| In this paper, the TiB2/AlN/Cu and TiB2/Cu functionally graded materials(FGMs), which have constitutive phases with much different sintering temperatures,were successfully fabricated via spark plasma sintering (SPS) method combinedwith a temperature gradient achieved. These FGMs will be used as electrodematerials of a solar thermoelectric modulus. The temperature distribution along thegraphite mold during SPS was systematically studied. The fabrication,microstructures and properties of the TiB2/Cu and TiB2/AlN composites were alsoinvestigated so as to explore the sinterability of the various composite layers of theabove FGMs.The results concerning temperature-field showed that a large temperaturegradient was produced along the longitudinal direction of the taper-shaped mold,which leads to a uniaxial heat loss during SPS. The longitudinal temperaturedistribution is expressed as:The temperature difference between the two ends of the specimen is expressed as:The longitudinal temperature distribution and the temperature difference in the moldwere found to depend on some physical factors, such as sintering current (I), radiusof mold cross-section(r0), electrical conductivity (σ)and thermal conductivity(k)of the specimen or mold, taper of the mold(θ),specimen thickness(h)andconditions of the uniaxial heat loss(c), etc., The fabrication of FGMs havingconstitutive phases with different sintering temperatures, such as the TiB2/AlN/Cu B B and TiB2/Cu in the present study, would be feasible by adjusting the above B B influencing factors or by increasing the temperature difference between two ends of the specimen. The sinterability of the TiB2/AlN/Cu and TiB2/Cu FGMs was thoroughly B B B B studied. For the TiB2/AlN/Cu FGM, the appropriate sintering route was found to be: B B a constant temperature of 1000℃kept at the copper end and a ramp-up speed of300 ℃/min. As a result, the TiB2/AlN/Cu FGM was found to have dense B Bmicrostructures, sound bonding between all the layers and good appearances. For thefabrication of the TiB2/Cu FGM, a two-step SPS processing should be utilized. B B The densification, microstructures and properties of the TiB2/Cu composites B B were also studied in this paper. There are three shrinkage stages for pure Cu duringSPS, and a complex densification behavior of the TiB2/Cu composite exhibits: the B B shrinkage of TiB2 and the three shrinkage stages of Cu have interacted during SPS. B BThe Cu and TiB2 phases were preserved in the TiB2/Cu composites as expected, and B B B B no new phases formed during SPS processing. The IACS value of the TiB2/Cu B B composites with >80%Cu is larger than 60%, as is indicative of good electrical conductivity. The TiB2/AlN composites were also fabricated via SPS method. The resultant B B materials were found to have dense and fine microstructures. The TiB2 phase is B B granular-shape and the AlN phase flake-shape, and no new phases were found. The AlN sintered at 1650℃has reached a perfect hardness of 12GPa,and the TiB2 Bsintered at 1700℃reached 32GPa,near to the highest value reported. TheB TiB230/AlN70 and TiB270/AlN30 composites were found to have high flexural B B B Bstrength. The fracture analysis indicated that the fracture of the AlN phase istransgranular and the fracture of the TiB2 phase is intergranular. The SPSed B B AlN/TiB2 FGMs were found to have uniform microstructures and sound bonding B B interfaces, and no defects such as cracks were observed. Since the SPS method usually can degrade greatly sintering temperatures, it was also used to fabricate the PSZ/W composites that have constitutive phases with...
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