Microstructural analysis of gas atomized Al-Cu alloy feedstock powders for cold spray deposition.

This work describes the micro- and nanostructures of inert gas atomized Al-Cu alloy powder particles over a range of compositions. For cold spray deposition, the microstructure and elemental distribution within the feedstock powder play a critical role in determining the final microstructure and properties of the fabricated material. A series of Al-Cu binary alloy powders, ranging from 2 to 5 wt% Cu, were produced by inert gas atomization and were then thoroughly characterized using electron microscopy and X-ray diffraction. The gas atomized powder particles, nominally 20 μm in diameter, presented a cellular structure with θ (Al 2 Cu) phase forming along the cell boundaries. The continuity and phase fraction of the θ phase increased systematically with copper content. No Guinier-Preston zones were observed in the powders, but small, incoherent θ phase particles were observed in the matrix near the cell boundaries. The as-atomized particles were observed to be in a non-equilibrium state with a reduced amount of θ phase and altered lattice parameters for the α and θ phases. A mild, post-atomization annealing returned the θ phase fraction and lattice parameters to their equilibrium values. [ABSTRACT FROM AUTHOR]