Numerical Modeling Chemical Vapor Infiltration of SiC Composites

Abstract

The multiphase field model for chemical vapor infiltration (CVI) of SiC/SiC composites is developed in this study, thereby to reproduce the microstructure evolution during CVI process and to achieve better understanding of the effect of process parameters (e.g., temperature, pressure, etc.) on the final product. In order to incorporate the thermodynamics of methyltrichlorosilane (MTS) pyrolysis into phase field model framework, the reduced chemical reaction mechanism is adopted. The model consists of a set of nonlinear partial differential equations by coupling Ginzburg-Landau type phase field equations with mass balance equations (e.g., convection-diffusion equation) and the modified Navier-Stokes equations which accounts for the fluid motion. The microstructure of preferential codeposition of Si, SiC under high ratio of H2to MTS is simulated and the potential risk of blockage of the premature pores during isothermal CVI process is predicted. The competitive growth mechanism of SiC grains is discussed and the formation process of potential premature pore blockage is reproduced.

A coupled numerical modelling and experimental approach in chemical vapour infiltration (CVI) process of SiC/SiC composites

“…The step increasing in the curves along section B indicates the location of gas/solid interface, with the left part in solid phase and the right part in gas phase. This shows that as time progresses, Table 1: Parameters used in the model [30].…”

“…The Lagrange multiplier l L was introduced to account for the sum of phase field in the system to be conserved. Details of the derivation and interpretation can be found in our previous works [30,33,34]. In the following sections, fluid flow, mass and heat transport will be coupled with phase-field order parameters, which account for the interfacial dynamics implicitly.…”

“…where c i is the molar concentration of gaseous species i, i ∈ indicates that the diffusion of each species in solid phases was disregarded due to its low diffusivity, u the velocity vector and D the diffusivity. Details of the derivation and interpretation can be found in our previous works [30,33,34].…”

“…(16) was the force term, which was chosen such that 'no-slip' condition can be accurately reproduced regardless of the diffusive interface thickness [35]. Details of the derivation and interpretation can be found in our previous works [30,33,34].…”

“…The density and heat capacity of the gaseous phase and solid phase differ greatly. Details of the derivation and interpretation can be found in our previous works [30,33,34]. In summary, the multiphase field model consists of the following coupled components: phase-field eqns.…”