AISI 4340 is an ultrahigh strength steel that combines properties such as deep hardenability, toughness and ductility. Such properties make it a material of choice in high stress aeronautical components, including landing gears.
However poor corrosion behaviour, especially with regard to stress-corrosion cracking, continues to limit its capabilities. Current prevention methods, such as expensive hard chrome plating, appear sub-optimal.
Cold spray is an emerging technology that is capable of applying a powder coating and high speeds by causing massive plastic deformation on contact with the substrate. It’s comparatively low delivery temperature, compared to more established thermal sprays, allows powder to retain bulk material microstructure and properties.
Kinetic metallization, a specific type of cold spray, was used to apply 316L stainless steel powder to 4340 substrates in an attempt to improve the steels corrosion resistance and characterize the coating.
Two variants of 316L stainless steel coatings were consistently applied to a 4340 substrate. 50wt% Al2O3 coating produced the thickest coating of 318µm per pass, as well as limited
signs of cracking in the microstructure and an average shear failure of 24.9MPa. Corrosion behaviour comparable to bulk stainless steel was achieved in both salt spray and polarization test.