RU2705817C1 - Method of forming near-surface hardened layer on titanium alloys - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention relates to machine building, particularly, to production of wear-, impact-, heat-, crack- and corrosion-resistant coatings, as well as to chemical-thermal treatment of surface, and can be used to increase reliability and durability of wide range of parts of machines from titanium alloys. Proposed method comprises spraying surface of article with nickel alloy film containing beta-stabilizing additives and processing said film by pulsed electron-beam exposure. Then, annealing is performed to initiate precipitation hardening due to formation of intermetallic phases in the near-surface layer.

EFFECT: higher quality of the formed surface hardened layer due to creation on the surface of the product of a layer containing beta-titanium and intermetallide phases.

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Description

The invention relates to the field of engineering, in particular to the production of wear-, impact-, heat-, crack- and corrosion-resistant coatings, as well as to chemical-thermal surface treatment, and can be used to increase the reliability and durability of a wide range of machine parts from titanium alloys .

Many methods are known for hardening the surface of titanium alloys using ion nitriding. For example, a nitriding method for titanium alloy products (US Pat. No. 5,443,663 A, 8/22/1995), comprising ion nitriding in a glow discharge plasma at a temperature of 480 ° C.

Also known is a method of nitriding in a nitrogen-argon gas mixture with a percentage of 60% N ₂ -40% Ar (patent RU 2611003 C23C 8/36 2006.01), which includes ion nitriding in a magnetic field at a temperature in the vacuum chamber of 650-750 ° C and voltage in the discharge gap of 500-600 V, first at a low pressure of said gas mixture of 10 ^-1 -1 Pa for 4 hours, and then at a pressure of said gas mixture of 100-300 Pa for 1 hour. This ensures the development of a developed diffusion zone with increased microhardness and depth of the nitrided layer on a titanium base.

The disadvantages of these methods are the insufficient microhardness of the nitrided layer and the long duration of the nitriding process.

The closest in the set of essential features is adopted as a prototype method, the essence of which is as follows. When hardening the surface of titanium alloy products, a metal coating of chromium or molybdenum or zirconium is applied and treated with compression plasma flows in a nitrogen medium at a pressure of 0.4-0.5 kPa with an energy density of 10-30 J / cm ² and the number of pulses 2-3 . Then nitriding is carried out by compression plasma flows at a nitrogen pressure of 1-3 kPa with an energy density of 1-10 J / cm ² and the number of pulses 10-15. Annealing of products is carried out for 60-75 minutes. At the same time, microhardness increases, the coefficient of friction of the surface layer of products decreases due to the creation of finely dispersed hardening phases.

Processing by compression plasma flows of the surface of titanium alloy products with a preliminary coating of chromium or molybdenum or zirconium provides for 10 ^-4 seconds melting of the surface layer of the product and the applied coating and their liquid-phase mixing, the formation of a supersaturated solid solution based on the high-temperature phase of titanium stabilized by atoms alloy coating of chromium or molybdenum, or zirconium. The use of nitrogen as a plasma-forming substance in the generation of compression plasma flows ensures the diffusion saturation of the surface layer with nitrogen atoms at the stage of its cooling and the formation of strengthening nitrides TiN and Ti ₂ N. Annealing of the product in vacuum promotes partial decomposition of the formed supersaturated solid solution based on the high-temperature phase of titanium with the release of fine particles of the low-temperature phase, providing additional hardening of the product. The hardening of the surface layer by the present method leads to a decrease in abrasive and adhesive wear, which leads to a decrease in the coefficient of friction of the surface of the product.

(see RF patent 2464355, publ. 20.10.2012).

The disadvantage of this technology is the saturation of the surface layer of titanium and its alloys with a gas α-stabilizer (nitrogen), which is detected in the form of a light surface layer with a high content of α phase, solid but brittle, which reduces ductility and resistance to fatigue failure.

The technical problem, the solution of which the claimed invention is directed, is the formation of technological parameters of the method based on objectively evaluated data.

The technical result consists in improving the quality of the formed surface hardened layer by creating a layer on the product surface containing beta-titanium and intermetallic phases.

The technical result achieved is achieved by the fact that in the method of forming a surface hardened layer on titanium alloys, which consists in applying a coating in a vacuum chamber and subsequent processing of this coating with concentrated energy flows, a nickel alloy containing beta-stabilizing alloying is sprayed onto the surface of the product additives, coating treatment with an electron beam source and subsequent annealing to initiate the dispersion solid process eniya due to the formation of the surface layer of intermetallic phases. In addition, chromium, manganese, molybdenum, niobium, and vanadium can be used as beta stabilizing alloying additives. In addition, a sprayed layer can be formed with a thickness of 0.2 to 0.4 μm at a voltage on the titanium target of 480V ± 10% and a current strength of 1A ± 10%. In addition, the synthesis of the surface beta titanium layer can be effected by applying a wide-aperture electron beam with a specific energy of 4.3 ± 2.5% J / cm ^{2 to the} film deposited by magnetron sputtering. In addition, hardening intermetallic phases in the surface layer of the product can be distinguished during subsequent annealing at a temperature of from 500 to 800 ° C.

In this case, it is possible to create a surface layer with a thickness of several micrometers with increased wear resistance due to the creation of a surface alloy based on beta titanium on the surface of the part, which provides maximum effects of solid solution hardening and dispersion hardening due to intermetallic phases. The latter are a class of materials whose use in various fields of technology is expanding rapidly due to unique sets of properties, including high melting points, increased mechanical strength, heat resistance and heat resistance, corrosion resistance in some aggressive environments where ordinary titanium is not sufficiently resistant. The technology does not exclude the possibility of subsequent application of other protective coatings to the modified object.

The essence of the claimed invention is illustrated by the following:

In FIG. 1 shows a diagram of a surface alloy,

In FIG. 2 shows a diffraction pattern from the surface of the titanium alloy VT 1-0

a) in the initial state;

b) after surface alloying with a nickel alloy using electron beam processing;

c) after annealing at 800 ° C for 45 minutes.

In FIG. Figure 3 shows an image of a transverse section, on which the structure of VT 1-0 alloy is visible after surface alloying with KhN77TYUR alloy (etching 1% solution HF): below — after electron beam treatment, above — after additional annealing at 800 ° C for 45 min

The method of forming a surface hardened layer on titanium alloys consists in applying a coating in a vacuum chamber and subsequent processing of this coating with concentrated energy flows. To form a hardened layer, a nickel alloy containing beta-stabilizing alloying additives is sprayed onto the surface of the product, the coating is treated with an electron beam source and then annealed to initiate the dispersion hardening process due to the formation of intermetallic phases in the surface layer. In addition, chromium, manganese, molybdenum, niobium, and vanadium can be used as beta stabilizing alloying additives. In addition, a sprayed layer can be formed with a thickness of 0.2 to 0.4 μm at a voltage on the titanium target of 480V ± 10% and a current strength of 1A ± 10%. In addition, the synthesis of the surface beta titanium layer can be effected by applying a wide-aperture electron beam with a specific energy of 4.3 ± 2.5% J / cm ^{2 to the} film deposited by magnetron sputtering. In addition, hardening intermetallic phases in the surface layer of the product can be distinguished during subsequent annealing at a temperature of from 500 to 800 ° C.

The processing is carried out in a facility that is a combination of a source of low-energy high-current electron beams RITM [Markov AV, Yakovlev EV, Petrov VI, Formation of Surface Alloys with a Low-Energy High-Current Electron Beam for Improving High-Voltage Hold -Off of Copper Electrodes, IEEE Transations on Plasma Science, 2013, v 41, 2177-2182.], And two magnetron sputtering systems in a single vacuum chamber. The generation of NSEC includes electron emission, beam formation in a plasma-filled diode, and its transportation in the plasma channel. The use of such a generation scheme makes it possible to obtain a microsecond (about 5 μs) beam with a current density of up to 10 ⁵ A / cm ² at an accelerating voltage of 15 to 30 kV, the magnitude of which determines the power density in the beam. The area of one-time processing is about 50 cm ² .

The impact of a pulsed electron beam causes the passage of an elastic wave, which is generated by pulsed electron-beam exposure. In this case, a jump in pressure, density, specific internal energy and other characteristics occurs in the substance, which propagates through it with a supersonic speed (~ 10 ³ m / s). Behind the front of the shock wave, the substance is involved in the motion, acquiring a mass velocity, the magnitude of which, although less than the speed of the shock wave itself, is of the same order. Shock compression is accompanied by phase, chemical and structural transformations. Moreover, due to the short duration of the irradiation process (~ 10 ^-5 s) and thermal inertia, heating caused by compression and internal friction is most likely not a physical factor that determines the behavior of a substance under such conditions. The main role in this case will be played by the mechanical activation of physico-chemical processes that are fast in the substance, which are mainly solid-phase.

The installation allows the deposition of films of different materials on the surface of the desired product and subsequent liquid-phase mixing of the film and substrate materials with an intense wide-aperture pulsed electron beam (Fig. 1). A metal film 2 is deposited from the target 1. Then, a pulsed electron beam 3 acts on the object with the film deposited on it. As a result, a surface alloy 4 is formed.

Conventionally, the direct production of a hardened surface layer enriched in intermetallic phases on parts made of titanium alloys can be divided into three successive steps: applying a film containing nickel and elements of beta stabilizers (Cr, Mn, V, Mo) on a titanium base, obtaining a surface beta titanium alloy using a wide-aperture concentrated energy source (Fig. 2b) and the synthesis of intermetallic compounds by dispersion hardening (Fig. 2c). The amount of the main element in the titanium alloy will have a direct effect on the content of the intermetallic phase in the surface layer, and, consequently, on the increase in wear resistance.

When using pulsed electron beams, energy is introduced into the surface region of the material to a depth of about 1 μm. A layer approximately equal to half the mean free path of the electrons melts almost immediately. The thickness of the metal film is formed in the range from 0.2 to 0.4 μm, in order to be able to simultaneously melt the film material and the substrate. The coating mode is not critical. With a coating thickness of less than 0.2 μm, the surface alloy is not sufficiently enriched with alloying elements, and the necessary structure is not formed. A titanium film thickness exceeding 0.4 μm leads to insufficient penetration of the substrate surface. In this case, the thickness of the surface alloyed layer decreases, and most of the deposited metal film evaporates.

Experiments in modes other than those declared (the results in the framework of this application are not presented) showed a significant decrease in quality due to the influence of the multidirectional factors described above.

Example

In order to increase the wear resistance of a part made of α-titanium alloy VT 1-0, a metal layer from a target obtained from a heat-resistant KhN77TYUR alloy 0.3 ± 0.05 μm thick was deposited on its surface using a magnetron sputter. Then the surface of the part was processed by a series of 5 pulses of a wide-aperture electron beam. Processing was repeated twice.

As a result of processing, a thin layer of a surface alloy of beta titanium alloyed with nickel and chromium (Fig. 2b) with a thickness of up to 3 μm was obtained. The heat affected zone was up to 15 μm. In FIG. Figure 3 shows the structure of the VT 1-0 alloy after surface alloying with the KhN77TYUR alloy (etching 1% solution HF): from the bottom, after electron beam treatment, from above, after additional annealing at 800 ° C for 45 min. After annealing in a vacuum oven at 800 ° C for 45 minutes, dispersed precipitates of the Ti ₂ Ni and Ti ₄ Cr intermetallic phases were observed in the surface alloy, which is confirmed by the data of X-ray diffraction analysis (Fig. 2c). Partial decomposition of the beta phase is also observed, the stability of which can be influenced by an increase or decrease in the aging temperature. The tests performed showed an increase in resistance to abrasive wear by more than two times.

The foregoing allows us to conclude that the task - to optimize the process parameters based on objectively measured data - is solved, and the claimed technical result - improving the quality of manufactured products - is achieved.

The analysis of the claimed technical solution for compliance with the conditions of patentability showed that the characteristics indicated in the formula are essential and interconnected with the formation of a stable population unknown at the priority date from the prior art, the necessary features sufficient to obtain the required synergistic (over-total) technical result.

The properties regulated in the claimed compound by individual features are well known in the art and require no further explanation.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed technical solution:

- an object embodying the claimed technical solution, when implemented, is intended to form protective coatings from finely dispersed composite powder, and may find application in engineering industries;

- for the claimed object in the form described in the claims, the possibility of its implementation using the methods described above and known from the prior art on the priority date of the means and methods is confirmed;

- the object embodying the claimed technical solution, when implemented, is able to ensure the achievement of the technical result perceived by the applicant.

Therefore, the claimed subject matter meets the patentability conditions of “novelty”, “inventive step” and “industrial applicability” under applicable law.

Claims (5)

1. A method of forming a surface hardened layer on a titanium alloy product, comprising applying a metal film in a vacuum chamber and then treating it with concentrated energy flows, characterized in that a nickel alloy film containing beta-stabilizing additives is sprayed onto the surface of the product as a metal film and, as the specified film processing, a pulsed electron-beam effect is performed, after which annealing is performed to initiate the dispersion process ionic hardening due to formation of a surface layer of intermetallic phases. 2. The method according to p. 1, characterized in that as beta-stabilizing alloying additives use chromium, manganese, molybdenum, niobium, vanadium. 3. The method according to p. 1, characterized in that the sprayed film is formed with a thickness of 0.2 to 0.4 μm when the voltage on the product in the form of a target from a titanium alloy 480 V ± 10% and a current strength of 1 A ± 10%. 4. The method according to p. 1, characterized in that as a near-surface hardened layer, a near-surface hardened beta-titanium layer is synthesized by exposing a nickel alloy film deposited by magnetron sputtering with a wide-aperture electron beam with a specific energy of 4.3 ± 2.5% J / cm ² . 5. The method according to p. 1, characterized in that the hardening intermetallic phases in the surface layer of the product are released during annealing at a temperature of from 500 to 800 ° C.

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