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The effect of chemical vapor infiltration process parameters on flexural strength of porous α-SiC: A numerical model

Joseph J. Marziale, Jason Sun, Eric A. Walker, Yu Chen, David Salac, James Chen

Abstract

The flexural strength variability of α-SiC based ceramics at elevated temperatures creates the need for an Integrated Computational Materials Engineering (ICME) framework that relates the strength of a specimen directly to its manufacturing process. To create this ICME framework a model must first be developed which establishes a relationship between the chemical vapor infiltration (CVI) process and parameters, the resulting mesoscale pores, and the overall macroscale flexural strength. Here a nonlinear single pore model of CVI is developed used in conjunction with a four-way coupled themo-mechanical damage model. The individual components of the model are tested and a sample system under a four-point bending test is explored. Results indicate that specimens with an initial porosity greater than 30% require temperatures below 1273 K to maintain structural integrity, while those with initial porosities less than 30% are temperature-independent, allowing for optimization of the CVI processing time without compromising strength.

The effect of chemical vapor infiltration process parameters on flexural strength of porous α-SiC: A numerical model

Abstract

The flexural strength variability of α-SiC based ceramics at elevated temperatures creates the need for an Integrated Computational Materials Engineering (ICME) framework that relates the strength of a specimen directly to its manufacturing process. To create this ICME framework a model must first be developed which establishes a relationship between the chemical vapor infiltration (CVI) process and parameters, the resulting mesoscale pores, and the overall macroscale flexural strength. Here a nonlinear single pore model of CVI is developed used in conjunction with a four-way coupled themo-mechanical damage model. The individual components of the model are tested and a sample system under a four-point bending test is explored. Results indicate that specimens with an initial porosity greater than 30% require temperatures below 1273 K to maintain structural integrity, while those with initial porosities less than 30% are temperature-independent, allowing for optimization of the CVI processing time without compromising strength.
Paper Structure (20 sections, 36 equations, 10 figures, 8 tables)

This paper contains 20 sections, 36 equations, 10 figures, 8 tables.

Table of Contents

  1. Introduction
  2. Integrated Computational Materials Engineering Framework
  3. Processing to porosity
  4. Porosity to properties
  5. Energy release rate and crack length scale
  6. Properties to performance
  7. Results/discussion
  8. Convergence testing
  9. Temporal convergence
  10. Grid convergence
  11. Coupled convergence
  12. FE mesh convergence
  13. CVI-reduced pore distributions
  14. Time of infiltration
  15. Temperature and pressure dependence
  16. ...and 5 more sections

Figures (10)

  • Figure 1: The two steps of the modeling process. (a): Evolution of a representative pore during CVI processing. (b): Four-point bending test with representative volume elements containing the pore shape obtain from the CVI processing.
  • Figure 2: The algorithm coupling gas concentration and pore size.
  • Figure 3: Average $L_{2}$ norm of the difference in pore profile between tests with time steps $\Delta t_{\text{CVI}} = \Delta t_{base} \times 2^p$ and a test with $\Delta t_{\text{CVI}}=\Delta t_{base}$.
  • Figure 4: Average $L_{2}$ norm of the difference in pore profile between tests with grid spacings $\Delta z_{\text{CVI}} = L/(N_{base}\times 2^{-p} -1)$ and a test with $\Delta z_{\text{CVI}}= L/(N_{base}-1)$, where $N_{base}=640$.
  • Figure 5: Average $L_2$ norm of the difference in pore profile between grids with $N\in[22, 158]$ and a grid with $N=160$. In all cases, $\Delta t_{\text{CVI}} \sim N^{-2}$, $\Delta z_{\text{CVI}} = L/(N-1)$.
  • ...and 5 more figures