Cold Spraying of Fe - Based Hard Metallic Glass Coatings

As compared to Thermal Spraying, the lower process temperatures in Cold Spraying allow to retain metastabile phases of the feedstock material, as for example amorphous structures in the processed coatings. Metallic glasses are brittle at ambient temperatures. Thus, cold spray parameters must be tuned for conditions that allow softening of the spray material for successful coating formation. Bulk metallic glasses that easily reach requested conditions are mainly based on early transition metals or and / or contain rare earth elements. In view of higher hardness, less costly feedstock powder and minimum reactivity with the environment, the presented studies focus on a fairly simple FeCoCrMoBC metallic glass.

 For successfully cold spraying this hard and brittle Fe-based metallic glass, necessary impact conditions are evaluated to meet the window of sprayability in cold spraying. By systematic variation of spray conditions for coating formation, influences of critical spray parameters on deformation morphologies, coating microstructures and coating properties were investigated in detail. Under optimum conditions, a deposition efficiency of 75 % could be reached for coatings that still have the same amorphous structure as the feedstock material and a hardness of about 1100 HV 0.3. This proves the high application potential of cold-sprayed amorphous coatings.