepared by a mixing-pressing-sintering-plasma rotating electrode atomization method, and then the molybdenum alloy complex precision structural member is prepared by using an electron beam melting forming method; then, the molybdenum alloy complex precision structural member is subjected to heat treatment, so as to eliminate residual thermal stress in the process of condensing from liquid drops to solid state of the powder in the electron beam melting forming process; finally, the molybdenum alloy complex precision structural member after the heat treatment is subjected to finishing to the product size, and then is subjected to inspection, cleaning and packaging. The molybdenum alloy complex precision structural member prepared by using the method has no cracks in the inside and the edge, has low O and N contents, and has good wear resistance.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, specifically relating to a method for preparing complex and precision molybdenum alloy structural parts using additive manufacturing technology. Background Technology

[0002] Refractory metal molybdenum is widely used in complex and precision structural components in industries such as aviation and aerospace due to its excellent properties, including high melting point, low coefficient of thermal expansion, good thermal conductivity, and resistance to most acid and alkali corrosion.

[0003] Currently, complex and precision molybdenum alloy structural parts are generally prepared by powder metallurgy. The density and structural properties of the prepared molybdenum alloy structural parts can meet industrial requirements. However, due to the low ductile-brittle transition temperature (DBTT) and poor plasticity of molybdenum alloys, their machinability is poor, which can easily lead to machining cracks and fractures when processing complex and precision structural parts. Moreover, the molybdenum alloy products prepared by traditional powder metallurgy methods have a certain degree of porosity. During processing, O2 and N2 in the air can easily penetrate and contaminate the molybdenum products, leading to grain boundary segregation and defects such as cracks or fissures. At the same time, traditional powder metallurgy processes can reduce the wear resistance of molybdenum alloys.

[0004] Additive manufacturing technology can directly form and manufacture complex and precision structural parts, effectively solving the problems of high processing difficulty of molybdenum alloys and avoiding pollution from oxygen and nitrogen introduced during processing, as well as cracks and fractures that occur during processing. At the same time, the tribological properties of molybdenum alloy structural parts prepared by additive manufacturing technology are also significantly improved. Therefore, the fabrication of crack-free, structurally complex precision molybdenum alloy structural parts using additive manufacturing technology has become a major means to overcome the difficulties in processing, low production efficiency, and poor wear resistance of complex precision structural parts used in aerospace. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing complex precision molybdenum alloy structural parts using additive manufacturing technology. The complex precision molybdenum alloy structural parts prepared by the method of this invention have no cracks inside and at the edges, low O and N content, and good wear resistance.

[0006] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0007] A method for fabricating complex precision structural parts of molybdenum alloy using additive manufacturing technology mainly includes the following steps:

[0008] S1. Preparation of 3D printing powder

[0009] S11. Weigh out Mo powder and TiC powder according to the mass percentages of Mo 50-70% and TiC 30-50%, and then mechanically mix the weighed Mo powder and TiC powder evenly to obtain a mixed powder.

[0010] S12. The mixed powder is placed in a flexible mold and subjected to cold isostatic pressing to obtain a powder blank;

[0011] S13. Sinter the powder blank at a temperature of 2050℃~2450℃ and a holding time of 2~6h to obtain a sintered blank with a density ≥95%.

[0012] S14. The sintered blank is placed in a plasma rotating electrode atomization device for atomization and powder preparation to obtain 3D printing powder. The 3D printing powder prepared by plasma rotating electrode atomization method has no agglomeration phenomenon, has a high degree of alloying, and the powder metallurgy process of molybdenum alloy itself provides convenience for the preparation of 3D printing powder by plasma rotating electrode atomization method.

[0013] S2. Fabrication of complex and precision molybdenum alloy structural parts using electron beam melting and forming method;

[0014] S3. Heat treatment is performed on complex and precision molybdenum alloy structural parts. The heat treatment temperature is 1550℃~1850℃ and the holding time is 2h~6h. Heat treatment can eliminate the residual thermal stress during the condensation of powder from droplets to solid during the electron beam melting and forming process.

[0015] S4. After heat treatment, the complex precision structural parts of the molybdenum alloy are precision machined to the product dimensions, and then inspected, cleaned and packaged.

[0016] Furthermore, in step S11, the Fehling particle size of Mo powder is 2.0–4.0 μm, and the Fehling particle size of TiC powder is 1.2–2.5 μm.

[0017] Furthermore, in step S12, the size of the flexible mold is Φ100×1000mm; the cold isostatic pressing pressure is 200~320Mpa, and the holding time is 10~30min.

[0018] Furthermore, in step S14, when using a plasma rotating electrode atomization device for atomization powder production, the plasma power is 35KW~50KW, the argon flow rate is 30~50L / h, and during operation, the sintered blank rotates on the rotating bed at a speed of 120~200r / min. The plasma flame must be directly facing the rotating sintered blank, with a distance of 1mm~6mm.

[0019] Furthermore, in step S2, the specific steps for preparing complex and precision molybdenum alloy structural parts using electron beam melting are as follows:

[0020] S21. Construct a three-dimensional model of a complex and precise molybdenum alloy structural component, and slice and layer the established three-dimensional CAD model according to the set powder layer thickness.

[0021] S22. The layered processing information is imported into the electron beam melting molding equipment. The high-energy electron beam is used to scan the 3D printing powder laid on the substrate of the electron beam melting molding equipment in layers and melt it at high temperature to obtain complex and precise molybdenum alloy structural parts.

[0022] Furthermore, the electron beam melting process has a power of 500–1200 W, a scanning speed of 12–20 mm / s, a powder feeding speed of 100–150 g / min, and a substrate thickness of 10 mm–30 mm.

[0023] Furthermore, in step S22, before laying the 3D printing powder, the substrate needs to be preheated. The preheating power is 200-400W, and the scanning speed is 6-12mm / s. The purpose of preheating is twofold: first, to clean the titanium alloy substrate and remove oil and impurities; second, to increase the temperature of the titanium alloy substrate, reduce the temperature difference between the titanium alloy substrate and the molten Mo-TiC alloy, reduce thermal stress, and reduce the generation of cracks during the 3D printing process.

[0024] Currently, the fabrication of pure molybdenum and molybdenum alloy structural parts suffers from numerous problems, including high melting point, high melt surface tension, severe spheroidization, and rapid solidification. These issues make them prone to cracking, fracture, and internal voids during 3D printing. Introducing TiC into Mo can reduce the surface tension of the molten molybdenum droplets, mitigating spheroidization. Simultaneously, the addition of TiC forms a second phase with Mo and O, effectively reducing stress concentration during the transition from the molten to the solid state of the Mo-TiC alloy and slowing down the solidification rate, thus reducing the occurrence of cracks and fractures in the processed parts. Finally, the addition of TiC can improve the tribological properties of pure Mo products to some extent, thereby extending the service life of molybdenum alloy structural parts.

[0025] The beneficial effects of this invention are:

[0026] 1) This invention prepares 3D printing powder through mechanical mixing, sintering, and plasma rotating electrode atomization, and then uses electron beam melting to prepare complex precision molybdenum alloy structural parts. The resulting complex precision molybdenum alloy structural parts have no cracks inside or at the edges, low O and N content, and all meet the ASTM B387-361 standard. The friction coefficient is <0.5 (while the friction coefficient of complex precision molybdenum alloy structural parts prepared by conventional powder metallurgy methods is ≥0.5), which meets the high wear resistance requirements of the aerospace industry and lays the foundation for the application of molybdenum alloys in the aerospace field.

[0027] 2) The raw materials selected for preparing the 3D printing powder in this invention are Mo powder and TiC powder. By adding TiC powder, the following advantages are achieved: a) It can reduce the surface tension of the molten droplets after the molybdenum melts, thus weakening the spheroidization phenomenon; b) TiC can form a second phase with Mo and O, which can effectively reduce the stress concentration of the Mo-TiC alloy during the process from molten to solid state, slow down the solidification rate, and thus reduce the occurrence of cracks and fractures in the structural parts; c) It can improve the friction performance of pure molybdenum products to a certain extent, thereby improving the service life of complex and precision molybdenum alloy structural parts. Detailed Implementation

[0028] The present invention will now be described in further detail, but this should not be construed as limiting the invention in any way.

[0029] A method for fabricating complex precision molybdenum alloy structural parts using additive manufacturing technology mainly includes the following steps:

[0030] Step 1: Select Mo powder and TiC powder, with the following composition by mass percentage: Mo: 50%-70%, TiC: 30%-50%. The Fisher particle size of the Mo powder is 2.0-4.0 μm, and the Fisher particle size of the TiC is 1.2-2.5 μm.

[0031] Step 2: Use a vacuum vertical ball mill and high-purity molybdenum abrasive to mechanically mix Mo powder and TiC powder for 12-24 hours.

[0032] Step 3: Place the mixed powder in a flexible mold for cold isostatic pressing to obtain a powder blank. The cold isostatic pressing method is used, with a pressing pressure of 200-320 MPa and a holding time of 10-30 min.

[0033] Step 4: Sinter the powder blank using a vacuum sintering furnace at a temperature of 2050℃-2450℃ and a holding time of 2-6 hours to obtain a sintered blank with a density ≥95%. Roughly process the blank and set it aside for later use.

[0034] Step 5: Prepare 3D printing powder using plasma rotating electrode atomization method. Plasma power: 35KW-50KW, argon flow rate: 30-50L / h. During operation, the sintered blank rotates on the rotating bed at a speed of 120-200r / min. The plasma flame must be directly facing the rotating sintered blank at a distance of 1mm-6mm.

[0035] Step 6: Prepare complex and precision molybdenum alloy structural parts using electron beam melting and forming. Specific parameters for electron beam melting and forming: power 500-1200W, scanning speed 12-20mm / s, powder feeding speed 100-150g / min, and titanium alloy substrate thickness 10mm-30mm.

[0036] Step 7: Place the complex and precision molybdenum alloy structural parts in a vacuum furnace for heat treatment at a temperature of 1550℃~1850℃ for 2h~6h.

[0037] Step 8: After heat treatment, the complex precision structural parts of the molybdenum alloy are precision machined to the product dimensions, then inspected, and after passing the inspection, they are cleaned and packaged.

[0038] It should be noted that the size of the flexible mold used in step three of this invention is Φ100×1000mm. Based on this, the sintered blank obtained in step four is a sintered rod.

[0039] In step six, the specific method for preparing complex and precise molybdenum alloy structural parts using electron beam melting is as follows: A three-dimensional model of the complex and precise molybdenum alloy structural part is constructed; the established three-dimensional model is sliced ​​and layered according to the set powder layer thickness; the layering processing information is imported into the electron beam melting equipment; the substrate is preheated with a preheating power of 200–400 W and a scanning speed of 6–12 mm / s; a high-energy electron beam is used to perform layered scanning and high-temperature melting of the 3D printing powder laid flat on the substrate of the electron beam melting equipment, thereby obtaining the complex and precise molybdenum alloy structural part.

[0040] The following examples and comparative embodiments illustrate that the molybdenum alloy prepared by the technical solution of the present invention has the technical effect of being free from cracks and fissures, having normal O and N content, and excellent wear resistance.

[0041] Example 1

[0042] A method for fabricating molybdenum alloy high-temperature grating structural components using additive manufacturing technology mainly includes the following steps:

[0043] Step 1: Select Mo powder and TiC powder, and compose them by mass percentage as follows: Mo: 50%, TiC: 50%, where the Fisher particle size of the molybdenum powder is 2.0 μm and the Fisher particle size of the TiC is 1.2 μm.

[0044] Step 2: Mechanically mix Mo powder and TiC powder using a vacuum vertical ball mill and high-purity Mo abrasive. Mixing time: 12 hours.

[0045] Step 3: Place the mixed powder in a flexible mold for cold isostatic pressing to obtain a powder blank. The size of the flexible mold is Φ100*1000mm, the cold isostatic pressing pressure is 200Mpa, and the holding time is 10min.

[0046] Step 4: Sinter the powder blank using a vacuum sintering furnace at a temperature of 2050℃ for 6 hours. The resulting sintered blank has a density of 6.41 g / cm³. 3 Rough processing, ready for use;

[0047] Step 5: Prepare 3D printing powder using plasma rotating electrode atomization method. Plasma power: 35KW, argon flow rate: 30L / h. During operation, the sintered blank rotates on the rotating bed at a speed of 120r / min. The plasma flame must be directly facing the rotating sintered blank at a distance of 1mm.

[0048] Step 6: Prepare complex and precision molybdenum alloy structural parts using electron beam melting and forming method. Electron beam melting and forming method power: 500W, scanning speed: 12mm / s, powder feeding speed: 100g / min, titanium alloy substrate thickness: 10mm.

[0049] Step 7: Place the complex and precision molybdenum alloy structural parts in a vacuum furnace for heat treatment at a temperature of 1550℃ for 2 hours.

[0050] Step 8: After heat treatment, the Mo-TiC alloy product is precision machined to the product dimensions, then inspected for defects such as cracks and voids, and then cleaned and packaged.

[0051] After inspection and testing, no cracks or fissures were found inside or outside the product. The O content was 26 ppm, the N content was 4 ppm, and the coefficient of friction was 0.24, all of which met the requirements of ASTM B387-361 standard. This indicates that the method for preparing Mo-TiC alloy can achieve one-piece molding, effectively solving the problems of poor processing performance and easy cracking of Mo alloy products. It also significantly controls the content of O and N elements, while improving the friction and wear resistance of Mo alloy, meeting the high wear resistance requirements of the aerospace industry.

[0052] Example 2

[0053] A method for fabricating molybdenum alloy heating furnace support structure using additive manufacturing technology mainly includes the following steps:

[0054] Step 1: Select Mo powder and TiC powder, with the following composition by mass percentage: Mo: 70%, TiC: 30%. The Fisher particle size of the Mo powder is 4.0 μm, and the Fisher particle size of the TiC is 2.5 μm.

[0055] Step 2: Mechanically mix Mo powder and TiC powder using a vacuum vertical ball mill and high-purity Mo abrasive. Mixing time: 24 hours.

[0056] Step 3: Place the mixed powder in a flexible mold for cold isostatic pressing to obtain a powder blank. The size of the flexible mold is Φ100×1000mm, the cold isostatic pressing pressure is 320Mpa, and the holding time is 30min.

[0057] Step 4: Sinter the powder blank using a vacuum sintering furnace at a sintering temperature of 2450℃. The resulting sintered blank has a density of 7.46 g / cm³. 3 Rough processing, ready for use;

[0058] Step 5: Prepare 3D printing powder using plasma rotating electrode atomization method. Plasma power: 50KW, argon flow rate: 50L / h. During operation, the sintered blank rotates on the rotating bed at a speed of 200 rpm. The plasma flame must be directly facing the rotating sintered blank at a distance of 6mm.

[0059] Step 6: Prepare complex and precision molybdenum alloy structural parts using electron beam melting and forming method. Electron beam melting and forming method power: 1000W, scanning speed: 20mm / s, powder feeding speed: 150g / min, titanium alloy substrate thickness: 30mm.

[0060] Step 7: Place the complex and precision molybdenum alloy structural parts in a vacuum furnace for heat treatment at a temperature of 1850℃ for 6 hours.

[0061] Step 8: After heat treatment, the molybdenum alloy structural parts are precision machined to the product dimensions, then inspected for defects such as cracks and voids, and then cleaned and packaged.

[0062] After inspection and testing, the product prepared in this embodiment showed no cracks or fissures, both internally and externally. The O content was 24 ppm, the N content was 5 ppm, and the coefficient of friction was 0.28, all of which met the requirements of ASTM B387-361 standard. This indicates that the method can produce molybdenum alloy structural parts in one piece, effectively solving the problems of poor processing performance and easy cracking of Mo alloy products. It also significantly controls the content of O and N elements, while improving the friction and wear resistance of Mo alloy, meeting the high wear resistance requirements of the aerospace industry.

[0063] Comparative Example 1

[0064] A method for preparing a molybdenum alloy structural component mainly includes the following steps:

[0065] Step 1: Select Mo powder and TiC powder, with the following composition by mass percentage: Mo: 50%, TiC: 50%. The Fisher particle size of the Mo powder is 2.0 μm, and the Fisher particle size of the TiC is 1.2 μm.

[0066] Step 2: Mechanically mix Mo powder and TiC powder using a vacuum vertical ball mill and high-purity Mo abrasive. Mixing time: 12 hours.

[0067] Step 3: Place the mixed powder in a flexible mold for cold isostatic pressing to obtain a powder blank. The size of the flexible mold is Φ100×1000mm, the cold isostatic pressing pressure is 200Mpa, and the holding time is 10min.

[0068] Step 4: Sinter the powder blank using a vacuum sintering furnace at a sintering temperature of 2050℃. The resulting sintered blank has a density of 6.41 g / cm³. 3 Rough processing, ready for use;

[0069] Step 5: Forge the sintered billet. Before forging, heat it in a hydrogen atmosphere furnace at 1650℃ for 40 minutes, and then forge it to a size of Φ50.8*1350mm.

[0070] Step 6: Place the forged billet in a vacuum furnace for heat treatment at a temperature of 1550℃ for 2 hours.

[0071] Step 7: After heat treatment, the Mo-TiC alloy product is precision machined to the product dimensions, then inspected for defects such as cracks and voids, and then cleaned and packaged.

[0072] This comparative example is based on Example 1, but without the powder preparation and electron beam melting operations; all other processing steps are the same as in Example 1. Inspection and testing showed that the product prepared in this comparative example had no internal or external cracks or other defects. The O content was 36 ppm, the N content was 7 ppm, and the coefficient of friction was 0.54, all meeting the requirements of ASTM B387-361 standards. This indicates that although traditional powder metallurgy methods for preparing Mo-TiC alloys can ensure the absence of internal and external cracks through process control, the internal O and N contents are higher than those of products prepared using additive manufacturing technology. Simultaneously, the coefficient of friction is also higher (lower O and N contents make the product less prone to cracking during processing, while a lower coefficient of friction results in better wear resistance). This demonstrates that Mo-TiC alloys prepared using additive manufacturing technology are easier to process and have better wear resistance than those prepared using traditional powder metallurgy methods.

[0073] Comparative Example 2

[0074] The only difference between Comparative Example 2 and Example 2 is that Comparative Example 2 does not include step seven.

[0075] Inspection and testing revealed microcracks at the edges of the product prepared in this comparative example. The O content was 24 ppm, the N content was 5 ppm, and the coefficient of friction was 0.28, all meeting the requirements of ASTM B387-361 standard. The presence of microcracks at the product edges indicates that without heat treatment, the thermal stress generated during electron beam melting and forming cannot be released, leading to cracking at the workpiece edges. However, the O and N content and wear resistance were unaffected.

[0076] Unless otherwise specified in the above embodiments and comparative examples, the conditions were performed under standard conditions or conditions recommended by the manufacturer. All reagents and instruments used, unless otherwise specified, were commercially available products.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the specific implementation of the present invention with reference to the above embodiments. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the pending claims.

Claims

1. A method for fabricating complex precision structural parts of molybdenum alloy using additive manufacturing technology, characterized in that, The main steps include the following: S1. Preparation of 3D printing powder S11. Weigh out Mo powder and TiC powder according to the mass percentages of Mo 50-70% and TiC 30-50%, and then mechanically mix the weighed Mo powder and TiC powder evenly to obtain a mixed powder. S12. The mixed powder is placed in a flexible mold and subjected to cold isostatic pressing to obtain a powder blank; S13. Sinter the powder blank at a temperature of 2050℃~2450℃ and a holding time of 2~6h to obtain a sintered blank with a density ≥95%. S14. Place the sintered blank into a plasma rotating electrode atomizing device for atomization and powder preparation to obtain 3D printing powder. S2. Fabrication of complex and precision molybdenum alloy structural parts using electron beam melting and forming method; S3. Heat treatment is performed on complex and precision molybdenum alloy structural parts. The heat treatment temperature is 1550℃~1850℃ and the holding time is 2h~6h. S4. After heat treatment, the complex precision structural parts of molybdenum alloy are precision machined to the product dimensions. After passing the inspection, they are cleaned and packaged.

2. The method for preparing complex precision structural parts of molybdenum alloy using additive manufacturing technology according to claim 1, characterized in that, In step S11, the Fehling particle size of Mo powder is 2.0–4.0 μm, and the Fehling particle size of TiC powder is 1.2–2.5 μm.

3. The method for preparing complex precision structural parts of molybdenum alloy using additive manufacturing technology according to claim 1, characterized in that, In step S12, the size of the flexible mold is Φ100×1000mm; the cold isostatic pressing pressure is 200~320Mpa, and the holding time is 10~30min.

4. The method for preparing complex precision structural parts of molybdenum alloy using additive manufacturing technology according to claim 1, characterized in that, In step S14, when using a plasma rotating electrode atomization device for atomization powder production, the plasma power is 35KW~50KW, the argon flow rate is 30~50L / h, and during operation, the sintered blank rotates on the rotating bed at a speed of 120~200r / min. The plasma flame must be directly facing the rotating sintered blank, with a distance of 1mm~6mm.

5. A method for preparing complex precision molybdenum alloy structural parts using additive manufacturing technology according to claim 1, characterized in that, In step S2, the specific steps for preparing complex and precise molybdenum alloy structural parts using electron beam melting are as follows: S21. Construct a three-dimensional model of a complex and precise molybdenum alloy structural component, and slice and layer the established three-dimensional model according to the set powder layer thickness. S22. The layered processing information is imported into the electron beam melting molding equipment. The high-energy electron beam is used to scan the 3D printing powder laid on the substrate of the electron beam melting molding equipment in layers and melt it at high temperature to obtain complex and precise molybdenum alloy structural parts.

6. A method for preparing complex precision molybdenum alloy structural parts using additive manufacturing technology according to claim 5, characterized in that, The electron beam melting process has a power of 500–1200W, a scanning speed of 12–20 mm / s, a powder feeding speed of 100–150 g / min, and a substrate thickness of 10 mm–30 mm.

7. A method for preparing complex precision molybdenum alloy structural parts using additive manufacturing technology according to claim 5, characterized in that, In step S22, before laying the 3D printing powder, the substrate needs to be preheated. The preheating power is 200-400W and the scanning speed is 6-12mm / s.