RU2536614C2 - Production of bars and thin wires from titanium-nickel system alloy with shape memory effect - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: set of invention relates to production of thin bars and wires with shape memory effect and superplasticity from alloys of nickel-titanium system to be used in aircraft engineering, radio electronics, medicine, etc. Proposed method consists on production of the alloy with shape memory effect. Bar-like blank is made from said alloy by compaction or helical rolling and heated to make the bar by rotary swaging in several steps to required size with intermediate heating between swaging steps. Blank is heated before rotary swaging to 300-500°C. Method of alloy production for further making of the bar consists in facing the high-strength graphite crucible walls and bottom by nickel plates. The rest mix is placed inside the crucible to fuse in vacuum induction furnace. The melt is held, teemed in vacuum into chill mould and cooled down to get the ingots. Thereafter, electrode is made from obtained ingots or from bard produced from said ingots. Electrode material is subjected to electron beam smelting in vacuum of at least 5x10^-3 Hg mm to form the ingot in copper casting mould.

EFFECT: wire production from bar by hot or cold drawing.

9 cl, 2 tbl

Description

The group of inventions relates to techniques for the production of thin rods and wires with a "shape" effect and superelasticity from nickel-titanium alloys with a "shape" effect, used in aviation, electronics, medicine, space technology, mechanical engineering and other technical fields.

Nickel-titanium alloys corresponding to the stoichiometric composition of the Ni-Ti intermetallic compound (from 46 to 58 weight percent nickel, the rest mainly titanium), as well as ternary alloys described by the formulas TiNi _x Co _1-x , TiNi _x Fe _1-x , TiNi _x Cu _1-x , TiNixV _1-x and TiNi _x Cr _1-x , where x is a coefficient varying from 0 to 1, in addition to the shape memory effect, possess a unique complex of physical and mechanical properties and find an ever wider application in various fields of technology and medicine.

A known method of producing wire from alloys with shape memory nickel and titanium based, including, in particular, processing the alloy with shape memory with cold working and low temperature annealing without re-compression (EP 0143580 A1, C22F 1/00, 06/05/1985 )

Although the known method eliminates the deformation of the product in the perpendicular direction, the quality of the wire remains low.

Closest to the proposed is a method of producing rods from nickels of the nickel-titanium system with a shape memory effect, according to which an alloy with a shape memory effect is created, semi-finished products are made from an alloy by compression or cross-screw rolling in the form of rods, they are heated to a temperature of 450-950 ° C and made from semi-finished bars by rotary forging; and a method for producing a wire from alloys of a nickel-titanium system with a shape memory effect, according to which rods are made according to the above method and wire is made from them by warm or cold drawing (RU 2162900 C1, publ. 02/10/2001).

The amount of carburization of the metal during melting is 0.02-0.05%. The nitrogen content in the alloy does not exceed 0.01%. The hydrogen content in the alloy does not exceed 0.008%. The oxygen content in the alloy does not exceed 0.15%. The minimum diameter of the resulting wire is 0.1 mm. During cyclic loading of the obtained rods and wire, the number of cycles to failure is 5000-7000.

The objective of the invention is the industrial production of semi-finished products from alloys with shape memory based on titanium nickelide, in particular thin rods and thin wires with improved mechanical characteristics and improved functional properties, such as cyclic durability at high loads, a high degree of shape recovery after applying an increased load (small residual deformation after application of increased load), increased ductility.

The technical result that provides a solution to the problem is to increase the cyclic durability of rods and wires from the specified alloy, reduce residual deformation after applying an increased load and provide the possibility of obtaining a thinner wire.

The technical result is achieved by a method of producing a bar from an alloy of a nickel-titanium system with a shape memory effect, characterized in that a blank is produced from a nickel-titanium system alloy with a shape memory effect by pressing or cross-screw rolling, which is then heated and subjected to rotational forging in several stages to the desired size with a degree of deformation of 5-25% at each stage with intermediate heating of the workpiece between the forging stages, while heating the workpiece before rotational forging and industrial weft heating is carried out to a temperature of 300-500 ° C for 30-180 minutes, and after reaching a total deformation of 40-90% between the forging step is performed additional annealing the preform at a temperature of 300-500 ° C for 30-180 minutes.

The achievement of the technical result is facilitated by special cases of the method:

- upon receipt of a bar with a diameter of 20-40 mm, heating the workpiece before rotational forging and intermediate heating is carried out in an electric chamber furnace for 30-180 minutes;

- upon receipt of rods with a diameter of 1.6-20 mm, the workpiece is heated before rotary forging and intermediate heating is carried out in an electric chamber furnace for 30-120 minutes, and the heated workpieces are fed to the rotational forging through a tube furnace with a workpiece temperature of 300-500 ° FROM.

The technical result is also achieved by a method of producing a wire from an alloy of a nickel-titanium system with a shape memory effect, according to which a wire is obtained from an alloy of a nickel-titanium system with a shape memory effect as described above and subjected to warm or cold drawing.

The achievement of the technical result is facilitated by special cases of the method:

- upon receipt of the wire by cold drawing, intermediate annealing is carried out at a temperature of 200-500 ° C for 0.05-30 minutes;

- upon receipt of the wire by warm drawing, heating of the wire in front of the wire is carried out to 200-500 ° C;

- for drawing wire with a diameter of 0.4-4.0 mm using a die of hard alloys with an angle of 2α equal to 6-12 degrees, and the length of the calibration zone of the die 40-70% of the diameter of the die;

- for drawing wire with a diameter of 0.02-4.0 mm using a die from single crystal diamond with an angle of 2α equal to 6-12 degrees, and the length of the calibration zone of the die 30-80% of the diameter of the die.

The problem is solved in that rotational forging (RK) at low temperatures of 300-500 degrees, with low-temperature annealing (300-500 ° C for 30-120 min) between the accumulated deformation of up to 90% and at the final stage allows to obtain a uniform ultrafine-grained uniform cross-sectional structure on thin rods. This provides a set of improved mechanical characteristics and functional properties of semi-finished products, suitable for the manufacture of either semi-finished products of smaller sizes, or finished products for medicine, robotics, the oil and gas industry, and the aerospace industry in size and volume. Further drawing at low temperatures of 200-500 ° C with low-temperature annealing (200-500 ° C for 0.05-30 min) between the accumulated deformation of up to 90% ensures the preservation and improvement of the obtained structure and properties. The use of a tool (die) with a certain geometry allows you to get the thinnest wire with a diameter of up to 0.020 mm, which has all of these properties. A wire with such dimensions and properties is indispensable in mini-designs and devices. The use of an alloy obtained using an improved double vacuum remelting scheme - vacuum induction (VIP) and electron beam (EBL), significantly reduces the content of impurities in the alloy and has a positive effect on cyclic durability.

Obtaining an alloy of the Nickel-titanium system with the effect of "memory" of the form was carried out as follows.

As the feedstock (mixture) for the production of ingots in vacuum induction furnaces used:

- titanium sponge grade TG-100, TG-110 in accordance with GOST 17746-79;

- sheets of titanium grade VT1-00; VT1-0 according to GOST 22178-76 (or sheet trim cut by non-gas welding);

- iodide titanium;

- primary nickel grade H0; H1y; H1 according to GOST 849-70.

The charge was weighed on an electronic precision balance with a weighing discreteness of 0.1 grams, which made it possible to accurately ensure the calculated chemical composition while observing the remaining technological regimes.

When laying the charge in the crucible, the method of initial lining of the walls and bottom of the crucible with nickel plates (for example, nickel cathodes chopped on guillotine shears) and laying the rest of the charge inside this nickel basket were used. Melting begins in a vacuum of 10 ^-2 -10 ^-3 mm RT.article After the entire charge was melted, the melt was held for 1-30 minutes prior to casting. Casting was carried out in vacuum at a temperature of 1250-1580 ° C in steel, or cast-iron, or graphite molds (both detachable and one-piece molds can be used).

Further, as the feedstock for the production of ingots in an electron beam multi-chamber furnace was used:

- ingots obtained in vacuum induction furnaces (machined), welded into electrodes;

- rods obtained from vacuum-induction remelting ingots by rolling on PVP mills or by pressing (machined), welded into electrodes.

For the electrode, vacuum-induction remelting ingots (VIPs) were taken from one series of heats (of a given chemical composition) or rods obtained from vacuum-induction remelting ingots from one series of heats. Billets (ingots, rods) were machined to remove oxides and surface slags and inclusions to a clean surface. The diameter of the workpieces was selected depending on the mold used (50-170 mm), the electrode length was chosen sufficient to obtain a full-fledged ingot suitable for subsequent redistribution (1000-2200 mm). To obtain the electrode of the desired length, the workpieces were welded together by welding in argon.

Melting was started under vacuum 2 × 10 ^-5 mm RT.article Melting time depends on the length of the electrode and the feed rate of the electrode. The electrode feed rate was chosen optimal for the formation of a good melt pool and the formation of an ingot and varied from 1.5 mm / min to 150 mm / min. The average melting time for an electrode with a diameter of 60-70 mm and a length of 1500-2200 mm is 1.5-3.5 hours. The working vacuum, depending on the melting rate and the gas content in the remelted metal, was at least 5 × 10 ^-3 mm Hg. The ingot was formed in a copper water-cooled mold with a diameter of 65-200 mm.

Electron beam remelting (EBL) consists in melting the initial billet (ingot, bar) in vacuum and subsequent crystallization. The main mechanism of refining metals in a vacuum is the evaporation of easily volatile metal impurities and the removal of volatile oxides of CO and CO ₂ or volatile metal oxides having a higher vapor pressure than that of a molten metal.

All this allows for the most complete and quick cleaning of impurities and to obtain good homogeneity of the ingot, high-quality metal in terms of the macrostructure of the ingots and the gas content. Deviations of the obtained nickel content from the calculated range within ± 0.1%. The carbon content in the alloy does not exceed 0.01%. The hydrogen content in the alloy does not exceed 0.003%. The total oxygen and nitrogen content in the alloy does not exceed 0.032%.

These characteristics of the ingots provide alloys with a phase transformation temperature that meets certain properties of the final product or semi-finished product and has enhanced functional properties compared with conventional methods. Reducing the level of impurities compared with the closest analogue: carbon from 0.05% to 0.01%, hydrogen from 0.008% to 0.003%, oxygen from 0.15% to 0.03% and nitrogen from 0.008 to 0.002% - increases the functional the properties of semi-finished products (bars, wire) obtained from ingots are 1.5-2 times (with cyclic loading of a wire element (5% deformation) - the number of cycles before failure increases from 5000-7000 to 10000-15000).

A method of producing a rod from an alloy of a nickel-titanium system was carried out as follows.

1. Obtaining rods by pressing.

Bars with a diameter of 20–50 mm were obtained by pressing a preformed billet with a diameter of 85–200 mm. The billet was obtained from the ingot by cutting the gate on a cutting machine and turning the surface of the ingot on the lathe until all surface defects (gas porosity, surface cracks, etc.) were removed. The billet was heated in electric furnaces or induction furnaces to a temperature of 800-1020 ° C. Before heating, the preform was coated with grease (glass graphite, talc, etc.). Pressing was carried out in 2-4 transitions depending on the initial diameter of the workpiece. At the first transition, the hood did not exceed 3, and at the last transition it could reach 30. The pressing speed did not exceed 35 mm / s.

2. Obtaining rods by the method of PVP (cross-helical rolling).

Cross-screw rolling allows you to get rods with a diameter of 8-160 mm directly from the ingot. The sprue was cut off from the ingot, and the ingot itself was turned to remove surface defects. Rolling is carried out as follows:

- heating the ingot in an electric furnace to a temperature of 750-1000 ° C;

- rolling the ingot in several stages (passes) with a degree of deformation on each pass of 5-25%, with intermediate heatings between the passes to the desired size.

Pressed or rolled billets in the form of rods with a diameter of 8-40 mm after mechanical processing were subjected to deformation on three to six rotary forging machines of different capacities to obtain a wire billet or thin rod.

Bars with a diameter of 20-39 mm were obtained from pressed or rolled billets on a high-power rotary forging machine. The billet was heated in an electric furnace to a temperature of 300-500 ° C for 30-180 min, after which forging with a deformation of 5-25% at each transition (stage) was carried out to the desired size. Between the transitions, the preform was intermediate heated to the same temperature. If the total deformation reached 40-90%, between the transitions annealing was performed in an electric chamber furnace at a temperature of 300-500 ° C for 30-180 minutes.

Rods with a diameter of 1.6-19 mm were obtained on rotary forging machines (RCMs) of medium and low power. The billet was heated to a temperature of 300-500 ° C for 30-120 minutes in an electric furnace, after which forging was carried out in several stages (transitions) “to the passage” with heating directly during feeding the billet to a rotary forging machine in a tubular gas furnace or in a tubular electric furnace installed in front of the rotary forging machine, to a temperature of 300-500 ° C with a deformation of 5-25% at each transition to the desired size. If the total deformation reached 40-90%, between the transitions annealing was carried out in an electric chamber furnace at a temperature of 300-500 ° C for 60-180 minutes.

The obtained bars are not only an intermediate blank for drawing, but also a finished product - a thin bar. The surface quality is ensured by the use of a special tool (finish strikers - they have a longer working surface as opposed to work strikers) and grinding the rods on a centerless grinding machine. The obtained rods have increased functional properties compared to rods obtained in a known manner (RU 2162900) - in particular, the tensile strength increases from 800 MPa to 1300 MPa, and the relative elongation increases from 5% to 25%. The residual deformation after loading with 5 cycles (with a strain of 6%) decreases from 1% to 0.3%.

A method of obtaining a thin wire from an alloy of a nickel-titanium system was carried out as follows.

The wire from alloys of the nickel-titanium system with a diameter of 0.40-4.0 mm was obtained from an intermediate billet - a bar obtained by the above method, by the method of warm drawing or cold drawing on a line of two single-pass drawing mills. A wire with a diameter of 0.020-0.40 mm was obtained by the method of warm or cold drawing on a line of two drawing six-wire mills. When using the cold drawing method, intermediate annealing was used at temperatures of 200–500 ° C for 0.05–30 min.

KLZ brand graphite with additives of 1.0-3% soap powder or synthetic lubricants were used as lubricants during cold drawing. When warm drawing used "aquadag" (colloidal solution of graphite in water).

With warm drawing, the wire heating in front of the wire was carried out in a slit dual-zone electric furnace 1.5-2.0 m long to temperatures of 200-500 ° C. The temperatures in the zones were independently regulated, which made it possible to set a higher temperature at the inlet to ensure uniform heating of the wire according to the technological regime. Drawing from a diameter of 4.0 to 2.5 mm was carried out in increments of 0.3-0.15 mm; from a diameter of 2.5 to 1.5 mm - in increments of 0.25-0.10 mm; from a diameter of 1.5 to 0.4 mm - in increments of 0.20-0.05 mm; from a diameter of 0.4 to 0.1 mm - in increments of 0.15-0.01 mm, from a diameter of 0.1 to 0.020 mm in increments of 0.009-0.001. The drawing speed depending on the diameter and chemical composition of the wire was regulated in the range of 0.01-1.3 m / s.

For drawing wire with a diameter of 4-0.4 mm, dies of hard alloys (VK3, VK6) with an angle of 2α equal to 6-12 degrees and a length of the calibration zone of the die equal to 40-70% of the diameter d of the die were used (GOST 9453-75 )

For drawing wire with a diameter of 0.4-0.020 mm, dies of single-crystal diamonds with tolerances in diameter from -0.0020 mm to -0.0004 with an angle of 2α equal to 6-12 degrees and a length of the calibration zone of the die equal to 30-80 are used. % of the diameter d of the die.

This technology allows you to get a thin wire from alloys with shape memory based on titanium nickelide with diameters up to 0.020 mm. Such a wire is widely used as an actuator in actuators and mini-devices. One of the basic requirements for these devices is high cyclic fatigue. The wire obtained by the proposed method withstands deformation of 8% - more than 10 × 6 times until fracture, which is more than an order of magnitude higher than the wire obtained in a known manner (RU 2162900).

Compliance with the requirements for the technology of producing wire from nickel-titanium alloys ensures a high level of its service properties - the degree of shape recovery (100% with deformation up to 15%), corrosion resistance, wear resistance, biocompatibility, damping and mechanical properties. The choice of the chemical composition of the initial ingot and the subsequent observance of a certain order of technological operations, the alternation of warm and cold drawing at the final stage allows us to obtain a wire that is as close as possible to the final product in properties, and in some cases is such.

The following is an example embodiment of the invention.

The starting material for producing the rods was three hot-deformed rods with a diameter of 20 mm of a NiTi alloy (Ni = 55.0% by weight), obtained:

1. From a single ingot of vacuum induction remelting by rolling on PVP mills at a temperature of + 1000 ° C (in a known manner).

2. From an ingot of vacuum-induction remelting and subsequent electron-beam remelting by rolling on PVP mills at a temperature of + 1000 ° C (the proposed method).

3. From an ingot of vacuum-induction remelting and subsequent electron-beam remelting by rolling on PVP mills at a temperature of + 1000 ° C (by the proposed method.

At the following stages, rods 1 and 2 are forged hot at temperatures of + 750 ° C on rotary forging machines up to a diameter of 2.8 mm and then hot drawn at temperatures of + 650 ° C produce a wire with a diameter of 0.4 mm. (The temperature, as in the known method is higher than in the proposed method.)

The bar 3 in the following stages, in accordance with the proposed method, is forged at a temperature of + 400 ° C on rotary forging machines up to a diameter of 2.8 mm with intermediate annealing at a temperature of + 400 ° C for 2 hours. Annealing was done after accumulation of deformation between passes 60 % Then it was dragged at a temperature of + 400 ° C to a diameter of 0.4 MM with intermediate annealing at a temperature of + 400 ° C for 2 hours. Annealing was done after accumulation of deformation between passes of 70%.

Samples of wire with a diameter of 0.4 mm, obtained from all three rods, were annealed before testing at a temperature of + 450 ° C for 30 min.

The wire obtained from the bar 3, with a diameter of 0.4 mm, was then dragged on six-time drawing mills on single-crystal diamond dies with an angle of 2α equal to 6 degrees and a length of the die calibration zone equal to 50% of the die diameter d (GOST 9453-75) at a temperature of + 300 ° C to a diameter of 0.020 mm with intermediate annealing: at a temperature of + 350 ° C for 30 minutes after accumulation of deformation between passes 80% (up to a diameter of 0.18 mm), next at a temperature of + 300 ° C for 20 min after accumulation of deformation between passes 90% (up to a diameter of 0.057 mm), next at a temperature of + 250 ° C for 10 min. after accumulation of deformation between passes 88% (up to a diameter of 0.020 mm). A wire sample was annealed at + 300 ° С for 0.05 min.

Comparative data on the percentage of impurities in the rods obtained by various methods of smelting are given in table 1.

Comparative data on the mechanical and functional properties are shown in table 2.

Thus, the proposed method for producing semi-finished products can significantly improve the mechanical and functional properties of thin rods and wire from alloys with shape memory based on titanium nickelide and use them for the manufacture of work items and parts in devices that are structurally limited in size and weight, but require increased service characteristics. This is especially true for mini-actuators and products used in medicine.

Claims (9)

1. A method of producing a rod from an alloy of a nickel-titanium system with a shape memory effect, characterized in that a nickel-titanium alloy with a shape memory effect is made by pressing or cross-screw rolling a bar stock, which is further heated and subjected to rotational forging several stages to the required size with a degree of deformation of 5-25% at each stage with intermediate heating of the workpiece between the forging stages, while heating the workpiece before rotational forging and intermediate heating are carried out before eratury 300-500 ° C for 30-180 minutes, and after reaching a total deformation of 40-90% between the forging step is performed additional annealing the preform at a temperature of 300-500 ° C for 30-180 minutes. 2. The method according to claim 1, characterized in that upon receipt of a bar with a diameter of 20-40 mm, heating the workpiece before rotational forging and intermediate heating is carried out in an electric chamber furnace for 30-180 minutes. 3. The method according to claim 1, characterized in that upon receipt of rods with a diameter of 1.6-20 mm, the workpiece is heated before rotational forging and intermediate heating is carried out in an electric chamber furnace for 30-120 minutes, and the heated workpieces are fed to rotary forging through a tube furnace with maintaining the temperature of the workpieces 300-500 ° C. 4. The method according to claim 1, characterized in that they use an alloy of a nickel-titanium system with a shape memory effect obtained by vacuum induction melting and subsequent electron beam remelting. 5. A method of producing a wire from an alloy of a nickel-titanium system with a shape memory effect, characterized in that from a nickel-titanium alloy with a shape memory effect by a method according to any one of claims 1 to 4, a bar is obtained which is subjected to warm or cold drawing. 6. The method according to claim 5, characterized in that in the manufacture of wire by cold drawing, intermediate annealing is carried out at a temperature of 200-500 ° C for 0.05-30 minutes. 7. The method according to claim 5, characterized in that upon receipt of the wire by warm drawing, heating the wire in front of the wire is carried out up to 200-500 ° C. 8. The method according to claim 5, characterized in that for drawing wire with a diameter of 0.4-4.0 mm, a die of hard alloys is used with an angle of 2α of 6-12 degrees and a length of the calibration zone of the die of 40-70% from the diameter of the die. 9. The method according to claim 5, characterized in that for drawing wire with a diameter of 0.02-4.0 mm using a die from single crystal diamond with an angle of 2α equal to 6-12 degrees, and the length of the calibration zone of the die equal to 30-80% from the diameter of the die.