Over the last few years, many classifications have been proposed for functionally graded materials (FGMs). In this Paper, critical review of different available classifications for FGM based on their physical, structural and manufacturing characteristics are presented. Advantages and limitations of each fabrication method for use in a given application is correspondingly considered. In addition, new classifications based on gradation control and accuracy, residual stresses, specific energy consumption, environmental impact evaluated throughout the complete life cycle and manufacturing costs are proposed. These classifications mainly reflect the needs of both FGM designers and industrial manufacturers. Based upon the presented classifications and the recent advances in analysis and production techniques, new major directions for FGMs research are proposed.

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Horizontal centrifugal casting machine was adopted to fabricate tubes of functionally graded materials (FGM) made of commercially pure aluminum reinforced with different weight fractions of SiC particles. Tubes with 2.5, 5 and 10%wt. SiCpwere produced in the speed range 800 to 1100 rpm. Wear experiments involving dry sliding under different loading conditions were conducted on samples taken from three consecutive layers across the wall of the FGM tubes. Analysis of variance (ANOVA) was used to determine the significant FGM production parameters and wear test parameters (normal load and test duration) affecting the wear resistance of the samples. Obtained wear test results have been used to build a regression model to predict the expected weight loss across the wall thickness of the tube depending on the production parameters and the loading conditions.