JPH0631462B2 - Film formation method by composite chrome plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a film forming method by composite plating with trivalent chromium for the purpose of improving wear resistance and corrosion resistance.

(Prior Art) The conventionally widely known bath structure of a chromium plating bath is mainly composed of hexavalent chromium (CrO ₃ ), and H as a catalyst root.
It is a so-called sergeant bath to which ₂ SO ₄ , H ₂ SiF _{6 and the} like are added. In recent years, research and development of plating from a bath mainly containing trivalent chromium has been carried out from the viewpoint of less pollution and saving of electric energy (Japanese Patent Publication No. 54-375).
64). Attempts have also been made to improve the wear resistance of chromium plating using a Sargent bath mainly composed of hexavalent chromium, and composite plating of hard particles such as SiC, Al ₂ O ₃ or diamond was investigated.

Further, composite plating has been known for use as a sharpener (Japanese Patent Publication No. 13-4963).

(Problems to be solved by the invention) Plating with a bath mainly containing trivalent chromium has the advantages of less pollution and less electricity consumption than a bath mainly containing hexavalent chromium, but on the other hand, the plating film becomes thicker. If it is less than 2 μm, it is uniform and has gloss, and hard plating is possible. However, it is not suitable for plating processing that requires thick plating because it causes bump-like deposition in long-term electrolytic plating. is there. Therefore, there is a problem that it can be put to practical use only when it is limited to a relatively thin plating that requires corrosion resistance. Further, the hexavalent chromium composite chrome plating had a significantly small amount of hard particles deposited, and could not be put to practical use.

Further, the composite plating for the abrader seems to use hexavalent chromium, but since the precipitation amount of hard particles is extremely small,
It was not practical as a plating for obtaining a general hard surface. Therefore, no examples were known.

(Means for Solving the Problems) However, the present invention succeeded in improving the thin film performance of chromium plating by co-depositing hard particles having wear resistance on trivalent chromium plating.

That is, chrome plating mainly composed of trivalent chromium cannot be thickly plated, and therefore its practical range is extremely limited. However, in the present invention, wear resistant hard particles are added to the trivalent chromium bath. It was found that the abrasion resistance was enhanced by the above method, and the heat treatment at 300 ° C. to 800 ° C. was performed, and the surface hardness was remarkably improved. Examples of the wear-resistant hard particles described above include diamond, SiC, Al ₂ O ₃ , Cr ₃ C ₂ ,
ZrB ₂ , B ₄ C, CBN, etc. are considered. Therefore, in the present invention, a single kind or a plurality of kinds of each of the above particles can be used in a predetermined ratio depending on the application. A plating film having wear resistance and hardness can be easily obtained.

The bath containing trivalent chromium as a main component is, for example, a trivalent chromium salt such as chromium chloride, chromium sulfate or chromium fluoride, a carboxylate salt such as formic acid and acetic acid, and an amino group and a carboxyl group such as glycine and dalutamic acid. One or more of the compounds described above are added, and further an electrical conductivity improver consisting of an alkali metal chloride such as NaCl or KCl, a sulfate, and a hydrogen compound of Group VIIb is added for adjustment.

Next, the present invention will be described in more detail.
Cr ⁺³ salt (eg CrCl ₃ , Cr ₂ (SO ₄ ) ₃ )
Plating becomes possible by using a bath in which a complexing agent is added. The action and effect of this complexing agent on electrodeposition are extremely important for electrodeposition. If a complexing agent is not used, a black film can be obtained but metal chromium cannot be electrodeposited. The inventor of this application studies the action mechanism of the complexing agent, finds that the complexing agent is adsorbed on the cathode surface, and electrodeposition proceeds, and further performs composite plating for the purpose of improving the chromium plating function. It was found that when diamond powder, SiC, etc., which are hard particles, were added to the bath in order to form a wear-resistant film, a chrome-diamond and chrome-SiC composite plating film was easily formed. Further, as a result of detailed studies on the chromium-based composite plating, it was found that the complex compound adsorbed on the cathode was remarkably effective in reducing the surface tension of the suspended particles. When the plating film of the present invention is heat-treated, the hardness tends to increase as the heating temperature increases, as shown in FIGS.
The hardness was rapidly increased by heating above ℃, stabilized at 400 ℃ or more, maintained a substantially constant hardness up to 800 ℃, the maximum value was found to be about double the increase before the treatment.

(Function) That is, according to the method of the present invention, the composite chromium plating of trivalent chromium is remarkably excellent in wear resistance and hardness,
And the required plating thickness can be obtained. Further, the heat treatment can dramatically increase the wear resistance and hardness.

Example 1 As a trivalent chromium plating bath structure, CrCl ₃ 6H ₂ O 100 g / l, HCOOK 80 g / l, NH ₃ Br 10 g / l, NH ₄ Cl 50 g / l, KCl 70 g / l, H ₃ BO ₃ 40 g / l were wet. Agent (sodium sulfosuccinate 0.5 ml / l + phenyl urethane 0.5 ml / l) 1 ml / l
Add it, adjust the bath to pH 3.0, age at 25 ° C for 24 hours, and then add artificial diamond (average particle size 0.5 μm) to 10
g / l and 10 g / l of graphite were added, and the mixture was stirred and suspended using a stirrer, and then electrodeposited for 60 minutes under an electrolytic condition of 8 A / dm ² using an anode carbon and a cathode stainless steel plate. The chromium plating thickness obtained at this time was 9 μm. The hardness of the electrodeposited chrome plating that did not eutectoid diamond using the above bath was Hv700, but the hardness of the chrome-diamond composite coating with eutectoid diamond was Hv90.
It was 0. The amount of eutectoid diamond in the chromium-diamond composite coating obtained under these conditions was 2.0 wt%. The plated product was heat-treated at 650 ° C. for 1 hour to obtain a test piece. Next, wear a wheel CS-1 with a taper wear tester.
0, load 1 kgf, wear amount after 10,000 rotations was calculated to be 2 mg / c for plating only without hard particles
m ² , and this test piece was 0.5 mg / cm ² . In the above embodiment, the amount of added diamond was 20 g / l or 30.
The diamond eutectoid amount of the chromium-diamond composite coating produced under the above electrolysis conditions was 2.5 wt%.
Or, it increased to 2.7 wt% as the amount of diamond added increased. Using these test pieces, a test was conducted under the same wear conditions as described above, and as a result, 0.4 mg / cm ² or 0.3 mg / cm ²
The wear amount was reduced.

(Example 2) The chromium plating bath of Example 1 was used, a ferrite electrode was used as the anode, a brass plate was used as the cathode, and 5 g / l of α-SiC (average particle size 0.5 μm) was added to the added fine particles. A Cr-SiC composite plating thickness of 9 [mu] m was obtained under the electrolytic conditions of. The hardness of the plating was slightly higher than that of Hv800 and chromium plating alone. The eutectoid amount of SiC was 0.5 wt%. Using this test piece, a test was conducted under the same wear conditions as in Example 1, and as a result, the loss on wear was 1.5 mg / cm ² . Furthermore, when the amount of SiC added to the bath was increased to 10, 20, 30 g / l, Cr-Si
The eutectoid amount of SiC of C composite plating is 2.4 wt%, 2.7 wt%
% And 3.0 wt%. Using this test piece, a test was conducted under the same wear conditions as in Example 1.
^{0mg / cm 2, 0.5mg / cm} 2, becomes abrasion loss of 0.4 mg / cm ^2, in accordance with increasing SiC co析量wear amount was reduced.

(Effect of the Invention) That is, according to the method of the present invention, since trivalent chromium is used to perform composite chromium plating containing hard particles, the plating film has high wear resistance and high hardness, and a required plating thickness is obtained. There is a remarkable effect such as being able to.

Further, there is an effect that the hardness can be remarkably increased by heat-treating the obtained composite chromium film.

In the conventional trivalent chromium plating, the hardness of the plating film was not satisfactory, but the conventional problems were solved by applying the composite plating of the present invention. Further, in the hexavalent chromium composite plating, there was a problem in the amount of eutectoid,
The trivalent chromium plating of the present invention solves this problem and enables composite chromium plating.

In the present invention, if a complex is formed, the electric conductivity may be deteriorated and the progress of plating may be hindered.
Mixing an alkali metal chloride such as Cl, a sulfate, and a hydrogen compound of Group VIIb has an effect of improving electric conductivity.

According to the method for forming a composite plating film of trivalent chromium of the present invention, pollution is less than that in the case of hexavalent chromium plating,
The wastewater treatment can be simplified and the amount of electricity used is almost 1 /
There is a significant effect on the implementation, such as a reduction of about 2.

[Brief description of drawings]

Fig. 1 is a graph showing changes in hardness due to heat treatment of hexavalent chromium plating and trivalent chromium plating, and Fig. 2 shows that diamond particles were mixed during trivalent chromium plating and that silicon carbide was mixed therein. FIG. 4 is a diagram showing a change in hardness due to heat treatment.

Claims (5)

[Claims] 1. Wear-resistant hard particles are added to and suspended in a bath in which a complexing agent and an electric conductivity improver are mixed with a trivalent chromium salt.
After adjusting the pH to 1 to 3, an insoluble electrode is used as an anode and a cathode is used as a material to be plated to generate a plating film by applying electricity to the plated material.
A method for forming a film by composite chromium plating, which comprises heat treatment at 0 ° C to 800 ° C. 2. The method for forming a film by complex chromium plating according to claim 1, wherein the trivalent chromium salt is chromium chloride, chromium sulfate or chromium fluoride. 3. A method for forming a film by complex chromium plating according to claim 1, wherein the complexing agent is a carboxylate such as formic acid and acetic acid, and a compound having an amino group and a carboxyl group such as glycine and daltadic acid. . 4. The composite chromium plating according to claim 1, wherein the conductivity improver is composed of an alkali metal chloride such as NaCl or KCl, a sulfate and a hydrogen compound of Group VIIb. Film formation method 5. Hard particles made of diamond, SiC, Al ₂
The method for forming a film by the composite chromium plating according to claim 1, wherein one or more kinds of O ₃ , Cr ₃ C ₂ , ZrB ₂ , B ₄ C, and CBN are used.