In-situ alloying of high entropy alloys by a laser cladding process

The group of high entropy alloys (HEA) is under increasing interest due to their unique high-temperature properties, such as excellent specific strength, superior corrosion resistance, exceptional ductility and fracture toughness. However, the manufacturing route of reliable HEA coatings is still technologically challenging and costy, in particular because of the high number of constituent elements (> 5). In-situ alloying by coaxial laser cladding can be a route to achieve both high quality HEA coatings with reasonable costs. In the current work laser powder cladding was applied (4 kW diode laser, 1 µm fiber, COAXpowerline nozzle). By four supply hoses simultaneously, one-element and binary powders have been alloyed in-situ during the process successfully. Chemical and microstructural homogeneity of the coatings have been approved by metallographic investigation. 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. Micro-hardness measurements and advanced scanning electron microscopy including EDS and EBSD were used to analyze the synthesized coatings. By this approach, CrMnFeCoNi and AlCoCrFeNi coatings could be manufactured reliably, demonstrating high chemical and structural homogeneity without macroscopic segregations and only containing small amounts of impurities.