Page 75 - MSAM-2-3

Materials Science in Additive Manufacturing Additive manufacturing of SiC composite

Although the carbon fibers suffered little corrosion
during the PIP process, and a certain degree of toughening
was achieved, the performance of the proposed continuous
fiber-reinforced SiC composite for additive manufacturing
was still lower than that of the continuous fiber-reinforced
SiC composite prepared by the conventional process
of two-dimensional woven carbon cloth laminated by
puncture combined with PIP. The main reason is that for
the ceramic precursor slurry to be impregnated into the
porous fiber-reinforced green parts smoothly, a large pore
space must be reserved in the design of green parts, which
is reflected in the forming parameters of the green parts
additive manufacturing process, where the ILD must be set
to a larger value. Such forming parameters result in, first,
a much lower percentage of the fiber-reinforced phase in
the final product of C /SiC composites than that of C /SiC
f
f
Figure 22. Three-point bending stress-displacement curves of carbon composites made by the conventional process. Second,
fiber/silicon carbide (C /SiC) (polyethylene terephthalate glycol) and C / f the large ILD will eventually result in a large number of
f
SiC (polylactic acid) composites in infill line distance-1.4 group.
closed pores in the C /SiC compound during the first few
f
PIP cycles, which are not connected to each other or to
composites: When the stress of the specimen is lower the outside world and cannot be filled by the ceramic
than the cracking stress of the matrix, the curve presents precursor slurry impregnation during the subsequent PIP
linear elastic characteristics. When the stress exceeds the cycles to produce SiC. The combination of the two effects
matrix cracking stress, the matrix cracks and expands, and eventually reduces the mechanical properties of the C /SiC
the stress-displacement curve of the composite exhibits a composites. f
nonlinear deformation characteristic. When the composite
stress reaches its maximum value, the matrix-fiber interface To overcome these problems, we first replaced PLA, a
starts to debond and fiber pullout occurs and the specimen commonly used raw material in FFF additive technology,
eventually fractures . with PETG, a resin matrix material with higher residual
[46]
carbon. Therefore, a pre-carbonization step was added
The mechanical properties of continuous fiber-
reinforced SiC composites could be obtained not before the carbonization step to partially carbonize and
pyrolyze the PETG resin to create additional micropores,
only directly from the test, but also from the fracture allowing the green parts to be impregnated with the
morphology. Figure 23A–F show the SEM results ceramic precursor even at a shorter ILD. But the results
captured from the cut surface of C /SiC (PETG) samples.
f
Figure 23G–L show the SEM result of the three-point showed little optimization. Taking the above into account,
bending section of C /SiC (PETG) sample. As can be seen the bending strength of the C /SiC (PETG) composites
f
f
from Figure 23A–L, the fiber pull-out phenomenon was (44.14 MPa) was nearly the same as that of the ILD-1.4 and
more obvious when ILD was shorter. With the increase of even ILD-1.2 C /SiC (PLA) composites (47.73 MPa).
f
the ILD, the ductile fracture section manifesting obvious The reasons for this can be complex and multifaceted:
fiber pull-out phenomenon was transformed into a very Firstly, due to the mechanism of FFF additive devices,
flat brittle fracture. Based on Figure 24, C /SiC (PLA) when the nozzle aperture of the heating head of the FFF
f
composites showed more obvious fiber pull-out, matrix- device is fixed (0.8 mm in all cases used above), there is
fiber interface debonding and crack deflection, which a lower limit to the setting of the ILD. When below this
are also consistent with the bending strength test results. range, the distance between deposited lines is too small
In addition, EDS scan results of samples described in and the nozzle has a certain range of apertures, the molten
Figures 23 and 24 also indicate the presence of carbon fiber prepreg filaments fed by the nozzle will undergo a lap
in the final product, and the carbon fiber did not suffer behavior similar to that in the welding process to a larger
serious damage during multiple pyrolysis processes at extent, which will affect the forming quality of the green
high temperatures. Therefore, continuous fiber-reinforced parts and the difficulty of impregnation of the precursor
SiC composite specimens with the maximum bending slurry. When the lap is too severe, it may even lead to the
property of 47.73 MPa were obtained, which can achieve a failure of the green parts forming. In this study, after several
certain degree of strengthening and toughening effect. pre-experiments, the lower limit of this infill line distance

Volume 2 Issue 3 (2023) 14 https://doi.org/10.36922/msam.1604