Chemical vapor infiltration of additively manufactured preforms: Pore‐resolved simulations and experimental validation

Abstract

The densification of additively manufactured porous preforms by chemical vapor infiltration (CVI) is studied using pore-resolved simulations and experiments. Experimentally, 3D printed silicon carbide (SiC) preforms are subject to CVI synthesis using methyltrichlorosilane (MTS) precursor to obtain high purity SiC/SiC composites. Optical images of the cross sections of the processed preforms are analyzed to obtain the spatial porosity distribution. The numerical method is based on a level set formulation to capture the spatial distribution and time evolution of the pore scale microstructural characteristics. The coupled transport and kinetic effects are represented using a dimensionless Thiele modulus. Simulations are initialized using representative synthetic preform geometries comprising of packed particles based on the size distribution of the powder used for 3D printing. The simulation results are validated against the experimental observations in terms of total density and the distribution of residual porosity. The densification characteristics, porosity classification, concentration profiles, and structure functions are analyzed as functions of processing temperature and Thiele modulus. K E Y W O R D S chemical vapor infiltration (CVI), direct numerical simulations (DNS), level set, Thiele modulusThis manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

The effect of chemical vapor infiltration process parameters on flexural strength of porous α$\alpha$‐SiC: a numerical model

“…In addition, a pore's tortuosity increases the path length of the transporting gas, 64 which increases infiltration time and residual porosity. The current study establishes a basic ICME framework relating pore radius to flexure strength, providing the foundation for future research effort in which the performance of more complex geometries 63,65,66 can be explored. Interested readers can refer to Vignoles, who reviewed various modeling strategies of CVI.…”

Effects of temperature inversion on densification in chemical vapor infiltration

“…All the analyses presented in this work consider silicon carbide preforms that are densified using CVI. Prior work by the authors 17 describes the experimental characterization of the powder used for 3D printing which is adopted in this work. The computational model representing the packed particles is created by randomly distributing non-interfering spherical particles in space within a representative volume element (RVE).…”

“…Naturally, it is challenging to derive a reduced model that is characterized by a single representative activation energy. Limiting to the scope of the present work, three candidate models are chosen: (1) Tsai et al 25 who developed an empirical three-step model based on major C and Si bearing species and verified it experimentally for a CVD process, (2) Ramanuj et al 17 who derived the activation energy based on CVI experiments using spherical preforms for a single-step kinetics model and (3) a plug flow CVD reactor (PFR) model using detailed pyrolysis 22 and deposition 24 kinetics (described in Section 2.4). Apparent activation energies from all the models are summarized in Figure 4.…”

“…For the PFR model, the net production rate of solid species is converted into a deposition speed using Equation (6). The model of Ramanuj et al 17 based on experimental porosity measurements has the highest value (𝐸 𝑎 = 460 kJ/mol). They also emphasize the role of non-uniform porosity distributions on this apparent activation energy.…”

“…Development of DNS methods for reactive porous media and application to CVI by the authors are outlined in Refs. 15, 17 which are leveraged in this work.…”