WO2003083181A2 - Process and device for forming ceramic coatings on metals and alloys, and coatings produced by this process - Google Patents
Process and device for forming ceramic coatings on metals and alloys, and coatings produced by this process Download PDFInfo
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- WO2003083181A2 WO2003083181A2 PCT/GB2002/004305 GB0204305W WO03083181A2 WO 2003083181 A2 WO2003083181 A2 WO 2003083181A2 GB 0204305 W GB0204305 W GB 0204305W WO 03083181 A2 WO03083181 A2 WO 03083181A2
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/615—Microstructure of the layers, e.g. mixed structure
- C25D5/617—Crystalline layers
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/18—Electroplating using modulated, pulsed or reversing current
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/005—Apparatus specially adapted for electrolytic conversion coating
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/024—Anodisation under pulsed or modulated current or potential
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/026—Anodisation with spark discharge
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/20—Electroplating using ultrasonics, vibrations
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
- C25D5/611—Smooth layers
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/627—Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance
Definitions
- the invention relates to the field of applying protective coatings, and in particular to plasma discharge, for example plasma-electrolytic oxidation, coating of articles made of metals and alloys. This process makes it possible rapidly and efficiently to form wear-resistant, corrosion-resistant, heat-resistant, dielectric uniformly-coloured ceramic coatings on the surfaces of these articles.
- the coatings are characterised by a high degree of uniformity of thickness, low surface roughness and the virtual absence of an external porous layer, the removal of which usually involves considerable expense in conventional coating processes.
- the process for producing the coatings and the device for implementing the process, described in this application can be used in engineering, the aircraft and motor vehicle industries, the petrochemical and textiles industries, electronics, medicine and the production of household goods.
- a process for producing a ceramic coating using industrial-frequency 50-60Hz current is known from WO 99/31303.
- the process enables hard coatings of thickness up to 200 ⁇ m, well-bonded to the substrate, to be formed on the surface of articles made from aluminium alloys.
- the main problem with this process is the formation of a considerable external porous layer of low microhardness and with numerous micro- and macro-defects (pores, micro-cracks, flaky patches).
- the thickness of the defective layer amounts to 25-55% of the total thickness of the ceramic coating, depending on the chemical composition of the alloy being processed and on the electrolysis regimes.
- Expensive precision equipment is used to remove the porous layer. If the article is of complex shape, with surfaces that are difficult for abrasive and diamond tools to reach, the problem of removing the defective layer becomes difficult to solve. This limits the range of application of the process.
- a process for forming ceramic coatings where the current has a modified sine wave form is known from US 5,616,229.
- This form of current reduces heat stresses in forming the ceramic layer and enables coatings of thickness up to 300 ⁇ m to be applied.
- industrial frequency current is used in this process, which leads to the formation of a relatively thick external porous layer with high surface roughness and relatively high energy costs.
- RU 2077612 for oxidising valve metals and alloys in a pulsed anode-cathode regime, in which positive and negative pulses of a special complex form alternate.
- the duration of the pulses and of the pause between a positive pulse and a negative one is 100-130 ⁇ sec, and the succession frequency is 50Hz.
- the current reaches its maximum (up to 800A dm 2 ), after which it remains constant for 25-50 ⁇ sec.
- the shorter pulses and far greater pulse powers enable the discharge ignition time to be reduced considerably, and the main reasons for the formation of the defective outer layers are eliminated.
- the pairs of powerful pulses alternate with unjustifiably long pauses, which leads to a low coating formation rate.
- the closest prior art to the proposed invention is the process described in RU 2070942 for oxidation using alternating positive and negative pulses of voltage, amplitude 100-500N and duration l-10 ⁇ sec, during which, at each of the anode half- periods, high- voltage positive pulses, amplitude 600-1000N and duration 0.1-l ⁇ sec, are also applied.
- the pulses When the pulses are applied, the total current at that moment rises, which creates favourable conditions for discharges.
- the problem with this process is the use of very short high- voltage positive pulses, which does not make it possible to create discharges of sufficient power. This leads to low productivity of the process, and it is also extremely difficult to implement the proposed process technically for industrial purposes. Summary of the present invention
- a process for forming ceramic coatings on metals and alloys in an electrolytic bath fitted with a first electrode and filled with aqueous alkaline electrolyte, in which is immersed the article, connected to another electrode, wherein a pulsed current is supplied across the electrodes so as to enable the process to be conducted in a plasma-discharge regime comprising the steps of:
- an apparatus for forming a ceramic coating on metals and alloys including an electrolytic bath with electrodes, a supply source for sending pulsed current to the electrodes, and at least one acoustic vibration generator, wherein:
- the supply source is adapted to supply the electrodes with high-frequency bipolar pulses of current having a predetermined frequency range
- the at least one acoustic vibration generator is adapted to generate acoustic vibrations in an electrolyte when contained in the bath, the acoustic vibrations having a predetermined sonic frequency range that overlaps with the frequency range of the current pulses.
- a ceramic coating formed by the process or apparatus of the first or second aspects of the present invention.
- a ceramic coating formed on a metal or alloy by way of a plasma-discharge process, the coating having an external porous layer comprising not more than 14% of a total coating thickness.
- a ceramic coating formed on a metal or alloy by way of a plasma-discharge process, the coating having a surface with a low roughness (Ra) of 0.6 to 2.1 ⁇ m.
- the bipolar current pulses may be alternating pulses, or may be supplied as packets of pulses, for example comprising two of one polarity followed by another of opposed polarity.
- Embodiments of the present invention seek to improve the useful properties of ceramic coatings such as resistance to wear, corrosion and heat, and dielectric strength, by improving the physico-mechanical characteristics of the coatings. Embodiments of the invention also solve the technical problem of producing hard microcrystalline ceramic coatings with good adhesion to a substrate.
- Embodiments of the invention also seek to improve the technical sophistication of the process of forming ceramic coatings by significantly reducing the time it takes to apply the coating itself, and the time spent in the finishing treatment thereof. Not only is the productivity of the oxidation process raised, but specific power costs are also significantly reduced.
- Embodiments of the invention additionally provide for the targeted formation of coatings with set properties by introducing refractory inorganic compounds into the electrolyte.
- Embodiments of the invention may also raise the stability of the electrolyte and increase its useful life.
- Embodiments of the apparatus of the present invention seek to provide improved reliability, versatility and ease of building into automated production lines.
- an article to be coated is connected to an electrode and placed in an electrolytic bath which has another electrode and which is filled with an alkaline electrolyte.
- the electrodes may be supplied with pulsed current so as to form a coating of a required thickness in a plasma-discharge regime, which is preferably a plasma electrolytic oxidation regime.
- Pulsed current may be created in the bath with a pulse succession frequency of 500Hz or more, preferably 1000 to 10,000Hz, with a preferred pulse duration of 20 to l,000 ⁇ sec.
- Each current pulse advantageously has a steep front, so that the maximum amplitude is reached in not more than 10% of the total pulse duration, and the current then falls sharply, after which it gradually decreases to 50% or less of the maximum.
- the current density is preferably 3 to 200
- A/dm 2 even more preferably 10 to 60A/dm 2 .
- the acoustic vibrations may be generated in the electrolyte by an aerohydrodynamic generator, the generator creating acoustic vibrations in the bath in a sonic frequency range that overlaps with a current pulse frequency range.
- Ultra-disperse powders (nanopowders) of oxides, borides, carbides, nitrides, suicides and sulphides of metals of particle size not more than 0.5 ⁇ m may be added to the electrolyte, and a stable hydrosol may be formed with the aid of the acoustic vibrations.
- the relatively brief current pulses reduce the discharge spark time, which makes it possible to carry out oxidation at higher current densities of 3 to 200A/dm .
- the properties of the plasma discharges themselves in high-frequency pulse regimes differ from those of the discharges obtained for oxidation at conventional industrial frequency (50 or 60Hz).
- An increase in the brightness and decrease in the size of the sparks can be observed visually, histead of sparks moving over the surface being oxidised, numerous sparks are seen to be discharging simultaneously over the entire surface.
- the preferred form of the current pulses ( Figure 1) facilitates the uniform initiation and maintenance of plasma discharges over the entire surface of the article.
- the plasma discharge processes do not require a constant high current value to be maintained.
- the steep front of the pulse and its rapid build-up to a maximum make possible a radical reduction in discharge initiation time.
- the current reduced to 50% or less of the maximum, enables the discharge process to be maintained efficiently.
- the steep front of the positive and negative pulses makes it possible rapidly to charge and discharge the capacitive load created both by the electrode system (bath-electrolyte-article), and by the double electric layer on the surface of the article being oxidised (electrolyte-oxide-metal).
- EP 1 042 178 for anodising non-ferrous alloys, in which vibratory agitation of the electrolyte is carried out by a vibro-motor and rotating blades, the electrodes being vibrated and rocked and a supply of compressed air being fed through a porous ceramic tube with pore size 10-400 ⁇ m.
- This enables the anodising process to be conducted at a relatively high current density of 10 to 15 A/dm 2 , considerably reducing the anodising time.
- this process is not efficient enough for plasma oxidation, since the rate at which relatively large air bubbles form in the electrolyte, and the frequency of the vibrations in the electrolyte, are low.
- the agitation of the electrolyte and the supply and removal of reagents in the electrode regions take place at the macro level. Furthermore, the technical implementation of this process is difficult from the design point of view.
- WO 96/38603 describes a process for spark oxidation with ultrasonic vibrations acting on the electrolyte. These vibrations facilitate the intensive renewal of the electrolyte in the discharge zone.
- ultrasonic vibrations in a liquid cause degassing and the coalescence of gas bubbles, which float to the surface. Up to 60% of the dissolved gas is separated out from the liquid in the first minute.
- the high power of the ultrasonic vibrations leads to cavitational surface erosion and destroys the ceramic surface, increasing the number of micro-cracks and pores due to hydraulic shocks as the cavitation bubbles burst.
- embodiments of the present invention relate to the formation of ceramic coatings in an alkaline electrolyte in a field of acoustic vibrations within a sonic (i.e. not ultrasonic) frequency range, the intensity of the vibrations preferably not exceeding lW/cm 2 .
- the acoustic vibrations may be generated by at least one aerohydrodynamic generator, which is an instrument that converts kinetic energy of a jet of liquid and air into acoustic vibration energy.
- aerohydrodynamic generator which is an instrument that converts kinetic energy of a jet of liquid and air into acoustic vibration energy.
- Such generators are distinguished by their simplicity, reliability and economy, and comprise a fluid inlet and a resonance chamber. Acoustic vibrations are induced in the resonance chamber of the generator as the electrolyte passes through it from the fluid inlet, followed by discharge of the electrolyte, as a result of which air from atmosphere is drawn into the generator via a special channel, mixed with the electrolyte and dispersed.
- the efficient removal of the heat created by the plasma discharges eliminates local overheating and ensures the formation of a good-quality ceramic coating of uniform thickness.
- the input of new portions of electrolyte with higher oxygen content intensifies the plasma-chemical reactions in the discharge zone and speeds up the coating formation process.
- the aqueous alkaline electrolytes used for plasma oxidation consist of colloid solutions, i.e. hydrosols. Like any colloid solutions, the electrolytes are liable to coagulation, flocculation and sedimentation. When the electrolyte has reached a certain level of coagulation, flocculation and sedimentation, it becomes ineffective and the quality of the coating deteriorates sharply. Thus, the effectiveness of the electrolyte may be determined by controlling the number and size of the colloid particles.
- Embodiments of the present invention enable the electrolyte to remain stable and efficient for a long time, due to the continuous breaking up of large particles that may form therein.
- the rate of displacement of the colloid particles increases and the number of active collisions of particles with each other, with the walls of the bath and with the surface of the article being oxidised rises, leading to dispersal of the particles.
- ultra-disperse insoluble powders preferably with particle size not more than 0.5 ⁇ m, in some embodiments not more than 0.3 ⁇ m, and a preferred concentration of 0.1 to 5 grams per litre, may be added to the electrolyte.
- This invention proposes the use of nanopowders, preferably with particle size up to 0.5 ⁇ m, in some embodiments up to 0.3 ⁇ m, a developed specific surface (not less than 10m 2 per gram) and which are distinguished by their high-energy state.
- the electrolyte, with the powders introduced into it with the aid of the acoustic vibrations, is brought to a state of a high-disperse stable hydrosol.
- the ultra-dispersed particles themselves are more resistant to coagulation and sedimentation.
- the use of acoustic vibrations causes further dispersion of the particles in the electrolyte and distributes them uniformly within the volume of the electrolyte.
- the acoustic effect intensifies the mixing of the particles and imparts to them an additional quantity of energy. Due to the additional charge carried by the micro- particles (they are charged by the ions of the electrolyte), a plasma-chemical reaction is activated in the discharge zone.
- the ultra-disperse particles entering the plasma discharge zone are partly sublimated and partly completely melted in with the growing oxide layer, forming a dense ceramic coating.
- the process of forming the coating is also accelerated and may reach 2-10 ⁇ m per minute, depending on the material of the substrate.
- the coatings produced are characterised by high structural stability and uniformity of thickness.
- oxides Al 2 O 3 , ZrO 2 , CeO 2 , CrO 3 , MgO, Si0 2 , TiO 2 , Fe 2 O 3 , Y 2 O 3 , and also mixtures thereof, compound oxides and spinels
- borides ZrB 2 , TiB 2 , CrB 2 , LaB 2
- nitrides Si 3 N 4 , TiN, AIN, BN
- carbides B 4 C, SIC, Cr 3 C 2 , TIC, ZrC, TaC, VC, WC
- sulphides MoS 2 , WS 2 , ZnS, CoS
- suicides WSi 2 , MoSi 2
- others oxides (Al 2 O 3 , ZrO 2 , CeO 2 , CrO 3 , MgO, Si0 2 , TiO 2 , Fe 2 O 3 , Y 2 O 3 , and also mixtures thereof, compound oxides and spinels)
- borides ZrB 2
- One feature of this invention is a considerable acceleration of the formation of a good quality ceramic coating if the oxidation process is combined with the use of high-frequency electrical pulses and the generation in the electrolyte of acoustic vibrations in the sonic frequency range.
- the acoustic vibration range must overlap with the current pulse frequency range. This increase in the rate of formation of the coating takes place without a significant increase in electricity consumption.
- the device of the present invention for forming ceramic coatings on metals and alloys includes a supply source and an electrolytic bath ( Figure 2).
- the supply source produces and supplies to the electrodes electrical pulses of alternating polarity. Positive and negative pulses of current can be sent alternately, one after the other or in alternating packs of pulses.
- the order and frequency of succession of the pulses, their duration and the current and voltage amplitudes may be regulated by a microprocessor, which controls the electrolysis process.
- the electrolytic bath in turn may consist of the bath itself, made for example of stainless steel and serving as one electrode, a second electrode to which the article being oxide-coated is connected, a cooling system for the electrolyte and a system for generating acoustic vibrations.
- the bath may be filled with an alkaline electrolyte of pH 8.5 to 13.5.
- the electrolyte cooling system may consist of a pump to pump the electrolyte, a coarse cleaning filter to trap particles of size more than lO ⁇ m, and a cooler.
- the temperature of the electrolyte is preferably kept within the limits 15 to 55°C during oxidation.
- the system for generating acoustic vibrations in the electrolyte may consist of an aerohydrodynamic generator (or several of them) fitted in the bath, a pressure gauge and valves regulating the intensity of a supply of the electrolyte and air to the generator.
- the parameters of the acoustic field in the electrolyte are regulated by altering the pressure of the flow of the electrolyte at the input of the aerohydrodynamic generator.
- the generator requires virtually no additional energy and is operated by the pressure of the jet of electrolyte driven by the pump, which may provide pressure from three to seven bars.
- a considerable advantage of the process of embodiments of the present invention is the fact that it makes it possible to produce dense microcrystalline ceramic coatings of thickness up to 150 ⁇ m, preferably from 2 to 150 ⁇ m, and microhardness 500 to 2100HN on metals in a relatively short time (from a few minutes to one hour).
- the coatings have low roughness, Ra 0.6 to 2.1 ⁇ m, and a very thin external porous layer, comprising not more than 14% of the total thickness of the coating. This eliminates, or significantly reduces, the need for subsequent laborious finishing of the surface (Figure 3).
- the coatings are characterised by high uniformity of thickness, even on articles of complex shape.
- the highly dispersed polycrystalline ceramic coatings consist of melted globules, up to several microns in size, firmly bonded to each other.
- This structure produces high physico-mechanical properties in the coatings, such as resistance to wear and corrosion, and dielectric strength.
- the addition to the electrolyte of solid nanopowders of a specific chemical composition provides for targeted changes in the structure, microhardness, strength and colour of the coatings, optimising the properties of the coatings for specific application conditions.
- Embodiments of the present invention enable a ceramic coating to be formed at a rate of 2 to lO ⁇ m/min, which considerably exceeds the rate of formation of hard ceramic coatings by known prior art processes.
- FIGURE 1 shows a preferred form of the time dependence of the form of the current pulses (positive and negative) passing in the circuit between the supply source and the electrolytic bath;
- FIGURE 2 shows an embodiment of the apparatus of the present invention.
- FIGURE 3 shows a cross section through a ceramic coating formed in accordance with a process of the present invention.
- Figure 1 shows a preferred form of the time dependence of the form of the current pulses (positive and negative) passing in the circuit between the supply source and the electrolytic bath.
- Each current pulse has a steep front, so that the maximum amplitude is reached in not more than 10% of the total pulse duration, and the current then falls sharply, after which it gradually decreases to 50% or less of the maximum.
- the device consists of two parts: an electrolytic bath (1) and a supply source (12), connected to each other by electrical busbars (15, 16).
- the electrolytic bath (1) in turn, consists of a bath (2) of stainless steel, containing an alkaline electrolyte (3) and at least one article (4) immersed in the electrolyte.
- the bath is supplied with a transfer pump (5) and a filter (6) for coarse cleaning of the electrolyte.
- An aerohydrodynamic generator (7) is fitted in the lower part of the bath (2).
- a valve (8) is provided to regulate the pressure of the electrolyte (3), and thus the frequency of the acoustic vibrations.
- a regulating valve (8) and a pressure gauge (9) are fitted at an input to the generator (7).
- a valve (10) is provided to regulate the flow rate of the air going to the generator (7).
- the electrolyte circulating system includes a heat exchanger or cooler (11) to maintain the required temperature of the electrolyte (3) in the course of oxidation.
- the supply source (12) consists of a three-phase pulse generator (13) fitted with a microprocessor (14) controlling the electrical parameters of the oxidation process.
- Figure 3 shows a cross section of a ceramic coating formed on a metal substrate (100).
- the ceramic coating consists of a hard functional layer (200) and a thin (less than 14% of the total coating thickness) external porous layer (300).
- the surface of the ceramic coating has low roughness (Ra 0.6 to 2.1 ⁇ m).
- the invention is clarified by examples of the implementation of the process.
- the specimens to be coated were in the form of a disc 40mm in diameter and 6mm thick.
- the specimens were degreased before oxidation. After oxidation, the specimens were washed in de-ionised water and dried at 100°C for 20 minutes.
- the electrical parameters of the process were registered by an oscilloscope.
- the quality parameters of the coating were measured from transverse micro-sections.
- a specimen of aluminium alloy 2014 was oxidised for 35 minutes in phosphate- silicate electrolyte, pH 11, at temperature 40°C. Bipolar alternating electrical pulses of frequency 2500Hz were supplied to the bath. The current density was 35A/dm 2 , and the final voltage (amplitude) was: anode 900V, cathode 400V. Acoustic vibrations were generated in the bath by an aerohydrodynamic generator. The pressure of the electrolyte at the input into the generator was 4.5 bars. A dense coating of a dark grey colour, overall thickness 130 ⁇ 3 ⁇ m, including an external porous layer 14 ⁇ m thick, was obtained. The roughness of the oxide-coated surface was Ra 2.1 ⁇ m, its microhardness was 1900HV, and the porosity of the hard functional layer (not the external porous layer) was 4%.
- a specimen of magnesium alloy AZ91 was oxidised for two minutes in a phosphate- aluminate electrolyte to which 2g/l of ultra-disperse Al 2 O 3 powder with particle size 0.2 ⁇ m was added.
- the temperature of the electrolyte was 25°C, pH 12.5.
- Bipolar alternating electrical pulses of frequency 10,000Hz were supplied to the bath in turn.
- the current density was lOA/dm 2 and the final voltage (amplitude) was: anode 520V, cathode 240V.
- Acoustic vibrations were generated in the bath using an aerohydrodynamic generator.
- the pressure of the electrolyte at the input to the generator was 4.8 bars.
- the coating obtained was dense, of a white colour, overall thickness 20 ⁇ l ⁇ m, including an external porous layer of thickness 2 ⁇ m.
- the roughness of the oxidised surface was Ra O.S ⁇ m
- the microhardness of the coating was 600HV
- the porosity of the functional layer was 6%.
- a specimen of titanium alloy Ti A16 V4 was oxidised for seven minutes in a phosphate-borate electrolyte to which 2g/l of ultra-disperse Al 2 O 3 with particle size 0.2 ⁇ m was added.
- the temperature of the electrolyte was 20°C, pH 9.
- Bipolar alternating electrical pulses of frequency 1,000Hz were supplied to the bath.
- the current density was 60 A/dm and the final voltage (amplitude) was: anode 500V, cathode 180V.
- Acoustic vibrations were generated in the bath using an aerohydrodynamic generator.
- the pressure of the elecfrolyte at the input to the generator was 4.0 bars.
- the coating obtained was dense, of a bluish-grey colour, overall thickness 15 ⁇ l ⁇ m, including an external porous layer of thickness 2 ⁇ m.
- the roughness of the oxidised surface was Ra 0.7 ⁇ m
- the microhardness of the coating was 750HV
- the porosity of the functional layer was 2%.
- the coating obtained was dense, of a light grey colour, overall thickness 65 ⁇ 2 ⁇ m, including an external porous layer of thickness 8 ⁇ m.
- the roughness of the oxidised surface was Ra 1.2 ⁇ m
- the microhardness of the coating was 900HV
- the porosity of the functional layer was 5%.
- the coating obtained was dense, of a dark grey colour, overall thickness 25 ⁇ l ⁇ m, including an external porous layer of thickness 2.5 ⁇ m.
- the roughness of the oxidised surface was Ra l.O ⁇ m
- the microhardness of the coating was 850HV
- the porosity of the functional layer was 5%.
- Bipolar electrical pulses one positive and two negative
- the current density was 50A/dm 2 and the final voltage (amplitude) was: anode 630V, cathode 260N.
- Acoustic vibrations were generated in the bath using an aerohydrodynamic generator.
- the pressure of the elecfrolyte at the input to the generator was 6.8 bars.
- the coating obtained was dense, white in colour, overall thickness 30 ⁇ l ⁇ m, including an external porous layer of thickness 3 ⁇ m.
- the roughness of the oxidised surface was Ra 0.9 ⁇ m
- the microhardness of the coating was 700HN
- the porosity of the functional layer was 3%.
- Table 1 also includes data from a known process of oxidising with industrial-frequency currents.
Abstract
Description
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Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2003580609A JP4182002B2 (en) | 2002-03-27 | 2002-09-23 | Process and apparatus for forming ceramic coatings on metals and alloys, and coatings produced by this process |
EP02765036.5A EP1488024B1 (en) | 2002-03-27 | 2002-09-23 | Process and device for forming ceramic coatings on metals and alloys |
AU2002329410A AU2002329410A1 (en) | 2002-03-27 | 2002-09-23 | Process and device for forming ceramic coatings on metals and alloys, and coatings produced by this process |
KR1020047014364A KR100871332B1 (en) | 2002-03-27 | 2002-09-23 | Process and device for forming ceramic coatings on metals and alloys, and coatings produced by this process |
NO20034936A NO20034936L (en) | 2002-03-27 | 2003-11-06 | Method and device for forming ceramic coatings on metals and alloys as well as coatings produced by this method |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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GB0207193.4 | 2002-03-27 | ||
GB0207193A GB2386907B (en) | 2002-03-27 | 2002-03-27 | Process and device for forming ceramic coatings on metals and alloys, and coatings produced by this process |
US10/123,010 | 2002-04-15 | ||
US10/123,010 US6896785B2 (en) | 2002-03-27 | 2002-04-15 | Process and device for forming ceramic coatings on metals and alloys, and coatings produced by this process |
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WO2003083181A2 true WO2003083181A2 (en) | 2003-10-09 |
WO2003083181A3 WO2003083181A3 (en) | 2004-09-10 |
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PCT/GB2002/004305 WO2003083181A2 (en) | 2002-03-27 | 2002-09-23 | Process and device for forming ceramic coatings on metals and alloys, and coatings produced by this process |
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EP (1) | EP1488024B1 (en) |
JP (2) | JP4182002B2 (en) |
CN (1) | CN100503899C (en) |
AU (1) | AU2002329410A1 (en) |
HK (1) | HK1059804A1 (en) |
NO (1) | NO20034936L (en) |
WO (1) | WO2003083181A2 (en) |
Cited By (22)
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EP1598591A2 (en) * | 2003-12-05 | 2005-11-23 | Welwyn Components Limited | Light emitting assembly |
WO2006075176A1 (en) * | 2005-01-15 | 2006-07-20 | Thermastrate Limited | Electrical power substrate |
CN100348780C (en) * | 2004-03-16 | 2007-11-14 | 天津大学 | Method of pulse plating nickel based nano composite plating layer and equipment |
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Also Published As
Publication number | Publication date |
---|---|
EP1488024A2 (en) | 2004-12-22 |
NO20034936L (en) | 2004-01-09 |
HK1059804A1 (en) | 2004-07-16 |
AU2002329410A1 (en) | 2003-10-13 |
JP4722102B2 (en) | 2011-07-13 |
JP2008038256A (en) | 2008-02-21 |
EP1488024B1 (en) | 2017-05-03 |
JP2005521794A (en) | 2005-07-21 |
NO20034936D0 (en) | 2003-11-06 |
CN100503899C (en) | 2009-06-24 |
WO2003083181A3 (en) | 2004-09-10 |
JP4182002B2 (en) | 2008-11-19 |
CN1623013A (en) | 2005-06-01 |
AU2002329410A8 (en) | 2003-10-13 |
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