Advances in Modeling of the Chemical Vapor Infiltration Process
- PDF / 423,032 Bytes
- 8 Pages / 420.48 x 639 pts Page_size
- 23 Downloads / 243 Views
ADVANCES IN MODELING OF THE CHEMICAL VAPOR INFILTRATION PROCESS THOMAS L. STARR Georgia Institute of Technology, Georgia Tech Research Institute, Atlanta, GA
ABSTRACT The technology of chemical vapor infiltration (CVI) has progressed dramatically over the past twenty-five years and stands now as the leading process for fabrication of high temperature structures using ceramic matrix Modeling techniques also have advanced from extensions of composites. catalyst theory to full 3-D finite element code with provision for temperature These modeling efforts offer insight into critical and pressure gradients. factors in the CVI process, suggest opportunities for further advances in process technology and provide a tool for integrating the design and manufacture of advanced components. Early modeling identified the competition between reaction and diffusion in the CVI process and the resulting trade-off between densification rate and Modeling of forced flow/thermal gradient CVI showed how the uniformity. evolution of material transport properties provides a self-optimizing feature to this process variation. "What-if" exercises with CVI models point toward potential improvements from tailoring of the precursor chemistry and development of special preform architectures. As a link between component design and manufacture, CVI modeling can accelerate successful application of ceramic composites to advanced aerospace and energy components.
INTRODUCTION As with any advanced structural material, incorporation of ceramic composites into mechanical systems seems frustratingly slow to materials limit such scientists. To the design engineer, however, several factors still One of these is fabricability - the ability to reliably produce applications. a finished component at a reasonable cost. Chemical vapor infiltration (CVI) offers considerable promise toward this end with fabrication of a number of near-net-shape components and implementation of commercial-scale production Modeling has been a key element in facilities in Europe and the U.S. development of CVI processing to this point and will be even more important in the future as CVI is used for fabrication of components of increasing size and complexity.
BRIEF HISTORY OF CVI MODELING 1
There are two variations of CVI in current practice , as illustrated in In isothermal CVI (ICVI) a gas mixture is introduced into a furnace Figure 1. Reactant diffuses into the pore spaces containing one or more fiber preforms. of the preform, reacting on the fiber surfaces to form the matrix material. While this variation of the process requires relatively simple equipment and suffers from some can accommodate a number of large, complex shapes, it limitation on component thickness and requires very long processing times, i.e. several hundred hours. In forced flow/thermal gradient CVI (FCVI) the reactant gas mixture is forced to flow through the preform and an applied temperature gradient controls the progress of densification in order to avoid While equipment for temperature premature pore closu
Data Loading...
