The electrical conductivity of niobium titanium alloy under different processing technology

With the development of economy and technology, the demand for electricity is increasing rapidly, and the pressure of electricity transmission is increasing day by day. Titanium alloy with high conductive ingot has the advantages of good corrosion resistance, high specific strength and thermal stability. In addition, many times of cold machining can improve the conductivity and mechanical properties of Nb-Ti alloy. In this paper, the Nb-Ti alloy billet prepared by vacuum smelting was forged by rotary forging machine, hot rolling, cold rolling and annealing experiments were carried out, and the influence of processing and heat treatment on its electrical conductivity was discussed, in order to find an economical and efficient production method of Nb-Ti alloy.

1. Experimental materials and process
1.1 Experimental Materials
The strength, toughness, corrosion resistance and cold and hot formability of type titanium alloy are higher or better than type titanium alloy and 10 type titanium alloy. Nb is a stable element of phase, its proportion is generally 10% ~ 40%, too low is not conducive to the formation of phase, and too high is not conducive to the performance and specific gravity of the alloy. Therefore, the proposed Nb element content ranges from 36% to 39%.Because Zr and Ti have the same crystal structure, can refine the grain, and improve the strength of the alloy without reducing the plasticity, the content of Zr is generally between 2% and 4%. In the experiment, the high purity elements of niobium, titanium and zirconium were smelted in zH-0.005 consumable arc furnace to produce 59.29% titanium, 37.58 niobium and 3.13% zirconium.

1.2 Experimental process
Vacuum smelting ingot after the cutting into a certain size of rod, the rotary forging bar under 1000 ℃ after through six times rolled into hot rolled plate, thickness of 2.0 mm on the cold rolling machine again after annealing rolled into manufacture, the final thickness of 0.6 mm of Nb, Ti alloy after cold rolled thin plate in the argon protective atmosphere furnace on heated to 900 ℃, heat preservation, 0.5 h annealing treatment. Voltammetric method was used to measure the resistivity of Nb-Ti alloy sheet under different processes using PF66K digital multimeter (current range is 1A) and PZ158A digital voltmeter (voltage range is 200mV).

2. Experimental results and analysis
2.1 Resistivity of Nb-Ti alloy bar under rotary forging process
The corresponding current and voltage values of 3 groups were measured for each sample, and the resistivity of the sample was calculated according to the voltage values of the sample at different current currents and the average value was calculated. It can be seen that the resistivity of Nb-Ti alloy bar is different due to the different technological parameters of rotary forging. In the case of the same reducing diameter, the higher the processing rate is, the lower the resistivity is. At the same processing rate, the resistivity of the alloy is also relatively high when the diameter reduction is large.

2.2 Resistivity of Nb-Ti alloy bar after rolling and annealing
Hot rolled plate shown in resistivity after annealing, known resistivity averages of 0.97855 x 10-6 Ω m., the hot annealing before 1.02019 x 10-6 Ω m. reduced. Resistance is essentially an index to measure the resistance of crystal lattice to the directional flow of electrons under the action of electric field. Because the effect of various point defects (such as vacancy and interstitial atoms) distributed on the resistance is greater than that of dislocation, the resistivity decreases after hot rolling annealing.

Resistivity of alloy after cold rolling, the average of the resistivity of 1.09216 x 10-6 Ω m. After cold rolling, due to the effect of cold machining, a large number of slippage system starts in the alloy, resulting in a large number of dislocation and point defects in the alloy, which increases the resistance to the transfer of conductive free electrons in the metal. Resistivity of alloy is 0.97855 x 10-6 before cold rolling of Ω m. dramatically increased.

Shown in resistivity of alloy after annealing, the average of the resistivity of 1.01963 x 10-6 Ω m. After recrystallization annealing, dislocation density and various point defects in the alloy were significantly reduced. Under the action of electric field, the resistance of free electron movement was reduced and the resistivity of the alloy was reduced. Therefore, the resistivity of annealed alloy is significantly lower than that of cold rolled alloy.

3. Conclusion
1) Ti:Nb:Zr=59.29:37.58:3.13 alloy ingots are obtained by vacuum smelting. After rotary forging, the bar surface is of good quality, and the plate is finally rolled into 0.6mm thick sheet after hot rolling and cold rolling.

In the process of rotary forging, the higher the processing rate is, the stronger the solid solution ordering degree is, and the resistivity is relatively low. The resistivity of Nb-Ti alloy bar increases with the increase of reducing diameter.

3) Machining deformation, especially cold machining, can activate a large number of sliding systems inside the alloy, resulting in a large increase in dislocation and point defects of the alloy, and increase in metal resistivity; After recrystallization annealing, dislocation density decreased significantly, various point defects in the alloy also decreased significantly, and the resistivity of the alloy decreased.