RU2391449C1 - Method of microarc oxidation of titanium wire for antifriction weldup - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to welding materials for special-purpose weldup pads in manufacturing of titanium alloy goods. The method involves microarc oxidation in water solution of liquid glass Na₂SiO₃ at the concentration of 20.0±2.0 g/l and the voltage of 320-340 V for 15±2 minutes at 20±1°C.

EFFECT: enhanced hardness of weldup metal up to 400-430 kgf/mm².

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Description

The invention relates to the oxidation of materials by electrochemical processing and can be used to oxidize a welding wire from titanium alloys used in the manufacture of ship fittings and mechanisms, chemical engineering products, etc.

Known welding wire made of titanium alloy grade PT-7M according to GOST 27265-87, which is used as a surfacing material for hardening rubbing surfaces after preliminary thermal oxidation in open air at a temperature of 750-800 ° C. Such processing leads to the formation of an oxide film on the surface of the wire, the oxygen of which is an alloying element during surfacing, thereby increasing the wear resistance of the product surface.

However, the operation of oxidation in air leads simultaneously to completely undesirable hydrogenation of the welding wire.

The hydrogen content in the wire increases from 0.002% to 0.015-0.020%, which is completely unacceptable during surfacing on the surface of titanium alloys.

In this regard, after oxidation, the wire is degassed to remove hydrogen in vacuum furnaces at a temperature of 750-900 ° C for 5-10 hours. It should be noted that almost all surfacing material is currently being prepared using this technology.

The disadvantages of this method of preparing the welding wire for surfacing are not limited only to the noted technological features, leading to the great complexity of wire preparation. A big drawback of surfacing made by thermally oxidized welding wire is the spread in hardness of the deposited layer, which is associated with an uneven distribution of oxygen. The values of hardness by volume of the deposited layer range from 270-500 kgf / mm ² (the optimal range is 350-430 kgf / mm ² ). Such fluctuations in hardness, and hence the instability of the antifriction properties of the deposited layer, lead to a forced limitation of the resource characteristics of products operating under cyclic loads (reinforcement, ship mechanisms).

In connection with the noted in the present invention, it is proposed to replace the thermal oxidation of the welding wire for surfacing with the method of microarc oxidation, which is largely free of the above disadvantages of thermal oxidation.

For the manufacture of surfacing material will be applied titanium wire grade 2B in accordance with GOST 27265-87.

The closest technical solution and adopted by us for the prototype is the Method of microarc oxidation (MAO) of titanium alloys with the aim of corrosion protection of other materials in contact with titanium in sea water, including an electrolytic process that occurs at a voltage of 315 to 330 V in a solution of trisodium phosphate with a concentration 11.5-14.0 g / l at a solution temperature of 25-30 ° C for 7-15 minutes, proposed by the Far Eastern Branch of the USSR Academy of Sciences (copyright certificate No. 1156410 of 11/05/83).

The disadvantage of this method is that the use of the MAO method as a means of corrosion protection involves the deposition of relatively thin oxide films on titanium - 5-10 microns. With such a thickness of the oxide film, the amount of oxygen in the surfacing material will be small and the hardness of the deposited metal HV will not exceed 300 kgf / mm ² .

Welding wire, as a material for antifriction surfacing, requires a significantly higher hardness of the deposited metal HV at the level of 350-430 kgf / mm ² , which can be achieved by increasing the oxygen content in the surfacing material by increasing the thickness of the oxide film to 200-250 microns.

The technical result of the invention is the development of a method of microarc oxidation of a titanium alloy for antifriction surfacing, which allows to obtain an oxide film on the surface of a titanium wire with a thickness of 220-250 microns and to increase the hardness of the deposited metal.

The technical result is achieved due to the fact that the MAO process is performed in an aqueous solution of liquid glass Na ₂ SiO ₃ according to GOST 13078-81 with a concentration of 20.0 ± 2.0 g / l at a voltage of 320-340 V for 15 ± 2 min at temperature 20 ± 1 ° С.

The use of a liquid glass solution of Na ₂ SiO ₃ with a concentration of 20.0 ± 2.0 g / l as an electrolyte makes it possible to obtain an oxide film of the required thickness on the surface of a titanium wire and obtain a hardness of the metal deposited using this surfacing material at a level of 400-430 kgf / mm ² .

Concrete example

In laboratory conditions, a welding wire of 2B titanium alloy was taken in accordance with GOST 27265-87 (Ti-base, Al - 2%, V-1.5%) and an electrolyte was prepared with a concentration of liquid glass of 18.0 g / l, 20.0 g / l and 22.0 g / l. After that, the coating was applied at a voltage of 320 V, 330 V and 340 V for 13 min, 15 min and 17 min at a temperature of 19 ° C, 20 ° C and 21 ° C, and an oxide film thickness of 220 μm was obtained, 235 μm and 250 μm, respectively.

Table 1 shows the parameters of the proposed and known methods.

An important factor that was noted in the study of surfacing performed by wire with MAO was the almost complete absence of pores in the surfacing. This is very important, since the porosity in the surfacing extremely negatively affects the performance of the surfacing and its elimination requires very laborious repair work (which is typical for surfacing materials obtained by thermal oxidation of titanium wire).

MAO modes were evaluated by measuring the hardness of the deposited metal. The above mode provides a stable range of distribution of hardness in the surfacing in the range of 400-430 kgf / mm ² . The hydrogen content in the surfacing is normal and does not exceed 0.003% (which is very important, since it does not require degassing of the wire before surfacing, as in thermal oxidation).

Technical and economic benefits from the application of this method in comparison with the prototype will be expressed in an increase in the service life and reliability of products of marine fittings and mechanisms made of titanium alloys by increasing hardness.

Table number 1 Method for microarc oxidation of titanium wire Method Parameters Coating properties No. p / p Way Electrolyte composition The concentration of electrolyte, g / l Voltage Time min Coating thickness, microns Hardness HV, kgf / mm ² Na ₂ SiO ₃ 18.0 320 13 220 400 one Proposed Na ₂ SiO ₃ 20,0 330 fifteen 235 415 Na ₂ SiO ₃ 22.0 340 17 250 430 2 Famous Na ₃ PO ₄ 11.5 315 7 5 280 Note. The table shows the average values for the results of 3 measurements.

Claims (1)

A method of microarc oxidation of a titanium wire for antifriction surfacing, including conducting the process in an electrolyte at a voltage of 320-340 V for 15 ± 2 min, characterized in that a liquid glass solution of Na ₂ SiO ₃ with a concentration of 20 ± 2 g / l is used as an electrolyte and the electrolytic process is carried out at a temperature of 20 ± 1 ° C.