Page 40 - MSAM-3-2

Materials Science in Additive Manufacturing LPBF of Ti-Al-graded multi-materials

79.30% and 20.70%, respectively, and an Al to Ti atomic thermal motion of Ti and Al elements, thereby accelerating
ratio of 3.8 found under the AlMgScZr molten pool. the reaction between Ti and Al.
During the LPBF fabrication of AlMgScZr, the graded layer Based on the results of the XRD pattern and
underwent remelting, and Ti atoms diffused toward the SEM analysis, Figure 8 illustrates the mechanism of
low concentration region under the influence of chemical microstructure evolution at the interface of LPBF-
potential graded, reacting with Al atoms to form TiAl . processed Ti6Al4V/AlMgScZr-graded multi-material
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3
At this stage, the acquisition of Ti atoms in the AlMgScZr parts. When the graded layer was formed on top of the
layer relied solely on the diffusion mechanism, leading to Ti6Al4V substrate, the previously solidified Ti6Al4V
insufficient Ti content and unfavorable growth for TiAl layer was remelted to achieve the metallurgical bonding.
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dendrites. Subsequently, the remelted Ti6Al4V was mixed into the
Figure 7 illustrates the distribution of Ti, Al, V, and molten pool of the graded layer through Marangoni
Mg elements at the interface between the Ti6Al4V layer convection. Due to the lower temperature and higher
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and the graded layer. A curved boundary line delineating liquid viscosity of the molten pool, the remelted Ti6Al4V
the molten pool can be observed, along which TiAl solidified rapidly, resulting in the formation of island-
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precipitated and formed short rod-like structures extending like segregations of Ti6Al4V. The higher melting point
toward the center. Based on the distribution of Ti and V of Ti6Al4V powders and the lower laser absorption rate
elements, it can be inferred that Ti6Al4V exhibited island- of AlMgScZr in the molten pool resulted in insufficient
like segregations at the interface. During the LPBF process melting of Ti6Al4V powders within the graded layer.
for forming the Ti6Al4V/AlMgScZr-graded layer, partial In addition, the Al elements in the graded layer reacted
melting of Ti6Al4V under the graded layer occurred with Ti to form rod-like TiAl along the boundary of the
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through thermal conduction, with subsequent introduction molten pool, which grew toward the center of the molten
into the graded layer through Marangoni convection. The pool. With increasing Al content, a small number of
higher melting point of Ti6Al4V led to rapid solidification TiAl fine dendrites precipitated above the rod-shaped
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of the molten Ti6Al4V. Furthermore, the presence of Al TiAl structures. As the deposition of the graded layer
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and Mg elements on both sides of the interface indicated continued, the elevated temperature of the molten pool
their diffusion across the interface. As the laser irradiated facilitated the complete melting of Ti6Al4V powders and
graded layer, the rapid melting of AlMgScZr powders the mixing of the Ti and Al elements under the influence
facilitated the diffusion of elements such as Al and Mg into of Marangoni convection. As a result, numerous TiAl
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the remelted Ti6Al4V layer. The elevated temperature of dendrites were formed in the graded layer with a Ti-to-Al
the molten pool, induced by laser irradiation, enhanced the atom ratio of approximately 3. During the fabrication

A B

C D E F

Figure 7. Element distribution of laser powder bed fusion-processed Ti6Al4V/AlMgScZr-graded multi-material parts at the interfacial molten pool.
(A) Scanning electron microscopic images of the interface. (B-F) Distribution of Ti, Al, V, and Mg elements. Scale bars: (A and B) 10 μm, magnification
×8000; (C-F) 5 μm, magnification ×4000.

Volume 3 Issue 2 (2024) 8 doi: 10.36922/msam.3088