NEW PERSPECTIVES TO IMPROVE PROPERTIESOF LASER CLADDED COATINGS APPLYINGEXTERNAL MAGNETIC FIELDS

摘要

Laser beam cladding is characterised by several positive aspects, as for example low dilutionrnof the base material, minimized heat input into the substrate and the possibility of a very localrntreatment. Laser cladding has established itself in practice only in some applications as forrnexample in gas turbine blades or repair of dies and inserts. Negative aspects of laser claddingrnare nowadays the low process efficiency and the high processing costs. The development ofrnhigh power laser sources in the last decade improved the process reliability and flexibility.rnThe use of diode lasers for example allows to enhance the efficiency of the laser process asrnabsorption is higher and the coated area is larger. A further possibility to improve processrncharacteristics is offered by the use of hybrid coating processes, which optimise the energyrnefficiency, as for example plasma assisted laser cladding.rnA more effective technique to improve laser cladding is the generation of an additional forcernon the melting pool through an external superposed magnetic field. Depending on thernmagnetic field strength and on the resulting force the geometry and the microstructure of thernlayer can be influenced positively.rnIn the first part of the paper investigations on model materials are carried out, in order tornobserve the main influences. In the second part the application on industrial coating systemsrnis reported.rnCompared to other conventional coating processes the use of an adjustable magnetic field andrnthe electric current is an easy tool to vary the geometry of the seam and to enhance coatingrnproperties, such as for example surface roughness.