Titanium component comprising a ceramized surface layer and method for obtaining the component

Abstract

The invention relates to a timepiece, jewellery or writing instrument component comprising a titanium substrate, said component being treated using a plasma micro-arc oxidation method that enables a ceramic coating (2) to be obtained on the surface of the substrate (7). The invention also relates to a method for producing the component by ceramization enabling a ceramic coating to be grown on the surface of the component by plasma micro-arc oxidation, comprising the following steps: immersing the substrate to be coated in an electrolytic bath composed of an aqueous alkali metal hydroxide solution, wherein the substrate forms one of the electrodes; and applying a current comprising positive and negative current pulses alternating with a frequency between 10 Hz and 10 000 Hz, where the current density of the current pulses is between 1 and 200 A / dm2 so as to apply a voltage, between the substrate and the cathode, of the order of 10 V to 1000 V. The substrate is a titanium alloy consisting essentially, by weight, of from 75% to 92% of titanium, from 4% to 8% of aluminum, from 1% to 3% of tin, from 2% to 6% of zirconium and from 1% to 8% of molybdenum.

Description

Titanium component comprising a ceramized surface layer and method for obtaining the component Technical field

[0001] The present invention relates to a component made of titanium alloy, preferably made of Ti6242 alloy. It also relates to a method for producing the component by ceramization making it possible to improve the aesthetic, mechanical, in particular tribological, properties of this component. State of the art

[0002] Application CH710708 describes a titanium-molybdenum component comprising a ceramized surface layer and its ceramization process. The ceramization process makes it possible to grow a ceramic coating on the surface of a component comprising a titanium-molybdenum substrate. The process described is of the plasma micro-arc oxidation type and comprises the steps of immersing the component to be coated in an electrolytic bath composed of an aqueous solution of alkali metal hydroxide, and applying a current comprising pulses of alternating positive and negative currents with a frequency of between 10 Hz and 10,000 Hz. The ceramized surface layer has a thickness preferably of between 10 and 50 micrometers and has a natural coloration of titanium oxide (pigeon gray).

[0003] Titanium surface treatment processes are also known as anodizing or anodic oxidation, also called anodizing. These processes allow for the production of numerous colors based on light interference phenomena. The TiCh titanium oxide layer does not exceed 0.2 micrometers.

[0004] The components thus obtained according to the various processes of the prior art have a choice of a very resistant and thick ceramic surface layer but with the natural coloring of titanium oxide (pigeon gray for example), or a layer of lesser thickness but with an original color. There is therefore a demand for parts having a different appearance, and in particular an original color, while having a ceramic surface layer of significant thickness and resistance.

[0005] To overcome these various drawbacks, the invention provides various technical means. Brief summary of the invention

[0006] First of all, a first object of the invention consists in providing a component having high resistance to wear as well as high resistance to a corrosive environment.

[0007] Another object of the invention is to provide a component having advantageous mechanical and chemical properties for applications in very varied fields, and in particular in watchmaking.

[0008] To this end, the invention provides a component comprising a titanium alloy substrate consisting essentially, by weight, of 4% to 8% aluminum (Al), 1% to 3% tin (Sn), 2% to 6% zirconium (Zr) and 1% to 8% molybdenum (Mo), the balance being titanium (Ti), treated using a plasma micro-arc oxidation process to obtain a ceramic coating on the surface of said substrate. Surprisingly, the ceramic oxide layer has an attractive blue or midnight blue coloring.

[0009] According to such a configuration, the ceramic coating located on the surface of the substrate has a thickness of between 5 and 150 micrometers, preferably 10 to 100 micrometers, even more preferably 20 to 60 micrometers.

[0010] According to a first variant, the substrate comprises one or more areas selected from holes, taps and threads. The interior of these areas selected from the holes, taps and threads of the component is also ceramized with a reduced thickness.

[0011] Advantageously, the titanium alloy substrate has an average hardness of between 250Hv and 500Hv.

[0012] According to an advantageous embodiment, the ceramic coating withstands a test of ten drops onto a bed of gravel at a height of 40 centimetres from the component, according to ISO 23160: 2011 standards.

[0013] According to another advantageous embodiment, the ceramic coating shows a surface condition comprising slight alterations after 36 hours of a test in accordance with standard ISO 23160: 2011.

[0014] Also advantageously, the component constitutes a component of watchmaking or watch movement, eyewear, jewelry, or even a writing instrument.

[0015] The invention also provides a method for producing the component by ceramization for growing a ceramic coating on the surface of a titanium alloy substrate consisting essentially, by weight, of 4% to 8% aluminum (Al), 1% to 3% tin (Sn), 2% to 6% zirconium (Zr), 1% to 8% molybdenum (Mo) and the balance being titanium (Ti). The method is a plasma micro-arc oxidation method comprising the following steps: immersing the substrate to be coated in an electrolytic bath composed of an aqueous solution of alkali metal hydroxide, the substrate forming one of the electrodes; and applying a current comprising alternating positive and negative current pulses with a frequency of between 10 Hz and 10,000 Hz.

[0016] According to a first embodiment, the current density of the current pulses is between 1 and 200 A / dm 2 so as to apply a voltage between the component and the cathode, of the order of 10 volts to 1000 volts, preferably 50 volts to 600 volts, even more preferably 100 volts to 350 volts.

[0017] A voltage between 10 volts and 1000 volts has the advantage of creating an electrolytic plasma necessary for the formation of the coating on the component.

[0018] According to another embodiment, the current pulses are separated by a dead time where no current is applied.

[0019] According to yet another embodiment, the duration of the dead time is preferably about 10% of the total duration of the current draw.

[0020] Thus the duration of the dead time is such that the voltage drops to zero. For example, each of the positive and negative current pulses may have a maximum amplitude followed by a decrease in current to a zero value.

[0021] Advantageously, the minimum average voltage is adjusted to be between 0 and 99.9% of the maximum voltage.

[0022] According to an alternative embodiment, a surface preparation comprising a micro-sanding step as well as a cleaning and degreasing step is carried out.

[0023] According to yet another embodiment variant, a micro-sanding step is carried out following the growth of the layer in order to partially eliminate the porous surface part.

[0024] Advantageously, components comprising one or more areas selected from holes, threads and tappings are subject to a first ceramization step.

[0025] Also advantageously, the components are then subject to strong ceramization. Brief description of the figures

[0026] All the details of the embodiment are given in the following description, supplemented by figures 1 to 4, presented solely for the purpose of non-limiting examples, and in which: figure 1 is a schematic view of an electrolysis installation; figure 2 is a sectional view of the component comprising a coating formed by the plasma micro-arc oxidation process, the coating comprising a dense ceramic layer and a porous external layer; figures 3A, 3B and 3C represent different views of a coating formed by an oxidation process similar to that of the invention; and figure 4 illustrates a watch case. Example(s) of embodiment of the invention

[0027] The invention provides a component comprising a titanium alloy substrate consisting essentially, by weight, of 75% to 92% titanium (Ti), 4% to 8% aluminum (Al), 1% to 3% tin (Sn), 2% to 6% zirconium (Zr) and 1% to 8% molybdenum (Mo), treated using a plasma micro-arc oxidation process to obtain a ceramic coating on the surface of said substrate.

[0028] Preferably, the invention provides a component comprising a titanium alloy substrate consisting essentially, by weight, of 80% to 92% titanium (Ti), 4% to 8% aluminum (Al), 1% to 3% tin (Sn), 2% to 6% zirconium (Zr) and 1% to 8% molybdenum (Mo), treated using a plasma micro-arc oxidation process to obtain a ceramic coating on the surface of said substrate.

[0029] The alloy may also include impurities or traces of impurities in varying proportions. Impurities are in particular chemical elements or compounds not intended to modify the properties of the alloy but whose presence and proportions depend on the initial purity of the metals used to form the alloy and the processes used to obtain the component. Said possible impurities represent at most 1%, preferably at most 0.5%, even more preferably 0.2% by weight of the alloy.

[0030] Preferably, the invention provides a component comprising a substrate consisting essentially, by weight, of 4% to 8% of aluminum (Al), 1% to 3% of tin (Sn), 2% to 6% of zirconium (Zr) and 1% to 8% of molybdenum (Mo), the balance being titanium (Ti).

[0031] Even more preferably, the invention provides a component comprising a substrate consisting essentially, by weight, of 4% to 8% of aluminum (Al), 1% to 3% of tin (Sn), 2% to 6% of zirconium (Zr) and 1% to 3% of molybdenum (Mo), the balance being titanium (Ti).

[0032] In particular, the alloy available under the reference TI6242 has this type of composition and is particularly interesting for use with plasma micro-arc oxidation processes. Such a composition allows the titanium component to have exceptional properties. The ceramic layer has a high resistance to corrosion as well as very good mechanical properties while having an attractive blue or midnight blue color.

[0033] Surprisingly, the ceramic oxide layer formed on alloys such as those mentioned above exhibits an attractive blue or midnight blue coloration. This coloration is the result of the formation of titanium oxide, for example, TiCh titanium oxide, and the presence of certain alloying elements within the substrate. The presence of 4% to 8% aluminum (Al), 1% to 3% tin (Sn), 2% to 6% zirconium (Zr), and 1% to 8% molybdenum (Mo) allows the formation of this blue or midnight blue ceramic oxide layer.

[0034] According to one embodiment, the invention provides a component 1 comprising a substrate 7 made of a titanium alloy TI6246. The substrate 7 is treated using a plasma micro-arc oxidation process making it possible to obtain a ceramic coating 2 on the surface of the substrate 7 made of titanium TI6246.

[0035] According to a preferred embodiment, the invention provides a component 1 comprising a substrate 7 made of a titanium alloy TI6242. The substrate 7 is treated using a plasma microarc oxidation process making it possible to obtain a ceramic coating 2 on the surface of the substrate 7 made of titanium TI6242.

[0036] Table 1 compares the mechanical properties of the titanium alloy TI6242 with those of a conventional titanium alloy (Ti-Grade 4) and type 316 L stainless steel. Table 1

[0037] Table 2 shows the chemical compositions of Ti 6242 alloy and Ti 6246 alloy. Table 2

[0038] Figure 2 is a cross-sectional illustration of the component 1 according to the invention. This component 1 comprises a coating 2 formed by the plasma micro-arc oxidation process. The coating 2 comprises a layer 21 of dense ceramic obtained by transformation of the substrate and forming approximately one-fifth of the total thickness of the coating 2. A porous external layer 22 growing on the substrate constitutes approximately four-fifths of the total thickness of the coating 2. For example, for a growth of 30 micrometers in excess thickness, approximately 6 micrometers of base substrate are transformed.

[0039] The coating 2 is formed by the substrate material 7 transformed during the oxidation process. The coating 2 extends by growth beyond the initial surface 8 of the component 1. An excess thickness is created relative to the initial surface 8 of the component 1 by the growth of the coating 2.

[0040] The ceramic coating has excellent properties against corrosion and wear. The good mechanical properties also promote the resistance of the coating, particularly during impacts or high mechanical stresses.

[0041] The thickness of coating 2 ranges from one to several tens of micrometers in holes and threads and from a few tens to a hundred micrometers on substantially smooth and homogeneous surfaces. The thickness of coating 2 has an impact on the thickness of the functional layer. A ratio of approximately 1 / 5 - 4 / 5 is observed between the inner layer 21 (1 / 5) and the outer layer 22 (4 / 5). The greater the thickness of coating 2, the greater the ratio between the inner and outer layers is likely to be. The ideal is to remain within the proportions of the order of 1 / 5 of the thickness for layer 21. The majority of the porous outer layer can also be reduced during a micro-sandblasting step.

[0042] Coating 2 thus obtained has a hardness of up to 2000Hv. This coating 2 therefore has excellent resistance to wear, impact and corrosion. Coating 2 also has a blue or midnight blue colour.

[0043] Generally speaking, the color of a material can be defined by its CIE L*a*b* coordinates, the CIE being the International Commission on Illumination: - the L* component corresponds to the brightness, it is between 0 (black) and 100 (white), - the a* component represents a range of 256 levels (8 bits), noted by an integer value, between red (+127), gray (0) and green (-128), the b* component represents a range of 256 levels (8 bits), noted by an integer value, between yellow (+127), gray (0) and blue (-

[0044] It should be noted that the CIE L*a*b* coordinates unambiguously separate the brightness information on the L* axis, and the color information on a plane defined by the two a* and b* axes. The L* component is highly dependent on the surface condition, and can be considered incidental in the definition of color.

[0045] The CIE L*a*b* coordinates can be obtained, in particular, using a conventional spectrophotometer, by measuring the reflectance properties as a function of the illumination wavelength. The a* and b* coordinates allow the chromaticity value of the C* alloy to be obtained (C* = (a*2 + b*2)1 / 2).

[0046] The following colorimetry measurements were carried out using a conventional spectrophotometer, for example a PerkinElmer LambdaFlex 950 model, with a CIE 1932 (2°) observer and a D65 illuminant. For example, on a matte sample, the coordinates obtained are as follows: L* = 36.36 a* = -0.20 b* = -4.82

[0047] The titanium alloy and its ceramic coating according to the invention are located in an area of ​​the CIE L*a*b* color space corresponding to a blue color. - Generally, the titanium alloy and its ceramic coating according to the invention have an a* value advantageously between -5 and +5, more advantageously between -3 and +3. - Generally, the titanium alloy and its ceramic coating according to the invention have a b* value advantageously between 0 and -20, more advantageously between -2 and -10, even more advantageously between -4 and -8. - Generally, the titanium alloy and its ceramic coating according to the invention have an L* value of between 10 and 100. - With a matt surface finish, the titanium alloy and its ceramic coating according to the invention will have an L* value advantageously between 10 and 60, even more advantageously between 20 and 50. - Alternatively, with a shiny surface finish, the titanium alloy and its ceramic coating according to the invention will have an L* value advantageously greater than 50, even more advantageously greater than 60.

[0048] Due to its properties such as blue or midnight blue color, this titanium alloy and its ceramic coating can be used in many fields and, more particularly, in the luxury industry.

[0049] The components 1 treated by the plasma micro-arc oxidation process may be mechanical watch movement components subjected to mechanical stresses, or watch exterior components subjected to aggressive environmental stresses, such as wear, humidity, etc. These components 1 may also belong to eyewear, leather goods or even writing instruments.

[0050] The process of producing the component by ceramization or micro-arc oxidation, otherwise known as electrolytic plasma oxidation, is carried out by electrolytic treatment. Figure 1 shows an example of an installation for electrolytic treatment.

[0051] According to Figure 1, the installation comprises a tank 3 containing an electrolytic bath 4. A cathode 5, as well as an anode corresponding to the component 1 to be coated are immersed in an electrolyte 4. This installation also comprises a current supply unit 6 capable of generating an alternating current 31.

[0052] The process for producing the component by ceramization or plasma micro-arc oxidation process comprises different steps. The first step consists, according to one embodiment, in immersing the component 1 to be coated in the electrolyte 4. Then the alternating current 31 is generated in order to apply a voltage between the component 1 and the cathode 5.

[0053] According to this embodiment, the electrolyte 4 may comprise an aqueous solution composed of alkali metal hydroxide such as potassium or sodium, and an oxyacid salt of an alkali metal. The electrolyte 4 is typically maintained at a temperature between 10°C and 55°C.

[0054] The applied current consists of positive and negative current pulses, alternating between a frequency of 10 and 10,000 Hertz. The current density of the current pulses is between 1 and 200 A / dm 2 in order to apply a voltage between component 1 and cathode 5 of the order of 10 to 1000 volts. A voltage of this order makes it possible to create an electrolytic plasma which is necessary for the formation of coating 2 on substrate 7.

[0055] According to another embodiment, the current pulses may also be separated by a dead time, during which no current is applied. The duration of the dead time is approximately 10% of the total duration of the current pulse, i.e., a duration such that the voltage drops to zero. For example, each of the positive and negative current pulses may have a maximum amplitude, followed by a current decrease to a zero value. Consequently, the voltage to be transmitted is cycled between a minimum voltage ("baseline") and a maximum voltage ("ceiling line"). The minimum voltage is preferably adjusted between a voltage between 0 and 99.9% of the maximum peak of the ceiling voltage.The base voltage (for example 30% of the ceiling voltage) will promote the formation of micro-electric arcs visible to the naked eye, while a higher base voltage (for example 60% of the ceiling voltage) will promote the creation of a continuous plasma, also visible to the naked eye. the naked eye (relative to retinal perception of 0.1 to 0.2 seconds). The influence of the choice of the minimum average basic voltages compared to the maximum voltage and therefore of the type of micro-arcs obtained makes it possible to control a more or less dense and homogeneous layer. The densification of the layer is also a function of the alternation frequency between the anodic and cathodic currents. Indeed, the growth of the nanoporous layer takes place under anodic current while under cathodic current the densification of the nanoporosities is observed.

[0056] Therefore, the choice of favoring a minimum voltage intensity compared to a maximum voltage makes it possible to control the result, namely the density and the more or less pronounced homogeneity of the layer of the ceramic coating 2. The densification of the layer is in fact a consequence of the alternation frequency between the anodic and cathodic currents.

[0057] The growth rate of coating 2 therefore depends on the type of frequency and the nature of the pulse emitted. More particularly, the growth rate depends on the passage between a cathodic and anodic current and the amplitude of the current. For example, the growth rate of coating 2 may be 1 micrometer per minute, for an applied voltage of 100 to 400 volts and a frequency of the order of 2000 hertz. The thickness of coating 2 thus obtained may vary between a thickness of tens of micrometers uniformly on the part, provided that the installation used to hold the component is suitable and does not modify the formation of micro-arcs, and a thickness of around a hundred micrometers. The plasma micro-arc oxidation process is described for example in document W003083181.

[0058] The intensity of the ceramization process varies depending on the component 1 to be coated. Thus, the ceramization of a component 1 comprising threaded, tapped and hole areas is said to be fine. This type of ceramization produces a coating 2 with a thickness of a few microns (for example, a thickness between 1 and 100 microns or between 10 and 50 microns) to densify and harden heterogeneous areas. Indeed, it is advantageous for areas with a particularly fine structure to be coated with a coating 2 that is less thick than on the rest of the surface of component 1.

[0059] Thus, according to a variant of the plasma micro-arc oxidation process, it makes it possible to initially obtain a coating 2 on the areas with fine structure.

[0060] Then, the ceramization is advantageously continued by a so-called strong ceramization. In the latter case, the layer of coating 2 extends from several tens to hundreds of micrometers. The finely structured areas are protected by seals in order to form coating 2 on the rest of the component 1. The seals used to mask the finely structured areas can be made of silicone or any other protective means resistant to plasma micro-arc oxidation treatment and which can be removed at the end of the process. This seal has the effect of creating a selective effect and preventing any growth of micro-arc oxidation on the areas protected by the silicone seal. Indeed, excessive ceramization on threaded areas, for example, could erode the thread.

[0061] Surface preparation is generally required before the ceramic component production process is carried out. Substrates 7 must be micro-sandblasted, cleaned and degreased with boiling water, or prepared using an alkaline cleaner. After cleaning, the part is rinsed with distilled water.

[0062] The components 1 which have been subjected to the plasma micro-arc oxidation process comprise an oxidized layer of ceramic making it possible to obtain various advantages. These advantages are high hardness, strong resistance to wear, shocks and corrosion, as well as a natural coloring of the oxide of the substrate 7 made of titanium TI6242. Such a process also makes it possible to obtain perfect adhesion between the ceramic coating 2 and the substrate 7. In fact, the ceramic layer is not projected onto the substrate 7 but is partly obtained by extension of the substrate 7. Finally, such a process makes it possible to coat the internal parts of the components 1 with a ceramic coating 2. This process finally generates a low coefficient of friction between the parts respectively treated, which makes it possible to envisage pivoting without lubricant.

[0063] By way of example, Figures 3A to 3C make it possible to observe the surface condition of the coating following a ceramization process similar to that of the invention, in this case on a watch exterior component. Figure 3A shows a rough surface condition. Figure 3B is a cross-section of a coating layer 2 obtained by growth. Figure 3C represents the surface of the coating after micro-sandblasting type tribofinishing.

[0064] Figure 4 shows, as an example, a watch case on which the micro-arc oxidation process has been carried out. The coating 2 has been formed on different parts of the watch case, such as the caseband 91, the lugs 92, the lever 93, and the crown cover 94, as well as on the bezel 95, and the crown 96.

[0065] A micro-sandblasting type tribofinishing step is preferably carried out following the ceramization process. This step makes it possible to obtain an optimum surface condition, free from the last micrometers of the porous ceramic layer 22.

[0066] The ceramic coating 2 obtained by such a process comprises a dense and uniform layer, with a thickness of between 5 and 150 micrometers, preferably 10 to 100 micrometers, even more preferably 20 to 60 micrometers.

[0067] The wear test aims first of all to evaluate the resistance of a component 1 comprising a ceramization coating 2 against ceramic balls. To do this, the sample is mixed with 2 kilos of ceramic balls with a diameter of 3 millimeters, half a liter of water and 10 cubic centimeters of wetting agent, for 36 hours. The rotation speed is 46 revolutions per minute.

[0068] After 6 hours of testing, the sample exhibits shiny surfaces. No change is observed after 36 hours of testing. The sample is therefore highly resistant to wear.

[0069] The second test is called "fine scratches". It consists of placing the sample along with 5 to 15 felt pens and 10 grams of "Bremor BR650" glass powder in a chamber with a diameter of 80 millimeters and a height of 60 millimeters including blotting paper walls. This is rotated for 24 hours at a speed of 90 rpm. The fine scratches test demonstrates excellent scratch resistance of the ceramic coating 2.

[0070] The ceramic coating 2 is also subjected to a drop test on a bed of gravel. This test, carried out in accordance with ISO 23160: 2011, consists of dropping the sample onto a bed of 8 centimeters by 500 square centimeters of ceramic chips 3 millimeters in diameter, 12 millimeters in length and with a hardness of 800 to 1000 Hv. The drop is made from a height of 40 centimeters. The watch case to be tested is loaded with a weight representing the weight of the mechanical movement normally integrated in the watch head. Following about ten drops on a bed of gravel and ceramic, very low impacts are observed at the edges of the components. The caseband therefore has excellent resistance to shocks and impacts on a bed of gravel.

[0071] The ceramic 2 coating is finally subjected to the synthetic sweat test in accordance with NIHS 96-50 and ISO 3160-2 standards. The tested parts are placed on a sweat-soaked support in an environment of 40 degrees and a relative humidity of 95 to 100%, for a period of 6 days. After 6 days of testing, corrosion pits are visible on the tested areas of titanium without ceramic coating. Therefore, the ceramic 2 coating creates a protective layer of the 7 titanium substrate TI6242. No corrosion is visible on the areas of the case coated with a ceramized layer. Reference numbers printed on the figures 1 component 2 coating 21 hard layer 22 porous outer layer 3 tanks 31 alternating current 4 electrolytic bath 5 cathode 6 power supply unit 7 Ti6242 titanium substrate 8 initial surface 9 watch case 91 build 92 horns 93 lever 94 crown cover 95 glasses 96 crown

Claims

Claims 1. Component (1) for watches, jewelers or writing instruments, comprising: a substrate (7) made of titanium alloy, a ceramic coating (2) on the surface of the substrate (7), said coating (2) being obtained by a plasma microarc oxidation process of said substrate (7) characterized in that said substrate is a titanium alloy consisting essentially by weight of 75% to 92% titanium, 4% to 8% aluminum, 1% to 3% tin, 2% to 6% zirconium and 1% to 8% molybdenum.

2. Component (1) according to the preceding claim, wherein said substrate is a titanium alloy consisting essentially by weight of 80% to 92% titanium, 4% to 8% aluminum, 1% to 3% tin, 2% to 6% zirconium and 1% to 3% molybdenum.

3. Component (1) according to one of the preceding claims, in which said ceramic coating has, according to the CIE L*a*b* color space: an a* value between -5 and +5, advantageously between -3 and +3; and a b* value between 0 and -20, advantageously between -2 and -10.

4. Component (1) according to one of the preceding claims, in which said ceramic coating (2) located on the surface of the substrate (7) has a thickness of between 5 and 150 micrometers, preferably 10 to 100 micrometers, even more preferably 20 to 60 micrometers.

5. Component (1) according to one of the preceding claims, in which the substrate (7) comprises one or more zones selected from holes, tappings and threads, and in which the ceramic coating (2) located inside these zones selected from holes, tappings and threads, has a thickness of between 1 and 100 micrometers, and preferably between 5 and 30 micrometers.

6. Component (1) according to one of the preceding claims, in which the substrate (7) is titanium TI6242 and has an average Vickers hardness of between 250Hv and 500Hv.

7. Component (1) according to one of the preceding claims, in which the ceramic coating (2) withstands a test of ten drops onto a gravel bed at a height of 40 cm from the component (1) according to ISO 23160: 2011 standards.

8. Component (1) according to one of the preceding claims, in which the ceramic coating (2) shows a surface condition comprising slight alterations after 36 hours of a test in accordance with standard ISO 23160: 2011.

9. A method of producing a component (1) by ceramization for growing a ceramic coating (2) on the surface of a titanium substrate (7) consisting essentially, by weight, of 75% to 92% titanium, 4% to 8% aluminum, 1% to 3% tin, 2% to 6% zirconium and 1% to 8% molybdenum, characterized in that the method is a plasma micro-arc oxidation method comprising the following steps: immersing the substrate (7) to be coated in an electrolytic bath (4) composed of an aqueous solution of alkali metal hydroxide, the substrate (7) forming one of the electrodes; and application of a current comprising positive and negative current pulses alternating with a frequency between 10 Hz and 10000 Hz, where the current density of the current pulses is between 1 and 200 A / dm2 so as to apply a voltage between the substrate (7) and the cathode (5), of the order of 10 V to 1000 V.

10. A ceramization method according to claim 9, wherein the current pulses are separated by a dead time where no current is applied.

11. A ceramization method according to claim 10, wherein the duration of the dead time is approximately 10% of the total duration of the current pulse.

12. Ceramization method according to one of claims 9 to 11, in which a surface preparation of the substrate (7), comprising a micro-sanding step as well as a cleaning and degreasing step, is carried out.

13. Ceramization method according to one of claims 9 to 12, in which a micro-sandblasting tribofinishing step is carried out.

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