RU2245385C2 - Method for production of composite shape memory titanium nickelide-based material - Google Patents

Abstract

FIELD: metallurgy, in particular shape memory materials for surgical tools.

SUBSTANCE: invention relates to method for production of composite shape memory titanium nickelide-based material. Method includes providing matrix from titanium nickelide melt reinforced with titanium armature, wherein starting batch contains 51.5-53.0 at % of nickel.

EFFECT: composite with improved reliability and functional characteristics.

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Description

Изобретение относится к медицинской технике и может использоваться при изготовлении материалов для хирургии.

The invention relates to medical equipment and can be used in the manufacture of materials for surgery.

One of the methods for improving the functional qualities of materials, including those used for medical purposes, is the composition of known materials with the deliberate selection of their range and selection of appropriate technology. Moreover, the transfer of the properties of the individual components to the formed composite is not necessarily additive. The study of these rather subtle and complex physicochemical processes is carried out by the material science section. Applied research results are often brought up to technical solutions that claim patent protection.

In the analogues of the prior art should include composite materials containing an alloy based on titanium nickelide. The medical aspect of the use of the latter is widely known and recognized.

Known composite material (and, accordingly, a method for its production) containing an aluminum matrix reinforced with titanium nickelide with the shape memory property [1]. To obtain this material, nickel-titanium reinforcement is poured with molten aluminum. The resulting composite has the advantage of low specific gravity, which in some areas of its application plays an important role. However, the properties of titanium nickelide desired from it — shape memory, superelasticity, and cyclic resistance — are weakly manifested due to the relatively low content of the latter.

For medical use, in most cases, this is a significant drawback, which indirectly damages the method of its production.

A known method of producing a composite material with shape memory based on titanium nickelide [2]. In it, the titanium matrix is poured with a melt of titanium nickelide having a temperature below the melting point of titanium. The subsequent stages of the technology to bring the resulting composite to the condition of use include traditional methods of hot rolling, extrusion and drawing. The use of titanium can reduce the specific gravity of the material, the dimensions of the device made from it while partially retaining the properties of titanium nickelide. The degree of conservation of these properties depends on the number of reinforcing elements, their shape and size. Variations of the latter are very diverse, respectively, and the properties of the composite produced. In General, the technology of the manufacturing method is relatively simple and available even for small-scale manufacturing, which is most used for medical purposes. The disadvantage of this method is the low reliability of the functional properties inherent in titanium nickelide. Studies have identified the cause of this deficiency. It consists of the following.

In the manufacture of a known (non-reinforced) homogeneous alloy based on titanium nickelide, a nickel content of 49.5-51.0 at.% Is selected for the maximum manifestation of the shape memory effect at temperatures below and above 37 ° C and with a nickel content of 50.2-51.5 at.% For the maximum manifestation of the effect of superelasticity . The presence of pure titanium (reinforcement) during the manufacture of the composite leads to an increase in the titanium content in the titanium nickelide compound and, accordingly, depletion of the nickel content. Going beyond the limits of homogeneous composition leads to a decrease in the quality of the material. Quantitatively, this process is not controlled and poorly managed. The fact of going beyond the homogeneous interval of titanium nickelide is found when testing the properties of the finished material, when any correction is almost impossible. Strict statistics of this phenomenon do not yet exist and, in general, the disadvantage can be interpreted as low reliability of ensuring the functional properties of the material.

The technical result of the proposed solution is to increase the reliability of ensuring the functional properties of the composite material characteristic of titanium nickelide.

The attainability of this technical result is due to the fact that in the method of producing a composite material with a shape memory based on titanium nickelide, including the formation of a matrix of titanium nickelide with titanium reinforcement, the matrix charge is selected with a nickel content of 51.5-53.0 at.%.

During the manufacture of a composite material, which, as a rule, is carried out by pouring a titanium nickelide melt (having a melting point below the melting temperature of titanium) into a mold with a prepared titanium reinforcing frame. At the temperature of liquid titanium nickelide, the surface layer of titanium interacts, titanium atoms mix with those in the mixture, and then crystallize upon cooling. It was found experimentally that the resulting addition of titanium concentration leads to a redistribution of the nickel and titanium content in titanium nickelide to its optimum, when the nickel concentration decreases to a normal technological homogeneous level of 49.5-51.0 at.%.

The drawings show:

figure 1. A method of obtaining a composite material with shape memory based on titanium nickelide:

1 - reinforcement, 2 - matrix,

figure 2. The graph of the temperature dependence of the strain (shape memory effect) for titanium nickelide,

figure 3. Graph of the temperature dependence of the strain (shape memory effect) for a composite material TiNi + Ti,

figure 4. The stress – strain curve (superelastic effect):

1 - for titanium nickelide,

2 - for a composite material TiNi + Ti.

Practical evidence of the attainability of the technical result is a comparative analysis of the deformation characteristics of the composite material obtained by the proposed method.

Example

Samples of the composite material were made by centrifugal casting in an inert atmosphere on a high-frequency installation VCHI1-4 / 1.76. A reinforcing cage 1 of twenty parallel and evenly spaced titanium wires with a diameter of 1.2 mm is placed in a cylindrical crucible of the installation. The mixture for producing a titanium nickelide melt is prepared with the following ingredients:

Nickel 52.5 at.%,

Titanium 47.5 at.%.

The titanium nickelide melt is obtained by induction heating and is poured into a crucible under the action of centrifugal forces. After cooling the matrix 2, the composite material was formed in the form of figure 1.

Evaluation of the properties of the obtained material was carried out on the basis of experimentally measured load-strain dependences characterizing the effects of shape memory and superelasticity.

1. Shape memory effect

The resulting sample is fixed with its ends to the fulcrum, weighed by the load at its midpoint and the strain is measured when the temperature changes in the direction of cooling of the sample (lower branch of the graph of FIGS. 2, 3) and heating it (upper branch). For martensitic materials, which include titanium nickelide, a sharp dependence of deformation in the region of the phase transition temperature is characteristic. As the temperature rises, shape recovery occurs, i.e. the reverse course of the deformation, but at a different temperature, which makes up the hysteresis effect, and not to the initial state, is the residual deformation. The magnitude of the hysteresis and the magnitude of the residual deformation judge the magnitude of the shape memory effect, i.e. about the quality of the material. From the graph of figure 3 it follows that the width of the hysteresis loop is approximately 95 °, and the permanent deformation is 8 arbitrary units. From experience with titanium nickelide it is known that these data correspond to the good quality of the composite. Comparing them with the graph for pure titanium nickelide shows a natural decrease in the effect.

2. The effect of superelasticity.

The rod is deformed under isothermal conditions at a temperature above the phase transition temperature. The upper branches of the graphs in figure 4 for pure titanium nickelide and the resulting composite correspond to the load of the sample, the lower - to unloading. Super-elasticity (rubber-like) is characterized by areas of a sharp dependence of the magnitude of deformation under load and unloading. Various trajectories of the graph also indicate a hysteresis of the process. The specific results presented confirm the good quality of the composite with respect to the preservation of these effects, and the statistics of material production - high reliability of the functional properties. Specific gravity in the specified concrete sample was 5.5 ± 0.1 g / cm ³ versus 6.44 ± 0.1 g / cm ^{3 of} pure titanium nickelide. In a number of cases of practical medicine, this result justifies the victim of a decrease in deformation parameters.

Sources used in compiling the description

1. Interface and Mechanical Properties of Ti-Ni-Wire reinforced Aluminum Matrix Composites. South Korea, 1998, 2, p. 5.

2. Shape memory Biomaterials and Implants. Proceedings of International Conference. June 28-30, 2001, Tomsk.

Claims (1)

A method of obtaining a composite material with a shape memory based on titanium nickelide, comprising forming a matrix from a titanium nickelide melt with titanium reinforcement, characterized in that the initial matrix charge is selected with a nickel content of 51.5 ÷ 53.0 at.%.

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