Microstructure of a Ti-50 wt% Ta alloy produced via laser powder bed fusion

doi:10.1007/s40195-020-01052-w

Abstract

Abstract:

Ti-Ta alloys have been widely studied for biomedical applications due to their high biocompatibility and corrosion resistance. In this work, nearly fully dense and in situ alloyed Ti-50 wt% Ta samples were fabricated by the laser powder bed fusion (LPBF) of mechanically mixed powders. With increased exposure time, and thereby increased laser energy density, insoluble Ta particles were almost dissolved, and a Ti-50 wt% Ta alloy was formed. Cellular and dendritic structures were formed due to constitutional undercooling, which was caused by the high cooling rate of LPBF process. Both retained β phases and α″ phases were observed in the LPBFed Ti-50 wt% Ta alloy. The α″ phase was found at the boundary of the cellular structures, where the tantalum content was not high enough to suppress the bcc lattice transition completely but could suppress the β phase → α′ phase transition.

Key words: Laser powder bed fusion, Ti-Ta alloys, Cellular and dendritic structures, Microsegregation, Phase transformation

Lei-Lei Xing, Cong-Cong Zhao, Hao Chen, Zhi-Jian Shen, Wei Liu. Microstructure of a Ti-50 wt% Ta alloy produced via laser powder bed fusion[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(7): 981-990.

Figures/Tables 10

Fig. 1 Laser scanning schematic diagram

Table 1 LPBF processing parameters for Ti-50 wt% Ta

Sample	P (W)	t (μm)	pd (μm)	T (μs)	h (μm)	E (J/mm³)
S1	200	30	40	80	80	167
S2	200	30	40	150	80	313
S3	200	30	40	300	80	625
S4	200	30	40	500	80	1042

Fig. 2 SEM and EDS micrographs for a pure titanium powder; b pure tantalum powder; c the Ti-50 wt% Ta powder; d EDS results corresponding to image c

Table 2 Element content at points A, B, and C in Fig. 4d

Point	Ti (wt%)	Ta (wt%)
A	60.8	39.2
B	53.3	46.7
C	41.5	58.5

Fig. 3 a-d Backscattered electron (BSE) micrographs of the cubic S1-S4 samples; e percent of unmelted Ta for S1-S4 samples

Fig. 4 BSE and EDS micrographs sample 4: a low-magnification microstructure; b dendrite and c cellular dendrite morphology; d high-magnification morphology; e EDS scanning results of cellular dendrites to graph d

Fig. 5 a Superimposed EBSD map of all Euler and BSE maps for sample 4 specimens; b, c EBSD phase map (the green regions represent the β phase, and the red regions represent the α” phase)

Fig. 6 X-ray diffraction pattern of S4

Fig. 7 a, b Bright-field TEM images for sample 4; c SADP pattern of the α” phase; d SADP pattern of the β phase; e dark-field TEM images of the α” phase

Table 3 Element contents of regions A and B in Fig. 7a

Region	Ti (wt%)	Ta (wt%)
A	53.9	46.1
B	50.5	49.5

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