WO2011101001A1

WO2011101001A1 - Metal component with marking and a method for manufacturing a metal component with marking

Info

Publication number: WO2011101001A1
Application number: PCT/EP2010/004203
Authority: WO
Inventors: Julius Nickl; Max Diedering; Tom NÄKE
Original assignee: GWP Gesellschaft für Werkstoffprüfung mbH
Priority date: 2010-02-19
Filing date: 2010-07-09
Publication date: 2011-08-25

Abstract

The present invention relates to a metal component comprising a marking of optically active particles in at least part of the surface layer of the metal component. The metal component is characterized in that the marking is introduced into the surface layer during the manufacturing of the component. Furthermore a method for manufacturing a metal component with a marking is disclosed. The method is characterized in that a marking material in the form of optically active particles or precursors of optically active particles are added to the material of the metal component during the manufacturing of the component and are transported to at least part of the surface layer of the metal component.

Description

Metal component with marking and a method for manufacturing a metal component with marking

The present invention relates to the marking of metals. In particular, the present invention relates to a metal component with a marking and to a method for manufacturing a metal component with a marking. The component will hereinafter also be referred to as a work piece.

The reliable identification and authentication of solid metal components and also metal coatings of components or coatings on metal substrates is starting to assume a more prominent role in metal manufacturing and in coating technology as well as in the field of the components and aggregates originating there from. The main reasons being that the back tracking of parts or components is desirable for quality management purposes. Furthermore, distinguishing of similar components which originate from different manufacturing processes is desirable. In addition, it should be possible to prove the manufacturing date for warranty purposes. Finally, it should be possible to identify OEM parts and unauthorized copies. In addition to identification of a component as such, also the identification of a coating batch may be desirable. Protection against counterfeits plays an enormous role in a business that produces high-quality design products. The protection against plagiarism plays an important role, the more a company produces and, the more secure the know-how is being held.

Casting of metallic components or work pieces is one of the most important and affordable methods of master forming. Nowadays many metallic components which may also be referred to as metal components are not marked at all but are solely identified at the resulting products. The marking on a cast metal component may be a forged number or a plate made of sheet metal. Important cast components may - depending on the field of application - be provided with an ingot, laser marking, or forged and needle punched number, which refers to the origin and to the manufacturing of the components. These numbers, however, only refer to the component and not to the production process with the respective melt batch or coating batch. In addition, these numbers are easy to counterfeit. Only a complex comparison of chemical and metallurgical analysis of the component or work piece with respective withheld samples may eventually lead to the identification of the component or coating.

In particular, marking of metals in the volume, i.e. in the mass of the component, is currently not performed to a considerable scale. Markings are for example given by metallurgical particularities such as high sulphur content in antique iron, a specific alloy composition, typical microstructure or impurities of specific ore deposits. These markings are, however, not suitable for industrial marking of mass products, because suitable reading devices are typically expensive laboratory devices and need expertise. In addition, the marking may only give an indication of the composition of the metal but can not provide further information such as the manufacturing date.

Also coatings of metal components are currently not marked to a considerable scale, so that a back tracking of the coating or the component which comprises the coating is currently not possible for mass products.

The problem to be solved by the present invention is thus to provide a solution for reliably marking components and their coatings which are at least partially made of metal. The present invention is based on the finding that this problem can be solved by appropriately including marking material in a metal structure.

According to a first aspect, the present invention thus relates to a metal component comprising a marking of optically active particles in at least part of the surface layer of the metal component. The metal component is characterized in that the marking is introduced into the surface layer during the manufacturing of the component. A metal component, which will hereinafter also be referred to as a work piece or product, according to the present invention is a component which at least partially consists of metal. The metal component may comprise a substrate or main body and a coating, which at least partially covers the surface of the substrate or main body. The substrate or main body may also be referred to as the core of the component. In this case, at least part of the coating represents the surface layer of the component, in which the marking is provided. Alternatively, the component consists of a single body, i.e. no coating is provided separately to the substrate but the uppermost layer of the component represents its surface layer, where the marking is provided. In this case, preferably the entire component consists of metal. According to the present invention also a work piece or product which is made of metal containing material is considered to be a metal component. Preferably at least part of the surface layer is made of metal. The surface layer may be of the same material as the underlying substrate or main body of the component.

The manufacturing of the component comprises the forming of the component or a substrate or main body thereof. The forming may be done by manufacturing methods such as casting. Furthermore, the manufacturing of the component according to the present invention may comprise manufacturing steps such as coating of a substrate of the component. In the latter case, the coating preferably at least partially consists of metal, whereas the main body of the component may consist of other materials such as ceramics, plastics or composites.

The metal which is used to form at least part of the marked component, may for example be iron, aluminium, zinc, manganese, nickel or titanium as well as their alloys. For the marking according to the present invention optically active particles are being used. According to the present invention, optically active particles are particles which either possess an inherent optical activity or which present an optical activity upon activation or excitation. Activation may be performed by irradiation, in particular irradiation by light. The optically active particles preferably posses luminescent properties. Luminescence herein denotes the process wherein energy absorbed by the particles is being irradiated from the particles without causing thermal oscillation of the atoms of the particles. One advantage of this preferred property is thus that the temperature of the surface wherein the particles are included, does not change during activation or excitation. In addition, luminescence characterizes the luminescent substance within the optically active particle. Preferably, the luminescence of the optically active particles follows the mechanism of phosphorescence. The phosphorescence herein denotes a special form of luminescence wherein energy is being stored between the adsorption and emission by holding the electron which causes the emission for a certain period of time. Thus the phosphorescence differs from the fluorescence. However, also fluorescent substances may be used for the optically active particles of the present invention. The emission from the particles may comply with the Stokes rules. This means that the radiation emitted from the substance has the same or a lower frequency as the radiation used for excitation of the substance. Substances, where the frequency of the emitted radiation is lower than the frequency of the radiation used for excitation, are also referred to as down-converting substances. According to the present invention, however, also substances emitting radiation of a higher frequency as the radiation directed to the substance. These substances are also referred to as up-converting substances.

The optically active particles are preferably added in an amount and particles size which is small enough to not affect the mechanical or chemical properties of the component and which are not visible to the human eye. The amount and particle size, however, are chosen to be large enough to allow for detection of the particles within the component, in particular in the surface of the component by irradiation. The optically active particles may be organic or inorganic by nature. In particular, ceramic particles have proven to be suitable for the inventive markings.

In particular, the optically active particles may comprise - chalcogenides like oxides, sulphides

- halides like fluorides, chlorides, bromides

- salts like BaZrO3, NaYF4, phosphates, vanadates, sulphates, cyanides, carbonates including mixtures

- Ill/V- and ll/VI-compounds like GaAs or ZnSe

- chelates and aromatic cyanides

- silicon

The characteristics of the particles may comprise

- dye-doped xerogels and aerogels,

- core-shell structures like CdSe/ZnS

- nano-shaped like nano-Si

Preferably the particles are doted or doped with transition elements and rare earth materials. Preferably doped oxides, oxichlorides or oxysulphides of the transition elements, in particular Zr02 or Y203 based materials (host lattice) are used as optically active particles for high temperature processes. Examples are Y203- YOF:Er,Yb, YbOCLEr, La202S:Er,Yb, Y202S: Yb, Tm.

The optically active particles thus are preferably luminescent nano particles (LNP), up-converting phosphors (UCP) or anti-stokes phosphors. The most efficient up- converting phosphors are yttrium-based inorganic crystals, such as yttrium fluoride (YF3), yttrium oxide (Y2O3), yttrium oxysulphide (Y202S), and sodium yttrium fluoride (NaYF4), in which Yb3+ as the absorber and a second trivalent rare earth ion (Er3+, Tm3+, Pr3+, Ho3+) as the emitter are co-doped. These inorganic crystals may be excited by multi photon excitation process of IR up-conversion. The IR to VIS (infrared to visible) conversion is about 1 - 3 % by excitation with 980 nm 1 W / cm2. Also other anti-stokes-luminescent material may be used. For example, when distributed up-converting phosphors are irradiated with wavelength of 940 and 980 nm (IR), respectively, light in the infrared, visible or even UV- range will be emitted by them.

According to the present invention presence of the optically active particles, in particular the emission of the optically active particles can be read and metal components, such as castings and/or coatings of metal components can be identified. For this identification a conclusive process for sustainable inclusion or application of luminescent particles with metallic castings and coatings is provided by the present invention.

Luminescent inorganic particles which may be used as optically active particles undergo a complex, multistep manufacturing process, which requires equivalent complex devices and know-how. It has, however, been found that the ceramic particles can be detected in such small quantities that they can be introduced or applied to a metal component and are not visible to the human eye. The optically active particles according to the present invention can even be detected through other materials. For example detection of the marking through packaging of the product is possible.

The particles which are used as the material for the marking according to the present invention may have a size of 20 μιη or smaller, e.g. 3 to 5 pm. Also particles of a size in the sub-pm-range, in particular nm-dimensions, may be used. The optically active particles may have an element composition, for example of Er, Yb-doped Y203 or In- doped Sn02. The particles are sufficiently fine and luminescent that a concentration which is not visible for the human eye is sufficient for the detection.

The intensity of emission (yield) and the wavelength (colour) are strongly dependent on the size, shape, crystallinity and size distribution of the particles. Optically active particles which are used for the marking of the present invention may be produced by preparing particles doped with trivalent rare earth ions in a precipitation method. Herein a transition metal may be dissolved together with trivalent rare earth (RE) oxides in nitric acid. The solution is aged and hydrocarbonate particles are co- precipitated. Subsequently, the particles are dehydrated, calcinated and sulphurised. Finally, the particles may be encapsulated. High quality up-converting phosphors may be produced with precise control of particle size, morphology, and a very homogeneous distribution of rare earth salts. For example, Y202S particles have been found to emit sharp and intense luminescent peaks. In order to synthesise the Y202S phosphors, yttrium hydroxycarbonate particles doped with trivalent rare earth ions may be prepared using a homogenous precipitation method. In this process, yttrium and rare earth oxides are dissolved in nitric acid. Spherical hydroxycarbonate particles are co-precipitated after ageing the solution at well defined conditions, e.g. YO(H20)n + NH2-CO-NH2 + RE3+-> Y(OH)(C03) H20 : RE3+

After dehydration, calcination the last step is a sulphurisation at 850 °C where part of the oxygen is replaced by sulphur, resulting in Y2O2S:RE3+

The Y202S particles may further be encapsulated with a uniform layer of amorphous silica or titania using a sol-gel approach based on the hydrolysis of tetraethyl orthosilicate or tetraethyl titanite, to convert the particles into inert, stable or wettable up-converting phosphors.

According to the present invention, the marking is introduced into the surface layer of the component during the manufacturing of the component. In particular, the material for the marking, i.e. the optically active particles or precursors thereof, are added during the manufacturing of the metal component. For example the precursors may be hydroxycabonates which are calcined during the mixture with the molten metal.

As the manufacturing of the metal component may comprise several steps, the addition of the optically active particles may be performed during one or more of these steps. If the manufacturing of the component only comprises the forming of the component, such as casting of the component, the optically active particles are added during this step. If the manufacturing includes the step of coating a substrate, the addition of the optically active particles preferably is performed during the coating step. The coating step is the step of the actual forming of the coating layer. This is preferably done on the substrate. The present invention, however, also comprises components where the coating layer which is to be applied to the surface of a substrate is prepared before the application to the substrate. In this case, the manufacturing of the component comprises the generating of a coating layer which is then subsequently applied to a substrate. In this case, the coating layer may be prepared as a sheet or foil to be applied to the surface of the substrate. The surface layer of the metal component according to the present invention is the upmost or outmost layer of the metal component and may extend into the mass or volume of the component. The surface layer, where the optically active particles are present, may have a depth of up to 1 mm. The inventive metal component where the marking is provided in its surface layer during the manufacturing of the metal component is advantageous, as the distribution of the marking material as well as the depth of the surface layer which includes the marking can be adjusted. The inventive metal component may include the marking material in a surface layer of greater depth and in a defined distribution compared to conventional marking methods. Hence, wear of the component will not disadvantageously affect the marking of the material. Even if the marking is only present in a coating layer of the metal component, the inventive introduction of the marking material during the manufacturing, in this case during the coating, allows for a inclusion of the marking material in the coating material which is strong. The inclusion of the optically active particles into a prepared coating layer is performed during the forming or generating of the coating layer. The inclusion may thus be performed before or during the application of the coating layer to a substrate of the component.

It has been found by the inventors, that despite the fact that the marking material is thoroughly included in a metal matrix or metal-containing matrix, the detection of the particles is still possible. In addition, the detection of the marking can be performed by use of a simple reading device. Such reading devices may be hand held devices which integrate an emission source, filter, detector and output. The emission is for example done by LEDs of total 10 - 100 mW power which illuminates the optically active particles in the component. In the vicinity of the emitter the detector is provided which may be shielded by an optical filter. Internal intelligence converts the emission/remission properties to a no/yes signal, a display or a read out. Commercially available devices for such detections are for example available from Sensor Instruments Entwicklungs- und Vertriebs GmbH in 94169 Thurmansbang, Germany.

According to one embodiment of the invention, the metal component comprises a metal coating and the marking is included in the coating, i.e. in the coating layer. The metal coating represents the surface layer of the metal component or at least part of the surface layer. In particular, the coating may comprise several layers of different materials. The coating may also be provided on the entire surface of a substrate or main body of the component or may only be provided in limited areas of the surface of the substrate or main body of the component. The metal coating may consist of metal or metal alloys. It may, however, also consist of other metal containing materials such as metal oxides.

By using a metal coating, the mechanical properties of the component can be improved. In particular, the wear or crack resistance of the metal component may be increased. As the marking is included in the coating and is introduced into the coating layer during the coating process, the distribution of the marking material may suitably be controlled. Marking enables the control of a coating process to ensure a complete and homogeneous layer and is suitable to easily detect failures or flaws, like for example missing areas.

According to a different embodiment, the metal component is a metal casting and the marking is present in the casting skin of the metal component. In this case, the marking material may be introduced into the molten metal batch before or during the casting step. In particular, the marking material may be added to the molten material. At this stage, the optically active particles are homogenously distributed in the molten metal. During the casting process, e.g. die casting, the particles may accumulate in the casting skin, due to the interaction of solidification and flowing. As the particles are present during the solidification, the partial oxidation and the forming of the casting skin, the particles are firmly included in the metallic matrix. As the particles, however, are present in the surface layer of the component, the detection thereof by irradiation is still possible. Finally, as the surface layer in this embodiment is not separately applied to the component but merely represents the outer layer of the metal component, a peeling off of the surface layer can be avoided. In addition, the outer dimensions of the metal component do not have to be changed to be able to apply the marking, as it is included in the surface layer. This is in particular advantageous for metal components where a limited manufacturing tolerance applies.

According to one embodiment, the distribution of the marking material in the surface layer is discontinuous. A discontinuous or inhomogeneous distribution of the marking material is advantageous as the marking may be used as code or pattern. In this case, the marking serves for more than a mere identification of components, but may provide additional information. For example the date of manufacturing, the name of the manufacturer, a graphic and other information may be included. Thereby, counterfeit products may easily be detected. The discontinuous distribution of the particles is possible, as according to the present invention, the marking material is introduced into the surface layer during the manufacturing of the metal component. Therefore, the surface of the metal component may be smooth, which is not possible with conventional codes which are applied onto a surface by, for example, printing. As the surface of the inventive component may be smooth, the risk of peeling off of the code from the surface, which exists with printed codes, does not exist. In addition, tampering with the code by mechanical force is also not possible, as the code is included in the surface layer which is made of metal. Where the marking in the form of a code is included in a coating on the component, the discontinuous distribution of the marking material may be achieved by interrupting the addition of the marking material during the coating process or by shielding parts of the surface of the main body to avoid adhesion of the marking material. According to one embodiment, the marking material comprises a mixture of optically active particles or of precursors of optically active particles. By using a mixture of particles, the optical properties of the marking material may be altered according to the current needs. Thereby, the identification or coding of a component or its coating may be detected in a more reliable fashion. The mixture may be a physical mixture of particles having different emission spectra. By overlapping of individual spectra a unique emission spectrum may be achieved, which makes the identification even more reliable. The effect of possible secondary excitation gives an even more complex emission spectrum, suitable for identification. The resulting emission spectra of a surface wherein optically active particles are included are dependent on various factors. These factors include:

- excitation energy, excitation intensity, excitation wave length distribution, exposition time

- surface characteristics like concentration of optically active particles, availability of optically active particles to light, roughness and porosity emission detection: sensitivity, resolution, emission decay

- signal processing: start and end of recording, threshold, underground, peak fit, calibration, decay analysis.

By being able to adapt the properties of the optically active particles by selection of amount, distribution and size as well as by kind of particles and mixture of kinds of optically active particles, the detection of the particles within a metal component can be optimized.

According to a further object, the present invention relates to a method for manufacturing a metal component with a marking. The method is characterized in that a marking material in the form of optically active particles or precursors of optically active particles are added to the material of the metal component during the manufacturing of the component and are transported to the surface layer of the metal component. Precursors of optically active particles are agents which under manufacturing conditions of the metal component will react or transform to create optically active particles. Precursors may for example be carbonate intermediates that will transform into oxides under heat of casting, e.g. 850 °C. The addition of the optically active particles or precursors thereof may be performed by mixing the particles or precursors into molten metal. In addition or alternatively, the particles may be provided in a mould release agent or a blackening of a mould. In the latter case, the particles will enter the surface layer of molten metal which is poured into the mould from the outside and will accumulate in the surface layer. Finally, the particles may be added as an agent or in an agent of a coating process. The agent may for example be a bath for galvanic coating, a cathode for plating, a powder or gas for a spray coating. In this case, the accumulation in the surface of the component occurs by means of the forming of the coating itself. Where the particles are provided from within the volume, e.g. by mixing them with molten metal before casting, the transport of the particles to the surface layer is preferably effected by change of temperature. In this case, where the particles are added to molten metal, the transport will occur due to solidification. Remaining particles in the bulk casted metal will be at very low concentration and the particles are homogeneously distributed so that no negative influence to mechanical or chemical behaviour appears. Where the particles are provided in a coating, the transport to the surface of the component will be carried out by means of application of the coating agents or a coating layer on the surface of a substrate. The application of the coating or coating layer may be performed by physical, chemical or other application methods. In particular, mechanical, electrochemical, thermal application methods or combinations thereof may be used. The coating may for example be applied by melting, spraying or electro chemical reactions.

The coating process may use the coating agents in different state. In particular, the coating may for example be effected from a liquid state of the coating agents. This coating may preferably be coating by hot dipping, hot-dip galvanizing or hot-dip tinning. Furthermore the coating may be effected with a coating agent in a kneadable state. In this case the coating process may be stopping. Furthermore the coating may be effected from a solid, granular or powder state of the coating agent. In this case the coating process may be electrostatic coating or thermal spraying. Also a coating from an agent in the gas or vapour state may be effected. This coating processes may for example be vacuum deposition. Finally the coating agent may be used in an ionized state. In this case the coating process may be a galvanic or chemical deposition. The coating may also be applied by means of welding or soldering.

The coatings that may be obtained with the inventive method may for example be a hot-dipped metal coating, a electrolytic metal coating, a diffusion coating, a plated coating, a thermally sprayed coating, a vacuum deposition coating or a metal coating obtained by deposition with or without external power source.

In all coating methods the optically active particles according to the present invention are added during the coating process. Where the coating is effected by welding, the optically active particles, with or without additional coating material, may for example be spread over the surface to be coated and subsequently the welding torch is directed to the surface, whereby the torch flame will melt part of the material of the surface and will thus introduce the optically active particles into the surface layer. This method is advantageous, as for example the whole surface may be covered with the optically active particles and only limited areas of the surface may be welded. Thereby, a code, writing or other pattern may be produced on the surface. Alternatively, if a code, writing or layer is desirable, the optically active particles may be added to the surface only in predetermined limited areas and subsequently the entire surface may be welded by line or spot welding. According to the present invention, the optically active particles may also be added to the welded coating, by using a process gas of the welding process which is contaminated with the optically active particles. In this case, the optically active particles will only be present after the coating in the areas where the surface has been welded. The process of coating by welding is schematically shown in Figure 1.

In Figure 1 a substrate 1 is shown, which may be a steel plate. The upper surface of the substrate 1 is dusted with optically active particles 5, as indicated on the left hand side of the substrate 1 in Figure 1. A burner 3 is positioned above the surface of the substrate 1 and is moved over the area of the surface. The process gases of the burner 3 are provided through the inlet pipes 31 , 32 of the burner 3. In the depicted embodiment, the burner 3 is a conventional welding torch. However, also other burners 3 may be used. For example, a plasma burner or an arch welding torch may be used. The burner 3 may be manipulated, to weld the surface of the substrate 1 along lines as indicated by the double sided arrow in Figure 1 and may be moved over the entire surface of the substrate 1. Alternatively, the burner 3 may be manipulated to only provide a flame towards the surface on predefined spots or areas of the surface. In the first case the entire surface of the substrate 1 will be provided with a marking made of the optically active particles 2. In the latter case, a pattern or code of the optically active particles in the surface layer of the substrate 1 may be formed, as shown in the right hand side of the substrate 1 of Figure 1.

Where the coating is applied by hot dipping, the optically active particles may be added to the hot melt before or while the substrate to be coated is immersed into the smelt. The optically active particles will be firmly included in the resulting plated coating.

The addition and the transport of the optically active particles may occur simultaneously. In particular where the marking is formed in a coating layer, the addition of the marking material to the coating material will preferably be carried out during the transport of the particles to the surface. For example in a spray coating process, the particles will be added to the coating material, when the coating material is already directed to the substrate or main body of the component. Where a film or foil of coating material which includes the optically active particles is produced and then applied onto the surface of a substrate of a metal component where it will be attached by melting or other mechanisms, the addition and the transport of the optically active particles is carried out subsequently.

One advantage of adding the marking to the material of the component and transporting the particles to the surface layer during the manufacturing of the metal component, is that the amount of marking material, its distribution, composition and even physical mixtures of optically active particles, such as LNP, may be altered during the process. An additional advantage is that also the depth of the surface layer, where the marking is included may be chosen to have a greater depth without having to change the outer dimensions of the metal component.

According to one embodiment, the optically active particles or precursors of the optically active particles are added to a coating material during the coating of the component. In addition to or alternatively to merely being able to identify the metal component, this embodiment also allows for an identification of the coating. Thereby the coating batch, the producer of the coating and other information may be derived from the marking in the coating. The coating of the component during which process step the optically active particles are added, according to the present invention includes the forming of the coating layer. This forming of the coating layer may be performed on the surface. In this case the optically active particles are added during the application of the individual components of the coating material onto the surface of the substrate. If the coating layer is formed before being applied to the surface of the substrate, the optically active particles will be added to the coating layer during its forming, e.g. pressing or rolling. Alternatively or additionally, the optically active particles or precursors of the optically active particles may be introduced into molten metal before casting of the metal component. This embodiment is advantageous for mass products which are exposed to wear.

According to one embodiment, the coating is a metal coating and is applied by spray coating or electro chemical deposition. Hence, the invention also relates to the marking of sprayed or galvanic coatings with optically active particles. In case of spray coating the particles or precursors may be added to the process material, i.e. to the spray coating precursors, in particular powder, gas, fuel and additives. The optically active particles or precursors of the particles may also be added to the pulverized, vaporised or molten coating material. In a high speed cold gas coating process the optically active particles may be used as coating material. The particles may also be added as powder on the surface of molten metal. In electro chemical deposition processes, the optically active particles may be present in the bath of the deposition process. Thereby, the particles will be included in the deposition layer on a substrate or main body which is to be coated. Alternatively, the particles may be included in the cathode material of the deposition process. In this case, the particles will migrate to the bath during the deposition process and will eventually be included in the coating. The electro chemical deposition may be performed with or without external input of electric energy. The metal coating may consist of gold, silver, copper, nickel, zinc, iron, chromium, aluminium and/or tin including their alloys.

In an alternative embodiment, the metal coating may be applied by preparing a foil or sheet of metal powder comprising the optically active particles and placing the foil or sheet onto the surface of a substrate of the component. The powder will preferably have such a composition, that it can be ignited, i.e. that an exothermic reaction will occur. Due to this thermal energy the powder will melt and will be firmly attached to the surface of the substrate. The coating layer including the optical particles will thus be soldered or welded onto the surface of the substrate. Powders that may be used for such a coating sheet or foil may for example be nickel and aluminium. As the optically active particles are included during the production of the sheet or foil, the amount and distribution within the film or foil can easily be adjusted and controlled.

Generally, coatings are used for decorative purposes, and to enhance both corrosion and wear resistance as well as electric conductivity and to protect against plagiatism. The inventive coating of a substrate or main body of the metal component may comprise several layers. For example a connecting or adhesion layer may be provided on the substrate, the optically active particle containing film will be provided on top of the connecting or adhesion layer, which again may be covered with a transparent, wear resistant ceramic layer, e.g. silica or thin oxide. In another example, a diffusion stopping interlayer is bonding the active particle containing layer to the substrate

According to one embodiment, the optically active particles or precursors of the optically active particles are pre-treated before being added to the material of the metal component. Pre-treatment according to the present invention may be a mechanical or chemical treatment. In particular, the particles may be milled, dispersed, singulated, metallised (by PVD, CVD or galvanic methods), mixed with flux material, mechanically alloyed and/or plasma activated. Also other treatments may be used to increase the wetablity of the particles with metals or the coating material.

The marked metal component may also be subjected to a surface treatment after manufacturing. For example the marked metal component may be anodized. If the particles are deposited on the surface like a pattern, letters or logo before the anodizing process starts, the particles are in a similar pattern incorporated into the resulting metal oxide; this is non-reversal and firmly fixed into the surface.

Advantages and features which are described with respect to the inventive method also apply to the inventive metal component and vice versa. According to the present invention, the optically active particles, for example luminescent ceramic particles, are preferably permanently included in or applied to a casting part or in a coating of a metal component or in part of the casting process, like additives. The particles are mainly present in the surface layer, which may be the upper layer of the metal, the oxide layer surrounding the metal or a coating layer. It has been found that luminescent ceramic particles, in particular LNPs, do not have an adverse influence on the casting process, do not diminish the functional material properties and sustain the further processing steps of the work piece and its final usage. Finally, the ceramic particles can be removed during recycling from the metal. The concentration of the ceramic particles is chosen to be as low as possible but high enough to ensure a reliable detection even after years. The concentration of the optically active particles in the surface layer may for example be in the range of more than 100 ppm (parts per million of weight). The optically active particles may for example be present in the surface layer in an amount of 5 to 50 mg/m2.

The invention will now be described again with reference to an example of a metal component with marking.

Manufacturing of marked aluminium alloy parts:

LNP suitable for the excitation with an wave length of 980 nm (IR) and having an emission wave length of 350 nm (green) is selected. 100 g LNP (Stardust, U.S.A.) having an average particle size of 3 - 5 pm is thoroughly milled with 0g of fluxing agent on a fluoride basis (F30/70), BraceTec, Germany). This preparation is spread on 1 kg of molten aluminium and may be stirred in under gas via an impeller, is further homogenized for 10 minutes at high revolution speed and under an Ar- stream, quality 4.5, of 10 l/min that is introduced into the melt. The preparation is left to rest until dross generation and is then poured under protective gas into 10mm bars. The homogeneity of the 10 percent melt (master batch) is determined from the solidified samples in cross section polish metallographic via EDX mapping and spectroscopic means. In addition, the singulation of the particles is confirmed. This material serves for seeding the melt resources for the aluminium die casting of up to three tons. The melt is enriched by addition of master batch up to 0,1 to 10,0 per mille of weight.

Light metal die casting moulds, such as rims for car tires, are filled via the aluminium die casting method with the seeded melt. During the injection process the LNPs accumulate due to the interactions of the solidification with the further flowing within the casting skin and are present in an increased concentration which is easy to detect by handheld devices without necessitating additional surface treatment. Also in the volume of the product a detectable concentration remains.

Possible features and embodiments of the inventive method for marking a metal component are given in the following clauses

1) Method of producing marked metals as well as components thereof and surfaces with optically active particles, in particular up- or down-converting phosphors or luminiscent nano particles (LNP), characterized in that the method comprises the following steps:

- Selection of suitable LNP (material compatibility, particle size, activation energy, emission, stability), preferably doped oxides, oxysulfides or fluorides of the transition elements, in particular Zr02 or Y2O3

- Pre-treatment of LNP for increasing the wetablity of metals and the treated surfaces thereof (dispersion preparation, singulation, metallising, flux agent, milling, mechanical alloying, plasma activation) and mixing of several kinds of particles

- Introduction of LNP into the metal to be marked, preferably aluminium, zinc, manganese or titanium as well as their alloys

- and applying of LNP into the surface, so that the detectability of the introduced or applied LNP, respectively, is generated.

2) Method according to clause 1 , characterized in that the production of the marking is effected in the liquid metal by introducing either i) LNP directly, ii) suitably pre-treated LNP or iii) LNP precursor agents, which only develop into LNP within the melt, is introduced into a metal melt.

3) Method according to clause 1 , characterized in that the LNP is contained in a pre-treated casting mould, preferably a facing or mould-release agent, and accumulates in the casting skin of the casting work piece.

4) Method according to clause 1 with 3, characterized in that the marking in the surface of the marked metal is made durable and visible by surface treating the work piece, preferably by anodising and integrating the LNP into the layer.

5) Method according to clause 1 and 4, characterized in that metals, preferably aluminium, are anodised with an electrolyte containing LNP and the LNP is integrated into the layer.

6) Method according to clause 1 , characterized in that LNP is mixed into the powder mixture of sinter components and due to the sinter process is present in the work piece in a distributed fashion.

7) Method according to clauses 1 , 3, 4 and 5, characterized in that LNP's are not homogenously distributed over the surface and represent a pattern or code.

Hereinafter the marking of components with marking material included in a coating layer will be described again in detail.

Marking of components by spraying

Spraying methods mainly comprise thermal spraying methods. These are considered to be important physical surface treatment and coating methods. With spraying, a surface coating of metallic, non-metallic and combined nature can be applied on almost any substrate. The fields of application are numerous. They reach from wear protection spraying on construction machines to the erosion protection layers on components for the aerospace industry. The main methods which may be used for the present invention are:

1. Plasma spraying 2. High velocity oxygen fuel spraying (HVOF)

3. Powder flame spraying

4. Wire flame spraying

5. Arc spraying

6. Laser spraying

7. Detonation spraying

8. Cold gas spraying with high gas velocities

One advantage of applying the coating onto the substrate or main body of the metal component by spray coating is that local coating, i.e. limited to a certain area of the substrate or main body, is possible. Such local coating can be used for partial coatings, logos, codes and combined also overlapping coatings.

A schematic set-up for plasma spray coating a substrate of a component with a coating layer including optically active particles is shown in the attached Figure 2.

A plasma source 4 is directed towards a substrate 1 on which a coating 5 is to be formed. Optically active particles 2 are added into the plasma flame 41 emerging from the plasma source 4. The optically active particles 2 may be added as a powder through a delivery pipe 6 or a rod including the optically active particles 2 may be brought into the plasma flame 41. At the same location or at a different location also powder of the coating material is added to the plasma flame 41. Thereby, a coating layer 5 wherein the optically active particles 2 are included is formed on the substrate 1. The addition of the optically active particles 2 may also be performed discontinuously. In particular, it is possible to alternately add coating material and optically active particles 2 to the plasma flame 41.

Galvanic coating

A different way of applying the coating according to the present invention is the electrochemical deposition of metallic precipitates (covers) on objects. Typical coatings are for example chromium plating, copper plating, nickel plating and zinc plating. The functional electroplating for example serves for corrosion protection, wear protection, catalysis or for improving the electrical conductivity. The functionality of plated covers can further be specifically influenced by inclusion of foreign particles. For example, diamonds or polytetrafluoroethylene particles may be included in a nickel layer.

According to the present invention, marking of galvanic coated work pieces as well as the targeted marking of work pieces via entire or local application of galvanic covers containing optically active particles such as LNP und the identification via suitable reading devices is disclosed.

For detecting the particle containing coatings commercially available devices of TechNeo GmbH or Sensor Instruments GmbH can be used. The general set-up of such devices has already been explained above.

The marking of a metal component by including the marking into a coating layer will now be described again with reference to two examples. Example 1)

Production of an iron substrate marked by plasma spray coating

With plasma spraying a powder or wire shaped coating material is processed. Herein the powder or material is partially or entirely melted by means of a plasma flame, is then distributed und sprayed onto a substrate. Typical coating materials are the following, wherein also combinations thereof may be used.

Oxides: AI2O3 / Cr2O3 / ZrO2 / SiO2 / TiO2 / Y2O3 etc.

Metals: Mo / Al / Ni / Zn / Fe / Si / Ti / Cu / Co / Cr / Wo etc.

Carbides: WC / Cr3C2 etc.

Plastics and composites: PA, PE, Teflon, CSiC

In the present example the following layer system is applied: Substrate: Iron

Adhesion base coating as connection layer between substrate and subsequent ceramic layer: "450 NS" (Sulzer Metco); this material is a powder mixtures of Nickel and Aluminium. Chemistry: Ni5AI

Particle Size: -90 +45 pm (-170 +325 mesh)

Morphology: Clad

This coating is dense and resistant to oxidation and abrasion. The coating is self- bonding and undergoes an exothermic reaction during spraying, resulting in excellent bonding to the substrate. The coating can be used up to 800°C (1470°F) as an oxidation resistant bond coat.

Ceramic cover layer AMDRY 6200 (Sulzer Metco); AI2O3, Ti02

Chemistry: AI203:Ti02 3:1

Particle Size: 22 +5 pm

Morphology: Angular / Blocky, Fused and Crushed

This coating provides resistance to abrasive wear, sliding wear and oxidation for service temperatures up to approximately 1100 °C. LNP: LUMILUX or LP-6922

Chemical composition modified Rare: Earth oxysulfide

Fluorescence colour green

Emission peak ~ 550nm & ~ 670nm

Required excitation wave length 980 nm

Medium particle size (Coulter Counter) 4.5 pm to 0.5 pm

Density 4.9 g / cm3

For the connection layer approximately 30g LNP LUMILUX Griin UC 2 of Honeywell or LP-6922 was added to 330g 450 NS (particle size 170-325 pm). For the ceramic cover layer approximately 30g LNP LUMILUX Grun UC 2 of Honeywell or LP-6922 was added to 330g AMDRY 6200 (particle size 17-27 μιη).

The materials were successively applied to the iron substrate via plasma spray coating.

During solidification, the LNP distributes homogeneously in the texture of the sprayed layers. In the layers a concentration of LNP which is easy to detect is present. Also a after a wear (thinning of the spray layer) a sufficient amount of LNP for detection remains at the surface. Due to the defined powder mixture both the coating as such as well as the final coated work piece are marked.

Example 2)

Production of marked galvanic nickel covers

During electrolytic nickel deposition on a steel sheet an electrolysis cell is used, which consists of a nickel anode, a steel cathode and a Watts bath.

The steel plate which is to be nickel plated is pre-treated with acetone and by electrolytic etching with 5 mol/l H2SO4 to activate its surface for the nickel plating. Subsequently the pre-treated steel plate is covered with nickel in a galvanizing cell.

The Watts bath contains at least a LNP portion (LUMILUX Grun UC 2 of Honeywell) of 200 ppm to obtain a detectable interaction with IR irradiation. The particle size of the LNPs is approximately 15 μηι.

With concentrations of 2, 0,2 and 0,02 % LNP in the Watts bath, the LNPs can also be detected with a portable test device.

The marking may also be effected locally at a determined location of the work piece. For this purpose the surface which is not supposed to be galvanized is screened with an inert material, so that no contact to the electrolyte is established. The surface which is to galvanized will be activated and is nickel plated with a LNP containing Watts bath. Subsequently the inert material is removed from the surface.

Alternatively to spray coating or galvanic coating a coating layer may be applied to a substrate by a melting process, which can also be referred to as a soldering or welding process. In this process, a coating foil or sheet is produced from metal powder mixed with LNP. The powder may for example have a composition of 3 parts nickel (Ni), 1 part aluminium (Al) and 1 per mille LNP. This mixture is formed into a sheet or foil. The foil is subsequently applied to the surface of a substrate, for example an iron substrate. Once applied to the surface, the foil will be ignited. Due to the exothermal reaction of nickel and aluminium, the foil will be melted or welded onto the surface of the substrate, thus forming a coating layer thereon. The LNP which were included in the foil will be present in the thus created coating layer and available for excitation/emission.

Possible features and embodiments of the inventive method for providing a marking in a coating of a metal component are given in the following clauses

1) Method characterized in that spray layers of metal, metal alloys, ceramics, composites, plastics and mixtures thereof are marked with optically active particles and that this leads to a detectable coating.

2) Method characterized in that a galvanic coating process for metallic coatings, preferably of gold, silver, copper, nickel, zing, iron, chromium, aluminium, tin is selected and the inclusion of optically active particles leads to a detectable coating. 3) Method according to clause 1 and 2, characterized in that appropriate optically active particles with an activation and emission it the infrared, visible or UV range are used for markings relating to material compatibility, particle size, activation energy, emission, detectability. 4) Method according to one of the above clauses, characterized in that inorganic particles, preferably oxides, fluorides, phosphates, sulphides or transition elements and rear earths mixed with anions, such as for example oxysulphides, mixed, preferably doped; is used as optical active particle

5) Method according to one of the above clauses, characterized in that organic- containing, optical active particles are used.

6) Method according to one of the above clauses, characterized in that physical mixtures of optically active particles are used and by overlapping of individual spectra a unique emission spectrum is activated, which serves for identification.

7) Method according to one of the above clauses, characterized in that optical active particles are added to the process materials, i.e. spray layer precursors, in particular powder as well as gases, fuel and additives, before the spraying process.

8) Method according to one of the above clauses, characterized in that optically active particles are added to the pulverized, dispersed and melted coating materials during the spraying process.

9) Method according to clause 1 , characterized in that optically active particles as coating material impact onto the work piece at a high speed in a cold gas coating process and adhere after their impact.

10) Method according to one of the above clauses, characterized in that optically active particles are applied as coating material in powder form onto partially melted work piece surfaces, adhere and are optically detectable.

11) Method according to one of the above clauses, characterized in that the coating is interrupted and represents an optically detectable, machine readable writing, logo or code.

12) Method according to one of the above clauses, characterized in that optical active particles are distributed in the bath during a galvanic deposition process and are deposited.

13) Method according to one of the above clauses, characterized in that optically active particles are present in the cathode material, distribute during the deposition process and are deposited. 14) Method according to one of the above clauses, characterized in that optically active particles are homogeneously present on the work piece or are locally present as a writing or code and establish a solid adhesion due to the galvanic deposition process.

15) Method according to one of the above clauses, characterized in that optically active particles are present in a distributed fashion in the bath during an electroless deposition process of metals, in particular of chemical nickel and are deposited.

16) Method according to one of the above clauses, characterized in that the marked coating is applied onto metals, ceramics, composites, plastics or other substrates and work pieces.

17) Method according to one of the above clauses for marking of components.

The excitation and detection of optically active particles within the surface layer of a metal component is schematically shown in Figure 3.

The substrate 1 as shown in Figure 3 is a rod. In the depicted embodiment the entire surface of the substrate 1 is covered with a coating layer 5. Within a predefined area 51 optically active particles 2 are included in the coating layer 5. The coating layer 5 is shown as a multilayer. In the depicted embodiment the coating layer 5 consists of two lower layers 50' and 50" as well as the top layer 50, wherein optically active particles 2 are included. The optically active particles 2 may be detected by a detection device or reader 7. The reader 7 may be a handheld device which comprises a light emission source 71 , for example in form of an LED (light emitting diode). In addition, a detector 72, for example a photo diode, is provided in the reader 7. If this reader 7 is positioned over the surface of the component, light which is emitted from the emission source will be absorbed by the optically active particles 2. The thus excited optically active particles 2 emit light waves, which will be detected by the detector 72 of the reader 7. The wave length of the light emitted by the optically active particles 2 will depend on the nature of the particles as well as the excitation or irradiation which is provided by the light emission source 71. With the present invention, a solution for reliably marking a product which is at least partially made of metal is provided. The core of the present invention is that optical active particles are used for marking the product and. that these particles are introduced into the surface layer of the metal component during the manufacturing thereof. The marking may be included in an outer layer of a component consisting of a single body or may be included in a coating on a substrate. The coating may consist of metal or metal alloys. However, also other metal containing materials may be used as coating material. In particular, metal oxides may be used as coating material.

Claims

1. Metal component comprising a marking of optically active particles in at least part of the surface layer of the metal component, characterized in that the marking is introduced into the surface layer during the manufacturing of the component.

2. Metal component according to claim 1 , characterized in that the component

comprises a metal coating and the marking is included in the coating.

3. Metal component according to claim 1 or 2, characterized in that the metal

component is a casting and the marking is present in the casting skin of the metal component.

4. Metal component according to anyone of claims 1 to 3, characterized in that the distribution of the marking material in the surface layer is discontinuous.

5. Metal component according to anyone of claims 1 to 4, characterized in that the marking material comprises a mixture of optically active particles or of precursors of optically active particles.

6. Method for manufacturing a metal component with a marking, characterized in that a marking material in the form of optically active particles or precursors of optically active particles are added to the material of the metal component during the manufacturing of the component and are transported to at least part of the surface layer of the metal component.

7. Method according to claim 6, characterized in that the optically active particles or precursors of the optically active particles are added to a coating material during the coating of the component.

Method according to claim 6 or 7, characterized in that the optically active particles or precursors of the optically active particles are introduced into molten metal before casting of the metal component.

Method according to anyone of claims 7 or 8, characterized in that the coating is metal coating and is applied by spray coating or electro chemical deposition.

10. Method according to anyone of claims 6 to 9, characterized in that the optically active particles or precursors of the optically active particles are pre-treated before being added to the material of the metal component.