Transport Processes in Chemical Vapor Deposition of Functionally Graded Materials: Fundamental Understanding through Combined Experiments and High-Fidelity Mathematical Modeling

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The objective of this research is to gain a fundamental understanding of the physical and chemical transport processes in the chemical vapor deposition (CVD) of functionally graded methods, through a combined experimental and computational investigation. A functionally graded material (FGM) may be defined as one in which the composition of the material varies gradually from one extreme to another. Functionally graded materials can successfully be used to join two disjoint materials such as metals and ceramics, or provide coatings on substrates in such a way as to provide a gradual variation of the thermal expansion coefficient. CVD involves the gradual deposition of a material on a substrate heated to a temperature where chemical reactions can take place, thus forming a thin layer of deposit. A typical CVD process involves complex interactions between flow, temperature, species concentrations, and reactor geometry. Understanding the precise interactions between the various flow variables is very essential to obtaining the optimum set of operating parameters, and their manner of variation.The fundamental issues addressed in the experiments will be the transient planar distributions of the chemical species transported by the carrier gas, and of temperature near the surface of the substrate. The objective of the computational study will be to develop a mathematical model of the transient flow, heat transfer and chemical reactions that occur during the graded deposition process.