Cold spray deposition characteristics of mechanically alloyed Cu-CNT composite powders

Copper (Cu)-carbon nanotube (CNT) composite surface coatings with CNT contents of up to 15 vol.% were fabricated by mechanical alloying (MA) and cold gas dynamic spray (CGDS) process. The MA powder and CGDS coating samples were characterized by weight and size measurements, optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The coatings were also examined by profilometry and porosimetry. The results showed that the particle sizes of MA composite powders and their deposition efficiencies (DEs) in CGDS decreased with the increase of CNT content. The DE also decreased with the increase of coating layers. The XRD results indicated that the composite powders and coatings had microstrains and undergone grain size reduction due to the deformation caused by MA and CGDS. The coating surface and internal microstructures had flattened lamellar features, which indicated severe deformation that resulted from impact during the deposition of particles as well as from the impact of the rebounded particles. Some internal pores were present along the interfaces of the deposited particles. The surface roughness values of the coatings were observed to be related to the sizes of the powder particles. The roughness tended to decrease with the reduction of particle sizes. Also, the coatings contained about 1.0-2.5 vol.% surface micropores. However, the comparison between the trend of the surface roughness and the quantity of surface pores did not show direct correlation. Composition analysis of the coatings revealed the uniform dispersion of CNTs within the coatings.