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Yang, et al.
distributed seed points. Then, the wireframe of the 3D in the fabrication of dense samples to manufacture porous
Voronoi diagram was extracted. The trabecular porous Ta scaffolds with relatively dense Ta struts. An optimized
structure can be constructed by employing the wireframe scanning strategy was employed to reduce the residual
to form a circular strut with a cross-sectional diameter stress produced during laser fusion process. After the
(D). The porosity of the trabecular scaffold can be fabrication, specimens were removed from the substrate
adjusted by changing the number of seed points and the using numerical control wire electrical discharge cutter
strut diameter. Indispensable repairs were conducted DK7732 (Changde Machinery Manufacturing Co., Ltd.,
by Materialise Magics 24.0 (Materialise N.V., Leuven, Taizhou, Jiangsu, China). The unfused Ta powders adhered
Belgium) to create CAD models for further process. to the sample surface were removed by sandblasting
During the laser fusion process, the raw material powders (Blaster 9060A, Hexin Sandblasting Equipment Co.,
at the boundaries of selected locations become fused Ltd., Shenzhen, Guangdong, China). Then, as-prepared
or half fused, increasing the strut diameter beyond its samples were subjected to annealing (Vacuum Annealing
designed value. In the same structure, the bigger the strut Furnace SLZK1100-45, Litan New Energy Development
diameter, the smaller the pore size and porosity will be. Co., Ltd., Suzhou, Jiangsu, China) for releasing residual
By our many optimizations and attempts, a deviation of thermal stress generated during the fabrication process.
approximately 2% between the porosity of AM trabecular The annealing procedures were conducted in a vacuum
Ta scaffolds and the designed models was summarized. atmosphere. First, the temperature rose at a rate of 5°C/
Therefore, to obtain Ta scaffolds with porosities of 65%, min to 300°C and held for 30 min, and then rose at the
75%, and 85%, cylindrical trabecular porous models with same rate to the plateau annealing temperature of 1000°C
porosities of 67%, 77%, and 87%, having the same outer and held for 120 min before dropped to room temperature.
geometry (diameter × height: 10 mm × 10 mm) and strut Finally, all specimens were ultrasonically and separately
diameter (250 μm), were designed, as shown in Figure 1. cleaned for 30 min in distilled water and ethanol. Ten
Fully dense pure Ta spherical powder with a samples of each model were fabricated.
particle size range of 15 μm and 45 μm (TEKNA
Advanced Materials Inc., Sherbrooke, QC, Canada) was 2.2. Morphological analysis
used to fabricate trabecular Ta scaffolds. The powder
microstructure and characteristics have been described in The strut diameters and average pore sizes of as-prepared
our previous work . Based on CAD data, samples were samples were measured from the optical micrographs
[25]
manufactured by Dazhou Medical Co., Ltd. (Shenzhen, with n = 10 for each porosity. Their overall porosities
Guangdong, China) using Farsoon FS271M (Farsoon were determined by the dry weighing method under
Technologies Co., Ltd., Changsha, Hunan, China), an normal atmosphere conditions with n = 10 for each
LPBF-based AM system equipped with a 500W Yb: YAG porosity. Sample dimensions were measured by digital
fiber laser with a spot size of 80 μm. The production step Vernier calipers 111-101-10G with an accuracy of
was performed in an argon environment with <0.05% 0.01 mm (Digital Measurement and Control Co., Ltd.,
oxygen to prevent oxidation. The process parameters Guilin, Guangxi, China) and derived from the average of
and scanning strategy have significant effect on the 3 measurements for each specimen. The dry weights of
microstructures and properties of LPBF parts [26,27] . We as-fabricated samples were measured using an electronic
employed the optimized processing parameters, including densimeter with a sensitivity of 0.0001 g (DK-120MD,
laser power, scan speed, fill distance, and layer thickness, Decca Precision Instrument Co., Ltd., Shenzhen,

Figure 1. Designed models of trabecular porous Ta scaffolds with nominal porosities of 67%, 77%, and 87%.

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