JPS5844738B2 - Composite plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite plating method in which a plating film composed of nickel, phosphorus, and insoluble fine particles is deposited and formed on a surface of a metal or a nonmetallic material coated with a metal film.

Recently, a composite plating method that forms a wear-resistant or lubricating film on a metal or non-metallic surface has been attracting attention.

This is a plating method in which insoluble fine particles such as silicon carbide are eutectoid in a metal matrix such as nickel.
It is called composite plating or dispersion plating because of its plating mechanism, and by appropriately selecting the type, size, and amount of eutectoid particles, it can be applied to conventional carburizing, nitriding,
It is known as a unique surface treatment method compared to so-called wear-resistant or lubricant surface treatments such as sulfurization, metal spraying, resin coating, hard anodizing, and hard chrome plating.

In other words, compared to these conventional surface treatment methods, it is possible to form a film with excellent wear resistance or lubricity on any base material without causing thermal deformation, and it also has good corrosion resistance. It is beginning to be put into practical use for internal surfaces, molding machine parts, slide parts, etc.

There are two methods for this composite plating: an electrolytic method and an electroless method. An example of the former is an electrolytic method in which inorganic fine particles such as silicon carbide are suspended and dispersed in an electrolytic nickel plating bath, mainly a Watt bath. In other words, nickel and fine particles are eutectoided by electroplating, and the latter example is a method in which inorganic fine particles such as silicon carbide are suspended in an electroless nickel bath containing nickel salt and hypophosphite as a reducing agent. There is a method that eutectoides nickel, phosphorus, and fine particles electrolessly, that is, by using the reducing power of hypophosphite ions while turbidly dispersing them.

As mentioned above, the advantages of composite plating compared to other conventional surface treatments are recognized and attracting attention, but both electrolytic methods and electroless methods have advantages and disadvantages.

In other words, although the electrolytic method has the advantage of faster deposition speed than the electroless method, it is directly affected by the current density depending on the shape of the product, resulting in variations in the plating thickness and the amount of eutectoid particles. Therefore, it is necessary to use an auxiliary electrode that averages the current density according to the shape of the item (even then, the plating thickness cannot be made uniform), and the amount of fine particles suspended in the plating bath is also much larger. Poor workability,
There are many difficulties in terms of quality and productivity.

On the other hand, the electroless composite plating method has the following advantages: the amount of fine particle eutectoid is stable, the plating film thickness is constant, the hardness and wear resistance are further improved by heat treatment, and there are no pinholes. Although it has advantages, it also has the disadvantage of slow deposition rate, which is also one of the reasons for the high cost of electroless composite plating.

As a result of analyzing the advantages and disadvantages of these two composite platings, the present inventors have discovered a composite plating method that compensates for each of the disadvantages and exhibits the respective advantages.

That is, according to the present invention, insoluble inorganic fine particles are suspended and dispersed in an electroless nickel plating bath containing nickel salt and hypophosphite, and direct current microelectrolysis is applied between the item in the bath and the insoluble anode. By flowing, a composite plating film consisting of nickel, phosphorus, and inorganic fine particles with a stable and uniform plating thickness with a stable eutectoid amount of phosphorus and fine particles is formed on the surface of the item, and plating can be performed within an appropriate current density range. By carrying out this process, a high quality composite plating film can be formed on the surface of an article made of any material without using any auxiliary anode, and an effective composite plating method with a wide range of floor applications is provided.

For example, in conventional electrolytic composite nickel plating, the product is used as a cathode and a consumable anode such as nickel is used as an anode.
Normally, electrolysis is performed at an average current density of 3/d- or L5 A/d-, and nickel is eutectoid with the fine particles in the bath. An extremely thick plating film is formed in the valleys or deep parts, and an extremely thin plating film is formed in the valleys or deep parts.

This difference manifests itself as a difference of 10 to 1, for example.
Even if a suitable auxiliary anode is used, it is difficult to achieve a 2:1 ratio.

Furthermore, while the amount (thickness) of nickel ions formed as metallic nickel is directly proportional to the current density, the eutectoiding of dispersed particles in the bath into the nickel matrix does not necessarily depend on the current density. Physical adsorption and chemical adsorption are thought to be the eutectoid mechanisms, rather than density. Therefore, the amount of nickel deposited (thickness The fine particles are co-deposited without being directly related to (a), and the amount of fine particles as well as the amount of nickel in the plating film is not constant.

This is true not only for nickel plating but also for cobalt plating and copper plating as long as electrolytic composite plating is used.

On the other hand, in electroless composite nickel plating, if plating is performed under certain plating bath composition and plating conditions, the shape of the product can be achieved regardless of whether the product is a metal or a non-metal such as plastic. Regardless of the amount of nickel, phosphorus, and dispersed fine particles, a fixed film with a constant amount of nickel, phosphorus, and dispersed particles can be obtained, and its thickness is exactly the same regardless of the shape or location of the product.
For example, when plating 10μ, the variation in plating thickness is 1
It has an extremely high precision of less than μ.

This is dominated by the reduction reaction of nickel ions by hypophosphite ions, etc., so if the surface of the product in contact with the liquid reacts under the same conditions, and the bath temperature and stirring conditions are constant, nickel, phosphorus, and other fine particles can be reduced. It forms a plating film with a constant amount of precipitation.

In principle, this is true not only for nickel but also for cobalt and copper.

However, because the precipitation is caused by the reduction reaction of hypophosphite ions, the average precipitation rate of electrolytic composite plating is 40μ/11
r to 60 μ'lh.
In electroless composite plating, 15μ/hr to 2
As low as 5μ/hr.

One method of increasing the deposition rate of electroless nickel plating is described in the paper by T., CFran Klin and S. Lueck (Plating and 5 surface Fin.
shing, +67, (1)50-51, (198
0)), a method of applying alternating current to an electroless nickel plating bath is known, but there has been no discussion as to whether this method is effective for composite plating, and other subsequent research is also unknown. do not have.

In addition, another method by the present inventors (Japanese Patent Application No. 55-012
(319) proposed an electroless composite plating method that uses gluconate as a complexing agent and is practical even at low temperatures, that is, the deposition rate is faster than other known electroless composite plating methods. , It is desired that the speed of this process be further increased in order to increase productivity.

The present invention will be explained in detail below using examples.

Example First, a plating bath having the following composition was prepared in a 51 beaker.

Nickel sulfate 30 El/1 Sodium glyconate 40 g, #sodium hypophosphite 259/1 209/l silicon carbide with an average particle size of 1 μm was dispersed and suspended in this, the pH was 6.0, the temperature was 75°C, and the bath was heated. Plating was performed while stirring the air.

The object to be plated (hereinafter referred to as TP) was a 5US304 stainless steel plate (50 mm x 50 mm x 1 mm thick), and the back surface was masked using an organic resist.

A SUS 304 stainless steel plate (50 mi x 1007 nrIL x 1 m1 rL thickness) was used as an insoluble anode, and the distance between the electrodes was 120 degrees.

After degreasing and activating the TP according to the conventional method of boiling degreasing, electrolytic degreasing, and acid immersion,
A slight direct current was applied from the anode, and plating was carried out for 2 hours.

In order to increase the reliability of the experiment for each condition, plating was repeated five times and evaluated based on the average value and variation.

Two measurement points were used: the center point and the corner of the TP.

This is to accurately evaluate the quality variations in the TP.

The evaluation items were the precipitation rate of the composite plating film, the precipitation ratio of nickel, phosphorus, and silicon carbide, surface hardness, surface roughness, wear resistance, morphology observation and appearance inspection, micro film thickness meter, weight analysis, and micro hardness. The samples were observed and evaluated using a meter, a surface roughness measuring device, a taper set abrasion tester, an abrasion friction tester, an electron microscope, and visually.

The results are shown in Figures 1, 2, and 3 and the following table.

* Loss of plated coating per 1000 revolutions ■From this result, the DC current condition is 0. IA/dd or 1. OA/
If plating is performed with d-, the deposition rate is 20% to 60% higher than when no current is applied, and the physical properties of electroless composite nickel plating are exactly the same as the excellent film composition, hardness, surface roughness, wear resistance, and structure. , and appearance can be obtained regardless of the location of the item.

This means that even if the actual item to be plated is not limited to the shape of this TP, but has a complex shape, it is possible to achieve high precision within the range of ±6 coefficients or less, regardless of the part. This shows that a composite plating film can be formed with a thickness of .

A more detailed evaluation of each test result is as follows.

First, the deposition rate of the composite plating film is only 0. IA
l4. Just by applying a DC current of =, it increases by 20%, and after that it gradually increases until it shows an increase of 60% at "/dm".

At 2A/dtri', the increase is further increased by 100φ, but this is no longer practical as the variation in plating thickness increases depending on the location.

The variation in plating thickness at IA/dd is plus or minus 6oφ, so the actual required film thickness accuracy is considered to be sufficient at plus or minus 10%.
It can be said that it is sufficiently effective up to rn.

Furthermore, from Fig. 1, 0. IA/d, = It is clear that an increase in the deposition rate is observed even with a smaller amount of direct current, and therefore, even with such an extremely small amount of current applied, the increase in the deposition rate can be compared to that achieved by ordinary electroless plating alone. Although it is more effective than the case, it is excluded in the present invention, which intends to increase the practical precipitation rate.

Furthermore, the results shown in FIG. 2 show that the amount of eutectoid silicon carbide in the plating film slightly decreases as the applied current increases.

This is because, when no current is applied at all, the eutectoid of silicon carbide is controlled by the chemical reaction during the reduction reaction of nickel ions by hypophosphite ions, the electric charge of fine particles, and the state of stirring. It is thought that this is because when electricity is applied, the precipitation of nickel or nickel and phosphorus takes priority over the eutectoid factor due to the direct current.

This is in good agreement with the fact that the phosphorus concentration in the film gradually decreases as the current increases, as seen in FIG.

However, both the amount of fine particle eutectoid and the phosphorus concentration were determined to be effective for the composite plating film formation rate between 0 and 1 A/di.
Considering 0A/dd, even if there is a slight decrease, it functions without any problems in terms of organization and physical properties, as will be described later.

The results of physical property evaluation are shown in the table.

That is, the hardness, abrasion resistance, and surface roughness are almost the same at a current density of 0.1/di to 1.0 k/dm, and the physical properties are sufficiently stable and uniform.

At a current density of 2 A/dm, it no longer has the characteristics of a composite plating film.

This is due to morphological defects that can be easily understood from the decreased contents of phosphorus and silicon carbide as shown in FIGS. 2 and 3.

In particular, in the surface roughness measurement and morphology observation of the 2A/dd plating film, the dispersion state of silicon carbide in the plating film was poor. I can even see it.

Therefore, in terms of physical property evaluation and morphology, the effective current density is 0.
．． 1 as /di or IA/di.

Note that these current densities range from 0.1 A/dm2 to 1.0
As a result of vacuum heat treatment of TP plated with 76m2 at 400°C for 2 hours, the wear resistance of Hv14001 was approximately three times that of hard chromium, and showed the same performance as that without energization.

That is, crystallization of nickel and phosphorus and increase in silicon carbide inclusion power were similarly observed due to heat treatment.

Similar tests were also conducted using molybdenum disulfide and boron nitride as solid lubricants for dispersed fine particles, and the results showed almost the same tendency as in the case of silicon carbide. It was recognized that it could be formed at high speed.

Furthermore, as a practical evaluation, we tried gears, shafts, molds, etc., and the same results as in the case of TP were obtained.

That is, the current density at each part of the item is 0.1 A7'a
As a result of using an average current density within the range of 76 m to 1.0 m, for example 0.3 A/d 7712, a composite plating film of silicon carbide type with physical properties as shown in the table was obtained as shown in Fig. 2. It was possible to form the composition as shown in FIG. 3 at a high speed as shown in FIG. 1.

Furthermore, if the surface of a non-metallic material such as plastic is electrolessly plated with nickel or the like using a known method, and then the composite plating method of the present invention is applied, the same form and formation as that formed on the metal surface can be obtained. It was confirmed that it can be done.

Furthermore, in the explanation of the present invention, the fine particles used were mainly silicon carbide, but as long as they are insoluble fine particles, other hard fine particles such as aluminum dioxide, cerium dioxide,
Tungsten carbide, titanium carbide, etc., graphite, carbon fluoride, etc. can be used as solid lubricants, and for nickel salts and hypophosphites, cobalt or copper can be used instead of nickel, and hypophosphorous acid A similar effect can be achieved when a borohydride is used instead of a salt.

Furthermore, citrate, glycolate, etc. can be used instead of gluconate.

As explained above, the present invention provides a method for dissolving nickel, phosphorous, and the fine particles onto the metal surface while passing a direct current on the metal surface in an aqueous solution containing the nickel salt, hypophosphite, and the fine particles. This is a new plating method that has a wide range of applications and can deposit and form a composite plating film with a stable structure and uniform thickness at a higher speed.

Therefore, if this method is applied to all kinds of parts that require wear resistance and lubricity, it will not only be possible to use conventional surface treatments such as hardening, nitriding, metal spraying, anodizing, and hard chrome plating, but also conventional electrolytic treatments. It exhibits superior functionality in terms of quality and/or productivity than composite plating or electroless composite plating.

[Brief explanation of the drawing]

Figures 1 to 3 show the test results in Examples of the present invention. Figure 1 is a diagram showing the relationship between energization conditions and variations in the deposition rate and plating thickness of the composite plating film, and Figure 2 is the relationship between energization conditions and variations in the plating thickness. FIG. 3 shows a relationship diagram between energization conditions and phosphorus concentration (ratio to nickel).

Claims (1)

[Claims] 1. In an electroless nickel plating bath containing nickel salts, hypophosphites and insoluble fine particles, a current density of 0 is applied to the metal surface.
．． IA/am or 1. A composite plating method in which a composite plating film consisting of nickel, phosphorus, and the fine particles is deposited and formed on the surface while applying a direct current of OA/dm from an insoluble anode.