Production of cages for prosthetic cardiac valves from commercially pure titanium

FIELD: metallurgy.

SUBSTANCE: proposed process of production of cages for prosthetic cardiac valves from commercially pure titanium comprises assembly and soldering of drawn wire and plate and thermal treatment. Prior to assembly, wire is annealed in vacuum furnace at 550-600°C for 30-40 minutes and cooled with furnace. After soldering, the cage is annealed in vacuum furnace at 550-600°C for 1.5-2 hours and cooled with furnace.

EFFECT: better manufacturability, lower labour input, high mechanical properties.

1 tbl, 1 ex

 

The invention relates to a method of manufacturing a welded products, mainly welded frames of artificial heart valves (X).

Known methods of manufacturing frames X machining (abroad - type Stellite Haynos) - see USSR author's certificate No. 1712459, C22F 1/10, publ. 15.02.1992. However, these methods are time consuming and do not allow to produce frames X complex forms.

A known method of manufacturing frames X titanium W 1-0 (α-β phase) (U.S. Pat. RF N 2012284 A61F 2/24, publ. 15.05.1994). The method includes the mechanical manufacture of the body and wings, Assembly, application of carbon coatings. The method includes heating rod, which is used to produce billets, forging and annealing. The heating rod is conducted to a temperature of ~900°C, forging full compression with double or triple draught of up to 30-50% with the subsequent drawing. Annealing forging during heat treatment produce electric chamber furnaces, heated to 670-680°C followed by cooling in air. The casing is secured in a fixed position and the sash is installed in the fixture, providing compression of the valves at the entry of the nest and smoothing when installed in the slot. The purpose is known of the invention is to improve the reliability of the valves. However, the patent does not contain indicators of these products. Furthermore, the method Trudie is OK.

The authors of this application tested tselnolitye samples made of titanium rod W 1-0 treated with the above method (the results are shown in the table).

As a prototype adopted a method of manufacturing a welded alloys of system cobalt-chromium-Nickel-molybdenum, mainly skeletons X as the most close to the sum of signs (ed. mon. The USSR № 1712459, C22F 1/10, publ. 15.02.1992). The method includes the Assembly and welded deformed wire drawing and plate heat treatment. Wire pre-deform the lug 50%. Spend electron beam welding wire to the plate at a voltage of 16 to 18 kV, a beam current of electrons 22-24 mA, the welding time is 0.9-1.2 s, the residual pressure in the vacuum chamber 133.10-4-135.10-5PA. Then carry out the tempering temperature 1100-1180°C in water, cold deformation by stretching with the degree of 15-20%, aged at 450-500°C for 10-15 hours

It should be noted the high complexity and duration of the method, which ultimately reduces its manufacturability. Mechanical characteristics quite high (see table).

There is a method of improving the proposed resolution.

The task is improving the way the prototype for the manufacture of frames X titanium as an alloy more technologically advanced, lightweight, which is important for such specific the products, as the frames of the IRS.

The technical result - improving the processability of the method by reducing the complexity and duration under high mechanical characteristics.

This technical result is achieved in that in the method of manufacturing frames X from commercially pure titanium, including the Assembly and welded deformed wire drawing and plates and heat treated prior to Assembly of the frame wire is annealed in a vacuum furnace at a temperature of 550-600°C for 30-40 minutes and cooled with the furnace, and after welding carry out the annealing of the frame in a vacuum furnace at a temperature of 550-600°C for 1.5-2 hours and cooling with the furnace.

The proposed method allows to produce frames X from commercially pure titanium, it is lighter, cheaper, has good weldability. The method is less time consuming for it excluded the operation of hardening, cold deformation and leave for 10-15 hours, weight reduction products, two times, at high fatigue characteristics.

The effect dovanojo annealing due to the fact that when passing it recrystallization makes the metal is thermodynamically more stable to the welding thermal cycle.

The purpose of the post-weld annealing is to reduce the level of internal stresses, the more homogeneous structure of the weld, reducing the hardness of the heat-affected zone, the training is a result of the removal work hardening, resulting from thermal deformation of the welding cycle, as well as the redistribution of hardening of the heat-affected zone during welding of the introduction of impurities of oxygen and nitrogen.

In the pre - and post-weld annealings achieves a more uniform distribution of properties in the influence zones of welding (weld and heat-affected zone).

The method is as follows.

Wire of commercially pure titanium deformed by the drawing and is annealed at a temperature of 550-600°C for 30-40 minutes, cooling with the furnace. Weld plates of the same material. After welding the frames is annealed at a temperature of 550-600°C in the same oven for 1.5-2 hours. Samples of finished frames X passed mechanical tests.

An example of the method.

Wire of commercially pure titanium W 1-0 deformed by drawing on 55% of the diameter 2±0.01 mm, length 45 mm and annealed at a temperature of 550-600°C for 30-40 minutes, cooled with the furnace. Made from the same material plate size of 12×12×1. Carried out the welding wire to the plate. Heat treatment and welding is carried out in vacuum with a residual pressure 133.10-4-135.10-5. Welding mode: accelerating voltage of the electrons 16-18 kV, a beam current of electrons 18-20 mA, welding 1,0-1,2 (as in the prototype).

After welding the frames were heat treatment - annealing in vacuum at a temperature of 550-600°C for 1.5-2 hours cooling with the furnace.

After annealing, the carcasses were subjected to mechanical and electrochemical polishing, and then testing the alternating symmetric cyclic bending with the determination of the endurance limit based on trials N=107cycles and intensity of accumulation of cyclic damage, characterized by the indices β1that β2in physiological solution of ringer-Locke.

The results of the mechanical tests are shown in table.

The table shows that the temperature of 600°C dovanojo annealing and 600°C post weld annealing provide the best combination of strength and plastic (relative elongation δ, relative narrowing Ψ) characteristics and better fatigue characteristics: the maximum value of the fatigue limit σ-1=235 MPa on the basis of trials N=107cycles, the minimum angles of the left (β1) and right (β2) branches of the fatigue curve in the double logarithmic coordinates.

With decreasing temperature dovanojo annealing below 550°C (500°C) decreases the limit of endurance and high angles of fatigue curves. Some reduction in fatigue limit compared to the prototype, due to the difference in the properties of titanium and alloys of the cobalt-chromium-Nickel-molibden.

With increasing temperature dovanojo annealing above 600 is C (650°C) observed the same result.

Decreasing the exposure time when devroom annealing less than 30 minutes (25 minutes) the process of crystallization is less full and less grain is resistant to growth in the welding process.

Increasing the exposure time when devroom annealing over 40 minutes (45 minutes) can lead to grain growth, which will adversely affect durability.

With decreasing temperature and post weld annealing below 550°C (500°f) less than fully reduced level of internal stresses, uneven distribution of properties in the welded joints.

With increasing temperature and post weld annealing above 600°C (650°C) decreases the limit of endurance.

Decreasing the exposure time when the post-weld annealing is less than 1.5 hours (1 hour) is incomplete reduction of internal stresses, the uneven distribution of properties along the length of the welded joints, partial removal of work hardening resulting from thermal deformation of svarochno cycle.

Increasing the exposure time when the post-weld annealing for more than 2 hours leads to lower level of mechanical properties due to grain growth.

A pilot batch of frames X has been tested on fiziologicheskii stands in conditions close to operational, and showed an increase in the durability of 1.4-1.5 times in comparison with frames that have not undergone the proposed treatment - annealing.

The proposed method allows to produce frames X more technological way, lighter, cheaper, with higher fatigue limit, which increases their durability.

The method meets the criteria of novelty, inventive step and industrial applicability.

td align="justify"> 550
Table
Mode TMOMechanical properties
T dovanojo annealing °CT post weld annealing °Cσin, MPaσin, MPaσ-1, MPaβ1β2δ, %Ψ, %
500600390394206,50,1310,02936,578
55060040030 of 211.50,1140,03133,078
time 30 mintime 1.5 hours
6006003903002350,1160,0283984
6506003762752010,1870,0334085
550500420330200is 0.1350,0342374,5
550400300of 211.50,1140,03133,078
550650355252,51770,2280,0449,5to 83.5
prototypeother units
1400-1525 N/mm21295-1415 N/mm2540-560 N/mm20,153-0,1460,286-0,28016-2251,5 is 54.5
tselnolitye frames X40 3842300,1310,0343578

A method of manufacturing frames of artificial heart valves from commercially pure titanium, including the Assembly and welded deformed wire drawing and plate and heat treatment, characterized in that prior to Assembly of the frame wire is annealed in a vacuum furnace at a temperature of 550-600°C for 30-40 minutes and cooled with the furnace, and after welding carry out the annealing of the frame in a vacuum furnace at a temperature of 550-600°C for 1.5-2 hours and cooling with the furnace.



 

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