Page 96 - IJB-8-1

Laser Additive Manufacturing of Zinc
alloying elements including Mg, silver (Ag), and cerium Based on the Equation 3, the z is a dynamic dependent
v
(Ce) with Zn matrix can form second phases [3,33,79] . During variable that changes monotonously from the z to 1 as the
e
laser melting Zn, the volume and size of the second R increases. In other words, the R is directly proportional
i
i
phases can be reduced in Zn matrix, which is attributed to the laser scanning velocity during LPBF.
to the characteristics of laser rapid solidification . In The influence of the scanning velocity on the
[94]
the molten pool formed by laser irradiation, the highly microstructure of Zn alloys is analyzed during LPBF,
supercooled melt causes rapid solid-liquid interface as displayed in Figure 6A. Usually, the relatively high
movement, which results in obvious deviation from scanning rate leads to the rapid solid-liquid interface
equilibrium at the interface. Although the total free energy movement, which causes the obvious deviation of the
[98]
of the melt decreases during crystallization, the chemical local equilibrium conditions near the interface . In this
potential of the minor components in the binary alloy condition, Al atoms possess insufficient diffusion time
tends to increase . In this case, the solute concentration and incorporate into the Zn matrix, thereby reducing the
[95]
far exceeds the equilibrium solid solution limit, which segregation of the second phase. With the decrease in
is called “solute capture” . Thus, solidification only scanning speed, the heat accumulation within the molten
[96]
involves short-range atom rearrangement at the interface pool is enhanced and difficult to dissipate, which leads
[99]
and no long-range diffusion movement, which proceed to a reduced cooling rate . An extended cooling period
much more rapidly than solute atomic diffusion. According is considered to provide improved kinetics qualifications
to the model of solute redistribution during continuous for grain growth, which results in grain coarsening.
growth with rapid solidification, the coefficient (z ) of Meanwhile, Al atoms avoid being engulfed by growing
v
solute distribution at the interface is determined by : solids and precipitate at the grain boundary. In addition,
[97]
alloying can improve the random orientation of grains
= (Z + Z / ) / (1+ RV R /V ) (3)
v e d i d and weaken the texture of LPBF-processed Zn matrix, as
Where, the z , R , and V are the equilibrium displayed in Figure 6B. Obviously, the preferable grain
d
i
e
segregation coefficient, the interface growth rate, and the orientation for Zn alloys is weakened, and the texture
diffusion rate of solute atom at the interface, respectively. components of (0001) plane diffuse randomly around.
A

B

Figure 6. (A) Cross-sections of THE laser powder bed fusion-processed Zn-Al parts obtained at various volume energy densities. Reprinted
from Journal of Alloys and Compounds, 798, Shuai C, Cheng Y, Yang Y, et al., laser additive manufacturing of Zn-2Al part for bone
repair: Formability, microstructure, and properties, 606-615, Copyright (2019), with permission from Elsevier . (B) Inverse pole figures
[32]
and corresponding pole maps for as-build Zn-based parts. All maps are observed along the building direction. Reprinted from Composites
Part B-Engineering, 216, Yang Y, Yang M, He C, et al., rare earth improves strength and creep resistance of additively manufactured Zn
implants, Copyright (2021), with permission from Elsevier .
[79]
82 International Journal of Bioprinting (2022)–Volume 8, Issue 1