Laser Functionalisation

With laser-based functionalization, the specific properties of materials can be specifically adjusted and intrinsic properties changed. Compared to integral approaches such as oven-based sintering and thermal processes, laser functionalization is distinguished by high spatial resolution since the functionalization only takes place where the irradiation is applied. Moreover, laser-based functionalization methods allow the energy required to be deposited in a very narrow range, for example in a 100 nm thick layer. Thanks to these possibilities, a number of process technologies have become established, and the institutes of the Fraunhofer Group for Light & Surfaces are examining them under aspects of process engineering as well as system-technology.

The processes can be divided into thermal processes such as:

• Laser hardening
  
• Laser cladding

as well as into non-thermal processes, such as:

• Plasma coating
• Photo functionalization

Depending on the process and the desired effect selectivity, lasers in deep UV (excimer lasers and frequency-converted lasers) are used as well as diode lasers, solid state lasers (fiber lasers) and long-wave infrared lasers.

Laser-Beam Hardening and Heat Treatment

Thanks to many years of extensive experience and interdisciplinary know-how from analyzing the application to optimally accomplishing laser processing tasks, Fraunhofer IWS and ILT offer the following services:

• Development and industry transfer of laser hardening processes using local controlled temperature fields with high power laser or induction, or a combination of both technologies such as laser-beam hardening or heat treatment in general, laser-beam soldering and laser-assisted roller plating
• Processing of development samples and prototypes
  
• System components for processes using local controlled temperature fields

In the field of heat treatment, the Fraunhofer ILT are investigating processes for the post-treatment of high-strength steels to make them easier to form. In addition, the institutes are focusing on local heat treatment processes; laser irradiation is used to heat the material locally to a temperature below the melting temperature. Depending on the wall thickness, only one edge layer or the entire cross-section (e.g. in the case of a sheet metal) is briefly heated. The heating rate, the maximum temperature and the cooling rate can be adjusted by a temperature control. Applications for metallic materials can be found in the edge hardening of components made of hardenable steel or cast iron, the softening of high-strength steels, the recrystallization of thin sheets and the stress-relieving of additively manufactured components. In the field of non-metallic materials, the group also looks at the crystallization of silicon layers as well as the annealing of transparent, conductive materials.

Laser and Plasma Coating

Laser coating processes often offer many new approaches to produce wear-resistant surfaces for component geometries and materials subject to great wear in which conventional hardening technologies fail.

At its disposal, Fraunhofer IWS has atmospheric plasma spraying (APS) as well as high velocity oxygen fuel (HVOF) and high velocity air fuel (HVAF) spraying processes with powders and suspensions to thermally coat components made of steel, light metals, ceramics, concrete and other materials containing metals, hard metals and ceramics. The use of suspensions instead of coating powders promises to have several advantages, including the ability to directly use finely dispersed powders and, thus, to save the production of special starting powders, but also the production of nanostructured layers. In addition, the group is examining the possibilities of producing thermally sprayed layers with a layer thickness below 100 μm. This could help to close the gap in the film thickness between CVD/PVD and conventional coating layers.

Laser Functionalization

For the functionalization of surfaces, Fraunhofer ILT uses various laser processes for micro- and macro-functionalization. In addition, it applies coatings having a thickness from 1 μm to several millimeters. In the case of thin layers, the application is first carried out by a printing process, followed by laser functionalization; in the case of thicker layers, the addition is directly applied in the form of wire or powder. Coating materials are metals, metal-based composites, for thin layers also ceramics and glass. Layer composites can also be applied.

Fraunhofer IST uses the laser functionalization as post-processing for surfaces produced by means of cold plasma spraying. In this process, the coating is applied with a plasma jet into which various solutions, dispersions or (sub-) micropowder are fed. Through the special plasma generation, thermally sensitive substrates and natural materials can also be coated.

Fraunhofer IWS provides new methods and industrial systems to produce two- and three-dimensional micro- and nanostructures on polymers, metals, ceramics and coatings. In addition to the topography, the electrical, chemical and mechanical properties can also be varied periodically.