Inter-particle bonding in cold spray deposition of a gas-atomised and a solution heat-treated Al 6061 powder

Abstract

The heat-treatment of a number of gas atomised aluminium alloys prior to cold spraying recently showed that the resultant microstructural modification was accompanied by an improvement in deposition; however, the relationship between the microstructural homogenisation occurring after recrystallisation and the increase in deposition efficiency and particle-particle bonding had not been investigated. In this study, Al 6061 gas atomised feedstock powder, before and after solution heattreatment, was cold sprayed and these materials were characterised using electron backscatter diffraction. The solution heat-treated Al 6061 powder showed large stress-free grains as opposed to the as-atomised feedstock powder which exhibited smaller grains with the presence of dislocations. The coating produced from as-received powder exhibited a homogeneous distribution of misorientation and lattice defects throughout the particles, whereas the coating produced from solution heat-treated powder showed an accumulation of dislocations in the interfacial zones. For the first time, a mechanism was proposed where this phenomenon was attributed to localised deformation of the heat-treated particle's exterior due to the dissolution of precipitates in the intermetallic network. The accumulation of dislocations in the interfacial area enhanced the rotation of subgrains to accommodate the plastic deformation, thus improving the particle-particle bonding.

Cold Spray Technology for Oxidation-Resistant Nuclear Fuel Cladding

“…It was theorized that spherical gas atomized powder was preferred for this work as it contained large grains and exhibited a low amount of work hardening in its as-manufactured state, allowing for good coating buildup. The Cr powder used in this study had a higher hardness (3.87 GPa) compared to the spherical gas atomized Cr powder (3.12 GPa) but was much softer than the milled Cr powder (6.65 GPa), even after annealing treatment of the milled powder (4.21 GPa) [7]. It is believed that the combination of reduction in work hardening from the powder fabrication process allowed for buildup of thick coatings (Fig.…”

“…It is believed that the combination of reduction in work hardening from the powder fabrication process allowed for buildup of thick coatings (Fig. 4) while the slightly irregular morphology allowed particles to pack together more effectively to provide for a dense coating [7].…”

“…Our previous research has shown cold spray Cr coatings have excellent oxidation resistance in both air and steam environments at temperatures ranging from 1100 -1300 °C [7], [8]. The deposition efficiency has been shown to strongly depend on the intrinsic properties of the feedstock powder, including powder manufacturing method, particle morphology, size, and hardness [9].…”

Microstructure, mechanical and wear resistance properties of low-pressure cold-sprayed Al-7 Mg/Al2O3 and Al-10 Mg/Al2O3 composite coatings

“…with in-flight contact of molten particle droplets of different sizes under the gas-atomisation production process during the powder production [23]. The particle size distribution of the Al-Mg alloys is displayed in Fig.…”

Sacrificial Thermally Sprayed Aluminium Coatings for Marine Environments: A Review

“…In contrast to thermal spraying processes, cold spray relies on the deposition of particles in the solid state, and these particles plastically deform upon impact [14]. Since the melting of the feedstock material is avoided, a coating with a negligible oxide content can be obtained.…”