Page 41 - MSAM-3-2

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

Figure 8. The illustration of the formation mechanism of TiAl intermetallic compound.
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of the AlMgScZr layer, the graded layer underwent
remelting. Higher energy input accelerated the diffusion
of Ti from the high-concentration region in the graded
layer to the low-concentration region in the AlMgScZr
layer. Finer TiAl dendrites precipitated in the AlMgScZr
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layer through the Ti-Al reaction. Research indicates
that the nucleation and growth dynamics of TiAl
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strongly depended on the concentration distributions
of Ti and Al, influencing the morphology of the TiAl
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IMC. In regions with insufficient Ti or Al, TiAl tends
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to precipitate finer dendrites or rod-like structures.
With a moderate concentration distribution (Al-to-Ti
atomic ratio of approximately 3), a large number of
TiAl dendrites are formed. In addition, cracks form at
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the interface between the graded layer and Ti6Al4 due
to the lattice type mismatch between Ti and Al and the Figure 9. The microhardness curves of laser powder bed fusion-processed
significant difference in thermal properties between the Ti6Al4V/AlMgScZr-graded multi-material parts at different scanning
two materials. speeds.

3.4. Mechanical properties of Ti6Al4V/AlMgScZr- Moreover, the variation in microhardness remained
graded multi-material parts relatively stable without significant increase, suggesting
Figure 9 demonstrates the variation in microhardness the absence of IMCs with high microhardness values at
across the interface of Ti6Al4V/AlMgScZr-graded multi- the interface. As the amount and size of TiAl decreased,
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material parts at different laser scanning speeds. The average microhardness consistently declined until reaching the
microhardness value of the Ti6Al4V was approximately AlMgScZr region. At a lower scanning speed of the graded
374 HV , consistent with values reported by Liu et al. layer (2400 mm/s), the average microhardness at the
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0.2
Similarly, the average microhardness value of AlMgScZr interface was the lowest (226 HV ) due to the presence
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was 122 HV , aligning closely with values reported by Xi of cracks resulting from thermal stress. Increasing the
0.2
et al. Overall, microhardness exhibited a gradual decrease scanning speed to 2800 mm/s led to the highest average
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from Ti6Al4V to the interface as the Ti6Al4V content microhardness at the interface, reaching 263 HV .
0.2
diminished and TiAl precipitated along the interface. However, with a further increase in scanning speed to
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Volume 3 Issue 2 (2024) 9 doi: 10.36922/msam.3088