CN107326402A - The preparation method of Nitinol - Google Patents

Abstract

The invention belongs to the technical field of rare metal refining, and in particular relates to a method for preparing a nickel-titanium alloy. Aiming at the problems that the existing method for preparing Ni-Ti alloy powder has high production cost and cannot be mass-produced, the present invention provides a method for preparing nickel-titanium alloy by molten salt electrolysis, which comprises the following steps: using pure titanium and pure nickel as two independent The anode and the metal material are used as the cathode, placed in the molten electrolyte to form an electrolytic cell, and two independent power supplies are used to supply power to the two anodes for electrolysis, and Ni-Ti alloy is co-deposited at the cathode; the molten electrolyte is titanium halide, halide Mixture of nickel and molten salt. The invention provides a new process for preparing nickel-titanium alloy by molten salt electrolytic co-deposition, which can directly obtain Ni-Ti alloy powder. The production cost of the alloy powder is below 400 yuan/kg, which is 80% lower than the cost of gas atomized alloy powder. The method of the invention has short production process, low production cost and high product yield, and has important practical significance.

Description

Preparation method of nickel-titanium alloy

technical field

The invention belongs to the technical field of rare metal refining, and in particular relates to a method for preparing a nickel-titanium alloy.

Background technique

The preparation of nickel-titanium alloys began in the 1940s. Until 1963, W. Buehler and others at the U.S. Naval Weapons Laboratory discovered that the NiTi alloy with a near atomic ratio had a shape memory effect, which set off a wave of research on shape memory alloys. .

With the deepening of research, many excellent properties have been found, such as: superelasticity, high specific strength, high fatigue life, high damping, corrosion resistance, wear resistance, good biocompatibility and other characteristics, so NiTi alloy can be widely used in aviation Aerospace, medical, civil, mechanical, control, electronics and other engineering fields.

The main industrial production method of NiTi alloy is melting and casting. The melting and casting method uses sponge titanium as raw material, and adds Ni according to the alloy composition for melting, usually using electron beam, argon arc, and plasma beam melting equipment, including material preparation, preparation of electrodes, primary vacuum consumable melting, secondary melting, and billet forging , secondary forging, rolling or extrusion and other processes, and finally get the finished bar or plate. Due to the strong sensitivity of nickel-titanium alloys to composition and processing, it is difficult to control the melting and processing of nickel-titanium alloys, which makes the processing cost of this process high and the production cycle is long. Therefore, the threshold for enterprises to enter the field of nickel-titanium alloys has been greatly increased. The yield of the NiTi alloy obtained by the smelting method is only 30-40%, resulting in extremely high production costs, which largely limits its popularization and application. Therefore, exploring new technologies for the preparation of low-cost and high-performance NiTi alloys has become an urgent problem in the development of shape memory alloy technology.

In recent years, the powder metallurgy process has developed rapidly. Powder metallurgy is a method of using metal powder as a raw material to form and sinter metal products. It is a processing method with less or no cutting, and the products produced have uniform performance. It can effectively reduce the production cost of titanium alloy, and has its unique advantages in the production of porous materials, complex shapes and small parts. Therefore, it has attracted the attention of scientific researchers at home and abroad.

At present, the relatively mature process for preparing Ni-Ti alloy powder is gas atomization powder making and rotating electrode method. The Ni-Ti alloy is melted at high temperature in a melting crucible, and then gas atomized or The centrifugal atomization is carried out by the rotating electrode method, and the microscopic morphology of the obtained powder is spherical. However, this process is only for small batch production to meet the needs of experiments, and it is still far away from industrialized products. The market price of this type of alloy powder is more than 2,000 yuan/kg, and the imported powder reaches 4,000-8,000 yuan/kg. The price is very expensive and the practicability is low.

Contents of the invention

The technical problem to be solved by the present invention is: the existing method for preparing Ni-Ti alloy powder has high production cost and cannot be produced in a large scale.

The technical scheme for solving the technical problems of the present invention is as follows: a preparation method of nickel-titanium alloy is provided. The method includes the following steps:

Pure titanium and pure nickel are used as two independent anodes, and metal materials are used as cathodes, which are placed in molten electrolyte to form an electrolytic cell, and two independent power supplies are used to supply power to the two anodes for electrolysis, and Ni-Ti alloy is co-deposited at the cathode; The molten electrolyte mentioned above is a mixture of titanium halide, nickel halide and molten salt.

Wherein, in the preparation method of the above-mentioned nickel-titanium alloy, the Ti content of the pure titanium ≥ 98wt%, is any one of sponge titanium, titanium plate, titanium rod or titanium wire; the Ni content of the pure nickel ≥ 99.0wt%, any one of electrolytic nickel, sponge nickel, nickel plate or nickel rod.

Wherein, in the above-mentioned preparation method of nickel-titanium alloy, the metal material of the cathode is any one of pure nickel, pure titanium, carbon steel or stainless steel.

Wherein, in the above-mentioned preparation method of nickel-titanium alloy, the titanium halide is TiF _n or TiCl _n , 2≤n≤3; the nickel halide is _NiF2 or NiCl2 _; the molten salt is alkali metal halide or alkaline earth metal halides.

Further, in the above method for preparing nickel-titanium alloy, the molten salt is at least one of LiF, NaF, KF, LiCl, NaCl, KCl, MgCl ₂ , CaCl ₂ or CaF ₂ .

Wherein, in the above-mentioned preparation method of nickel-titanium alloy, the mass ratio of Ti ⁿ⁺ to Ni ²⁺ in the titanium halide and nickel halide added with molten salt is 1:0.5˜1.23.

Wherein, in the above-mentioned preparation method of nickel-titanium alloy, the cathode current density during electrolysis is ≥0.6 A/cm ² , preferably 0.8-2.0 A/cm ² .

Wherein, in the preparation method of the above-mentioned nickel-titanium alloy, the current density of the titanium anode during electrolysis is ≤0.3A/cm ² ; preferably ≤0.1A/cm ² .

Wherein, in the preparation method of the above-mentioned nickel-titanium alloy, the current density of the nickel anode during the electrolysis is ≥1.0A/cm ² ; preferably 1.2-2.0A/cm ² .

Wherein, in the preparation method of the above-mentioned nickel-titanium alloy, the ratio of the electric current intensity of the titanium anode to the nickel anode during the electrolysis is 1:1.5-3.

Wherein, in the above-mentioned preparation method of nickel-titanium alloy, the electrolysis temperature during the electrolysis is 670-900°C.

The beneficial effects of the present invention are as follows: the present invention provides a new process for preparing nickel-titanium alloy by molten salt electrolytic co-deposition, which can directly obtain Ni-Ti alloy powder, and the production cost of the alloy powder is below 400 yuan/kg, compared Powder cost (2000 yuan/kg) has dropped by 80%. The method of the present invention can obtain finished parts only through limited technological processes such as "electrolytic powder making-press molding-sintering". Secondary forging, rolling or extrusion, etc., and finally get the finished bar or plate", the process flow is greatly shortened, and the raw material utilization rate of the whole process flow can reach 75-85%, and the Ni-Ti alloy obtained by the melting method can be obtained The rate is only 30-40%. Therefore, the method of the invention has short production process, low production cost and high product yield, which has important practical significance.

Instructions attached

Shown in Fig. 1 is the electrolyzer described in embodiment 1;

Fig. 2 shows the XRD analysis graph of the product prepared in Example 1-3.

detailed description

The invention provides a kind of preparation method of nickel-titanium alloy, comprising the following steps:

Pure titanium and pure nickel are used as two independent anodes, and metal materials are used as cathodes, which are placed in molten electrolyte to form an electrolytic cell, and two independent power supplies are used to supply power to the two anodes for electrolysis, and Ni-Ti alloy is co-deposited on the cathode; The molten electrolyte mentioned above is a mixture of titanium halide, nickel halide and molten salt.

Wherein, the molten salt is at least one of alkali metal halides or alkaline earth metal halides.

Wherein, the alkali metal halide is a compound formed by an alkali metal element and a halogen element, including MgCl ₂ , CaCl ₂ or CaF ₂ , and the alkali metal halide used in the present invention is at least one of them.

Wherein, in the above method for preparing nickel-titanium alloy, the alkaline earth metal halide is at least one of LiF, NaF, KF, LiCl, NaCl or KCl.

Wherein, in the above-mentioned method for preparing nickel-titanium alloy, the metal material of the cathode is any one of pure nickel, pure titanium, carbon steel or stainless steel.

In the above-mentioned method for preparing a nickel-titanium alloy, the titanium halide is TiF _n or TiCl _n , where 2≤n≤3. Taking TiCl _n as an example, n=2 means only TiCl ₂ , n=3 means only TiCl ₃ , 2≤n≤3 means both TiCl ₂ and TiCl ₃ , which is a mixture of the two. In the above method for preparing nickel-titanium alloy, the nickel halide is NiF ₂ or NiCl ₂ .

In the above method for preparing nickel-titanium alloy, the mass ratio of Ti ⁿ⁺ to Ni ²⁺ in the titanium halide and nickel halide added with molten salt is 1:0.5-1.23.

In the above-mentioned method for preparing nickel-titanium alloy, the possible electrochemical reactions of the titanium anode are shown in (1)(2)(3):

Ti－2e→Ti ²⁺ (1)

Ti ²⁺ -e→Ti ³⁺ (2)

Ti－3e→Ti ³⁺ (3)

In order to facilitate the control of the alloy composition of the cathode precipitation, so that the titanium anode only undergoes the reaction shown in formula (1) and avoids the reaction (2) (3), it is necessary to control the current density of the titanium anode to <0.3A/cm ² , and the preferred range is <0.1 A/cm ² .

In the above-mentioned method for preparing nickel-titanium alloy, the electrochemical reaction that described nickel anode takes place is shown as (4) (5):

Ti ²⁺ -e→Ti ³⁺ (4)

Ni－2e→Ni ²⁺ (5)

Due to the presence of Ti ²⁺ in the electrolyte, it is difficult to react (5) at the nickel anode. To ensure the smooth dissolution of nickel into the electrolyte, it is necessary to control the nickel anode to have a high overpotential, so the current density of the nickel anode must be controlled to be >1.0A/cm ² , the preferred range is 1.2-2.0A/cm ² .

In the above-mentioned method for preparing nickel-titanium alloy, the electrochemical reaction that described negative electrode takes place is shown as (6) (7):

Ti ³⁺ +e→Ti ²⁺ (6)

Ti ²⁺ +e→Ti (7)

Ni ²⁺ +2e→Ni (8)

On the cathode, Ti ³⁺ is reduced to Ti by two steps, and Ni ²⁺ is reduced to Ni by one step.

At 700°C (vsAg/Ag-), the standard electrode potentials of Ti and Ni are:

It can be seen that the standard potential difference between Ni and Ti is 1.08V. If the two are to reach the same level in potential, the concentration of Ti ²⁺ needs to be adjusted to be about 10 ¹¹ times that of Ni ²⁺ , which is obviously unrealistic in actual operation. .

Since it is difficult to find co-deposition conditions simply by changing the concentration conditions, the influence of kinetic factors must be considered. If the control cathode has a higher overpotential, at a certain current density, Ni ions undergo concentration polarization during cathode reduction, and the potential shifts negatively to the precipitation potential of Ti, and the reaction (8) occurs simultaneously under the premise of preferential reaction (8). 6) (7), at this time, Ni ions and Ti ions are discharged at the cathode at the same time to meet the requirements of the total current. Using this principle, Ni and Ti co-deposition can be realized.

In order to realize that the cathode has a higher overpotential, the cathode current density is greater than 0.6A/cm ² during electrolysis. Preferably 0.8-2.0A/cm ² .

And in order to ensure that the ratio of Ti ⁿ⁺ and Ni ²⁺ in the electrolyte remains stable, the current ratio of titanium anode and nickel anode should be controlled to be 1:1.5~3 during electrolysis. According to the experimental research, under this power transmission ratio, the ratio of Ti ⁿ⁺ and Ni The molar ratio of ²⁺ was kept at 1:1.

In order to ensure the activity of each ion in the electrolysis process, it is necessary to control the temperature to be higher than 670°C. If the temperature is too high, the equipment cannot bear it and the economy is not good. Therefore, the optimal electrolysis temperature is controlled at 670-900°C.

The specific implementation of the present invention will be further explained below in conjunction with the examples, but it does not mean that the protection scope of the present invention is limited to the scope described in the examples.

The molten salt described in the examples is NaCl-KCl in equimolar ratio.

Embodiment 1 prepares nickel-titanium alloy with the method of the present invention

Sponge titanium and nickel wire are used as anode respectively, pure titanium rod is used as cathode, and a mixture composed of _2wt % TiCl2 and _2.18wt % NiCl2 is added to NaCl and KCl in equal molar ratio to form an electrolytic cell. The two anodes are powered, and the line connection and electrode layout are shown in Figure 1. Control titanium anode current density 0.1A/cm ² , cathode current density 2.0A/cm ² , nickel anode current density 2.0A/cm ² , electrolysis temperature 670°C, titanium anode and nickel anode current intensity ratio 1:1.5, after electrolysis The product obtained from the cathode was washed with dilute hydrochloric acid to obtain 9.8 g of the product, and the phase analysis was carried out by XRD. The results are shown in Figure 2 (1-1). From the results, it can be seen that the product is a Ni-Ti alloy.

Embodiment 2 prepares nickel-titanium alloy with the method of the present invention

Using titanium rods and nickel wires as anodes and carbon steel rods as cathodes, and adding a mixture of 0.5wt% TiCl3 and _0.55wt % NiCl2 to NaCl and _KCl in equal molar ratios as electrolytes to form an electrolytic cell, two independent power supplies Power is supplied to the two anodes, and the line connection and electrode layout are shown in Figure 1. Control titanium anode current density 0.05A/cm ² , cathode current density 0.8A/cm ² , nickel anode current density 1.2A/cm ² , electrolysis temperature 900°C, titanium anode and nickel anode current intensity ratio 1:3, after electrolysis The product obtained from the cathode was washed with dilute hydrochloric acid to obtain 10.5 g of the product, and the phase analysis was carried out by XRD. The results are shown in Figure 2 (1-2), and the results showed that the product was a Ni-Ti alloy.

Embodiment 3 prepares nickel-titanium alloy with the method of the present invention

Using pure titanium shavings and electrolytic nickel sheets as anodes and nickel rods as cathodes, and adding a mixture of 0.5wt% TiCl3, 1.0wt% TiCl2 and _1.64wt % NiCl2 to _NaCl and _KCl at an equal molar ratio as the electrolyte to form an electrolytic cell, Two independent power supplies are used to supply power to the two anodes respectively, and the line connection and electrode layout are shown in Figure 1. Control titanium anode current density 0.1A/cm ² , cathode current density 1.0A/cm ² , nickel anode current density 1.5A/cm ² , electrolysis temperature 800°C, ratio of titanium anode to nickel anode current intensity 1:2, after electrolysis The product obtained from the cathode was washed with dilute hydrochloric acid to obtain 15.1 g of the product, and the phase analysis was carried out by XRD. The results are shown in Figure 2 (1-3), and the results showed that the product was a Ni-Ti alloy.

Table 1 obtains the product chemical composition for three embodiments.

The alloy powder prepared by the method of the present invention and the commercially available product impurity content contrast of table 1

As can be seen from the test results in Table 1, the nickel-titanium alloy powder prepared by the method of the present invention has a lower impurity content than commercially available alloys due to the electrolytic refining effect in the process, and the production process is simpler and the cost is lower. Has obvious economic benefits.

Claims (10)

1. the preparation method of Nitinol, it is characterised in that comprise the following steps：

Using pure titanium, pure nickel as two assistant anodes, metal material is placed in fused electrolyte as negative electrode and constitutes electrolytic cell, With two independent current sources to two anode supplies, it is electrolysed, Ni-Ti alloys is obtained in cathode codeposition；Described melting electricity Solution matter is the mixture of halogenated titanium, nickel halogenide and fused salt.

2. the preparation method of Nitinol according to claim 1, it is characterised in that：The Ti contents of described pure titanium >= 98wt%, is any one in titanium sponge, titanium plate, titanium rod or titanium silk；Ni contents >=99.0wt% of described pure nickel, is electricity Solve any one in nickel, sponge nickel, nickel plate or nickel rod.

3. the preparation method of Nitinol according to claim 1 or 2, it is characterised in that：The metal material of described negative electrode Expect for any one in pure nickel, pure titanium, carbon steel or stainless steel.

4. the preparation method of the Nitinol according to any one of claims 1 to 3, it is characterised in that：Described halogenated titanium For TiF_nOr TiCl_n, 2≤n≤3；Nickel halogenide is NiF₂Or NiCl₂；Described fused salt is alkali halide or alkaline-earth metal halogen Compound.

5. according to the preparation method of any described Nitinol of Claims 1 to 4, it is characterised in that：Described fused salt is LiF、NaF、KF、LiCl、NaCl、KCl、MgCl₂、CaCl₂Or CaF₂At least one of.

6. according to the preparation method of any described Nitinol of Claims 1 to 5, it is characterised in that：The addition fused salt Ti in halogenated titanium, nickel halogenideⁿ⁺With Ni²⁺Mass ratio be 1 ﹕ 0.5~1.23.

7. according to the preparation method of any described Nitinol of claim 1~6, it is characterised in that：The negative electrode during electrolysis Current density >=0.6A/cm²。

8. according to the preparation method of any described Nitinol of claim 1~7, it is characterised in that：Titanium sun during the electrolysis Electrode current density≤0.3A/cm²。

9. according to the preparation method of any described Nitinol of claim 1~8, it is characterised in that：Nickel sun during the electrolysis Electrode current density >=1.0A/cm²。

10. according to the preparation method of any described Nitinol of claim 1~9, it is characterised in that：Titanium sun during the electrolysis Pole and nickel anode power transmission current strength ratio are 1 ﹕ 1.5~3.