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Materials Science in Additive Manufacturing In situ electromagnetic field manipulation during LMD

A B

C D

Figure 9. β-grain size distribution of different samples: (A) EM-0; (B) EM-1; (C) EM-2; and (D) EM-3

sample EM-1 (Figure 7B) mainly consists of large columnar A B
grains. This is attributed to the slow heat dissipation rate in
the middle area caused by the effect of multiple remelting,
which promotes the formation of directionally grown
columnar crystals. The coarse columnar crystals were not
observed in sample EM-1 under an electromagnetic field
of 39.40 mT (Figure 7H), but equiaxed grains were present.
Long columnar grains (Figure 8B and E) were present
in sample EM-2 as the electromagnetic field intensity C D
increased to 57.12 mT. A similar observation was also noted
in Figure 6C.
The flow velocity direction in the molten pool becomes
disordered under the action of Lorentz force (Figure 6),
thereby interfering with grain growth and refinement.
Hence, complete grains cannot be observed; only grain
boundaries can be found, evidenced by the coarse grains in
sample EM-3 under an electromagnetic field of 72.93 mT Figure 10. Phase map of different samples: (A) EM-0; (B) EM-1;
(Figure 8H). A similar result is observed in Figure 6D, which (C) EM-2; and (D) EM-3. Scale bars: 700 µm
can be attributed to the inhibitory effect of the Lorentz force
on speed v in the molten pool flow. This inhibition reduces structure. The microstructure comprises a combination
1
the molten pool cooling rate and promotes grain growth. of equiaxed and columnar grains, with the small α-phase
interwoven to form a network structure. This is attributed
From the high-magnification SEM images, samples to the area at the bottom being in contact with the substrate,
EM-0 (Figure 7D-F), EM-1 (Figure 7J-L), EM-2 as well as the large temperature gradient, both of which
(Figure 8D-F), and EM-3 (Figure 8J-L) exhibit a similar facilitate the formation of equiaxed grains. Conversely, the

Volume 4 Issue 1 (2025) 12 doi: 10.36922/msam.8332