RU2400321C1 - Procedure for equal-channel angular pressing work pieces out of titanium or stainless steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to process of mechanical treatment of metals by pressing with intensive plastic deformation and can be used for fabrication of nano-crystal hardly-deformed metals. The procedure consists in preparation, cleaning and work-pieces pressing. An intermediate layer of nickel is preliminary applied on surface of work-pieces. Further a plastic layer of copper of not less 80-100 mcm thickness is applied by the method of galvanic coating in electrolyte. Also work pieces are successively pressed at 500-1000 MPa pressure in the range of temperature 450-500°C.

EFFECT: reduced power consumption at pressing, improved processability, improved mechanic characteristics of work-piece and reduced oxidation and tribo-technical indices of process.

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Description

The present invention relates to a technology for the mechanical processing of metals by pressure under intense plastic deformation and can be used for the manufacture of nanocrystalline difficult to deform metals or semi-finished products with improved physical and mechanical properties.

The relevance of the problem solved by the invention is based on the need to develop new structural materials with significantly improved physical and mechanical properties, because the choice of structural materials for their use in high reliability structures is determined by the ratio between high ductility and mechanical strength. Metallic materials have the best such ratio. The increase in the strength properties of metallic materials in production was mainly due to the development of alloys with a new chemical and phase composition. Scientific research outlined new ways to improve the properties of structural materials due to the targeted formation of micro- and nanocrystalline structures. The variety of powder metallurgy methods - compaction of nanopowders, intensive plastic deformation (IPD) - provides ample opportunities for obtaining nanomaterials.

To obtain high-density homogeneous materials, comprehensive (isostatic) pressing is used, including the method (IPD) - torsion under high pressure.

Conventional deformation methods — rolling, drawing, pressing, etc. — ultimately lead to a decrease in the cross section of the workpiece and do not allow to achieve large degrees of grain refinement. Non-traditional methods (for example, equal-channel angular pressing), allow you to deform the workpiece without changing the cross-section and shape and achieve the necessary high degrees of deformation and grinding of grain. To date, the nano- and submicrocrystalline structure in the course of SPD has been obtained in aluminum, iron, titanium, and their alloys. This structure leads to improved physical and mechanical properties.

A known method of equal-channel angular pressing (RF patent No. 2240197, IPC B21J 5/00, published on November 20, 2004), which includes preparing samples, conducting combined intensive plastic deformation in combination with low-temperature annealing to relieve internal stresses.

The disadvantages of this method include the significant wear of the stamp, insufficiently high processability of the process of angular equal-channel pressing due to the lack of effective means providing protection against oxidation, high ductility and formability of the samples, tribological performance at elevated temperatures.

Known as a prototype is a method of equal-channel angular pressing, including the preparation of metal samples, cleaning, the formation of an intermediate plastic layer of copper or steel in the form of shells on the surface of the samples and subsequent pressing of the blanks (I.V. Aleksandrov et al., Grinding the microstructure in intense plastic tungsten deformation, J. "Physics of metals and metal science", 2002, vol. 93, No. 5, p.105-112).

However, the prototype did not provide the possibility of reducing the pressing forces, improving manufacturability by reducing the stamp wear, mechanical characteristics (ductility, formability) of the workpieces, the continuity of the plastic coating layer, reducing oxidation and tribological characteristics of the pressing process at elevated temperatures (about 450-500 ° C) .

The task of the inventors is to develop a method of equal channel angular pressing of titanium or stainless steel preforms, in which relatively low efforts were achieved during the pressing process, and the preforms formed at high temperature would be reliably protected from oxidation, and the physical and mechanical properties of the finished products were increased.

A new technical result when using the proposed method is to provide the possibility of reducing the pressing forces, improving manufacturability by reducing the wear of the stamp and improving the mechanical characteristics (ductility, formability) of the workpieces, the continuity of the plastic coating layer, reducing oxidation and tribological characteristics of the pressing process at elevated temperatures (about 450-500 ° C).

These tasks and a new technical result are ensured by the fact that in the known method of equal channel angular pressing of titanium or stainless steel preforms, including preparing the preforms, cleaning and pressing them, according to the invention, an intermediate layer of nickel is initially applied to the surface of the preforms, then the intermediate layer is applied a plastic layer of copper with a thickness of at least 80-100 microns by galvanic coating in an electrolyte and subsequent pressing of the workpieces is carried out at 500-100 MPa in the temperature range 450-500 ° С with preservation of the intermediate and plastic layers.

The proposed method is implemented in the following sequence. Initially, metal blanks made of either titanium or stainless steel are subjected to traditional mechanical (including ultrasonic) and chemical treatment to prepare the surface for galvanic deposition of the plastic layer, for which the outer layer consisting of an oxide film and particles of mechanical impurities is first removed mechanically , then the cleaned surface is subjected to chemical etching using mineral acids and reagents.

Then, an intermediate layer of zinc and then nickel is deposited on the prepared surfaces by galvanic method at a temperature of 70-90 ° C for 20 minutes. As shown experimentally, this significantly contributes to an increase in the adhesive strength of the interaction of the plastic layer with the surface of the samples.

The thickness of the intermediate layer is controlled at calculated time intervals to obtain the required coating thickness (not more than 2-5 microns).

Next, a plastic layer of copper (or cadmium) is applied to the formed intermediate layer using an electrolyte based on copper sulfate (or, respectively, based on cadmium salts) until a coating layer thickness of 80-100 μm is reached. The thickness control of the copper layer is carried out by the gravimetric method.

Subsequent control tests indicate a significant increase in the adhesion of the formed surface films of the target coating using this treatment. The test results are summarized in table 1.

The process of forming a plastic layer of copper is carried out under the following conditions:

Current density 2 A / dm ² .

The exposure time is 4-5 hours.

Temperature 40 ° C.

The coating thickness of copper is 80-100 microns.

The thickness of the resulting copper coating layer is controlled by the gravimetric method, for which the mass of samples is determined before and after galvanic metallization.

Then the samples are subjected to combined intensive machining under the following conditions:

- pressing blanks at a pressure of the order of ~ 500 MPa

- the temperature range of pressing 450-500 ° C.

When implementing the method of equal-channel angular (ECG) pressing, the workpiece is repeatedly pressed in special equipment through two channels with the same cross sections intersecting at an angle of 90 °. If necessary, in the case of difficult to deform materials, deformation is carried out at elevated temperatures or at increased angles of intersection of the channels. In this case, special requirements are imposed on the heat resistance and tooling strength.

In the process of ECG pressing, strong refinement of the microstructure can be achieved relatively easily after one or several passes, both in pure metals and in alloys. However, ensuring the formation of homogeneous ultrafine-grained (UFG) structures with high-angle grain boundaries by ECG pressing requires a significantly larger number of passes (usually 8 or more).

Using the proposed method provides the possibility of reducing the pressing force, improving manufacturability by reducing the wear of the stamp, increasing the number of passes, which allows to improve the mechanical characteristics (ductility, formability) of the sample, the continuity of the plastic coating layer, reduce oxidation and tribological characteristics of the pressing process at elevated temperatures (about 450-500 ° C).

The possibility of industrial application is confirmed by the following examples of specific performance.

Example 1. Initially, the surface preparation of metal samples is carried out. In the conditions of this example, the technology for applying a plastic plating layer of copper on titanium samples includes the following operations:

- sandblasting;

- degreasing in a solution of the composition (g / l): trisodium phosphate 35-40,

soda ash 35-40,

at a temperature of 60-80 ° C for 10-15 minutes in the ultrasonic installation;

- washing in hot water;

- washing in cold water;

- etching in a solution of the composition (g / l): hydrochloric acid 15-25,

hydrofluoric acid 10-15,

at room temperature for 1-2 minutes;

- washing in cold water;

- clarification in a solution of nitric acid (400-900 g / l) at room temperature for 25-30 seconds;

- washing in cold water;

- activation in a solution of hydrochloric acid (380-400 g / l) at room temperature for 5-10 seconds;

- washing in cold water;

-processing in ethylene glycol at room temperature for 10-15 seconds;

- zinc treatment in a solution of the composition (g / l): zinc oxide 20-35,

hydrofluoric acid 60-90,

ethylene glycol 80-90 ml,

at room temperature for 2-4 minutes;

- washing in cold water;

- removal of the zincate film in a solution of nitric acid (400-900 g / l) at room temperature for 10-20 seconds;

- washing in cold water;

- processing in ethylene glycol at room temperature for 10-15 seconds;

- the second zincate treatment in a solution of the composition (g / l): zinc oxide 20-35,

hydrofluoric acid 60-90,

ethylene glycol 80-90 ml,

at room temperature for 2-4 minutes;

- washing in cold water;

- chemical nickel plating in a solution of the composition (g / l): nickel sulfate 30-35,

sodium hypophosphite 20-25,

sodium acetate 10-15,

acetic acid 12 ml / l,

at a temperature of 70-90 ° C for 15-20 minutes;

- washing in cold water;

- copper plating in the electrolyte composition (g / l): copper sulfate 100-250,

sulfuric acid 50-100,

ethyl alcohol rectified 10-30 ml / l,

current density 2 A / dm ² , temperature 15-45 ° C, time 4-5 hours;

- washing in cold water;

- gravimetric method for controlling the thickness of a copper coating;

- pressing the blanks at a pressure of ~ 500 MPa in the temperature range 450-500 ° C, while the intermediate and ductile metal layers are retained until the finished products are delivered to the consumer.

The photo shows a view of a VT 1-0 titanium sample after the second pass during ECG pressing, where the interfaces between the layers and the nanostructure of the material are visible.

The results of the control tests are summarized in table 1.

Example 2. Initially, the surface preparation of metal samples is carried out. In the conditions of this example, the technology of applying a plastic plating layer of copper on samples of stainless steel 12X18H10T includes the following operations:

- Degreasing with Vienna lime powder;

- washing in hot water;

- washing in cold water;

- etching in a solution of the composition (g / l): nitric acid 350-400,

hydrofluoric acid 20-25,

at room temperature for 20 minutes;

- washing in cold water;

- preliminary nickel plating in the electrolyte composition (g / l):

nickel chloride 200-250,

hydrochloric acid 50-100,

current density 3-5 A / dm2, temperature 15-25 ° C, time 5-15 min;

- washing in cold water;

- copper plating in the electrolyte composition (g / l): copper sulfate 100-250,

sulfuric acid 50-100,

ethyl alcohol rectified 10-30 ml / l,

current density 2 A / dm ² , temperature 15-45 ° C, time 4-5 hours;

- washing in cold water;

- gravimetric method for controlling the thickness of a copper coating;

- pressing the blanks at a pressure of ~ 1000 MPa, temperature 450 ° C, while the intermediate and plastic metal layers remain until the finished products are delivered to the consumer.

The results of the control tests are summarized in table 1.

As experimental studies have shown, the use of the proposed method provides the ability to reduce pressing forces, improve manufacturability by reducing stamp wear, increasing the number of passes, which improves the mechanical characteristics (ductility, formability) of the sample, the continuity of the plastic coating layer, reducing oxidation and tribological performance of the pressing process at elevated temperatures (about 450-500 ° C).

Table 1 Production Examples Process parameters Characterization of sample preparation Manufacturability of pressing Features Benefits Prototype Labor-consuming mechanical conversion with steel or copper shells ~ 2 mm thick. The pressing force is ~ 1560 MPa. Single use of a plastic layer (cover) - The proposed method Example 1 Electroplated copper coating ~ 0.08-0.1 mm thick Press force ~ 500 MPa Press temperature 450-500 ° С The plastic layer of copper is not removed 1. Reduced stamp wear. 2. The ability to conduct ~ 10-12 or more passes Example 2 Electroplated copper coating ~ 0.08-0.1 mm thick The pressing force is ~ 1000 MPa. Press temperature 450 ° С The plastic layer of copper is not removed 1. Reduced stamp wear. 2. The ability to conduct ~ 7 or more passes

Claims (1)

A method of equal channel angular pressing of titanium or stainless steel preforms, including preparing the preforms, cleaning and pressing them, characterized in that initially an intermediate layer of nickel is applied to the surface of the preforms, then a plastic layer of copper with a thickness of at least 80-100 microns is applied to the resulting intermediate layer by galvanic coating in an electrolyte and carry out subsequent pressing of the workpieces at a pressure of 500-1000 MPa in the temperature range 450-500 ° C while maintaining an intermediate and plastic wow layers.

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