Page 74 - MSAM-2-3

Materials Science in Additive Manufacturing Additive manufacturing of SiC composite

A B

C D

Figure 21. Carbon fiber/silicon carbide (C /SiC) composite mechanical properties tests. (A and C) Three-point bending and fracture toughness test results
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of C /SiC (polyethylene terephthalate glycol) composite. (B and D) Three-point bending and fracture toughness test results of C /SiC (polylactic acid)
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composite.
more prominent because the continuous fiber-reinforced in the impregnation volume and therefore cannot affect the
SiC composites prepared by the PIP method had more bending strength of the final product.
internal closed pores and more defects. Especially when Based on the comparison shown in Figure 21, it
the density of the green parts was very low, the holes is known that the bending strength of C /SiC (PETG)
between the fiber skeletons became very large, resulting composites was lower than that of C /SiC (PLA) composites
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in plenty of macroscopic pores in the continuous fiber- for the same ILD (ILD-1.4). This is because the PETG-
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reinforced SiC composites. As a result, more pores would based green parts generate more pyrolyzed carbon during
be left behind inside the composites, essentially affecting carbonization due to the high residual carbon composition
the test results and resulting in errors of the bending in the PETG matrix material, generating many pyrolyzed
strength. Moreover, when the ILD decreased, for instance, carbon impurities in the final product and affecting the
from 1.2 to 1.0 mm, the flexural strength declined from overall performance of the SiC composites. Similar to the
44.14 MPa to 32.81 MPa. This is because the porosity of bending strength, the fracture toughness showed a similar
the green part specimens decreased by a large margin, and trend, but it was the ILD-1.6 group of C /SiC (PLA) that
it was difficult for the green part specimens to impregnate achieved a maximum fracture toughness of 1.04 MPa·m
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1/2
PCS, thus resulting in the decrease of bending strength due to the large fracture toughness test error caused by the
of the final C /SiC composite. An increase of the ILD, for uneven surface of continuous fiber-reinforced specimens,
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example, from 1.8 to 1.9 mm, did not significantly reduce so the ILD-1.4 of C /SiC (PLA) and ILD-1.9 groups may
the bending strength; in fact, the bending strength of have some deviations.
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the specimens did not change much. This phenomenon
is attributed to the fundamental inability of the ceramic Figure 22 shows the stress-displacement curves of
precursors to completely fill the macroscopic pores due to C /SiC (PETG) composites and C /SiC (PLA) composites in
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the already large voids in the green part specimens. The three-point bending with an ILD of 1.4. Among them, the
incomplete filling of the pores leads to the fact that even an stress-displacement curves of C /SiC (PETG) composites
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increase in the ILD cannot bring about a greater reduction show the typical characteristics of fiber-reinforced ceramic
Volume 2 Issue 3 (2023) 13 https://doi.org/10.36922/msam.1604