CN106694890A - Ball-milling-high-pressure torsion method for circulatory solidification of waste titanium cuttings - Google Patents

Abstract

The present invention proposes a ball mill-high-pressure torsion method for recycling and solidifying titanium waste chips, which includes the following steps: (1) titanium chip recovery pretreatment: cleaning titanium chips to remove oil and impurities; (2) ball milling of titanium chips: (1) ball milling the pretreated titanium chips; (3) room temperature and high pressure torsion curing of the titanium chips: performing room temperature and high pressure torsion curing on the titanium chips after the ball milling in step (2). In this method, the micron-level refinement of the outer dimensions of titanium chips is firstly achieved through a ball milling process. The oxides on the chip surface are fully broken and dispersed under the collision and grinding of steel balls, and ultra-fine structures are also formed inside the chips. Then, at room temperature, the high-pressure torsion technology is used to further refine the grains through the composite action of axial ultra-high pressure and transverse strong shear, realize the nanostructure of the chip solidification process, and realize the full densification of remanufactured titanium materials.

Description

Ball milling-high pressure torsion method for circular solidification of waste titanium chips

technical field

The invention relates to metal material processing technology, in particular to a ball milling-high pressure torsion method for circularly solidifying titanium waste chips.

Background technique

The traditional technology for waste metal swarf recycling is high temperature melting and casting. However, high-temperature melting and casting consumes a lot of energy, pollutes heavily, and has low efficiency. The cast structure has coarse grains and poor mechanical properties. In order to avoid high temperature melting and casting, solid phase recycling technology has been developed. Through the literature search of the prior art, it is found that the application of equal channel angular pressing (ECAP) technology to the processing of metal chips can refine the grains, improve the microstructure of remanufactured materials, and improve the mechanical properties. . Lapovok et al. published the article "Multicomponent materials from machining chips compacted by equal-channel angular pressing" on pages 1193-1204 of Volume 49 of "Journal of Materials Science" in 2014, reporting that Through the mutual mixing of aluminum chips and magnesium chips, multi-component alloy materials are regenerated by ECAP; Luo et al published "Recycling of titanium machiningchips by severe plastic deformation consolidation ( Severe Plastic Deformation Solid State Cycle of Titanium Cuttings)" proposes to recycle discarded grade 2 titanium (ASTM Grade 2) cuttings and re-manufacture bulk materials by ECAP technology.

High-pressure torsion (HPT) is another severe plastic deformation technique for preparing bulk nano-metal materials. Valiev and Langdon published "The art and science of tailoring materials by nano-structuring for advanced properties using SPD techniques" on pages 677-691 of Volume 12 of "Advanced Engineering Materials" in 2010. The Science and Technology of Chemistry) pointed out that HPT technology is very effective for the preparation of nanocrystals. For example, HPT technology is used to rotate pure copper for 5 passes at a pressure of 6GPa and room temperature to obtain an ultra-fine microstructure of less than 100nm. In contrast, if pure copper is treated with ECAP technology, the microstructure is only refined to ~200nm after 12 passes. Obviously, the refinement efficiency of HPT technology is higher than that of ECAP technology. Moreover, HPT can realize the plastic processing of materials at low temperature or room temperature under the action of ultra-high pressure. For example, the plastic forming ability of high-strength hexagonal close-packed titanium is far inferior to that of copper, and it is difficult to plastically deform at room temperature. Zhao et al. published the article "Microstructure and properties of pure titanium processed by equal-channel angular pressing atroom temperature" on "Scripta Materialia" 2008, Volume 59, pages 542-545 , at room temperature with ECAP deformation treatment of titanium once. However, in order to reduce the deformation resistance, the angle of the ECAP die was increased from 90 degrees to 120 degrees, and the extrusion rate was also low (0.5mm/s), which reduced the strain accumulation rate and processing efficiency of ECAP. In comparison, HPT technology can efficiently realize room temperature processing of titanium materials.

Ball milling (BM for short) is a severe plastic deformation technique widely used in the preparation of ultrafine powder materials. The retrieval of prior art documents found that Mahboubi Soufiani et al. published "Formation mechanism and characterization of nanostructured Ti6Al4V alloy prepared by mechanical alloying" on "Materials and Design" 2012, volume 37, pages 152-160 Formation Mechanism and Characterization)" reported that Ti-6Al-4V alloy materials with nanoscale (less than 100nm) were synthesized by BM technology using micron powders of titanium, aluminum and vanadium as raw materials. In addition, Zadra published the article "Mechanicalalloying of titanium" on "Materials Science and Engineering A" 2013, Volume 583, pages 105-113. The initial raw material is Ti powder with an average particle size of less than 150 μm. treatment to obtain ultra-fine powder of pure titanium less than 25 μm, and successfully obtain bulk titanium material through spark plasma sintering.

The recycling and remanufacturing of waste metal resources is one of the keys to sustainable development. Titanium is a metal resource with high smelting costs. It has excellent biocompatibility, good corrosion resistance, and suitable mechanical properties. It is an important material for manufacturing medical devices, artificial joints, and large energy and chemical containers. However, in order to manufacture high-precision titanium structures, a large machining allowance needs to be designed, and a large amount of raw materials will be converted into waste chips. The traditional high-temperature melting and casting process has high energy consumption, heavy pollution, low efficiency, and the casting structure has coarse grains and poor performance. Therefore, it is necessary to improve the treatment method of titanium waste chips to overcome the above defects.

Contents of the invention

The purpose of the present invention is to provide a ball milling-high pressure torsion method for cyclic solidification of waste titanium chips, to prepare fully densified block superhard nano-titanium materials from waste titanium chips, and to realize efficient, clean recycling and reuse of waste titanium chips.

The technical scheme that the present invention adopts for solving its technical problem is,

A ball milling-high pressure torsion method for circular solidification of titanium waste chips, comprising the following steps:

(1) Titanium chip recovery pretreatment: cleaning titanium chip, removing oil and impurities;

(2) Ball milling of titanium chips: performing ball milling on the pretreated titanium chips in step (1);

(3) Room temperature and high pressure torsion curing treatment of titanium chips: the titanium chips after the ball milling in step (2) are subjected to room temperature and high pressure torsional curing treatment.

The specific process of step (1) is to use titanium chips generated by end milling grade 2 titanium as raw materials, and use an ultrasonic cleaning device to clean them to remove oil and impurities in the raw materials; wherein, the ultrasonic cleaning device uses 99.9% ethanol as the raw material. detergent.

The specific process of step (2) is to put the titanium chips pretreated in step (1) into the ball milling container of the ball mill, the running speed of the ball mill is 300rpm, the total running time of the ball mill is 15 hours, and pause for 12 minutes every hour of operation ; Wherein, the mass ratio between chips and steel balls is 15:1, and the diameter of steel balls is 10mm; meanwhile, add 1wt.% stearic acid as a process control agent in the ball mill container, and fill it with argon as a protective atmosphere .

The specific process of step (3) is to put the titanium chips after ball milling in step (2) into an oven for drying, then put them into a high-pressure torsion mold, put the titanium chips in the mold into the upper punch of the high-pressure torsion device and Between the lower anvils, the hydraulic system applies ultra-high pressure in the axial direction of the upper punch and is rotated by the lower anvils; the oven temperature is 60°C, and the drying time is 30 minutes; the outer diameter of the mold the inside diameter of The height is 60mm; the ultra-high pressure is 5Gpa, and the number of rotations is 5 times.

This method uses waste Ti chips as raw materials, and combines BM and HPT technologies to circularly prepare large-size, bulk and high-hardness nano-Ti materials. In the BM-HPT technology of the present invention, the ultra-fine cutting of Ti chips is firstly realized through the BM technology. The oxide (TiO ₂ ) on the chip surface is completely broken under the collision and rubbing of steel balls. Then, solidification and nanocrystallization of BM-Ti chips were carried out by HPT process at room temperature. In the HPT system, an ultra-high pressure of 5 GPa is applied in the direction of the longitudinal axis. At the same time, through the active friction of the rotating support (lower anvil), a torque is applied to the cross-section of the material, resulting in a combined plastic strain composed of axial compression and transverse shear. After the extrusion and torsion process, the strain amount gradually increases, and finally Obtain nanocrystalline materials with uniform structure, realize full-dense solidification of BM-Ti chips, and completely eliminate pore defects.

The advantages of the present invention are:

The traditional technology for recycling waste metal chips is remelting + casting. However, high-temperature melting and casting consumes a lot of energy, pollutes heavily, and has low efficiency. The cast structure has coarse grains and poor mechanical properties. In order to avoid high temperature melting and casting, solid phase treatment can be used. However, the existing ECAP and BM technologies each have their limitations when treating Ti chips in solid phase. Ti is easy to oxidize, and the oxide on the chip surface exists in the form of _TiO2 , which is tough in texture. Although the oxide can be broken and dispersed to a certain extent after multiple passes of ECAP treatment, the continuous distribution of larger oxides will form a microstructure. Metallurgical defects that weaken the mechanical properties of the material. At the same time, there is a refinement limit in ECAP processing, that is, when the dynamic recrystallization and strain refinement effects are balanced, it will be difficult for ECAP to further refine the microstructure to the nanometer level. On the other hand, although BM technology can effectively prepare ultrafine powder. However, after BM treatment, subsequent processing procedures such as hot pressing sintering or powder extrusion/forging must be carried out to obtain bulk materials, and in these procedures, due to the influence of factors such as long heating (sintering) time and dynamic recrystallization, Grain coarsening will occur, weakening the strength of the material. These technical issues have not yet been well resolved.

The BM-HPT technical solution proposed by the present invention overcomes the above limitations and can realize the technical effects described in the present invention. First, the micron-scale refinement of Ti chip dimensions is achieved through the BM process. The surface oxide (TiO ₂ ) of the chip is fully broken and dispersed under the collision and grinding of the steel ball, and an ultra-fine structure is also formed inside the chip. Then, at room temperature, the HPT technology is used to further refine the grains through the composite action of axial ultra-high pressure and lateral strong shear, and realize the nanostructure during the solidification process of chips. Compared with high-temperature processes such as melting and casting and powder metallurgy, room temperature HPT technology can further refine the ultra-fine structure of BM treatment, and completely eliminate microscopic defects under the action of ultra-high pressure (5GPa), and realize the full densification of remanufactured Ti materials. In addition, the texture of BM-HPT processed materials is weak, and the isotropy level of properties is high, which has important technical significance for hexagonal close-packed Ti, which is easy to produce texture. According to this method, starting from grade 2 Ti (ASTM Grade 2) cuttings, through the implementation of BM-HPT remanufacturing, a fully densified bulk Ti material is obtained, and its microhardness is ~3GPa, which is significantly higher than that of grade 2 Ti commercial rods. Hardness (~1.4GPa). After the preparation of BM-HPT, the hardness and uniformity of the regenerated Ti material were significantly improved.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the HPT process device adopted in the ball milling-high pressure torsion method for cyclic solidification of titanium waste chips proposed by the present invention. In the figure, 1, Ti chips, 2, upper punch, 3, lower anvil.

detailed description

In order to make the technical means, creative features, goals and effects achieved by the present invention easy to understand, the present invention will be further elaborated below in conjunction with illustrations and specific embodiments.

The method proposed in the present invention is a ball milling-high-pressure torsion method for cyclic solidification of waste titanium chips. The specific steps include: Ti chip recycling pretreatment, Ti chip BM treatment, and room temperature HPT curing treatment of BM-Ti chips.

1. Ti swarf recovery pretreatment: use the swarf generated by end milling grade 2 Ti (ASTM Grade 2) as the raw material, collect the swarf, and use Inductively coupled plasma atomic emission spectroscopy (ICP-AES for short) The chemical composition (mass percentage, wt.%) was analyzed, and the analysis results are shown in Table 1. It can be seen from Table 1 that the chemical composition (oxygen content) of the milled grade 2 Ti chips meets the ASTM standard range. At the same time, 99.9% ethanol is used to clean Ti chips in an ultrasonic vibration tank to remove oil and impurities in raw materials.

2. BM processing of Ti chips: Put the Ti chips obtained in step (1) into a steel BM container, and the mass ratio between chips and steel balls (10 mm in diameter) is 15:1. At the same time, 1 wt.% stearic acid was added as a process control agent, and the BM container was filled with argon as a protective atmosphere to prevent excessive oxidation of chips during BM. The rotational speed of the planetary BM machine is 300 rpm; the total running time of BM is 15 hours. During the operation of BM, Ti chips are cold-welded, hardened and broken under the impact and rubbing of steel balls. Through BM processing, the dimensions and surface oxides of Ti chips can be significantly refined. At the same time, the friction temperature between chips and steel balls is reduced by circulating liquid nitrogen outside the container, and the machine will pause for 12 minutes every hour of operation. After BM, the chemical composition of chips was analyzed by ICP-AES, and the analysis results are shown in Table 1. It can be seen from Table 1 that the oxygen content of Ti chips processed by BM under the protection of argon only slightly increased (from 0.15wt.% to 0.17wt.%), while the Fe content increased from 0.10wt.% to 0.64wt. .%.%.

3. Room temperature HPT curing treatment of BM-Ti chips: The HPT curing process device is shown in Figure 1. Put the BM-Ti chips into the oven, dry at 60°C for 30 minutes, and then put them into a steel disc-shaped HPT mold (outer diameter of the mold the inside diameter of height 60mm). Put the BM-Ti chips 1 placed in the mold between the upper punch 2 and the lower anvil 3 of the HPT device, and then apply ultra-high pressure (5GPa) axially on the upper punch through the hydraulic system, and the lower anvil Rotate 5 times to provide strong radial shear strain, and prepare high-density samples under the action of axial-radial compression-shear composite strain.

The chemical composition of the BM-HPT sample was analyzed by ICP-AES, and the results are shown in Table 1. It can be seen from Table 1 that the oxygen content of BM-HPT remanufactured Ti material increased from 0.15wt.% of the original cuttings to 0.17wt.%, which still meets the oxygen content of Tier 2 (ASTM Grade2), while the N content (<0.01 wt.%) unchanged. The HPT processing step does not affect the chemical composition of the material. The hardness is tested by a microhardness tester. The average hardness of BM-HPT remanufactured Ti material is ~3GPa, that is, at a level similar to the oxygen content of grade 2 Ti, the yield is higher than that of grade 2 Ti commercial bars (ASTM Grade 2) Strength (~1.4GPa).

Table 1 is the chemical composition of the initial Ti chips, BM treatment (BM-Ti) and BM-HPT remanufacturing (BM-HPTTi) chips analyzed by ICP-AES technology.

Table 1

This method uses the composite remanufacturing technology combining BM and HPT to successfully prepare bulk high-hardness Ti material. Give full play to the advantages of BM and HPT technology, through the implementation of BM process, the chip surface oxide (TiO2) is completely broken; in the process of HPT processing, the shape of the material remains unchanged, so it can be processed repeatedly to obtain the designed strain , Completely eliminate metallurgical defects, and realize full densification of remanufactured materials. Moreover, the implementation of HPT is carried out at room temperature. Compared with high-temperature melting and casting (~1200°C), powder metallurgy (~900°C), or ECAP (~600°C) and other technologies, HPT can efficiently realize grain nanoscale.

The BM-HPT composite technology is highly controllable, which not only obtains nanostructures, but also eliminates the segregation of metallurgical defects in the material. Due to the composite effect of axial ultra-high pressure and transverse strong shear in the subsequent HPT processing of BM-Ti chips, the nanostructure of the chip solidification process is realized, and its morphology can be further reformed and refined. The isotropy level of the material is improved, which is of great significance for the hexagonal close-packed Ti which is easy to form texture. Therefore, the hardness (∼3 GPa) of BM-HPT regenerated Ti material is significantly higher than that of commercial Ti material (∼1.4 GPa) with similar oxygen content level (ASTM Grade 2)

The BM-HPT preparation technology can significantly improve the hardness of recycled materials and avoid high-temperature melting and casting. It is a low-cost, efficient and clean metal resource recycling technology, which is suitable for high smelting cost metals represented by Ti Resource recycling and reuse.

The above embodiments are only to illustrate the technical conception and characteristics of the present invention, and its purpose is to allow those skilled in the art to understand the content of the present invention and implement it, and cannot limit the protection scope of the present invention. All equivalent changes or modifications should fall within the protection scope of the present invention.

Claims (10)

1. The ball milling-high pressure torsion method of titanium discarded swarf recycling solidification, it is characterized in that, comprises the following steps: (1) Titanium chip recovery pretreatment: cleaning titanium chip, removing oil and impurities; (2) Ball milling of titanium chips: performing ball milling on the pretreated titanium chips in step (1); (3) Room temperature and high pressure torsion curing treatment of titanium chips: the titanium chips after the ball milling in step (2) are subjected to room temperature and high pressure torsional curing treatment. 2. The ball milling-high-pressure torsion method of circulating solidified titanium waste chips according to claim 1, characterized in that in step (1), the titanium chips generated by end milling grade 2 titanium are used as raw materials, and the ultrasonic cleaning device is used to carry out Washing to remove oil and impurities from raw materials. 3. The ball milling-high pressure torsion method for circulating and solidifying titanium waste chips according to claim 2, characterized in that the ultrasonic cleaning device uses 99.9% ethanol as the cleaning solution. 4. The ball milling-high pressure torsion method of the waste titanium chips cyclically solidified according to claim 1, characterized in that, in the step (2), the titanium chips after the pretreatment of the step (1) are placed in the ball milling container of the ball mill, The running speed of the ball mill is 300rpm, and the total running time of the ball mill is 15 hours, with a pause of 12 minutes every hour of running. 5. The ball milling-high pressure torsion method for circular solidification of titanium waste chips according to claim 4, characterized in that the mass ratio between chips and steel balls is 15:1, and the diameter of the steel balls is 10mm. 6. The ball milling-high pressure torsion method of recycling and solidifying titanium waste chips according to claim 4, characterized in that 1wt.% stearic acid is added to the ball milling container as a process control agent, and argon is charged as a protective atmosphere . 7. The ball milling-high pressure torsion method of titanium waste chips cyclically solidified according to claim 1, characterized in that, in step (3), the titanium chips after step (2) ball milling are put into an oven for drying, and then put into The high-pressure torsion mold puts the titanium chips placed in the mold between the upper punch and the lower anvil of the high-pressure torsion device, and applies ultra-high pressure to the axial direction of the upper punch through the hydraulic system, and is rotated by the lower anvil. 8. The ball milling-high pressure torsion method for circular solidification of titanium waste chips according to claim 7, characterized in that the temperature of the oven is 60° C., and the drying time is 30 minutes. 9. The ball milling-high pressure torsion method of recycling and solidifying titanium waste chips according to claim 7, characterized in that the outer diameter of the mold is the inside diameter of Height 60mm. 10. The ball milling-high pressure torsion method for circular solidification of titanium waste chips according to claim 7, characterized in that the ultra-high pressure is 5Gpa, and the number of rotations is 5 times.