Funktionalisierung von Bauteiloberflächen durch Mikro-Laserauftragschweißen

The system technology and process development for decreasing the achievable structure sizes (track geometry) for the micro laser cladding process with powder as additive material is presented. The main focus during the system technology development lies on the components powder feeder, powder distributor, transport tubes and powder nozzle including the shielding gas system. Aim is to allow the feeding of non flowable powders (powder particle sizes d50< 10 µm), to decrease the powder focus diameter of the powder nozzle, to achieve a good protection of the melting pool with shielding gas and to avoid powder agglomeration in the transport tubes. By integrating a brush feeder and using 316L with d50= 4,7 µm as additive material the realization of single tracks with a track geometry (hES x bES x t) of 25 x 6 x 1 µm3 is shown. With a coaxial powder nozzle, an outer shielding gas nozzle and the adaptation of the gas flows powder focus diameters between 200 and 240 µm can be realized. During the process development of tracks with a width between 25 and 50 µm typical process deviations as overspray are discussed and a systematic approach concerning the topography and dilution of single tracks and layers in dependence of the process parameters is presented. Beside the results of the basic investigations performed with iron based alloys as additive material results with precious metals (gold and silver) for the manufacturing of contacts on bipolar plates for fuel cells and tantalum for the manufacturing of x-ray markers on stents are presented. By laser cladding of gold contacts with a contact geometry of 60 x 30 µm2 on bipolar plates (d= 100 mm) of metallic fuel cells the degradation of an assembled fuel cell stack can be reduced by factor 2 and the output power increased by 30% so that the output power is comparable to conventional bipolar plates made of carbon. For the selective laser cladding with gold as additive material only 1/100 of the amount of material is necessary compared with a conventional galvanic coating. By laser dispersing tantalum particles in an area of 1 x 1.5 mm2 on nitinol stents with a wall thickness of 200 µm the feasibility of this process is shown for the manufacturing of x-ray visibility markers