THERMAL-EXPANSION OF AN SIC PARTICLE-REINFORCED ALUMINUM COMPOSITE

Using a push-rod dilatometer, we measured between 76 and 390 K the thermal expansion of a particle-reinforced-composite wrought plate obtained by powder-metallurgy methods. The particles, 30% by volume, consisted of monocrystals of alpha-SiC with sizes near 10-mu-m. The matrix consisted of a 6061 aluminum alloy with original particle sizes near 20-mu-m. We found the perpendicular thermal expansivity, alpha-3, higher by 26% than the in-plane thermal expansivity, alpha-1 congruent-to alpha-2. These values differ from a rule-of-mixture prediction by -3 and -23%, respectively. All three alpha-i components lie outside the Rosen-Hashin bounds. Levin's isotropic model agrees within 10% with the alpha-1-alpha-2-alpha-3 average. Both the anisotropy and the bounds violation result from microstructural non-homogeneity arising from processing. Rosen and Hashin's transverse-isotropic-symmetry relationships account approximately for these effects by introducing the anisotropic elastic constants. Using neutron diffraction, we determined that the SiC particles are textureless.