WO2017134282A1

WO2017134282A1 - Joining of components by means of energetically activated reactive particles

Info

Publication number: WO2017134282A1
Application number: PCT/EP2017/052472
Authority: WO
Inventors: Georgios Dimitrios Theodossiadis; Max Robert BIEGLER
Original assignee: Technische Universität München
Priority date: 2016-02-05
Filing date: 2017-02-03
Publication date: 2017-08-10

Abstract

Described is a method for the integral joining of components, comprising: a) mechanically applying core-shell particles to at least one joining surface of at least one component, wherein the particles are applied via a gaseous dispersant onto the meltable joining surface or via a thermoadhesive liquid dispersant or a thermoadhesive solid dispersant onto the meltable or non- meltable joining surface; b) contacting the joining surfaces of the components to be joined; c) activating the core-shell particles; d) integral joining of the components by the activated particles, as well as adhesion compositions.

Description

JOINING OF COMPONENTS BY MEANS OF

ENERGETICALLY ACTIVATED REACTIVE PARTICLES

Description

Field of the invention

The present invention refers to the connection or joining technology sector, in particular to joining or connecting parts, such as components, by way of metal- containing single-or multi-layered particles optionally in combination with thermal adhesives.

Background of the invention

Many methods are available for connecting components. Important aspects are type and shape of the components, thermal load, expenditure, bond strength, and flexibility. A connection is possible with or without a connecting medium. For instance it is known to connect metallic components by welding, wherein the components have to be heated at least at the joint to such an extent that the material fuses there. Welding requires great efforts, adequate accessibility of the tool, and thermally stresses the parts to be connected.

Another possibility is the integral connection of components consisting of similar or dissimilar materials by using a connecting medium. For instance, reactive adhesives, such as two-component adhesives, or hot-melt adhesives can be used as adhesion promoters or connecting medium for components. Metallic components may also be soldered.

These connecting media, however, entail various drawbacks. For instance, reactive adhesives cure very rapidly without the possibility of correcting possible flaws when joining surfaces of components are put together, so that there remains little time for a user to work accurately. Thermoreactive adhesives or hot-melt adhesives as adhesion promoters or joining medium normally require the supply of external thermal energy for curing with the help of a heating device that is arranged downstream as a further stage in the process. This, however, entails the drawback that all of the components to be joined must be exposed to thermal stress. Moreover, this causes long process times for producing the integral joint connection as well as possible structural transformations of the joining materials by the globally introduced thermal energy. This is also true for joining by way of soldering, wherein solder materials, such as for instance hard solder, are used as joining medium. In this case, too, all of the components to be joined must be heated for hard soldering, which thermally stresses the components on the whole.

Another possibility of joining metallic surfaces is described in DE 10 201 1 008 31 1 . Here, a reactive nickel-aluminum nanofilm is used that is built up of many individual layers of nickel and aluminum, with the layers being each present in nanometer thickness. The individual layer thickness may for instance be in a range between 25 and 150 nm. The total thickness of the film is individually adjustable during production, but there will only be the predetermined thickness available for use. The nanofilm shows a strongly exothermal reaction upon electrical or thermal activation, and reaction temperatures of up to 1500°C and even more can be achieved for a few milliseconds. This thermal energy is to be used in production technology so as to integrally interconnect two components. To this end the nanofilm is centrally positioned between the joining partners and ignited. During the exothermal reaction the joining partners will fuse in the edge region and the firm joining bond evolves after decay of the reaction while a defined compressive stress is applied simultaneously.

However, the known nanofilms have drawbacks. The method for producing nanofilms is cost-intensive and time-consuming. In a vacuum atmosphere, atoms are ejected out of aluminum and nickel targets, for instance by using plasma or by electron bombardment. The detaching atoms will deposit on a substrate. To ensure periodic layer buildup, the targets are alternatingly used. The time spent on the production of such a nanofilm with a total thickness of only a few μιτι is several hours up to days. Moreover, the system technology required is very cost-intensive and can only be handled by experts.

Another drawback is that the ignition of the nanofilm must be carried out by so- called starting flags, i.e. exposed regions that project out of the joining surface. The starting flag as well as the reaction product are brittle and electrically conductive and may cause electric short-circuiting. Although the thickness of the nanofilm can be set during production, the finished nanofilm is invariable in its energy content. Hence, the nanofilm cannot be adapted to the joining process. Moreover, due to the brittle material behavior, it is difficult to connect other joining surfaces as even surfaces.

EP1 927 420 discloses another type of joining. Here, metallurgical bonds of two joining partners are created by superalloys of for instance nickel, aluminum, boron and silicon. The fusion of the superalloy particles takes place by way of microwave excitation, whereby the components to be joined are connected by way of a microwave-induced brazing technique. Here, one resorts to the physical principle that smaller particles are more susceptible to microwave radiation. However, the manufacturing method for such superalloys is very complex. Moreover, this technology can just be used for soldering metallic joining partners. In the method described, an alloy is used as a joining medium and is not produced, so that energy produced during alloy formation cannot be used.

US2012/001521 1 discloses the manufacture of particles with an aluminum core and a nickel cover or shell with the help of a galvanic exchange reaction and their use for producing nanostructures. Nanoparticles in which the core is more or less surrounded by a shell are formed by galvanic exchange reaction. These metallic nanoparticles are applied to the joining surface either by way of suspension application in ethanol or electronically by electrospinning or electrospraying techniques together with polymers, such as polyethylene oxide. Before the joining process can be induced by contacting both components and by microwave radiation, the nanoparticles (maximum average particle size 200 nm) must however be compressed on the substrate by way of UPC (Ultrasonic Powder Consolidation) at high pressures (up to 200 MPa).

Although this connection technique is more independent of the joining surface material than in the previously mentioned processes, the technology is restricted to structures in the nanometer range. The particle size of up to 200 nm is restricted by the electrospinning technology. Likewise, the application for components larger than microstructures is not feasible with this technology. Furthermore, the UPC method for large components is neither financially nor technically qualified. The high stress caused by the high-pressure ultrasound induces damage to the material, for instance microcracks. Furthermore, a high energy is needed for the exertion of high pressures, whilst UPC cannot be applied over the whole surface in the case of large joining surfaces. Moreover, there is an increased safety risk for the user. Furthermore, the electrospinning technology is too expensive for a universal industrial application because of its high voltage needed for the electric field used for electrospinning. Likewise, the application to uneven surfaces is not possible with this technique.

It was therefore the object of the present invention to provide a safe joining or connecting method for micro- and macro-components that can be used as universally as possible and is suited for joining, connecting, bonding, jointing uneven and even joining surfaces, which may consist of the same or different materials, and for joining, connecting, bonding, jointing many different materials.

Furthermore, it was the object to provide a joining medium that can be produced at low costs and on a large scale and that can be used flexibly for different materials and surfaces and can establish or form firm, stable connections.

It was another object to provide a method which can be carried out within a very short period of time and guarantees an energy- and time-efficient working method.

Specifically, a method should be provided whereby both meltable and non- meltable joining surfaces can be joined without a substantial thermal or energetic load on the component.

These objects are achieved with a method as defined in claim 1 and with an adhesion composition as defined in claim 13.

The following definitions are used for the description and the claims of the present invention.

The term "core-shell particle" designates composite particles or joining particles with a central core which is surrounded by at least one shell or cover which may consist of one or more, chemically and/or physically heterogeneous phases, particularly of one element or plural dissimilar metals/elements or different intermetallic phases. At least one shell encases the core completely or substantially completely; it is also possible that more than one shell, such as a few shells can encase the core. These shells, in turn, may consist of an element/metal or dissimilar elements/metals or intermetallic phases. As a rule, the particles are built up such that at least one metal is contained in the shell, e.g. nickel, and at least one metal is contained in the core, e.g. aluminum. The term does not encompass particles produced by electroplating with only a partial envelope.

The terms "shell" and "cover" are interchangeably used.

The term "component" as used in the present description describes a three- dimensional article, such as a workpiece, an element or a unit which has at least one region or area on the surface that can be brought into contact with a surface or a part of the surface of another article and can thereby be connected. The component may consist of any material suited for the manufacture of an article, for instance carbon fiber-reinforced plastic material, elastomer, thermoplastic material, thermoset material, concrete, solder, cement, timber, building block, metal, a metal alloy, ceramic or another material or building material, or any mixture thereof. A component may consist of one piece or may be composed of several pieces or regions. A component may consist of one material or plural materials, or have a core of one or plural materials and be covered with one or plural layers. In other words, the component may have any suitable buildup.

The term "joining surface" designates a surface or a region or a part of a surface of a component that is to be connected to another surface. A joining surface may be any even or uneven material surface of a component or a part thereof, wherein the joining surface is meltable or non-meltable. In the joining process, the joining surface is contacted with at least one further joining surface of a joining partner, wherein an integral or material joining is induced by activation of core-shell particles, as described below.

The term "joining" shall comprise any type of joining, jointing, binding, connecting, bonding, etc. This term designates inter alia the integral, permanent, non- detachable connection of joining surfaces. The term non-detachable means that the connection cannot be disengaged without destruction. The unit formed thereby is also called binding or connection element. The term "dispersant" as is here used designates a carrier medium in which particles can be dispersed (e.g. distributed). The dispersant or carrier medium may be gaseous, flowable or liquid, or solid.

The terms "thermoadhesive" or "thermoreactive" describe an adhesive or reactive behavior which occurs upon energy supply/heat supply whilst an external energy is applied that causes melting or a chemical reaction that will then create an adhesion effect between joining surfaces.

The term "meltable" as used in connection with a material means that the material can be converted by thermal or other energetic influence into a flowable or liquid aggregate state without the material chemically decomposing or corroding significantly.

When the term "contacting" is used, this means that two connection elements or workpieces are spaced apart at a macroscopically minimal distance sufficient to generate adhesion of the two connection elements or workpieces at least in an area by using the inventive method or joining medium of the present invention.

The term "activation" must be understood in the present case in an energetic sense, so that by influence of an external energy source the kinetic activation energy for instance of a core-shell particle is overcome for alloy formation.

The term "integral" describes the mutual adhesion of components through joining surfaces, which is caused by a joining medium, whereby the integral connection can take place by way of metallic bonding, by covalent interaction, by ionic interaction, by induced dipoles, by hydrogen bond and/or by van der Waals interactions. Integral connections can only be disengaged by destruction. The term "integral joining" comprises integrally connecting, materially connecting, materially joining and materially bonding. These terms can be used interchangeably.

The terms "joining medium" or "joining agent" refer to the joining particles of the invention which are applied to at least one surface for joining joining surfaces and supply the thermal energy for joining. A substance that imparts an integral bond between two joining surfaces is defined as "adhesion medium". Thermoadhesive or thermoreactive agents, such as adhesives or glues, can be used as adhesion medium. The term "adhesion medium" includes both reactive adhesion agents and melt adhesion agents.

The terms "adhesive" and "glue" shall encompass all agents that are suited for connecting two surfaces, for instance hot glues, multicomponent glues, instant glues, hot-melt adhesives, etc.

The term "thermoadhesive" concerns adhesives that upon heat supply cause adhesion. The term includes thermoreactive and thermoadhesive glues.

The term "mechanical application" refers to application variants of the joining particles in which just energies based on the laws of Newtonian mechanics and conventional thermodynamics act on the particles, but not to the use of electric or magnetic or electromagnetic fields or other variants for energetic mass transfer generation.

The term "particle size" refers to the size of the core-shell particles, more exactly to the diameter of the particles. The size or diameter can be determined in methods known per se, such as laser diffraction, or with the help of a laser or scanning electron microscope. For a "fast" check of the particle size, sorting with sieves can also be carried out as long as the size is not in the low nanometer range. When reference is made in the present application to the particle size, the indicated value refers to the diameter of core-shell particles determined by way of laser microscope.

The joining particles according to the invention may be microparticles; particles with a size, i.e. diameter, in the micrometer range, i.e. 1 to 999 μιτι, are called microparticles, e.g. particles with a size in the range of 1 to 500 μιτι, 1 to 200 μιτι, 2 to 100 μιτι, or 5 to 50 μιτι.

The term "joining particles" encompasses microparticles and may also include nanoparticles. According to the invention joining surfaces are united or combined. This uniting may be a positioning of the component in a suitable arrangement; it may also be a contacting under a minimum compressive stress, wherein the minimum compressive stress may be in a range of 0.1 MPa to 100 MPa, e.g. 1 to 20 MPa. The term "contacting" shall here comprise any mechanical joining operation with or without compressive stress or also electromagnetic joining.

The method of the invention and the adhesion composition of the invention are described in more detail hereinafter.

According to the invention a method is provided for joining of joining surfaces, the method comprising the following steps:

a) mechanically applying core-shell particles to at least one joining surface of at least one component, either dispersed in a gaseous dispersant or in a flowable, liquid or solid dispersant which may additionally contain a thermoadhesive and/or a thermoreactive agent;

b) contacting the components to be joined;

c) activating the core-shell particles; and

d) integral joining of the components by the activated particles.

The subject of the present invention is a method in which for the joining of components, joining particles are used that after activation are exposed to a chemical heat-releasing reaction. This thermal energy is used for the local fusion of the joining surface in the edge region of the joining particles or for the activation of a chemical reaction of thermoadhesive or thermoreactive agents that leads to a connection between the at least two joining surfaces and components, respectively. The particles used according to the invention are applied with a dispersant onto the joining surface such that they will remain there until the two joining surfaces are brought together and activation is started. Hence, the present invention provides a method that enables the joining of very different materials with simple means, that can be carried out easily and yields a strong bond.

The joining media used according to the invention are particles consisting of at least two elements, wherein at least one element, e.g. a metal, forms the core and at least one further element, e.g. a metal, forms the shell. More than two elements may be contained, wherein core and/or shell may respectively consist of one or plural elements. Further elements may optionally be added, for instance boron or silicon. Normally, such particles are made from the respective metals, for instance in that a second metal is deposited on a metal core. A joining medium according to the invention may consist of similar or dissimilar joining particles, i.e. a joining medium can only comprise one type (based on size and/or composition) of joining particles; this may include a mixture of joining particles of different size ranges and/or a mixture of joining particles of different composition and/or of different buildup.

The joining particles used according to the invention consist of a core and a shell, wherein the shell encloses the core completely or substantially completely, so that the core is protected from the environment. The joining particles must be built up of such elements/metals that are able to form an alloy and release heat during alloy formation. Core and shell may each consist of an element/metal or a mixture of elements/metals, wherein at least one element/metal in the core must be different from at least one element/metal in the shell to permit the alloying reaction. Joining particles may also be built up of a core with a shell, wherein the shell may consist of recurrent layers, which may create more boundary layers. Such particles have a greater reactivity because the speed of the alloy formation also depends on the size of the boundary.

Examples of elements that may form core or shell of the joining particles of the invention are on the one hand the elements aluminum, titanium, niobium, tantalum, vanadium, manganese, silicon or a combination thereof, and on the other hand nickel, cobalt, copper, iron, chromium, boron, molybdenum or a combination thereof. One or more elements can respectively be selected from the two groups. The metals of both groups may be present either in the core or in the shell, whereby preferably always at least one metal of the one group is in the core and at least one element of the other group is in the shell. It has been found that an advantageous combination is one that comprises aluminum on the one hand and nickel on the other hand, wherein preferably the core consists of aluminum, on which a shell of nickel has been deposited.

Suited for use with the present invention are particularly joining particles that have a core of aluminum and optionally further elements/metals, and a shell of nickel and optionally further elements/metals. The manufacture of such particles is known in the prior art and can be carried out easily. There are different methods for the manufacture of such joining particles, but it is only possible to use those methods that yield so-called core-shell particles in which the core is covered by the shell substantially completely. Not suited are for instance galvanic exchange reactions.

The joining particles according to the invention may for instance be produced by autocatalytic deposition of a metal on a core of a different material. Known are for example methods in which the second metal is deposited on particles consisting of a metal, e.g. aluminum particles, from complex metal compounds, e.g. complex compounds of nickel. Such methods are known and have been described for instance in the following literature: US 3,198,659, Mallory, G.: Electroless Plating. In: Mallory, G.; Hajdu, J. (editors): The Fundamental Aspects Of Electroless Nickel Plating. New York: Noyes Publications William Andrew, Publishing 1990, pp. 1-56. ISBN: 978-0815512776; Mallory, G.; Hajdu, J. (editors): Electroless Plating Fundamentals and applications. New York: Noyes Publications William Andrew Publishing 1990. ISBN: 978-0815512776; (03.08.1965). For autocatalytic nickel plating the agglomeration of nickel atoms from a metal salt solution on a substrate such as aluminum can e.g. be carried out by autocatalytic reaction with the help of a reducing agent such as hydrazine.

When the joining particles are activated by energetic radiation, for instance microwaves, the core starts to melt, and the diffusion coefficients of the metals will rise. With an increasing thermal energy and absorbed microwave radiation the materials will inter-diffuse and an alloy will thereby be formed. This alloy formation produces reaction heat and the released enthalpy will be used for joining. A special advantage of the use of the joining particles according to the invention is that the energy is released after activation within a few milliseconds and only for a very short period of time, which will therefore only result in a very local fusion of the joining partners.

The particles can be activated with high-frequency or high-energy radiation, for instance microwave radiation. Devices that emit microwave radiation are known, wherein frequency, power and exposure time can be set in a simple way. A possibility of providing microwaves is the use of a magnetron that produces electromagnetic radiation and comprises a hollow conductor with which the radiation can be deflected into the desired direction. Hence, use is here made of directed, powerful electromagnetic radiation for activating the joining particles. The suitable frequency and power can respectively be adapted to the joining particles. Irradiation with laser beams is also expedient.

In the case of joining particles comprising an aluminum core and a nickel shell, the aluminum will absorb the energy upon irradiation and will melt. The nickel diffuses into the melt and dissolves therein. This chemical reaction leads to exothermicity.

An advantage of the present invention is that the intensity and speed of the exothermal reaction and thus the released heat can be adjusted easily, so that the suitable type and amount of joining particles can be selected for each combination of joining surfaces. Exothermicity can be adjusted inter alia through the size of the particles, the selection of the metals involved in the reaction and their molar ratio, the ratio of the layer thicknesses of core to shell and particle size, respectively, and also via the materials of the surfaces to be joined that have an influence on reaction enthalpy and thermal properties.

It has for instance been found in the use of particles with an aluminum core and a nickel shell that a suitable reaction heat is produced if the metal in the core (Al) to the metal in the shell (Ni) is present in a stoichiometric ratio of 3:1 to 1 :3, suitably in a range of 2:1 to 1 :2, and preferably in a range of about 1 :1 . By the molar or stoichiometric ratio and other parameters, such as layer thickness of the particles, it is possible to control the exothermicity of the activated core-shell particles during alloy formation. Exothermicity can also be controlled by the type of the metals involved in the alloy reaction. For instance, exothermicity is lower for an intermetallic phase having a low thermodynamic stability. The skilled person can thus calculate the combination best suited or determine it in routine tests.

The heat emitted in the reaction can be calculated from the type of metals and the ratio of the metals involved in the alloy reaction, depending on the materials to be joined and the presence or absence of further constituents. Apart from the metals and optionally other elements useful in alloy formation, such as silicon and/or boron, the particles do normally not contain any constituents. It is important that no constituents are contained that could disturb alloy formation or later the formation of the connection element because this would weaken the connection of the joining surfaces.

Another important parameter is the particle size. It has been found that joining particles that have a size in the micrometer range are particularly well suited for the method according to the invention because they show a suitable combination of duration and magnitude of the heat emission. If the particles are too small, the heat generated is not enough or the heat is emitted too rapidly. If the particles are too large, excessive energy may evolve and e.g. air inclusions may be created, especially when glues are used. An advantage of the present invention is that the energy input can be set accurately so as to avoid these drawbacks.

It has been found that particle sizes in the range of about 0.01 μιτι to about 500 μιτι are well suited for the method according to the invention. Preferably, joining particles are used with a mean particle size in the range of about 0.5 μιτι to about 150 or about 200 μιτι and particularly of about 2 μιτι to about 100 μιτι or about 5 to about 50 μιτι. Depending on the application intended, i.e. on the type of the materials to be joined and the presence or absence of adhesive materials, it may be useful to employ substantially monodisperse, multidisperse or even very polydisperse particle products.

The method according to the invention can be used for joining joining surfaces of the most different articles that may consist of the most different materials. The method is suited for joining three-dimensional articles that have at least one joining surface, wherein the joining surface may be even or uneven, and wherein the joining surface may be the whole surface of a three-dimensional article, the whole surface on one side, or a portion thereof. The method according to the invention is not limited to a specific form of the surface. On the contrary, the method according to the invention makes it possible to join surfaces of any shape that can be brought into contact with one another.

Furthermore, the method according to the invention is qualified to join surfaces consisting of the same or a different material. The surfaces to be joined may consist of the same material, a similar material or of entirely different materials. A joining surface may be a surface of a three-dimensional article or a part thereof or may be a layer applied to the article. In cases where the material of the article to be joined is not fusible, the article may carry a corresponding coating at least at the place to be joined.

Hence, the invention offers the possibility of connecting joining surfaces of any possible dimensions and in many shapes. To this end the core-shell particles used according to the invention as joining media can be applied in different ways, while being distributed in a dispersion medium, so that they can be used for small and also large components. The method according to the invention can therefore be used both for microscopic components, such as silicon wafers and small electronic subassemblies, and for larger components, such as cables, cable holders, or for macroscopic plates, e.g. plastic building panels, or hybrid mixed composites. Owing to the universal usability of the joining medium according to the invention and of the joining method according to the invention, joining surfaces can also be joined together at difficult locations that are hardly accessible. For instance, components can easily be joined together overhead.

According to one aspect of the present invention meltable joining surfaces are interconnected. In this case at least the part of the surface of the article to be joined, which part is used for joining, must be meltable or made meltable, e.g. by application of a layer.

According to a further aspect of the present invention two articles can be connected via their joining surfaces with the help of additional auxiliaries, excipients or technical adjuvants, more exactly by using an adhesive agent, such as a melt-type adhesive agent or a reactive adhesive agent. Melt-type adhesive agents are compositions or agents which will melt upon heat supply and form the connection element, which imparts adhesion between the joining surfaces, during subsequent solidification. Reactive adhesive agents are agents or compositions with constituents reacting with one another under predetermined conditions upon heat supply, thereby forming a connection element.

Examples of melt-type adhesive agents are thermoplastic materials, such as polyolefins, or hot melt adhesives, such as hot glues. Such agents are known per se and commercially available. The melt-type adhesive agents can for instance be applied as a layer onto at least one joining surface, at least in the joining area. It can be applied prior to the application of the joining particles, together with the joining particles, or thereafter. The heat needed for the melting and subsequent bonding can be provided selectively via the joining particles. The melt-type adhesive agent can be applied in a manner known per se. A pre-treatment may possibly be required.

Examples of reactive adhesive agents are reactive glues, for instance single- or multi-component glues, instant adhesives, etc. Such agents are known per se and are commercially available. Examples are adhesives based on isocyanates, such as Terolan 1510 (obtainable from Henkel, Germany), or based on polyurethane, such as nolax (obtainable from nolax AG, Switzerland).

A great advantage in both variants is that the use of the joining particles according to the invention allows a very flexible setting of the conditions under which the joining reaction, i.e. the formation of the connection element, takes place. An accurate adjustment is possible as to when, where and how much of the necessary heat is provided and thus where and when the joining reaction takes place.

The use of adhesion agents is particularly required whenever at least one of the components to be connected has a non-joinable surface. If for instance at least one component consists of a non-meltable material, such as a thermosetting plastic, ceramic, glass, carbon fiber-reinforced plastic, the component can be coated fully or in part with a layer of an adhesion agent, e.g. a thermoplastic layer, or a reactive adhesive may be applied, simultaneously with or before or after the application of the joining particles according to the invention.

For instance metals, metal alloys, solder coatings, elastomers or thermoplastic materials as well as all articles coated at least on the joining surface with one of the materials described are suited for the method of the invention using an at least partial fusion of the joining surface. Coating is here carried out in a manner known per se, by for instance dipping an article into a solution or a melt of the coated material, by applying ultrasound. Suitable methods are known to the skilled person. The method according to the invention is very versatile and flexible and suited for any combination of joining surfaces, i.e. two meltable and also two non-meltable surfaces or also a meltable and a non-meltable surface can be joined.

The individual stages of the method according to the invention shall be explained in more detail hereinafter. In a first stage the core-shell particles according to the invention are applied mechanically to at least one joining surface of at least one component. The particles may be applied in different ways. It is important that the particles are applied such that they adhere at least temporarily to the surface until the further joining surface is placed thereon and the two surfaces are possibly pressurized. This temporary adhesion can be achieved with different means.

In one embodiment that is particularly suited for meltable surfaces, the core-shell particles according to the invention can be applied while dispersed in a gaseous dispersant by using kinetic energy. The particles can here be applied to one of the joining surfaces or also to both joining surfaces. Preferably, the particles are applied to a joining surface and the second joining surface is then contacted with the first joining surface and optionally kept under pressure.

A method that is well suited for the application of joining particles is by cold spray technology such as cold gas spraying. The core-shell particles are here brought in a defined amount into a spray device, e.g. a spray gun. To avoid an aggregation of metallic particles, ultrasound can e.g. be used. A spray device suited for the application process has for instance a Laval nozzle by which the gas carrier medium is conveyed at a defined pressure. If the joining particles are introduced into the spray device, these are accelerated by reason of the compression in front of the Laval nozzle and the subsequent sudden expansion upon nozzle exit to several 100 m/s. The spray device is directed onto the area to be coated and the accelerated particles impinge on the joining area. Upon impingement of the particles on the joining area high kinetic forces are generated by the sudden deceleration and these cause plastic deformation and thus adhesion of the particles of the invention to the joining surface. With the spray device the joining particles can be applied in a desired layer thickness and quantity. Optionally, both joining surfaces may also be acted upon with joining particles from the spray device. The gas used for this type of application only serves as a carrier material. Each gas used for such spray devices is therefore qualified as long as it does not react with the joining particles, i.e. is inert. Suitable gases or gas mixtures are known. Nobel gases, e.g. argon, or other inert gases such as nitrogen or carbon dioxide are normally used for this.

The mechanical application of the joining particles to the joining surface has the effect that the particles continue to adhere to the joining surface at least temporarily. This makes it possible to conduct the joining process without any time pressure and allows precise working. This avoids irreversible damage during the joining process and inadequately prepared joining regions. Moreover, this type of application allows the use of any shape and surface as a joining surface because the particles can be applied to even and also uneven joining surfaces. The only restriction of the joining surfaces to be joined is just the mutual accessibility of joining surfaces.

With the method according to the invention it is possible to carry out joining methods in a gentle way for the components, i.e. without the components being exposed to massive, energetic, thermal or mechanical loads. For instance a thermal load as during welding or brazing is avoided between two metallic components.

The method according to the invention is gentle on the used materials of the components since the activation of the core-shell particles just requires a very short-term energy supply, and the exothermal reaction by alloy formation only occurs within the millisecond range and ideally interconnects the joining partners. Hence, a very rapid as well as time- and energy efficient joining of joining partners is possible.

Moreover, the present invention makes it possible to fix the point of time of the activation of the joining medium itself, so that an operation without time pressure is possible and corrections can be made after the positioning of the joining surfaces.

With the method according to the invention it is also possible to combine or join components with one another, in which the meltable and/or non-meltable joining surfaces to be joined are of the same or of a different material. A look at a combination of components with exclusively meltable joining surfaces reveals that for instance metal-metal combinations with different metals or metal-metal alloy combinations of different components or even combinations of elastomeric materials or thermoplastics with joining surfaces of metallic materials are possible. This once again underlines the universal applicability of the method.

The application from the gas phase of the core-shell particles can be used for all kinds of surfaces; it is above all suited for the connection of components where at least one meltable surface exists. However, a joining surface may also be coated with a flowable dispersion and acted upon independently thereof with joining particles in a gas dispersion. Upon application with an applicator the particles are flung or accelerated with kinetic energy onto the surface where they then continue to adhere by way of physical forces. The use of a dispersion of the pure joining particles in the carrier gas without further constituents is preferred as joining medium because other constituents might disturb the formation of a connection element.

Due to application to the meltable surface which takes place owing to solid-solid wetting, in which the contact angle between joining surface and core-shell particles is < 90°, with the help of the kinetic energy of the core-shell particles, the core- shell particles are not activated, but just adhere to the solid medium in a stable form. This advantageous application method for joining two or more meltable joining surfaces is possible for all material combinations, also for even or uneven materials and also at hardly accessible locations. Preferably, cold gas spray processes are used that can easily be used in industry, both in the high-pressure and low-pressure range.

When flowable, liquid or solid adhesion agents are used, both meltable joining surfaces and non-meltable joining surfaces, which are of the same material or of different materials, can be joined together as the adhesion agent provides for the connection, e.g. by thermal curing of thermoadhesive media. A thermoadhesive medium is here understood to be an adhesion agent that for instance upon supply of heat polymerizes or fuses, wherein after completion of the reaction or after cooling an integral bond is created between the two joining partners. Furthermore, in the method according to the present invention also the component may be of the same material as or of a material differing from the meltable and/or non-meltable joining surfaces. This means that for instance non-meltable components can be coated with a meltable joining surface or covered with an adhesion layer. To this end for instance thermosetting plastics may be coated with a thermoplastic layer so that the joining process is operative after the mechanical application of the core-shell particles from the gas phase, liquid phase or solid phase. This once again demonstrates the universal applicability of the method. Specifically, in this connection one of the meltable and/or non-meltable joining surfaces may comprise an additional metal coating, a metal alloy coating or an elastomeric or thermal plastic coating. These coatings can be produced with methods as are known to the skilled person, for instance with dip or ultrasonic coating.

The method according to the invention is very flexible as it offers the possibility of setting many parameters and thereby of setting the activation of the joining particles, reaction enthalpy and thermal energy and/or adhesion. The particle size of the core-shell particles is one of the parameters that can be set easily. The activatability of the particles, the quantity of the thermal reaction energy and the time course can be controlled through the particle size. The smaller the particle size, the lower is the activation energy required. Particles in the micrometer range form rather stable dispersions as compared to nanoparticles, which simplifies working with the joining particles.

Owing to the above-indicated characteristics it is possible to adapt the thermal reaction energy of the joining particles to the respective requirements regarding components and material quality and to find the best combination of characteristics for each product in routine tests.

Another embodiment of the present invention refers to the use of an adhesion agent, e.g. an adhesive, to connect two parts. In all cases where the surface to be joined is not meltable, an adhesion promoter must be used that interconnects, i.e. for instance glues, the two surfaces to be joined. For this embodiment, in addition to the joining particles of the invention, a thermoadhesive or thermoreactive substance is applied, normally in a carrier material. There are various variants for this. On the one hand, a thermoadhesive agent can be applied in dispersed form in a liquid or flowable dispersant onto one or both surfaces to be joined and the joining particles can subsequently be applied in a manner known per se for instance by using a gaseous dispersant. It is also possible to disperse the joining particles into the thermoadhesive or thermoreactive dispersion medium and to apply the combination of both in a manner known per se. The dispersion medium used for the application of adhesion agent and/or joining particles shall be inert to the constituents on the one hand, i.e. the dispersant should not influence or should hardly influence the reactivity of the thermoadhesive or thermoreactive agent. On the other hand, after reaction this dispersant should not leave any residues, at least not residues that could weaken the connection element formed. If, for instance, a gel that contains hydrocarbons was applied as adhesion promoter for the joining particles, a connection element could subsequently form between the two surfaces that would also include the hydrocarbons and the decomposition products thereof from the dispersant. This would produce weak points that might cause fracture of the connection element.

An example of the use of an adhesion agent is a thermoadhesive or a thermoreactive glue in a dispersant, wherein after application an adhesive precursor is activated only by reaction and the precursor is then included in the adhesive. Further constituents should not be present in the adhesive medium, especially not those that could disturb the activation of the joining particles or the joining process.

If a thermoadhesive or thermoreactive adhesion agent is used for the method according to the invention, the joining method is more or less independent of the quality of the surface of the components to be joined. In such a case the connection is imparted by the adhesive, so that in this case an adhesive has to be chosen of the type that is compatible with the base, i.e. the joining surface, and can adhere thereto to an adequately strong degree. The adhesive bond to be used for a specific surface is known to the skilled person and an optimal adhesive composition can easily be found in routine rests.

In a further variant, the method according to the invention can also be carried out by using a solid hot-melt adhesive. To this end either the joining particles can be distributed in the solid hot-melt adhesive (after the fusion thereof and with subsequent solidification). Or it is possible to apply a layer of a meltable adhesive to the surface to be joined and then to equip it with core-shell particles.

A thermoadhesive liquid dispersant or a liquid thermoreactive adhesive can cure by exothermal enthalpy of the alloy formation of the core-shell particles. Examples of thermoreactive adhesives are adhesives based on polyurethane, or liquid adhesives assembled from a pre-polymer that have further non-polymerizable bonds that will only polymerize by thermal initiation. For this embodiment the joining particles can be applied particularly easily while being dispersed in the liquid thermoreactive adhesive. The particles can further induce the liquid thermoreactive adhesive to further polymerize by way of reaction enthalpy and reaction energy of the alloy formation. The joining surfaces of the respective components can also be joined together by curing of the adhesive.

After the core-shell particles have been applied by way of dispersion onto the joining surfaces, the joining surfaces are contacted, i.e. positioned and joined together. Contacting can be performed with or without pressure. For instance, pressure can optionally be exerted on the surfaces to keep them in the correct position. When pressure is exerted, the compressive stress should be set such that the dispersions and the particles, respectively, do not fall out, and a deformation of the components is also not caused. Suitable conditions have been described above.

A further essential step of the method according to the invention consists in the activation of the core-shell particles according to the invention.

To initiate the desired alloy reaction, enough energy must be supplied to start the exothermic reaction. The activation for the initiation of the exothermal reaction of the particles can take place in different ways. The activation can for instance take place by way of electromagnetic radiation, e.g. microwave radiation, infrared radiation or UV radiation, or electric voltage. The application of electric voltage for activating the particles is however only expedient in components consisting of conductive materials, i.e. when joining surfaces and material of the components are electrically conductive at the same time. It has been found that an activation of the particles with electromagnetic radiation, particularly with microwaves, is advantageous. Microwaves can migrate through many materials substantially without any loss of energy and produce heat only at the place where the electromagnetic radiation is absorbed. This results in high efficiency. Irradiation can for instance be generated with an LC resonant circuit, a klystron or a magnetron; a magnetron is preferably used. The quantity and penetration depth of the adsorbed energy into the irradiated material can be adjusted by adjusting the frequency, power and duration of the irradiation, which in turn is dependent on the respectively used particles and the elements/metals contained therein. The activation with the electromagnetic radiation then initiates alloy formation which, in turn, selectively releases heat. With this enthalpy heat it is then possible to either fuse the surface, e.g. at the point where the particles are present, or it is possible to induce reaction of an adhesive applied to the particles. In contrast to the known nanofilm, the joining particles of the invention do not require any starting flags; this further facilitates the method.

For instance at a power of 800 W, at a wavelength of 10-15 cm and at a frequency of 2.3-2.5 GHz, the joining particles according to the invention can be ignited within a few seconds. These parameters can be adapted by the skilled person to the components to be joined, the respectively used joining particles and the method used. For instance, the electromagnetic irradiation may be a continuous wave radiation or may be pulsed.

The short-term activation through electromagnetic radiation has the effect that the component is not exposed to thermal stress or other energetic factors that might cause disadvantageous deformation, corrosion or similar disadvantageous change on the component. The electromagnetic radiation may here be applied in the millisecond range, whereupon the exothermal reaction takes place in the millisecond range. The radiation may be pulsed or permanent; continuous wave radiation is for instance expedient.

After application of the particles to the joining surfaces, the contacting of the joining surfaces and the activation of the particles, the desired reaction - fusion in the upper layer or reaction of the reactive adhesive - is started and leads to an integral joining of the components by the activated particles. After completion of the joining reaction a composite component is obtained consisting of at least two components connected via at least one connection element. The joining reaction is completed when the reaction of a reactive adhesion agent is substantially terminated or the joining material has solidified again upon use of a melt-type adhesion agent. The joining method according to the invention creates at least one connection element between components or joining surfaces on components, which connection element very firmly adheres to the base and simultaneously exhibits a strong cohesive force. The connection between the components is formed by fusion and merging of the surfaces of the components, resulting in a connection element that is extremely strong. When the surfaces are metallic, alloy islands, which also ensure a strong bond of the parts, are created at the places where the joining particles are applied. In the case where a flowable, liquid or solid adhesive medium has been used, a strong bond is also created between the components because of the reaction of the active bonds in the adhesive, which reaction has taken place on the correct site and at the correct time. At any rate a very reliable, strong, permanent connection element is thereby formed.

The present invention also refers to an adhesion composition for joining joining surfaces that contains a) core-shell particles, wherein their particle size is between about 0.5 μιτι and about 500 μιτι, preferably about 1 and about 200 μιτι, and particularly preferably about 5 and about 50 μιτι; and b) a thermoadhesive or thermoreactive dispersant.

The adhesion composition according to the invention has a core-shell particle loading between about 1 mass % and about 50 mass %, preferably between about 3 mass % and about 40 mass %, and particularly preferably between about 5 and about 20 mass %. Due to these load degrees of the liquid dispersant the intensity of the exothermicity can be adjusted again. If a higher exothermicity and/or a more simple activation are needed, particle loading can be increased accordingly. Inversely, particle loading can be decreased if a lower exothermicity is needed after activation of the particles.

In a further embodiment the adhesion composition comprises core-shell particles with such an elemental composition that at least one of the elements Al, Ti, Nb, Ta, V, Mn, Si, or a combination thereof, preferably Al or Ti, is present in the shell or the core, respectively, and at least one of the elements Ni, Co, Cu, Fe, Cr, W, and Wo, or a combination thereof, preferably Ni or Co, is correspondingly present in core or shell, respectively. In other words either one of the elements Al, Ti, Nb, Ta, V, Mn, Si, or a combination thereof, preferably Al or Ti, is either in the shell or the core. If one of these elements is present in the core then at least one of the elements Ni, Co, Cu, Fe, Cr, W, and Wo, or a combination thereof, preferably Ni or Co, is present in the shell and vice-versa.

The adhesion composition according to the invention with core-shell particles imparts a reaction, for instance polymerization or melt, of the thermoreactive or thermoadhesive liquid or solid constituents of the adhesion agent, whereby the joining of the components is caused by hydrogen bonds, by induced dipole-dipole or van der Waals interactions or ionic interaction between joining medium and the joining surfaces. For instance, the adhesion composition according to the invention may contain a liquid thermoreactive adhesive, e.g. an adhesive based on polyurethane or isocyanate. The adhesive may for instance contain a pre-polymer which has further, non-polymerizable bonds that only polymerize by the thermal initiation.

The adhesion composition according to the invention can also comprise a solid thermoadhesive adhesion agent. Here, the solid hot-melt adhesive can be applied to the surface simply mechanically in methods known to the skilled person. After the joining surfaces have been joined, this hot-melt adhesive can be melted by corresponding particle activation. After termination of the exothermal reaction the hot-melt adhesive will cure, thereby joining the previously contacted components.

By the elemental composition of the core-shell particles the exothermicity of the reaction can be selectively adjusted and controlled because for instance particles with nickel shell and aluminum core create a different diffusion-caused reaction enthalpy than do the corresponding inverse particles. Furthermore, the alloy formation enthalpy is different between different elements, so that the demand for thermal energy of the joining process can be exactly matched to the respective joining surfaces.

A further adjustable parameter is the stoichiometric ratio of the metals forming the core-shell particles (and later the alloy) because the exothermicity of the activated core-shell particles can be controlled during alloy formation owing to the stoichiometric ratio of the metals. Due to the corresponding intermetallic phases which result from the alloying reaction and which are defined by the stoichiometric ratio, the exothermicity of the alloy formation can also be defined. For an intermetallic phase that has less thermodynamic stability, the exothermicity defined by the stoichiometric ratio of the core-shell components is also less. When for instance nickel and aluminum are used as shell metal and core metal, respectively, the ratio of the two metals is suitably between 3:1 and 1 :3, preferably between 2:1 and 1 :2, for instance 1 :1 .

Claims

1 . Method for the integral joining of components, comprising:

a) mechanically applying core-shell particles to at least one joining surface of at least one component, wherein the particles are applied via a gaseous dispersant onto a meltable joining surface or via a thermoadhesive liquid dispersant or a thermoadhesive solid dispersant onto a meltable or non- meltable joining surface;

b) contacting the joining surfaces of the components to be joined;

c) activating the core-shell particles;

d) integral joining of the components by the activated particles.

2. Method according to claim 1 , characterized in that the meltable and/or non- meltable joining surfaces of the components to be joined are even or uneven independently of one another.

3. Method according to any one of claims 1 or 2, characterized in that the meltable and/or non-meltable joining surfaces of the components to be joined are of the same material or of a different material.

4. Method according to any one of claims 1 to 3, characterized in that at least one of the meltable and/or non-meltable joining surfaces comprises a metal coating, a metal alloy coating, a solder coating or an elastomeric or thermoplastic coating.

5. Method according to any one of claims 1 to 4, characterized in that the core- shell particles have an elemental composition, so that at least one of the elements Al, Ti, Nb, Ta, V, Mn, Si, or a combination thereof, preferably Al or Ti, is present in the shell or core, respectively, and at least one of the elements Ni, Co, Cu, Fe, Cr, W, and Wo, or a combination thereof, preferably Ni or Co, is correspondingly present in the core or shell, respectively.

6. Method according to claim 5, characterized in that at least aluminum and nickel are used as metals, and the stoichiometric ratio of shell metal to core metal is between about 3:1 and about 1 :3, preferably 2:1 to 1 :2.

7. Method according to any one of claims 1 to 6, characterized in that the core- shell particles have a particle size of 0.01 μιτι to 500 μιτι, preferably of 0.5 μιτι to 200 μιτι, particularly preferably of 1 μιτι to 100 or 40 μιτι.

8. Method according to any one of claims 1 to 7, characterized in that the activation takes place by way of electromagnetic radiation or electric voltage.

9. Method according to any one of claims 1 to 8, characterized in that the electromagnetic radiation comprises microwave radiation, laser radiation, IR radiation or UV radiation.

10. Method according to any one of claims 1 to 9, characterized in that an adhesion agent is used which is applied before, at the same time as or after the joining particles.

1 1 . Method according to any one of claims 1 to 10, characterized in that the adhesion agent contains at least a thermoadhesive and/or thermoreactive agent, optionally dispersed in a dispersant, and wherein the adhesion agent is liquid or solid.

12. Method according to any one of claims 1 to 1 1 , characterized in that the particles are applied with a spray device, particularly in a cold spray process.

13. Adhesion composition for joining joining surfaces, comprising

a) core-shell particles, wherein their particle size is between 0.5 μιτι and 50 μηη;

b) at least one thermoadhesive adhesion agent.

14. Adhesion composition according to claim 13, characterized in that the core- shell particle loading of the dispersant is between 1 mass % to 50 mass %, preferably between 1 mass % to 40 mass %, particularly preferably between 1 mass % to 20 mass %.

15. Adhesion composition according to any one of claims 13 or 14, characterized in that the core-shell particles have an elemental composition, so that at least one of the elements Al, Ti, Nb, Ta, V, Mn, Si, or a combination thereof, preferably Al or Ti, is present in the shell and the core, respectively, and at least one of the elements Ni, Co, Cu, Fe, Cr, W, and Wo, or a combination thereof, preferably Ni or Co, is correspondingly present in the core and shell, respectively.

16. Adhesion composition according to any one of claims 13 to 15, characterized in that at least nickel and aluminum are present as metals, and the stoichiometric ratio of shell metal to core metal is between 3:1 and 1 :3 and 2:1 and 1 :2.

17. Adhesion composition according to any one of claims 13 to 16, characterized in that the thermoadhesive dispersant comprises a solid hot-melt adhesive, a liquid thermoreactive adhesive, concrete, or cement.