Recovery method of titanium alloy powder for additive manufacturing

Abstract

The invention discloses a recovery method of titanium alloy powder for additive manufacturing, and relates to the technical field of titanium alloy materials, the recovery method comprises the following steps: step 1, sheath material selection and processing: carbon steel with good welding performance is preferably selected as a sheath material; the size of the sheath is designed according to the actual ingot shape condition; 2, selecting raw materials, namely mixing titanium alloy spherical powder and micron-sized titanium alloy powder with the granularity of 15-300 mu m and the same brand, and performing an HIP + VAR process to obtain a titanium alloy cast ingot with more uniform material components and smaller element content range; a conventional titanium alloy powder hot isostatic pressing process needs a high treatment temperature which is generally between 930 DEG C and 1050 DEG C, the density of a blank after hot pressing is required to be close to 100%, according to the method, the material hot isostatic pressing treatment temperature is required to be 600 DEG C to 650 DEG C, an electrode blank with certain strength meeting VAR smelting can be obtained, energy consumption is reduced, and meanwhile the requirement for the performance of hot isostatic pressing equipment is extremely low.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy materials, and in particular to a method for recovering titanium alloy powder for additive manufacturing. Background Art

[0002] In recent years, additive manufacturing is one of the most cutting-edge and promising technological development directions in the field of intelligent manufacturing, and metal materials as printing consumables must develop in parallel with additive manufacturing. Titanium alloys have been widely used in aviation, aerospace, chemical industry, biomedicine and other fields due to their advantages such as high specific strength, good high and low temperature performance, and corrosion resistance, and the market demand prospects are very broad. Titanium alloy spherical powders used for additive manufacturing are mainly produced by gas atomization (GA) and plasma rotating electrode (PREP) methods. The particle size distribution of titanium alloy spherical powders prepared by these two processes is between 15 and 300 μm. The additive manufacturing process prefers powders with a size of 15-150 μm and good sphericity, without satellite powder and sequins, while low-quality metal powders with large size (coarse powder) and poor sphericity currently have no suitable application market and recycling process, resulting in excessive market backlogs, most of which are used in traditional industries such as metallurgical additives and fireworks.

[0003] Patent application number CN202111200996.7 reports a low-cost recycling method for titanium alloy spherical coarse powder. Fill the titanium alloy spherical coarse powder into a ceramic tube or a titanium alloy thin-walled tube, knock or vibrate it to make it dense, and then put it vertically into a vacuum sintering furnace and keep it at 1000-1050°C for 2-6 hours. After cooling, take it out of the furnace, remove the ceramic tube, and process it into GA electrode rods as needed. This patent is limited to the recycling and processing of low-oxygen titanium alloy powder. In addition to the target powder, the powder prepared after sintering and re-atomization (GA) also produces a considerable proportion of coarse powder. This type of coarse powder is oxygenated at 200-400ppm, which is close to or exceeds the upper limit of oxygen content of 800-1000mmp required for atomization of titanium alloy rods. It can no longer be recycled for the second time through the "sintering-GA" process to prepare GA electrode rods. In addition, the rod blanks sintered by this process are small in size and have low recovery efficiency. It is not the preferred process for large-scale recovery of coarse powder.

[0004] Titanium alloy powders have high sphericity, yield strength, and large critical shear stress for the flow between particles, which hinders the deformation and flow of powders. The deformation of pressed powders at room temperature is small, and it is impossible to obtain a compact with a certain strength, and thus it cannot be directly recovered by vacuum consumable arc furnace smelting (VAR). However, under certain temperature conditions, by applying isostatic pressure, titanium alloy spherical powders can be "diffusion-connected" to form electrode rods with a certain strength, and then directly recovered by VAR smelting.

[0005] This technology combines the application advantages of hot isostatic pressing (HIP) and vacuum melting (VAR) in titanium materials to design a process that is efficient, clean, low in oxygen content, and can recycle a large amount of titanium alloy coarse powder. Titanium alloy powder is used to prepare electrode rods through isostatic pressing, and multiple electrode rods are assembled and welded as consumable electrodes, and then smelted into titanium alloy ingots of corresponding grades. The titanium alloy ingots prepared by this method avoid the risk of introducing high-density inclusions such as tungsten and molybdenum due to the use of hydraulic presses and argon arc welding equipment; using this process, only one VAR smelting is required to obtain titanium ingots with small element content and uniform composition, which minimizes oxygen content increase. At the same time, large-sized ingots (about 1 meter in diameter) can be obtained. Titanium alloy ingots have increased the application field of high value-added titanium products; in addition, compared with the titanium ingots prepared by the traditional method of sponge titanium, the yield rate is higher, and the yield rate is about 99% without sawing the riser. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for recycling titanium alloy powder for additive manufacturing, so as to solve the problem of efficient, clean and large-scale recycling of titanium alloy coarse powder, improve the material recovery rate, and obtain titanium alloy ingots with low oxygen and extremely small composition difference.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for recycling titanium alloy powder for additive manufacturing, comprising the following steps:

[0008] Step 1: Sheath material selection and processing: The sheath material is preferably carbon steel with good welding performance; the sheath size is designed according to the actual ingot shape;

[0009] Step 2: Raw material selection: spherical powder of titanium alloy of the same grade with a particle size of 15-300 μm;

[0010] Step 3: Powder processing: Use a 300mm sieve to screen the powder to remove inclusions. After screening, mix the titanium alloy powder through a double cone or V-shaped mixer to ensure that titanium alloy powders of the same brand with different batches and particle sizes are mixed evenly. The mixing process requirements are as follows: evacuate to below 10Pa, fill with argon to make the mixer pressure reach 1~5ⅹ104Pa, pour the powder in the material tank into the mixer, and fill with Ar to positive pressure;

[0011] Step 4: Powder filling and degassing: Powder filling and vibration are carried out in the atmosphere or vacuum conditions; after powder filling, degassing, vibration and sealing are carried out under the condition of vacuum degree not greater than 5×10-1Pa, and the powder vibration density is not less than 2.5g / cm 3 ;

[0012] Step 5: HIP treatment: Place the powder bag as a whole in a hot isostatic pressing furnace, evacuate the air and press it, keep the pressure at 90-110MPa, the temperature at 600-650℃, and keep it at this temperature for 1-2h;

[0013] Step 6: Remove the sheath: Use machining or pickling to remove the iron sheath and a certain thickness of diffusion material to ensure that the surface of the electrode rod is clean after the sheath is removed, without foreign matter or oil stains;

[0014] Step 7: Electrode preparation: multiple electrode rods of the same size are welded end to end as electrode units to form a whole cylindrical consumable electrode;

[0015] Step 8: Vacuum melting: The prepared cylindrical electrode is subjected to VAR melting, and the melting process parameters are: welding vacuum degree ≤5.0Pa, leakage rate ≤1.0Pa / min, melting current 15~25KA, and melting voltage 30~35V.

[0016] Preferably, according to step one, the general design specification of the sheath is φ500~1000×800~2000mm, and heat treatment is required after the sheath is welded.

[0017] Preferably, according to step three, the mixer speed is 6-12 r / min, and the mixing time is 0.5-1 h; after the mixing is completed, the gas in the mixer is discharged to achieve internal and external pressure balance, and the valve is opened to collect the powder.

[0018] Preferably, according to step 4, the compaction process conditions are as follows: the motor vibration frequency is 10-20 Hz, and the vibration is continued for 5 to 10 minutes to ensure that the powder does not fall off.

[0019] Preferably, according to step five, the density requirement after HIP is not less than 90%, and the sheath has no cracks, air leakage, etc.

[0020] Preferably, according to step seven, the in-furnace welding process parameters are: welding vacuum degree ≤5.0Pa, gas leakage rate ≤1.0Pa / min, and welding current 3-10KA.

[0021] Preferably, according to step eight, a titanium ingot with uniform composition can be obtained through one VAR smelting.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] After the micron-grade titanium alloy powder of the present invention is mixed, a titanium alloy ingot with more uniform material composition and smaller element content range can be obtained through HIP+VAR process;

[0024] Conventional titanium alloy powder hot isostatic pressing process requires a relatively high processing temperature, generally between 930 and 1050°C, and requires the density of the blank after hot pressing to be close to 100%. This method requires the material hot isostatic pressing processing temperature to be 600-650°C to obtain a certain strength to meet the requirements of VAR smelting electrode blanks, which reduces energy consumption and has extremely low requirements on the performance of hot isostatic pressing equipment;

[0025] The process is simple and can be recycled in large quantities, with a recycling rate of up to 99%, and large-sized titanium alloy ingots can be obtained, which increases the application areas of high value-added titanium products. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of titanium alloy powder recovery according to the present invention. DETAILED DESCRIPTION

[0027] See also Figure 1 , the present invention provides a technical solution:

[0028] Embodiment 1:

[0029] A method for recycling titanium alloy powder for additive manufacturing comprises the following steps:

[0030] Step 1: Sheath material selection and processing: The sheath material is preferably carbon steel with good welding performance; the sheath size is designed according to the actual ingot shape;

[0031] Step 2: Raw material selection: spherical powder of titanium alloy of the same grade with a particle size of 15-300 μm;

[0032] Step 3: Powder processing: Use a 300mm sieve to screen the powder to remove inclusions. After screening, mix the titanium alloy powder through a double cone or V-shaped mixer to ensure that titanium alloy powders of the same brand with different batches and particle sizes are mixed evenly. The mixing process requirements are as follows: evacuate to below 10Pa, fill with argon to make the mixer pressure reach 1~5ⅹ104Pa, pour the powder in the material tank into the mixer, and fill with Ar to positive pressure;

[0033] Step 4: Powder filling and degassing: Powder filling and vibration are carried out in the atmosphere or vacuum conditions; after powder filling, degassing, vibration and sealing are carried out under the condition of vacuum degree not greater than 5×10-1Pa, and the powder vibration density is not less than 2.5g / cm 3 ;

[0034] Step 5: HIP treatment: Place the powder bag as a whole in a hot isostatic pressing furnace, evacuate the air and press it, keep the pressure at 90-110MPa, the temperature at 600-650℃, and keep it at this temperature for 1-2h;

[0035] Step 6: Remove the sheath: Use machining or pickling to remove the iron sheath and a certain thickness of diffusion material to ensure that the surface of the electrode rod is clean after the sheath is removed, without foreign matter or oil stains;

[0036] Step 7: Electrode preparation: multiple electrode rods of the same size are welded end to end as electrode units to form a whole cylindrical consumable electrode;

[0037] Step 8: Vacuum melting: The prepared cylindrical electrode is subjected to VAR melting, and the melting process parameters are: welding vacuum degree ≤5.0Pa, leakage rate ≤1.0Pa / min, melting current 15~25KA, and melting voltage 30~35V.

[0038] According to step one, the general design specification of the sleeve is φ500~1000×800~2000mm, and heat treatment is required after the sleeve welding is completed; according to step three, the mixer speed is 6~12r / min, and the mixing time is 0.5~1h; after mixing, the gas in the mixer is discharged to achieve internal and external pressure balance, and the valve is opened to collect the powder; according to step four, the compaction process conditions are as follows: the motor vibration frequency is 10-20HZ, and the continuous vibration is 5~10min to ensure that the powder does not fall; according to step five, the density requirement after HIP is not less than 90%, and the sleeve has no cracks, leakage, etc.; according to step seven, the furnace welding process parameters: welding vacuum ≤5.0Pa, leakage rate ≤1.0Pa / min, welding current 3~10KA; according to step eight, after one VAR smelting, a titanium ingot with uniform composition can be obtained.

[0039] Embodiment 2:

[0040] Step 1: Sheath material selection and processing: The sheath material is low-carbon steel 20# steel with good welding performance. According to the specifications of the VAR smelting furnace water-cooled copper crystallizer, a sheet iron sheath with a size of φ670×1500mm is made and heat-treated. After the heat treatment is completed, alcohol cleaning is performed to ensure that there are no impurities or foreign matter on the inner wall;

[0041] Step 2: Raw material selection: This time, Ti6Al4V spherical powders of 53-106μm, 53-250μm and >180μm from different batches were selected. The weighted value of the O element content of the selected powder was calculated to be 0.0805%, which can represent the actual content of the O element in the powder after mixing. The powder was sieved with a 300mm sieve. After the sieving was completed, the Ti6Al4V titanium alloy powders from different batches were evenly divided into several material tanks by weight to ensure that the batch and weight of the titanium alloy powder in a single material tank were the same;

[0042] Step 3: Powder mixing: evacuate the double cone mixer to below 10Pa, fill it with argon to make the mixer pressure reach 1ⅹ104Pa, open the valve of the material tank, pour the powder into the mixer, after all the powder is poured into the mixer, close the valve of the mixer, cover it with a blind cover, and fill it with Ar to positive pressure; the mixer speed is 10-12r / min, the mixing time is 0.5-1h, after the mixing is completed, the gas in the mixer is discharged to the internal pressure difference of 0Mpa, to achieve internal and external pressure balance, open the valves of the mixer and the material tank to collect the powder;

[0043] Step 4: Powder filling of the package: Fill the selected Ti6Al4V powder into the package cleaned in step 1, and vibrate the powder. The powder filling and vibrating are carried out under atmospheric conditions. The vibrating process conditions are as follows: the motor vibration frequency is 15-20HZ, and the vibration is continued for 10-15min until the powder does not fall off;

[0044] Step 5: Degassing: evacuate the entire tooling containing the Ti6Al4V powder package and weld and seal it. The vacuum degree in the package is not greater than 0.5Pa;

[0045] Step 6: HIP treatment: Place the entire package containing Ti6Al4V powder in a hot isostatic pressing furnace, evacuate the air and press it, keep the pressure at 100MPa, the temperature at 600℃, and take it out of the furnace after holding it for 1h, and obtain a titanium alloy electrode rod with a density of 91%;

[0046] Step 7: Remove the jacket: Remove the outer iron sheet of the titanium alloy rod by mechanical processing. After removing the jacket, the surface of the electrode rod is clean and free of foreign matter and oil stains;

[0047] Step 8: assembling and welding the electrode rods obtained in step 7 end to end as electrode units; the welding process parameters in the furnace are: welding vacuum degree ≤5.0Pa, gas leakage rate ≤1.0Pa / min, welding current 3-10KA;

[0048] Step 9: After the furnace welding is completed, the whole Ti6Al4V consumable electrode obtained in step 8 is melted; the melting process parameters are: welding vacuum degree ≤5.0Pa, gas leakage rate ≤1.0Pa / min, melting current 18~23KA, melting voltage 32~35V;

[0049] Step 10: After one vacuum consumable arc furnace smelting, a Ti6Al4V ingot with a diameter of φ720 mm can be obtained.

[0050] Under this process, the composition of the Ti6Al4V titanium alloy ingot is as follows:

[0051]

[0052] The ingot obtained in this way has a more uniform composition and extremely low oxygen content.

Claims

1. A method for recycling titanium alloy powder for additive manufacturing, characterized in that: The following steps are involved: Step 1: Sheath material selection and processing: The sheath material is preferably carbon steel with good welding performance; the sheath size is designed according to the actual ingot shape; Step 2: Raw material selection: spherical powder of titanium alloy of the same grade with a particle size of 15-300 μm; Step 3: Powder processing: Use a 300mm sieve to screen the powder to remove inclusions. After screening, mix the titanium alloy powder through a double cone or V-shaped mixer to ensure that titanium alloy powders of the same brand with different batches and particle sizes are mixed evenly. The mixing process requirements are as follows: evacuate to below 10Pa, fill with argon to make the mixer pressure reach 1~5ⅹ104Pa, pour the powder in the material tank into the mixer, and fill with Ar to positive pressure; Step 4: Powder filling and degassing: Powder filling and vibration are carried out in the atmosphere or vacuum conditions; after powder filling, degassing, vibration and sealing are carried out under the condition of vacuum degree not greater than 5×10-1Pa, and the powder vibration density is not less than 2.5g / cm 3 ; Step 5: HIP treatment: Place the powder bag as a whole in a hot isostatic pressing furnace, evacuate the air and press it, keep the pressure at 90-110MPa, the temperature at 600-650℃, and keep it at this temperature for 1-2h; Step 6: Remove the sheath: Use machining or pickling to remove the iron sheath and a certain thickness of diffusion material to ensure that the surface of the electrode rod is clean after the sheath is removed, without foreign matter or oil stains; Step 7: Electrode preparation: multiple electrode rods of the same size are welded end to end as electrode units to form a whole cylindrical consumable electrode; Step 8: Vacuum melting: The prepared cylindrical electrode is subjected to VAR melting, and the melting process parameters are: welding vacuum degree ≤5.0Pa, leakage rate ≤1.0Pa / min, melting current 15~25KA, and melting voltage 30~35V.

2. The method for recycling titanium alloy powder for additive manufacturing according to claim 1, characterized in that: According to step 1, the general design specification of the sheath is φ500~1000×800~2000mm, and heat treatment is required after the sheath is welded.

3. The method for recycling titanium alloy powder for additive manufacturing according to claim 1, characterized in that: According to step three, the mixer speed is 6-12 r / min, and the mixing time is 0.5-1 h; after the mixing is completed, the gas in the mixer is discharged to achieve internal and external pressure balance, and the valve is opened to collect the powder.

4. The method for recycling titanium alloy powder for additive manufacturing according to claim 1, characterized in that: According to step 4, the compaction process conditions are as follows: the motor vibration frequency is 10-20HZ, and the vibration is continued for 5-10 minutes to ensure that the powder does not fall off.

5. The method for recycling titanium alloy powder for additive manufacturing according to claim 1, characterized in that: According to step five, after HIP, the density requirement is not less than 90%, and the sheath has no cracks, air leakage, etc.

6. The method for recycling titanium alloy powder for additive manufacturing according to claim 1, characterized in that: According to step seven, the welding process parameters in the furnace are: welding vacuum degree ≤5.0Pa, gas leakage rate ≤1.0Pa / min, and welding current 3-10KA.

7. The method for recycling titanium alloy powder for additive manufacturing according to claim 1, characterized in that: According to step eight, a titanium ingot with uniform composition can be obtained through one VAR smelting.

Images