SI23538A - Hard protective coating with the possibility of changing their color - Google Patents

Abstract

The subject of the invention is hard protective coating with the possibility of changing their color. On the working surface of base material, which is ordinary tool steel or carbide, are applying some micrometers thick of hard coating. Coating after the invention consists the following layers: a bottom layer of hard coating that protects substrate from corrosion and wear; intermediate reflective layer, a well reflects light in the visible spectrum and protects the substrate against wear and corrosion and semitransparent outer layer that protects substrate from corrosion and wear, and together with the intermediate layer sets the color of the substrate. The top layer is made of material that partially leaves visible light and is made of nitrides, carbides, carbonitrides, oxsinitrides or borides

Description

Hard protective coatings with the ability to change their color

The subject of the invention are hard protective coatings with the possibility of changing their color. On the work surface of the base material, which is usually tool steel or carbide hardness, a few micrometers of thick hard coating is applied.

View the problem

For the processing of a wide variety of materials, tools that operate under extreme tribological loads are used in industrial production. The tools must therefore be as resistant as possible to wear, corrosion, oxidation and adhesion of the workpiece. As a rule, the wear resistance of the tool is increased by applying a few micrometers of thick hard coating to the work surface of the base material, which is usually tool steel or carbide hardness. Such coatings must be very hard and tough and thermally, corrosion and oxidation stable.

In addition to the physical and mechanical properties of hard coatings, their color is also important. On shroud-protected tools that have a distinctive color, it can be easier for the operator to notice the wear of the tool before serious damage to its surface occurs. The characteristic color of the coating also makes it easier to separate the tools by purpose and make them easier to identify. The color of the tool also helps to make the tool maker recognizable. More than 60 different commercially available PVD coatings have been used in production, which are intended for specific applications, so the characteristic color of the tool can improve inventory control.

A decorative coating is a thin layer of material that is applied to the surface of a product in order to change its appearance. Decorative coatings must have a distinct color and shine, and be resistant to smudging and corrosion. These properties largely combine ceramic hard coatings. Most commonly, nitrides, carbides, carbonitrides and oxynitrides of transition metals and carbon-based coatings are used to prepare hard decorative coatings. The color of the coatings depends on the composition or the composition. stoichiometry. Stoichiometric CrN is metallic in color, TiC is dark gray, TiN, ZrN and HfN is gold. By changing the stoichiometry, different colors can be achieved: e.g. for TiN, gold or brown may be obtained depending on the ratio of titanium to nitrogen. By partially substituting metal and non-metallic atoms, the color can be varied over a very wide part of the spectrum. A typical example is (Ti, Al) N, where the color varies from silver, gold to dark purple, for varying proportions of aluminum and

-2 with nitrogen. These (C, N) have a red-gold or purple color for different stoichiometers. The typical thickness of decorative coatings is 0.5-1 pm.

The color of an object is due to the interaction of light with matter. There are several physical mechanisms that cause the formation of color. Color can be produced by dispersion (eg prism light), interference (eg filters), slope (eg mesh), scattering (eg granules) or absorption (eg absorption by atoms, molecules or crystals). The substance itself can also emit light (such as a neon lamp). The color of non-transparent substances such as ceramic coatings is due to absorption. Color is determined by the interaction of incident light with bound and free electrons. Visible light has an energy comparable to the binding energy of valence electrons (1.5 to 3 eV) and can therefore excite valence electrons in higher energy states. If the color of a substance is determined by the electronic structure of the substance, we are talking about the intrinsic color of the substance. The electronic structure of the TiN, ZrN and HfN valence bands is very similar to the electronic structure of gold, so these coatings have a distinctive golden color. By changing the composition of the layers, we change the structure of the electronic states and therefore their color.

Most decorative hard coatings utilize the intrinsic colors of a particular material. For example, the TiN coating, which has an intrinsic gold color and good mechanical properties, is very commonly used. The color of such coatings may vary to some extent with the composition of the material, but typically only two or three colors can be achieved. In our invention, however, the color is due to the interference of light from two boundary surfaces. The color is due to the reinforcement or. attenuation of certain visible wavelengths of visible light at the air / layer and layer / substrate boundaries. Light is amplified when the phase shift of light is reflected off the layer / substrate, 360 ° relative to the reflected light from the air / layer boundary. However, the light wave attenuation occurs when the phase shift is 180 °. The phase shift of light depends on the thickness of the layer and the refractive index of the layer; the product of these two quantities is called optical thickness. The interference enhances the light of some wavelengths of the visible spectrum, while others diminish the color of the object.

Interference occurs when the top layer is transparent to visible light. If the layer is not transparent, then the intrinsic color of the top layer is observed. Distinctive interference colors are only obtained when the substrate strongly reflects visible light. If the substrate is translucent for light, such as e.g. in the case of glass, then the interference color is not pronounced or. we don't even notice it. The interference phenomenon on translucent substrates is used for anti-reflection purposes e.g. on glasses or lenses of photographic lenses. The purpose of anti-reflective layers is to reduce reflected light and not to create interference colors. Intense interference colors are observed on substrates that have a high reflectance in the visible part of the spectrum (eg on mirrors). Metals (e.g.

-3Silver, aluminum, gold), metal alloys (brass), semiconductors (silicon) and certain compounds (eg nitrides, carbides).

Intense interference colors are achieved with a transparent layer and a reflective base. Materials that are translucent over the entire visible light spectrum and can be applied in the form of thin layers are typically oxides, fluorides or sulfides. The problem with the interference colors achieved with translucent layers is that the color depends on the viewing angle of the surface. With the angle the interference condition (optical path) changes, so we see the interference or. rainbow colors. The angular dependence can be avoided by adding coloring agents to the oxide coatings (eg anodizing). However, in such a case the surface color is no longer due to interference but to the intrinsic color of the dye.

The state of the art

The decorative coating is applied in order to change the color and shine of the surface of an object. In addition to the aesthetic function, it is important that decorative coatings protect the base material from wear and corrosion. Decorative covers apply to various products, such as: surgical instruments, gaming devices, household products (mats, knives, scissors), bathroom products (taps, pipes), home products (hooks, handles, hinges), car parts ( exhaust pipes, rims), recreational products, personal effects (glasses frames, watches, jewelry, pen parts), various decorative items, etc. Decorative coatings refer to substrates made of different materials: plastics, metals, metal alloys, ceramics and others. Often, an electrochemical coating is applied to the surface of the product to offset the surface and protect it from corrosion.

Decorative coatings are applied by different processes. The following processes are applied in industrial production: varnishing, painting, electrochemical processes (anodization, electroplating) and non-current processes. By painting and painting, polymer decorative coatings are applied to the products. The advantage of varnishing is the simple application of various coatings to the surfaces of complex shapes. Polymer decorative coatings provide good enough protection for products used in less invasive environments, while poorer protection in more invasive environments, e.g. exposure to UV light.

Decorative coatings made with electrochemical processes provide better protection against external influences. An example of an electrochemical process is surface anodization. At

-4 this process produces an oxide layer on the surface when an electrical current flows between the cathode and the anode (product surface); the product must be immersed in a suitable electrolyte. Anodization is mainly used for the protection and decoration of aluminum and aluminum alloy surfaces, as well as for magnesium, zinc and titanium alloys. Anodizing the aluminum surface produces a few micrometers thick oxide layer with a hardness of about 180 HV, which is well resistant to abrasion and corrosion. The layer is translucent and very porous, so the pores can be filled with pigments; different colors can be achieved in this way. The disadvantage of anodizing is that we cannot cover steel substrates with this process. The electrochemical process also applies hard chromium layers with a characteristic metallic color and strong luster. In addition to its decorative function, chrome plating also offers good protection against wear and corrosion. The materials that can be prepared by electrochemical processes are therefore pure metals and their alloys and oxides. These coatings are much harder than polymer coatings and therefore offer better abrasion protection. The limitation of electrochemical processes is to apply the layers only to substrates that are electrically conductive.

In addition to classic decorative coating processes, physical (vacuum) steam-vapor deposition (PVD) applications have also been introduced on the market. In PVD processes, the target material is vaporized (by evaporation by heating and by spray using plasma) and transferred to the substrate. In doing so, a reactive gas is introduced, which together with the dispersed material forms a high hardness compound on the substrates.

When applying decorative hard coatings, a complete range of colors can be obtained by selecting different materials and different composition or structure of the layers. Most often, for decorative purposes, PVD coatings with gold color are used. Thus, TiN has been used for a long time, which has a characteristic golden color and is mechanically very resistant to tearing and corrosion. ZrN and HfN also have a golden color. Multi-component coatings are also used as decorative coatings, e.g. (Ti, Al) N or (Ti, Ca) N, (Ti, Mg) N. By changing the element concentration, different colors can be achieved, e.g. at (Ti, Al) N we can achieve colors from silver to gold and dark purple.

With patent US6245435, Moen Inc. protector PVD process for the application of hard decorative coatings to the surfaces of various objects. The coating consists of two layers. The lower layer is corrosion and abrasion resistant (Ti, Zr, SiO ₂ , SiO _x C _y H _z , A1 ₂ O ₃₎ A10 _x C _y H _z , Zr ₃ N ₄ , Zr _x N _y C _z , Hf ₃ N ₄ , Hf _x C _y N _z ,) and the top layer is nitride (ZrN, ZrCN, HfN, HfCN), which has a color different from gold. The advantage of zirconium and hafnium nitrides over TiN is that in contact with air or water, they form special phases (eg zr ₃ N ₄ ) that well prevent corrosion.

Patent US7179546 is a protected product with a decorative hard coating having the color of brass, nickel or stainless steel. The coating replaces the use of organic protective coatings.

Organic coatings are mostly used to protect brass products such as candle holders, hooks, handles, pedestals, but they are not very durable when exposed to UV light. To protect against UV light, they patented a coating made by a PVD process consisting of several layers. The layers on the surface of the product are as follows: nickel or polymer layer, chromium layer, metal layer, thin metal oxide layer, sequence of metal and sub-stoichiometric nitride layers, transition metal nitride color layer and very thin metal oxide layer, which further protects against corrosion .

GB 2455991 patent application from the Dutch company Hauzer Techno-Coatings describes how to paint the surface of a metal product using four different approaches. The essence of all processes is the simultaneous or alternate application of a rigid judgment layer (SiO _x , SiN, SiON, AI2O3, TiO ₂ , Cr ₂ O3, ZrO _x ) and nanoparticle-shaped metal phases (eg gold, silver, platinum, copper). The color depends on the density of the metal nanoparticles in the layer and on the thickness of the translucent layer. Light of selected wavelength is absorbed on metal nanoparticles due to excitation of plasmonic oscillations. The interference of light reflected on the surface of the translucent layer and those reflected from the surface of the substrate shall be avoided either by the thickness of the translucent layer being greater than the coherent length of the light used (coherent length for light emanating from the incandescent tungsten filament in the bulb is a few pm). Another approach is to increase the density of metal nanoparticles. However, since this reduces the sheen, the authors have proposed a combination of a top layer containing metal nanoparticles and thicker bottom transparent layers. The color of reflected light can be further influenced by the choice of reflective layer on the surface of the product. A spray with four application springs was used to apply all of these coatings. The bases are mounted on a bracket that provides multiple rotation. Two targets are e.g. made of aluminum, from which aluminum oxide is deposited by reactive spraying. In the next phase, the substrates are moved before the target of the precious metal (gold, silver, platinum, copper). In spite of the oxygen atmosphere, pure metal is applied to the substrates, nucleating in the form of small islets. Their size depends on the target's electrical power. In the next application phase, the oxide layer is applied again.

Description of the invention

The invention is described by means of pictures showing:

Figure 1: Schematic diagram of the magnetron sputtering device for hard decorative hard coatings> ·

-6Figure 2: Schematic diagram of the layered structure of a decorative hard coat with a specific color. 1 - substrate, 2 intermediate reflecting layer, 3 - upper semipermeable layer

Figure 3: Photograph of samples with a layer (Ti, Al) of N of different thicknesses (20-70 nm) on a TiN layer of -400 nm thickness.

Figure 4: The reflectance spectra of layer (Ti, Al) N 20-70 nm thick on the TiN layer. The patterns are shown in Figure 3.

Figure 5: CIELABa *, b * color values in layer (Ti, Al) N of 20-70 nm thickness on TiN layer Figure 6: Layer diagram of the decorative hard coating layer. 1 - substrate, 2 - protective hard coating, 3 - intermediate reflective layer, 4 - visible light semi-permeable layer Figure 7: Photo of cutters with decorative hard coating of blue. The layer structure is shown in Figure 6.

The invention discloses a novel method of preparing colored multilayer hard PVD coatings. What is new to the present invention is that instead of the oxide layers, semi-permeable materials that absorb some of the wavelengths of light but allow enough light to produce intense interference colors are used for visible light. In the process of the invention, the interference colors are achieved by applying a multilayer structure to the substrate of a particular product, e.g. tools. The multilayer structure consists of three layers: 1.) a protective hard layer that protects the substrate from wear and corrosion, 2.) a thin reflective layer that well reflects part of the visible spectrum, and 3.) an interference layer that is partially transparent to visible light and together with the reflective layer determines the color of the product. Such a multi-layered structure can combine the protective and decorative properties.

Appropriate materials must be used to achieve intense metallic sheen. The protective layer can be single-layer, multi-layer or nanostructured. It is made of nitrides e.g. TiN, CrN, (Ti, Al) N, carbides e.g. TiC, CrC, carbonitrides e.g. These (C, N) oxides e.g. AI2O3 or borides e.g. T1B2. The intermediate reflecting layer from the point must be of material which has a high reflectance in the visible part of the electromagnetic spectrum; these may be metals, borides, nitrides, carbides or carbonitrides. The top layer, however, must be of a material which partially transmits visible light. Suitable materials for the visible light semi-permeable layer are nitrides, carbides, transition metal borides or a carbon-based layer. An essential requirement is that it has a large refractive index and is thin enough to transmit some of the visible light and cause interference colors. The aforementioned materials that are suitable for the top layer are considered to have a suitable thickness between about 1 nm and 300 nm. The advantage of semi-permeable materials is that they paint only minimally

-7Change with viewing angle and surface has a distinct metallic sheen. Nitride hard coatings such as e.g. A1N, (Al, Ti) N, (Ti, Al) N. The advantage of these layers is that they are highly resistant to wear and corrosion.

Color-coated objects can be axially symmetrical tools or some other object intended for the user: e.g. kitchen utensils, dishes, parts of bathroom accessories such as handle, plumbing faucet, parts of sports aids, accessories for personal use e.g. glasses, watches, zippers, buttons, car parts e.g. Exhaust Pipe. The substrate material may be tool steel or carbide solid, other metals and their alloys, plastics, ceramics, nitrided or otherwise treated surfaces. It is important that the color of the product is even. The uniform color of the object with complicated geometry is achieved by applying a uniformly thick top layer as evenly as possible. For products with complicated geometry, such as tools, it is difficult to provide evenly thick layers. If the interference layer is not uniformly thick throughout the product, then the product has different colors. Computer simulation of the layering process of a multi-layered structure can provide uniform color throughout the tool surface. In principle, an even color is achieved only if the object is axially symmetrical.

Multilayer hard coatings, which are the basis of colored coatings, are prepared by spraying in a device having four magnetron springs, as shown in Figure 1. The choice of targets for individual springs depends on the type of multilayer structure we want to prepare. Technological process for the application of multilayer hard coatings to substrates or surfaces. tools consist of several successive steps. Prior to application of the coating, the substrates must be cleaned to ensure good adhesion of the coating to the substrate. The cleaning process is carried out in four stages: 1.) mechanical cleaning e.g. sandblasting, polishing, 2.) dry cleaning in an ultrasonic bath with various detergents, rinsing in deionized water and drying in hot clean air; 3.) see the heating of the substrates in vacuum - degassing; 4.) etching with ions in the vacuum chamber. The last two phases are done in the bedding device.

After cleaning the substrates, thin layers are applied in the vacuum chamber according to Figure 1. The vacuum chamber should be exhausted to high vacuum (~ 10 ' ³ Pa). This is followed by heating the substrate to a temperature of about 450 ° C. Overheating is followed by ion etching of substrates with Ar and Kr ions at an operating pressure of about 0.1 Pa. At this stage, the tools are at a negative electrical potential. This is followed by the application of a multilayer spray coating of four magnetron sputtering springs. Target voltages are around -500V and typical target voltages are around 10 kW. In addition to inert gases such as Ar, Kr also introduces nitrogen into the vacuum chamber. Part of the ions of inert and · «·

-8reactive gas is also accelerated to substrates at a negative voltage between 80 and 100V. These high-energy particles enhance adhesion and affect the microstructure of the coating. To apply multilayer structures, a PVD system with targets of different materials must be used. The multilayer structure is applied by rotating the substrate from one target to another. In industrial coating applications, this is done so that the table on which the substrates are, e.g. tools, circling between spatially separated targets. Substrates typically rotate around three axes to ensure that the thickness of the layers on a tool of complex shape is as uniform as possible.

Hard protective coatings with the ability to change their color according to the invention relate to substrates which can be tools or other functional product such as kitchen utensils, parts of bathroom accessories, sports aids, utensils for personal use and the basis of tool steel, carbide solid, metal, metal alloy, ceramic, nitrided or otherwise treated surface. The protective coatings according to the invention are characterized in that they consist of the following layers:

a) a lower protective layer of hard coating that protects the substrate from wear and corrosion,

b) an intermediate reflecting layer that reflects light well in the visible part of the spectrum and protects the substrate from wear and corrosion, a visible light cream partially permeable that protects the substrate from wear and corrosion and together with the intermediate layer determines the color of the substrate.

Implementation examples

The following is a description of two examples of decorative hard coatings. The first embodiment shows patterns of different colors of the (Ti, Al) N layer on the TiN layer. In another embodiment, the milling cutter with a blue decorative hard cover is shown.

Example 1

Figure 1 shows a diagram of a magnetron sputtering device for hard coatings. In vacuum chamber 1, there are four magnetron springs 2-5, a table for carrier substrates 6, and six satellites 7 on which tool clamps 8. The table 6, which rotates about its center 9, is with

-9 gears connected to satellites rotating about its center 10. The rotation about the third axis is disconnected and is determined by a spring 11 which rotates the base 12 for a certain angle at one turn around the other axis 10. A system is also installed in the vacuum chamber 1. for the supply of reactive and working gas 13, heaters 14 and vacuum pumps 15.

The layer application process consists of three parts: heating, ion etching and application of individual layers. In the first phase, the pressure in the vacuum chamber 1 with the vacuum pumps 15 is reduced to ~ 4mPa. Then heaters 14 are activated, which heat the vacuum chamber to -450 ° C, which allows degassing and heating of the substrates to the operating temperature. In the second phase, the plasma cleans the substrates 8. The plasma is ignited with the help of argon working gas and the target voltages 1 ^ 4. Plasma ions etch substrates for 10 to 30 min. During etching, table 1 with tools 8 rolls around three axes 10-12. Ionic etching takes place in two regimes: unidirectional and pulsed. In the third phase, individual layers are applied to the substrates 8. This is achieved by connecting high voltage to targets 2-5, which creates a plasma near the targets. Plasma ions accelerate toward target 2-5 and eject atoms from it, which are scattered throughout the space of the vacuum chamber 1. At the same time, a working gas is introduced into the chamber, e.g. nitrogen 13, which together with the scattered atoms forms a layer of e.g. nitride. The gas pressure during spraying is -1 Pa.

Figure 2 shows a scheme of a two-layer structure of a decorative hard cover 2-3 based on product 1. The top layer 3 is semi-permeable, while the intermediate layer 2 reflects light well in the visible part of the spectrum. The implementation of this scheme is shown in Figure 3, where the top layer is semi-permeable (Ti, Al) N, the intermediate reflective layer TiN, and the substrate is stainless steel. The layers were made by magnetron sputtering according to the procedure described above. First, only a layer of TiN -400 nm thick was applied, and then a layer (Ti, Al) N of different thicknesses, from about 20 to 70 nm. Figure 3 clearly shows that the color of the samples varies with the thickness (Ti, Al) N of the layer from yellow, purple, dark purple to blue.

Figure 4 shows the reflectance spectra of the samples in Figure 3. From the reflectance spectra it can be seen that the two-layer TiN / (Ti, Al) N structure strongly absorbs light of some wavelengths. The absorption minimum depends on the thickness of the top layer. As the thickness of the top layer increases, the absorption minimum shifts to longer wavelengths, thus changing the color of the two-layer structure. Figure 5 shows CIELABa *, b * color values that vary widely with the thickness of the (Ti, Al) N layer.

-10Example 2

The second example describes a three-layer decorative hard cover. Figure 6 shows the scheme of the three-layer structure 2-4 based on product 1. The three-layer structure 2-A consists of a lower protective layer 2, an intermediate reflective layer 3 and a top semi-permeable layer 4. All three layers 2-4 are made of hard coating materials e.g. . TiN, CrN, TiC, ZrN, (Ti, Al) N. It is essential for the formation of interference colors that the top layer 4 is partially transmitted to light and that the intermediate layer 3 reflects well the visible portion of the light spectrum. The function of the bottom layer is to protect the surface of the product from wear and corrosion.

An example of a blue three-layer structure (Ti, Al) N / TiN / (Ti, Al) N on milling cutters is shown in Figure 7. The three-layer coating was made in the same way as described in Example 1. Such a decorative hard coating provides good protection cutters against wear and corrosion and gives them a distinctive blue color. The color of a product with a complicated surface such as a milling cutter can vary considerably due to the uneven application of the top coat. This problem has been solved by computer simulation, which can calculate the thickness of individual layers on substrates with complicated surfaces. By knowing the initial positions and geometry of the vacuum system and the sputtering process, a trajectory can be calculated to ensure that the layers are applied evenly and thus in a uniform color.

Claims (5)

Patent claims 1. Hard protective coatings with the possibility of changing their color where the substrate may be a tool or any other functional product such as kitchen utensils, parts of bathroom accessories, sports aids, accessories for personal use and the substrate is tool steel, carbide solid, metal, metal alloy , ceramic, nitrated or otherwise treated surface, characterized in that they consist of the following layers: c) a lower protective layer of hard coating that protects the substrate from wear and corrosion, d) an intermediate reflecting layer that reflects light well in the visible part of the spectrum and protects the substrate from wear and corrosion; e) visible light cream partially permeable layer that protects the substrate from wear and corrosion and determines the color of the substrate together with the intermediate layer. Coatings according to claim 1, characterized in that the lower protective layer is made of materials such as nitrides, carbides, carbonitrides, oxides and borides. Coatings according to claim 1, characterized in that the intermediate reflecting layer is of a material which has a high reflectance in the visible part of the electromagnetic spectrum and is of materials such as nitrides, carbides, carbonitrides, borides, metals or alloys. Coatings according to claim 1, characterized in that the top layer is between 1 nm and 300 nm thick, which transmits some of the visible light and is made of materials such as nitrides, carbides, carbonitrids, oxides and borides. Coatings according to claim 0, characterized in that the layers are made by physical vapor deposition processes such as vaporization or sputtering.