Method for setting shape of nickel-titanium springs

Abstract

FIELD: method for producing springs.SUBSTANCE: method of producing springs with a shape memory effect or superelasticity from titanium nickelide alloy wire with a Ni content of 50.5-51.1 at.% and a diameter of 0.6 to 2 mm. The wire is wound at room temperature onto mandrels with a diameter of 8 to 40 mm. Heat-fixing annealing is carried out at a temperature of 330-500 °C for 30-200 minutes with quenching in water to implement the shape memory effect of springs or annealing at 550-600 °C for 15-25 minutes with quenching in water to achieve the super-elastic effect of the springs.EFFECT: possibility to manufacture springs from a hyperequiatomic titanium nickelide alloy with the ability to control the complete restoration of shape upon heating.1 cl, 1 tbl, 4 ex

Description

[0001] This invention relates to metallurgical production, specifically to a method for producing springs with a shape memory effect or superelasticity from titanium nickelide (TiNi) alloy wire. It can be used as a functional component in a temperature-sensitive sensor. The use of titanium nickelide springs is relevant in the automotive and aircraft industries, as well as in the medical industry, particularly in minimally invasive surgery, where there is a particular need for reliable functional components that combine superelasticity or shape memory with high strength characteristics.

[0002] A known method for producing springs from titanium nickelide alloy (50–50.5 at.% Ni) with a shape memory effect [Patent RU 2309192 C2, published 10 / 27 / 2007] involves heating the spring to temperatures of 500–600 ºC using an electric current, followed by shaping. Final heat treatment is performed at the final stage of spring manufacturing. The disadvantages of this spring manufacturing method include the use of electric current, which does not always ensure controlled and uniform heating of the wire due to high heating rates and varying wire diameters. Furthermore, when springs are heated to temperatures above 600 ºC, recrystallization processes occur in titanium nickelide alloys, leading to softening and may adversely affect the mechanical and functional properties of the springs, including the completeness of shape restoration.

[0003] A known method for manufacturing springs is a method for obtaining a spring from titanium nickelide [Patent RU 2564771 C2, published. 10.10.2015], which consists of winding the spring at a temperature of 18-40 ºC, followed by annealing in a muffle furnace at a temperature of 500-520 ºC for 60 minutes with cooling in the furnace to 18-23 ºC. At the final stage of spring manufacturing, thermal cycling is carried out under axial load in the temperature range of 90-24 ºC. The disadvantage of this method of spring manufacturing is that the finished product will have only the shape memory effect at room temperature, since the wire of equiatomic composition TN-1 (Ti-50.0 at.% Ni) was chosen as the material for the manufacture of springs. In addition, the proposed annealing temperature is insufficient to reduce the end temperature of the reverse martensitic transformation (MT) (A к) to temperatures below room temperature. Furthermore, the disadvantages of the proposed method include the inclusion of an additional step in the spring production process, which involves thermal cycling under load, which increases the spring production time.

[0004] The technical result achieved by the invention consists of producing springs of various diameters from nickel-titanium alloy wire that are capable of restoring their shape both at room temperature and when heated, i.e., exhibiting both superelasticity and shape memory. This method also enables the production of springs from wire of various diameters with comparable functional characteristics.

[0005] The technical result is achieved by tightly winding a titanium nickelide alloy wire with a Ni content of 50.5-51.1 at.% with a diameter of 0.6 to 2 mm onto a metal rod or tube of circular cross-section with a diameter of 8 to 40 mm at room temperature. The ends of the spring are rigidly fixed to the mandrel with clamping screws. After winding, to implement the shape memory effect in the finished spring, the rod or tube with the wire wound on it is annealed at a temperature of 330-500 ºC for 30-200 minutes with quenching in water to obtain a temperature of the end of the reverse magnetic field above room temperature (A к > T комн ),. To achieve the superelastic effect, a rod or tube with wire wound on it is annealed at a temperature of 550-600 ºС for 15-25 minutes with quenching in water to obtain a temperature at the end of the reverse magnetic field below room temperature (A к < T комн ) .

[0006] The essence of the claimed method is that the wire is wound onto mandrels at room temperature (22°C). The next step is annealing the springs by quenching them in water. The purpose of this operation is to heat-set the springs and adjust the temperature. к Annealing at temperatures of 330-500 ºC for 120 minutes is accompanied by polygonization processes, which has a positive effect on the complex of properties. In addition, in titanium nickelide alloys with a Ni content of at least 50.5 at.%, static aging processes occur in this annealing temperature range, accompanied by the precipitation of particles of the excess Ti3Ni4 phase. The precipitation of particles of the excess phase during static aging leads to depletion of the matrix in nickel, resulting in an increase in temperature A кrelative to the initial state before heat treatment. Annealing in the temperature range of 550-600 ºC for 15-25 minutes with quenching in water is not accompanied by static aging processes, and, consequently, the temperature A к remain below room temperature, which allows the springs to achieve a superelastic effect. Furthermore, a temperature of 600°C is the lower threshold for the onset of recrystallization, and a short annealing time does not significantly degrade the properties.

[0007] The method is carried out as follows. One free end of a wire with a diameter of 0.6 to 2 mm made of titanium nickelide with a Ni content of 50.5-51.1 at.% is rigidly fixed to a mandrel with a diameter of 8 to 40 mm using clamping screws. The wire is then wound around the mandrel at room temperature with a minimum distance between turns with constant tension on the second free end of the wire. Upon completion of winding, the second end of the wire is also rigidly fixed with a second clamping screw. At the final stage of spring manufacturing, the springs are heat treated at a temperature of 330-500 ºC for 30-200 minutes with quenching in water to obtain a temperature of A к above room temperature – above 22 ºС (shape memory effect), or at a temperature of 550-600 ºС for 15-25 minutes with quenching in water to obtain temperature A к below room temperature (superelasticity effect).

[0008] The results of testing the claimed method are given in the form of specific examples.

[0009] Example #1. The starting material was a wire of hyperequiatomic Ti-50.8 at.% Ni alloy with a diameter of 0.6 mm. The free end of the wire was secured to the beginning of an 8 mm diameter mandrel, after which the spring was wound at room temperature with the tightest possible spacing between turns. After winding was complete, the second free end of the wire was secured to the end of the mandrel. The next step was annealing at 550 ºC for 25 minutes with quenching in water. The resulting spring exhibited superelasticity with a temperature of A к = -7 ºС.

[0010] Example #2. The starting material was a wire of hyperequiatomic Ti-50.8 at.% Ni alloy with a diameter of 2 mm. The free end of the wire was then secured to the beginning of a 40 mm diameter mandrel. The spring was then wound at room temperature with the tightest possible spacing between turns. After winding was complete, the second free end of the wire was secured to the end of the mandrel. The next step was annealing at 600 ºC for 20 minutes with quenching in water. The resulting spring exhibited superelasticity with a temperature of A к = 6 ºС.

[0011] Example #3. The starting material was a 2 mm diameter wire of hyperequiatomic Ti-50.8 at.% Ni alloy. The free end of the wire was then secured to the beginning of a 40 mm diameter mandrel. The spring was then wound at room temperature with the tightest possible spacing between turns. After winding was complete, the second free end of the wire was secured to the end of the mandrel. The next step was annealing at 500 ºC for 120 minutes with quenching in water. The resulting spring exhibited a shape memory effect with a temperature of A к = 46 ºС.

[0012] Example #4. The starting material was a wire of hyperequiatomic Ti-50.8 at.% Ni alloy with a diameter of 0.6 mm. In the first step, the free end of the wire was secured to the beginning of an 8 mm diameter mandrel. The spring was then wound at room temperature with the tightest possible spacing between turns. After winding was complete, the second free end of the wire was secured to the end of the mandrel. The next step was annealing at 450 ºC for 200 minutes with quenching in water. As a result of this processing, a spring exhibiting a shape memory effect with a temperature of A was obtained. к = 33 ºС.

[0013] Reverse MP end temperatures (A к ) for the obtained springs, as well as for the original wire, are presented in Table 1.

[0014] Table 1.

[0015] Original 0.6 mm Original 2 mm Example #1 Example #2 Example #3 Example #4 Temperature Ak, ºС 18 42 -7 6 46 33

[0016] The technical and economic benefits of the proposed method include the ability to manufacture springs from TiNi alloy wire that exhibit both shape memory and superelasticity, as well as the ability to precisely control the temperature of complete shape recovery through heat treatment. Springs manufactured using the proposed method will enable the creation of various temperature-sensitive elements and sensors for use in such technical fields as aircraft and automotive manufacturing, as well as in medical devices.

Claims

A method for producing springs with a shape memory effect or superelasticity from titanium nickelide alloy wire containing 50.5-51.1 at.% Ni and with a diameter of 0.6 to 2 mm, characterized in that the wire is wound at room temperature onto mandrels with a diameter of 8 to 40 mm, followed by heat-setting annealing at a temperature of 330-500 °C for 30-200 minutes with quenching in water to achieve the shape memory effect of the springs, or annealing at 550-600 °C for 15-25 minutes with quenching in water to achieve the superelastic effect of the springs.