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Page 20 of 25 Dela Cruz et al. Microstructures 2023;3:2023012 https://dx.doi.org/10.20517/microstructures.2022.33

Figure 11. The relationship between crystal misorientation (average KAM) and temperature gradient derived from the simulated
thermal profile of the melt pool as a function of LED at differing depths from the melt pool.

demonstrated for the first time that a Fe-30Mn-6Si alloy with a known combination of biodegradable and
SMA properties can be built using the LPBF technique from a homogenised metal powder. The LPBF
parameters were investigated by varying the laser power, scan speed, and re-scan strategy. A density of over
99% was achieved at a range of LED from 0.30 J/mm to 0.88 J/mm, with 0.44 J/mm as the recommended
LED for a high-density product. The resultant microstructure was shown to respond with the laser power
and scan speed settings, and the changes in microstructure were explained using the FEA analysis of the
melt pool profile derived from the single laser track scan. For example, the microstructure transitioned from
one that was highly columnar and textured at high laser power to one that was fine and nearly equiaxed
with weak texture at low laser power. Increasing the scan speed at high laser power setting eliminated the
strong texture and increased the grain size. However, laser re-scanning of the solidified layer remelted the
columnar grains and re-solidified them into non-uniform microstructure.

The hardness of the as-built LPBF alloys was also systematically assessed. The relationships between grain
size, types and amounts of phases, and crystal misorientation on the hardness of both the reference and the
LPBF alloys at different process settings were investigated. The hardness of the single-phase austenitic
reference alloy was found to be affected by the grain size and residual strain. In the LPBF alloy, the fraction
of ε phase strongly influenced the hardness. The pre-existing, thick ε plates may have blocked the nucleation
and growth of the stress-induced ε plates in the LPBF alloy, which effectively hardened the LPBF alloy.
Overall, this study expanded the processing capability of the LPBF technique by fabricating a Fe-Mn-Si alloy
from a homogenised powder and elucidated the influence of processing parameters on the microstructure
and the hardness of the product.

DECLARATIONS
Authors’ contributions
Conception, design, writing, and editing: Dela Cruz ML, Yakubov V, Li X, Ferry M
Data collection and analysis: Dela Cruz ML, Li X, Ferry M
FEA simulation methodology and analysis: Yakubov V, Dela Cruz ML
All authors contributed to the manuscript and were involved in discussion.