CN112501596A

CN112501596A - Fluorine-free and palladium-silver-free activation method before chemical nickel plating on titanium surface

Info

Publication number: CN112501596A
Application number: CN202011274932.7A
Authority: CN
Inventors: 史兴岭; 任建; 姜荪; 徐玲利
Original assignee: Jiangsu University of Science and Technology
Current assignee: Zhenjiang Yonggu Surface Treatment Technology Co.,Ltd.
Priority date: 2020-11-13
Filing date: 2020-11-13
Publication date: 2021-03-16
Anticipated expiration: 2040-11-13
Also published as: CN112501596B

Abstract

The invention discloses a fluorine-free and palladium-silver-free activation method before chemical nickel plating on the surface of titanium, which comprises the steps of placing a pretreated titanium substrate in a sodium hydroxide solution for treatment, and then carrying out heat treatment; neutralizing the titanium matrix subjected to alkali treatment by using a dilute nitric acid solution of which the concentration is not more than 0.01mol/L, and taking out the matrix for cleaning after the treatment is finished; and (3) placing the titanium matrix subjected to neutralization treatment in a silver nitrate solution at the temperature of 100-200 ℃ for silver activation treatment, and taking out the matrix for cleaning after the treatment is finished. The invention is a fluoride-free and palladium-free activation method, which has simple process engineering, uniform nano-silver loading and good activation effect on the premise of ensuring the activation effect, and can realize the uniform deposition of a subsequent nickel layer; the activation process uses conventional medicines, is environment-friendly and pollution-free, and can be suitable for large-batch continuous production.

Description

Fluorine-free and palladium-silver-free activation method before chemical nickel plating on titanium surface

Technical Field

The invention relates to a surface treatment method, in particular to an activation method before chemical nickel plating on a titanium surface.

Background

Titanium (Ti) and its alloy have abundant reserves in the earth's crust, and have excellent mechanical properties, low density and strong corrosion resistance, so its application in aerospace, pharmaceutical and chemical industry, third class medical instrument field is gradually extensive. However, Ti also has some non-negligible disadvantages, such as low surface hardness, poor wear resistance, dense oxide film resulting in large contact resistance, low electrical conductivity, poor solderability, and the like. In order to improve the surface properties of Ti, expand its application range and prolong its service life, it is often subjected to surface treatment. Chemical nickel plating has good deep plating capability, uniform and compact plating layer, high hardness, strong chemical stability and good brazing performance, and is widely applied at present, and in view of the above, new research and new methods for nickel plating on the titanium surface are continuously developed in recent years.

The "heterogeneous autocatalytic reduction" is the basic principle of electroless nickel plating. It is believed that the nickel deposition reaction can be automatically carried out as long as the stable potential of the metal surface in the electroless nickel plating solution is lower than-0.6V, such as metal materials like steel, cobalt, nickel, etc. Although titanium and its alloy have strong chemical activity, because of the strong affinity among surface atoms, oxygen, nitrogen and water molecules, it is easy to form compact oxide film, so although its standard potential is about-1.63V, the potential in nickel plating solution is often about-0.5V, which results in that the chemical nickel plating reaction can not occur. Therefore, much research on chemical nickel plating on the surface of titanium focuses on the activation pretreatment of the Ti surface to promote the growth of the plating layer.

The traditional colloid palladium can have good activation effect on the material to be activated on the surface before plating, can directly activate the titanium surface after cleaning and degreasing, and does not need complex pretreatment such as shot blasting, acid washing and the like. However, palladium is expensive, the commercial price of colloidal palladium is about 2000 yuan/kg, and although the activation effect is good, the consumption is relatively large in large-scale production, accounting for 20-40% of the total cost of electroless plating, and the cost of electroless plating is high.

The hydrogen fluoride has extremely strong capability of dissolving oxide, and can effectively remove the oxide film on the titanium surface and expose the fresh surface in the plating solution environment. Therefore, a considerable part of the current research on "palladium-free" activation of titanium and its alloys before nickel plating has been conducted using hydrofluoric acid etching, hydrofluoric acid-zinc immersion, hydrofluoric acid-nickel immersion, fluoride conversion films. Although activation can be realized by adopting hydrofluoric acid treatment, the process reaction is violent and is not easy to control, and the hydrogen absorption phenomenon of the titanium matrix in a strong acid solution is serious; in addition, hydrofluoric acid is extremely volatile, in the prior art method, the usage amount of 40% concentration hydrofluoric acid exceeds 25ml/L (the actual content of hydrofluoric acid exceeds 10%), even if a strong ventilation system is arranged in an operation room, the problems of permanent damage to the health of workers, excessive pollutant discharge, serious equipment corrosion and the like are caused. These become the fatal bottleneck problem of the technology which limits the large-scale production of hydrofluoric acid activated titanium surface and chemical nickel plating.

It can be seen that, although the palladium activation and fluorine activation methods can realize the activation before the chemical nickel plating on the titanium surface, they all have obvious disadvantages, such as high price and cost, serious environmental pollution and health hazard, and the like.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the defects in the prior art, the invention aims to provide a fluorine-free and palladium-silver-free activation method before chemical nickel plating on the surface of titanium, which has the advantages of simple process engineering, uniform nano-silver load and good activation effect, and can realize uniform deposition of a subsequent nickel layer; and the method is a fluorine-free and palladium-free activation method, uses conventional medicines in the activation process, and is environment-friendly and pollution-free.

The technical scheme is as follows: the invention discloses a surface activation method before chemical nickel plating of a titanium substrate, which comprises the following steps:

(1) alkali heat treatment: placing the pretreated titanium matrix in a sodium hydroxide solution, carrying out alkali treatment, taking out the matrix after the treatment is finished, cleaning, and then carrying out heat treatment;

(2) and (3) neutralization treatment: neutralizing the titanium matrix subjected to alkali treatment by using a dilute nitric acid solution at room temperature, and taking out the matrix for cleaning after the treatment is finished;

(3) silver activation treatment: and (3) placing the neutralized titanium matrix in a silver nitrate solution for silver activation treatment, and taking out the titanium matrix for cleaning after the treatment is finished.

Wherein, the cleaning water adopts deionized water.

In the step (1), the pretreatment comprises polishing, oil removal and cleaning of the surface of a titanium substrate; the concentration of the sodium hydroxide solution is 5-10mol/L, the alkali treatment temperature is 70-100 ℃, the alkali treatment time is 1-6 hours, and the sodium hydroxide solution completely submerges the titanium matrix in the treatment process so as to realize uniform nanocrystallization of the whole surface of the matrix, and then the matrix is fully cleaned; the proper concentration of the sodium hydroxide determines whether the surface of the titanium matrix can form a nano-mesh structure, and further whether the uniform deposition of the nano-silver can be promoted. The heat treatment temperature after the alkali treatment is 400-500 ℃, and the heat treatment time is 1-2 hours.

In the step (2), the cleaning water is deionized water, the concentration of dilute nitric acid in the neutralization treatment is not more than 0.01mol/L, and the neutralization is carried out until the pH value of the cleaning water is 6.0-7.0. And the concentration of the dilute nitric acid exceeding the concentration range can obviously influence the subsequent silver activation treatment effect.

According to the invention, ultra-low concentration silver ions are adopted, and in the step (3), the concentration of the silver nitrate solution is 0.00001-0.01mol/L, the treatment temperature is 100-. When the silver nitrate concentration is less than 0.00001mol/L, the nano titanium substrate surface cannot form enough silver to show excellent activation effect; and when the concentration of silver nitrate is higher than 0.01mol/L, the silver carrying amount of the surface of the nano titanium substrate is not obviously increased, and the concentration of the silver nitrate solution is preferably controlled between 0.00001 and 0.01 mol/L.

Furthermore, the titanium substrate after the activation treatment is subjected to subsequent chemical nickel plating treatment, and the interval time between the titanium substrate and the titanium substrate is not more than seven days.

In the prior art, the approaches for realizing silver activation before plating include a silver ammonia solution-reducing agent method, a surface organic group silver reduction method, a chemical reducing agent addition method and a photo-reduction method, and although the methods can also realize the deposition of silver on the surface of a material, the methods have certain defects, such as unstable solution, low activation efficiency, serious waste, long activation time and the like. For example, silverAlthough the ammonia solution-reducing agent method has a good activation effect, the solution has poor stability, and silver azide (AgN) is precipitated after a long time₃) Silver nitride (Ag)₃N), silver (Ag) imide₂NH) and even ammonium nitrate are easy to explode, and the batch automatic production cannot be realized. The surface organic group silver reduction method depends heavily on the number of active groups on the surface of the material and the reduction performance, and has low efficiency and poor deposition effect. The method of adding the chemical reducing agent is characterized in that silver ions in the reaction tank uniformly react, a small amount of silver particles are deposited on the surface of a sample to realize activation, most of silver nitrate is wasted, the silver particles cannot be guaranteed to be closely arranged on the surface of the sample, and the method cannot be applied to batch production. The photoreduction method is that under the irradiation of ultraviolet light, silver ions can be reduced into nano silver, but the photoreduction energy input is limited, the activation process needs a long time, and light is easily blocked, so that the photoreduction method is completely not suitable for complex devices, and is unrealistic in the automatic continuous production process. In addition, in the above activation method, in order to increase the silver loading amount on the sample surface, a silver nitrate solution having a high concentration (much greater than 0.1mol/L) is often used, which also sharply increases the cost.

The invention provides a brand-new activation method of fluoride-free palladium-free silver before chemical nickel plating on the surface of titanium, wherein a nano net formed by nano silk threads is constructed on the surface of the titanium matrix through alkali treatment, and the nano structure is stabilized through heat treatment; then silver ions are reduced into nano silver particles on the nano silk thread by heating silver nitrate solution; the nano-wire promotes the hydrothermal reduction reaction of silver, provides a carrier for the growth of nano-silver, and does not generate uniform reduction reaction of silver in the solution; the size of the nano silver is influenced by the size of the nano wire, is smaller than the diameter of the nano wire, and is uniform in size and arrangement. Therefore, the treatment method provided by the invention can effectively realize the surface activation of the titanium substrate before nickel plating, and is a fluorine-free palladium-free silver activation method before the nickel plating on the surface of the titanium substrate. The activation energy of silver can play a role in catalyzing nickel plating, but the activation performance of the silver-plated nickel.

Therefore, on the premise of ensuring the activation effect, the method has the advantages of simple process engineering, uniform nano-silver load and good activation effect, and can realize the uniform deposition of the subsequent nickel layer; the method is a fluorine-free and palladium-free activation method, uses conventional medicines in the activation process, is environment-friendly and pollution-free, and can be suitable for large-scale continuous production. When the method is applied to actual production, the flexibility is stronger, and subsequent chemical plating treatment is not required to be carried out immediately; and the subsequent chemical plating treatment must be immediately carried out in the prior art.

Has the advantages that:

(1) the activating agent of the invention does not need expensive palladium, but has good activating effect and high cost performance.

(2) In the method provided by the invention, the solution in each step does not use fluoride which has serious threat to the environment and human health, and the method is an environment-friendly activation process.

(3) In the method provided by the invention, the solution in each step is prepared by adopting a conventional reagent, so that the stability is good, and the risks of long-time denaturation, decomposition and even explosion do not exist.

(4) The method provided by the invention can ensure that the nano silver particles are rapidly deposited on the surface of the nano titanium, and the nano silver is more in quantity and uniformly distributed.

(5) In the method provided by the invention, the reduction of silver only occurs on the nano structure, and the silver ions in the solution do not have comprehensive reduction reaction, so that most of the silver ions are preserved, the solution can be repeatedly used, and the cost is reduced.

(6) The method provided by the invention has the advantages of very simple operation steps, use of conventional instruments and equipment in electroplating and chemical plating factory workshops, no need of immediately performing subsequent chemical plating treatment, and strong time flexibility, thereby being particularly suitable for batch production.

Drawings

FIG. 1 is an SEM picture of the surface microstructure of a titanium sample after silver activation;

FIG. 2 shows the results of EDS analysis of the surface composition of titanium samples after silver activation;

FIG. 3 shows the XPS high resolution scanning result of silver element on the surface of a titanium sample after silver activation;

FIG. 4 is an SEM picture of the surface microstructure of a titanium sample after nickel plating;

fig. 5 is a graph showing the trend of silver content on the titanium surface after activation in silver nitrate solutions of different concentrations.

Detailed Description

The present invention will be described in further detail with reference to examples.

Example 1:

the method for activating the fluorine-free palladium-free silver before chemical nickel plating on the surface of the titanium comprises the following steps:

(1) pretreatment of titanium substrates

Firstly, grinding a pure titanium substrate by 400 # sand paper and 800# sand paper in sequence, then ultrasonically cleaning the pure titanium substrate in acetone and deionized water for 5 minutes in sequence, taking out the pure titanium substrate, and airing the pure titanium substrate in air for later use.

(2) Alkaline heat treatment

And (3) putting the pretreated sample into a polypropylene reaction container, adding enough 5mol/L sodium hydroxide solution to ensure that the solution completely submerges the sample, and sealing. The reaction vessel was placed in a constant temperature electric oven at 80 ℃ and kept warm for 5 hours. After the heat preservation is finished, the mixture is fully washed by deionized water, and is treated for 1 hour at 500 ℃ after being dried by air.

(3) Neutralization with nitric acid

After the heat preservation is finished, the sample is taken out by using tweezers, washed by deionized water, neutralized for 10 seconds in 0.01mol/L nitric acid solution, washed by the deionized water continuously, and the pH value of the washing water is continuously monitored by using a precise pH test paper until the pH value is 6.0-7.0.

(4) Silver activation treatment

Putting the sample into 0.001mol/L silver nitrate solution at 120 ℃ by adopting a hydrothermal reaction kettle, and treating for 20 minutes; after the treatment, the sample was taken out and washed several times with deionized water.

The titanium substrate after activation by the above method was observed by SEM and the results are shown in FIG. 1. A large number of parallel scratches are formed on the surface of the titanium substrate ground by abrasive paper; after the alkali heat treatment, the scratches are covered by a three-dimensional network structure, and the network structure is formed by nano wires with the diameter of about 20-50 nm; after silver activation, the nano-wires have densely arranged nano-particles with a size of about 10-20 nm.

Elemental analysis of the micro-area was performed using an X-ray energy spectrometer (EDS) to confirm that silver had been incorporated onto the titanium surface, as shown in fig. 2.

To further confirm the chemical state of silver, the silver element on the surface was analyzed by X-ray photoelectron spectroscopy (XPS), and the results are shown in fig. 3. According to the element peak shape, the silver can be judged to exist on the surface of the titanium substrate in a single chemical state, and the silver can be determined to be in the single chemical state according to the binding energy.

Combining the results of SEM, EDS and XPS analyses, it was confirmed that a large number of uniformly distributed nano silver particles were deposited on the titanium surface by the above treatment.

To verify the silver activation effect, the treated sample was immediately plated (in this example, after a subsequent electroless nickel plating process was performed within 1 hour) in an electroless nickel plating solution at 85 ℃ for 15 minutes. Wherein the plating solution is prepared according to the formula of a classic chemical nickel plating solution: nickel sulfate: 30g/L, sodium hypophosphite: 40g/L, sodium citrate: 20g/L, lactic acid: 20g/L, glycine: 5g/L, sodium acetate: 10g/L, pH value: 4.2 to 5.2.

After chemical nickel plating, a uniform and bright coating is formed on the surface of the sample. FIG. 4 is a surface SEM topography of the silver activated titanium substrate after nickel plating. It can be seen that after plating, the net structure on the surface of the titanium substrate disappears, and the titanium substrate is replaced by a coating formed by closely arranged cellular tissues, which is the typical appearance of an amorphous chemical nickel plating layer, the plating layer is uniform and compact, the whole surface of the substrate is covered, cracks and plating leakage are avoided, and the thickness of the plating layer is 5.2 microns.

Example 2:

the basic procedure of this example is the same as the matrix of example 1, except that the concentration of the silver nitrate solution is reduced to 0.00001 mol/L. SEM observation and analysis show that nano silver particles which are distributed more uniformly are formed on the nano reticular structure, small gaps are formed among the particles, and the particles are not arranged closely; the appearance is bright after nickel plating, under SEM observation, the amorphous nickel-phosphorus plating layer is uniform and compact, no obvious defect exists, and the thickness of the plating layer is 2.1 microns.

Comparative example 1:

the basic procedure of this example is the same as the matrix of example 1, except that the concentration of the silver nitrate solution is reduced to 0.000001 mol/L. SEM observation and analysis show that the nano silver particles on the nano reticular structure can not be distributed on the surface of the nano silk thread, and part of the nano silk thread is exposed; compared with the example 1, the appearance brightness of the sample after nickel plating is obviously reduced, and under the observation of SEM, the amorphous nickel-phosphorus plating layer is not compact and cannot completely cover the matrix, so that the phenomenon of plating leakage occurs.

Example 3:

the basic procedure of this example is the same as the matrix of example 1, except that the solution concentration of silver nitrate is increased to 0.1 mol/L. SEM observation and analysis show that uniform nano silver particles are formed on the nano reticular structure, and the particles are closely arranged and completely cover the nano wires; the appearance is bright after nickel plating, under SEM observation, the amorphous nickel-phosphorus plating layer is uniform and compact without defects, and the thickness of the plating layer is 5.5 microns.

Further, the activation treatment of the titanium nanocrystals was performed in silver nitrate solutions having concentrations of 0.1, 0.01, 0.001, 0.0001, 0.00001, 0.000001, and 0.00000001mol/L, and the content of silver element was measured by EDS, and the results are shown in fig. 5. It can be seen that when the silver nitrate concentration exceeds 0.01mol/L, no more silver adheres to the titanium surface even if the concentration is increased by 10 times; when the concentration of silver nitrate is lower than 0.000001mol/L, the silver content of the titanium surface is extremely low.

Example 4:

the basic steps of this example are the same as the matrix of example 1, except that the solution temperature of silver nitrate is increased to 200 degrees celsius. SEM observation and analysis show that uniform nano silver particles are formed on the nano reticular structure; the appearance is bright after nickel plating, and the amorphous nickel-phosphorus plating layer is uniform and compact under SEM observation, and the thickness of the plating layer is 5.3 microns.

Example 5:

the basic steps of this example are the same as the matrix of example 1, except that the solution temperature of silver nitrate is reduced to 100 degrees celsius. SEM observation and analysis show that although the nano silver particles cover most of the area of the nano silk thread, the nano silver particles are not closely arranged, and obvious gaps are formed among the particles; the appearance is bright after nickel plating, under SEM observation, the amorphous nickel-phosphorus plating layer is relatively uniform, no plating leakage is found, and the thickness of the plating layer is 2.0 microns.

Comparative example 2:

the basic steps of this example are the same as the matrix of example 1, except that the solution temperature of silver nitrate is reduced to 90 degrees celsius. SEM observation and analysis show that only a few nano silver particles exist on the nano reticular structure, and most of the nano silk threads are exposed; the brightness of the sample after nickel plating is not obviously improved, and under SEM observation, the cell structure of the amorphous nickel-phosphorus alloy only covers part of the titanium substrate, so that the plating leakage area is larger.

Example 6:

the basic procedure of this example is the same as the matrix of example 1, except that the treatment time in the solution of silver nitrate is extended to 30 minutes. SEM observation and analysis show that uniform nano silver particles are formed on the nano reticular structure; the appearance is bright after nickel plating, and the amorphous nickel-phosphorus plating layer is uniform and compact under SEM observation, and the thickness of the plating layer is 5.5 microns.

Example 7:

the basic procedure of this example is the same as the matrix of example 1, except that the treatment time in the solution of silver nitrate is shortened to 10 minutes. SEM observation and analysis show that nano silver particles are formed on the nano reticular structure, but the silver particles are not closely arranged; the appearance is bright after nickel plating, and the amorphous nickel-phosphorus plating layer is uniform and compact under SEM observation, and the thickness of the plating layer is 2.5 microns.

Comparative example 3:

the basic procedure of this example is the same as the matrix of example 1, except that the treatment time in the solution of silver nitrate is reduced to 5 minutes. SEM observation and analysis show that the nano-silver particles formed on the nano-mesh structure are less, and most of the area of the nano-silk thread is exposed; after the sample is plated, the appearance of the sample is not obviously bright, and under the observation of SEM, the cellular structure of the amorphous nickel-phosphorus alloy is dispersedly distributed on the surface of the sample, and a compact plating layer is not formed.

The test results of the above examples 1 to 7 and comparative examples 1 to 3 are summarized, and as shown in table 1 below, it can be seen that when the surface activation method of the present invention is used to treat a titanium substrate, the surface of the titanium substrate is deposited with densely and uniformly distributed nano silver particles, the appearance of the chemically plated nickel is bright, and the plating layer is uniform, dense and free of defects.

TABLE 1 results of examples 1 to 7 and comparative examples 1 to 3

Example 8:

this example is substantially the same as example 1, except that: the alkali treatment temperature in the step (2) is 100 ℃, and the time is 1 hour; the heat treatment temperature is 450 ℃, and the time is 0.5 hour; and the samples after the activation treatment are divided into five groups of samples, and are respectively placed for 1 day, 2 days, 3 days, 5 days and 7 days, and then are subjected to chemical nickel plating, and the chemical nickel plating formula is the same as that adopted in the example 1.

After chemical nickel plating, uniform and bright coatings are formed on the surfaces of the five groups of samples; after plating, the net structure on the surface of the titanium matrix disappears, and the coating layer formed by the closely arranged cellular tissues is replaced by the net structure, is uniform and compact, covers the whole surface of the matrix, and has no cracks or plating leakage.

It can be seen that the titanium substrate has excellent stability before plating by adopting the surface activation method of the invention, and the treatment methods in the prior art all need to be finished immediately in the same day.

Example 9:

this example is substantially the same as example 1 except that the alkali treatment temperature in step (2) is 70 ℃ and the time is 6 hours; the heat treatment temperature is 400 ℃, and the time is 0.5 hour; the concentration of the dilute nitric acid solution in the step (3) is 0.001mo 1/L. And the appearance and nickel plating effect of the alloy are observed, and the result is consistent with that of the example 1.

Comparative example 4:

this comparative example is the same as the matrix of example 1, except that only the alkali treatment is carried out in step (2), i.e., the pretreated sample is placed in a polypropylene reaction vessel, sufficient 5mol/L sodium hydroxide solution is added to completely submerge the sample, and the vessel is sealed. The reaction vessel was placed in a constant temperature electric oven at 80 ℃ and kept warm for 5 hours. And after the heat preservation is finished, fully cleaning the glass by using deionized water, and airing for later use.

The treatment result shows that the nano-network structure on the titanium surface almost completely disappears, the quantity of the loaded nano-silver particles is obviously reduced, and a uniform and continuous nickel-plated layer is not formed on the surface of the sample.

Comparative example 5:

this comparative example is the same as the substrate of example 1 except that the nitric acid solution in step (3) is replaced with hydrochloric acid and sulfuric acid.

The processing result shows that the deposition effect of the nano silver particles is poor, the nano wires are not completely covered, and silver-containing grain-shaped deposits are occasionally visible on the nano net structure, the deposits contain Ag and Cl or Ag and S elements and should be AgCl or AgSO₄And (4) depositing.

Claims

1. A fluorine-free and palladium-free silver activation method before chemical nickel plating on a titanium surface is characterized by comprising the following steps:

(1) immersing the pretreated titanium matrix in a sodium hydroxide solution for alkali treatment, taking out the matrix after the treatment is finished, cleaning, and then carrying out heat treatment;

(2) neutralizing the titanium matrix subjected to alkali treatment by using a dilute nitric acid solution, and taking out the matrix for cleaning after the treatment is finished;

(3) and (3) placing the neutralized titanium matrix in a silver nitrate solution for silver activation treatment, and taking out the titanium matrix for cleaning after the treatment is finished.

2. The method of activating freon-free palladium-free silver before chemical nickel plating on a titanium surface according to claim 1, wherein: in the step (1), the concentration of the sodium hydroxide solution is 5-10 mol/L.

3. The method of activating freon-free palladium-free silver before chemical nickel plating on a titanium surface according to claim 1, wherein: in the step (1), the temperature of the alkali treatment is 70-100 ℃, and the treatment time is 1-6 hours.

4. The method of activating freon-free palladium-free silver before chemical nickel plating on a titanium surface according to claim 1, wherein: in the step (1), the heat treatment temperature is 400-500 ℃, and the heat treatment time is 0.5-1 hour.

5. The method of activating freon-free palladium-free silver before chemical nickel plating on a titanium surface according to claim 1, wherein: in the step (2), the concentration of the neutralized dilute nitric acid solution is not more than 0.01 mol/L.

6. The method of activating freon-free palladium-free silver before chemical nickel plating on a titanium surface according to claim 1, wherein: in the step (3), the concentration of the silver nitrate solution is 0.00001-0.01 mol/L.

7. The method of activating freon-free palladium-free silver before chemical nickel plating on a titanium surface according to claim 1, wherein: in the step (3), the temperature of the silver activation treatment is 100-200 ℃, and the treatment time is 10-30 min.