Ultra-fine grain two-phase alpha-beta titanium alloy with improved level of mechanical properties, and method for its obtainment

FIELD: metallurgy.

SUBSTANCE: invention refers to nanostructured materials with ultra-fine grain structure, and namely two-phase alpha-beta titanium alloys which can be used for manufacture of semi-finished products and products in different branches of engineering, machine-building industry and medicine. Proposed alloy has microstructure consisting of ultra-fine grains of alpha-phase and beta-phase with the size of less than 0.5 mcm. In alloy microstructure the amount of grains with grain shape coefficient of not more than 2 is not less than 90%; at that, more than 40% of grains have wide-angle borders, and average density of dislocation is not more than 1014 m-2. the method for obtaining ultra-fine grain two-phase alpha-beta titanium alloy involves heat treatment with heating of a billet at the temperature of not more than 0.6 T"пп", further multicycle intense plastic deformation with achievement of accumulated true deformation degree e≥4. Then, plastic deformation is performed so that the billet shape is changed at the rate of less than 10-1 s-1 in several cycles to provide deformation degree ε≥50%.

EFFECT: improving strength and fatigue properties and preserving high ductility.

5 cl, 2 dwg, 1 tbl, 1 ex

 

The invention relates to the field of nanostructured materials with ultrafine-grained (UMP) structure, in particular, two-phase alpha-beta (α+β)-titanium alloys that may be used for the manufacture of semi-finished products and products in various fields of engineering, mechanical engineering, medicine, as well as to methods of processing these materials to form structures, ensuring a high level of mechanical properties.

Two-phase (α+β)- titanium alloys according to the degree of alloying belong to the class of alloys with equivalent molybdenum [Mo]EQ.. equal to from 2.5 to 10% [Kolachev B.A., Polkin I.S., Talalaev, E Titanium alloys in different countries: a Handbook. // M: VILS. 2000, 316 S. (s-16)]. Such alloys are usually alloyed aluminum and β-stabilizers for fixing the β-phase. In alloys of this class in the annealed condition, the amount of β-phase can range from 5 to 50%. In this regard, the mechanical properties vary within fairly wide limits. These alloys are most widely spread in Russia and abroad, especially the alloy Ti-6Al-4V, which is due to its successful doping [Materials Properties Handbook: Titanium Alloys, R.Boyer, G.Welsch, E.Collings, - ASM International, 1998, 1048 p. (p.486-488)]. The aluminum in the alloy increases the strength and heat resistant properties, and vanadium is one of the few elements that improve not only the mechanical properties, the about and plasticity. From the alloys of the Ti-6Al-4V receive rods, tubes, profiles, forgings, stamping, plates, sheets, strip and foil. They are used for the manufacture of welded and modular designs of aircraft, a number of structural elements, aviation, rocketry, and also for manufacturing of medical implants in traumatology, orthopedics, dentistry.

Mechanical properties (α+β)-titanium alloys depend on the parameters of the evolving microstructure in the process of obtaining a semi-finished product and its thermomechanical processing [Materials Properties Handbook: Titanium Alloys, R.Boyer, G.Welsch, E.Collings, - ASM International, 1998, p.522-527; Kolachev B.A., Polkin I.S., Talalaev, E Titanium alloys in different countries: a Handbook. // M: VILS. 2000, 316 S. (p.37, 96-152)].

The formation of lamellar (lamellar) structures in the alloy increases the strength with some decrease in ductility, while they have good crack resistance and fracture toughness. Equiaxial structure (usually with the grain size of the α-phase of 15-20 microns) provides the optimum combination of strength and ductility and, as a consequence, the fatigue resistance [Materials Properties Handbook: Titanium Alloys, R.Boyer, G.Welsch, E.Collings, - ASM International, 1998, 1048 p. (p.533-539); Kolachev B.A., Polkin I.S., Talalaev, E Titanium alloys in different countries: a Handbook. // M: VILS. 2000, 316 S. (.183-186)]. Thus reducing the size of structural components (zeropercent α-phase and/or plates of the secondary α-phase) improves resistance to fatigue failure. For example, in the alloy Ti-6Al-4V with a grain size of 2 μm, the fatigue limit can reach 650 MPa at a symmetric cycle of loading (R=-1) [Kolachev B.A., Polkin I.S., Talalaev, E Titanium alloys in different countries: a Handbook. // M: VILS. 2000, 316 S. (p.184)].

In order to achieve the optimal combination of fatigue strength and fracture toughness the most known methods of thermomechanical processing aimed at making the semis mixed globular-plate or fine-grained equiaxial structure.

For example, mixed globular-lamellar microstructure in the material can be obtained by rolling in the β-region with regulated cooling rate, and then molding at a temperature not higher than the temperature of polymorphic transformation (TPPto 100°C (JP 3219060, IPC SS 14/00, C22F 1/18, publ. 26.09.1991, the); thermo-mechanical processing, including rolling and heat treatment for the transformation (α+β) patterns in the microstructure (α+α2+β) (EP 0843021, IPC C22F 1/18, publ. 20.05.1998,); hot deformation consistently lie (α+β)-fields of temperature (RU # 2266171, IPC C22F 1/18, publ. 20.12.2005 g); heat treatment with heating in the interval above the recrystallization temperature and below TPPfollowed by rapid cooling (EP 1849880, IPC C22F 1/18, publ. 31.10.2007); the combination of heat treatment at temperatures up to and the and above T PPand isothermal forging with the degree of deformation ε=50...80% at a temperature of 300°C below TPP(EP 2172576, IPC C22F 1/18, publ. 07.04.2010,).

Fine-grained equiaxial microstructure with a grain size of α-phase of about 1-5 μm can be obtained, for example, cernovodeanu processing (RU # 2115759, IPC C22F 1/18, publ. 20.07.1998,); speed deformation at a temperature in the (α+β)-region (RU # 2196189, IPC, C22F 1/18, publ. 10.01.2003,); the combination of heat treatment in the β-region, hot stamping (α+β)region and the final heat treatment (US 2009133786, IPC C22F 1/18, publ. 28.05.2009 g).

All described methods allow to obtain a higher level of strength and ductility due to the formation of either fine-grained or mixed globular-lamellar microstructure. The increase in the proportion of structural elements of the plate reduces the fatigue strength, but increases the fracture toughness. Conversely, increasing the share of fine-grained equiaxial structure leads to an increase in the endurance limit with simultaneous decrease in fracture toughness. However, these methods do not allow to get in two-phase titanium alloys microstructure with grains of α-phase is less than 1 micron.

Metals and alloys with grain size less than one micron are ultrafine-grained (UMP) materials. In recent years, for the floor is to be placed widely used methods of intensive plastic deformation (SPD). However, inside ultramatic grains in the structure obtained by SDI, there are other nanostructured elements: secondary phases, dislocation substructure, nanodevice and others, so such UMP materials belong to the class of bulk nanostructured materials [R.Z. Valiev, I.V. Alexandrov. Bulk nanostructured metallic materials. - M.: ICC called "Akademkniga", 2007 - 308 S. (p.3)]. However, the formation of UMP structures containing predominantly of large-angle boundaries (BUG), misoriented relative to neighboring grains at angles from 15 to 90°, allowing you to reach in metals and alloys have unique properties, including high strength and fatigue. For example, nanostructured titanium has the strength in 2-2,5 times higher than conventional titanium [RU No. 2383654, IPC C22F 1/18, WV 3/00, publ. 10.03.2010].

Known alloy Ti-6Al-4V with submicrocrystalline structure obtained SDI comprehensive method of forging. The microstructure of the alloy was characterized by grains and subgrains α and β-phase with an average size of 0.4 μm, a high level of internal stresses and elastic distortion of the crystal lattice, as evidenced by nonuniform diffraction contrast and high density of dislocations on electroniccommerce the image patterns. [S. Zherebtsov, G. Salishchev, R. Galeyev, out by Maekawa K., Mechanical properties of Ti-6Al-4V titanium alloy with submicrocrystalline structure produced by severe plastc deformation. // Materials Transactions. 2005; V.46(9): 2020-2025.]. The specified technical solution, as the closest to the claimed technical solution is taken as a prototype.

A method of obtaining the alloy Ti-6Al-4V equiaxial structure with grains of α-phase of about 80 nm, a high density of dislocations, using severe plastic deformation by torsion (IPDC) at room temperature. One disadvantage of this method is the very small size of the sample discs with a diameter of 10 mm and a thickness of 1 mm, which limits their practical application. The strength of the alloy after IPDC reached high values (1750 MPa), however, plasticity is so small that the alloy becomes very fragile. [Stolyarov V.V., Shestakova L.O., built solid, A.I., V.V. Latysh, Valiev THIS, Y.T. Zhu, T.C. Lowe Mechanical properties of nanostructured titanium alloys processed using severe plastic deformation. // In: Proceeding of the 9thInt. Conf. Titanium-99, Nauka. 2001. V.1. p.466].

Known methods for producing UMP patterns with the size of the elements is less than 1 micron in massive workpieces, allowing to increase the level of strength and fatigue characteristics of two-phase titanium alloys. For example, the way in forging a comprehensive, on which the workpiece is subjected to sequential compression along the axes Z, X and Y with maintenance-free plastic flow, after which the workpiece is in the form of a convex prisms subjected to stepwise deformation(RU # 2388566, IPC C22F 1/18, publ. 22.07.2008,). The formation of the QMS structure with an average grain size of 0.4 μm in the alloy Ti-6Al-4V comprehensive forging in the temperature range of 450-800°C to prior martensitic microstructure in the workpiece is allowed to increase the strength up to values of 1300 MPa with elongation of 7% [S.Zherebtsov, G.Salishchev, R.Galeyev, K.Maekawa, Mechanical properties of Ti-6Al-4V titanium alloy with submicrocrystalline structure produced by severe plastic deformation. // Materials Transactions. 2005; V.46(9): 2020-2025.].

The known method combined thermomechanical processing of two-phase titanium alloys, including heat treatment, intensive plastic deformation of the workpiece by the method of equal-channel angular pressing (pressing) at a temperature of 600°C. and extruding at a temperature of 300°C With a drawing ratio of not less than 1.2 in multiple passes (RU # 2285740, IPC C22F 1/18, B21J 5/00, publ. 20.10.2006,). This way, as the closest to the claimed technical solution is chosen as a prototype. The result of this treatment, in billets of alloy Ti-6Al-4V is formed UMF structure with grains/subgrains α-phase in the range from 0.2 to 0.5 μm. With strength reached values of σB=1360 MPa, which is 40% above the original value, whereas the ductility of the alloy was about 8% [Saitova LR, I.P. Semenova, G.I. Raab, Valiev R.Z., the Enhancement of the mechanical properties of the alloy Ti-6Al-4V, use the I equal-channel angular pressing and subsequent plastic deformation // Physics and technology of high pressure, Donetsk, 2004, vol. 14, No. 4. - P.19-24].

The methods described above lead to the formation of UMP patterns in massive workpieces, however, to reduce the size of grains of α-phase is smaller than 0.4...0.5 μm cannot, therefore, a tensile strength above 1400 MPa to achieve the almost impossible. Thus formed in the billet microstructure usually has high internal stresses due to the strong distortion of the crystal lattice and a high dislocation density (about 1015m-2), which reduces the stock of the ductility and elongation drops to 6-7% [S. Zherebtsov, G. Salishchev, R. Galeyev, out by Maekawa K., Mechanical properties of Ti-6Al-4V titanium alloy with submicrocrystalline structure produced by severe plastic deformation. // Materials Transactions. 2005; V.46(9): 2020-2025; Saitova LR, I.P. Semenova, G.I. Raab, Valiev R.Z., the Enhancement of the mechanical properties of the alloy Ti-6Al-4V using equal-channel angular pressing and subsequent plastic deformation // Physics and technology of high pressure, Donetsk, 2004, vol. 14, No. 4. - P.19-24].

The objective of the invention is to increase the strength and fatigue properties with preservation of good plasticity (α+β) - titanium alloys by creating uniform in the longitudinal and transverse cross-section of the workpiece ultrafine-grained structure.

The problem is solved by a two-phase alpha-beta titanium alloy having a microstructure consisting of ultramagic grains alpha f the PS and the beta phase with a size less than 0.5 μm, which unlike the prototype in the microstructure of the alloy, the proportion of grains with an aspect ratio of the grains is not more than 2 not less than 90%, and more than 40% of the grains have a large-angle boundaries, and the average dislocation density not higher than 1014m-2.

The task is also solved by a method of obtaining UMP two-phase alpha-beta titanium alloy, comprising heat treatment by heating the workpiece at a temperature not above TPP, SDI with the number of cycles that provide the necessary accumulated true strain degree, then the subsequent plastic deformation by changing the shape of the workpiece, which in contrast to the prototype after heating the workpiece immediately subjected to high-cycle SDI with achievement of the accumulated true strain e≥4, which is carried out at a temperature of T=0.6 TPP, followed by a plastic deformation by changing the shape of the workpiece at a speed less than 10-1with-1several iterations to ensure that the degree of deformation ε≥50%.

According to the invention SDI carry equal channel angular pressing (pressing) or equal-channel angular pressing on the scheme Conform (pressing).

According to the invention, the plastic deformation of the workpiece by changing the shape of the workpiece is performed by extrusion or rolling, or drawing.

p> According to the invention the workpiece after plastic deformation shape change are annealed at a temperature of not higher than T=0.4 TPPin for 1...4 hours.

The proposed UMP alloy structure and the ways in which this can provide a higher level of strength and fatigue properties.

This technical result is achieved due to a number of structural and phase transformations in two-phase titanium alloys.

Heating billets of the alloy Ti-6Al-4V at temperatures below TPPallows you to reduce the share of globular primary α-phase to 20%, which inhibit the growth of grains of the β-solid solution. If heating the alloy above TPP, is the uncontrolled growth of grains of the β-phase, which can reach 200-300 microns. [Materials Properties Handbook: Titanium Alloys, R. Boyer, G. Welsch, E. Collings, - ASM International, 1998, 1048 p. (p.490)]. Subsequent deformation of the deforming workpiece in the apparatus, which are heated to a temperature not higher than T=0.6 TPPaccompanied by phase transformation of β-solid solution of β→α'(α)+βOSTwith the education records of the α-phase, the size of which is limited by the grain size of the β-phase. In the structure there is a small number of primary grains of αp-phase. Received on the 1st cycle SDI (α+β) mixed microstructure with about 80% of the plate secondary α-phase, between which are located β-phase, and 20% grain αpphase, provides a good deformation ability of the material during subsequent cycles SDI [Materials Properties Handbook: Titanium Alloys, R. Boyer, G. Welsch, E. Collings, - ASM International, 1998, 1048 p. (p.490)].

It is known that the necessary conditions for the formation of UMP structure comprising mainly of large-angle boundaries, which allows to achieve an unusually high strength metal materials, is the implementation of intensive plastic deformation at relatively low temperatures (below the recrystallization temperature) and achieve true of the accumulated strain is e≥4 [R.Z. Valiev, I.V. Alexandrov. Dimensional nanostructures of metal materials. - M.: ICC called "Akademkniga", 2007 - 308 S. (str-328)]. This approach is implemented during severe plastic deformation method for multi-pass equal channel angular pressing (pressing) or its modification pressing the scheme Conform at relatively low temperatures, i.e., not above T=0.6 TPP. The microstructure development of twinning and slip dislocation in the grains of the primary αpphase and the plates of the secondary α-phase formation of new dislocation subgrants that with the growth of the accumulated strain is transformed into angle. Usually about the appearance of the microstructure of the large angle boundaries is illustrated by the increasing number of the quality reflexes and a more uniform distribution in concentric circles on electron diffraction, taken from the investigated area of the structure. The size of the grains and subgrains α-phase after pressing is reduced to approximately 0.4 μm [R.Z. Valiev, I.V. Alexandrov. Dimensional nanostructures of metal materials. - M.: ICC called "Akademkniga", 2007 - 308 S. (str-328)]. Simultaneously with the grinding of the α-phase, β-phase is localized in isolated areas in the form of grains not larger than 1 μm, its volume fraction after SDI as a result of collapse of the β-solid solution is reduced from 12 to 8% [Demakov S.L., Elkina O.A., Illarionov A.G., Karabanov M.S., A.A. Popov, I.P. Semenova, Saitova LR, Sitnikov N.V. Effect of rolling deformation on the formation of ultrafine-grained structure in two-phase alloy obtained by severe plastic deformation // Physics of metals and metallography, 2008, t, No. 6, S-646].

After SDI plastic deformation at temperatures above T=0.6 TPPfor example, with hood procurement not less than 50% leads to additional refinement of the microstructure, i.e. the reduction of the sizes of grains and subgrains α - and β-phases due to the emergence of new dislocation boundaries and transformation of small angle boundaries in angle [Saitova LR, I.P. Semenova, G.I. Raab, Valiev R.Z., the Enhancement of the mechanical properties of the alloy Ti-6Al-4V using equal-channel angular pressing and subsequent plastic deformation // Physics and technology of high pressure is to the Donetsk, 2004, vol. 14, No. 4. - P.19-24]. Temperature-speed conditions of deformation (rate of less than 10-1c-1; temperature T=TPPused in the proposed method of treatment, close to the manifestation of symptoms superplasticity in UMP alloy, which contributes to production of grains of α - and β-phases with a shape factor of not more than 1:2 relative to the equilibrium boundaries and bolsheului the misorientation due to thermally activated processes of recovery and dynamic recrystallization characteristic of superplastic deformation [I.P. Semenova, Saitova LR, Raab G.I., Valiev R.Z. Sorpluticyla behavior of ultrafine-grained alloy Ti-6Al-4V ELI, obtained by severe plastic deformation // Physics and technology of high pressure, Donetsk, 2006, t.16., No. 4. - P.84-89., Valiev THIS, R.K. Islamgaliev, I.P. Semenova Superplasticity in nanostructured materials: New challenges // Materials Science and Engineering A, Vol.463 (2007), P.2-7]. The final annealing at a temperature not higher than T=0.4 TPPin for 1...4 hours can further reduce the overall density of lattice dislocations inside the grains almost 1014m-2you can estimate the x-ray analysis and/or transmission electron microscopy. At higher annealing temperatures and/or increased duration of heating along with the processes of return processes of recrystallization, the cat is which can lead to inhomogeneous grain growth and a significant escalation patterns, that will lead to the inevitable loss of strength.

Thus, increasing the strength of the alloy have the greatest contribution of grain boundary hardening by reducing the grain size of the α-phase is less than 0.5 μm in accordance with the known ratio of the Hall-Petch for yield strength [Cox, J.V., Physics of strength and plasticity. TRANS. from English., the compilation. M.: metallurgy, 1972. 304 S.], as well as due to the formation of large angle grain boundaries, the total share of which not less than 60%, which in comparison with low-angle and special borders make the greatest contribution to hardening. While large-angle grain boundaries contributes to the improvement of ductility due to involvement in the grain boundary deformation processes, in particular, the accumulation of dislocations at grain boundaries. The presence of interphase boundaries separate ultramatic grains of β-phase distributed in the structure, increasing the total length of the large angle boundaries [THIS Valiev, Nanostructuring of metals by severe plastic deformation for advanced properties. // Nature Materials, 2004, V. 3, pp.511-516.; THIS Valiev, T.G. Langdon, The art and science of tailoring materials by nanostructuring for advanced properties using SPD techniques, Adv. Eng. Mater. (special issue: Bulk Nanostructured Materials, eds.: THIS Valiev, H. Hahn, T.G. Langdon), Vol.12, issue 8 (210), pp.677-691.]. An additional contribution to plasticity gives the relative low density of dislocations (less than 1014m-2inside ultramatic grains, equiaxial shape, which characterized the tsya coefficient of not more than 1:2, relative to the equilibrium boundary, which increases the uniformity of plastic flow and reduces the likelihood of early localization of deformation, which is usually characterized by an increase in the uniform elongation curves of strain [E. Ma. Eight routes to improve the tensile ductility of bulk nanostructured metals and alloys, JOM (2006) P.49].

The dependence of the fatigue limit of the size of the grain is often described by a formula similar to the dependence of the Hall-Petch for yield strength. In most cases, the reduction of grain size to ultramega range (less than 1 micron) fatigue properties of metallic materials increase [A. Vinogradov, S. Hashimoto, Multiscale phenomena in fatigue of ultra-fine grain materials - an overview. // Materials Transactions. 2011. V.42(1). pp.74-84]. However, the formation in metals and alloys UMP structure does not always lead to increased fatigue life, which may be due to their limited plasticity, which depends not only on grain size, but also on such features of the structure, as state boundaries, the shape of the grains, the distribution of second phase and others In particular, sufficient plasticity UMP alloy obtained by the proposed method, is provided by the formation of relative equilibrium grain boundaries of α and β phases, the dislocation density not exceeding 1014m-2and equiaxial shape of the grains, reducing the stress concentration at the boundaries in the course of the deformation elongation. The achievement of high strength and ductility in the alloy allows to achieve higher levels of fatigue durability [I.P. Semenova, Yakushina E.B., Nurgaleeva V.V., Valiev THIS Nanostructuring of Ti-alloys by SPD processing to achieve superior fatigue properties // International Joint Materials Research (formerly Z. Metallk.), Vol.100 (2009), 12, P.1691-1696]. Thus the formation of ultramagic mainly equiaxial α - and β-grains, on the one hand, increases the path of propagation of cracks, and interphase boundaries increase the frequency of stops cracks that contributes to maintaining sufficient fracture toughness, thereby contributes to the overall durability of the UMP alloy.

In General, the formation described above UMF patterns in the (α+β)-titanium alloys in the proposed set of features of the invention resulting in increased mechanical strength, while maintaining sufficient ductility and fatigue resistance.

The invention is illustrated by drawings, where figure 1 shows a schematic illustration of the UMP patterns of two-phase alloy after processing by the proposed method, and figure 2 - image of the microstructure of alloy VT6 obtained by transmission electron microscopy after treatment by the proposed method: svetlopoli image (a), the individual grains of β-phase (b); electronography (s).

The method is as follows.

Preparation of two-phase (α+β)-the titans is the first alloy is subjected to heat treatment, i.e. heating below the temperature TPPat 15°C for at least 1 min per 1 mm cross-section, after which the structure of the material consists of β-solid solution and the primary grains of α-phase with the ratio of their volume share of approximately 80% and 20%, respectively. Next, the workpiece is subjected to high-cycle intense plastic deformation with achievement of the accumulated true strain e≥4, which is carried out at a temperature of T=0.6 TPP. After cooling the deformed billet to room temperature it is formed ultrafine-grained structure with a grain size of the α-phase is less than 0.5 μm, β-phase is localized in isolated areas in the form of grains not larger than 1 μm (figure 1).

After SDI plastic deformation by changing the shape of the workpiece at a temperature of T=0.6 TPPwith a speed of less than 10-1with-1several iterations to ensure that the degree of deformation ε≥50% leads to additional refinement of the structure in which the size of the grains and subgrains α - and β-phase can reach 100...200 nm. Grain α - and β-phases are predominantly large-angle boundaries. Reduced rate of strain contributes to the formation of equiaxial shape of the grains and the transformation of low-angle boundaries in angle.

Severe plastic deformation of the workpiece can be carried out m togami equal channel angular pressing or equal channel angular pressing on the scheme Conform.

Plastic deformation by changing the shape of the grains can be carried out by methods of extrusion, rolling or drawing.

The workpiece may be subjected to annealing at a temperature not higher than T=0.4 TPPin for 1...4 hours to further reduce the total density of dislocations.

After processing they control the mechanical properties at room temperature and the control of the microstructure.

An example of a specific application.

Took the rod of the two-phase (α+β)titanium alloy VT6 with a diameter of 20 mm and a length of 100 mm, the Temperature of polymorphic transformation alloy amounted to 965°C. the Rod was heated to a temperature of 950°C for 20 minutes. Hot rod was moved in deforming the snap and subjected to the ECA-pressed in several cycles according to the above method. The heating temperature deforming the snap was 550°C. the Angle of intersection of the channels f=120°. The number of consecutive cycles of pressing was equal to 6, the result was achieved cumulative true strain degree e=4.2V. The resulting billets were machined to a diameter of 19 mm

In the next step, the rod was subjected to extrusion speeds of deformation does not exceed 10-1with-1with the total number of cycles is equal to 6. The temperature for the first 2 cycles was 450°C, and for the next 2 cycles was reduced to 350 and 250°C, according to the respectively. The last 2 cycles of extrusion was carried out at a temperature of 450°C With a minimum speed of deformation (about 10-2with-1). By the extrusion of the workpiece diameter decreased from 19 to 10 mm (ε~70%). After deformation of the workpiece was subjected to annealing in air at 300°C for 4 hours.

From the resulting billets were fabricated samples for studies of microstructure and mechanical properties. Analysis of the microstructure was carried out by the method of transmission electron microscopy (TEM)on a Jeol 2100 EX. Using x-ray analysis (PCA) on a Rigaku diffractometer conducted phase analysis and evaluation of the dislocation density. Mechanical testing of the samples was carried out in accordance with the requirements of GOST 1497-84.

Received UMP structure in the workpiece alloy (figa, b), which was formed during the implementation of the proposed method of treatment, has an average grain size of 150 nm. The grain boundaries have a clear diffraction contrast on electroniccommerce the image patterns (figa, b), indicating that their bolsheului misorientation. Electronography (figs) is characterized by evenly spaced around the circumference of reflexes without significant azimuthal blur, which also indicates the formation of large angle grain boundaries. Inside the grains, the dislocation density does not exceed 1 14m-2that is also confirmed by the x-ray structure analysis. β-phase distributed in the microstructure in the form of separate grains with an average size of 120 nm, assessment by xfa its volume fraction was approximately 8%.

The control of mechanical properties at room temperature showed the values shown in the table. For comparison, the table shows the mechanical properties of the alloy to thermomechanical processing on the proposed method, and properties after processing by a known method prototype.

Table
Mechanical properties of alloyStatus alloy
The delivery statusAfter processing by the method prototypeAfter treatment by the proposed method
Tensile strength, MPa94013701615
Yield strength, MPa84012701535
Total elongation, %16 119
Uniform elongation, %81,03,5
Relative narrowing, %453745
The fatigue limit (bending with rotation), MPa550695740

The data in the table show that the processing result by the proposed method achieved significantly higher strength and fatigue limit with maintaining good ductility compared with the processing in accordance with the prototype. The proposed type UMP patterns has the potential to further increase the strength of the alloy. In particular, obtaining the alloy UMP patterns with an even smaller grain size 100...80 nm will provide the tensile strength of up to 1750 MPa. This important parameters UMP patterns it should be noted-angle orientation of the boundaries, the low density of lattice dislocations, which promotes a more uniform flow of plastic deformation and reduces the likelihood of early localization of deformation. Along with the significant what procenium this type UMP structure allows you to maintain good ductility, which is characterized by elevated values of relative and uniform elongation unlike UMP patterns obtained by a known method prototype.

Thus, the proposed invention allows to form a two-phase (α+β)-titanium alloys ultrafine-grained structure providing material high mechanical strength and resistance to fatigue by maintaining good ductility, which is achieved by using severe plastic deformation of alloys in certain temperature and high-speed modes.

1. Two-phase alpha-beta titanium alloy having a microstructure consisting of ultramagic grains of alpha-phase and beta-phase with a size less than 0.5 μm, characterized in that the microstructure of the alloy, the proportion of grains with an aspect ratio of the grains is not more than 2 not less than 90%, and more than 40% of the grains have a large-angle boundaries, and the average dislocation density not exceeding 1014m-2.

2. A method of obtaining a two-phase alpha-beta titanium alloy with ultrafine-grained structure, including heat treatment by heating the workpiece at a temperature not higher than the temperature of polymorphic transformation (TPP), severe plastic deformation with the number of cycles that provide the necessary accumulated true strain, then subsequent plastic de is ormatio change the shape of the blank, characterized in that after heating the workpiece immediately subjected to high-cycle intense plastic deformation with achievement of the accumulated true strain e≥4, which is carried out at a temperature of T=0.6 TPP, followed by a plastic deformation by changing the shape of the workpiece at a speed less than 10-1with-1several iterations to ensure that the degree of deformation ε≥50%.

3. The method according to claim 2, characterized in that severe plastic deformation perform equal-channel angular pressing or equal channel angular pressing on the scheme Conform.

4. The method according to claim 2, characterized in that the plastic deformation by changing the shape of the workpiece is performed by extrusion or rolling, or drawing.

5. The method according to claim 2, characterized in that the workpiece after plastic deformation shape change are annealed at a temperature of not higher than T=0.4 TPPin for 1...4 hours



 

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2 cl, 6 dwg, 3 tbl

FIELD: metallurgy.

SUBSTANCE: method to produce a blank of a blade of gas turbine engines (GTE) with ultra-fine grain structure from titanium alloys includes preliminary heating of the blank to temperature below temperature of polymorphous conversion and treatment by means of multiple intensive plastic deformation with changing of deformation directions in several cycles. Treatment is carried out under isothermic conditions at identical temperature of the blank and the punch. In each cycle deformation is carried out at temperature of alloy annealing according to stages, which include setting of the cylindrical blank in the closed punch, open setting with production of the blank in the form of a disc, flattening to the disc rib in the closed punch for production of the blank with the square section, its setting in the closed punch to the cylindrical blank. Number of treatment cycles is determined based on achievement of the extent of accumulated deformation of at least five. Then closed setting of the blank is carried out at the temperature of 50-100°C below the alloy annealing temperature, squeezing into the cylindrical blank, having two different diameters of cross section for a blade foot and airfoil, and flat stamping of the blade blank.

EFFECT: homogeneous ultra-fine grain structure is produced in a blade blank, providing for high physical and mechanical and operating properties of a blade.

2 dwg

FIELD: metallurgy.

SUBSTANCE: thermomechanical device includes a working member made in the form of one pre-deformed element or several pre-deformed and parallel and/or in-series connected elements from alloy based on titanium with shape memory effect. The working member is made in the form of a rod with working part of cylindrical or rectangular shape and fixing parts in the form of expansions on the rod ends, the sectional area of which is at least by five times more than the sectional area of its working part.

EFFECT: achieving maximum possible translational relative movements of the member at variation of its temperature at the temperature interval of reverse martensitic transformation of material.

6 dwg, 1 ex

FIELD: metallurgy.

SUBSTANCE: proposed method comprises smelting of alloy, making slab, machining its surface, hot, warm, and cold rolling, sintering and ageing. Smelted is pseudo-beta-titanium alloy with aluminium content not higher than 5.0 wt % and molybdenum equivalent No eq. ≥ 12 wt %, calculated by the following formula: Mo eq. wt % = %Mo + %Ta/4 + %Nb/3.3 + %W/2 + %V/1.4 + %Cr/0.6 + +%Fe/0.5 + %Ni/0.8 + %Mn/0.6 + %Co/0.9. Semi-finished 8-2 mm-thick rolled stock produced in hot and cold rolling is subjected, prior to cold rolling, to quenching at Tpt+(20-50°C) for 0.1-0.5 h with cooling. Cold rolling is performed to sheet thickness of 6-1 mm in signal-phase beta-state in two and more steps in several passes with 1-6%-reduction in one pass and total reduction at every step of 30-50%. Note here that intermediate quenching is carried out between said steps in conditions identical to quenching of semi-finished rolled stock before cold rolling.

EFFECT: high-quality rolled thin sheets.

5 dwg, 2 tbl

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy, particularly, to forming semis from titanium alloy BT6 and may be used in machine building, aircraft engineering and medicine. Proposed method comprises annealing at 850°C with holding for an hour in furnace to create globular (α+β)-structure and multipass rolling combined with affecting semis to pulsed electric current with density of 50-200 A/mm2, frequency of 830-1000 Hz, pulse duration of 100-120 ms to ensure total true strain degree of e>1 and to form nanocrystalline structure in semi. Note that, after every pass, semi is water cooled. Higher forming capacity of alloy is provided for.

EFFECT: higher strength at optimum ductility.

5 cl, 1 dwg, 1 tbl, 1 ex

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy, particularly, to plastic deformation of metals, namely, to production of thin sheets from (α-β)-, pseudo-β, β-titanium alloys. Proposed method comprises preparing stack consisting of the main and clad layers for rolling, assembling said stack, welding, degassing, hot rolling of clad sheet, subsequent rolling and thermal treatment, and surface finishing. Said stack is assembled of the main layer composed of large-size blank from difficult-to-deform titanium alloy and two clad layers from unalloyed titanium used as temporary layers. Clad sheet is rolled in several passes at temperature above and below that of polymorphic transformation Tpt. Note here that after rolling said clad layers are removed in surface finishing.

EFFECT: production of thin high-surface-finish sheets from ((α-β)-)-, pseudo-β, β-titanium alloys.

2 dwg, 4 tbl, 1 ex

FIELD: metallurgy.

SUBSTANCE: beta-titanium alloy with ultrafine-grained structure consists of beta-phase gains with mean size not exceeding 0.5 mcm, precipitations of secondary alpha-phase particles of spherical shape and mean size not exceeding 0.5 mcm and volume fraction in the structure making at least 40%. Proposed method comprises intensive plastic deformation and thermal treatment. Thermal treatment is carried out before deformation by heating to temperature exceeding that of polymorphic conversion by 5-15°C for, at least, one minute for 1 mm of diameter cross-section and quenching in water. Intensive plastic deformation is performed by equal-channel angular pressing with changing deformation direction through 90 degrees after every deformation cycle at (T"пп"-200…T"пп"-150)°C with total accumulated deformation e≥3.5 and subsequent quenching in water.

EFFECT: higher strength and fatigue characteristics of alloys.

2 cl, 1 tbl, 1 ex

FIELD: nanotechnologies.

SUBSTANCE: invention relates to the field of superconductivity and nanotechnologies, namely, to the method for production and processing of composite materials on the basis of high-temperature superconductors (HTSC), which may be used in devices of energy transmission, for development of current limiters, transformers, powerful magnetic systems. The method to process a high-temperature superconductor representing a composite structure made of a substrate material with applied buffer layers of metal oxides, a layer of a superconducting material of metal oxides, above which a protective layer of silver is applied, consists in radiation of the specified structure with an ion beam of heavy noble gases with energy from 48 to 107 MeV with a flux of 2×1010 - 5×1010 ion/cm2 and density of ion flux of 2.6×10-8 - 6.5×10-8 A/cm2 maintaining temperature from 30°C to 100°C, with provision of relief of internal elastic stresses in the composite structure.

EFFECT: improved characteristics.

3 dwg, 1 tbl

FIELD: metallurgy.

SUBSTANCE: method involves the following stages: formation of a basic consumable electrode by melting with the help of at least one stage of vacuum arc melting of common primary γ-TiAl-alloy containing titanium and/or at least one β-stabilising element in the amount that is not enough in comparison to the obtained basic β-γ-TiAl-alloy, arrangement on the above basic consumable electrode of titanium and/or p-stabilising element in the amount corresponding to the above insufficient amount of titanium and/or β-stabilising element, with uniform distribution as to length and periphery of the basic consumable electrode, addition to the basic consumable electrode of the above arranged amount of titanium and/or β-stabilising element so that homogeneous basic β-γ-TiAl-alloy is obtained at final stage of vacuum arc melting process.

EFFECT: invention allows creating homogeneous basic β-γ-TiAl-alloy without formation of any cracks.

10 cl, 5 ex, 4 dwg

FIELD: metallurgy.

SUBSTANCE: sheet is made from pure titanium and contains titanium and unavoidable impurities. It features yield point of 215 MPa or higher, mead size d of the grain making 25 mcm of larger and 75 mcm or smaller, and hexagonal crystalline structure. Appropriate grains in hexagonal crystalline structure feature means Schmidt factors (SF) of twins 11-22 with rolling direction oriented along their axes. Means Schmidt factor (SF) and grain means size d satisfy the following relationship: 0.055≤[SF/√d]≤0.084. Heat exchanger plate comprises sheet of pure titanium and as integral component.

EFFECT: high ductility and strength, heat exchange plate with such sheet.

2 cl, 6 dwg, 3 tbl

FIELD: metallurgy.

SUBSTANCE: thermomechanical device includes a working member made in the form of one pre-deformed element or several pre-deformed and parallel and/or in-series connected elements from alloy based on titanium with shape memory effect. The working member is made in the form of a rod with working part of cylindrical or rectangular shape and fixing parts in the form of expansions on the rod ends, the sectional area of which is at least by five times more than the sectional area of its working part.

EFFECT: achieving maximum possible translational relative movements of the member at variation of its temperature at the temperature interval of reverse martensitic transformation of material.

6 dwg, 1 ex

FIELD: metallurgy.

SUBSTANCE: alloy based on titanium with shape memory effect for bone implants and method for its treatment are proposed. Alloy contains the following, wt %: Ti 71.0-74.0, Nb 19.0-23.0, Ta and/or Zr 4.0-9.0. At room temperature the alloy has nano-sized structure consisting of cubic metastable β-phase, orthorhombic α"-martensite, hexagonal ω-phase and hexagonal α'-martensite, and alloy elasticity modulus does not exceed 25 GPa. Alloy treatment method involves hot pressure shaping of an alloy ingot based on titanium at initial temperature of 900-950°C and final temperature of 700-750°C, thermomechanical treatment by multi-pass cold deformation with total degree of reduction of 31 to 99%, annealing after deformation at the temperature of 500-600°C and final quenching in water. Then, mechanical pseudoelastic cycling of the obtained workpiece is performed under conditions of single-axis tension till 2% of deformation is achieved during 50-100 cycles and removal of load.

EFFECT: alloy has long-term service life of bone implants due to low elasticity modulus close as to the value to bone tissue and pseudoelasticity effect.

5 cl, 1 tbl, 1 ex

FIELD: metallurgy.

SUBSTANCE: invention may be used in structures operated at up to 650°C, for example, parts of gas turbine engine high-pressure compressor housing and blades Proposed titanium-based alloy comprises the following components in wt %: Al - 5.7-6.7, Sn - 3.0-4.5, Zr - 3.0-4.5, Mo - 0.5-1.4, Nb - 0.2-0.6, W - 0.01-0.3, V - 0.3-0.9, Fe - 0.01-0.07, Si - 0.3-0.52, C - 0.03-0.10, O - 0.03-0.14, Ti making the rest. Note here that (V+Nb)≤1.1 wt %. Proposed alloy features higher strength at temperatures exceed 600°C.

EFFECT: higher operating temperatures of parts.

2 tbl, 5 ex

FIELD: metallurgy.

SUBSTANCE: proposed alloy comprises the following elements, in wt %: carbon - 0.03-0.07, iron - 0.15-0.25, silicon - 0.05-0.10, nitrogen - 0.010-0.030, aluminium - 0.05-0.50, boron - 1.5-3.5, titanium and impurities making the rest.

EFFECT: higher efficiency of absorption, better working properties.

3 tbl, 1 ex

FIELD: metallurgy.

SUBSTANCE: proposed alloy contains the following components, wt %: aluminium 0.3÷0.7, zirconium 7.0÷15.0, niobium 1.0÷2.0, oxygen 0.2÷0.3, carbon 0.05÷0.15, silicon 0.10÷0.35, iron 0.1÷0.6, hafnium of not more than 1.0, titanium is the rest; at that, sum of iron and aluminium is not more than 1.0 wt %.

EFFECT: creation of alloy with optimum ratio of alloying elements, which has high mechanical properties, including the value of elasticity modulus and having no adverse effect on a living organism.

1 tbl

FIELD: metallurgy.

SUBSTANCE: beta-titanium alloy with ultrafine-grained structure consists of beta-phase gains with mean size not exceeding 0.5 mcm, precipitations of secondary alpha-phase particles of spherical shape and mean size not exceeding 0.5 mcm and volume fraction in the structure making at least 40%. Proposed method comprises intensive plastic deformation and thermal treatment. Thermal treatment is carried out before deformation by heating to temperature exceeding that of polymorphic conversion by 5-15°C for, at least, one minute for 1 mm of diameter cross-section and quenching in water. Intensive plastic deformation is performed by equal-channel angular pressing with changing deformation direction through 90 degrees after every deformation cycle at (T"пп"-200…T"пп"-150)°C with total accumulated deformation e≥3.5 and subsequent quenching in water.

EFFECT: higher strength and fatigue characteristics of alloys.

2 cl, 1 tbl, 1 ex

FIELD: process engineering.

SUBSTANCE: invention relates to machine building, particularly, to working wheel parts used in liquid-propellant rocket engine fuel systems. Proposed working wheel is composed a disc. Proposed method comprises casting ingot from refractory alloy, making pellets from said ingot, filling said pellets in vacuum into capsule shaped to a disc, sealing said capsule, hot isostatic pressing of blank with holding, depressurising and lathing said capsule to make the part of required geometry. Ingot is cast from refractory titanium alloy containing the following elements in wt %: aluminium - 5.0-7.5, zirconium - 3.0-5.0, tungsten - 0.5-7.5, hafnium - 0.005-0.2, titanium making the rest. Pellets are shaped to 40-300 mcm-dia spheres. Said hot isostatic pressing is executed in gasostatic extruder at P=150-160 MPa, T=920±10°C, while holding is carried out for 2.5-3.5 hours.

EFFECT: higher strength and creep resistance, high heat resistance at working temperatures of up to 750°C.

2 cl, 1 tbl

FIELD: metallurgy.

SUBSTANCE: proposed titanium alloy contains the following components in wt %: aluminium 6.0-7.5, zirconium 3.0-5.0, tungsten 6.0-7.5, hafnium 2.5-4.0, tantalum 2.5-4.0, titanium making the rest.

EFFECT: decreased weight, higher reliability, durability and strength.

2 cl, 1 tbl

FIELD: chemistry.

SUBSTANCE: invention relates to a biodegradable highly filled thermoplastic composition used in making films and consumer packaging. The composition contains polyethylene, biodegradable filler in form of potato starch, process additives: oligoepoxy ether with molecular weight of 1800-3500 and content of epoxy groups of 2.0-4.0% in nano-form and nonionic and cationic surfactants.

EFFECT: obtained composition has good process parameters, articles made from the composition are biodegradable under the effect of light, moisture and soil microflora.

2 tbl, 6 ex

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