Laminar Fe-based amorphous composite coatings with enhanced bonding strength and impact resistance

Laminar coatings comprising a multi-amorphous Fe48Mo14C15Y2C15B6 layer and a crystalline NiCrAl layer were prepared by the high-velocity oxygen fuel technique. The structures of the coatings were studied with X-ray diffraction, scanning electron microscopy and cross-sectional transmission electron microscopy, while the various mechanical properties, such as hardness, strength, interfacial toughness, bonding strength and impact resistance, were investigated by micro/nanoindentation, three-point bending and adhesion testing as well as by tup-drop impacting coupled with finite element method simulations. The results show that composite coatings exhibit an almost fully compact structure at interfaces between the amorphous layer and the NiCrAl layer with an attractive combination of high hardness and bonding strength, good interfacial toughness and high impact resistance with respect to the monolithic amorphous coating. The maximum bonding strength and impact resistance obtained in the laminar coatings reached 40 MPa and 21.2 J, respectively, which are respectively a ∼54% and a 10-fold increase over the monolithic coating. The enhancement of the bonding strength results from the formation of the localized metallurgical bonding as well as complete wettability between the NiCrAl layer and the amorphous layer, which is observed by high-temperature contact angle tests. The improvement in the impact resistance of the composite coatings results from hindering crack propagation and mitigation of stress concentration due to the addition of the soft NiCrAl multilayers. The present work may pave a way to the development of durable, tough and highly impact resistant amorphous-matrix composite coatings for applications in severe loading conditions.