Medical Ti-6Al-7Nb for K-wire(kirschner wire)

Medical Ti-6Al-7Nb for K-wire(kirschner wire)

Ti-6Al-7Nb alloy is a promising alloy for human implants. It has high strength, excellent corrosion resistance, biocompatibility, basically harmless to human body, and also has the advantages of strong plasticity and excellent abrasiveness. It is the potential harmful effect of V in conventional Ti-6Al-4V alloy for human implantation that promotes the development of biological Ti alloy without V, and should conceive Ti-6Al-7Nb alloy. The alloy is characterized by substituting Nb for V. its mechanical properties are equivalent to that of Ti-6A1-4V. Its plane fracture toughness is about 10% higher than that of Ti-6A-4V. It has been widely used in clinical practice abroad and has a great tendency to replace Ti-6Al-4V alloy.

1. Experiment

The experimental material is made of grade 0 special sponge titanium, mixed according to the brand and reputation alloy composition, pressed electrode group welding, melted into 370mm alloy ingot three times in vacuum consumable arc furnace, and its (a) is measured by metallographic method+ β)/ Phase change point (TB) ingot is peeled on the surface, the bottom of the ingot is cut off, and heated to β In the phase zone, the billet is forged by a 2500 ton oil press, the surface defects are ground, and then heated to the two-phase zone. It is rolled into 9.5mm bar wire blank twice, and then heated to the lower part of the phase change point. After 30kW drawing machine and 11kw reel drawing machine, it is repeatedly heated and multi-mode drawn to Φ4.0mm below of The Kirschner wires are usually annealed, straightened, polished, heat treated and sampled to measure the mechanical properties of the wire.

2. Result and Conclusion

2.1 Ti-6a1-7nb titanium alloy transformation point and ingot chemical composition

The phase transition point of Ti-6Al-7Nb titanium alloy is 965 ℃, and the chemical composition analysis of Ti-6Al-7Nb titanium alloy ingot is shown in Table 1 The data in the table is the measured analysis value of the ingot with the cap and bottom removed from the ingot and taken at 300mm from both ends, which meets the requirements of gb/t13810 standard for titanium and titanium alloy processing materials for surgical implants. The composition deviation is small and relatively uniform.

Table 1 Ti-6Al-7Nb ingot chemical composition

2.2  Table 2 shows the room temperature mechanical properties of wires drawn at different temperatures of the same specification. From the data in the table, it can be seen that the room temperature mechanical properties of wires drawn at different temperatures of the same specification (final drawing temperature) vary greatly. This is because different processing temperatures reflect different degrees of hardening tendency in the deformation process, although the process of hot working deformation is accompanied by the process of property recovery. But at the same time, it also caused the accumulation of hardening. If the processing temperature is higher, the strength hardening index will be lower. On the contrary, if the processing temperature is lower, the strength hardening will be significantly improved. The results show that the transformation temperature of ti-6a1-7nb alloy tends to move downward with the increase of tensile deformation, and the processing temperature should also be adjusted downward.

Table 2  Mechanical properties of wire after processed

2.3 Table 3 It refers to the room temperature mechanical properties of wires drawn to the same specification at different drawing temperatures and annealed in the same annealing system. It can be seen from the data in the table that the mechanical property strength index changes little after stress relief annealing, but the elongation and reduction of area of plastic index after fracture are improved. The research shows that the properties of ti-6a-7nb wire prepared by hot drawing method are extremely unstable. It is necessary to eliminate stress through heat treatment, soften the alloy, improve its comprehensive properties, and facilitate the smooth progress of subsequent straightening and polishing processes.

Table3   Mechanical properties of wire after annealed

Conclusion

1)For the processing of ti-6a1-7nb titanium alloy high-strength wire, the selected heating system moves down with the increase of deformation. The realization of high strength depends on the accumulation of hardening to a certain extent.

2) The comprehensive performance of ti-6a1-7nb titanium alloy wire after heat treatment at 510-530 ℃ for 4-8h and furnace cooling is better.