Friction-stir processing of a cold sprayed AA7075 coating layer on the AZ31B substrate: Structural homogeneity, microstructures and hardness

Post-Process Treatments on Supersonic Cold Sprayed Coatings: A Review

“…During FSP, the heat input and strong shear forces generated from the friction would produce severe plastic deformation of the Ni and Ti particles, as indicated by the material flow distribution, resulting in the formation of Ni-Ti intermetallic phases ( Figure 8) [64]. Moreover, microstructural features at the cold sprayed AA7075/AZ31B interface after FSP showed that diffusion occurred based on the presence of elements between the coating and substrate and a thin intermetallic phase formed under frictional heating and plastic deformation, which promoted material intermixing ( Figure 9) [60]. Therefore, after employing FSP, metallurgical bonding between the AA7075 coating and AZ31B substrate was improved by a combination of mechanical mixing and inter-diffusion, which promoted the formation of a thin intermetallic phase [60].…”

“…Moreover, microstructural features at the cold sprayed AA7075/AZ31B interface after FSP showed that diffusion occurred based on the presence of elements between the coating and substrate and a thin intermetallic phase formed under frictional heating and plastic deformation, which promoted material intermixing ( Figure 9) [60]. Therefore, after employing FSP, metallurgical bonding between the AA7075 coating and AZ31B substrate was improved by a combination of mechanical mixing and inter-diffusion, which promoted the formation of a thin intermetallic phase [60]. Due to a large amount of heat input during FSP, diffusion and intermetallic phases were observed in cold sprayed coatings after FSP [64].…”

“…In this case, the FSP parameters should be tailored to better Figure 9. EDS elemental mappings from the FSPed AZ31B/AA7075 interface (adapted from reference [60], with permission from © Elsevier).…”

Interfacial bonding mechanisms between aluminum and titanium during cold gas spraying followed by friction-stir modification

“…Formation of this thermodynamically-stable titanium aluminide phase at the interaction layer which produced a well-bonded interface between the aluminum substrate and titanium coating layer after cold spraying and subsequent FSP modification is a result of involved thermo-mechanical phenomena [37,54]. Therefore, this "interaction layer" actually can be considered as a "reaction layer" by formation of a new chemical compound at the interface based on the inter-diffusion of elements during thermo-mechanical process.…”

“…This modification technique has been employed for the purpose achieving desirable material properties, including; (i) fabrication of ultra-fine grained metals to attain high strain rate superplasticity [28,29], (ii) production of metal-matrix nanocomposites [30][31][32][33], (iii) homogenizing of powder metallurgy products [34][35][36], and (iv) eliminating the casting defects [27]. More recently, FSP was implemented as an effective post-processing technique to consolidate pores and remove the micro-cracks, enhance the uniformity, refine the microstructure, and subsequently improve the mechanical performance of cold sprayed coatings [37][38][39][40][41][42][43][44][45]. One possible and important effect of the FSP modification step can be its action as a thermo-mechanical treatment to improve the cohesive bonding strength of a cold sprayed interface by activating solid-state diffusion phenomena which can avoid possible detrimental grain coarsening during post annealing heat-treatment [38,39].…”