Laser powder bed fusion additive manufacturing, microstructure evolution, and mechanical performance of carbon nanotube-decorated titanium alloy powders

Coated Metal Powders for Laser Powder Bed Fusion (L-PBF) Processing: A Review

“…The deriving coated powders are characterized by homogeneous dispersion of the hybrid coating on the metal powders, suitable particle size and distribution, good flowability, and enhanced surface roughness leading to an increased laser absorptivity. In a more recent study Zhou et al [62] used CNTs for coating titanium alloy powders. The One coating process through powder immersion involving the use of solutions is electroless plating [120].…”

“…The electrostatic attraction allows to assemble spontaneously metal powders and the coating particles during hetero-agglomeration [128,129]. Electrostatic self-assembly guarantees good flowability and the possibility of depositing structures such as carbon nanotubes (CNTs), preventing their destruction [62,63,116,128]. Zhou et al [116] used CNTs and nano Al 2 O 3 to coat metal powders.…”

“…The deriving coated powders are characterized by homogeneous dispersion of the hybrid coating on the metal powders, suitable particle size and distribution, good flowability, and enhanced surface roughness leading to an increased laser absorptivity. In a more recent study Zhou et al [62] used CNTs for coating titanium alloy powders. The oxidized surface of the metal powder is positively charged and, due to the electrostatic attraction, it reacts with CNTs: an increase in the surface roughness has been detected coupled to a consequent increase in laser absorptivity.…”

“…Kun et al [110] used TiC nanoparticles, resulting in an increased tensile strength (914 MPa) with a ductility comparable to the uncoated Ti powders. Zhou et al [62] determined that CNTs react with the Ti matrix generating TiC and leading to an increase of hardness compared to Ti and the titanium matrix composites produced by traditional processes; the final microstructure is finer with a uniform distribution of TiC particles. Liu et al [48] produced Ti-6Al-4V samples starting from powders coated with CNTs; this material is characterized by a higher ultimate tensile strength (1255 MPa instead of 1078 MPa), yield strength (1162 MPa instead of 964 MPa), and lower elongation (3.2% from 4.2%) compared to the material produced from uncoated Ti-6Al-4V powders.…”

“…Coated powders are adopted in the L-PBF process both for improving their processability (especially for increasing the laser absorptivity and powders' flowability) and/or the properties of the final parts. For increasing laser absorptivity, at the emission wavelength of the laser commonly adopted in L-PBF (1064 or 1070 nm), an increase of powders' surface roughness can be provided [62,63]. Another solution might be coating powders with a material characterized by a lower reflectance [17][18][19]21,[63][64][65].…”