The method of applying a chromium coating

 

(57) Abstract:

The invention can be used to protect the surface of the moving parts of mechanisms. The method comprises the deposition on a substrate chrome plating electrolytic method of chrome-containing solutions in the presence of a catalyst, on the first layer additionally precipitated chromium thermal dissociation of hexacarbonyl chromium, the thickness of the additional layer is 5 to 15% of the thickness of the first coating layer. table 1.

The invention relates to mechanical engineering and can be used to protect the surface of the moving parts of mechanisms.

A known method of applying to the surface of the product (substrate) chrome coatings by thermal dissociation vapor hexacarbonyl chromium [1]. The method is carried out at a temperature of the substrate from 350 to 800oC in a vacuum of about 1 to 10-1mm RT. Art. when continuous pumping system. The number of carbonyl vapor fed to the reactor is governed by the temperature of the crystal hexacarbonyl chrome sublimator and typically is in the range from 40 to 80oC. Under these conditions, the rate of coating is from 20 to 150 μm/h

Characteristic of the">

However, when the deposition of such coatings in these modes, the adhesive strength of their steel substrate is insufficient, and in the machining of parts is observed the formation of cracks in the coating and partial detachment from the substrate.

Known electrolytic method of applying a chromium coating and, in particular, with the use of high-speed self-regulating chromium electrolytes [2]. The method is carried out on the basis of catalytic anions in the form of sparingly soluble compounds of the following composition [3], g/l:

1) 250 chromic anhydride, 5-6 sulfate strontium, 8-10 calcium fluoride, sulfate-fluoride electrolyte (SF);

2) 230-250 chromic anhydride, 18-20 potassium silicofluoride, 8-10 calcium fluoride, fluoride-crematories electrolyte (FCF).

The process is carried out at a temperature of electrolyte 40 to 70oC and a cathode current density of 30-70 A/DM2. In these conditions get shiny chrome coating with a small internal stresses characterizing the high strength of the coating to the substrate. However, the maximum microhardness of such coatings does not exceed 800-900 kg/mm2.

The task of the invention to provide coatings. This problem is solved by the proposed method, the coating of the self-regulating chromium electrolytes, followed by additional deposition of chromium thermal dissociation of carbonyl vapor of chromium, the thickness of the additional layer is 5-15% of the thickness of the first layer.

The method is as follows. Sample as the cathode is placed in hromsoderzhashchej electrolyte specific composition comprising catalyst. The deposition of chromium is carried out at 50-60oC, current density And 60-70/DM2. The sample after leaching is placed in a vacuum chamber on a graphite heater. The vacuum chamber, the sample is heated up to 350-500oC and is supplied from the pre-heated sublimator pair of hexacarbonyl chromium. Duration of 7-10 minutes On the surface of the heated sample pairs hexacarbonyl chromium decompose with the formation of additional chrome plating, the thickness of the additional coating layer is 5-15% of the thickness of the first layer.

Example 1. A sample of Art. 3 is placed as a cathode in sulfate-fluoride (SF) electrolyte composition: 250 g/l of chromic anhydride, 6 g/l of strontium sulfate and 8 g/l of calcium fluoride. The deposition of chromium CR is C is removed from the electrolyte, washed with distilled water, dried, wipe the inner side moistened with ethyl alcohol, and put the camera on a graphite heater. Then the vacuum system until sufficient pressure 5 10-2mm RT. Art. the Sample is heated to 350oC and served from preheated to 40oC sublimator pair of hexacarbonyl chrome with vacuum. On the surface of the heated sample pairs hexacarbonyl chromium decompose with the formation of additional coverage. The residual pressure in the apparatus is reduced to 1 to 10-1mm RT. senior process Duration 7-10 minutes

The thickness (a) primary and secondary layers is determined by calculation on the weight gain of the sample. The thickness of the layers is respectively 40 and 3 μm. Microhardness (Hcdetermine the device PMT-3. The microhardness of the first layer 750 kg/mm2the second layer 1400 kg/mm2. Other examples are given in the table.

As seen from the examples 1-3, the proposed method obtained the chrome coating with high microhardness while maintaining strong adhesion of the coating to the substrate.

This invention involves an inventive step, since it was not known that when applied to pervia, since experimentally it was shown that the coating system Cr-Cr (in the case of a chromium substrate and Cr-carbonyl coating layer) does not possess the strength of coupling, as evidenced by the example 4.

In example 4, the coating only the carbonyl method on a substrate of chromium, obtained by a metallurgical method. There is cracking of the coating and its partial detachment from the chrome substrate. Microhardness preserved the chrome coating is quite high and is 1250 kg/mm2.

Sources of information

1. Syrkin Century, Carbonyl metals. - M.: Metallurgy, 1978.

2. Borisov, A. the process of chrome plating spools of valves in high-speed self-regulating electrolytes /Sat. The improvement of means of mechanization of agriculture non-Chernozem zone. - Chelyabinsk, CHUMASH, 1981, S. 46.

3. Yuriev L. I., Kozlov, I. P., Borisov, A. Physico-mechanical properties of electrolytic chromium obtained from self-regulating electrolytes /Sat. Repair of machines and technical metal. - M.: MYISP, 1975, S. 43.

The method of applying a chromium coating on a substrate by electrolytic deposition of chromium is niteline deposition of chromium thermal dissociation vapor hexacarbonyl chromium, the thickness of the additional layer is 5 to 15% of the thickness of the first coating layer.

 

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