Page 34 - MSAM-1-3

Materials Science in Additive Manufacturing Photocatalytic PA6/TiO powder for LPBF
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A B

C D

Figure 5. Morphologies of PA6 powders precipitated at different holding temperatures: (A) 120°C, (B) 122.5°C, (C) 127.5°C, and (D) 130°C.

3.2. Effects of dissolved concentration on powder
properties
When the powder was prepared in large quantities, the
dissolved concentration of PA6 increased, resulting in a
huge difference in particle morphology. Figure 7 shows
the changes in morphologies under the concentration
conditions of 100 g/L, 150 g/L, and 200 g/L. When the
concentration was increased to 100 g/L, the powder surface
became rough and uneven, accompanied by the generation
of small particles. The powder under the concentration of
150 g/L gradually acquired a porous surface. When the
concentration reached 200 g/L, obvious characteristics of
multiphase nucleation could be observed. A single particle
was formed by the agglomeration of small particles. There
was a large number of network structures between the
Figure 6. Particle size distributions of PA6 powders precipitated at particles, indicating that the particles have already adhered
different holding temperatures. to each other before they grew up.

From a comprehensive analysis, the increase in dissolved
The small-sized particles from low holding temperatures concentration leads to the emergence of contradictory
are caused by an incomplete particle growth process after phenomena. On the one hand, porous-surfaced powders
nucleation, while those from high holding temperatures and rod-like powders were produced. The rod-like
are caused by secondary nucleation with additional powders and porous-surfaced powders appeared only
adhesion of surface substances. The heat preservation after slow cooling and long-term heat preservation,
near the precipitation temperature of 125°C can form indicating that the increase in concentration has the
particles with a narrow particle size distribution, a same effect as the long-term heat preservation. On the
uniform particle size, and a smooth surface particle, other hand, the agglomeration and inter-bonding of small
which is beneficial to the HT-LPBF process. particles occurred, which are similar to the small particles

Volume 1 Issue 3 (2022) 5 https://doi.org/10.18063/msam.v1i3.14