Method of combined intense plastic deformation of workpieces

FIELD: metallurgy.

SUBSTANCE: equichannel angular pressing of a cylindrical workpiece is performed. Ultra-fine structure with the grain size of 200-300 mcm is formed in the workpiece metal. Then the workpiece is cut into disks with each of them being subject to intensive plastic deformation by torsion with the help of two rotating strikers. Deformation of torsion is carried out under the room temperature and the pressure of 4-6 GPa with the number of strikers' revolutions n≤2. Therewith the homogeneous nanocrystalline structure with the grain size of ≤100 mcm is formed.

EFFECT: improved physical and mechanical properties of the material being processed.

2 cl, 1 tbl, 1 ex

 

The invention relates to a pressure treatment of materials and can be used to obtain nanocrystalline blanks metals and alloys with improved physical-mechanical properties for applications in engineering, aircraft engine industry, in medicine for the manufacture of implants.

A method of processing metals equal channel angular pressing (pressing), and to get metal ultrafine-grained (UMP) structure providing improved physical-mechanical characteristics (V.M. Segal Plastic working of metals by simple shear / V.M. Segal, I. Reznikov, A.S. Drobyshevski, V.I. Kopylov // Izvestiya an SSSR. The metals. - 1981. - S-123). Pressing is deformed billet shift in the zone of intersection of the channels of equal cross-section. The workpiece is repeatedly pressed in a special snap-through two channels with the same cross sections, intersecting generally at an angle from 90 to 120°. In the case of hard materials, the deformation is carried out at elevated temperatures. Method of pressing allows you to get the UMP-structure with a grain size of about 200 nm in solid samples with a diameter from 10 to 60 mm and a length of from 100 to 350 mm (Valiev R.Z., Alexandrov I.V. Bulk nanostructured metallic materials: synthesis, structure and properties. - M.: ICC called "Akademkniga", 2007. - 398 (C).

Defects in the current pressing is the following. It is impossible to grind the grain of the metal to the nanocrystalline (NC) state with a grain size less than 100 nm (Valiev R.Z., Alexandrov I.V. Bulk nanostructured metallic materials: synthesis, structure and properties. - M.: ICC called "Akademkniga", 2007. - 398 (C).

Know of any other way of processing of metals and alloys - severe plastic deformation by torsion under high pressure (IPDC). IPDC allows to achieve the highest degrees of deformation(e=7-10)and form NC structure in materials. The strain pattern was proposed PV by Bridgman (Bridgman P. Studies in large plastic flow and fracture. Effect of high hydrostatic pressure on the mechanical properties of materials / P. the Bridgman; Per. s angl. A.I. Lighter; Ed. by L. F. Vereshchagin. - M.: Institute. literature, 1955. - 444).

The disadvantages of this method are as follows. It is known that when IPDC the degree of deformation of e depends on the radius R of the sample by the formula:e=ln(2πnr/l), where e is the logarithmic degree of deformation, n is the number of revolutions of the forging dies (anvils), and Dr. who is responsible radius and thickness of the specimen at the point which is determined by the degree of deformation. In this regard, the structure of the samples after IPDC at low revs Boykov heterogeneous (Valiev R.Z., Alexandrov I.V. Bulk nanostructured metallic materials: synthesis, structure and properties. - M.: ICC called "Akademkniga", 2007. - 398). To achieve the sample homogeneous nanostructures method IPDC requires a sufficiently large number of turns (usually n≤5), when necessary to process high pressure (5 GPA or more) can lead to destruction of the sample and snap.

Closest to the claimed method is a combination of intensive plastic deformation (EN 2240197, IPC B21J 5/00, C22F 1/18, publ. 20.11.2004), in which the process is executed in the following sequence: deformation by torsion in the screw channel, then equal channel angular extrusion, the billet is additionally subjected to low-temperature annealing for stress relief.

The disadvantage of the prototype is the inability to grind the grain of the metal to the nanocrystalline (NC) state with a grain size less than 100 nm, which does not provide the processed material high physical-mechanical properties.

Object of the invention is the improvement of physical and mechanical properties of the processed metal, in particular the increase in hardness due to the creation of meth is the homogeneous nanostructures with a grain size less than 100 nm.

The problem is solved by the method of combination of intensive plastic deformation of workpieces, including deformation by torsion and equal channel angular pressing. Unlike the prototype deformation of the torsion is carried out after equal-channel angular pressing, in which the cylindrical workpiece to form ultrafine-grained structure with a grain size of 200-300 nm, and then the workpiece is cut into disks, and each disk is subjected to severe plastic deformation by torsion by means of two rotating heads, upper and lower, and the torsional deformation is carried out at room temperature under a pressure of 4-6 GPA, when the number of revolutions Boykov n≤2, ensuring the formation of a homogeneous nanocrystalline structure in the workpiece with the grain size ≤100 nm.

According to the invention on the surface of the lower striker made groove.

The technical result is achieved by a combination of pressing+IPDC in these modes, which allows to form in the material homogeneous nanocrystalline structure with a grain size ≤100 nm, resulting in increased mechanical characteristics of the material.

The method is as follows.

At the first stage cylindrical billet is subjected to pressing at these temperatures and number of cycles, ensuring the formation of a homogeneous the MOH structure of the selected material with a grain size of 200-300 nm.

After the pressing of the workpiece are removed from the tooling and cooled to room temperature. Being controlled microstructure and microhardness in the blank.

After pressing the cylindrical billet is cut into disks with a thickness of 0.8-1.5 mm Further procurement-the disc is IPDC at room temperature under a pressure of 4-6 GPA and the number of revolutions Boykov n=1-2. As a result of this processing is an additional grinding of the grain to the size of ≤100 nm with the formation in the workpiece material NC structure. After IPDC again they control the microstructure and microhardness of the sample.

An example of a specific implementation.

As the blanks used the rod of titanium Grade-4 with a diameter of 20 mm and a length of 80 mm At the first stage, the workpiece was subjected to pressing at a temperature of 450°C number of cycles n=5. As a result, the material formed a homogeneous UMP structure with a grain size of about 300 nm.

After pressing the workpiece was removed from the tooling and cooled to room temperature. Held control of microstructure and microhardness obtained billets.

Then the workpiece was cut into discs with a thickness of 1.1 mm and a diameter of 20 mm

In the next step, the blank disk was subjected IPDC on the strikers with a diameter of 20 mm with a groove on the surface of the lower firing pin depth of 0.7 mm, under a pressure of 6 GPA is the number of revolutions Boykov n=2. In IPDC the grinding of the grain of the workpiece material, which leads to the formation of the PC structure with a grain size less than 100 nm for an entire blank disc. After IPDC re-performed the control of the microstructure and microhardness.

The table shows the comparative values of microhardness in samples from Ti Grade-4, obtained by traditional schemes and by the present method.

Processing typeHv (microhardness, MPa
3000In the centre of the sampleOn the edge of the sample
Pressing3000
IPDC n=240005000
Pressing+IPDC n=250005000

The table shows that as a result of processing by the present method in the material of the workpiece homogeneous nanocrystalline structure and high values of microhardness.

Thus, the proposed method can improve the physical and mechanical properties of the processed metal, in castnet is to increase the microhardness, due to the creation of homogeneous metal nanostructures with a grain size less than 100 nm. This treatment allows to obtain nanostructured samples of titanium and alloy TiNi, including for the manufacture of medical implants.

1. The method of combination of intensive plastic deformation of metallic workpieces, including deformation by torsion and equal-channel angular pressing, characterized in that the deformation of the torsion is carried out after equal-channel angular pressing, in which the cylindrical metal billet to form ultrafine-grained structure with a grain size of 200-300 nm, and then the workpiece is cut into disks, and each disk is subjected to severe plastic deformation by torsion by means of two rotating heads, upper and lower, and the torsional deformation is carried out at room temperature under a pressure of 4-6 GPA at the number of revolutions Boykov n≤2, ensuring the formation of a homogeneous nanocrystalline structure in the workpiece with the grain size ≤100 nm.

2. The method according to claim 1, characterized in that on the surface of the lower striker made groove.



 

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