Functionally-graded materials

Miyamoto, Y., et al., Functionally Graded Materials Design, Processing, Applications, Kluwer, 1999. 

Chemical vapor deposition (CVD) of carbon from propane is the main reaction in the fabrication of the C/C composites [1,2] and the C-SiC functionally graded material [3,4,5]. The carbon deposition rate from propane is high compared with those from other aliphatic hydrocarbons [4]. Propane is rapidly decomposed in the gas phase and various hydrocarbons are formed independently of the film growth in the CVD reactor. The propane concentration distribution is determined by the gas-phase kinetics. The gas-phase reaction model, in addition to the film growth reaction model, is required for the numerical simulation of the CVD reactor for designing and controlling purposes. Therefore, a compact gas-phase reaction model is preferred. The authors proposed the procedure to reduce an elementary reaction model consisting of hundreds of reactions to a compact model objectively [6]. In this study, the procedure is applied to propane pyrolysis for carbon CVD and a compact gas-phase reaction model is built by the proposed procedure and the kinetic parameters are determined from the experimental results. 

Figure 1.81 Conceptual diagram of functionally graded materials (FGMs). From M. Koizumi and M. Niino, Overview of FGM research in Japan, MRS Bulletin, XX(1), 19 (1995). Reproduced by permission of MRS Bulletin.

Though the term functionally graded materials is relatively young, the concept is not. Nature has been producing FGMs for a long time. Figure 1.82 shows a cross... 

Suresh, S., and A. Mortensen, Fundamentals of Functionally Graded Materials Processing and Thermomechanical Behavior of Graded Metals and Metal-Ceramic Composites, Ashgate Publishing Co., Brookfield, VT (1999). 

In the development of functionally graded materials, there are two approaches. One is to eliminate the boundary of laminated-type composites, thereby eliminating discontinuities in the properties at the boundary. The other option is to make non-uniform distributions of dispersoids in a homogeneous composite, thus creating multiple functions within the material.2 Therefore, continuous variation in composition, microstructure and so on, results in change in properties as a function of position in the component.6... 

Although the functionally graded materials concept has been known since 1972, the production of functionally graded SiAlON ceramics is still a subject to explore. Especially, the formation mechanisms of the functional gradient structure have not yet been fully understood. If diffusion mechanisms are explored, compositional design would be easy and the thickness of the graded... 

Damzik, R.J., Neubrand, A., Rodel, J. (2000), Functionally graded materials by electrochemical processing and infiltration application to tungsten/copper composites , J. Mat. Sci., 35, 477 186. 

Ichikawa, K. (2001), Functionally Graded Materials in the 21st Century, Kluwer Academic, Boston, MA. 

Kieback, B., Neubrand, A., Riedel, H. (2003), Processing techniques for functionally graded materials , Mater. Sci. Eng., A362, 81-105. 

Shen, Z., Nygren, M. (2002), Laminated and functionally graded materials prepared by spark plasma sintering , Key Eng. Mater., 206-213, 2155-2158. 

Yeo, J.G., Jung, Y.G., Choi, S.C. (1998), Design andmicrostructureofZr02/SUS316 functionally graded materials by tape casting , Materials Letters, 37, 304—311. 

Functionally graded materials (FGMs) are multifunctional materials, which contain a spatial variation in composition and/or microstructure for the specific purpose of controlling variations in thermal, structural or functional properties. Also in the ceramics composites field, a wide range of functionally graded (FG) ceramics are available. Hence, a possible classification of the different classes is made in this chapter. 

As a new concept in advanced materials research and development, introduced in the mid-1980s, functionally graded materials (FGMs) are defined as materials whose spatial distribution of microstructure and/or composition is tailored and quantitatively controlled in order to achieve an improvement in properties... 

The calculation of thermal stresses in functionally graded materials is already a relatively old topic (Yang et al., 2003). Two methods can be distinguished analytical methods and finite element methods. However, the complicating effect of the elastic modulus variation with the position severely limits the scope of problems that can be solved analytically. Therefore, the majority of the analytical work has been for FGM films or other simple structures (Becker et al., 2000). Analytical models have been developed for the calculation of thermal stresses for 1-D FGM symmetrical plates (Jung et al., 2003), non-... 

Fundamentals of Functionally Graded Materials, by S. Suresh and A. Mortensen, A, Institute of Materials, Published by Woodhead, Cambridge, UK, 1998. 

Functionally Graded Materials Design, Processing and Applications, edited by Y. Miyamoto, W.A. Kaysser, B.H. Rabin, A. Kawasaki and R.G. Ford, published by Kluwer Academic Publishers, Boston/Dordrecht/London, 1999. 

Becker, T.L., Cannon, R.M., Ritchie, R.O., (2000), An approximate method for residual stress calculation in functionally graded materials , Mech. Mat., 85-97. 

Chen, C., Awaji, H., (2003), Transient and residual stresses in a hollow cylinder of functionally graded materials , Mat. Sci. Forum., 423-425, 665-670. 

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