CN106513690A - Ball milling-isometric angle extrusion-annealing method for pure titanium waste chip circular curing - Google Patents

Abstract

The ball milling-equal angular extrusion-annealing method of recycling and solidifying pure titanium waste chips, including: (1) titanium chip recovery pretreatment; (2) ball milling treatment of titanium chips; (3) loading of ball milled titanium chips into Equal diameter angular extrusion die; (4) Equal diameter angular extrusion room temperature preprocessing: install the die filled with titanium chips on the hydraulic press, and the back pressure punch provides a constant back pressure of 150-200 MPa, and continuously increases the feed The pressure of the punch, when the pressure provided by the feed punch reaches 680-720MPa, stop the equal-diameter angular extrusion process; (5) Equal-diameter angular extrusion high-temperature curing processing: heat the mold to 570-590°C, Under the action of the valve, the two punches that control the inlet and outlet channels of the mold alternately provide a curing pressure of 1.0-1.2GPa and a back pressure of 150-200MPa, and perform 4-8 passes continuously; (6) Annealing: the step (5 ) The bulk Ti material obtained in the vacuum heat treatment furnace was heated to a temperature range of 800-900°C, kept for 10 hours, and cooled to room temperature in air to complete the annealing treatment.

Description

Ball milling-equal angular extrusion-annealing method for circular solidification of pure titanium waste chips

technical field

The invention relates to a metal material processing method, in particular to a ball milling-equal angular extrusion-annealing method for circularly solidifying pure titanium waste chips.

Background technique

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 Ti 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. Solid phase recycling and remanufacturing is an effective way to achieve efficient and clean recycling of metal resources because it avoids high-temperature melting and casting. 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 machiningchips 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 recycled by ECAP; Luo et al. published "Recycling of titanium machining chips by severe plastic deformation consolidation ( Severe Plastic Deformation Solid State Cycle of Titanium Cuttings)" proposes to recycle waste grade 2 titanium (ASTMGrade 2) cuttings and remanufacture bulk materials by ECAP technology. In addition, Valiev et al. published the article "The innovation potential of bulk nanostructured materials" (the innovation potential of bulk nanostructured materials) on "Advanced Engineering Materials" 2007, Volume 9, pages 527-533, proposing a two-step method for processing bulk ultrafine-grained materials, The technology includes two steps of ECAP pre-extrusion with a 120-degree rotation angle and final extrusion. Through this integrated manufacturing process, micro-electromechanical parts with an axisymmetric ratchet profile can be prepared from rods. 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)" reports the preparation of nanoscale (less than 100nm) Ti-6Al-4V alloys using titanium, aluminum, and vanadium micron powders as raw materials by BM technology. In addition, Zadra published the article "Mechanical alloying of titanium" on pages 105-113 of Volume 583 of "Materials Science and Engineering A" in 2013. The Ti powder whose initial raw material is less than 150 μm is first processed by BM to obtain Pure titanium ultrafine powder less than 25μm, and obtain bulk titanium material by spark plasma sintering.

The traditional technologies for the recycling of waste metal chips are remelting 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 sintering can be used. However, titanium (Ti) is an active metal that is easy to oxidize, and the oxide on the chip surface exists in the form of _TiO2 , which has a tough texture. Although the oxide can be broken and dispersed to a certain extent after multiple passes of ECAP treatment, the larger The continuous distribution of oxides will form metallurgical defects in the microstructure, weakening the mechanical properties of the material. At the same time, after the powder is processed by BM, subsequent processing procedures such as hot pressing sintering or powder extrusion/forging are required to obtain bulk materials. In these processes, due to factors such as long heating (sintering) time and dynamic recrystallization, Grain coarsening will occur, weakening the strength of the material. The above technical problems have not been well resolved.

Contents of the invention

The purpose of the present invention is to provide a ball milling-equal angular extrusion-annealing method for cyclic solidification of pure titanium waste chips, so as to overcome the shortcomings of the prior art, diffuse and ablate oxides, and prepare fully densified large-size bulk Ti materials , to achieve efficient and clean recycling of waste Ti chips.

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

A ball milling-equal angular extrusion-annealing method for circular solidification of pure titanium waste chips, comprising the following steps:

(1) Titanium chip recycling pretreatment: cleaning the titanium chip raw material to remove oil and impurities in the raw material;

(2) Ball milling treatment of titanium chips: put the pretreated titanium chips into a ball mill container containing steel balls, add a process control agent at the same time, and perform ball milling treatment under the protection of an inert gas atmosphere;

(3) Fill the titanium chips treated by ball milling into the equal-diameter angular extrusion die: wrap the cylindrical billet with steel foil, the diameter of the billet is smaller than the diameter of the die channel, and wrap a layer of solid lubricant outside the steel foil, and the billet-steel Put the foil-solid lubricant layer into the mold channel, take out the billet, form a solid lubricant layer-steel foil cavity, and fill the cavity with titanium chips processed by ball milling;

(4) Equal-diameter angular extrusion room temperature preprocessing: Install the mold filled with titanium chips on the hydraulic press, and the back pressure punch provides a constant back pressure of 150-200 MPa, and continuously increases the pressure of the feed punch. When the pressure provided to the punch reaches 680-720MPa, stop the equal-diameter angular extrusion process;

(5) Equal-diameter angular extrusion high-temperature curing processing: heat the mold to 570-590°C, and under the action of the hydraulic reversing valve, the two punches that control the inlet and outlet channels of the mold alternately provide curing pressure of 1.0-1.2GPa and back pressure 150-200MPa, 4-8 consecutive passes;

(6) Annealing: Heat the bulk Ti material obtained in step (5) to a temperature range of 800-900°C in a vacuum heat treatment furnace, keep it warm for 10 hours, and air cool to room temperature to complete the annealing treatment.

In step (1), the raw material of titanium chips is chips generated by grade 2 titanium obtained through end milling, and ultrasonic cleaning is used for cleaning, and the washing liquid used is 99.9% ethanol.

In step (2), the ball milling time is 10-20 hours, and the rotating speed is 280-350rpm. The mass ratio between titanium chips and steel balls is 12-20:1, and the diameter of steel balls is 7-12mm. The process control agent is stearic acid or pure iron powder, and the added amount of the process control agent is 0.5-2wt%. The inert gas is nitrogen, argon or helium. The inert gas is nitrogen, argon or helium. During the ball milling process, liquid nitrogen is circulated outside the container, and the machine is paused for 10-15 minutes every 1-2 hours.

In step (3), the steel foil is annealed stainless steel foil, and the solid lubricant is graphite paper or tinfoil paper. After the ball-milled titanium chips are filled into the solid lubricant-steel foil cavity, the chips are initially compacted with a manual press.

The advantage of the present invention is that, by implementing BM treatment in the method, the oxide (TiO ₂ ) on the chip surface can be completely broken under the collision and rubbing of steel balls. Effectively prevent the continuous distribution and aggregation of larger oxide defects. On this basis, the ECAP-annealing process is implemented to obtain fine-grained materials with uniform structure, and to completely eliminate defects such as pores and oxides. Using this technology to process grade 2 Ti (ASTM Grade 2) cuttings, a bulk nano-Ti material with an oxygen content of ~0.28wt% is obtained, and its yield strength is about 400-450MPa. Remanufactured Ti material achieves higher yield strengths (300-350 MPa) than commercial bars of Grade 2 Ti (ASTM Grade 2) at levels similar to the oxygen content of Grade 2 Ti (ASTM Grade 2). It is an efficient and clean solid-phase recycling treatment technology for metal resources, which avoids high-temperature melting and casting, and is suitable for the recovery and remanufacturing of metal resources with high smelting costs represented by Ti.

Description of drawings

Figure 1 is the optical microstructure of Ti material processed by BM-ECAP;

Figure 2 is the annealing system of BM-ECAP processed Ti material.

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.

1. 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) to analyze Its chemical composition (mass percentage, wt.%) and 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 treatment 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 BM process, Ti chips undergo cold welding, hardening and crushing under the impact and rubbing of steel balls. Through BM processing, the dimensions of Ti chips and surface oxides 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 the chips 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-treated Ti chips only increased slightly (from 0.15wt% to 0.17wt%) under the protection of argon, while the iron content increased from 0.10wt% to 0.64wt%. It is caused by the abrasion of the steel ball (and the wall of the steel container) and the mixing of chips during the BM process.

3. Fill the BM-treated Ti chips into the ECAP mold: first wrap the cylindrical steel billet (its diameter is slightly smaller than the diameter of the ECAP channel) with annealed stainless steel foil, and then wrap a layer of graphite paper (solid lubricant) outside the steel foil. Put the steel billet-steel foil-graphite paper into the ECAP channel, and take out the steel billet to form a graphite paper-steel foil cavity. Put the Ti chips obtained in step (2) into the cavity, and then use a manual press to compact the chips initially.

4. ECAP room temperature preprocessing of BM processing Ti chips: install the ECAP mold filled with Ti chips in step (3) on the hydraulic press, and carry out ECAP preprocessing at room temperature to further improve the compactness of chips and prevent BM Dealing with Ti chips being over-oxidized during ECAP high-temperature curing processing. In this step, the back pressure punch of the ECAP mold provides a constant back pressure of ~200MPa; when the pressure of the feeding punch reaches ~700MPa, the ECAP process is stopped and the room temperature preprocessing is completed. As determined by the Archimedes method, the relative density of Ti chips preprocessed by ECAP at room temperature is >99.0%.

5. ECAP high-temperature curing processing: wrap the mold with an armored electric blanket, heat to a certain level (for example, 590°C) below the recrystallization temperature of Ti (~600°C), and stabilize the temperature at ±1°C by a temperature controller range. Carry out ECAP high-temperature curing processing for the Ti chip compact obtained in step (4). ECAP processing rate ~ 10mm/min. Under the action of the programmable logic controller and the hydraulic reversing valve, the two punches of the inlet and outlet channels of the ECAP mold (the feed punch, which can provide curing pressure; the back pressure punch, which can provide back pressure) can be alternately provided Cure pressure (~1.2GPa) and back pressure (~200MPa). Thus, ECAP processing can accumulate multiple passes in succession (without taking samples between passes). After 4 passes of processing, a fully densified (relative density >99.9% as determined by the Archimedes method) bulk remanufactured Ti material is obtained. Multi-point observation under the scanning electron microscope did not find the existence of microscopic pores. As determined by the Archimedes method, the bulk remanufactured Ti material achieves full densification (relative density nearly 99.99%). The chemical composition of Ti 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 Ti remanufactured by BM-ECAP increased from 0.15wt% of the original cuttings to 0.28wt%, which is still close to the oxygen content of grade 2 Ti (ASTM Grade 2). At the same time, by wire-cutting ~4.00×4.00×6.00mm samples, and carrying out performance tests on a universal material testing machine, it was found that the yield strength of the remanufactured Ti material was 400-450MPa.

6. Annealing: Heat the bulk Ti material obtained from the high-temperature curing step (5) to ~850°C in a vacuum heat treatment furnace, keep it warm for 10 hours, and air cool to room temperature to complete the annealing treatment.

Table 1 is the chemical composition of the initial Ti chips, BM-treated (BM-Ti) and ECAP-annealed Ti chips analyzed by ICP-AES technology.

Table 1

element o N C Fe Initial Ti chips (wt.%) 0.15 <0.01 <0.01 0.10 BM-Ti chips (wt.%) 0.17 <0.01 0.22 0.64 BM-ECAP-annealed Ti chips (wt.%) 0.28 0.05 0.27 -

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 (9)

1. The ball milling-equal angular extrusion-annealing method of pure titanium discarded chips cyclically solidified, is characterized in that, comprises the following steps: (1) Titanium chip recycling pretreatment: cleaning the titanium chip raw material to remove oil and impurities in the raw material; (2) Ball milling treatment of titanium chips: put the pretreated titanium chips into a ball mill container containing steel balls, add a process control agent at the same time, and perform ball milling treatment under the protection of an inert gas atmosphere; (3) Fill the titanium chips treated by ball milling into the equal-diameter angular extrusion die: wrap the cylindrical billet with steel foil, the diameter of the billet is smaller than the diameter of the die channel, and wrap a layer of solid lubricant outside the steel foil, and the billet-steel Put the foil-solid lubricant layer into the mold channel, take out the billet, form a solid lubricant layer-steel foil cavity, and fill the cavity with titanium chips processed by ball milling; (4) Equal-diameter angular extrusion room temperature preprocessing: Install the mold filled with titanium chips on the hydraulic press, and the back pressure punch provides a constant back pressure of 150-200 MPa, and continuously increases the pressure of the feed punch. When the pressure provided to the punch reaches 680-720MPa, stop the equal-diameter angular extrusion process; (5) Equal-diameter angular extrusion high-temperature curing processing: heat the mold to 570-590°C, and under the action of the hydraulic reversing valve, the two punches that control the inlet and outlet channels of the mold alternately provide curing pressure of 1.0-1.2GPa and back pressure 150-200MPa, 4-8 consecutive passes; (6) Annealing: Heat the bulk Ti material obtained in step (5) to a temperature range of 800-900°C in a vacuum heat treatment furnace, keep it warm for 10 hours, and air cool to room temperature to complete the annealing treatment. 2. The ball milling-equal angular extrusion-annealing method of cyclic solidification of pure titanium waste chips according to claim 1, characterized in that, in step (1), the raw material of titanium chips is grade 2 titanium obtained by end milling The generated chips are cleaned by ultrasonic cleaning, and the washing liquid used is 99.9% ethanol. 3. The ball milling-equal angular extrusion-annealing method of cyclic solidification of pure titanium waste chips according to claim 1, characterized in that, in step (2), the ball milling time is 10-20 hours, and the rotating speed is 280-350rpm . 4. The ball milling-equal angular extrusion-annealing method of cyclic solidification of pure titanium waste chips according to claim 1, characterized in that, in step (2), the mass ratio between titanium chips and steel balls is 12-20 :1, the diameter of the steel ball is 7-12mm. 5. The ball milling-equal angular extrusion-annealing method of pure titanium waste chips cyclically solidified according to claim 1, characterized in that, in step (2), the process control agent is stearic acid or pure iron powder, and the process The adding amount of the control agent is 0.5-2wt%. 6. The ball milling-equal angular pressing-annealing method for circular solidification of pure titanium waste chips according to claim 1, characterized in that, in step (2), the inert gas is nitrogen, argon or helium. 7. The ball milling-equal angular extrusion-annealing method of pure titanium waste chips cyclically solidified according to claim 1, characterized in that, in step (2), during the ball milling process, liquid nitrogen is circulated outside the container , and the machine pauses for 10-15 minutes every 1-2 hours of operation. 8. The ball milling-equal angular extrusion-annealing method of cyclically solidified pure titanium waste chips according to claim 1, characterized in that, in step (3), the steel foil is annealed stainless steel foil, solid lubricant Graphite paper or tinfoil. 9. The ball milling-equal angular extrusion-annealing method of cyclic solidification of pure titanium waste chips according to claim 1, characterized in that, in step (3), the titanium chips processed by ball milling are loaded into the solid lubricant- After the steel foil cavity, the chips are initially compacted with a manual press.