High Entropy Alloys generated with laser cladding

The group of high entropy alloys (HEA) is under increasing interest due to the wide possibility of tailorable properties that far surpass conventional alloys. Depending on the alloy system unique high-temperature properties, such as excellent specific strength, superior corrosion resistance, exceptional ductility and fracture toughness are achievable. However, the manufacturing route of reliable HEA coatings is still technologically challenging and costly, in particular because of the high number of constituent elements (> 5). In this contribution the production of HEA alloys by laser cladding using powder as well as wire is demonstrated. Particularly interesting is the possibility of in-situ alloying with laser powder cladding as a cost-effective alternative to the use of pre-alloyed compositions. Furthermore the economically, environmentally and industrially safe laser wire cladding is used for the production of HEA layers too. This process allows a material efficiency of almost 100%. The coating deposition was been carried out using coaxial cladding systems COAXpowerline and COAXwire, both developed by Fraunhofer IWS and a 4 kW diode laser (890-1060 nm) for the powder process and a 4 kW fiber laser (1064 nm) for the wire system. The coatings have been characterized in terms of chemical and microstructural homogeneity by optical analysis of cross-sections. Additionally Vickers micro-hardness-, abrasive wear measurements and advanced scanning electron microscopy including EDS and EBSD have been used. Upon the inherent high solidification rate during processing grain refinement could be observed. It also allows a significant reduction in element separation, thus reducing or even eliminating homogenization annealing. By this approach, CrMnFeCoNi and AlxCoCrFeNi coatings could be manufactured reliably, demonstrating high chemical and structural homogeneity without macroscopic segregations and only containing small amounts of impurities. In the AlxCoCrFeNi system, the lattice structure could be easily adjusted via the Al content. A switching form the solid-solution phase fcc to bcc was observed at Al contents > 15 at%, which resulted in an hardness increase from 200 HV to 600 HV in the system. Laser cladding has the potential to be established a simple, cost-effective and environmentally friendly process for the production of HEA based coatings.