Page 95 - IJB-8-1

Zhou, et al.
A B

C

Figure 5. (A) Single track on the deposited layers at different scanning speed. Reprinted from Materials & Design, 155, Wen P, Voshage M,
Jauer L, et al., laser additive manufacturing of Zn metal parts for biodegradable applications: Processing, formation quality, and mechanical
properties, 36-45, Copyright (2018), with permission from Elsevier . (B) Electron backscatter diffraction (EBSD) orientation maps and
[48]
(C) pole figures of Zn samples fabricated at different scanning speeds with 300, 500, and 700 mm/s. Adapted with permission from Qin Y,
Wen P, Xia D, et al., effect of grain structure on the mechanical properties and in vitro corrosion behavior of additively manufactured pure
Zn, 2020, 33 .
[82]
perpendicular to the front of solidification and the θ is random orientation for LPBF-processed Zn matrix, and
the angle between and unit direction perpendicular to their average grain width reaches 5.9 μm. Meanwhile,
the front of solidification. According to the Equation 2, the number and size of twinning also reduced. The results
unfavorably oriented grains become blocked and stop indicate that the preferred growth directions of favorably
growing when some growth directions are far away from oriented grains are well consistent with the direction
thermal flow direction during LPBF. with the thermal gradient directions, while their adjacent
The microstructure of Zn parts of LPBF is displayed grains misorient at a certain angle in respect of the heat
in Figure 5B. Due to Zn with hexagonal close packed flow direction during rapid solidification. In addition, due
structure, the preferred grain growth direction is <0001> to relatively fast solidification of molten liquid in molten
direction, which shows the highest growth rate . It is pool under the condition of increasing scanning speed, the
[91]
worth noting that the grains showing in blue within formation of massive nucleation leads to relatively large
the coarse columnar grains possess different growth density and randomly oriented grains, which weakens
orientation angle due to the influence of twinning. It texture of LPBF-processed Zn matrix . As displayed in
[93]
is attributed to a significantly large crystal axis ratio Figure 5C, with the increase of scanning speed, texture
of 1.856 for Zn as compared with an ideal hexagonal strength gradually weakened.
crystal (1.732), which easily leads to the occurrence Given the fact that LPBF precisely adjusts the
of massive twinning on the (1012) plane . With the microstructure for Zn, the special microstructures for
[92]
increase of scanning speed, the columnar grains along the a series of biological Zn-based materials developed by
build direction become fine polygonal grains with more alloying technology are also widely studied. Usually, the

International Journal of Bioprinting (2022)–Volume 8, Issue 1 81